Comment on “Review of research and assessments on the efficacy of sea lion exclusion devices in reducing the incidental mortality of New Zealand sea lions Phocarctos hookeri in the Auckland Islands squid trawl fishery”

The New Zealand sea lion, Phocarctos hookeri, is the deepest- and longest-diving sea lion. We were interested in whether the diving ability of this animal was related to changes in its at-sea and diving metabolic rates. We measured the metabolic rate, water turnover and diving behavior of 12 lactating New Zealand sea lions at Sandy Bay, Enderby Island, Auckland Islands Group, New Zealand (50 degrees 30′S, 166 degrees 17′E), during January and February 1997 when their pups were between 1 and 2 months old. Metabolic rate (rate of CO(2) production) and water turnover were measured using the (18)O doubly-labeled water technique, and diving behavior was measured with time/depth recorders (TDRs). Mean total body water was 66.0+/−1.1 % (mean +/− s.d.) and mean rate of CO(2) production was 0. 835+/−0.114 ml g(−)(1)h(−)(1), which provides an estimated mass-specific field metabolic rate (FMR) of 5.47+/−0.75 W kg(−)(1). After correction for time on shore, the at-sea FMR was estimated to be 6.65+/−1.09 W kg(−)(1), a value 5.8 times the predicted standard metabolic rate of a terrestrial animal of equal size. The mean maximum dive depth was 353+/−164 m, with a mean diving depth of 124+/−36 m. The mean maximum dive duration was 8.3+/−1.7 min, with an average duration of 3.4+/−0.6 min. The deepest, 550 m, and longest, 11.5 min, dives were made by the largest animal (155 kg). Our results indicate that the deep and long-duration diving ability of New Zealand sea lions is not due to a decreased diving metabolic rate. Individual sea lions that performed deeper dives had lower FMRs, which may result from the use of energetically efficient burst-and-glide locomotion. There are differences in the foraging patterns of deep and shallow divers that may reflect differences in surface swimming, time spent on the surface and/or diet. Our data indicate that, although New Zealand sea lions have increased their O(2) storage capacity, they do not, or cannot, significantly reduce their at-sea metabolic rates and are therefore likely to be operating near their physiological maximum.

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Philopatry and site fidelity of New Zealand sea lions (Phocarctos hookeri)

Wildlife Research ◽

10.1071/wr07053 ◽

2008 ◽

Vol 35 (5) ◽

pp. 463 ◽

Cited By ~ 38

Author(s):

B. Louise Chilvers ◽

Ian S. Wilkinson

Keyword(s):

New Zealand ◽

Site Fidelity ◽

Breeding Area ◽

Quantitative Investigation ◽

Sea Lion ◽

Breeding Sites ◽

Auckland Island ◽

Sea Lions ◽

Breeding Habitats ◽

Phocarctos Hookeri

The New Zealand sea lion (NZ sea lion), Phocarctos hookeri, is New Zealand’s only endemic pinniped, and one of the worlds rarest otariids. It is classified as ‘Threatened’ based primarily on the low number of breeding sites and restricted distribution. In New Zealand, a species listed as ‘threatened’ is required to be managed to allow its recovery and removal from the list within 20 years. For NZ sea lions this is dependant on the establishment of new breeding areas. However, understanding the recolonisation processes for pinnipeds is still in its infancy with factors such as philopatry needing more research to understand individual dispersal and the recolonisation process. This paper presents the first quantitative investigation into the level of site fidelity and philopatry to breeding beaches in NZ sea lions. Data from resights of NZ sea lions marked as pups from the northern Auckland Island breeding area suggest that both site fidelity and philopatry are important characteristics of this species. Our results show that overall: (1) females have a higher resighting rate than males, particularly at natal sites; (2) female non-natal resightings are predominantly restricted to locations within the northern Auckland Island breeding area (an area of ~10 km2), whereas male resightings are more widely dispersed (up to 700 km to NZ mainland); and (3) philopatry occurs for both sexes, but is more predominant in females than males, with males displaying delay related to sexual and social maturity. The colonisation of new breeding habitats rarely occurs when philopatry is strong and population density is low, stable or declining such as seen for NZ sea lions. Therefore, this research indicates that management of NZ sea lions needs to minimise anthropogenic mortality and encourage population growth to maximise density at breeding sites and encourage females to disperse to establish new breeding areas.

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Historical population size of the threatened New Zealand sea lion Phocarctos hookeri

Journal of Mammalogy ◽

10.1093/jmammal/gyv187 ◽

2015 ◽

Vol 97 (2) ◽

pp. 436-443 ◽

Cited By ~ 7

Author(s):

Catherine J. Collins ◽

B. Louise Chilvers ◽

Matthew Taylor ◽

Bruce C. Robertson

Keyword(s):

New Zealand ◽

Population Size ◽

Effective Population Size ◽

Carrying Capacity ◽

Effective Population ◽

Sea Lion ◽

Sea Lions ◽

Target Values ◽

Phocarctos Hookeri

Abstract Marine mammal species were exploited worldwide during periods of commercial sealing in the 18th and 19th centuries. For many of these species, an estimate of the pre-exploitation abundance of the species is lacking, as historical catch records are generally scarce and inaccurate. Genetic estimates of long-term effective population size provide a means to estimate the pre-exploitation abundance. Here, we apply genetic methods to estimate the long-term effective population size of the subantarctic lineage of the New Zealand sea lion (NZ sea lion), Phocarctos hookeri . This species is predominantly restricted to the subantarctic islands, south of mainland New Zealand, following commercial sealing in the 19th century. Today, the population consists of ~9,880 animals and population growth is slow. Auckland Island breeding colonies of NZ sea lion are currently impacted by commercial trawl fisheries via regular sea lion deaths as bycatch. In order to estimate sustainable levels of bycatch, an estimate of the population’s carrying capacity ( K ) is required. We apply the genetically estimated long-term effective population size of NZ sea lions as a proxy for the estimated historical carrying capacity of the subantarctic population. The historical abundance of subantarctic NZ sea lions was significantly higher than the target values of K employed by the contemporary management. The current management strategy may allow unsustainable bycatch levels, thereby limiting the recovery of the NZ sea lion population toward historical carrying capacity.

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Pattern Of Immigration Of New Zealand Sea Lions Phocarctos Hookeri To Otago, New Zealand: Implications For Management

Australian Mammalogy ◽

10.1071/am02107 ◽

2002 ◽

Vol 24 (1) ◽

pp. 107 ◽

Cited By ~ 23

Author(s):

SD Mcconkey ◽

S Heinrich ◽

C Lalas ◽

H Mcconnell ◽

N Mcnally

Keyword(s):

New Zealand ◽

Breeding Season ◽

Carrying Capacity ◽

Management Strategy ◽

Age Classes ◽

Diagnostic Features ◽

Sea Lions ◽

Trawl Fishery ◽

Species Population ◽

Phocarctos Hookeri

The present management strategy for New Zealand sea lions Phocarctos hookeri assumes that kills in a squid trawl fishery around Auckland Islands, the species population base, have prevented an increase in abundance of sea lions. This strategy also assumes that emigration will be initiated as the population reaches carrying capacity, and that emigration rates will be density dependent. We used the combination of photographic identification of individuals and diagnostic features of age classes to estimate immigration rates of P. hookeri to Otago, South Island, New Zealand. Most immigrants were males = 2 years old at arrival, and included animals tagged as pups at Auckland Islands. Estimates for total numbers of immigrants to Otago from four consecutive cohorts, 1991/92 - 1994/95, varied three-fold through a period of constant annual pup production at Auckland Islands. The greatest influx was from the 1993/94 cohort, a breeding season that predated the enforcement of early closures of the squid fishery. We suggest published records from the Auckland Islands indicate that this population is already at carrying capacity. If so, then factors other than, or in addition to, pup production and fishery mortality have an impact on emigration rates.

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Long-term survival and reproductive success of New Zealand sea lions (Phocarctos hookeri) treated with ivermectin as pups

Wildlife Research ◽

10.1071/wr15120 ◽

2015 ◽

Vol 42 (8) ◽

pp. 660 ◽

Cited By ~ 2

Author(s):

S. A. Michael ◽

B. L. Chilvers ◽

W. D. Roe ◽

B. D. Gartrell

Keyword(s):

New Zealand ◽

Management Tool ◽

Juvenile Survival ◽

Sea Lion ◽

Term Survival ◽

Long Term Survival ◽

Growth And Survival ◽

Sea Lions ◽

Phocarctos Hookeri

Context Hookworms (Uncinaria spp.) are a common parasite of neonatal fur seals and sea lions around the world and may contribute to decreased pup growth and survival. Removal of these parasitic burdens by administration of the anthelmintic ivermectin has been trialled in New Zealand (NZ) sea lion (Phocarctos hookeri) pups at Sandy Bay, Enderby Island, with initial benefits in growth and survival reported. Long-term effects, however, are not known. Aims To determine the impact of ivermectin treatment administered in the first month of life, on long-term survival and fecundity in a sample of NZ sea lion pups. Methods For a sample of treated and control pups born between 2002 and 2004, resighting data to 2012 was assessed with the Cox proportional hazards analysis to evaluate survival to maturity and fecundity. Key results Sample size was a limiting factor as juvenile survival was very low, but a trend of improved survival was observed in the ivermectin-treated group. Year of birth was significant due to the effects of a bacterial epizootic in the first year of the trial. Reproductive rate was not significantly different between groups. Conclusions The effect of disease and parasitism on the survival of NZ sea lions is apparent, contributing to early pup mortality, with potentially wider-ranging implications for juvenile survival and beyond. Implications Further research is warranted to investigate anthelmintic treatment of NZ sea lion pups as a safe and effective management tool to improve survival and recruitment in declining populations.

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Abundance, distribution and status of the New Zealand sea lion, Phocarctos hookeri

Wildlife Research ◽

10.1071/wr98022 ◽

1999 ◽

Vol 26 (1) ◽

pp. 35 ◽

Cited By ~ 46

Author(s):

Nicholas J. Gales ◽

David J. Fletcher

Keyword(s):

New Zealand ◽

Breeding Site ◽

Close Monitoring ◽

Sea Lion ◽

Trawl Fishery ◽

Mitigation Action ◽

Breeding Seasons ◽

Pup Mortality ◽

Campbell Island ◽

Phocarctos Hookeri

The abundance of the New Zealand sea lion, Phocarctos hookeri, was estimated using a model that incorporated estimated pup production. Pups are born at only five sites, four of which are at the sub-Antarctic Auckland Islands, which lie to the south of New Zealand. The remaining breeding site is at Campbell Island in the same region. Pup production was estimated during the 1994/95 and 1995/96 breeding seasons from mark–recapture studies at the two largest sea lion rookeries, at the Auckland Islands (Sandy Bay and Dundas Island), which account for almost 90% of total pup production for the species. Pup production for the other sites was estimated from direct counts or, in the case of Campbell Island, from recent tagging data. Total pup production estimates for all sites during the 1994/95 and 1995/96 breeding seasons are 2640 and 2807 respectively. During the four-week pupping season, pup mortality at most sites was estimated to be about 10%. The estimates of absolute abundance based on pup production for the two breeding seasons were 11 700 (95% confidence interval (CI): 10 500–13 100) and 12 500 (95% CI: 11 100–14 000) respectively. This population abundance is among the smallest reported for a species within the Otariidae. The highly localised, and historically reduced distribution make this species vulnerable to impact and warrants particular attention from conservation managers. In particular, the potential impact of the annual bycatch of P. hookeri in a trawl fishery requires close monitoring and, ideally, some mitigation action.

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