New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

Bromaghin, Jeffrey F.; Lance, Monique M.; Elliott, Elizabeth W.; Jeffries, Steven J.; Acevedo‐Gutiérrez, Alejandro; Kennish, John M.

doi:10.7755/fb.111.1.2

Cited by 35 publications

(58 citation statements)

References 59 publications

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“…We were able to identify differences between two relatively close haul-out sites, which may allude to larger behavioral differences, such as prey specialization or habitat exploitation by different haul-out site groups. Prey specialization, with forage fish specialists and salmon specialists, has already been documented for harbor seals in southern Puget Sound [28] and likely explains the variation in diet and foraging behavior observed for harbor seals in this study [20], [50]. Bird Rocks and Padilla Bay showed similar variations in the use of different bout types; however, seals from Bird Rocks significantly changed the ratio of Type I to Type II bouts between seasons while seals from Padilla Bay did not.…”

Section: Discussionsupporting

confidence: 61%

Fine-Scale Variability in Harbor Seal Foraging Behavior

et al. 2014

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Understanding the variability of foraging behavior within a population of predators is important for determining their role in the ecosystem and how they may respond to future ecosystem changes. However, such variability has seldom been studied in harbor seals on a fine spatial scale (<30 km). We used a combination of standard and Bayesian generalized linear mixed models to explore how environmental variables influenced the dive behavior of harbor seals. Time-depth recorders were deployed on harbor seals from two haul-out sites in the Salish Sea in 2007 (n = 18) and 2008 (n = 11). Three behavioral bout types were classified from six dive types within each bout; however, one of these bout types was related to haul-out activity and was excluded from analyses. Deep foraging bouts (Type I) were the predominant type used throughout the study; however, variation in the use of bout types was observed relative to haul-out site, season, sex, and light (day/night). The proportional use of Type I and Type II (shallow foraging/traveling) bouts differed dramatically between haul-out sites, seasons, sexes, and whether it was day or night; individual variability between seals also contributed to the observed differences. We hypothesize that this variation in dive behavior was related to habitat or prey specialization by seals from different haul-out sites, or individual variability between seals in the study area. The results highlight the potential influence of habitat and specialization on the foraging behavior of harbor seals, and may help explain the variability in diet that is observed between different haul-out site groups in this population.

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Section: Discussionsupporting

confidence: 61%

Fine-Scale Variability in Harbor Seal Foraging Behavior

et al. 2014

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“…Harbor seals feed predominantly on Clupeidae (herring) and Gadidae (cod and hake), but also feed opportunistically (Thomas et al 2011) from just a few to over 100 km from their (capture) haul-outs (Peterson et al 2012). Steelhead trout were not identified as prey in a fairly extensive year-round analysis of harbor seal diet around the San Juan Archipelago , Bromaghin et al 2013. However, steelhead presence in seal diets may have been overlooked due to the lack of detectability of steelhead hard parts in diet composition analyses and because the relative number of steelhead available as prey compared to other prey types is inherently small.…”

Section: Introductionmentioning

confidence: 99%

Predator-prey interactions between harbor seals and migrating steelhead trout smolts revealed by acoustic telemetry

Berejikian

Moore²,

Jeffries³

2016

Mar. Ecol. Prog. Ser.

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Changes in the Puget Sound ecosystem over the past 3 decades include increases in harbor seal (Phoca vitulina) abundance and declines in many of their preferred prey species. Harbor seals were outfitted with acoustic telemetry receivers and GPS tags to investigate spatial and temporal interactions with steelhead trout Oncorhynchus mykiss smolts implanted with acoustic transmitters. A total of 6846 tag detections from 44 different steelhead trout smolts (from an initial group of 246 smolts released into 2 rivers) were recorded by the 11 recovered sealmounted receivers. Central Puget Sound seal receivers detected a greater proportion of smolts surviving to the vicinity of the haul-out locations (29 of 51; 58%) than Admiralty Inlet seal receivers (7 of 50; 14%; p < 0.001). Detection data suggest that none of the tagged smolts were consumed by the 11 monitored seals. Nine smolts were likely consumed by non-tagged harbor seals based partly on detections of stationary tags at the seal capture haul-outs, although tag deposition by other predators cannot be ruled out. Smolts implanted with continuously pinging tags and smolts implanted with tags that were silent for the first 10 d after release were detected in similar proportions leaving Puget Sound (95% CI for the difference between proportions: −0.105 to 0.077) and stationary at harbor seal haul-outs (95% CI: −0.073 to 0.080). This study suggests that harbor seals contribute to mortality of migrating steelhead smolts, and we hypothesize that documented changes in the Puget Sound ecosystem may currently put steelhead smolts at greater risk of predation by harbor seals and possibly other predators.

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“…Consistent with our DAP findings, Candy and Quinn [27] found that during the summer in Johnstone Strait, British Columbia, Canada, Chinook salmon swam deeper and had greater rates of vertical movement during the night than day. The nighttime bounce diving by Chinook salmon in summer and fall may result from them ascending to feed on prey that undergo nighttime DVM toward the surface [28,29] and then descending to avoid marine mammal predators including harbor seals [30,31] and southern resident killer whales [32,33]. However, we did not test any behavioral hypotheses to explain the DAPs, and their ecological purpose requires further examination.…”

Section: Discussionmentioning

confidence: 86%

Interpreting vertical movement behavior with holistic examination of depth distribution: a novel method reveals cryptic diel activity patterns of Chinook salmon in the Salish Sea

2017

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Aquatic organisms exhibit a variety of diel changes in vertical movement that are investigable through the use of biotelemetry. While certain species do not change their movements between day and night, others exhibit diel vertical migration (DVM) or a diverse range of diel activity patterns (DAPs). Consequently, day-night differences in depth distribution may be stark and easily detectable, or more subtle and difficult to identify. To augment the discovery and classification of cryptic diel vertical movement behavior, we developed and utilized a novel method that analyzed entire depth distributions while comparing diel period, season, and season/diel period models. This analysis revealed a seasonally variable DAP previously unreported in Chinook salmon (Oncorhynchus tshawytscha). In summer and fall, Chinook salmon in the Salish Sea juxtaposed shallow and confined daytime movements with nighttime bounce diving. This DAP was reversed in winter, when they occupied deeper sections of the water column during the day, resulting in a substantially overlapping, but more even depth distribution than at night. These results demonstrate the analytical utility of accompanying other metrics with holistic examination and visualization of the entire distribution of depth data. Additionally, we highlight the need to use a framework that answers all of the following questions: (1) does the target species exhibit seasonal variation in depth, (2) does it undergo DVM, (3) if it does not undergo DVM, does it follow a DAP, and (4) if it follows a DAP, what is the difference in vertical movement behavior between diel periods?

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New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

Cited by 35 publications

References 59 publications

Fine-Scale Variability in Harbor Seal Foraging Behavior

Fine-Scale Variability in Harbor Seal Foraging Behavior

Predator-prey interactions between harbor seals and migrating steelhead trout smolts revealed by acoustic telemetry

Interpreting vertical movement behavior with holistic examination of depth distribution: a novel method reveals cryptic diel activity patterns of Chinook salmon in the Salish Sea

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