Sea lions in the southern squid fishery (Part 1) Ben Steele-Mortimer

Photo Credit: Tamzin Henderson

The New Zealand sea lion/ rāpoka, a taonga (treasure) species, is one of the rarest sea lion species in the world and is classified as nationally vulnerable.

Historically, sea lions have faced several human related threats, including being hunted by Māori and commercial sealers, and incidentally caught in trawl fisheries. In recent years, environmental stressors like disease and ocean change have put greater strain on the survival of this species.

Over the past 30 years, the seafood industry has been committed to reducing impacts on the sea lion population, through the development of mitigation tools and effective management.

Sea lion & squid overlap

The New Zealand southern squid fishery overlaps with the foraging range of sea lions, on the two relatively small but important fishing grounds adjacent to the Auckland Islands rookeries and outside of the 12 nautical mile Marine Reserve.

Sea lions are sometimes observed following fishing vessels, pulling fish out of the net while it is being hauled and anticipating discarded fish waste. Ever since the fishery was discovered in the mid-1970s by scientific survey vessels, sea lion interactions have been reported.

Diagram of Sea Lion Exclusion Device

In the early 1990s, New Zealand sea lion captures in the Auckland Island or southern squid fishery (SQU 6T) caused great concern to the seafood industry, with an estimated 70-140 sea lions being caught in the nets annually.

At the time, few measures in place adequately reduced the risk to these marine mammals and the monitoring of the fleet was relatively poor, with low numbers of government observers present in a fleet of up to 50 vessels.

The Southern Squid Fishery Operational Plan was implemented in 1992, setting a limit on the number of sea lion captures that, when reached, closed the fishery for the remainder of the fishing year. Motu

Maha Marine Reserve was also established within the Territorial Sea, which provided further protection, noting however that fishing did not occur within 12 nm.

Since the 1990s, the sea lion population has been extensively studied, and science undertaken by DOC, MPI and NIWA, comprehensive and robust. There are estimated to be around 9,850 NZ sea lions in New Zealand (including 2,000 breeding females), with about 68% of the entire population breeding on the Auckland Islands.

SLEDs reduce captures

Concern increased as to the viability of the sea lion population.

Over the past 20 years in particular, Industry and government have made significant progress to reduce risk to sea lions.

Introduction of Sea Lion Exclusion Devices (SLEDs) around 2000 became one of New Zealand’s most successful fisheries incidental capture mitigation strategies, recognised globally for its effectiveness.

Today, as a result of the work of industry, government agencies and the engagement and cooperation of the deepwater fleet, the risk to sea lions from fishing activity is significantly reduced.

SLEDs are designed to allow sea lions, once inside, to exit squid trawl nets (Figure 1). Initial designs were based on turtle exclusion devices used in the Australian prawn fishery and were altered to suit the physiology of sea lions and the larger trawl nets.

Strict rules replace ad hoc

With government support, Deepwater Group and its operators began implementing SLEDs across the entire squid fleet. Initial deployment was ad hoc with no standards, specifications or checks. Since 2006, Deepwater Group has required that certified (i.e. annually checked and manufacturer-approved) SLEDs be used in the SQU 6T fishery at all times. SLED use in the SQU 6T fishery has increased from 44% of tows in 2002 to 100% of tows from 2006 onwards (Thompson et al 2015).

This full rollout of certified SLEDs has resulted in a substantial reduction in the number of observed sea lion captures; from 1 capture per 100 tows in 2005 to an average of less than one capture per 1,000 tows after 2010—with 100% observerreported adherence to the SQU 6T Operational Plan in recent years. In addition, after 2013, observer coverage in SQU 6T increased from around 30% to 90%, improving the certainty and quality of information reported.

Studies indicate most sea lions survive following an exit from SLEDs.

Collaborative research and investment in the Auckland Islands

DOC leads a field project to count sea lion pups on the Auckland Islands between February and March each year, at a cost of between $150,000 and $300,000 annually. Quota owners meet 90% of the cost—the government, the balance.

Since 2003, the industry has contributed over $4 million to monitor the population.

In the late 1990s when population monitoring became routine, there were increasing pup counts on the Auckland Islands. This was followed by a gradual decline in numbers after 2002, with an outbreak of Klebsiella pneumoniae— while at the same time, the fishing fleet was decreasing in size and capture rates of sea lions were declining. In 2014, the pup count dropped by 18% on the previous year and was the lowest count since 1995.

Sea lions are facing multiple challenges. Next month we will find out what more is being done to help understand these taonga species and threats.

Additional information may be found at the links below. 

doc.govt.nz/globalassets/documents science-and-technical/nztcs29entire.pdf 

deepwatergroup.org/wp-content/uploads/2018/11/MMOPVersion-9-2.pdf 

mpi.govt.nz/dmsdocument/38189/direct 

moanaproject.org/recent-marine-heatwaves

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