Jim Roberts: Myths no help to struggling sea lions

Dr Jim Roberts says myths about sea lions distort the science and may divert resources into ineffective conservation measures.
Dr Jim Roberts says myths about sea lions distort the science and may divert resources into ineffective conservation measures.

Dr Jim Roberts is a National Institute of Water and Atmospheric Research fisheries scientist whose research with New Zealand sea lions has included population modelling, diet and reproductive biology.

As a scientist working closely with New Zealand sea lions, I am concerned by recently published claims about the species for which there is weak scientific evidence.

The dramatic decline of the Auckland Islands population of NZ sea lions is a genuine concern for the species' long-term viability. The Ministry of Primary Industries and the Department of Conservation have responded with a threat management plan.

A consultation paper has been released for public comment, sparking a number of media articles containing myths and misinformation, which, in my view, are counterproductive to the conservation of the species.

Myth - NZ sea lions mainly eat squid

Southern arrow squid make up less than one-fifth of their diet. Furthermore, survival and breeding rates of sea lions at the Auckland Islands were poor during a period when squid were abundant. This does not suggest squid fishing is causing the fall in sea lion numbers.

But there is strong evidence of nutritional stress in sea lions at the Auckland Islands and it is possible commercial fish catches may be a factor since other key prey, including hoki and red cod, are caught.

However, the abundance of these species will be responding to changes in climate as well as fishing, making it difficult to determine the ultimate causes of nutritional stress. This task is made even harder when dietary studies are misrepresented.

Myth - The threat management plan ignores death caused by sea lion exclusion devices

Since 2006, sea lion exclusion devices have been standard equipment in squid trawls around the Auckland Islands. They allow sea lions to escape from nets and have led to a major reduction in observed captures, but there is concern that sea lions drown or die from injuries after passing through the device.

The threat management plan does not ignore these deaths. The plan's risk assessment model looked at the effects of commercial trawl mortality, including a scenario where all that passed through the device died, their pups ashore died and all future pups were lost. Even this most pessimistic scenario does not explain the whole of the sea lion population decline.

The Auckland Islands population has been dealing with something much bigger than trawl mortality and we urgently need to know what this is.

Myth - Bacterial disease has killed few pups since the 2002 and 2003 epidemics

Bacterial disease was first noticed killing pups at the Auckland Islands in 1998, with epidemics in 2002 and 2003 attributed to Klebsiella pneumoniae. This disease has since become endemic (a constant presence in the population) and is the main killer of pups during the summer field season.

The duration of this endemic is unusual for a seal species and coincides with a protracted period of low pup survival.

Myth - Smaller populations don't merit as much attention

Encouragingly, over the past 20 years we have seen the seal lion recolonise Stewart Island and the NZ mainland. We have also seen the population rise on Campbell Island, where a third of all pups are now born.

Having many breeding sites helps protect a species against catastrophic events. However, half of pups born at Campbell Island have been dying in the first few weeks and the causes - provisionally starvation and drowning in wallows - clearly need attention.

Because of their close proximity to humans, the Stewart Island and mainland populations face a very different set of threats. We must afford these fledgling populations the protection they need to persist and realise their growth potential.

These myths are harmful because they distort the science and may divert resources into ineffective conservation measures.

Although not explicitly addressed by the threat management plan, misinformation is a genuine threat to the conservation of New Zealand sea lions.

• More information can be found at www.niwa.co.nz/nzsealions

- NZ Herald

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