Aquatic and Threats Unit

Wellington, New Zealand

Aquatic and Threats Unit

Wellington, New Zealand
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Chilvers B.L.,Aquatic and Threats Unit | Chilvers B.L.,Massey University
Polar Biology | Year: 2017

The breeding success, foraging strategies and abundance of penguin species are thought to vary according to the quality of near-shore marine environments. Little blue penguins (LBP), Eudyptula minor, in particular, are considered a candidate species for assessing near-shore marine productivity and integrity due to their limited foraging ranges and reliance on local resources, particularly during breeding. However, to assess their ability to be near-shore ecosystem indicators an understanding of what their “normal” dive patterns and population parameters from across New Zealand are needed. This research investigates diving behaviours and feather stable isotope values (as indicators of diet) of LBPs from southern (Pearl Island, Stewart Island/Rakiura, Nov. 2011) and central (Adele Island, Abel Tasman, Nov. 2012) New Zealand (NZ), two areas not previously studied, and compares them with LBPs from other areas of NZ. The diving behaviours of LBPs across NZ, are highly variable, not obviously linked with local geography and bathometry. These results and the NZ wide comparison indicates that LBPs are environmentally adaptable, which may make them difficult to use as ecosystem indicators across sites. However, with increasing knowledge of diving behaviours and population parameters of LBPs within a region, they are likely to be indicators of local changing marine environment. © 2017 Springer-Verlag Berlin Heidelberg

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).

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.

Ansmann I.C.,University of Queensland | Parra G.J.,Flinders University | Parra G.J.,South Australian Research And Development Institute | Chilvers B.L.,Aquatic and Threats Unit | Lanyon J.M.,University of Queensland
Animal Behaviour | Year: 2012

Although human activities are known to affect the social behaviour of group-living animals, the resilience of animals' social structure to disturbance is poorly understood. In the 1990s, bottlenose dolphins, Tursiops aduncus, in Moreton Bay, Australia, formed two distinct social communities ('trawler' and 'nontrawler dolphins') based on foraging interactions (or lack thereof) with commercial prawn trawlers. Members of the two communities almost never associated, despite overlapping home ranges. Since then, changes to fisheries legislation have substantially reduced trawling in Moreton Bay. We used association analyses and social network metrics to compare patterns of sociality among bottlenose dolphins across two periods: 1997-1999 (during trawling) and 2008-2010 (post trawling). Over this decade, their social network became less differentiated and more compact (average geodesic distance between individuals decreased), with significantly more and stronger associations between individuals (mean and maximum half-weight indices increased). The previously described partitioning into two communities has disappeared, with former 'trawler' and 'nontrawler dolphins' now dispersed over the entire social network and associating with each other. This restructuring suggests that although fisheries can influence the social behaviour of bottlenose dolphins, their social structure represents a complex adaptive system that is resilient to disturbance. © 2012 The Association for the Study of Animal Behaviour.

Osborne A.J.,University of Otago | Zavodna M.,University of Otago | Chilvers B.L.,Aquatic and Threats Unit | Robertson B.C.,University of Otago | And 3 more authors.
Heredity | Year: 2013

Marine mammals are often reported to possess reduced variation of major histocompatibility complex (MHC) genes compared with their terrestrial counterparts. We evaluated diversity at two MHC class II B genes, DQB and DRB, in the New Zealand sea lion (Phocarctos hookeri, NZSL) a species that has suffered high mortality owing to bacterial epizootics, using Sanger sequencing and haplotype reconstruction, together with next-generation sequencing. Despite this species' prolonged history of small population size and highly restricted distribution, we demonstrate extensive diversity at MHC DRB with 26 alleles, whereas MHC DQB is dimorphic. We identify four DRB codons, predicted to be involved in antigen binding, that are evolving under adaptive evolution. Our data suggest diversity at DRB may be maintained by balancing selection, consistent with the role of this locus as an antigen-binding region and the species' recent history of mass mortality during a series of bacterial epizootics. Phylogenetic analyses of DQB and DRB sequences from pinnipeds and other carnivores revealed significant allelic diversity, but little phylogenetic depth or structure among pinniped alleles; thus, we could neither confirm nor refute the possibility of trans-species polymorphism in this group. The phylogenetic pattern observed however, suggests some significant evolutionary constraint on these loci in the recent past, with the pattern consistent with that expected following an epizootic event. These data may help further elucidate some of the genetic factors underlying the unusually high susceptibility to bacterial infection of the threatened NZSL, and help us to better understand the extent and pattern of MHC diversity in pinnipeds. © 2013 Macmillan Publishers Limited All rights reserved.

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.

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.

Auge A.A.,University of Otago | Chilvers B.L.,Aquatic and Threats Unit | Moore A.B.,University of Otago | Davis L.S.,University of Otago
Marine Ecology Progress Series | Year: 2011

The New Zealand sea lion Phocarctos hookeri historically bred on the New Zealand mainland (South and North Islands). Subsistence hunting and later commercial sealing reduced its distribution to 3 breeding areas at the spatial edges of its historical distribution range, in the Auckland Islands (AI) and on Campbell Island. Here, we present foraging areas and foraging trips of female New Zealand sea lions from the Otago Peninsula, where a recolonising population has been found in the core of the historical range of the species. We compare the results with data from the AI in order to assess the theory that the spatial margin of a species' distribution represents the lower end of habitat suitability. Female New Zealand sea lions at Otago had significantly smaller foraging ranges than females at the AI (mean 65% Kernel ranges: 47 ± 25 km2 versus 687 ± 109 km2), made shorter foraging trips (mean 11.8 ± 2.3 h versus 66.2 ± 4.2 h), and spent 40% less time at sea overall. Juvenile females at Otago from age 2 onwards could access foraging grounds used by adult females nursing pups; this is unlikely to be the case at the AI due to the large distances and associated depths of foraging grounds. Our study illustrates the theory that spatial marginality is related to habitat marginality. Existing management measures to mitigate the impact of bycatch in fisheries on declining remnant colonies around the AI were modelled based on populations exploiting optimal habitat. They should now integrate this new information. © Inter-Research 2011.

A common issue faced in wildlife management is how to assess the uncertainty of potential impacts on the viability of a species or population. The pup production of New Zealand (NZ) sea lions (Phocarctos hookeri) has declined 50% in the last 12 years at their main breeding area, the Auckland Islands. The two major known atypical impacts on NZ sea lions are as follows: (1) the direct mortality as bycatch of trawling and (2) bacterial epizootics, which can affect reproduction and mortality. Both of these impacts include high levels of uncertainty, with fisheries data being variable due to percentage observer coverage and the effect of sea lion exclusion devises, while the timing and severity of bacterial epizootics are not predictable. In this paper, an age-structured model of the NZ sea lion population at the Auckland Islands was built to examine the predicted effects of fisheries mortality and catastrophes (bacterial epizootics), both separately and then combined, on population viability over a 100-year period using the VORTEX population viability analysis programme. These models are then compared against 15 years of empirical field data to determine the actual level of impacts being observed. Model results indicate that although naturally occurring epizootics reduce the growth rate of the population, it does not cause a decline in the Auckland Island population. However, sustained fisheries bycatch at current estimated levels, particularly considering its potential impact on adult female survival, could result in a population decline and possible functional extinction over the modelled time period. © 2011 Springer-Verlag.

Chilvers B.L.,Aquatic and Threats Unit
Journal of Zoology | Year: 2012

Annual censuses of New Zealand (NZ) sea lions Phocarctos hookeri at the subantarctic Auckland Islands have indicated a decline in pup production of over 40% during the first decade of the 2000s. With this significant decline and likely decline in the population as a whole, population ecology theory hypothesizes that life-history traits such as reproduction rate, survival or growth should improve, particularly if density-dependency is playing a significant role in the population. This research examined whether changes in NZ sea lion pup production were associated with changes in adult abundance or population life-history traits in an attempt to clarify potential causes of decline. Since 1998/1999, daily surveys of Sandy Bay, Enderby Island, were undertaken during the NZ sea lion breeding season (December-February). These surveys confirm that the number of adults at the breeding area has significantly declined during the period of pup production decline. There was no difference between years in mean pup birth date, but the ratio of pups to females ashore during peak pupping varied significantly. The sex ratio of pups at birth also varied from year to year, but with no significant variation overall. Pup mortality varied significantly only during years of epizootic events (1997/1998, 2001/2002 and 2002/2003). Pup birth mass showed little variation between 2000/2001 and 2006/2007, increasing slightly in the last 3 years of study. Pup mass at 3 weeks, although highly variable, showed no trend during the period of decline. Despite the significant decrease in pup production and breeding animals, not all life-history traits relating to pup mass and survival or female fecundity improved. Research suggests that indirect fishing-related pressures may influence some of these traits and that the NZ sea lion population was unlikely to have been influenced by density-dependent factors or to have been at or near carrying capacity before the decline. © 2012 The Authors. Journal of Zoology © 2012 The Zoological Society of London.

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