An assessment of age and growth of violet cod (Antimora rostrata) in the Ross Sea, Antarctica

Abstract

Violet cod (Antimora rostrata) are a bycatch of the longline fishery for toothfish (Dissostichus mawsoni and D. eleginoides) in the Ross Sea, Antarctica. The productivity of this species in Antarctica was unknown, so counts of zones visible in sectioned otoliths of A. rostrata were used to estimate growth parameters. Von Bertalanffy parameters (with 95 % confidence intervals) derived for male and female fish combined are L ∞, 82.2 ± 20.9 cm total length; K, 0.047 ± 0.034 year−1; and t 0, −0.6 ± 6.0 years. Violet cod in the Ross Sea appear to have low productivity; they are slow-growing and relatively long-lived, with a maximum estimated age of 41.5 years. There was no apparent difference between sexes in length at age, although males are poorly represented in the longline catch. The growth rate of violet cod in Antarctic waters appeared to be faster than for the same species around New Zealand, about 20° of latitude to the north. The growth parameters must be considered preliminary because the otoliths are quite difficult to interpret, the sampled fish do not represent the full-length distribution of the population (i.e. small fish were absent), and the ageing technique has not been validated.