Comparing temporal patterns in body condition of ringed seals living within their core geographic range with those living at the edge

Abstract

Ecological theory suggests that demographic responses by populations to environmental change vary depending on whether individuals inhabit central or peripheral regions within the species' geographic range. Here, we tested this prediction by comparing a population of ringed seals Pusa hispida located at high latitudes as part of their core range (core) with a population located at the southern extremity of their range (peripheral). First, we compared the two regions' environmental trends in timing of sea-ice breakup and freeze-up, open-water duration and the North Atlantic Oscillation (NAO). We found that the core region shifted to progressively warmer conditions in the early 1990s; whereas, in the peripheral region, the warming trend shifted in 1999 to one with no warming trend but high inter-annual variability. Next, we examined how body condition, inferred from blubber depth, responded to temporal changes in sea-ice and climatic variables-variables that have been shown to influence ringed seal demography. Core seals displayed minimal seasonal changes in body condition; whereas peripheral seals displayed a 20-60% amplitude seasonal change in body condition with a phase shift to earlier initiation of fat accumulation and loss. Finally, we tested for interannual differences and found that both core and peripheral seals responded similarly with decreased body condition following more positive NAO. Environmental variables influenced body condition in opposite directions between the two regions with core seals declining in body condition with later spring breakup and shorter open-water duration, whereas peripheral seals showed opposite relationships. Seals living at the core likely benefit from an evolved match between adaptation and environmental variation resulting in dampened seasonal and interannual fluctuations in body condition. Knowledge of how different populations respond to environmental change depending on geographic location within a species range can assist in anticipating population specific responses to climate warming.

Seal body condition and atmospheric circulation patterns influence polar bear body condition, recruitment, and feeding ecology in the Chukchi Sea

“…We identified that indicators of recruitment were higher during, or following, years with lower winter AOs (Table 6; Figure 6) consistent with previous studies that have similarly shown increased frequency of predation (Pilfold et al, 2015; Rode et al, 2018), increased proportions of ringed seal in adult female and juvenile diets (McKinney et al, 2017), and lower hair cortisol levels (Bechshoft et al, 2013) during years with lower winter AOs. Lower winter AOs have also been associated with increased abundance and productivity of ringed seals (Ferguson et al, 2020; Nguyen et al, 2017) and may represent aspects of sea ice conditions important to polar bear foraging, such as sea ice thickness (Park et al, 2018; Rigor et al, 2002), that are not reflected in satellite data of sea ice area and concentration. In Svalbard, body mass of adult male and female polar bears, cubs per female per year, and the proportion of females accompanied by cubs were similarly negatively correlated with the AO (Derocher, 2005) suggestive that the winter AO may be an important factor influencing cub production, survival, or both across Arctic systems.…”

“…We also considered the potential for the winter AO to affect polar bear recruitment, body condition, diet, and feeding probability because the AO appears to capture aspects of environmental conditions important to polar bear feeding ecology that are not reflected directly in the limited sea ice and prey metrics available (i.e., Derocher, 2005;McKinney et al, 2017;Pilfold et al, 2015;Rode et al, 2018). When the winter AO index is lower, older thicker ice occurs in the central Arctic (Rigor et al, 2002) and lower AOs have been associated with higher densities and body condition in ringed seals (Ferguson et al, 2005(Ferguson et al, , 2020. Although the seasonal extent of sea ice can be quantified via satellite data, there are likely other features of sea ice (e.g., the availability of leads and thickness) that affect polar bear predation rates, some or all of which may be indicated by the winter AO.…”

Biomarkers in Ringed Seals Reveal Recent Onset of Borealization in the High- Compared to the Mid-Latitude Canadian Arctic

“…This is in accordance with the decreasing blubber thickness of ringed seals from the CAA since 1990 (Harwood et al, 2020), and coincides with our finding of a decreasing trophic position over time. Ferguson et al (2020) forecasted reproductive difficulties and higher mortality for ringed seals in the low Arctic, which showed greater seasonal fluctuation in body condition compared to ringed seals from the high-Arctic. This could be amplified by the longer exposure of ringed seals to the less lipid-rich food web in the mid-Arctic compared to ringed seals in the CAA.…”

“…It is likely that such changes in zooplankton dynamics also occurred at lower latitudes. The CAA is typically more ice-covered throughout the year and has exhibited stronger environmental change compared to Southern Baffin Bay (Figure 2), and Hudson Bay since 1990 (Ferguson et al, 2020). The consistency in Cor-δ 15 N trophic values of ringed seals from Baffin Island in the last 25 years suggests that the food web structure in Southern Baffin Bay has remained stable since the 1990s.…”

“…Here, we used the trophic position of ringed seals (Pusa hispida), a generalist ice-dependent Arctic predator, to assess latitudinal differences in multi-decadal trends in food chain length in the Canadian Arctic. Ringed seals are circumpolar, and have an extensive distribution in northern Canada, occurring continuously across latitudes from Newfoundland and Labrador to the Arctic basin (Ferguson et al, 2020). They are predators and display high plasticity in their diet with dietary items consisting of a wide variety of pelagic invertebrates, e.g., mysids and amphipods species, and forage fish, e.g., Arctic cod (Boreogadus saida) and capelin (Mallotus villosus; Ogloff et al, 2019;Bengtsson et al, 2020).…”