How NZ risks sea lions' survival

NET DANGER: Sea lion pups swim near the Auckland Islands. The number of pups born there between 1998 and last year was halved.
NET DANGER: Sea lion pups swim near the Auckland Islands. The number of pups born there between 1998 and last year was halved.

Squid fishing around the subantarctic Auckland Islands is no longer hurting the declining New Zealand sea lion population, according to Primary Industries Minister David Carter.

Mr Carter relies on 'evidence' that sea lion exclusion devices (SLEDs) are 'significantly more effective than previously thought'.

SLEDs are meant to allow sea lions to get out of a net without drowning.

Mr Carter went on to congratulate the fishing industry for the successful design and implementation of these devices.

In the past two decades, sea lions have drowned in the trawl nets of mostly foreign chartered squid boats, with 90 per cent of squid fishing carried out by foreign chartered boats.

These deaths are thought to be behind the disastrous halving of the number of seal pups born in the Auckland Islands between 1998 and last year.

Given this known impact of fishing, the minister's conclusion is probably dangerously premature.

Prime among the issues is that the ministry does not know whether SLEDs are working as intended.

A SLED is meant to allow only living sea lions to exit the net.

Dead ones should be retained for fisheries scientists to count and determine how effective the SLEDs are. The ministry proposes that the decline in observed sea lion deaths shows SLEDs are working, with Mr Carter highlighting in his decision 'no reported sea lion captures in [the fishery] during the past two completed seasons, with more than 1100 of the trawl tows observed'.

But, without hard evidence SLEDs retain dead sea lions in nets, it is just as likely that tinkering with SLED design since 2004 has led to dead sea lions being ejected from nets and going undetected.

A panel of veterinary pathologists raised this in 2010 when examining SLEDs, while other people in sea lion management have noted the problem.

However, instead of conducting scientific experiments to see if SLEDs retain dead sea lions, the ministry has relied on circumstantial evidence and fishing industry assurances they are working. This is unacceptable.

The ministry's conclusion of improved SLEDs function also rests on sea lions not receiving life-threatening injuries when exiting nets via SLEDs. Biomechanical modelling - a type of crash- test dummy experiment - says there is a 3 per cent chance a sea lion will be concussed if it collides with a SLED and may drown as a result.

Armed with this 3 per cent probability, the ministry concludes that 97 per cent of sea lions will exit SLEDs uninjured and survive. One ministry scientist told me this math is 'intuitive'.

The problem is this 'intuition' overlooks the 2010 expert panel's statement that SLED collisions are unlikely to be the main cause of sea lion deaths in trawl nets.

They used evidence from overseas (the same evidence used by the ministry for their modelling) showing seals drown in nets when detained too long, not from colliding with SLEDs. So if SLEDs are not retaining dead sea lions - the issue is obvious.

The ministry says this type of 'cryptic mortality' is not of consequence for our sea lion population, pointing to population modelling using a complex model - the Breen, Fu and Gilbert (BFG) model - which says such drowning mortality has no effect on the extinction risk of sea lions.

Serious concern has also been raised with the BFG model, which repeatedly throws up biologically implausible conclusions, such as that sea lions will die off without fishing pressure.

The model also asserts, paradoxically, that fishing can drown more than 250 sea lions annually without species decline.

The ministry has heeded concerns about that model and is reviewing it. But it is astounding the ministry continues to rely heavily on this model to conclude that fishing is no longer impacting on our sea lions.

A precautionary approach is to use last year's management regime until the BFG model is expertly reviewed. This would be more consistent with the sea lion's threatened status, allowing the necessary scrutiny of the model and providing certainty to the fishing industry.

If the Government has got this wrong, with sea lion deaths now beyond our ability to detect because they are ejected from SLEDs, then Mr Carter's plan to double fishing in the squid fishery will be disastrous for New Zealand's sea lions.

Dr Bruce Robertson is a senior lecturer and sea-lion researcher in Otago University's zoology department.

The Dominion Post