Distribution, morphology and ecology of Macrourus whitsoni and M. caml (Gadiformes, Macrouridae) in the Ross Sea region
Samples collected in 2008 led to the identification of a new species of Southern Ocean grenadier, Macrourus caml, which had hitherto been identified as M. whitsoni. The first comparison of the distribution and ecology of the two species of Macrourus in the Ross Sea region is presented. The number of rays in the left pelvic fin and number of rows of teeth in the lower jaw allowed the two species to be distinguished both in the laboratory and by scientific observers at sea. The species were sympatric by depth (900–1 900 m) and by spatial area within CCAMLR Subareas 88.1 and 88.2. There was a small but significant increase in the proportion of M. whitsoni caught with depth. Catches of females of both species exceeded that of males (especially for M. caml). Macrourus caml grows slower, reaches a larger size, lives longer and is heavier for a given length than M. whitsoni. Female sexual maturity is reached at shorter length in M. caml than M. whitsoni but at a similar age (50% sexual maturity at 16 y). Gonad staging suggests extended spawning periods, beginning before December and continuing after February. Stomach and intestine contents data show both species are euryphagous predators and scavengers, with evidence of piscivory and both benthic and pelagic feeding. Amphipods were one of the main crustaceans consumed. Data tentatively suggest that M. caml may feed more benthically than M. whitsoni, but the sample size was very small. Using stable isotope analysis, trophic level was estimated at 4.4–4.5 (M. caml) and 4.1–4.3 (M. whitsoni), consistent with one or both of these species being a main prey of Antarctic toothfish.