The objective of this project was to document the decline in yellowfin tuna catch in New Zealand using catch record from commercial tuna longliners and clubs affiliated to the NZ Sport Fishing Council (NZSFC). Summary catch and effort data from all tuna fleets in the Western and Central Pacific was as available from the Secretariat of the Pacific Community (SPC) Oceanic Fisheries Programme public access database.

Yellowfin tuna have been caught in New Zealand waters since the 1960s. Their numbers have always fluctuated from year to year, but catches have been very low since 2005. The once thriving sport fishery has all but vanished. There is circumstantial evidence that an increase in tuna longline fishing effort in the subtropical SW Pacific, north of New Zealand, is a factor in this decline. This is most evident with a sharp increase in the number of longline hooks set and yellowfin caught in 2000, which was followed by reduced abundance in NZ waters. However, the year with the highest catch by our Pacific Island neighbours (10,000 t in 2004) was a reasonable year in the NZ sport fishery (992 fish in 2004), followed by the best year in the last decade in 2005 (1290 yellowfin for NZSFC clubs).

The Western and Central Pacific Fisheries Commission is trying to control fishing effort in the region, with particular concern for bigeye, yellowfin and more recently albacore. One of the conservation and management measures proposes limiting yellowfin harvest to the average annual catch from 2000-2004. This target was reached in 2010, however there are exceptions and alternatives that have limited the effectiveness of the measure and it was not replaced but further weakened at the March 2012 meeting. Given the political nature of these decisions and the bench mark years used, it is unlikely that these measures will go far enough to restore abundance of yellowfin in New Zealand to that seen in the 1980s. Further work in to the range contraction of highly migratory species since the introduction of industrial fishing methods is needed.

The best hope for New Zealand fishers is that natural conditions will result in particularly good spawning and recruitment yellowfin will spread out as far as northern New Zealand once again, as appeared to happen in the mid 2000’s.

Further research:

This paper was presented to the New Zealand Highly Migratory Species Fisheries Planning group. It was then revised and presented as an information paper for the Science Committee of the Western and Central Pacific Fisheries Commission. Since then several papers have been published on range contraction of tuna and billfish in the Pacific. (see ‘Relationship between abundance and range size in longline target species’ WCPFC-SC10-2014/MI-WP-06)