Environment-Recruitment Relationships and Catch Data Based Analysis of Movement Patterns in New Zealand Snapper (Chrysophrys auratus)

Abstract

Fluctuations in the levels of an exploited stock can cause significant fisheries management challenges. The Australasian Snapper (Chrysophrys auratus) is New Zealand’s most valuable recreational and commercial fish. Although they are well studied, it has been decades since the effects of environmental variables on recruitment (year class strength (YCS)) and movement of New Zealand snapper have been examined. Furthermore, catch data has not previously been used to verify their seasonal and long-term movement patterns. Several environmental variables were used in the analyses (e.g. sea surface temperature (SST), air temperature, wind run, wind speed, wind stress, Trenberth indices, sunshine, radiation, rainfall, mean sea level pressure, Southern Oscillation Index (SOI), Interdecadal Pacific Oscillation (IPO), chlorophylla, photosynthetically active radiation, diffusion attenuation coefficients at 490nm and ocean productivity). Generalized linear models were run for the SNA 1 and SNA 7 fisheries, using annual recruitment estimates from stock assessment models that incorporated age data from otolith samples. Mean April-June SST explained the most variation in YCS in SNA 1 and mean annual SOI in SNA 7. Mean annual IPO was the next most explanatory term for both areas. Movement patterns of the Hauraki Gulf stock were examined using commercial longline and trawl catch data. Seasonal and Trend decompositions using Loess smoothers were completed using mean monthly catch per unit effort (CPUE) to explore seasonal and long-term trends in movement. This showed that monthly CPUE generally followed current understandings of seasonal movement patterns. Long-term trends in catch distributions were compared to long-term environmental trends, which showed that catch distributions may follow long-term trends in SST, the SOI and the IPO. The study confirms evidence of environmental influences on population recruitment, which should ideally be accounted for within fisheries management decisions, especially with predicted ocean warming. It also shows the potential of catch data to verify current understandings of seasonal and long-term movement patterns by snapper, and that fisheries data may be used to inform the biology of an exploited species. The importance of future research will increase with a changing climate and future studies should utilise longer time-series of data as they become available.