Dynamics of White Shark Predation on Pinnipeds in California: Effects of Prey Abundance

Brown, Adam; Lee, Derek; Bradley, Russell W.; Anderson, Scot D.

doi:10.1643/ce-08-012

Cited by 28 publications

(35 citation statements)

References 24 publications

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“…Long‐term population monitoring and tagging studies have produced robust data streams on the seasonal presence of adult white sharks and elephant seals along the central coast of California (Brown et al, ; Jorgensen et al, , ). We summarized phenological data on coastal shark visitation to mainland and island monitoring sites (Southeast Farallon Islands, Tomales Point, Año Nuevo) from published acoustic tagging studies with continuous monitoring spanning multiple years (Jorgensen et al, , ).…”

Section: Methodsmentioning

confidence: 99%

“…Seasonal increases in elephant seal ( Mirounga angustirostris ) abundance at haul out sites along the California coast provide discrete foraging opportunities and help define the ontogenetic shifts and migratory patterns in white sharks (Brown, Lee, Bradley, & Anderson, ; Jorgensen et al, ; Pyle, Klimley, Anderson, & Henderson, ). At birth white sharks are piscivorous and are largely restricted to warm, nearshore areas in the Southern California Bight and northern Baja California (Dewar et al, ; Lowe et al, ; Weng et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…The heightened metabolic demands of endothermy (Carey et al, ) drive white shark prey preferences (Curtis et al, ; Klimley, Pyle, & Anderson, ). Elephant seals are a favored prey of adult white sharks due to their significant energy stores of blubber (Brown et al, ; Stephens, Boyd, McNamara, & Houston, ). By contrast, sea otters insulate themselves with a thick fur coat and provide little comparative caloric value for feeding white sharks.…”

Section: Introductionmentioning

confidence: 99%

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Non‐trophic impacts from white sharks complicate population recovery for sea otters

Moxley

Nicholson

Houtan

2019

Ecology and Evolution

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Complex interactions between protected populations may challenge the recovery of whole ecosystems. In California, white sharks (Carcharodon carcharias) mistargeting southern sea otters (Enhydra lutris nereis) are an emergent impact to sea otter recovery, inhibiting the broader ecosystem restoration sea otters might provide. Here, we integrate and analyze tracking and stranding data to compare the phenology of interactions between white sharks and their targeted prey (elephant seals, Mirounga angustirostris) with those of mistargeted prey (sea otters, humans). Pronounced seasonal peaks in shark bites to otters and humans overlap in the late boreal summer, immediately before the annual adult white shark migration to elephant seal rookeries. From 1997 to 2017, the seasonal period when sharks bite otters expanded from 2 to 8 months of the year and occurred primarily in regions where kelp cover declined. Immature and male otters, demographics most associated with range expansion, were disproportionately impacted. While sea otters are understood to play a keystone role in kelp forests, recent ecosystem shifts are revealing unprecedented bottom‐up and top‐down interactions. Such shifts challenge ecosystem management programs that rely on static models of species interactions.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Non‐trophic impacts from white sharks complicate population recovery for sea otters

Moxley

Nicholson

Houtan

2019

Ecology and Evolution

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“…In the northeastern Pacific Ocean, white sharks were once considered a nearshore species that preyed primarily on pinnipeds, a perception arising from many studies focused on coastal sites near pinniped colonies where shark foraging behavior was easy to observe [8]–[13]. This view has been challenged by recent satellite tagging data from white sharks off the coast of California and Baja California, Mexico, which revealed migration between the North American continental shelf and two offshore areas (18 to 26°N and 125 to 140°W) [14]–[17].…”

Section: Introductionmentioning

confidence: 99%

Ontogenetic and Among-Individual Variation in Foraging Strategies of Northeast Pacific White Sharks Based on Stable Isotope Analysis

et al. 2012

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There is growing evidence for individuality in dietary preferences and foraging behaviors within populations of various species. This is especially important for apex predators, since they can potentially have wide dietary niches and a large impact on trophic dynamics within ecosystems. We evaluate the diet of an apex predator, the white shark (Carcharodon carcharias), by measuring the stable carbon and nitrogen isotope composition of vertebral growth bands to create lifetime records for 15 individuals from California. Isotopic variations in white shark diets can reflect within-region differences among prey (most importantly related to trophic level), as well as differences in baseline values among the regions in which sharks forage, and both prey and habitat preferences may shift with age. The magnitude of isotopic variation among sharks in our study (>5‰ for both elements) is too great to be explained solely by geographic differences, and so must reflect differences in prey choice that may vary with sex, size, age and location. Ontogenetic patterns in δ15N values vary considerably among individuals, and one third of the population fit each of these descriptions: 1) δ15N values increased throughout life, 2) δ15N values increased to a plateau at ∼5 years of age, and 3) δ15N values remained roughly constant values throughout life. Isotopic data for the population span more than one trophic level, and we offer a qualitative evaluation of diet using shark-specific collagen discrimination factors estimated from a 3+ year captive feeding experiment (Δ13Cshark-diet and Δ15Nshark-diet equal 4.2‰ and 2.5‰, respectively). We assess the degree of individuality with a proportional similarity index that distinguishes specialists and generalists. The isotopic variance is partitioned among differences between-individual (48%), within-individuals (40%), and by calendar year of sub-adulthood (12%). Our data reveal substantial ontogenetic and individual dietary variation within a white shark population.

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“…However, independent data show that records of white shark predations at the southeast Farallon Islands decrease substantially after our sampling efforts in November (Klimley et al, 1992;Klimley and Anderson, 1996;Brown et al, 2010) and efforts at Año Nuevo Island and Tomales Point span the known coastal residency period. However, the observations to date at Año Nuevo Island in this data set are limited and efforts to increase sampling at this location have occurred.…”

Section: Discussionmentioning

confidence: 88%

Estimating apparent survival of sub-adult and adult white sharks (Carcharodon carcharias) in central California using mark-recapture methods

et al. 2015

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Quantifying life history parameters of marine top predators is challenging, as observations are difficult and uncertainty in sex assignment can confound the determination of sex specific parameters. However, these parameters are critical for accurate population assessments and understanding of population dynamics. Using mark recapture observations at white shark foraging aggregation sites, we tested for differences in survival between sexes and estimated apparent survival for sub-adult and adult white sharks in neritic waters off central California. We used 6 years of mark-recapture data and a model that accounted for imperfect detection and imperfect sex assignment. Empirical information based on direct observations suggests that there are no sex-specific or temporal differences in survival during the study period and that survival was estimated to be 0.90; SE = 0.04. Additionally, after animals whose sex was unknown throughout the study period were probabilistically assigned to sex, the ratio in this sample is estimated to be 2.1 males for every female observed. This estimated ratio is lower than the observed ratio of 3:1. We demonstrate that the estimated capture probability for males was roughly twice as high as that for females (0.41, SE = 0.06 and 0.19, SE = 0.07 respectively). Together these results suggest (1) that the sex ratio is uneven but not as skewed as uncorrected observation data would suggest and (2) that unequal mortality in older age classes are not the cause of the observed sex bias but more likely results from disparate mortality earlier in life or differences in behavior. Future research is needed to explore the potential causes of the observed sex bias.

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Dynamics of White Shark Predation on Pinnipeds in California: Effects of Prey Abundance

Cited by 28 publications

References 24 publications

Non‐trophic impacts from white sharks complicate population recovery for sea otters

Non‐trophic impacts from white sharks complicate population recovery for sea otters

Ontogenetic and Among-Individual Variation in Foraging Strategies of Northeast Pacific White Sharks Based on Stable Isotope Analysis

Estimating apparent survival of sub-adult and adult white sharks (Carcharodon carcharias) in central California using mark-recapture methods

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