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- 1. Impact of Gray Whales on Benthic Communities Caitlin Stewart
- 2. Gray Whales ➢ Easily recognized due to color and lack of a dorsal fin. ➢ Adults can be 36-50 ft long and weigh up to 45 tons. ➢ Mainly located in the North Pacific ocean (travel for feeding and migration). (NOAA)
- 3. What is site fidelity?
- 4. Habitat and Population Status ➢ 2 main populations ○ Eastern ■ United States and Canada ○ Western ■ Russia and Japan ➢ Primarily a coastal species ➢ Extremely long migrations
- 5. What do gray whales typically eat?
- 6. Diet ➢ Opportunistic feeders ➢ Planktonic or benthic diets ➢ Main food sources?
- 7. Impact on Benthic Community ➢ Disruptive bottom feeders ➢ Gray whales tend to return to the same feeding grounds. ➢ Cover tens of kilometers when feeding ➢ Many animals found dislodged and injured after whale feedings. (Oliver 1985)
- 8. How are gray whales able to feed off the bottom of the ocean?
- 9. How do Gray Whales Feed? ➢ Unlike any other whale species ➢ Gray whale feeding habits (Bird, 2020)
- 12. Can you think of any possible positives of gray whale feeding?
- 13. Are there positives of gray whale feeding? ➢ Easy to look at the negatives ➢ Possible positives! ➢ Benthic productivity ➢ Food for surface feeding birds? (Bird, 2020) (Grebmeier, 1992)
- 14. What other mammals feed in a similar way to gray whales?
- 15. What other mammals feed in the benthos? ➢ Walruses! ○ Massive benthic bioturbation ○ Nutrient flux ➢ 3 million metric tons of benthic biomass/year (Ray 2006)
- 16. Why are gray whales so important? ➢ In the process of becoming endangered ○ Why? ➢ Loss of whales = detrimental impacts ○ Climate change ○ Carbon concentrations ➢ Waste products
- 17. Restoration ➢ Curiosity towards boats leads to vessel strikes ➢ Many obstacles on their migration routes ○ Vessel strikes ○ Entanglement ○ Sound pollution ○ Pollution ➢ NOAA fisheries and other organizations work to conserve gray whales
- 18. Works Cited Anderson, E., & Lovvorn, J. (2008). Gray whales may increase feeding opportunities for avian benthivores. Marine Ecology Progress Series, 360, 291–296. https://doi.org/10.3354/meps07359 Oliver, J. S., & Slattery, P. N. (1985). Destruction and opportunity on the sea floor: Effects of gray whale feeding. Ecology, 66(6), 1965–1975. https://doi.org/10.2307/2937392 Filatova, O. A., Fedutin, I. D., Pridorozhnaya, T. P., & Hoyt, E. (2022). Bottom-feeding gray whales eschrichtius robustus demonstrate a finer scale of site fidelity than pelagic-feeding humpback whales megaptera novaeangliae on an Arctic feeding ground. Polar Biology, 45(6), 1013–1021. https://doi.org/10.1007/s00300-022-03048-x Moore, S., Grebmeier, J. M., & Davies, J. R. (2003). Gray whale distribution relative to forage habitat in the northern Bering Sea: Current conditions and retrospective summary. Canadian Journal of Zoology, 81(4), 734–742. https://doi.org/10.1139/z03-043 Rice, D., Wolman, A., & Braham, H. (n.d.). The Gray Whale, Eschrichtius robustus. NOAA. Retrieved from https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/MFR/mfr464/mfr4643.pdf Coyle, K. O., Bluhm, B., Konar, B., & Blanchard, A. (2007). Amphipod prey of gray whales in the Northern Bering Sea: Comparison of biomass and distribution between the 1980s and 2002–2003. Deep Sea Research Part II: Topical Studies in Oceanography, 54(23-26), 2906–2918. https://doi.org/10.1016/j.dsr2.2007.08.026 Oliver, J. S., & Slattery, P. N. (1985). Destruction and opportunity on the sea floor: Effects of gray whale feeding. Ecology, 66(6), 1965–1975. https://doi.org/10.2307/2937392 Alter, S. E., Rynes, E., & Palumbi, S. R. (2007). DNA evidence for historic population size and past ecosystem impacts of Gray Whales. Proceedings of the National Academy of Sciences, 104(38), 15162–15167. https://doi.org/10.1073/pnas.0706056104 Brower, A. A., Ferguson, M. C., & Schonberg, S. V. (2017). Gray whale distribution relative to benthic invertebrate biomass and abundance: Northeastern Chukchi Sea 2009–2012. Deep Sea Research Part II: Topical Studies in Oceanography, 144, 156–174. https://doi.org/10.1016/j.dsr2.2016.12.007 Grebmeier, J., & Harrison, N. (1992). Seabird feeding on benthic amphipods facilitated by gray whale activity in the Northern Bering Sea. Marine Ecology Progress Series, 80, 125–133. https://doi.org/10.3354/meps080125 Brüniche-Olsen, A., Westerman, R., Kazmierczyk, Z., & Vertyankin, V. V. (2018). The Inference of Gray Whale (Eschrichtius Robustus) historical population attributes from whole-genome sequences. BMC Evolutionary Biology, 18(1). https://doi.org/10.1186/s12862-018-1204-3 Moore, S. E., & Huntington, H. P. (2008). Arctic marine mammals and climate change: Impacts and resilience.Ecological Applications, 18(sp2). https://doi.org/10.1890/06-0571.1 Sanchis, C., Soto, E. H., & Quiroga, E. (2021). The importance of a functional approach on benthic communities for aquaculture environmental assessment: Trophic groups – a polychaete view. Marine Pollution Bulletin, 167, 112309. https://doi.org/10.1016/j.marpolbul.2021.112309 Schonberg, S. V., Clarke, J. T., & Dunton, K. H. (2014). Distribution, abundance, biomass and diversity of benthic infauna in the Northeast Chukchi Sea, Alaska: Relation to environmental variables and marine mammals. Deep Sea Research Part II: Topical Studies in Oceanography, 102, 144–163. https://doi.org/10.1016/j.dsr2.2013.11.004 Gammal, J., Norkko, J., Pilditch, C. A., & Norkko, A. (2016). Coastal hypoxia and the importance of benthic macrofauna communities for ecosystem functioning. Estuaries and Coasts, 40(2), 457–468. https://doi.org/10.1007/s12237-016-0152-7
Editor's Notes
- The impact of gray whales on benthic communities.
- So this is just some background about gray whales that I think is important to know before jumping into the main topic. The gray whale is easily recognizable because of its mottled gray color and lack of a dorsal fin. Instead of a fin it actually has a low hump and knobs around the dorsal ridge which can be quickly spotted when a whale surfaces. An adult gray whale can be up anywhere from 36-50 feet long and weigh between 16 and 45 tons. Gray whales are mainly located in the North Pacific ocean. However they do travel into more coastal areas to feed and of course because of migration. An important thing to understand is what is site fidelity?
- So does anyone know what site fidelity is? So site fidelity is the tendency of individuals to return to the same area repeatedly or remain in an area for an extended period of time. This allows for whales to know when and where they will be able to find food. Understanding a species site fidelity is extremely important in order to understand their biological profile and to work towards conservation. This is extremely relevant for gray whales because while they do tend to return to the same areas- and this may make you think that at least the disruptions are localized and not too expansive- these whales can cover tens of kilometers per day while feeding. This is an opportunity for many disruptions.
- There are 2 main populations of gray whales. The eastern population which is found along the coasts of the United States and Canada. And the western population, which is found along the coasts of Russia and Japan. The eastern population spends summers north of alaska and migrates south towards mexico for the winter. The western population spends most of their time off of the coast of russia and their migration routes are not well known. Gray whales are without a doubt the most coastal of the large whales. It is rare to see them further than 20-30 kilometers off shore. They predominantly are found in shallow coastal waters of the north Pacific ocean. Gray whales travel extremely large distances and have one of the world’s longest migrations- making a yearly round trop of around 15000 to 20000km.
- So now that you have some background about gray whales we can talk a little bit about their diet. Gray whales are opportunistic feeders. They are primarily bottom feeders but they can eat planktonically or benthically depending on a couple factors. The main foods that gray whales eat are crustaceans, plankton, larvae, and really anything that they can suction up from the floor while feeding.
- Gray whales are very disruptive bottom feeders. The feeding of these whales can disturb parts of the intertidal and subtidal sediments and of course the benthos. They remove the infaunal vertebrate prey and sediments through powerful suction. This can alter the abundances of benthic invertebrates for up to months after the feeding. This also stirs up a lot of sediment. Because of the fact that gray whales tend to return to the same feeding grounds, it can cause extensive disruptions. Another important piece of information is that even though gray whales return to generally the same area, they can cover tens of kilometers a day when feeding. This is an opportunity for many disruptions. A study was done in the Bering Sea where benthic communities were sampled and analyzed. Many of the animals that were seen were either injured, dislodged or both. This is a strong indicator of the dramatic impact that gray whales have on the hierarchy of benthic communities.
- Alright so does anyone know how gray whales are able to feed off of the bottom of the ocean?
- Gray whales feed unlike other whale species such as the humpback and blue whales. They feed regularly directly off of the bottom of the ocean. To do this, they roll onto one of their sides and swim along the bottom while suctioning up sediment and prey. (TALK ABOUT HOW ONE SIDE IS AFFECTED) After the whale has finished feeding, the sediment and water is filtered out of their bodies and this results in a large sediment stream. These sediment streams are a strong indicator of benthic feeding and can be easily identified in drone footage due to their size.
- So these are a few photos of the aftermath of a gray whale feeding. Of course you can see the giant plumes of sediment that are flowing behind the whale in the top photo and in the bottom you can see how one movement of these whales can stir up a ton of sediment. The location of whale feeding can also be identified due to the pits that occur as a result of these feedings. These pits can range anywhere from 2-20m^2 so they are pretty extensive and easily recognizable. They can be seen by using side-scan sonar which is a method used to map the seafloor. To give you a scale of how disruptive these feedings are, it is usually a 2 month recovery period for the pits to return back to normal conditions.
- https://www.youtube.com/watch?v=mwBM_hHQv-M So I’m not going to make you guys watch the whole thing but this is just a video I found that is a great showcase of gray whale feeding so we can watch a minute of that now. As you can see it goes down to the bottom and turns on its side so that it can suction up the sediments and prey from the benthos.
- Of course, it would be pretty easy to only talk about the negative impacts of gray whale feeding. But there have been findings that the foraging behavior of these whales can help to maintain the sand substrate and helps to maintain and balance the levels of benthic dwelling amphipods. So while it is obviously a pretty violent disturbance and has long lasting impacts- it may play a large role in benthic productivity. Another positive of gray whale feeding is that when the whale is feeding, some animals are being brought to the surface. Some of these animals include benthic amphipods- when they are brought to the surface they are able to become a food source for surface feeding birds. The local distributions of these birds is therefore somewhat shaped by whale feeding activity and their diet can show the benthic population structure. This is another reason why understanding the patterns of these feedings is important- it isn’t only impacting the benthos!!
- Another marine mammal that greatly impacts the benthos is the walrus. Walruses play a very large role especially in the arctic. It has been found that walrus feeding strongly influences productivity and ecological function via benthic bioturbation and nutrient flux. Nutrient flux is the mixture of nutrients and sediments from the seafloor into the overlying water column. It is known that walruses consume around 3 million metric tons of benthic biomass per year. This obviously is a very large scale impact! The long term bioturbation caused by these walruses result in significant changes in sediment and the community structure in the benthos, as well as magnifying nutrient flux. Unfortunately, the effects of climate change and sea ice moving north could result in the walrus’ ecological role to be diminished or lost. This could result in the benthic ecosystem being devastatingly altered and many resources would not be distributed as they are now.
- While it is not something that is fun to think about, gray whales are becoming increasingly endangered. Due to oil and gas pollution, getting caught in fishing gear and ship collisions, there are many factors that are causing harm to these creatures. Unfortunately, the loss of these gray whales would have detrimental environmental impacts. Gray whales tend to feed on phytoplankton, krill, and other small organisms as we talked about before. These organisms are responsible for absorbing a ton of carbon from the atmosphere. In the absence of whales, there would more likely than not be an increase in the rate of climate change and a rise in carbon amounts. Another reason that whales are vital is because their waste that is produced after eating is an important nutrient for phytoplankton and other marine animals. Loss of these nutrients could cause incredibly large problems for the ocean and the animals in it.
- Gray whales are unfortunately known for their curiosity toward boats and are the focus of whale watching and ecotourism along the west coast. Due to their long migrations, they face many obstacles along the way such as vessel strikes, entanglement, sound pollution and more that can put them in danger or kill them on their route. NOAA fisheries along with other organizations work to conserve gray whales by trying to reduce fisheries interactions, noise, pollution, and more through public input, research, and outreach. Hopefully due to these efforts we will see increases in population sizes of gray whales and they can continue to help the oceans to thrive.