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Assessing the effectiveness of the Great Australian Bight Marine Park in protecting the endangered

Abstract

The Australian sea lion (Neophoca cinerea) is listed as vulnerable under the Australian EPBC Act and as endangered on the IUCN Red List. Low fecundity and philopatry in females, typically small breeding colonies and retracted species range served to increase the impact of fishery by-catch mortality on their conservation. The Great Australian Bight Marine Park (GABMP) was proclaimed in 1998 in part to protect several small colonies of Australian sea lions residing at Bunda Cliffs, South Australia. Demersal shark gillnetting also occurs across the region and is permitted within the GABMP for six months each year. There is evidence to suggest Australian sea lions are sometimes killed when they become entangled in gill-nets. This study was conducted to determine i) the effectiveness of the GABMP in protecting Australian sea lions from by-catch mortality in shark gill-nets and ii) the impact they may have on the population.

The animals tracked spent only 27.7% of their time inside the GABMP and each averaged trip distances well beyond the park boundary into waters where gill-netting occurs year round. Observations were made from gill-netting vessels in the region and four by-catch mortalities were recorded, three of which occurred within the GABMP. Estimates extrapolated from fishing effort data suggested 22 Australian sea lion mortalities occurred across the GAB region during the last breeding cycle and 152 have occurred over the last decade. A suite of population viability analyses (PVA) were used to study the impact of by-catch mortality on the Bunda Cliffs population. Depending on the values used for population size and growth rate, outcomes ranged from a moderate decline to quasi-extinction in the next 2-5 breeding cycles. Difficulty in interpreting the PVAs is discussed.

The findings of this study indicate Australian sea lions residing at Bunda Cliffs are i) inadequately protected by the GABMP, ii) poorly understood with regard to current population size and historical trends, and iii) potentially at risk of extinction. We recommend i) the GABMP be closed permanently to shark gill-netting and restrictions be imposed on effort in adjacent waters, and ii) if fishing is to continue, improvements be made to the current population monitoring program at Bunda Cliffs to monitor impacts. This study is a precursor to ongoing research into the broader impacts of fishing on this vulnerable and endangered species and sets the scene for bringing about major changes to fishing practices to ensure their future conservation.