Stable Isotope Models Predict Foraging Habitat of Northern Fur Seals (Callorhinus ursinus) in Alaska

Stable isotopes of C and N differ in their ability to reconstruct diets of cattle fed C3-C4 forage diets

Stable isotopes are useful for estimating livestock diet selection. The objective was to compare δ13C and δ15N to estimate diet proportion of C3-C4 forages when steers (Bos spp.) were fed quantities of rhizoma peanut (Arachis glabrata; RP; C3) and bahiagrass (Paspalum notatum; C4).Treatments were proportions of RP with bahiagrass hay: 100% bahiagrass (0%RP); 25% RP + 75% bahiagrass (25%RP); 50% RP + 50% bahiagrass (50%RP); 75% RP + 25% bahiagrass (75%RP); and 100% RP (100% RP). Feces, plasma, red blood cell (RBC), and hair were collected at 8-days intervals, for 32 days. Two-pool mixing model was utilized to back-calculate the proportion of RP based on the sample and forage δ13C or δ15N. Feces showed changes using δ13C by 8 days, and adj. R2 between predicted and observed RP proportion was 0.81 by 8 days. Plasma, hair, and RBC required beyond 32-days to reach equilibrium, therefore were not useful predictors of diet composition during the study. Diets were best represented using fecal δ13C at both 8-days and 32-days. By 32-days, fecal δ15N showed promise (R2 = 0.71) for predicting diet composition in C3-C4 diets. Further studies are warranted to further corroborate fecal δ15N as a predictor of diet composition in cattle.

A Synthesis of Laaqudax^ (Northern Fur Seal) Community Surveys and Commercial Fishery Data in the Pribilof Islands Marine Ecosystem, Alaska

Indigenous communities on the Pribilof Islands have longstanding cultural and economic ties to their marine ecosystem and, in particular, to laaqudan (in Unangam Tunuu) or northern fur seals (NFS; Callorhinus ursinus). Indigenous and Local Knowledge holders from the Pribilof Islands have long expressed concerns about declines in NFS abundance, and research increasingly suggests that nutritional limitation is a key factor in the decline. Using a co-production of knowledge approach, we explore perceptions of NFS ecology and commercial fishery interactions in the Pribilof Islands Marine Ecosystem (PRIME). We synthesize results from community surveys and analyses of commercial pollock (Gadus chalcogrammus) fishery catch data from 2004–2018 relative to documented NFS foraging areas. Community survey results highlighted ecosystem changes and nutritional limitation as primary drivers of recent declines in Pribilof Islands NFS. Consistent with these results, pollock catch data indicate there are concentrated areas of pollock harvest over time near the Pribilof Islands where female NFS forage. These results reinforce the value of considering Indigenous and Local Knowledge and western science together to better understand ecosystem interactions. Our findings also support the consideration of Indigenous and Local Knowledge-based approaches in combination with spatiotemporal management to mitigate NFS nutritional limitation and Pribilof Islands NFS declines.

Factors affecting energy expenditure in a declining fur seal population

Quantifying metabolic rates and the factors that influence them is key to wildlife conservation efforts because anthropogenic activities and habitat alteration can disrupt energy balance, which is critical for reproduction and survival. We investigated the effect of diving behaviour, diet and season on field metabolic rates (FMR) and foraging success of lactating northern fur seals (Callorhinus ursinus) from the Pribilof Islands during a period of population decline. Variation in at-sea FMR was in part explained by season and trip duration, with values that ranged from 5.18 to 9.68 W kg^-1 (n = 48). Fur seals experienced a 7.2% increase in at-sea FMR from summer to fall and a 1.9% decrease in at-sea FMR for each additional day spent at sea. There was no effect of foraging effort, dive depth or diet on at-sea FMR. Mass gains increased with trip duration and were greater in the fall compared with summer, but were unrelated to at-sea FMR, diving behaviour and diet. Seasonal increases in at-sea FMR may have been due to costs associated with the annual molt but did not appear to adversely impact the ability of females to gain mass on foraging trips. The overall high metabolic rates in conjunction with the lack of any diet-related effects on at-sea FMR suggests that northern fur seals may have reached a metabolic ceiling early in the population decline. This provides indirect evidence that food limitation may be contributing to the low pup growth rates observed in the Pribilof Islands, as a high metabolic overhead likely results in less available energy for lactation. The limited ability of female fur seals to cope with changes in prey availability through physiological mechanisms is particularly concerning given the recent and unprecedented environmental changes in the Bering Sea that are predicted to have ecosystem-level impacts.