Dolphin Communication: IT’S TOO LOUD! WHAT?! IT’S TOO LOUD! WHAT DID YOU SAY?!

Author: Virginia Chau

Hi! Can you hear me? No? Hold on a sec. Hello there! You’re probably wondering why I couldn’t hear you? Well, that’s because my neighbors were fighting and playing loud music. So, my housemates and I just told them to be quiet. Similar to my situation, Representative Cunningham honked an airhorn to demonstrate the effects of seismic blasting in the ocean. Now, imagine the loudest and most annoying sound possible, and then play that almost every minute. That is exactly what marine animals hear when there are many ships around, as they create extra noise in the ocean. This is extremely detrimental to the communication between species, especially those who use echolocation to talk. For example, Bottlenose dolphins, Tursiops truncatus, will naturally work together in a group. Dolphins would often work together to herd fish into a ball, creating a prey ball (1). While surrounding the prey ball, dolphins will typically pick fish from the sides, under or through the ball (1). However, without communication, they probably wouldn’t be able to effectively communicate to create this strategy.

Before we talk more about the effects of sound on dolphins, you may need some background information on them. Bottlenose dolphins can be seen in coastal temperate to tropical water (2). They have a spindle neck with a streamlined body form (4). These dolphins can grow to 3-4 m, and adults weigh about 150–650 kg (2). Their slightly stocky bodies are grey, have a domed melon, and a medium-sized beak (2). They typically eat fish and squid (3). Bottlenose dolphins can live to at least 40 years, with some females living to be 60 years old (3). Dolphins will reach sexual maturity and begin reproducing between 5 and 15 years old (3). Once pregnant, females will remain so for 12 months (3). After mothers have given birth, they will nurse their calf for 20 months, and the calf will stay with her for 3 to 6 years (3).

While dolphins are not considered a threatened species, their environment is being affected by the amount of sound pollution in the ocean. Dolphins use echolocation and a series of clicks in order to communicate and understand their surroundings. As a result, the amount of manmade noise in the oceans is affecting the dolphin’s communication. Mid-frequency sonar from these ships can cause temporary hearing loss in bottlenose dolphins (5). There needs to be repeated exposure to generate effects (5). So far, we only see a temporary effect with prolonged sonar. But, because there is always constant sonar coming from ships, Dolphins are experiencing long-term hearing loss. Sonar has reduced the hearing abilities of dolphins, reducing their ability to communicate when foraging. When a dolphin’s ability to hear is lost, they can miss important information or signals.

In order to talk to each other, dolphins need to communicate louder to overpower noise produced by ships, requiring a lot of energy. Many marine species are producing longer or more repetitive vocalizations to compensate for the extra noise in the ocean. However, this comes at the cost of energy, resulting in a shift in metabolic rate. Vocalization can increase their metabolic rate by 1.2 to 1.5 times from that of their resting metabolic rate (6). Due to the loss of hearing and energy costs of lengthened vocalizations, it has become increasingly difficult for dolphins to communicate. Remember, when I talked about how dolphins create balls of fish to forage? This strategy takes communication, but with their hearing loss, dolphins end up spending unnecessary time and energy on repetitive communication.

Another adaptation dolphins have used to compete against boats is to use shorter, less complex vocalizations to communicate with each other (7). The reduced clicking and vocalization means less information is being shared resulting in less effective communication. This is a clear example of the effects of sound pollution because the loss of information can affect parent-offspring proximity and group cohesion. The time calves stay with mothers is important to survival, as the young learn the pod’s communication and survival skills. 

Right now, there is not much being done to reduce the amount of noise in the ocean. However, we can reduce the amount of noise in the ocean by not supporting cruise ships or buying items internationally. I recognize that there are places like Japan and Hawaii that need their items shipped, but we should put a limit to the amount we are shipping. Dolphins are extremely majestic and intelligent creatures, so we should do our best to keep the environment the way it was intended. Otherwise, new generations won’t know what dolphins are. Their extinction can cause a horrible chain reaction in the marine ecosystem.

Citations

1. Vaughn-Hirshorn, R. L., Muzi, E., Richardson, J. L., Fox, G. J., Hansen, L. N., Salley, A. M., Dudzinski, K. M. & Würsig, B. (2013). Dolphin underwater bait-balling behaviors in relation to group and prey ball sizes. Behavioural processes, 98, 1-8
2. Cozzi, B., Huggenberger, S., Oelschläger, H., Demma, M., Gorter, U., & Oelschläger, J. (2016). Anatomy of dolphins : insights into body structure and function. Academic Press is an imprint of Elsevier.
3. Fisheries, N. (n.d.) Common Bottlenose Dolphin. NOAA, www.fisheries.noaa.gov/species/common-bottlenose-dolphin.
4. F.E. Fish, J.T. Beneski, D.R. Ketten. Examination of the three-dimensional geometry of cetacean flukes using computed tomography scans: hydrodynamic implications Anat. Rec. Adv. Integr. Anat. Evol. Biol., 290 (2007), pp. 614-623
5. Mooney, T. A., Nachtigall, P. E., & Vlachos, S. (2009). Sonar-induced temporary hearing loss in dolphins. Biology letters, 5(4), 565-567.
6. Holt, M. M., Noren, D. P., Dunkin, R. C., & Williams, T. M. (2015). Vocal performance affects metabolic rate in dolphins: implications for animals communicating in noisy environments. Journal of Experimental Biology, 218(11), 1647-1654.
7. Fouda, L., Wingfield, J. E., Fandel, A. D., Garrod, A., Hodge, K. B., Rice, A. N., & Bailey, H. (2018). Dolphins simplify their vocal calls in response to increased ambient noise. Biology letters, 14(10), 20180484.

Image Credits

"Dolphins and Ships"  by Denni Schnapp 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/" data-sk="tooltip_parent">https://creativecommons.org/licenses/by-nc-sa/2.0/

airhorn via http://bigredbarrel.com and the blu show" by scottobear 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/