Maniscalco JM et al. (2020), Contemporary diets of walruses in Bristol Bay, ...

ECB-ART-48499

PeerJ 2020 Jan 01;8:e8735. doi: 10.7717/peerj.8735.

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Contemporary diets of walruses in Bristol Bay, Alaska suggest temporal variability in benthic community structure.

Maniscalco JM , Springer AM , Counihan KL , Hollmen T , Aderman HM , Toyukak M .

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Background: Pacific walruses (Odobenus rosmarus divergens) are a conspicuous and important component of the Bristol Bay ecosystem and human social systems, but very little is known about walrus ecology in this region, principally their feeding ecology. The present work provides contemporary data on the diets of walruses at four haulout locations throughout Bristol Bay between 2014 and 2018. Methods: We analyzed scat and gastrointestinal tract samples from these animals using quantitative polymerase chain reaction to amplify prey DNA, which allowed for diet estimates based on frequencies of prey item occurrence and on the relative importance of dietary items as determined from DNA threshold cycle scores. Results: Diets were highly diverse at all locations, but with some variation in composition that may be related to the time of year that samples were collected (summer vs. autumn), or to spatial variability in the distribution of prey. Overall, polychaetes and tunicates had the highest frequencies of occurrence and relative abundances in 2014-15, but a major change in diet appears to have occurred by 2017-18. While some sample sizes were small, diets in these later years contrasted sharply, with a greater prevalence of sea cucumbers and mollusks, and reduced importance of decapods and fishes compared to the earlier years. Prey identified in scat samples from one collection site also contrasted sharply with those reported from the same location in 1981. The apparent temporal shifts in walrus prey may represent a changing benthic ecosystem due to warming waters in recent decades.

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Genes referenced: LOC100887844 polr3a

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References [+] :

Beck, Sex differences in grey seal diet reflect seasonal variation in foraging behaviour and reproductive expenditure: evidence from quantitative fatty acid signature analysis. 2007, Pubmed

	Figure 1. Bristol Bay, Alaska study area showing Pacific walrus sample collection sites (starred).
	Figure 2. Comparisons of relative proportions of dietary items fed to captive walruses and the mean proportions of these items detected in their scat samples based on threshold cycle (Ct) values ± SE.
	Figure 3. Frequency of occurrence of Pacific walrus prey genera detected in >5% of samples (31 of 36) collected at four different sites within the study area and pooled by study site.
	Figure 4. Principal components plot of walrus diet items.Principal components plot based on percent frequency of occurrence of dietary items from Pacific walruses in Bristol Bay, Alaska. Arrow vectors represent the loadings by sample area (HI.14-15 = Hagemeister Island, RI.15 = Round Island in 2015, CS.15 = Cape Seniavin, IZ.15 = Izembek NWR, RI.17-18 = Round Island in 2017–2018).
	Figure 5. Relative abundance (>1%) of prey items in the diets of Pacific walruses based on Ct values ± SE pooled among study sites.
	Figure 6. Plot of the first two principal coordinates in a multidimensional scaling analysis based on Bray–Curtis dissimilarity matrix of Pacific walrus diets in Bristol Bay, Alaska.