Rates of increase in gray seal (Halichoerus grypus atlantica) pupping at recolonized sites in the United States, 1988–2019

Abstract

Gray seals were historically distributed along the northeastern coast of the United States, but bounties and lack of protection reduced numbers and they were rarely observed for most of the 20th century. Once protections were enacted, the population started to rebound. Here, we describe the recolonization and recovery of gray seals in the United States, focusing on the re-establishment of pupping sites. We fit individual generalized linear models to various time series (1988–2019) to estimate rates of increase in observed pup counts at four of the more data-rich sites. Annual rate of increase at individual sites ranged from −0.2% (95% CI: −2.3–1.9%) to 26.3% (95% CI: 21.6–31.4%). The increase in sites and number of pups born in the United States is driven by population growth and immigration from Canadian colonies and is part of a larger recovery of the Northwest Atlantic population. Wildlife protection, a healthy source population, habitat availability, and species traits that allow for dispersal and high productivity were all important factors in this recovery.

Fine-scale vertical habitat use of white sharks at an emerging aggregation site and implications for public safety

“…Although grey seals occur along Cape Cod year-round (Moxley 2016;Wood et al 2020), white sharks are seasonal visitors (Skomal et al 2017), which suggests that their occurrence in the region is determined, at least in part (see Huveneers et al 2018a for an overview of alternative explanations), by the suitability of thermal habitat (Casey and Pratt 1985;Curtis et al 2014;White et al 2019). Like other lamnid sharks, white sharks can maintain an elevated body temperature relative to the ambient water temperature via a series of countercurrent heat exchangers (Bernal et al 2001).…”

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

“…Another new colony on Green Island (43 41.3 0 N, 66 08.5 0 W) near Yarmouth, Nova Scotia, Canada (Figure 1) was found in southwest Nova Scotia in 2018. (Hayes et al, 2017;Wood et al, 2019). The historic pupping site on Muskeget Island in Massachusetts was reestablished in 1988 while the breeding colonies established Green Island in the mid-1990s and Seal Island in 2000, may also have supported colonies historically (Mansfield & Beck, 1977;Wood et al, 2019).…”

“…Pup production in the Gulf of St. Lawrence, along coastal Nova Scotia and at Sable Island has been estimated intermittently since the 1960s (Bowen et al, 2003(Bowen et al, , 2007(Bowen et al, , 2011den Heyer et al, 2017;Hammill et al, 1998Hammill et al, , 2007Hammill, Gosselin, et al, 2017). Colonies in northeastern United States are some of the most recently established (1980s) and have been monitored periodically (Waring et al, 2016;Wood et al, 2011Wood et al, , 2019.…”

Grey seal Halichoerus grypus recolonisation of the southern Baltic Sea, Danish Straits and Kattegat

“…The site has not recovered, and currently, few if any pups are born annually in Schleswig-Holstein (Cremer et al 2019). In the Northwest Atlantic, the population dynamics of grey seals have gone through similar dynamics as in Europe: hunting for oil, bounty hunting and lack of protection have reduced numbers dramatically, before recovery latter half of the 20th century (Wood et al 2020). This led to local extinction in the United States.…”

“…Early development in recolonised grey seal pupping sites in the United States during the 1990s and early 2000s are hard to compare to sites in the southern Baltic Sea as monitoring was not comprehensive in the early stages of colonisation in the United States. However, the Muskeget Island colony (Massachussetts) grew from a handful of pups to more than 300 annually within a decade, in a large part fuelled by immigration, while Monomoy Island (Massachussetts) data suggest pup production mostly in single digits for 18 years, before a rapid growth to many hundred pups annually (Wood et al 2020).…”