A Protracted Foraging and Attendance Cycle in Female Juan Fernández Fur Seals

Abstract

Previous studies of fur seals suggest that the attendance patterns and consequent temporal patterning of energy transfer from mother to pup follows a latitudinal cline. While data from subpolar, tropical, and some temperate latitude species support the postulated cline, data for the temperate latitude Juan Fernández fur seal do not. Maternal foraging trips and associated visits ashore were the longest of all otariids studied to date. The first foraging trip postpartum averaged 10.2 d (n= 51 females, range 1–22.5), foraging trips combined averaged 12.3 d (n= 100, range 1.0‐25.0), and visits ashore averaged 5.3 d (n= 91, range 0.3‐15.8) over the three seasons of study. Only duration of lactation was intermediate between subpolar and tropical strategies as predicted. Dive records suggest that these females feed almost exclusively at night at depths of less than 10 m and at distances of more than 500 km offshore. The prey species of this fur seal, primarily myctophids and squid, migrate to the surface at night and are patchily distributed. Foraging trip length varied between years in conjunction with shifts in seasurface temperature and type of prey consumed. We suggest that distribution of prey, irrespective of latitude, dictates foraging patterns of fur seals and leads to the exceptionally long foraging trips and visits ashore observed in this species.

Sea lions in drag, fur seals incognito: Insights from the otariid deviants

“…This mode of foraging is, hereafter, referred to as "benthic' foraging. In contrast, lactating fur seals generally undertake longer trips (3-23 days), during which diving is mostly nocturnal (Boyd et al 1991, Francis et aL 1998, Harcourt et al 2001, Beauplet et al 2004). The dives occur in bouts to the deep scattering layer, with a pronounced diel variation in depth that reflects the vertical migration of their prey (Boyd et al 1994, Harcourt et aL 1995, Georges et al 2000a, and foraging occurs mostly in oceanic frontal structures or continental shelf-edges with upwelling regions , This mode of foraging is hereafter referred to as "epipe/agic' foraging.…”

“…Since the development in the mid-19 70s of electronic time-depth recorders (TORs) for measuring diving activity and satellite-telemetry methods for monitoring the at-sea movements of animals, there have been numerous studies investigating the foraging behavior of lactating otariid seals (e,g., Francis et al 1998; Thompson et al 1998;Costa andGales 2000, 2003). There are nine species of fur seals (plus one subspecies) and five species of sea lions (plus one subspecies) (Reijnders et al 1993) and these studies have revealed two broadly divergent patterns for the two groups.…”

Pup growth of the guadalupe fur seal, Arctocephalus townsendi

“…This is consistent with data of species in which the energy delivery per trip has been studied (Table 6, fur seals: northern, Antarctic, South African, Subantarctic, New Zealand, Galapagos, South American fur seals; sea lions: Steller's and California) (Costa 1991b;Figueroa-Carranza 1994). The 43% fat content of the milk in this species with a mean of 11.5 day foraging trips (Figueroa-Carranza 1994) is similar than that reported for other temperate species that makes long foraging trips, such as the Sub Antarctic fur seal (A. tropicalis) with 42.8% and nine day foraging trips (Georges et al 2001) and the Juan Fernández fur seal 41% with 10 day foraging trips (Francis et al 1998) and it is consistent with the high rates of growth of the pups of these species.…”

“…According to this theory the females of Guadalupe fur seal that forages at long distance from the rookery with round trips averaging 2,375 ± 1,389 km, and a mean distance to feeding grounds of about 444 ± 151 km from Guadalupe Island (Gallo-Reynoso et (Croxall et al 1985) and northern fur seals (Callorhinus ursinus) which travel 160-200 km (Loughlin et al 1987;Goebel et al 1991) and similar to that of the Juan Fernández fur seal (A. philippii) which travel around 500 km to their feeding grounds (Francis et al 1998). In contrast, Figure 5.…”

“…The attendance period lasted 5.1 -6.5 days (1992 and 1993 respectively). The 43.2% fat rich milk of Guadalupe fur seal females (Figueroa-Carranza 1994), is higher in energy density than that reported for other temperate species, and similar to that of the Sub Antarctic fur seal (Arctocephalus tropicalis) with a mean of 42.8%, (Georges et al 2001) and the Juan Fernández fur seal with 41% (Francis et al 1998;Georges et al 2001). In general maternal strategies in fur seals are well known for the sub polar and tropical species, but not much is known about the maternal strategies of temperate fur seals (Schultz and Bowen 2004).…”