Do Gray Whales Count Calories? Comparing Energetic Values of Gray Whale Prey Across Two Different Feeding Grounds in the Eastern North Pacific

Hildebrand, Lisa; Bernard, Kim S.; Torres, Leigh G.

doi:10.3389/fmars.2021.683634

Cited by 15 publications

(34 citation statements)

References 79 publications

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“…Of the prey species identified in this study period and area, N. rayii and A. tridens represent opposite ends of the caloric quality spectrum, with Holmesimysis sculpta as a caloric intermediary (Hildebrand et al 2021). Despite not having the highest quality, H. sculpta did have the highest abundance and showed a significant positive relationship with foraging behavior, unlike the other prey items.…”

Section: Discussionmentioning

confidence: 75%

“…Daily caloric preyscapes for MR and TC were then created by multiplying species-specific abundance preyscapes by the mean caloric value for each species (2.42, 1.60, and 1.25 kJ g −1 wet weight for Neomysis rayii, Holmesimysis sculpta, and Atylus tridens, respectively; Hildebrand et al 2021). A total caloric layer was calculated by summing the daily speciesspecific caloric layers together.…”

Section: Spatial Prey Layersmentioning

confidence: 99%

“…A total caloric layer was calculated by summing the daily speciesspecific caloric layers together. Caloric content of zooplankton species relevant in this study did not differ between study years (Hildebrand et al 2021), and therefore we did not account for annual caloric differences in our daily caloric preyscapes.…”

Section: Spatial Prey Layersmentioning

confidence: 99%

“…PCFG whales are generalist feeders, with reported prey including benthic amphipods, mysids, cumaceans, crab larvae, ghost shrimp, and herring roe (Darling et al 1998, Dunham & Duffus 2001. This breadth in diet adds complexity to the decision-making of foraging PCFG gray whales, as several of these prey species have significantly different caloric values (Hildebrand et al 2021). Ideally, the prey species with the highest caloric value would also be the most ubiquitous and least energetically expensive prey item to capture and consume, such that predators like gray whales truly could expend very little energy to secure high energetic rewards (OFT; MacArthur & Pianka 1966).…”

Section: Introductionmentioning

confidence: 99%

“…To our knowledge, individual baleen whale foraging decisions relative to available prey quality and quantity have not been addressed previously at this micro scale. We address fundamental hypotheses regarding OFT including (1) gray whale foraging behavior will be higher in areas of high relative prey quantity and quality compared to areas used for search and transit behavior states, and (2) individual whales will select areas where the prey community is dominated by the mysid Neomysis rayii, which is significantly higher in caloric content (Hildebrand et al 2021), rather than areas dominated by other zooplankton species. Foraging behavior and habitat use are often assessed through prey quantity metrics, which may not reveal the entire ecological picture (Österblom et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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Trade-offs in prey quantity and quality in gray whale foraging

Hildebrand

Sullivan

Orben

et al. 2022

Mar. Ecol. Prog. Ser.

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To forage optimally, predators face complex decisions regarding target prey distribution, quantity, and quality. We paired theodolite tracking of gray whales Eschrichtius robustus in Port Orford, Oregon, USA, with concurrent sampling of their zooplankton prey to examine foraging decisions relative to prey quantity (abundance) and quality (caloric content). We tested the hypotheses that whales (1) feed more than search or transit in areas with high quantity and quality prey and (2) select foraging habitat dominated by the calorically rich mysid Neomysis rayii. Relative prey abundance was assessed through standardized image analysis of camera drops, and zooplankton prey community was determined from net tows. These data were spatially interpolated and modeled to generate daily layers of species-specific prey abundance and calories (20 m grid) for comparison to whale behavior derived from tracking data. Whales fed significantly more in areas with higher prey abundance and calories than where they searched and transited. Whales increased foraging effort as overall prey availability increased, yet foraging probability was significantly correlated with the quantity and quality of the mysid Holmesimysis sculpta, which has significantly lower calories than N. rayii. However, during the study period, the maximum abundance of N. rayii was 4 times lower than that of H. sculpta and never reached the quantity threshold determined by a logistic regression needed to support whale foraging behavior. Hence, gray whale prey selection involves trade-offs between prey quantity and quality to maximize energetic gain, and prey quality should be considered alongside abundance in ecological studies investigating predator decision-making.

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Section: Discussionmentioning

confidence: 75%

Section: Spatial Prey Layersmentioning

confidence: 99%

Section: Spatial Prey Layersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Trade-offs in prey quantity and quality in gray whale foraging

Hildebrand

Sullivan

Orben

et al. 2022

Mar. Ecol. Prog. Ser.

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Bubble blasts! An adaptation for buoyancy regulation in shallow foraging gray whales

Bird,

Pirotta,

New

et al. 2024

Ecology and Evolution

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Foraging efficiency is key to animal fitness. Consequently, animals evolved a variety of kinematic, morphological, physiological, and behavioral adaptations for efficient locomotion to reduce energy expenditure while moving to find, capture, and consume prey. Often suited to specific habitat and prey types, these adaptations correspond to the terrain or substrate the animal moves through. In aquatic systems, adaptations focus on overcoming drag, buoyancy, and hydrostatic forces. Buoyancy both benefits and hinders diving animals; in particular, shallow divers constantly contend with the costs of overcoming buoyancy to dive and maintain position. Pacific Coast Feeding Group (PCFG) gray whales forage in shallow habitats where they work against buoyancy to dive and feed using various foraging tactics. Bubble blasts (underwater exhalations) have been observed during several foraging tactics performed by PCFG whales. As exhalations aid buoyancy regulation in other diving animals, we hypothesize that bubble blasts are performed by longer, more buoyant whales in shallower water and that bubble blasts increase dive duration while accounting for size and tactic. We test our hypotheses using Bayesian linear mixed effects models and a 7‐year dataset of drone footage containing concurrent individual morphological and behavioral data. We find that while headstanding – a stationary, head‐down tactic – bubble blasts are performed by longer, more buoyant whales and extend the dive duration, whereas whales using forward‐swimming tactics are less likely to bubble blast. Our results suggest that PCFG gray whales may use bubble blasts as a behavioral adaption to mitigate the cost of energetically expensive tactics in their shallow habitat foraging niche.

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