Seasonal variation in the diet of New Zealand fur seals (Arctocephalus forsteri) at Otago Peninsula, New Zealand

Abstract

We examined the diet of New Zealand fur seals (Arctocephalus forsteri) at a rookery on Otago Peninsula, New Zealand, by analysing diagnostic remains from 500 faecal samples and 84 regurgitates collected between July 1993 and September 1994. In total, 27 taxa (species or genera) were identified. Small fish were numerically dominant in faecal samples, with five fish species (three species of lanternfish (Myctophidae), ahuru (Auchenoceros punctatus) and juvenile red cod (Pseudophycis bachus)) accounting for over 90% of prey items. Regurgitates occurred only seasonally and contained predominantly cephalopod remains (99% of prey items). Numerical analyses may prove misleading as an indicator of the composition of seal diet because the contribution of large fish that dominate estimates of prey biomass are underrepresented. Estimates of prey biomass were made by combining estimates from both faecal and regurgitate samples. Possible biases created by using this method are considered. A seasonal variation in prey composition was apparent, with arrow squid (Nototodarus sloanii) dominant in summer and autumn, replaced by a combination of barracouta (Thrysites atun), mackerel (Trachurus sp.) and New Zealand octopus (Octopus maorum) in winter and spring.

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

“…Size data were collated only for the four most numerically abundant prey species identified in each diet study. Similar data were obtained for epipelagic Antarctic fur seals (Reid andArnauld 1996, Goldsworthy et al 1997) and New Zealand fur seals (A. forsterr) (Fea et al 1999); and benthic feeding Australian sea 1ions (Gales and Cheal 1992; R. Campbell, Dept. of Fisheries, Western Australia, unpuhI.…”

Folklore and chimerical numbers: Review of a millennium of interaction between fur seals and humans in the New Zealand region

“…New Zealand fur seals typically forage at night offshore over the edge of the continental shelf and over the continental slope Harcourt & Davis 1997;Mattlin et al 1998;Fea et al 1999). Current knowledge of their diet stems from six studies that have highlighted the spatial and seasonal differences around the South Island (Street 1964;Rapson 1969;Tate 1981 ;Carey 1992;Dix 1993b;Fea et al 1999).…”

“…Current knowledge of their diet stems from six studies that have highlighted the spatial and seasonal differences around the South Island (Street 1964;Rapson 1969;Tate 1981 ;Carey 1992;Dix 1993b;Fea et al 1999). With the exception of benthic octopus species, the major contributors to prey biomass were pelagic, schooling species targeted by commercial fisheries: arrow squid {Nototodams sloanii), barracouta (Thyrsites atun), hoki, and jack mackerel (Trachurus spp.…”

“…Second, Carey (1992) concluded that small, noncommercial fish species were targeted. However, although small fish predominated numerically in recent studies, they contributed only a small proportion towards the total prey biomass (Fea et al 1999). Third, unsubstantiated anecdotal observations have been taken as indicative of fur seals targeting species of no or low commercial importance, for example frostfish (Lepidopus caudatus) in Duncan (1991).…”

“…Deliberate legal kills and the potential for harvesting New Zealand fur seals typically forage offshore, a pattern that has largely avoided overlap and conflict with recreational fisheries (Fea et al 1999) and inshore commercial fisheries. However, some individuals have been observed foraging near shore (Sorensen 1969a), and fur seals occasionally take fish from recreational set nets and fishing lines (Lalas pers.…”