Analysis of variables influencing finfish by-catch in the krill fishery in Area 48

This report presents the results of a method used to explore potential explanatory variables influencing finfish bycatch in the krill fishery of Area 48. Records of finfish bycatch in the Area 48 krill fishery collected by observers on the FV Saga Sea were analysed over the period 2007/08-2011/12. The majority of fish caught were either small juveniles or larvae, dominated by Myctophidae (lanternfish) and Channichthyidae (icefish) with lower levels of Nototheniidae present. The influence of potential explanatory variables was investigated using a delta-lognormal modelling approach. Time of day, krill catch, sea surface temperature, bottom depth and fishing depth and season were all significantly associated with the presence of finfish bycatch in the Saga Sea krill fishery for at least one family and Subarea specific model, however, the majority of variables were not significantly correlated with the abundance of finfish bycatch. This may be partly due to the low numbers of hauls with positive incidences of bycatch of the finfish family groupings. Results indicated that there was a wide disparity in the influence of the explanatory variables on the presence of finfish in bycatch, which varies markedly by taxonomic grouping to the family level and CCAMLR Subarea. There were, however, some trends which persisted across Subareas and families, the most notable observed trend being the reduced likelihood of catching all families of finfish investigated in dense krill aggregations, which is consistent with the literature. These predictive models were used to estimate bycatch rates per tonne of krill catch for Channichthyidae, Nototheniidae and Myctophidae to predict total finfish bycatch of the Area 48 Saga Sea krill fishery and quantify the impact of this bycatch on the finfish stocks (Peatman et al., 2012).