{"id":3210,"date":"2020-01-06T14:18:36","date_gmt":"2020-01-06T21:18:36","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/gemmlab\/?p=3210"},"modified":"2020-09-16T16:43:33","modified_gmt":"2020-09-16T23:43:33","slug":"what-are-the-ecological-impacts-of-gray-whale-benthic-feeding","status":"publish","type":"post","link":"https:\/\/blogs.oregonstate.edu\/gemmlab\/2020\/01\/06\/what-are-the-ecological-impacts-of-gray-whale-benthic-feeding\/","title":{"rendered":"What are the ecological impacts of gray whale benthic feeding?"},"content":{"rendered":"\n

Clara Bird<\/a>, Masters Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab<\/p>\n\n\n\n

Happy new year from the GEMM lab! Starting graduate school comes with a lot of learning. From skills, to learning about how much there is to learn, to learning about the system I will be studying in depth for the next few years. This last category has been the most exciting to me because digging into the literature on a system or a species always leads to the unearthing of some fascinating and surprising facts. So, for this blog I will write about one of the aspects of gray whale foraging that intrigues me most: benthic feeding and its impacts. <\/p>\n\n\n\n

How do gray whales\nfeed?<\/strong><\/h2>\n\n\n\n

Gray whales are a unique species. Unlike other baleen whales, such as humpback and blue whales, gray whales regularly feed off the bottom of the ocean (Nerini, 1984). They roll to one side and swim along the bottom, they then suction up (by depressing their tongue) the sediment and prey, then the sediment and water is filtered out of the baleen. In fact, we use sediment streams, shown in Figure 1, as an indicator of benthic feeding behavior when analyzing drone footage (Torres et al. 2018).<\/p>\n\n\n\n

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Figure 1. Screenshot of drone video showing sediment streaming from mouth of a whale after benthic feeding. Video taken under NOAA\/NMFS permit #21678<\/em> <\/figcaption><\/figure>\n\n\n\n

Locations of benthic feeding can be identified without directly observing a gray whale actively feeding because of the excavated pits that result from benthic feeding (Nerini 1984). These pits can be detected using side-scan sonar that is commonly used to map the seafloor. Oliver and Slattery (1985) found that the pits typically are from 2-20 m2<\/sup>. In some of the imagery, consecutive neighboring pits are visible, likely created by one whale in series during a feeding event. Figure 2 shows different arrangements of pits.<\/p>\n\n\n\n

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Figure 2. Different arrangements of pits created by feeding whales (Nerini 1984).<\/em> <\/figcaption><\/figure>\n\n\n\n

Aside from how fascinating the behavior is, benthic feeding is also interesting because it has a large impact on the environment. Coming from a background of studying baleen whales that primarily feed on krill, I had not really considered the potential impacts of whale foraging other than removing prey from the environment. However, when gray whales feed, they excavate large areas of the benthic substrate that disturb and impact the habitat.<\/p>\n\n\n\n

The impacts of benthic feeding<\/strong> <\/h2>\n\n\n\n

Weitkamp et al. (1992) conducted a study on gray whale benthic foraging on ghost shrimp in Puget Sound, WA, USA. This study, conducted over two years, focused on measuring the impact of benthic foraging by its effect on prey abundance. They found that the standing stock of ghost shrimp within a recently excavated pit was two to five times less than that outside the pit, and that 3100 to 5700 grams of shrimp can be removed per pit. From aerial surveys they estimated that within one season feeding gray whales created between 2700 and 3200 pits. Using these values, they calculated that 55 to 79% of the standing stock of ghost shrimp was removed each season by foraging gray whales. Interestingly, they found that the shrimp biomass within an excavated pit recovered within about two months.<\/p>\n\n\n\n

Oliver and Slattery (1985) also\nfound a recovery period of about 2 months per pit in their study on the effect\nof gray whale benthic feeding on the prey community in the Bering Sea. They\nsampled prey within and outside feeding excavations, both actual whale pits and\nman-made, to test the response of the benthic community to the disturbance of a\nfeeding event. They found that after the initial feeding disturbance, the\nexcavated area was rapidly colonized by scavenging lysianassid amphipods, which\nare small (10 mm) crustaceans that typically eat dead organic material. These\namphipods rushed in and attacked the organisms that were injured or dislodged\nby the whale feeding event, typically small crustaceans and polychaete worms.\nWithin hours of the whale feeding event, these amphipods had dispersed and a\ndifferent genre of scavenging lysianassid amphipods slowly invaded the\nexcavated pit further and stayed much longer. After a few days or weeks these\npits collected and trapped organic debris that attracted more colonists.\nIndeed, they found that the number of colonists remained elevated within the\nexcavated areas for over two months. <\/p>\n\n\n\n

Notably, these results on how the\ndisturbance of gray whale benthic feeding changes sediment composition support\nthe idea that this foraging behavior maintains the sand substrate and therefore\nhelps to maintain balanced levels of benthic dwelling amphipods, their primary\nsource of prey in this study area (Johnson and Nelson, 1984). Gray whales scour\nthe sea floor when they feed and this process leads to the resuspension of lots\nof sediments and nutrients that would otherwise remain on the seafloor.\nTherefore, while this feeding may seem like a violent disturbance, it may in\nfact play a large role in benthic productivity (Johnson and Nelson, 1984;\nOliver and Slattery, 1985).<\/p>\n\n\n\n

These ecosystem impacts of gray\nwhale benthic feeding I have described above demonstrate the various stages of\ninvaders after a feeding disturbance, and the process of succession. Succession\nis the ecological process of how a community structure builds and grows.\nPrimary succession is when the structure grows from truly nothing and secondary\nsuccession occurs after a disturbance, such as a fire. In secondary succession,\nthere are typically pioneer species that first appear and then give way to\nother species and a more complex community eventually emerges. Succession is\nwell documented in many terrestrial studies after disturbance events, and the\nprocesses of secondary succession is very important to community ecology and\nresilience.<\/p>\n\n\n\n

Since gray whale benthic foraging\ndoes not impact an entire habitat all at once, the process is not perfectly\ncomparable to secondary succession in terrestrial systems. Yet, when thinking\nabout the smaller scale, another example of succession in the marine environment\ntakes place at a whale fall. When a whale dies and sinks to the ocean floor, a\nsmall ecosystem emerges. Different organisms arrive at different stages to\nscavenge different parts of the carcass and a food web is created around it. <\/p>\n\n\n\n

To\nme the impacts of gray whale benthic feeding are akin to both terrestrial disturbance\nevents and whale falls. The excavation serves as a disturbance, and through secondary\nsuccession the habitat is refreshed via stages of different species colonization\nuntil the system eventually returns to the pre-disturbance levels. However,\nlike a whale fall the feeding event leaves behind injured or displaced\norganisms that scavengers consume; in fact seabirds are known to take advantage\nof benthic invertebrates that are brought to the surface by a gray whale feeding\nevent (Harrison, 1979).  <\/p>\n\n\n\n

So much of our research is focused\non questions about how the changing environment impacts our study species and\nnot the other way around. This venture into the literature has provided me with\nan important reminder to think about flipping the question. I have enjoyed\nstarting 2020 with a reminder of how cool gray whales are, and that while a\ndisturbance can initially be thought of as negative, it may actually bring\nabout important, and positive, change.<\/p>\n\n\n\n

References<\/h2>\n\n\n\n

Nerini, Mary. 1984. \u201cA Review of Gray Whale Feeding\nEcology.\u201d In The Gray Whale: Eschrichtius Robustus<\/em>, 423\u201350. Elsevier\nInc. https:\/\/doi.org\/10.1016\/B978-0-08-092372-7.50024-8.<\/p>\n\n\n\n

Oliver, J. S., and P. N. Slattery. 1985. \u201cDestruction and\nOpportunity on the Sea Floor: Effects of Gray Whale Feeding.\u201d Ecology<\/em> 66\n(6): 1965\u201375. https:\/\/doi.org\/10.2307\/2937392.<\/p>\n\n\n\n

Torres, Leigh G., Sharon L. Nieukirk, Leila Lemos, and Todd\nE. Chandler. 2018. \u201cDrone up! Quantifying Whale Behavior from a New Perspective\nImproves Observational Capacity.\u201d Frontiers in Marine Science<\/em> 5 (SEP).\nhttps:\/\/doi.org\/10.3389\/fmars.2018.00319.<\/p>\n\n\n\n

Weitkamp, Laurie A, Robert C Wissmar, Charles A Simenstad,\nKurt L Fresh, and Jay G Odell. 1992. \u201cGray Whale Foraging on Ghost Shrimp\n(Callianassa Californiensis) in Littoral Sand Flats of Puget Sound, USA.\u201d Canadian\nJournal of Zoology<\/em> 70 (11): 2275\u201380. https:\/\/doi.org\/10.1139\/z92-304.<\/p>\n\n\n\n

Johnson, Kirk R., and C. Hans Nelson. 1984. \u201cSide-Scan Sonar\nAssessment of Gray Whale Feeding in the Bering Sea.\u201d Science<\/em> 225 (4667):\n1150\u201352.<\/p>\n\n\n\n

Harrison, Craig S. 1979. \u201cThe Association of Marine Birds\nand Feeding Gray Whales.\u201d The Condor<\/em> 81 (1): 93.\nhttps:\/\/doi.org\/10.2307\/1367866.<\/p>\n","protected":false},"excerpt":{"rendered":"

Clara Bird, Masters Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab Happy new year from the GEMM lab! Starting graduate school comes with a lot of learning. From skills, to learning about how much there is to learn, to learning about the system I will be studying in depth for … Continue reading What are the ecological impacts of gray whale benthic feeding?<\/span><\/a><\/p>\n","protected":false},"author":9938,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[188686,1310686],"tags":[1834,1310532,1324,677522,44681,1310685,634945,1946,529],"class_list":["post-3210","post","type-post","status-publish","format-standard","hentry","category-current-projects","category-behavior-and-body-condition","tag-behavior","tag-clara-bird","tag-ecology","tag-foraging-ecology","tag-gray-whale","tag-gray-whale-individual-behavior-and-body-condition","tag-gray-whales","tag-impact","tag-whales"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3210","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/users\/9938"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/comments?post=3210"}],"version-history":[{"count":3,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3210\/revisions"}],"predecessor-version":[{"id":3215,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/3210\/revisions\/3215"}],"wp:attachment":[{"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/media?parent=3210"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/categories?post=3210"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/tags?post=3210"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}