Characterisation and CPUE analyses of the New Zealand albacore fishery

This paper presents an updated characterisation and CPUE analysis of the New Zealand albacore (Thunnus alalunga) fishery. In New Zealand, albacore are landed to a single Fishery Management Area (FMA) ALB 1. Landings vary from year to year, with an increasing trend from the early 1970s to the early 2000s followed by a decline after 2003, and have fluctuated around 2000 t to 3000 t since 2006. Albacore within the New Zealand fishery waters are part of the South Pacific Ocean stock which is distributed from the equator south to about 50^∘S, and from the Australian east coast to the South American west coast. The broader stock is managed by two Regional Fisheries Management Organisations (RFMOs); the Inter American Tropical Tuna Commission (IATTC) manages the eastern part of the stock, while the western part is managed under the Western and Central Pacific Fisheries Commission (WCPFC). In the WCPFC Convention Area, albacore are landed in a number of fisheries but primarily from longline (94.6%) and troll (4.9%) fisheries, with 77% of the troll catch and <1% of the longline catch coming from New Zealand fishery waters.

The present analysis was undertaken to provide information for the regional stock assessment undertaken by the Pacific Community (SPC) and focuses primarily on the troll fishery which lands the bulk of the catch in New Zealand, but longline data are also included. The analysis describes the fisheries targeting and catching albacore in New Zealand, and undertakes a CPUE standardisation of the commercial troll fishery. Data for the fishery description included the catch and effort from 1990 to 2020 from albacore troll target sets, all other troll activity, and all trips where ALB 1 was specified as the target or recorded as bycatch. For the CPUE analysis, catch-effort data for albacore target trolling only were modeled using maximum-likelihood generalised linear models (GLMs) predicting the catch as a function of spatial, temporal and environmental predictors. The models provided a minimal standardising effect, producing CPUE series that show little long-term trend. For the years up to the 2008 fishing year, the series reported in this analysis closely follows the trend reported in the previous analyses conducted in 2010 and 2017. Overall, the series, which now extends 30 years, fluctuates without trend over the last two decades. The standardised CPUE index is likely a reflection of availability and/or catchability, rather than an indication of abundance, and is discussed in terms of the coverage of the juvenile portion of albacore stock in New Zealand waters by the troll fishery.

Recommendations for future work include: investigating temporal and spatial trends in the compositional data from market sampling to determine if there is utility in these data for informing size disaggregated CPUE; and, investigating drivers of availability of juvenile albacore to the New Zealand troll fishery, and which environmental datasets may be useful for predicting climate change effects on availability.