Links between climate variation and the year class strength of New Zealand hoki (Macruronus novaezelandiae) Hector

Abstract

Hoki (Macruronus novaezelandiae) Hector year class strength (YCS) varies substantially from year to year. In this study, potential links between hoki YCS estimates for western and eastern stocks, and time series of the Southern Oscillation Index (SOI), satellite sea surface temperatures (SST), synoptic weather patterns, depth of the mixed layer (western stock only), and wind speeds are explored. The results indicate that favourable recruitment in the western stock is correlated with a negative SOI and associated conditions such as lower SSTs, early onset of deep water mixing and synoptic weather patterns that result in a higher incidence of southwest (SW) flow. Favourable recruitment in the eastern stock appears to be correlated with periods of westerly flow, particularly from the SW, but also the north‐west (NW). Regression studies showed that when inter‐correlation was minimised, 95% of the variation in YCS of the western stock was explained by four variables—SOI in autumn, the onset of winter mixing, SST in spring, and NW spring weather patterns. In the eastern stock, 88% of the variation in YCS was explained by SW and NW winter weather patterns and the average speed of SW winds in winter through Cook Strait. Although the underlying mechanisms are not proven, the climate variables which appear to be linked to favourable recruitment for both western and eastern stocks, also favour upwelling and the physical transportation of larval hoki from the spawning grounds into their respective inshore nursery areas.