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.

Age and growth of Antimora rostrata (Moridae, Gadiformes, Teleostei) from the Kerguelen and Crozet Islands in the southern Indian Ocean

“…In the Southern Ocean, the number of males in the Lazarev and Weddell seas was higher than females at depths of 1100-1800 m (Vedishcheva et al, 2019). Furthermore, at depths of 800-2000 m in the Ross Sea, the percentage of females was up to 90% (Horn & Sutton, 2015), which is similar to our data (78% vs. 22%). In our opinion, the sex ratio of blue antimora in different areas is dependent not only on depth surveyed but also on type of fishing gear used.…”

“…The majority of authors who studied the age of blue antimora using otoliths (Fossen & Bergstad, 2006;Horn & Sutton, 2015;Orlov et al, 2018b;Vedishcheva et al, 2019) note the challenges associated with the difficulty in interpreting the otolith zones, which was quite evident in our studies. In this study, we consider all visible rings as annuli similar to other previous studies where age estimations were unvalidated.…”

“…Since the beginning of the 1980s, when determining the age of fish, a "break and burn" method of age determination on otoliths has been widely used, which has proved to be good for demersal (including deep-water) fish of the west coast of the USA and Canada (Beamish & McFarlane, 1987). Taking into account that blue antimora, like many deep-sea fish, is probably a long-lived species (Fossen & Bergstad, 2006;Horn & Sutton, 2015;Magnússon, 2001;Orlov et al, 2018b;Vedishcheva et al, 2019), age was determined in accordance with the methods developed specifically for some long-lived deep-sea fish (Beamish & Chilton, 1982).…”

“…Blue antimora is a bentho-pelagic deep-sea species that is capable of forming dense concentrations. It is caught as bycatch in bottom trawl and longline fisheries (Fossen & Bergstad, 2006;Horn & Sutton, 2015;Iwamoto, 1975;Kulka, Simpson, & Inkpen, 2003) and considered as a promising commercial target (Priede, 2017).…”

“…Published information about the life cycle of A. rostrata is limited and fragmentary (Collins, Priede, & Bagley, 1999;Gordon & Duncan, 1985;Iwamoto, 1975;Kulka et al, 2003;Novikov & Timokhin, 2009;Wenner & Musick, 1977). The age and growth of blue antimora have been studied in the waters of Iceland (Magnússon, 2001), the Ross Sea and New Zealand waters (Horn & Sutton, 2015) and the Lazarev and Weddell seas (Vedishcheva, Korostelev, Gordeev, & Orlov, 2019), as well as in several areas of the North Atlantic, including the waters of both coasts of Greenland and the Mid-Atlantic Ridge (Fossen & Bergstad, 2006;Orlov, Vedishcheva, Trofimova, & Orlova, 2018b). However, no age validations were provided in publications documenting those studies.…”