Characterisation of skate catches in the Ross Sea region

The toothfish fishery in the Ross Sea region (CCAMLR Subareas 881 and 882) has been operating since the 1996–97 fishing season. The fishery has increased to an annual Antarctic toothfish (Dissostichus mawsoni) catch of about 3000 t. Skates form a small proportion of the total catch (typically 2% or less). In this paper we summarise the current available fisheries and biological information for skates in the Ross Sea Region, including the data collected in the two “Year of the Skate” fishing seasons in 2008/09 and 2009/10. The composition of the skate catch by species is uncertain; it is estimated that about 33 000 starry skates were landed, and 55 000 released in the Ross Sea region by all vessels to the end of the 2009–10 fishing season, and about 4300 Eaton cf. skates were landed and 4600 released in the same region over the same period of time. There were also differences in the distribution of the two species, starry skates generally being found deeper and more to the west than Eaton cf. skates in the Ross Sea region. Scaled length frequencies showed no change in distribution between 2003 and 2008 for landed starry skates, whilst tagged starry skates had a lower proportion of large individuals than landed starry skates. Eaton cf. skates had a different length frequency, with a narrower distribution centred around a larger average size than starry skates. This larger distribution is consistent with other studies suggesting Eaton cf. skates might grow to larger sizes than starry skates. During the “Years of the Skate”, a total of about 3300 starry skates and 700 Eaton cf. skates were tagged and 13 starry skates and 3 Eaton cf. skates were recaptured and successfully linked to a tag event. In total there have now been a total of 179 tags recaptured but only 128 have been successfully linked. There was no evidence of growth retardation linked with the capture and tagging event. Tag loss rates of T-bar tags were similar to those calculated for toothfish. The “Years of the Skate” have been instrumental in collecting further data on skates, in particular length and tagging data. The quality of the tagging database has also improved since it has been centrally managed by CCAMLR. It has shown the value of collecting large amounts of data in specific years rather than small amounts of data in many years. An updated risk assessment of the skate population in the Ross Sea region should be carried out.