Spatio-temporal diet variability of the California sea lion Zalophus californianus in the southern California Current Ecosystem

Lowry, MS; Nehasil, SE; Moore, John E.

doi:10.3354/meps14096

Cited by 11 publications

(7 citation statements)

References 68 publications

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“…The fact that pollock increased in abundance and was the dominant groundfish in the Gulf at the time of the decline (the 1970s-1980s, Mueter and Norcross, 2002, also suggested diet composition may be more important than simply prey abundance. Diet diversity per se may not simply reflect the status of the prey field to sea lions as simple measures of diet diversity may be unrelated to population trends (Fritz et al, 2019) and switching from rich, preferred prey to unpreferred and more diverse prey during poor conditions may also occur (Lowry et al, 2022). Increased diet diversity also occurred after the PMH in the winter diet of Steller sea lions around Chiswell, due to a strong reduction in capelin coupled with an increased utilization of a variety of benthic and poorer-quality prey (Maniscalco, 2023).…”

Section: Discussionmentioning

confidence: 99%

Reduced survival of Steller sea lions in the Gulf of Alaska following marine heatwave

et al. 2023

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The North Pacific marine heatwave of 2014–2016 (PMH), one of the most geographically-extensive and severe marine heatwaves on record, resulted in widespread and persistent perturbation of the Gulf of Alaska and California Current ecosystems. Negative effects of the PMH on marine mammals have been observed, but are not yet well understood. The endangered Steller sea lion Eumetopias jubatus is an important top predator in the Gulf of Alaska that is also particularly vulnerable to sudden or severe ecosystem shifts. We examined survival of 4,178 known-aged Steller sea lions marked from 2000 to 2016 from Kodiak Island through Southeast Alaska, using mark-recapture models and 12,811 resightings collected from 2001 to 2021. Survival of adult females aged 3–15 was reduced -0.05 to -0.23 during the PMH in the areas east, but not west, of Cook Inlet. Survival of Kodiak females was unaffected by the PMH, but survival of Sugarloaf females aged 5–8 was reduced -0.13 from summer 2015 to summer 2016. Lowest survival in Southeast Alaska occurred from summer 2016 to summer 2017, but was also reduced from summer 2014 to summer 2016. Reduced survival continued post-PMH in Kenai Peninsula/Prince William Sound, but not in Southeast Alaska. Survival of adult males was insensitive to the PMH, except in Southeast Alaska where male survival was reduced -0.25 from summer 2016 to summer 2017. Prolonged or intermittent high adult female mortality may reduce population growth and initiate regional declines. Survival response of Steller sea lions to the PMH varied regionally despite similar patterns of ocean warming throughout our study area, suggesting areas east versus west of Cook Inlet were affected differently by the PMH, perhaps due to habitat and oceanographic differences.

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Section: Discussionmentioning

confidence: 99%

Reduced survival of Steller sea lions in the Gulf of Alaska following marine heatwave

et al. 2023

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“…The former seems more likely, given how closely large pelagic predators group in the crossregion biplot. This grouping also suggests similar feeding habits for these predators over both southern and Central California regions on a diverse array of pelagic prey, including gadids, perciforms, beloniforms, clupeids, myopsid squid, and oegopsid squid (e.g., Melin et al, 2012a;Preti et al, 2012;Thompson et al, 2019;Lowry et al, 2022).…”

Section: Ecological Implicationsmentioning

confidence: 86%

“…Northern Fur Seal samples were therefore attributed to both bioregions. California Sea Lion diet composition data are mainly derived from adult females sampled in the Channel Islands (Melin et al, 2012a;Lowry et al, 2022). Adult females from San Clemente and San Nicolas Island typically forage within the Southern California Bight and were therefore assigned to the Southern California bioregion.…”

Section: Biogeographic Designationsmentioning

confidence: 99%

“…Consequently, it is essential that results be interpreted and applied with an eye to what component of a predator population was sampled. For example, diet data for California Sea Lion predominantly originated from nursing females foraging from Channel Islands rookeries (Melin et al, 2012a;Lowry et al, 2022). Subadult and adult males of the same species migrate north during the non-breeding season, where they have access to prey species that are not available within foraging range of the rookeries.…”

Section: Caveats and Considerationsmentioning

confidence: 99%

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Trophic guilds of marine predators in the California Current Large Marine Ecosystem

Bizzarro,

Field,

Santora

et al. 2023

Front. Mar. Sci.

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Quantifying trophic relationships of marine species is fundamental to the construction and performance of ecosystem models, development of effective ecosystem-based fisheries management strategies, and support of trait-based approaches to ecological risk assessment. Accounting for food web dynamics in taxonomically diverse ecosystems, such as the California Current Large Marine Ecosystem (CCLME), is especially challenging because of the sheer number of trophic linkages and their inherent variability. Consequently, analyses that can inform the most appropriate means of aggregating species or other taxonomic groups into assemblages or guilds are critical to reducing system complexity for modeling and management, particularly when data are limited. To provide a methodological approach that is globally applicable in such cases, we define trophic guilds within biogeographic regions of the CCLME, compare results among these regions, and discuss ecological and management implications. Within each biogeographic region, predator guilds were clearly demarcated by foraging habitat (benthic, nearshore pelagic, offshore pelagic), scale of foraging movements, and trophic position. Furthermore, trophic guilds were distinctive for each region, with species composition and the noted ecological characteristics largely driving guild structure. Predator species that are reliant on continental slope and offshore foraging habitat, such as adult Pacific Hake, have diets that are representative of these areas and are similar throughout the CCLME. Generally, larger, more mobile predators that typically feed in deeper offshore waters, including swordfish, sea lions, and sharks clustered together in multiple bioregions along the coast; all reliant primarily on fishes and squids. Throughout bioregions, groundfishes preyed on benthic invertebrates (e.g., decapods, amphipods, polychaetes), while shelf-oriented pelagic predators, including smaller salmon, preyed on pelagic invertebrates (e.g., euphausiids, copepods, gelatinous zooplankton). A large number of forage taxa that are well represented in this study have dynamics largely dependent on oceanographic conditions at a regional scale (e.g., decapods), basin scale (e.g., copepods), or a combination of both (e.g., euphausiids, Northern Anchovy). Such distinctions indicate that spatial and temporal scales of coherence of predators and prey also must be considered in development of ecosystem models and evaluation of management strategies. Our study quantifies the spatial coherence of predator guilds integrated over decades within and across bioregions of the CCLME, providing an improved understanding of regional ecosystem functioning. The analytical approach we developed may be easily extended to address similar ecological and ecosystem based fisheries management priorities in other marine regions.

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“…Frequency of occurrence (FO) is a robust metric in diet analysis studies for quantifying prey prevalence, while avoiding the pitfalls inherent in other gut content metrics (Baker et al, 2014), especially as methods of diet sample collection and processing varied across taxa and collections. FO is calculated as the total number of stomachs [or scats for marine mammals inhabiting onshore colonies, see (Lowry et al, 2022)], containing a prey taxon of interest, divided by the total number of non-empty stomachs for that given predator taxa. We first determined which of the predators in the CCTD database had consumed any mesopelagic fish prey (Figure 1A).…”

Section: Methodsmentioning

confidence: 99%

Mesopelagic fishes are important prey for a diversity of predators

et al. 2023

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Through daily vertical movements, mesopelagic fishes contribute to global carbon export and, when eaten, link primary consumers to higher trophic level predators. Although the importance of mesopelagic fishes as prey to individual predator species has been explored, a comprehensive assessment of mesopelagic fishes as prey at the scale of a large marine ecosystem would advance our observing, modeling, and predicting of biodiversity and ecosystem function. We use diet samples from over 105,000 individual predators from 143 taxa in the California Current Ecosystem (CCE) to quantify and evaluate the role of mesopelagic fishes as prey. For 11 predator taxa, including protected mammal species, pelagic squids, a shelf-edge-associated rockfish and highly migratory species, mesopelagic fishes occurred in greater than 25% of all diet samples, likely comprising an important source of prey. Of the 143 taxa represented, individuals from 36 taxa, or 25% percent of all predator taxa in the database, consumed at least one mesopelagic fish species, including economically important fishery species such as Bluefin tuna (16% of all non-empty diet samples), Albacore (19%), Swordfish (50%), Humboldt squid (52%), and Pacific hake (4%). Compared with coastal pelagic fish species (essential prey in the CCE), mesopelagic fish were more frequently encountered in the diets of 21 predator taxa. Lanternfish (family Myctophidae) were the most common prey and consumed by the greatest diversity of predators (32 taxa), but an additional 16 families of mesopelagic fishes were also consumed by predators, highlighting the diversity of organisms inhabiting mesopelagic depths. Mesopelagic fishes were found in the diets of predators collected from shelf depths to well offshore, accentuating the role of mesopelagic fishes as prey across habitats, especially for predators foraging over the slope and further offshore. Our work illuminates the importance of mesopelagic fishes as prey to a diversity of economically valuable and protected species, underscoring the need to incorporate mesopelagic fishes more comprehensively into food web models, global carbon budgets and ultimately our understanding of ecosystem function.

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Spatio-temporal diet variability of the California sea lion Zalophus californianus in the southern California Current Ecosystem

Cited by 11 publications

References 68 publications

Reduced survival of Steller sea lions in the Gulf of Alaska following marine heatwave

Reduced survival of Steller sea lions in the Gulf of Alaska following marine heatwave

Trophic guilds of marine predators in the California Current Large Marine Ecosystem

Mesopelagic fishes are important prey for a diversity of predators

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