MARINE MAMMAL SCIENCE, **(*): ***–*** (*** 2011) C 2011 by the Society for Marine Mammalogy DOI: 10.1111/j.1748-7692.2011.00487.x Individual foraging site fidelity in lactating New Zealand fur seals: Continental shelf vs. oceanic habitats ALASTAIR M. M. BAYLIS South Australian Research and Development Institute, (Aquatic Sciences), PO Box 120, Henley Beach, Adelaide, South Australia 5022, Australia and School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia and Falklands Conservation, PO Box 41, Stanley, FIQQ1ZZ, Falkland Islands E-mail: [email protected] BRAD PAGE JANE MCKENZIE SIMON D. GOLDSWORTHY South Australian Research and Development Institute, (Aquatic Sciences), PO Box 120, Henley Beach, Adelaide, South Australia 5022, Australia ABSTRACT Wide-ranging marine central place foragers often exhibit foraging site fidelity to oceanographic features over differing spatial scales (i.e., localized coastal upwellings and oceanic fronts). Few studies have tested how the degree of site fidelity to foraging areas varies in relation to the type of ocean features used. In order to determine how foraging site fidelity varied between continental shelf and oceanic foraging habitats, 31 lactating New Zealand fur seals (Arctocephalus australis forsteri1)were satellite tracked over consecutive foraging trips (14–108 d). Thirty-seven foraging trips were recorded from 11 females that foraged on the continental shelf, in a region 1Currently the Marine Mammal Society’s Ad-hoc Committee on Taxonomy (Committee on Taxonomy 2009) lists New Zealand fur seals as Arctocepahlus australis forsteri based on the findings presented in Brunner et al. (2004). This taxonomic revision did not include a more recent analysis of the molecular phylogeny and divergence of the pinnipeds by Higdon et al. (2007), which identified A. forsteri being basal to A. australis, and limited support for the two taxa being subspecies. Based on this study, we believe the full species name A. forsteri should be retained. 1 2 MARINE MAMMAL SCIENCE, VOL. **, NO. **, 2011 associated with a coastal upwelling, while 65 foraging trips were recorded from 20 females that foraged in oceanic waters. There were no significant differences in the mean bearings (to maximum distance) of individual’s consecutive foraging trips, suggesting individual fidelity to foraging areas. However, overlap in area and time spent in area varied considerably between continental shelf and oceanic foragers. Females that foraged on the continental shelf had significantly greater overlap in consecutive foraging trips when compared to females that foraged in oceanic waters (overlap in 5 × 5 km grid cells visited on consecutive trips 55.9% ± 20.4% and 13.4% ± 7.6%, respectively). Females that foraged on the continental shelf also spent significantly more time within the same grid cell than females that foraged in oceanic waters (maximum time spent in 5 × 5 km grid cells: 14% ± 5% and 4% ± 2%, respectively). This comparatively high foraging site fidelity may reflect the concentration of productivity associated with a coastal upwelling system, the Bonney Upwelling. Lower foraging site fidelity recorded by seals that foraged in oceanic waters implies a lower density/larger scale habitat, where prey are more dispersed or less predictable at fine scales, when compared to the continental shelf region. Key words: foraging behavior, marine mammals, pinnipeds, Bonney Upwelling, Subtropical Front, South Australia. Central place foragers are constrained in foraging distance and duration by the fasting abilities of their offspring (Orians and Pearson 1979). Accordingly, foraging strategies have evolved to maximize the efficiency and rate of energy gain (Ydenberg et al. 1992). The tendency for an individual to repeatedly return to the same area to forage has been widely documented among marine central place foragers (e.g., Irons 1998, Bonadonna et al. 2001, Hedd et al. 2001, Broderick et al. 2007, Chilvers 2008). From an optimal foraging perspective, foraging site fidelity is likely to be advantageous in long-lived species that exhibit breeding site fidelity and forage in regions where resources are to some degree predictable over both spatial and temporal scales (Irons 1998, Weimerskirch 2007). In such situations, familiarity with predictable resources may enhance foraging efficiency and foraging success, and maximize energy gain over the lifetime of an animal (Gentry 1998, Irons 1998, Bradshaw et al. 2004, Gende and Sigler 2006). However, wide-ranging central place foragers such as seals and seabirds often use multiple oceanographic features over varying spatial scales (Lea and Dubroca 2003, Beauplet et al. 2004, Weimerskirch 2007, Baylis and Nichols 2009). For example, Australian sea lions (Neophoca cinerea) forage in both inshore (shallow) and outer-shelf (deep) habitats (Baylis et al. 2009), whereas lactating Antarctic (Arctocephalus gazella) and northern (Callorhinus ursinus) fur seals utilize both continental shelf and oceanic habitats (Staniland and Boyd 2003, Robson et al. 2004), and short tailed shearwaters (Puffinus tenuirostris) employ a dual-foraging strategy to exploit both continental shelf and distant frontal zones (Einoder 2010). Distinguishing how foraging site fidelity varies between discrete habitats provides insights into foraging plasticity that may have important ecological, conservation, and evolutionary implications. Few studies have tested the degree to which foraging site fidelity is influenced by the type of ocean feature utilized. New Zealand fur seals (A. australis forsteri) breeding in the state of South Australia provide a unique opportunity to test how foraging site fidelity varies in relation to discrete oceanographic features. Lactating New Zealand fur seals are wide-ranging central place foragers that display a high degree of philopatry (McKenzie 2006). BAYLIS ET AL.: NEW ZEALAND FUR SEAL FORAGING SITE FIDELITY 3 During their 8–11 mo lactation period, females regularly alternate between foraging at sea and nursing their pup ashore (Goldsworthy 2006). Females forage in associa- tion with two distinct oceanographic features. A nearby (36–190 km) but seasonally variable (occurs in summer/autumn) wind-driven coastal upwelling, the Bonney Upwelling (Lewis 1981) and a distant (380–1,000 km) but permanent oceanic front, the Subtropical Front (STF) (Tomczak et al. 2004, Baylis et al. 2008a). Previous studies have revealed lactating seals that foraged on the continental shelf performed both shallow (<30 m) and deep dives (50–80 m) and preyed mainly on redbait (Emmelichthys nitidus) and Gould’s squid (Notodarus gouldi) (Page et al. 2006, Baylis et al. 2008b, Baylis and Nichols 2009). In contrast, lactating seals that foraged in association with the STF performed predominantly shallow dives (<30 m) almost exclusively during night hours and were thought to have preyed mainly on myc- tophids (Baylis et al. 2008b, Baylis and Nichols 2009). Differences in diet and dive behavior suggest foraging strategies are influenced by prey type, distribution, and prey behavior, which vary according to continental shelf and oceanic habitats. In addition, the vast difference in travel distances to utilize nearby continental habitats compared to distant oceanic habitats also implies that foraging site fidelity will vary between these two habitats. Identifying the degree of New Zealand fur seal foraging site fidelity to discrete oceanographic features is of particular interest because five colonies within ca. 200 km (Liguanea Island, North and South Neptune Island, Cape du Couedic, and Cape Gantheuame) account for 82% of the Australian population (ca. 85,000 individuals; Goldsworthy and Page 2007). The relatively small area in which the population is concentrated makes the Australian population of New Zealand fur seals potentially vulnerable to changes within this region of critical breeding and foraging habitat. The degree of foraging site fidelity exhibited has potentially important implications for species management and conservation because foraging site fidelity may affect an individual’s ability to respond to changes in the distribution of prey or to broad-scale environmental changes (Chilvers 2008). Recent studies at four key colonies have described New Zealand fur seal foraging site fidelity based on directional persistence of consecutive foraging trips, but within the context of colony specific foraging areas (Baylis et al. 2008a). In general, females from the Cape Gantheaume colony exploited continental shelf waters associated with the Bonney Upwelling during autumn and shifted foraging effort to the STF during winter months (Baylis et al. 2008b). Over the same time period of autumn and winter, females from Cape du Couedic, North Neptune Island, and Liguanea Island colonies almost exclusively foraged in distant oceanic waters associated with the STF (Baylis et al. 2008a). The current study compares foraging site fidelity of lactating New Zealand fur seals that foraged in continental shelf waters to those that foraged in distant oceanic waters. MATERIALS AND METHODS Study Site and Animal Handling This study was conducted in 2005 and 2006 at four sites; in March–September 2005 at Cape Gantheaume (36◦04S, 137◦27E) and Cape du Couedic (36◦03S, 136◦42E) on Kangaroo Island and in April–August 2006 at Cape du Couedic, North Neptune Island (35◦13S, 136◦03E), and Liguanea Island (34◦59S, 135◦37E) (Fig. 1). This study was conducted as part of a concomitant study presented in 4 MARINE MAMMAL