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Wellington, New Zealand

Robertson B.C.,University of Otago | Chilvers B.L.,Aquatic and Threats Unit
Mammal Review | Year: 2011

1 The New Zealand (NZ) sea lion Phocarctos hookeri is NZ's only endemic pinniped and is listed as 'nationally critical'. The species breeds in the NZ sub-Antarctic: 71% of the population at the Auckland Islands (2010 pup production: 1814±39) and the remaining 29% on Campbell Island (726 pups in 2010). 2 Pup production at the Auckland Islands has declined by 40% since 1998 (1998: 3021 pups produced): only 1501 pups were born in 2009. This decline is directly linked to philopatric females not returning to breeding areas. While the Auckland Island population has declined, the Campbell Island population appears to be increasing slowly. 3 Potential reasons for the decline in the Auckland Island population, but not in the Campbell Island population, include non-anthropogenic factors: (i) disease epizootics, (ii) predation, (iii) permanent dispersal or migration, (iv) environmental change; and anthropogenic impacts: (v) population 'overshoot', (vi) genetic effects, (vii) effects of contaminants, (viii) indirect effects of fisheries (i.e. resource competition) and (ix) direct effects of fisheries (i.e. by-catch deaths). Of the nine potential reasons examined here, six can be discounted (ii-vii). Bacterial epizootics (i) occur in the NZ sea lion population, but their impact has predominantly increased pup mortality, which is unlikely to cause the severe decline observed, as pup mortality throughout the species is naturally high and variable. 4 The most plausible hypotheses, based on available evidence, are that the observed decline, in particular, the decreasing number of breeding females in the Auckland Island population, is caused by (viii) fisheries-induced resource competition and (ix) fisheries-related by-catch. By-catch is the main known anthropogenic cause of mortality in the species. Competition with fisheries resulting in resource competition, nutrient stress and decreased reproductive ability in NZ sea lions should be a priority area for future research. © 2011 The Authors. Mammal Review © 2011 Mammal Society. Source


Leung E.S.,University of Otago | Chilvers B.L.,Aquatic and Threats Unit | Nakagawa S.,University of Otago | Moore A.B.,University of Otago | Robertson B.C.,University of Otago
PLoS ONE | Year: 2012

Sexual segregation (sex differences in spatial organisation and resource use) is observed in a large range of taxa. Investigating causes for sexual segregation is vital for understanding population dynamics and has important conservation implications, as sex differences in foraging ecology may affect vulnerability to area-specific human activities. Although behavioural ecologists have proposed numerous hypotheses for this phenomenon, the underlying causes of sexual segregation are poorly understood. We examined the size-dimorphism and niche divergence hypotheses as potential explanations for sexual segregation in the New Zealand (NZ) sea lion (Phocarctos hookeri), a nationally critical, declining species impacted by trawl fisheries. We used satellite telemetry and linear mixed effects models to investigate sex differences in the foraging ranges of juvenile NZ sea lions. Male trip distances and durations were almost twice as long as female trips, with males foraging over the Auckland Island shelf and in further locations than females. Sex was the most important variable in trip distance, maximum distance travelled from study site, foraging cycle duration and percent time at sea whereas mass and age had small effects on these characteristics. Our findings support the predictions of the niche divergence hypothesis, which suggests that sexual segregation acts to decrease intraspecific resource competition. As a consequence of sexual segregation in foraging ranges, female foraging grounds had proportionally double the overlap with fisheries operations than males. This distribution exposes female juvenile NZ sea lions to a greater risk of resource competition and bycatch from fisheries than males, which can result in higher female mortality. Such sex-biased mortality could impact population dynamics, because female population decline can lead to decreased population fecundity. Thus, effective conservation and management strategies must take into account sex differences in foraging behaviour, as well as differential threat-risk to external impacts such as fisheries bycatch. © 2012 Leung et al. Source


Riet-Sapriza F.G.,Proyecto Pinnipedos | Costa D.P.,University of California at Santa Cruz | Franco-Trecu V.,Proyecto Pinnipedos | Marin Y.,Laboratorio Of Tecnologia Pesquera | And 5 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

Resource competition between fisheries and marine mammal continue to raise concern worldwide. Understanding this complex conflict requires data on spatial and dietary overlap of marine mammal and fisheries. In Uruguay the South American sea lions population has been dramatically declining over the past decade. The reasons for this population decline are unknown but may include the following: (1) direct harvesting; (2) reduced prey availability and distribution as a consequence of environmental change; or (3) biological interaction with fisheries. This study aims to determine resource overlap and competition between South American sea lions (SASL, Otaria flavescens, n=10) and the artisanal fisheries (AF), and the coastal bottom trawl fisheries (CBTF). We integrated data on sea lions diet (scat analysis), spatial and annual consumption estimates; and foraging behavior-satellite-tracking data from lactating SASL with data on fishing effort areas and fisheries landings. We found that lactating SASL are benthic divers and forage in shallow water within the continental shelf. SASL's foraging areas overlapped with CBTF and AF fisheries operational areas. Dietary analysis indicated a high degree of overlap between the diet of SASL and the AF and CBTF fisheries catch. The results of our work show differing degrees of spatial resource overlap with AF and CBTF, highlighting that there are differences in potential impact from each fishery; and that different management/conservation approaches may need to be taken to solve the fisheries-SASL conflict. © 2012 Elsevier Ltd. Source


Auge A.A.,University of Otago | Auge A.A.,James Cook University | Chilvers B.L.,Aquatic and Threats Unit | Moore A.B.,University of Otago | Davis L.S.,University of Otago
Animal Conservation | Year: 2014

The efficiency of spatial conservation measures for threatened species depends mostly on the proportion of time that animals spend within the protected areas. We illustrate this with our case study of the population of recolonizing female New Zealand (NZ) sea lions Phocarctos hookeri (n=13) at Otago Peninsula, South Island, NZ. Human interactions at sea, where sea lions forage, are of concern, and spatial management measures have been proposed. Understanding the level of foraging site fidelity of these animals was consequently essential. We used satellite tracking of individuals across three autumns to assess foraging site fidelity and year-round on-land sighting surveys over 2.5 years as proxy to foraging areas outside autumns. Each individual exhibited a high level of autumnal site fidelity for foraging areas between years (64% overlap between 65% Kernel ranges with a 3-km buffer) while using beaches along a 12-km stretch of coastline during 96±8% (range 79-100%) of their time onshore. As a proxy for foraging areas outside autumns, these animals exhibited a high level of site fidelity to this stretch of coastline throughout the year. Breeding females were sighted there during 86% of months (range=73-100%) and non-breeding females during 69% of months (range=58-90%). The site fidelity of these animals indicates that protected areas would be efficient in this case and highlights the importance of studying foraging site fidelity in mobile predators to design efficient conservation measures. © 2013 The Zoological Society of London. Source


Chilvers B.L.,Aquatic and Threats Unit | Amey J.M.,802 Waikouiti Palmerston Rd | Huckstadt L.A.,University of California at Santa Cruz | Costa D.P.,University of California at Santa Cruz
Polar Biology | Year: 2011

Detrimental interactions between marine mammals and fisheries are increasing worldwide. The ability to manage these interactions requires the knowledge of where and how interactions occur and the effects they have on species. Many pinnipeds are central place foraging colonial breeders who are restricted in foraging range during breeding. Here, we use a utilization distribution approach to examine the foraging habitats of lactating New Zealand (NZ) sea lions (Phocarctos hookeri) from Dundas and Enderby Islands, Auckland Islands. Annually, the NZ sea lions which breed on these two islands produce 83% of this Nationally Critical species' pups. Satellite transmitters were attached to 55 females during 2001-2007. Data showed that NZ sea lions utilize the entire Auckland Island shelf with partial habitat partitioning between females from the two breeding islands. This habitat partitioning results in differing degrees of overlap with fisheries and therefore possible differing fishery-related impacts on breeding areas. © 2010 The Author(s). Source

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