Spatial and temporal variation of an ice-adapted predator’s feeding ecology in a changing Arctic marine ecosystem

Abstract

Spatial and temporal variation can confound interpretations of relationships within and between species in terms of diet composition, niche size, and trophic position (TP). The cause of dietary variation within species is commonly an ontogenetic niche shift, which is a key dynamic influencing community structure. We quantified spatial and temporal variations in ringed seal (Pusa hispida) diet, niche size, and TP during ontogeny across the Arctic-a rapidly changing ecosystem. Stable carbon and nitrogen isotope analysis was performed on 558 liver and 630 muscle samples from ringed seals and on likely prey species from five locations ranging from the High to the Low Arctic. A modest ontogenetic diet shift occurred, with adult ringed seals consuming more forage fish (approximately 80 versus 60 %) and having a higher TP than subadults, which generally decreased with latitude. However, the degree of shift varied spatially, with adults in the High Arctic presenting a more restricted niche size and consuming more Arctic cod (Boreogadus saida) than subadults (87 versus 44 %) and adults at the lowest latitude (29 %). The TPs of adult and subadult ringed seals generally decreased with latitude (4.7-3.3), which was mainly driven by greater complexity in trophic structure within the zooplankton communities. Adult isotopic niche size increased over time, likely due to the recent circumpolar increases in subarctic forage fish distribution and abundance. Given the spatial and temporal variability in ringed seal foraging ecology, ringed seals exhibit dietary plasticity as a species, suggesting adaptability in terms of their diet to climate change.

Coupled changes between the H‐Print biomarker and δ15N indicates a variable sea ice carbon contribution to the diet of Cumberland Sound beluga whales

“…In an environment such as Cumberland Sound, it is possible that the impact of transient species on prey availability could be somewhat less for predatory species with a wider geographical range. For example, over the same sampling period, Cumberland Sound ringed seals, although broadly associated to the same region, exhibited lower H‐Prints and more variable δ 15 N when compared to those from beluga, consistent with a diverse omnivorous diet of sympagically associated prey both within and outside of the Sound (Yurkowski et al ). Therefore, one possible explanation for the change in carbon source reaching beluga could be related to reducing sea ice (Perovich and Richter‐Menge ) and the associated transition toward increased in situ pelagic primary production in these circumstances (Grebmeier et al ).…”

Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators

“… Sources include the following: (1) Yurkowski et al. (in press), (2) Loseto et al. (), (3) Marcoux et al.…”

“…Similarly, ringed seals have been reported to mainly consume Arctic cod in the high Arctic with higher dietary proportions of Capelin, Sand lance, and invertebrates at lower latitudes (Yurkowski et al. in press). The combination of a high WIC/TINW ratio and a low TINW for ringed seals and beluga whales inhabiting the high Arctic suggests dietary specialization at the population level where each species only consumes one prey type or functional group in this case being pelagic forage fish, mainly Arctic cod.…”

“…) and ringed seals (Yurkowski et al. in press) from the benthic and pelagic environments, including zooplankton, shrimp, and fish to account for spatial variation in the absolute stable isotope values and ranges among prey sources (Table ), which, when unaccounted for, can confound the interpretations of WIC (Matthews and Mazumber ). The stable isotope values from potential prey items included Calanus sp., Themisto libellula , euphausiids , benthic shrimp, Arctic cod, Capelin, Sand lance, and Sculpin (see Table for δ 13 C and δ 15 N ranges of prey sources).…”

“…), which varies with age, space (Yurkowski et al. in press), and season (Young and Ferguson ). Beluga whales mainly consume pelagic forage fish, such as Arctic cod ( Boreogadus saida ; Loseto et al.…”