Links between climate variation and year class strength of New Zealand hoki(Macruronus novaezelandiae): An update

Abstract

Hoki (Macruronus novaezelandiae Hector) year class strength (YCS) varies substantially from year to year. We examined associations between YCS and climate variables including the Southern Oscillation Index (SOI), satellite sea surface temperatures (SSTs), synoptic weather patterns, wind speeds, and the depth of the west coast, South Island, New Zealand, mixed layer. We evaluated the predictions of a model developed 2 years ago to predict YCS of the western and eastern New Zealand hoki stocks from similar climate variables. New predictive models were developed using updated data. Strong year classes of the western hoki stock were associated with cooler SSTs, a negative SOI, and westerly or south-westerly flow along the west coast of the South Island. We accordingly predict a moderately strong 1997 year class and weak 1998 and 1999 year classes for the western stock of hoki. The current model cannot predict eastern stock year class strengths with confidence.

Decadal temperature changes in the Tasman Sea

“…There is the suggestion that the warm conditions could have played a role in poor recruitment in the Hoki fishery through the late 1990s. The survival rate of Hoki larvae is dependent on food supply through their early development, and this food is dependent on the evolution of the mixed layer through early winter (Bull & Livingstone 2001; J. Grieve pers.…”

Links between climate and recruitment of New Zealand hoki(Macruronus novaezelandiae)now unclear

“…The YCSs were not corrected for spawner abundance because, for the data available, there is no clear relationship between YCS and spawner abundance (Francis 2006a). These YCSs were broadly similar to those used by Bull & Livingston (2001) but there were some marked differences. The previous eastern YCSs showed wider variation than the present ones and, for the western YCSs, the previous values were lower in early years, and higher in later years, than the present ones (Fig.…”

“…Bull & Livingston (2001) (1980. A wider range of YCS estimates was available for the present study but the first three and last two years were not used because the associated estimates were too imprecise (Fig.…”

“…Once such correlations have been established they can both increase the accuracy of estimates of recruitment for year classes that have already entered the fishery, and allow prediction for those that will recruit in the near future. In New Zealand, potentially useful climate-recruitment relationships have been found for snapper Pagrus auratus (Block &Schneider, 1801) (Francis et al 1997), rock lobster Jasus edwardsii (Hutton, 1875) (Booth et al 2000), gemfish Rexea solandri (Cuvier, 1832) (Renwick et al 1998), and hoki Macruronus novaezelandiae (Hector, 1871) (Bull & Livingston 2001).…”

“…Separate fisheries occur in each of these four areas. Bull & Livingston (2001) analysed climaterecruitment relationships for hoki and found a strong link for the western stock, but none for the eastern stock. In this paper we update these analyses and extend them in several ways.…”