Can Sockeye Salmon Outswim Climate Change?

Author: Dahlia Shammas


Sockeye salmon, also known as Oncorhynchus nerka, are very unique animals. They have a distinctive and prehistoric look, as well as a unique lifestyle. They are well known for their strenuous and dangerous journey back to their home stream to spawn (lay and fertilize eggs). This journey is hard enough for sockeye salmon because of predation and how much energy it takes to travel upstream to spawn. Now, anthropogenic (human-caused) climate change has presented another challenge for sockeye during migration. Climate change has led to increased river temperatures in the summer during salmon migration, changing their behavior, physiology, and mortality rates.(1)

Sockeye salmon play an important role in the lives of many species, including ours. They are economically, culturally, and ecologically important. They are one of the most commercially fished species in British Columbia, Canada, and Alaska, United States.(2) They are also culturally very important to the St'át'imc people, the original inhabitants of Fraser River in British Columbia. Sadly, climate change has had negative impacts on how they traditionally fish and preserve sockeye.(3) Ecologically, they are a highly nutritious food source for many animals including bears, birds, wolves, sharks, fish, and other marine mammals. Some species like bears rely on sockeye salmon as a crucial source of energy. Additionally, their carcasses provide nutrition to animals and valuable nutrients such as nitrogen and phosphorus to the environment.

Sockeye salmon are found along the west coast of North America in the Northern Pacific Ocean. This blog post will focus mainly on sockeye salmon that inhabit Fraser River in British Columbia, Canada. Both male and female sockeye salmon look similar in size and color. Males are slightly brighter in color and have a large dorsal hump as can be seen in the photo above. Both sexes range in size from 20 to 28 inches.(4) Most sockeye salmon are anadromous, meaning they are born in freshwater rivers or lakes, travel to the ocean where they spend most of their adult life, and then travel back to their home stream to spawn. In freshwater, their diet consists of zooplankton, amphipods (shrimp-like creatures), and insects.(5) After migrating to the ocean they continue to feed on zooplankton but also eat fish and the occasional squid.(5) After birth, they mature in freshwater for one to three years before migrating to the Pacific ocean. After two to three years in the ocean, they migrate back to their home stream to spawn.(5) Most sockeye start this migration in June and July. Their spawning time varies depending on the population and can take place anywhere between June and December.(5) When they reach their home stream, females dig holes known as redds with their tails and deposit between 2,000 to 4,500 eggs.(5) Males often compete to fertilize the eggs and the females then cover them up with gravel to protect them from the elements and potential predators. After spawning only once, the salmon have fulfilled their lifetime reproductive duty and usually die within weeks.

This blog post will elaborate on how climate change is affecting sockeye salmon behavior, physiology, and mortality. Warmer river temperatures have advanced the timing of their migration to spawn by at least two weeks.(1) Warmer waters have also led to physiological adaptations at the population level for these harsher conditions as well as cardiac collapse when temperatures get too high.(6) A rise in parasitic and fungal infections is also seen in higher water temperatures which could lead to decreased fitness and death.(1) Increased temperatures are also correlated with higher mortality rates of adult salmon as they migrate upstream back to their spawning grounds.(6)



Some sockeye salmon populations are migrating earlier to their spawning grounds because of warmer river temperatures in the summer caused by climate change.(1) Historically, populations of salmon start the migration to spawn in the summer around the same time, rarely changing that timing by more than a week.(1) Many populations exhibit a holding behavior, where they rest for 2-6 weeks in the Strait of Georgia (close to the Fraser River) before continuing their journey upstream.(1) Since 1995, this holding behavior has been abandoned by many populations of salmon.(1) Instead, these populations of sockeye advance their migration upstream by 2-8 weeks, significantly increasing the amount of time spent in freshwater compared to historical populations.(1) This is because their population-specific spawning dates do not change even though their migration time has advanced by at least two weeks.(1) This behavioral change in migration is cause for concern because early river entry has been associated with high levels of mortality ranging from 60%-90%.(1)



Rising river temperatures have had significant impacts on the physiology of sockeye salmon. Salmon burn energy quicker, could have increased stress levels, and possibly die if the water temperature gets too high. Some sockeye populations have developed physiological adaptations that allow them to better survive in higher temperatures. These cardiorespiratory adaptations include greater aerobic scope, increased heart size, and improved coronary supply.(6) A greater aerobic scope is defined as the increased capacity of oxygen consumption of an animal during exercise. Coronary supply is the rate at which oxygenated blood is pumped to the heart. These cardiorespiratory adaptations are different among populations in the Fraser River.(6) Each population of sockeye salmon has a different tolerance to temperature. This physiological limitation is possibly due to cardiac collapse caused by increased temperatures.(6)



Climate change has significantly raised the mortality rates of sockeye salmon during migration. As previously mentioned, warmer river temperatures have caused some salmon to prematurely migrate upstream to spawn. Early-entry salmon populations have elevated mortality rates from 60%-90% as a direct cause of historically higher migratory temperatures.(4) Exposure to higher river temperatures can result in the quick depletion of energy reserves that salmon rely on when they stop feeding during migration.(1) These reserves are crucial for spawning and if they are used too early exhausted salmon will not successfully reproduce, lowering fitness (the ability to produce viable offspring).(1)

Warmer water temperatures because of climate change also promote parasitic and external fungal infections in sockeye salmon.(1) An example being the parasite Parvicapsula minibicornis, which is found in the kidney.(1) This paper states that the infection rate of this parasite dramatically rose in sockeye salmon populations that experienced an increase in river temperature. It was also noted that warm-treated salmon (18°C) had more external fungal infections than cold-treated salmon (10°C).(1) A rise in parasitic and fungal infections can lead to increased mortality rates among sockeye salmon. The mechanisms by which they do this are not yet clear, but it is shown that they lead to increased metabolic stress and overuse of energy stores. This lowers overall fitness and could ultimately lead to death.



Climate change has increased temperatures in rivers where sockeye migrate, causing behavioral change, physiological adaptation, and increased mortality rates at the population level. Warmer water temperatures can advance the river entry time of salmon populations, increasing mortality rates by 60%-90%. Some sockeye populations have developed physiological adaptations that improve cardiorespiratory performance in warmer river conditions. Additionally, high water temperatures can lead to death because of cardiac collapse. Rising temperatures also increase parasitic and fungal infections, which can lead to decreased fitness and increased mortality rates. Exposure to warmer waters lowers the overall chance of survival and reproduction of some sockeye salmon populations. This is particularly concerning for salmon because they only reproduce once in their lifetime. If their health is threatened on their journey to spawn they might not ever successfully reproduce.

Some efforts are being made to conserve sockeye salmon populations. An article by The Nature Conservancy stated that in Alaska, streams are being restored from damage caused by logging. Alaskan rainforests are also being restored by the Hoonah Native Forest Partnership.(7) This is beneficial to salmon because they need strong tree roots in river banks for stability, shade, and protection. There are also multiple organizations educating the public about sockeye salmon and how humans threaten them.(7) Researchers at the Eagle Fish Hatchery of the Idaho Department of Fish and Game are also working hard to preserve sockeye salmon populations. Their goal is to change from a hatchery-based recovery system to one that relies more on salmon reproduction in the wild. They want to ultimately avoid the extinction of sockeye salmon and support sport and tribal harvest needs. More about their efforts can be read here.

A lot is still unknown about how climate change affects sockeye salmon. The environmental factors that influence migration should be further explored. More research should be done to see if sockeye salmon as a species are changing their migratory behavior in a beneficial or harmful way. How parasitic and fungal infections increase mortality rates in sockeye salmon should be investigated. Specifically, the impacts of the parasite Parvicapsula minibicornis on energy use and kidney function. Additionally, it is very important to determine whether sockeye salmon can physiologically and behaviorally adapt in time in order to survive and eventually thrive in increasing river temperatures. Hopefully, through continued research and conservation efforts, sockeye salmon will be able to adapt and “outswim” the negative effects of climate change.


  1. Crossin GTCT, Hinch SGHG, Cooke SJCJ, Welch DWWW, Patterson DAPA, Jones SRMJRM, et al. Exposure to high temperature influences the behaviour, physiology, and survival of sockeye salmon during spawning migration. Can J Zool [Internet]. 2008 Feb 18 [cited 2021 Apr 23]; Available from: https://cdnsciencepub-com.oca.ucsc.edu/doi/abs/10.1139/Z07-122
  2. Sockeye Salmon [Internet]. Oceana. [cited 2021 Apr 23]. Available from: https://oceana.org/marine-life/ocean-fishes/sockeye-salmon
  3. Jacob C, McDaniels T, Hinch S. Indigenous culture and adaptation to climate change: sockeye salmon and the St’át’imc people. Mitig Adapt Strateg Glob Change. 2010 Dec 1;15(8):859–76.
  4. Sockeye salmon identification - King County [Internet]. [cited 2021 Apr 23]. Available from: https://kingcounty.gov/services/environment/animals-and-plants/salmon-and-trout/identification/sockeye.aspx
  5. Fisheries N. Sockeye Salmon | NOAA Fisheries [Internet]. NOAA. 2021 [cited 2021 Apr 23]. Available from: https://www.fisheries.noaa.gov/species/sockeye-salmon
  6. Eliason EJ, Clark TD, Hague MJ, Hanson LM, Gallagher ZS, Jeffries KM, et al. Differences in Thermal Tolerance Among Sockeye Salmon Populations. Science. 2011 Apr 1;332(6025):109–12.
  7. 5 Ways People Are Helping Wild Salmon [Internet]. [cited 2021 May 7]. Available from: https://www.nature.org/en-us/about-us/where-we-work/united-states/alaska/stories-in-alaska/alaska-five-ways-we-help-salmon/

Image Credit

Two sockeye salmon swimming in different directions” by Milton Love, Marine Science Institute, University of California, Santa Barbara, CA 93106. Obtained from Wikipedia https://en.wikipedia.org/wiki/Sockeye_salmon#/media/File:Sockeye_salmon_swimming_right.jpg.This photograph has been released into the public domain by its author, Milton Love and is available under the Creative Commons CC0 License.

"Fraser River, Canada, near the "West Fraser Historic Trail" (north of Lillooet)” by China Crisis. Obtained from Wikipedia. This photograph is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license.



The Port Jackson Shark and Climate Change Down Under

Author: Joshua Kim


Australia’s beautiful Gold Coast is home to some of the most biologically diverse ecosystems in the entire world. Along the 70+ kilometers of sand, sun, and seaside pubs you might be able to catch a glimpse of Heterodontus portusjacksoni. The Port Jackson shark is a type of bullhead shark that’s endemic to the temperate, coastal region of southern Australia and the Western Pacific. Over the years, Australia has seen a large number of climate driven events that have left the surrounding coast in ruins. The extensive burning of fossil fuels, the recent widespread wildfires, as well as the disappearance of the Great Barrier Reef have played a huge role in managing shark populations. Though the International Union for Conservation of Nature (IUCN) has assessed the Port Jackson shark as “Least Concern” in their conservation status, recent studies have shown that the management of apex predators such them can give us a glimpse into the future of ecosystem management.


What makes the Port Jackson shark so resilient?

The large, blunt headed shark is easily distinguishable amongst other species. Often disregarded as a form of released bycatch, the Port Jackson shark shows its resilience in the presence of humans. The migratory species makes its way south in the summer and returns north to breed during the winter months. The journey to these breeding sites provides a space for them to maintain steady birth/death ratios which in combination with relatively quick development allow sustained populations. On top of this, it makes its living off of native mollusks, urchins, and small fish mainly found in the intertidal where they don’t have many natural predators. More information on the Port Jackson shark’s life cycles can be found here (5).

Underlying this picturesque environment are numerous anthropogenic threats that call for action! Being in conditions where temperatures and chemistry are constantly changing can be so exhausting on an animal. Generally, species have all sorts of ways to adapt to these changes, however, these changes have been happening a lot faster than these animals can adapt. Climate change can reduce the variability of species as well as impact overall biodiversity of an ecosystem leading to a greater loss of function. Studies have demonstrated that the “evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species” (Radchuk et al 2019). This article delves deeper into that issue (4).


So how does the Port Jackson shark handle the heat?

Like most other sharks, the Port Jackson shark uses its keen sense of smell (olfaction) in order to hunt and find food (2). Alternatively, they can compensate this with their other senses (vision, electroreception, mechanoreception), however, at a much lower success rate. This is extremely significant because when temperatures rise, increased metabolisms usually follow.

Think of when yourself sitting in a sauna. You’re not doing much except for sitting there in a hot room. Eventually you start sweating, your heart rate increases, and you start burning calories. As these calories are being burned your metabolism is boosted and your body tries to compensate and maintain homeostasis, a physiological method to maintain a stable internal equilibrium.

Increased human activity and fossil fuel production have contributed to a 1C increase in the average global temperature. You can find more information on the impacts of fossil fuels here. That 1C may not seem a lot in terms of the weather we experience, but when we think of the world as a whole, that could be absolutely detrimental.


You’re telling me it’s not just getting hot?

With temperatures rising, lands on fire, and the world in shambles what more can you ask for? Ocean acidification, carbon dioxide being absorbed from the atmosphere to ocean, is the cause for much of the climate change we have seen in the last few decades. Studies show that H. portusjacksoni suffer from extremely higher rates of embryonic mortality with about 98% of losses due to egg predation (1). In layman’s terms this means that slow development isn’t preferred. However, that’s very the case in ocean acidification.

As mentioned before, the Port Jackson shark relies heavily on its sense of smell, however, the study mentioned here has found that CO2 levels had a direct impact on the sharks’ ability to use olfaction (3). This means that the sharks that were tested were not able to effectively hunt and therefore weren’t able to get the energy needed for the day. In the case of the Port Jackson shark, this can lead to significant changes in predator-prey relationships and the transfer of energy within a food chain.


So, what can you do to help?

Getting a paper in on time let alone tackling the ever-present threat of climate change in our daily lives can be a very daunting task. It may not seem like much, but our efforts matter. The momentum we carry matters. The influence and power of scientifically backed knowledge matters. Here’s some resources you might find helpful in practically applying what we know:

  • Get involved with your community! As stated before, conservation of the Port Jackson shark stands as a glimpse into the future to what our world can look like if the necessary steps towards conservation and accountability aren’t taken.
    • Many universities have conservation programs available to students
    • Research locally threatened species
    • Check your facts! It’s important to be involved and outspoken, however, we never want to spread false information.



  1. Barnes, C., Maxwell, D., Reuman, D. C. & Jennings, S. Global patterns in predator-prey size relationships reveal size dependency of trophic transfer efficiency. Ecology 91, 222– 232 (2010).
  2. Dixson, D. L., Jennings, A. R., Atema, J. & Munday, P. L. Odor tracking in sharks is reduced under future ocean acidification Glob. Change Biol. 21, 1–9 (2014).
  3. Pistevos, J., Nagelkerken, I., Rossi, T. et al. Ocean acidification and global warming impair shark hunting behaviour and growth. Sci Rep 5, 16293 (2015). https://doi.org/10.1038/srep16293
  4. Radchuk, V., Reed, T., Teplitsky, C. et al. Adaptive responses of animals to climate change are most likely insufficient. Nat Commun 10, 3109 (2019). https://doi.org/10.1038/s41467-019-10924-4
  5. Rosa, R. et al. Early-life exposure to climate change impairs tropical shark survival. Proc. Soc. B 281, 20141738 (2014).

Image Credits

  1. File:Heterodontus portusjacksoni wilsons promontory.jpg by Mark Norman / Museum Victoria is licensed with CC BY 3.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/3.0
  2. "Port Jackson Shark mouth" by TCL 1961 is licensed with CC BY-NC-SA 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/2.0/

Zebrafish: The Underwater Lab Rat

Author: Benjamin Weaver

Keywords: Biomedical, climate change, physiology, development, zebrafish

9/10 Scientists Recommend This FIsh

Imagine you are relaxing by a small creek or river. What is the first thing you think of? Is it the sound of gurgling water, the chirping of birds, the refreshing feeling of a quick dip into the cold water? I’d wager that the first thing you think about wouldn’t be the tiny fish darting around from bank to bank. Most people would probably only consider the small fish as entertaining to watch and try to catch as they scurry away from small nets. However, certain species of these tiny fish have huge value to society. The zebrafish, Danio rerio, is a small freshwater fish found from Pakistan to Myanmar, from west to east, and from Nepal to the Indian state of Karnataka from north to south (1). While this fish species is very small, ranging from 2-5cm in length, they are highly valuable species for biomedical research. This species is valuable for this type of research because of its quick development, small size, and other factors. They are used to test the effects of certain chemicals, products, to understand developmental processes, and study genetics. But I’ll digress before things get too in-depth and complicated. The important thing to understand is that these fish are very valuable. However, this species is facing threats due to the effects of climate change such as increasing water temperature and decreasing water pH levels (more acidic). To make matters worse, very little is known about this species in its natural habitat, as most research is done in a lab setting, with lab-raised fish being studied. This makes understanding the impacts of climate change difficult because there may be differences in natural and laboratory fish. However, from what is understood, it is clear that changes to this fish’s environment can have profound effects on its development.

Warm Water Means More Daughters

Studies on the effects of increasing water temperature show that there are multiple impacts on zebrafish. A 2012 study showed that zebrafish sex is affected by water temperature, meaning at different temperatures, a zebrafish egg is more likely to become a male or female (2). This study found that as water temperature increased, the percentage of eggs that became female fish increased. This pattern continued up to their final test temperature, and the researchers concluded that at a certain temperature, all the fish would be female. This study was done in a laboratory setting and was mainly interested in the implications that having only female fish would have on biomedical research. However, wild zebrafish would also be impacted because with fewer male fish in a river, female zebrafish may have difficulty finding a mate. Unfortunately, this is not the only impact of higher water temperature. A 2015 study found that increased water temperature also causes deformities while the fish is developing. Past a certain temperature (32 ℃) there were also higher death rates (3). This study also found that these impacts were most greatly felt in embryos, meaning that increased temperature will make it harder for a new generation of zebrafish to survive to adulthood. Combined with the higher number of females at higher temperatures, this could severely affect this species ability to reproduce and survive.

Too Salty For My Taste

Another impact of climate change is increased salinity. This can further stress zebrafish because it impacts the functioning of their bodies. To put this in perspective, think about what happens when you get too hot. You start to sweat to try and cool off. Past a certain temperature, you can’t cool off fast enough and start to get dizzy and may even get heatstroke. Similarly, higher salinity requires a fish to do something similar to sweating. It needs to control how salty its body is, and if the salinity is too high, it will also be negatively affected like we are in too hot of temperatures. A 2019 study found that when zebrafish are still embryos, they are particularly sensitive to increased salinity because they cannot respond as well. This causes higher death rates and also causes zebrafish to hatch from their eggs earlier to try and escape super salty or acidic conditions (4). This earlier hatching may cause problems for these fish later in life, but no study has been done to determine this.


In terms of understanding the impacts of climate change on zebrafish, there is much work to still be done. In fact, much of this research may not be representative of zebrafish in their natural habitat because they were conducted in laboratories. However, from what is known about their natural habitat and life history, there are several key features about these fish that should give us hope for conserving them in the wild. We know they are found in calmer, shallow waters in smaller creeks and tributaries (1). If these small creeks are blocked or modified such that these calmer pools no longer exist, the habitat for these fish will continue to decrease. Additionally, it is important to limit the amount of waste we dump into rivers and creeks as this will also negatively affect the already stressed habitat of zebrafish. On a more global scale, there needs to be greater action to mitigate climate change, as rising temperatures pose a significant threat to this species. Most importantly, researchers need to focus more attention on understanding these fish in their natural habitat because the limited knowledge makes it difficult to effectively protect these fish. If these objectives can be accomplished, I believe that zebrafish will continue to survive in the wild and provide us the ability to conduct important biomedical research now and in the future. 


Useful Links: https://www.nature.com/articles/pr2008227; https://blogs.biomedcentral.com/on-biology/2015/11/19/little-fish-big-role/


  1. R. E. Engeszer, L. B. Patterson, A. A. Rao, D. M. Parichy, Zebrafish in The Wild: A Review of Natural History And New Notes from The Field. Zebrafish. 4, 21–40 (2007).
  2. D. G. Sfakianakis, I. Leris, C. C. Mylonas, M. Kentouri, Temperature during early life determines sex in zebrafish, Danio rerio (Hamilton, 1822). Journal of Biological Research-Thessaloniki. 17, 68–73 (2012).
  3. C. Pype, E. Verbueken, M. A. Saad, C. R. Casteleyn, C. J. Van Ginneken, D. Knapen, S. J. Van Cruchten, Incubation at 32.5°C and above causes malformations in the zebrafish embryo. Reproductive Toxicology. 56, 56–63 (2015).
  4. J. Ord, Ionic Stress Prompts Premature Hatching of Zebrafish (Danio rerio) Embryos. Fishes. 4, 20 (2019).

Credit to Image 1: "Danio rerio (Danio zebra/Zebra danio)" by berarma is licensed under CC BY-SA 2.0

Credit to Image 2: "File:Aquarias Danio rerio-science institute 01.jpg" by real name: Karol Głąb pl.wiki: Karol007 commons: Karol007 e-mail: kamikaze007 (at) tlen.pl is licensed under CC BY-SA 3.0

Salmon Superheroes Fight Climate Change in Their Bodies!

Author: Jesse James Forrey

Keywords: Chinook Salmon, climate change, physiology, hypoxia

    Salmon have an incredible ability to breathe in the freshwater of rivers and streams as well as in the salt water of oceans. These fish have a special talent to breathe in these different environments and because they can go from inland waterways to the open ocean and back again, they are unique transporters of nutrients between ecosystems. Think of them like postal workers that can make special deliveries that others can’t! Now imagine trying to make that delivery but it is 110० out. Sounds hard right? Salmon are fighting these kinds of intense temperatures and other changes in the water caused by humans. They are dealing with global warming as well as water that is harder to breathe in and showing us just how tough a fish can be!


A little about Salmon
    Salmon are amazing creatures. They live all over the world in the Atlantic and Pacific Oceans and near dozens of different countries! Pacific Chinook Salmon are also known as King Salmon, or Oncorhynchus tshawytscha to scientists, and are some of the biggest of the salmonids. They eat little fish and macroinvertebrates (insects) and can grow to be over 100 pounds (1)! Like most salmon, Chinook are anadromous, which means they live most of their lives in the big salty oceans but swim freshwater rivers and streams to breed and lay their eggs (2). The ability to adjust to these different environments is kind of like a person living on the earth for most of their life, but going to the moon to have a baby and being able to breathe without a mask! This requires special physiological adaptations (changes they make to their bodies) to be able to adjust how oxygen moves into and through them from the water. Also like most other salmon, adult Chinook salmon return to the same rivers where they spawned from, swimming upstream as far as they can until they reach those same rocky banks. Pretty amazing! How do they know how to do that? They are very strong fish!


Climate Change Makes Things Hard

    We all know climate change is real and it turns out rising temperatures not only have direct effects (like how it can feel intense to be in a really hot bath), but also indirect effects. For example, warmer water has different properties than colder water, including less dissolved oxygen. The amount of dissolved oxygen, or DO, in water is for fish what oxygen in the air is for us. It is what we are hoping to bring into our bodies when we breathe! So the more DO in water, the more oxygen fish will get when they breathe and the better off they will be. Warmer water holds less DO, so with climate warming not only will it be hotter but it will also be harder to breathe in certain areas! And this is just one example of indirect and complicated impacts of warming waters.

    Lots of people are studying climate change and the prediction is that things are going to keep getting hotter. Studying how salmon are doing in these intensifying conditions leads to worry  and some hope as well! 


How Hot is too Hot?

    We have all lived through hot days and maybe have spent the hottest parts inside with air conditioning, swimming in a pool or lake, or running in sprinklers. It is a normal response for many animals to find shelter when experiencing extreme weather. Salmon do not always have a cooler area to retreat to and more often than not have to just live in the warmer water of their streams. Scientists have studied how adult Chinook hearts respond to increasing temperatures and found that smaller fish were able to withstand higher temperatures compared to big fish (3). Imagine a bunch of kids were in a giant bath that was slowly getting hotter, and that the biggest kids were the first to get out and say “This is too hot!” This is interesting because if river and stream water keeps getting hotter, then big fish are going to have a harder time! 


Breathing through it all

    So we know that warming water will have less oxygen for Chinook, and less oxygen makes it harder to breathe, but fear not! These salmon seem to have a little extra breathing support built in! A team of researchers in Canada determined that salmon hearts were specifically well built to sustained hypoxic, or low oxygen conditions. Many mammals respond to low oxygen by shutting down parts of their bodies in a way that uses less oxygen (helping them not die), but this study found that Chinook are good at the force and don’t slow down (4). They seem to be set up to keep living healthy lives in low oxygen environments! Which may be important as rising water temperatures carry less oxygen.


But What About Salmon Babies?!

Do young salmon respond the same way as the adult fish in these studies? That is unclear, but we do know that water temperature affects how young salmon grow. Chinook salmon lay their precious eggs in rocky rivers and creek beds in areas called redds. Embryos grow in their eggs at different speeds  depending on the temperature and other conditions of the water they are in. Salmon scientists at the University of California Davis set up an experiment where they transferred groups of embryos from the wild to artificial environments and let them grow with different temperatures and oxygen levels. They found that growing up in higher temperatures actually helped Salmon tolerate higher temperatures, but not at all ages or life stages. Growing up in hypoxia (low oxygen levels) supported better ability to deal with low oxygen levels when older (5). The scientists also noticed different results among different individuals, showing both something called variability (which is like chance, or multiple possible outcomes) and plasticity (kind of like flexibility, or the ability to respond in different ways in different environments) (5). 

It seems at certain points as they grow, growing embryos and baby Chinook have different needs, and that they only have so much energy to deal with different kinds of stress! This makes sense in the way that we also grow at different rates and different ways at different times. Most children learn to walk and talk one at a time, because it takes so much energy to learn how to do either of those things that we can’t do both at the same time.  


Salmon Can’t Actually All Die Right? Not if we help!

    We hope salmon populations will be able to continue to thrive and even grow! Even as climate change threatens to intensify, a lot of people are working to support salmon. Studies like the ones mentioned are helping us understand how warming water and hypoxia may impact their bodies, and scientists are working with others to create important management plans. Indigenous peoples’ voices like the Winnemum Wintu are reaching wider audiences and offering possible actions. Already threatened salmon populations are facing new threats. Even as they have the hearts to help them keep breathing, they will need our help to be able to continue to access their river homes and to fight the impacts of climate change. They may be superheroes, but even the strongest heroes need sidekicks! Join the Salmon Super Team! We can look for solutions together! Get involved with the Run For Salmon to support the Winnemum Wintu’s efforts to protect their salmon. Check out these articles about California Salmon and the importance of Native knowledge in saving salmon from KCET for more information, or visit the Salmonid Restoration Federation to see what some folks are doing. No matter where you live, or how old you are, you can help the Salmon! 


  1. Chinook Salmon (Oncorhynchus tshawytscha) - Species Profile, (available at https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=920).
  2. K. W. Zillig, R. A. Lusardi, P. B. Moyle, N. A. Fangue, One size does not fit all: variation in thermal eco-physiology among Pacific salmonids. Rev Fish Biol Fisheries. 31, 95–114 (2021).
  3. T. D. Clark, E. Sandblom, G. K. Cox, S. G. Hinch, A. P. Farrell, Circulatory limits to oxygen supply during an acute temperature increase in the Chinook salmon (Oncorhynchus tshawytscha). American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 295, R1631–R1639 (2008).
  4. A. K. Gamperl, M. M. Vijayan, C. Pereira, A. P. Farrell, Beta-receptors and stress protein 70 expression in hypoxic myocardium of rainbow trout and chinook salmon. Am J Physiol. 274, R428-436 (1998).
  5. A. M. Del Rio, B. E. Davis, N. A. Fangue, A. E. Todgham, Combined effects of warming and hypoxia on early life stage Chinook salmon physiology and development. Conserv Physiol. 7 (2019), doi:10.1093/conphys/coy078.


Images were found searching the Creative Commons database at https://search.creativecommons.org/ with the search term Chinook Salmon, and Warming.

How Being a Picky Eater is Affecting Our Health: the Orange Spotted Filefish

Author: Brianna Delgado

Have you ever been lucky enough to catch a glimpse of an Oxymonacanthus longirostris, otherwise known as the orange-spotted filefish? More importantly, will you ever have this fortune? The orange-spotted filefish is a small and gorgeous light turquoise fish with vibrant orange spots. This unique looking fish is also known as the longnose filefish because its face ends with an elongated thin mouth, which almost looks like a yellow pipe cleaner! This fish lives amongst the shallow coral reefs in the Indo-Pacific Oceans (1). The filefish depends heavily on having a healthy home environment, because it doesn’t just live in the coral reefs it feeds there too! The filefish is on a strict coral diet and feeds on the polyps of the corals. Sadly, due to coral bleaching events this beautiful animal may go hungry, habitat-less, or even disappear altogether.

What is coral bleaching and why does it happen?

Coral bleaching is what occurs when healthy corals experience stress due to changes in their environment (2). This phenomenon gets its name from the color that the corals turn once they are bleached. What were once healthy, bright, and vibrant corals then turn into drab white corals. One change in environment that is known to stress corals out is a change in temperature. Climate change has contributed to a warming of our oceans, and as our oceans become warmer, our corals become more stressed. This is only one factor that is contributing to an increase in coral bleaching. You can read more about what changes may cause coral bleaching at the National Ocean Service's online ocean facts page(2).

So why can’t the orange-spotted filefish eat something else?

Essentially, the orange-spotted filefish is a very picky eater. It mostly feeds on the corals of the genus Acropora (3). Unfortunately, science has shown that acroporid corals are one of the most at risk corals for bleaching (3). Not only does the fish strictly feed on this type of coral, it has a preference as well. Think of it as loving ice cream, but only wanting to have the chocolate flavored ice cream. When not given their favorite ice cream flavor, the orange-spotted filefish doesn’t throw a tantrum, but its health declines instead. Research has shown that when the fish do not have their favorite flavor of coral available to them they tend to do poorly. Researchers conducted an experiment (4) to see how the orange-spotted filefish would respond when they were given their favorite flavor of coral versus when they were given their least favorite flavor of coral. The experiment showed that the fish that were given their least favorite flavor of coral experienced weight loss, a lower energy reserve, and didn’t reproduce during the time of the experiment. On the other hand, the fish that were given their favorite coral flavor had much better health and reproduced on 49% of the nights spent in the experiment. This study shows how important having healthy acroporid corals available to this species is for their reproductive success, growth, and energy levels. Scientists worry that without the fish’s favorite type of coral around the fish are at risk of going extinct.

In the late 90’s, researchers were able to identify the key differences in a population of orange-spotted filefish before and after a coral bleaching event occurred in 1998 (3). Their observations showed that many of the fish they observed disappeared, had much lower growth rates, and shortened their breeding season by a month (3). The researchers doing this study also observed that fish were increasing the size of their territories (3). This species eats within its own territory, so this means the fish were traveling further than usual in order to find food. It is likely that the fish were going further to find their favorite food because there was less available food in their usual territories due to coral bleaching. This is bad news for the filefish because not only is it hungry, but it’s using more energy in order to feel full. Can you imagine having to walk miles to different grocery stores in order to get each of the ingredients necessary for making your meal? I’m hungry just thinking about it.

Research has shown us how important it is for the survival of this species to have their favorite food. So, what can we do to help?

Coral reefs face many threats that can affect them directly in the water or indirectly, from far and wide. This being said, no matter how close or far you live from coral reefs you can take measures to prevent any direct or indirect harm to coral reefs and the species that depend on them. Here are a few practices you can incorporate into your own daily routine to protect our coral reefs, courtesy of the United States Environmental Protection Agency(5):

  • Recycle and dispose of trash properly.
  • Minimize use of fertilizers.
  • Use environmentally-friendly modes of transportation.
  • Reduce stormwater runoff.
  • Save energy at home and at work.
  • Be conscious when buying aquarium fish.
  • Spread the word! 

Collectively, we can make a difference to help ensure the beautiful orange-spotted filefish can always eat its favorite treat. Practicing daily activities such as recycling properly can minimize the amount of plastic debris that can find its way into our oceans. Using less fertilizers in our gardens can also lower the chances for harming the quality of water that later ends up in the ocean. These are a couple of examples of actions that can be taken to prevent indirect harm of coral reefs. Taking these preventative measures and pairing them with collaborative work within our communities can make a large impact. Together we can educate one another on this issue and find more solutions to help conserve this species and the biodiversity within our oceans.



  1. T. Kokita, A. Nakazono, Seasonal variation in the diel spawning time of the coral reef fish Oxymonacanthus longirostris (Monacanthidae): Parental control of progeny development. Mar. Ecol. Prog. Ser.199, 263–270 (2000).
  2. NOAA, What is coral bleaching? Natl. Ocean Atmos. Adminstration(2016).
  3. T. Kokita, A. Nakazono, Rapid response of an obligately corallivorous filefish Oxymonacanthus longirostris (Monacanthidae) to a mass coral bleaching event. Coral Reefs.20, 155–158 (2001).
  4. R. M. Brooker, G. P. Jones, P. L. Munday, Prey selectivity affects reproductive success of a corallivorous reef fish. Oecologia. 172, 409–416 (2013).
  5. EPA, What You Can Do to Help Protect Coral Reefs. United States Environ. Prot. Agency(2018).


Image Credits

Richard Ling, CC BY-SA 2.0, via Wikimedia Commons

Holobionics, CC BY-SA 4.0, via Wikimedia Commons

Acropora at English Wikipedia, CC BY-SA 3.0, via Wikimedia Commons

The Real Threat of the Pacific Ocean, Not Who You May Think it is

Author: Allison Butterworth

Anyone who has taken a trip to the pacific ocean during the summer has the same fear when entering the water, sharks. In most cases, White Sharks are painted as the “bad guy” in the ocean and they typically play  the role of  a harmful species. Easily identified by their grey or blue skin color, their triangular dorsal fin, and large sharp teeth, seeing one of these species can cause great concern. Especially for humans spending time in the ocean, it seems one of the greatest threats is the Great White Shark. However, Great white sharks might be the ones facing a life altering threat, that threat being climate change.  


The White Shark is one of the most important species in the marine ecosystem. As the top predator, the White Shark plays an important role in maintaining a balance among the many species that make up the marine ecosystem (2). As climate change progresses, the threat to White Sharks and their ecosystem also becomes more critical. In only some parts of the world White Sharks are now considered an endangered species and laws preventing fishing and hunting of White Sharks have been implemented in an attempt to help save the species (2). Harvesting of Sharks is only one of the threats facing the White Sharks. Ocean warming also has a significant impact on the life cycle of Sharks. White Sharks migrate among the pacific ocean annually to participate in mating and searching for food. They typically prefer cold to warm waters and migrate as the ocean temperature changes throughout the year. As the ocean temperatures increase, the migratory patterns of the sharks are changing significantly. White Sharks are now being found along the west coast from Mexico to Alaska. Since the temperature of the water signals to the shark it is time to migrate, their migratory patterns have been disrupted by the increasing ocean temperatures. Another threat to the White Shark is the amount of contaminants entering the ocean. The White Sharks mainly prey on seals, otters, and other large animals. These species are found in coastal environments, some of which are close to human settlements. The contaminants and pollutants produced by humans often end up in their neighboring coastal communities and threaten the health of the species in the marine ecosystem. 


A study by Mull et al.(4) gives more insight to how certain contaminants are leading to physiological problems for White Sharks. The researchers examined the amount of contaminants in the liver tissue, red muscle tissue, and white muscle tissue in Juvenile White Sharks. Juvenile sharks were used in this study because they typically spend the majority of the beginning of their life in a nursery close to urban developments that produce a high amount of contaminants. One specific contaminant that caused significant concern was the level of mercury found in the muscle tissue of the sharks. Sharks typically have a healthy balance of mercury and selenium in their muscle tissues, however the researchers discovered an unproportional ratio of mercury to selenium. This was concerning because it suggests the possibility for mercury poisoning in the young sharks. Mercury poisoning can lead to changes in behavior, emaciation, cerebral lesions, and imparied gonadal development, all of which can be life-threatening to the shark. 


Another cause of concern for the researchers was the level of DDT (an insecticide shown to the right that is now banned in the U.S.) in the liver tissue of the sharks. This was concerning because the liver is an essential organ and any threat to the organ can be detrimental. Although DDT has been banned in the U.S. since 1972, the high levels in the liver tissue suggest the DDT used before the ban still has significant effects on the environment.  


A second study by Mull et al. (1) further investigates the process in which the contaminants are entering the juvenile White Sharks. Researchers used the same methods as their previous study to help them in determining what is causing such high levels of contaminants in the White Sharks. In this study they focused more closely on the levels of DDT found in juvenile White Sharks. Similarly to their previous study, the researchers determined the DDT levels in the sharks were significantly higher compared to other shark species. The researchers believe that due to the extremely high levels of DDT and significantly young age of the sharks, the DDT may have been transferred from the mother to the shark during development of the juvenile shark in utero. The researchers believe that the sharks would be too young to have accumulated DDT levels that high through their diet alone, and they suggest the levels of DDT in the mother influence the levels in her offspring. 


Although White Sharks are perceived as one of the greatest threats, the contaminants from humans and climate change are a much greater threat to the White Sharks. The contaminants found in the ocean have shown to have detrimental physiological effects on White Sharks. Research has shown high mercury levels and high DDT levels found in tissues of juvenile sharks can cause damage to essential physiology of the sharks. There has been some preliminary research done to determine how contaminant levels in the tissues of White Sharks have been absorbed, but there is still a need for further research. More research would have to be performed to determine if the source of high DDT levels and high mercury levels are being transferred from the mother to the child, from the diet of the juvenile, or a mixture of both. In order to protect and help maintain our oceans it is important to consider conservation efforts for the White Shark. As an apex predator of the marine ecosystem, the White Shark is responsible for helping maintain a healthy and balanced relationship among the species in the marine environment. Our oceans are one of the most diverse ecosystems on the planet so it is important to protect the predator that helps maintain the environment.


(1) C. Mull, K. Lyons, M. Blasius, C. Winkler, J. O’Sullivan, C. Lowe, Evidence of Maternal Offloading of Organic Contaminants in White Sharks (Carcharodon carcharias). PLOS One (2013). 

(2) Great White Sharks. nps, (available at https://www.nps.gov/pore/getinvolved/supportyourpark/upload/Great-White-Sharks.pdf) 

(3) Great White Shark. Oceana, (available at https://oceana.org/marine-life/sharks-rays/great-white-shark#:~:text=The%20largest%20 predatory%20fish%20in,is%20the%20great%20white%20shark.&text=Reaching%20len gths%20of%20up%20to,to%20a%20life%20of%20predation). 

(4) Mull, Christopher & Blasius, Mary & O’Sullivan, John & Lowe, Christopher. (2012). Heavy Metals, Trace Elements, and Organochlorine Contaminants in Muscle and Liver Tissue of Juvenile White Sharks, Carcharodon carcharias, from the Southern California Bight. Global Perspectives on the Biology and Life History of Great White Sharks. 59-75. 10.1201/b11532-7. 


Photo Credits
"Great White Shark" by Elias Levy is licensed under CC BY 2.0https://commons.wikimedia.org/wiki/File:Great_White_Shark_(14730723649).jpg

"1955. Ford tri-motor spraying DDT. Western spruce budworm control project. Powder River control unit, Oregon." by USDA Forest Service is marked with CC PDM 1.0https://commons.wikimedia.org/wiki/File:1955._Ford_tri-motor_spraying_DDT._Western_spruce_budworm_control_project._Powder_River_control_unit,_Oregon._(33059292645).jpg

Climate Change is the Biggest Bully of the Ocean According to Hybrid Groupers

Author: Carolina Fulginiti

Key words: Homeostasis, Basal Metabolism, Hyperventilation, Anabolic Energy

A Changing Climate

Climate change started to emerge at the beginning of the industrial revolution. It has lately been creating a big negative impact on the oceans. This is because climate change created by human activities induces an increase of atmospheric CO2 that is being absorbed into the ocean at alarming rates. This is causing the oceans pH levels to decrease which in other words means the oceans are acidifying that is resulting in an increase in water temperature all over the world. To learn more information on ocean acidification and its impact on ocean life, refer to here. Warmer water temperatures is an issue worldwide but it is a bigger problem in tropical waters like the Indo-Pacific. This is because the organisms that live there are already living at the maximum temperature that their bodies can tolerate (1). Most of these organisms have adapted to these tropical waters making it their ideal water temperature. So any change in temperature can be extremely harmful to tropical organisms like Hybrid Groupers.

What is a Hybrid Grouper?

A Hybrid Grouper are two species of Grouper fish, the Tiger Grouper and the Giant Grouper (Mycteroperca tigris × Epinephelus lanceolatus), that have mated together to form the Hybrid Grouper population. These fishes are tropical water species that live in the Indo-Pacific. Juveniles spend most of their time on the coast while adults spend most of their time offshore, where they live depends on their size (2). This is because bigger Hybrid Groupers are capable of fighting off threats more easily than smaller Hybrid Groupers. Hybrid Groupers can be found at close proximity to rocky bottoms or coral reefs which are abundant in the Indo-Pacific (3). Larvae and Juveniles feed on plankton like Copepods and other zooplankton while adults feed on crustaceans and fish. This makes sense because they eat according to their size; smaller Hybrid Groupers eat smaller animals (plankton) and larger Hybrid Groupers eat larger animals. These fish are protogynous hermaphrodites which means they are females at birth and are able to switch sex to males (3). It is not known if Hybrid Groupers always change sex into males or if they only do it if there is a shortage of males for breeding. The ideal temperature for these fish to breed in is around 24ºC to 30ºC which is also their ideal temperature to live in (2). To learn more about these amazing fish, you can visit here.

Climate Change impacting Hybrid Groupers

Climate change is bringing more acidic water and warmer water temperatures to the Indo-Pacific where Hybrid Groupers live. Their ideal water temperature is between 24ºC and 30ºC (1) so increasing the water temperature from this range can kill them. In order for these fish to survive, they have to create physiological responses to deal with the stress of climate change. These fish deal with stress by creating a trade-off between using more energy for physiological traits that are needed in order for them to survive. The other traits that they use when temperatures are normal and are not needed for survival use up less energy so that more energy can be used to help them survive. These animal’s bodies have to respond quickly to the changing environment and allocate the energy efficiently so less harm is done. We are going to look at how one specific female Hybrid Grouper in the Indo-Pacific responds to climate change.

Feeding Behavior

This Hybrid Grouper is one of the many fish exposed to warmer water temperatures and an increase in water acidity. She responds to this type of stress by inducing hyperventilation. Hyperventilation is a response that is common in fish when they are exposed to environments with high amounts of CO2. This is because it causes a decrease in the amount of CO2 in the blood (4). She also responds to climate change stress by inducing protein mobilization where protein is used in the muscle and liver tissues as anabolic energy to support basal metabolism (1). Anabolic energy is the process of synthesizing complex molecules from simpler ones and this case is the building of proteins from amino acids (5). To have a refresher about metabolism and how it works in the body, you can go here. Basal metabolic rate is the minimum amount of energy needed to fuel basic functions. So she uses proteins to allocate energy into increasing their basal metabolism and ventilation rate in order to stay alive. This means that the energy that is used to keep herself alive is energy that is taken from other physiological functions like foraging for food. 

Growth Rate

Another way this fish responds to climate change is that she tends to be smaller when exposed to stress. This is because she is following the same patterns as they did with feeding behavior where she spends less energy on growth rate and more energy trying to maintain homeostasis (1). Where homeostasis is the state of equilibrium inside an organism’s body. Stressors like climate change deviate her homeostatic conditions and she is doing everything possible to try to maintain homeostasis. As I mentioned before, her feeding intake decreased because less energy is being used for food foraging so she will grow at a slower rate (1). This shows that growth rates are not just impacted by temperature but also by feeding behavior, location, type of species, stage maturity, and other physiological traits.

Glycogen and Ammonia Production

The last way this fish responds to climate change stress is by preserving and sacrificing glycogen to support her basal metabolism. Glycogen is one of the main sources of energy for Hybrid Groupers. Preserving glycogen and using other molecules like proteins and lipids to produce glucose, that is used as energy, to support basic metabolic processes (6). When this fish is exposed to an acidic environment, she sacrifices glycogen in both her muscle and liver to use as energy. This is because more energy needs to be used in acidic environments for survival (1). Using more glycogen as energy is also the case for this fish to excrete ammonia production. Waterborne ammonia that includes NH4+ and NH3 are toxic to fish and need to be excreted from their bodies (3). Increase in water acidity is causing ammonia excretion to be done more ineffieciently that can potentially kill this fish if there is a significant build up. 

Hybrid Groupers cannot survive on their own!

As you can see, there are a lot of different changes and responses that are going on in this Hybrid Grouper when she is exposed to a stressful environment. There are likely more responses going on in her body at this time but I only focused on three of them. These responses are complicated ways that these fish expend energy to try to stay alive. I want to note that this is not ideal for them and many fish don’t survive because of the imbalance of energy expenditure. Also, Hybrid Groupers are just one of the many species of Groupers that live in our oceans and they can either respond similarly to this fish or drastically different. As a next step, more research experiments can be done with Hybrid Groupers, like the fish mentioned above, and other species of Groupers together to be able to compare and contrast the results of each species in one area. More research on Groupers available to the public is essential for creating awareness of how dangerous climate change can be for tropical marine life. Once more information is available to the public, then conservation efforts can start to try to save these fishes from being exposed to stressful environments that can potentially kill them.


Photo Credits:

  1. Sea Surface pH: Plumbago, CC BY-SA 3.0 , via Wikimedia Commons
  2. Hybrid Grouper: Kerapu Online, CC BY-NC-SA 2.0, no changes have been made: https://www.flickr.com/photos/kerapuonline/15692244232/in/photostream/

Literature Cited

  1. Y. A. Thalib, R. S. Razali, S. Mohamad, R. Zainuddin, S. Rahmah, M. A. Ghaffar, H. J. Liew, Environmental changes affecting physiological responses and growth of hybrid grouper – the interactive impact of low ph and temperature. Environmental Pollution, 271, 116375 (2021).
  2. J. W. Jr. Tucker, Species profile grouper aquaculture. Southern Regional Grouper Aquaculture, 721, 1-11 (1999).
  3. L. T. Seng, Grouper culture. Tropical Mariculture, 423-448 (1998).
  4. R. Ern, AJ. Esbaugh, Hyperventilation and blood acid-base balance in hypercapnia exposed red drum (Sciaenops ocellatus). J Comp Physiol B., 186(4), 447-60 (2016)
  5. S. Malmquist, K. Prescott, “Energy and Metabolism” in Human Biology, License: Creative Commons Attribution NonCommercial
  6. Y. Tseng, P. Hwang, Some insights into energy metabolism for osmoregulation in fish. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, 148, 419-429 (2008).

Fishing for answers: Pacific salmon

Authors: Kelly Morimoto, Juliana Cizeron, Eugene Tseng, Sarah Wood

When you think of salmon, what comes to mind? Grilled and drizzled in lemon and butter? Served on a bagel with cream cheese? Or maybe dipped in soy sauce and on top of your favorite sushi roll? You may also remember learning about the salmon life cycle at school, or your kids might even have a field trip to a hatchery planned this year. Salmon has become a staple in many people’s lives, but its great popularity has not come without consequences. Before we talk about those consequences, let’s get acquainted with salmons’ lives before they reach the dinner table.

Salmon have one of the most interesting and challenging life cycles in the animal kingdom. Hatched as small fry in freshwater rivers, they must journey out to estuaries and bays to slowly adjust their body to the saltier waters of the ocean.1 Salmon will spend 2-3 years in the ocean, feeding on invertebrates and eventually fish and squid as they get bigger. After growing to be more than two feet long, the salmon are sexually mature and must return to their home river. Much changed from when they left as small fry, male salmon return with bright colors, hunchbacks, and dramatically hooked jaws.2 Salmon must undergo a long, arduous journey upriver, scaling strong currents and sometimes steep banks to return to the place where they were born. Females, silvery grey and brimming with eggs, will use their fins to dig a small nest to protect their young. After females deposit them in the nest, a male salmon will complete the process by externally fertilizing the eggs. This final energy expenditure is too much for the salmon parents, who die soon after mating, leaving their offspring to fend for themselves as they navigate the same streams and currents their parents did.3

The short and physically taxing life cycle of a salmon leaves them vulnerable to human disturbance both in the ocean and in rivers. Through routine overfishing, habitat destruction, and the acceleration of climate change, humans have caused dramatic declines in salmon numbers all along the Pacific northwest. In the past, people have tried quick fixes such as supplemental hatcheries, but they have overlooked some important details in the process. You’ve probably heard different ideas about why salmon are suffering, and it’s easy to get lost in the murky waters of misinformation. So today, our goal is to break it all down for you. Why might hatcheries not be such a good thing after all? How does climate change really impact salmon? Read on to fish for the answers with us.

Something smells fishy . . . examining salmon hatcheries

Hatcheries: both a common field trip for 5th graders, and a simple, feel-good solution to declining salmon populations. Their goal is noble—raise and release salmon into the wild to allow them to mate and create more salmon. Of course, nothing in nature is ever that simple. The truth is, hatcheries are a subject of much debate within the scientific community, and have produced mixed results. That’s not to say that hatcheries are bad and should be shut down, but they do need to be closely monitored for potential problems. For example, researchers in British Columbia discovered that wild coho salmon (Oncorhynchus kisutch) are significantly more physically fit than hatchery-raised coho salmon (7). You might be wondering, how do you measure salmon fitness? Well, instead of making the salmon participate in water aerobics, these scientists surgically implanted transmitters in both wild and hatchery-raised salmon. These transmitters gave them information about how fast the salmon were travelling, the types and amounts of chemical signals they made in their body, as well as if the salmon survived the journey. They found that not only do wild salmon survive 18% more than hatchery salmon, but that they travel out to the ocean twice as fast! These factors, along with the fitness chemicals being monitored by scientists, indicate that wild salmon are overall healthier, and more likely to survive in the ocean. These significant differences between wild and hatchery-raised salmon should raise some questions. Are enough hatchery salmon surviving to mate and help increase the population? And if they do mate, are they passing on their less fit genes to future generations? 

Another group of scientists says yes, these undesirable traits are getting passed on. Hatchery environments make life easy for salmon to encourage rapid growth, which allows female salmon4 to maximise their own reproduction by having many, smaller sized eggs. These eggs are better suited for hatchery life, as they will survive easily there, but the same cannot be said for the outside world. In Vancouver Island and British Columbia in Canada, wild and supplemented populations of chinook salmon (Oncorhynchus tshawytscha), have been observed to display a significant decrease in egg size over the past twenty years (6). However, their non-supplemented, wild population counterparts on Vancouver Island did not show as large of a trend. Though the consequences of these ever-shrinking eggs have yet to be measured in earnest, researchers worry that these small egg sizes will affect future generations of wild salmon. The recorded existence of such an effect in the captive breeding and release programs’ environments suggests that unintentional selection is occurring and causing wild salmon populations to evolve smaller egg sizes at a rapid pace. In other words, we are accidentally changing the way fish develop, act, and reproduce. We may even be increasing features that are bad for survival, known as maladaptive traits, which undermine the very goals of reintroducing farmed fish to natural populations. 

We’re in Hot Water! Climate Change and Salmon

While the recent rise in temperature makes winter a lot more enjoyable, it is threatening the lives of our fish friends, including salmon. Studies in British Columbia have recently linked high river temperatures to high death rates in salmon as they travel upriver to mate. To make matters worse, this increase in water temperatures also causes delayed growth in any surviving fish (8). This was demonstrated in a clever study where healthy salmon were collected and placed in artificial freshwater environments meant to mimic the river water the salmon travel in. Pink and sockeye salmon5 died significantly more at higher temperatures. Death rates would even reach 98% in simulated river environments at 19° celsius!6 Interestingly, sex significantly impacted the survival rate and maturity of the salmon. Females subject to high temperatures were more likely than males to grow slowly and reached sexual maturity later in life. On average, males had higher survival rates than their female fish counterparts. Despite these variations between the different sexes and species, all salmon had significantly higher mortality rate in higher temperature. Funnily enough, data says that the fish should be able to withstand this temperature range, which raises the question: why are these fish dying so rapidly? The scientists who conducted this study believe it may be due to stress induced by the high river temperature. Unfortunately, females seem to be more susceptible to this stress, and thus die more frequently. More studies need to be conducted to hopefully help us identify the exact mechanism as to why these salmon are stressed and dying. Regardless, this paper highlights the detrimental effects of increased river temperatures, and the importance of protection for our B-12 rich salmon! 

Similarly, another study found that female coho salmon experience a 20% greater rate of mortality when compared to males (4). In British Columbia, Canada, researchers raised cohos in the lab, and watched how resilient the fish are to stress at different temperatures. Turns out that, much like your favorite superhero, salmon are very capable of bouncing back from challenges! However, the super salmon’s kryptonite is warming waters, since their resiliency only works when the water is a comfortable temperature. With just a 5° celsius increase in temperature, female coho salmons’ survival plummets. In ecology, female survival is incredibly important. Males can theoretically mate with many females without many negative consequences, but those delicious roe on your sushi roll are much more biologically expensive for females to make. Think of how rich roe is; females pack in all the nutrients their babies need to hatch and survive for a while in the riverbed. Because females can only make so many eggs, they are often a limiting factor for population growth. Decline in the number of females is bad news for the species. But the bad news doesn’t stop there: climate change hurts salmon, which in turn impacts animals that eat salmon such as orcas, dolphins, whales, seals, sea lions, birds, bears, and even humans.7

What Can I Do? Saving salmon is an upriver battle

Here’s the good news: there’s still time for salmon to make a comeback! There are a few simple things you can do to help. As we decide what to eat for dinner, we have to make smart choices. Know where your salmon is coming from, and if it is a sustainable business. Seafood Watch8 is an app for your smartphone, that helps you find tasty salmon that is best for the planet too. Salmon originally declined due to overfishing, so if we regulate how much we eat, we can avoid depleting their populations any further (and turn to supplemental hatcheries less!). Another great step is simply educating yourself; just by reading this blog post, you’re now a little better equipped to make informed choices about your food and the Earth (and you got some fun trivia too)! So next time you indulge in tasty salmon, give a little thanks for the long journey it underwent, as well as the work that scientists are doing to ensure that 50 years from now, salmon can still be on a roll.9


  1. A process known as “smoltification”.
  2. Fun fact: their genus (Oncorhynchus) is Onkos "hooked" and rhynchos "nose".
  3. Our sources, and some extra info, if you want it - Chinook Salmon Identification - King County, Coho Salmon Identification - King County, Alaska Department of Fish and Game, U.S. National Park Service (1-3 in works cited)
  4. Known as “dams”.
  5. Oncorhynchus gorbuscha and Oncorhynchus nerka
  6. 66.2 degrees fahrenheit.
  7. Salmon facts from the Vancouver Aquarium. https://www.vanaqua.org/education/aquafacts/salmon
  8. Seafood Watch from the Monterey Bay Aquarium. https://www.seafoodwatch.org/ 
  9. Pun intended!


Don’t take our word for it, you can read about it too!

  1. Chinook salmon identification - King County, (available at https://www.kingcounty.gov/services/environment/animals-and-plants/salmon-and-trout/identification/chinook.aspx)
  2. Coho salmon identification - King County, (available at https://www.kingcounty.gov/services/environment/animals-and-plants/salmon-and-trout/identification/coho.aspx).
  3. Coho Salmon Species Profile. Alaska Department of Fish and Game, (available at https://www.adfg.alaska.gov/index.cfm?adfg=cohosalmon.main).
  4. A. K. Teffer, S. Hinch, K. Miller, K. Jeffries, D. Patterson, S. Cooke, A. Farrell, K. H. Kaukinen, S. Li, F. Juanes, Cumulative Effects of Thermal and Fisheries Stressors Reveal Sex-Specific Effects on Infection Development and Early Mortality of Adult Coho Salmon (Oncorhynchus kisutch). Physiol. Biochem. Zool. 92, 505–529 (2019).
  5. Frequently Asked Coho Salmon Questions (U.S. National Park Service), (available at https://www.nps.gov/articles/frequently-asked-coho-salmon-questions.htm).
  6. D. D. Heath, J. W. Heath, C. A. Bryden, R. M. Johnson, C. W. Fox, Rapid Evolution of Egg Size in Captive Salmon. Science. 299, 1738–1740 (2003).
  7. C. M. Chittenden, S. Sura, K. G. Butterworth, K. F. Cubitt, N. P. Manel‐la, S. Balfry, F. ØKland, R. S. McKinley, Riverine, estuarine and marine migratory behaviour and physiology of wild and hatchery‐reared coho salmon Oncorhynchus kisutch (Walbaum) smolts descending the Campbell River, BC, Canada. Journal of Fish Biology (2008) (available at https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1095-8649.2007.01729.x).
  8. K. M. Jeffries, S. G. Hinch, E. G. Martins, T. D. Clark, A. G. Lotto, D. A. Patterson, S. J. Cooke, A. P. Farrell, K. M. Miller, Sex and proximity to reproductive maturity influence the survival, final maturation, and blood physiology of Pacific salmon when exposed to high temperature during a simulated migration. Physiol. Biochem. Zool. 85, 62–73 (2012).

Do Rockfish Act Like Humans in Stressful Situations?

Authors: Elsie Herman, Kaitlyn Meeks, Ryan Ortiz

Rockfish, a diverse range of fish species found in the Northern Pacific, are facing more than just a dinner plate with the rising threats of climate change. From the coast of California up to Washington, rockfish have a lot to worry about as the pH of the ocean has begun to decline, causing waters to become more acidic. Coastal waters undergo drastic changes in pH due to coastal upwelling, a process that allows cold, deep, and oxygen rich waters to move towards the surface pushing warmer, nutrient rich waters deeper into the water column. This alters the pH of the water throughout the water column affecting bottom dwelling creatures such as rockfish. Ocean acidification amplifies these changes due to the reaction that occurs between carbon dioxide and seawater (2). Seawater breaks down carbon dioxide into acidic compounds called carbonic acid that aid in lowering the pH of the water. When increasing the amount of carbon dioxide burned into our atmosphere, much of those emissions end up in our oceans, increasing the production of carbonic acid and consequently aiding in ocean acidification. These changes can alter bodily function in vulnerable organisms such as juvenile rockfish (4). 


You’re Not Alone, Rockfish Also Lose All Motivation During Bad Weather (Water).

When it’s cold outside, we love to stay in and lounge around. Rockfish have a similar tendency to slow down when the water is bad. Because they are still developing, increased pH of the water leads young rockfish to change certain body functions such as their metabolism: the build-up and break-down of bodily compounds to create enough energy for the organism to survive (1). During a combination of upwelling events that decrease the amount of available oxygen in the water and ocean acidification, rockfish find it harder to produce enough energy, increasing their metabolism to compensate. This is both exhausting for the fish and causes them to move slower, which compromises their ability to escape predation threats. While hungry predators love the chance to snag an easy meal, rockfish populations are not so happy with these developments. Rockfish can live to be over a hundred years old and do not reach sexual maturity until late in their life (6). With slower moving rockfish being hunted down to small populations, the future of rockfish in the North Pacific is less certain. A reduction in carbon entering ocean systems could aid greatly in helping rockfishes’ metabolism become motivated once again (1) . 

Conservation Physiology Journal: https://watermark.silverchair.com/coy038.pdf?


Rockfish Are Having Trouble Getting Their Act Together.

The environment that you grow up in is important. It determines how you act, how you think, and even your personality. The same can be said for rockfish. The environment that they live in can alter their behavior and physiology. A team of researchers collected juvenile blue and copper rockfish and submitted them to treatments of different pH levels over several weeks (3). After that period of exposure, the rockfish were then put through a number of behavioral and physiological tests. That’s like putting several toddlers in stressful conditions and then testing them. Copper rockfish showed changes in behavioral lateralization, which is a bias between turning their bodies left or right (3). Copper rockfish had a right bias. It may not sound so bad on the surface, but it is critical for escape reactions from predators. Say your being chased by a bear and you can only make right turns when running away. Not very effective is it? Copper rockfish also showed a decrease in critical swim speed. This means that they measured the maximum swim speed the rockfish can sustain before getting tired (3). This is quite problematic if trying to escape from a predator. Finally, the copper rockfish showed a decrease in their aerobic scope. An aerobic scope is an organism’s tolerance range. The smaller the scope, the smaller the range. In Contrast, blue rockfish showed little change in behavior and physiology. This is due to where juveniles can be found, in deep benthic regions of the where pCO2 levels are higher giving it a higher tolerance than its copper counterpart (3).

PLOS: https://journals.plos.org/plosone/article/file?


Feeling the Stress? So are Rockfish

Studies have shown that other animals, even juvenile rockfish, may experience stress in anxiety-inducing situations in a similar manner to humans. GABAa is a chemical in your brain that is supposed to calm your nervous system by preventing excess information from being processed in your brain, so it can focus on what's important (5). However, when rockfish are exposed to stressful living situations like more acidic ocean water, the GABAa receptor in the brain no longer functions, preventing the nervous system from being calmed down. When these fish experience stress due to the lack of functioning GABAa receptors it is shown that they will move into darker spaces to protect themselves. Does this sound like anybody you know? It sounds a lot like humans to me. When I experience anxiety I know that I want to curl up in a ball and hide in my dark room alone. It has been proven that even if these fish have experienced higher stress levels due to more acidic water they can eventually return to their normal selves. While it may take humans a bit longer, as long as the pH levels return to normal for at least 12 days, juvenile rockfish will return to their normal selves (5).

Royal Society of Publishing: https://royalsocietypublishing.org/



Ocean acidification is having negative effects on rockfish. It makes it difficult to obtain enough energy, alters their behavior, and increases their anxiety. It sounds serious, and it is. However, scientists have but scratched the surface, there is still more to learn and a possible solution to the troubles rockfish face. Say you went in for a check-up at the doctors and they found something wrong with you and were able to treat it before it got worse. That what it is for rockfish. There are signs that these problems can be reversible, like stress (5fin). Scientists have found the problem now, which gives us time to find a solution. In the meantime, instead of waiting, we can try to reduce our own CO2 emissions by carpooling or using reusable items. Every small step is a big movement forward. 



We would like to thank Andy Murch, Eiko Jones and Plymouth Marine Laboratory for giving us permission to use their photos.


Literature Cited

1. B. E. Davis, L. M. Komoroske, M. J. Hansen, J. B. Poletto, E. N. Perry, N. A. Miller, S. M. Ehlman, S. G. Wheeler, A. Sih, A. E. Todgham, N. A. Fangue. 2018. Juvenile rockfish show resilience to CO2-acidification and hypoxia across multiple biological scales. Conservation Physiology. 6, (2018).


2. H. Yoon, C. Park, S. Moon, K. Han, H. Suh, Y. An, S. Choi. Comparative stomach contents and growth of the juvenile black rockfish Sebastes inermis reared in illuminated and unilluminated cages. Fisheries Science. 74, 657-661(2008).  


3. S. L. Hamilton, C. A. Logan, H. W. Fennie, S. M. Sogard, J. P. Barry, A. D. Makukhov, L. R. Tobosa, K. Boyer, C. F. Lovera, G. Bernardi. Species-specific responses of juvenile rockfish to elevated pCO2: from behavior to genomics. PLoS ONE. 12, 1-23 (2017).


4. S. J. Bobko, S. A. Berkeley. Maturity, ovarian cycle, fecundity, and age-specific parturition of black rockfish (Sebastes melanops). Fish Bulletin. 102, 418-429 (2004).


5. T. J. Hamilton, A. Holcombe, M. Tresguerres. CO2-induced ocean acidification increases anxiety in rockfish via alteration of GABAA receptor functioning. Proceedings of the Royal Society B: Biological Sciences. 281, 1-7 (2014).


6. W. H. Lenarz, T. W. Echeverria. Sexual dimorphism in Sebastes. Environmental Biology of Fishes. 30, 71-80 (1991).  


Jones, E. (n.d.). Copper Rockfish Juvenile . photograph. Retrieved from https://www.eikojonesphotography.com/ngg_tag/juvenile-copper-rockfish/#gallery/juvenile-copper-rockfish/4793/cart


Ocean Acidification . (n.d.). photograph. Retrieved from https://www.pml.ac.uk/Research/Research_topics/



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