Contrasting trends in gray seal (Halichoerus grypus) pup production throughout the increasing northwest Atlantic metapopulation

Abstract

The northwest Atlantic subspecies of gray seal (Halicheorus grypus grypus) has been increasing for more than a half century and has reestablished breeding colonies in Canadian and US waters. In 2016, visual, oblique, and vertical large-format digital photographic surveys were conducted at all known breeding colonies in the northwest Atlantic. Total pup production in the northwest Atlantic was estimated to be 109,000 (SE = 17,500) pups. At 87,500 (SE = 15,100) pups, Sable Island accounts for 80% of total pup production. Regional differences in pup production trends are evident. Pup production in the Gulf of St. Lawrence and along the eastern shore of Nova Scotia has been relatively stable. Since 2004, the rate of increase in pup production at Sable Island has slowed to about 5%-7% per

Enhanced chlorophyll-a concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?

“…Our conceptual model does not differentiate between males and females the same, so we have estimated peak haul out as the average of time hauled out for males and females. Notably the timing of the peak haul out from satellite telemetry on the island in mid-January is consistent with birth distribution models (Bowen et al, 2007;den Heyer et al, 2020), estimates of mean pup birthdate from individually marked adults (Bowen et al, 2020), and the reproductive biology of the seals. The model 205 is built around three hypotheses:…”

“…Another remarkable phenomena is the winter increase in chl-a standing stocks in the leeward region of SI (SOM5) that is consistent with the increase of seal population on SI over the last 20 years. From the late 1990's to the late 2010's the population has continuously increased at a rate of about 5-7% per year (Figure 6 den Heyer et al, 2020). We demonstrated that the average chl-a increased within the plume southward of Sable Island at a faster rate than the surrounding control boxes in winter.…”

Reproductive success is influenced by early development: the covariation of natal body size and reproductive performance in grey seals (Halichoerus grypus)

“…The copyright holder for this preprint (which this version posted July 12, 2021. ; https://doi.org/10.1101/2021.07.10.451928 doi: bioRxiv preprint 2021). Sable Island supports the largest breeding colony of grey seals in the world with an estimated 87,500 pups (SE = 15,100) born on the island in 2016, comprising 80% of the total grey seal pup production in the Northwest Atlantic (den Heyer et al 2021).…”

“…The Sable Island grey seal breeding colony has increased dramatically over the past half century with near maximum population growth of 13% per year between the 1960s and late 1990s (Bowen 2011) and a reduced rate of increase of 4% from 1997 to 2016 (den , den Heyer et al 2021. Female grey seals born during a period of exponential population growth in the 1980s and 1990s had apparent juvenile survival probabilities to reproductive recruitment of 0.7-0.8 (den Heyer et al 2013).…”

“…On Sable Island, grey seal pup production (a proxy for population size) has increased dramatically over the past half century with near maximum population growth of 13% per year between the 1960s and late 1990s (Bowen 2011) and a reduced rate of increase of 5-7% per year since 2004 (den , den Heyer et al 2021. Associated with declines in population growth, juvenile apparent survival to reproductive recruitment has decreased by more than half from an average of 74% in cohorts born 1985-1989to 33% in cohorts born 1998(den Heyer et al 2013.…”