The Economic Impacts of Humpback Whale Depredation on Hatchery‐Released Juvenile Pacific Salmon in Southeast Alaska

Chenoweth, Ellen M.; Criddle, Keith R.

doi:10.1002/mcf2.10061

Cited by 6 publications

(5 citation statements)

References 59 publications

(117 reference statements)

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“…Within the last decade, humpback whales have been reported for the first time feeding on juvenile Pacific salmon ( Oncorhynchus spp.) at hatchery release sites in Southeast Alaska (Chenoweth et al., 2017) with documented economic impacts (Chenoweth & Criddle, 2019). Depredation, including by marine mammals, is commonly associated with energetic benefits partially offsetting risks of close human contact (Hamer et al., 2012; Mathias et al., 2012; Tixier et al., 2015).…”

Section: Introductionmentioning

confidence: 99%

Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

et al. 2021

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The relative energetic benefits of foraging on one type of prey rather than another are not easily measured, particularly for large free‐ranging predators. Nonetheless, assumptions about preferred and alternative prey are frequently made when predicting how a predator may impact its environment, adapt to environmental change or interact with human activities. We developed and implemented a process‐based model to investigate the potential energetic benefit (PEB) of in situ foraging opportunities in rorqual whales. The model integrates and evaluates the energetic importance of measured prey patch characteristics (prey distribution, energy content and predator avoidance) and predator characteristics (morphometrics, foraging tactics and feeding rates). We applied the model to test the assumption that hatchery‐released juvenile salmon are an ‘easy meal’ for humpback whales compared to more common prey: herring and krill. In 11 out of the 13 foraging situations considered, whales were found to be feeding in a manner where net energy gain was greater than the energetic costs of non‐foraging swimming. Humpback whale PEB for hatchery‐released juvenile salmon fell within the range of the PEB for krill and herring but varied by species, from relatively high PEB for chum salmon to relatively low for coho salmon. Our model provides behavioural insight as well, indicating that shallow feeding may be more important for reducing energy expenditure through slower lunge speeds than for increasing prey capture. The model also provides a means of identifying prey patch characteristics, with prey aggregation playing the largest role in determining PEB despite being a poor overall proxy for PEB, supporting the use of the complex model framework. Modelling approaches are especially valuable where they can use reasonable assumptions to substitute for lack of reliable observations, thereby integrating a range of interacting factors into a single framework. Additionally, because process‐based models can be used to make predictions outside the range of previously observed conditions, they will be increasingly useful in a changing climate. A free Plain Language Summary can be found within the Supporting Information of this article.

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Section: Introductionmentioning

confidence: 99%

Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

et al. 2021

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“…In general, humpback whales are known for their intelligent feeding tactics and their ability to develop new tactics (e.g., trap-feeding) [ 44 ]. For example, a group of humpback whales in Alaska has been found to prey on hatchery salmon right as they are released by waiting in shallow waters nearby [ 45 ]. The initial observations of trap-feeding involved two juvenile whales, indicating that young whales may be actively involved in developing new foraging tactics, such as feeding on fish and krill aggregations near fish farm sites.…”

Section: Discussionmentioning

confidence: 99%

Aquaculture related humpback whale entanglements in coastal waters of British Columbia from 2008–2021

Storlund,

Cottrell,

Cottrell

et al. 2024

PLoS ONE

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Over the past two decades, increasing numbers of humpback whales have been returning to feed in the inshore waters of British Columbia (BC) where marine aquaculture farms are situated. This has led to growing concerns that the presence of aquaculture farms may pose an entanglement threat to humpback whales. However, it is not known whether aquaculture facilities attract humpback whales, or whether there are factors that increase the likelihood of humpback whale, becoming entangled and dying. We examined eight reports of humpback whales interacting with Atlantic salmon farms in BC from 2008 to 2021 to evaluate the conditions that may have contributed to their entanglements. Of the eight entangled humpbacks, three individuals died and five were successfully disentangled and released. All were young animals (1 calf, 7 subadults). Multiple factors were associated with two or more of the reported incidents. These included facility design, environmental features, seasonality, humpback whale age, and feeding behaviour. We found that humpback whales were most commonly entrapped in the predator nets of the aquaculture facilities (6/8 incidents), and were less often entangled in anchor support lines (2/8). The presence of salmon smolts did not appear to be an attractant for humpback whales given that half of the reported entanglements (4/8) occurred at fallowed salmon farms. Almost all of the entanglements (7/8) occurred in late winter (prior to the seasonal return of humpbacks) and during late fall (after most humpbacks have migrated south). Overall, the number of humpback whales impacted by fish farms was small compared to the numbers that return to BC (> 7,000) and accounted for <6% of all types of reported entanglements in BC. Human intervention was required to release humpback whales at fish farms, which points to the need to have well-established protocols to minimize entanglements and maximize successful releases.

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“…For each lost lunge, we drew a value of krill density from the pooled lognormal krill density distribution. Given the length of the simulated individual (affecting buccal size, as per Pirotta et al, 2018b , 2019 ), krill energy density in the California Current ( Chenoweth, 2018 ) and assimilation efficiency ( Lockyer, 1981 ), lost lunges were translated into total (gross) energy lost on a day, representing the daily energetic cost of that disturbance scenario.…”

Section: Methodsmentioning

confidence: 99%

Context-dependent variability in the predicted daily energetic costs of disturbance for blue whales

Pirotta

Booth

Cade

et al. 2021

Conservation Physiology

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Assessing the long-term consequences of sub-lethal anthropogenic disturbance on wildlife populations requires integrating data on fine-scale individual behavior and physiology into spatially and temporally broader, population-level inference. A typical behavioral response to disturbance is the cessation of foraging, which can be translated into a common metric of energetic cost. However, this necessitates detailed empirical information on baseline movements, activity budgets, feeding rates and energy intake, as well as the probability of an individual responding to the disturbance-inducing stressor within different exposure contexts. Here, we integrated data from blue whales (Balaenoptera musculus) experimentally exposed to military active sonar signals with fine-scale measurements of baseline behavior over multiple days or weeks obtained from accelerometry loggers, telemetry tracking and prey sampling. Specifically, we developed daily simulations of movement, feeding behavior and exposure to localized sonar events of increasing duration and intensity and predicted the effects of this disturbance source on the daily energy intake of an individual. Activity budgets and movements were highly variable in space and time and among individuals, resulting in large variability in predicted energetic intake and costs. In half of our simulations, an individual’s energy intake was unaffected by the simulated source. However, some individuals lost their entire daily energy intake under brief or weak exposure scenarios. Given this large variation, population-level models will have to assess the consequences of the entire distribution of energetic costs, rather than only consider single summary statistics. The shape of the exposure-response functions also strongly influenced predictions, reinforcing the need for contextually explicit experiments and improved mechanistic understanding of the processes driving behavioral and physiological responses to disturbance. This study presents a robust approach for integrating different types of empirical information to assess the effects of disturbance at spatio-temporal and ecological scales that are relevant to management and conservation.

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The Economic Impacts of Humpback Whale Depredation on Hatchery‐Released Juvenile Pacific Salmon in Southeast Alaska

Cited by 6 publications

References 59 publications

Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

Confronting assumptions about prey selection by lunge‐feeding whales using a process‐based model

Aquaculture related humpback whale entanglements in coastal waters of British Columbia from 2008–2021

Context-dependent variability in the predicted daily energetic costs of disturbance for blue whales

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