To progress development of a semi-quantitative and spatially explicit risk assessment for skates in the Ross Sea region, we summarise skate catch and mark-recapture data through the 2016/17 fishing season, noting that on average 89% of skates by weight are released alive (45 of 51 t annually).
Catch data show that most of the skate catch consists of Amblyraja georgiana and that this species is the only one with enough mark-recapture data to examine movement patterns and estimate local biomass. Much of the A. georgiana catch occurs in SSRUs 88.1H and 88.1I in an area remaining open to fishing with respect to the Ross Sea region Marine Protected Area.
For consistency in comparisons, we use S-series t-bar tags released on skates and recaptured as part of the “Year of the Skate” experiment in the 2009 and 2010 fishing seasons to estimate local Chapman biomass using CCAMLR procedures for the 2010–2016 seasons (excluding 2012).
We estimated that the exploitation rate of the current catch of skates (the sum of the retained catch of skates and the catch of released skates with zero survival assumed), would be about 0.6% of the Chapman estimate of biomass estimated from the tag release and recapture data. This is less than half of the gamma for this species, which we estimated to be between 1.6 and 2.8%.
However, there is still uncertainty in the impact of exploitation on skates, and hence we recommend that a 2-year skate tagging programme in the Ross Sea region be used to provide additional biomass estimates in coming seasons. This tagging programme could use the regulatory approach adopted in 2009 and 2010 with simple additions to CMs 41-01 Annex C and CM 41-09. Furthermore, we provide an experimental design and background information to allow progress in developing validated ages for A. georgiana and for examining the effect of injuries on mortality rates of released skates.