{"id":6003,"date":"2025-02-03T10:32:38","date_gmt":"2025-02-03T17:32:38","guid":{"rendered":"https:\/\/blogs.oregonstate.edu\/gemmlab\/?p=6003"},"modified":"2025-02-03T10:32:38","modified_gmt":"2025-02-03T17:32:38","slug":"new-publication-shows-humpback-whale-distribution-in-the-northern-california-current-is-related-to-krill-swarm-biomass-energetic-density-and-species-composition","status":"publish","type":"post","link":"https:\/\/blogs.oregonstate.edu\/gemmlab\/2025\/02\/03\/new-publication-shows-humpback-whale-distribution-in-the-northern-california-current-is-related-to-krill-swarm-biomass-energetic-density-and-species-composition\/","title":{"rendered":"New publication shows humpback whale distribution in the Northern California Current is related to krill swarm biomass, energetic density, and species composition"},"content":{"rendered":"\n

By Rachel Kaplan, PhD candidate, Oregon State University College of Earth, Ocean, and Atmospheric Sciences and Department of Fisheries, Wildlife, and Conservation Sciences, Geospatial Ecology of Marine Megafauna Lab<\/em><\/em><\/p>\n\n\n\n

What does a whale look for at mealtime? Is it a lot of food, its quality, or the type of food? An improved understanding of what makes krill swarms, an important prey item, appetizing for humpback whales can help us anticipate where and when we will see them in our ocean backyard, the Northern California Current (NCC) foraging grounds. In a new paper<\/a>, we found that humpback whale presence in the NCC is tied to several different metrics of krill swarm quality and quantity, particularly species composition (what types of krill are in the swarm), energetic density (the caloric richness of the average mouthful), and biomass (how much krill is in the swarm). Interestingly, relationships between humpback whales and these krill swarm quality metrics are variable in time and space, dependent on whether the whale is foraging on or off the continental shelf and if it is early or late in the foraging season.<\/p>\n\n\n\n

This study required a special, fine-scale dataset of simultaneous observations of krill and whales at sea. While GEMM Lab members conducted marine mammal surveys<\/a>, we simultaneously observed the prey that whales had access to, using active acoustics (essentially a fancy fish finder) to profile the water column and net tows to collect krill. When we put all these data streams together, we found that increases in biomass, energetic density, and the amount of a particular species, Thysanoessa spinifera<\/em>,<\/em> in a krill swarm were positively related to humpback whale presence. These results suggest that humpback whales balance multiple prey quality factors to select feeding areas that offer both plentiful and high-quality krill.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n
\"\"<\/a>
Figure 1. Top photo: Marine mammal observers Clara Bird (left) and Dawn Barlow (right) collect humpback whale distribution data. Bottom photo: At the same time, Talia Davis (left) and Rachel Kaplan (right) collect krill samples.<\/em><\/figcaption><\/figure>\n\n\n\n

Species composition<\/em><\/p>\n\n\n\n

Euphausia pacifica<\/em> and T. spinifera <\/em>are the two most common krill species in the NCC region, and other research has shown that many krill foragers, including blue whales, seabirds, and fish, preferentially consume T. spinifera<\/em>. Although this pickiness is well-warranted \u2013 individual T. spinifera<\/em> tend to be larger than E. pacifica <\/em>and much higher in calories during the late foraging season \u2013 targeting this juicy prey item could place humpback whales in competition with these other species, which may make it harder for them to find a square meal. Nevertheless, we found positive relationships between the proportion of T. spinifera<\/em> in a krill swarm and humpback whale presence, suggesting humpback whales do in fact preferentially prey upon T. spinifera<\/em>, particularly during the late foraging season (about July-November).<\/p>\n\n\n\n

Energetic density<\/em><\/p>\n\n\n\n

Humpback whales\u2019 preference for T. spinifera<\/em> during the late foraging season may be due to its higher caloric content. Although the two krill species offer a similar number of calories early in the foraging season,we found that the energetic density of T. spinifera<\/em> was elevated during the late foraging season, after productive upwelling<\/a> conditions have revved up the food web over several months. Krill swarm energetic density had a positive effect on humpback whale occurrence, particularly in the late season when T. spinifera<\/em> and E. pacifica<\/em> have significantly different caloric contents. Interestingly, this positive relationship was not present onshore during the early season, when the two krill species have similar caloric contents.<\/p>\n\n\n

\n
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Figure 2. In terms of caloric content, <\/em>Thysanoessa spinifera krill like this one are the winners in the NCC region! They pack on the milligrams through the productive summer season, making them advantageous prey for hungry whales.<\/em><\/figcaption><\/figure>\n<\/div>\n\n\n

Humpback whales also target forage fish on the continental shelf that have higher energetic densities than krill, indicating that whales may selectively forage on fish \u2013 even though it is more energetically expensive to capture them. Variation in seasonal and spatial relationships with krill swarm energetic density may explain why humpback whales prey-switch, selecting prey based on availability and quality. As flexible foragers, humpback whales can consistently target higher-quality swarms that offer more energy per lunge.<\/p>\n\n\n\n

Biomass<\/em><\/p>\n\n\n\n

Biomass, or the total amount of krill in a swarm, was the single best predictor of humpback whale presence that we tested. This result emphasizes the importance of large krill swarms in explaining where humpback whales forage. We found that krill swarm biomass tended to be higher offshore, where swarms were also located deeper in the water column. During the late season offshore, krill quality (elevated due to higher late season caloric contents) together with quantity (higher offshore biomass) may make these offshore swarms the most favorable for foraging whales, despite being deeper.<\/p>\n\n\n\n

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Figure 3. When humpback whales \u201cfluke,\u201d as seen in this picture, it may indicate the beginning of a foraging dive to capture prey.<\/em><\/figcaption><\/figure>\n\n\n\n

Future food webs<\/em><\/p>\n\n\n\n

Environmental conditions are changing in the NCC, with events like marine heatwaves and strong El Ni\u00f1o events shifting food webs. E. pacifica <\/em>and T. spinifera <\/em>may respond to climate change differently based on their life history strategies. Distributional shifts, such as the disappearance of T. spinifera<\/em> from the NCC during the 2014\u20132015 \u201cBlob\u201d marine heatwave that transformed the northeast Pacific Ocean, could diminish or entirely remove this key prey item. As a result of such climate and environmental changes, humpback whales may encounter lower quality prey and\/or shifts in prey distribution that could make it harder for them to find a meal. In changing oceans, better understanding krill prey quality for humpback whales will shape improved tools for conservation management.<\/p>\n\n\n

 <\/h2>\n","protected":false},"excerpt":{"rendered":"

By Rachel Kaplan, PhD candidate, Oregon State University College of Earth, Ocean, and Atmospheric Sciences and Department of Fisheries, Wildlife, and Conservation Sciences, Geospatial Ecology of Marine Megafauna Lab What does a whale look for at mealtime? Is it a lot of food, its quality, or the type of food? An improved understanding of what … Continue reading New publication shows humpback whale distribution in the Northern California Current is related to krill swarm biomass, energetic density, and species composition<\/span><\/a><\/p>\n","protected":false},"author":10751,"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":[1310817,1310535],"tags":[677522,635445,712816,712836,513,1237922],"class_list":["post-6003","post","type-post","status-publish","format-standard","hentry","category-opal","category-oregon-whale-distribution","tag-foraging-ecology","tag-gemm-lab","tag-humpback-whale","tag-krill","tag-marine-mammals","tag-northern-california-current"],"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\/6003","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\/10751"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/comments?post=6003"}],"version-history":[{"count":1,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/6003\/revisions"}],"predecessor-version":[{"id":6009,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/posts\/6003\/revisions\/6009"}],"wp:attachment":[{"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/media?parent=6003"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/categories?post=6003"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.oregonstate.edu\/gemmlab\/wp-json\/wp\/v2\/tags?post=6003"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}