Relating the distribution of a semi-demersal fish, Macruronus novaezelandiae, to their pelagic food supply

The Chatham Rise to the east of New Zealand underlies the Subtropical Front and is an important region for deepwater fisheries, as well as being a nursery region for hoki, Macruronus novaezelandiae, the species that supports New Zealand's largest fishery. The spatial distribution and abundance of mesopelagic fish, which are a major food resource for hoki, are influenced by the location of banks on the western and eastern Chatham Rise. Analysis of three austral summer fisheries surveys allowed us to relate the spatial distribution of mesopelagic fish to the distribution and condition of hoki. The highest biomass of mesopelagic fish on the Chatham Rise was associated with the banks at its western and eastern ends. The intensity of the hotspots was strongest in 2002-03 and weakest in 2001-02. Concentrations of hoki occurred on the western banks in 2001-02 and 2002-03, but the western intensification was strongest in 2002-03, as was the case for mesopelagic fish. There were significant regional differences in the length-weight relations for hoki across the Chatham Rise and year 3++ hoki (>65cm) were ≈3-5% heavier for a given length on the western Chatham Rise. The catch rate of hoki was correlated with the abundance of vertically migrating mesopelagic fish, especially on the western Chatham Rise. We infer that the greater weight at length of year 3++ hoki on the western Chatham Rise was due to the greater abundance of the mesopelagic fish that they prey upon.