The report presents a methodology that can be used to estimate the total finfish bycatch of the Area 48 krill fishery and quantify the impact of bycatch on the finfish stocks using data that is currently available, applied to data collected by Scientific Observers on the FV Saga Sea.
Estimates of bycatch rates per tonne of catch were made at a family level for Channichthyidae, Nototheniidae and Myctophidae species using delta-lognormal GLMs presented in Martin et al. (2012). The bycatch rates were applied to estimates of krill catch to estimate precautionary total bycatch numbers of each family for both low sea-ice and normal sea-ice years. Biological parameters for Champsocephalus gunnari and Notothenia rossii were used to convert total bycatch numbers to biomass at age of 50% maturity removed from stocks due to finfish bycatch at a family level, for Channichthyidae and Nototheniidae species respectively. Family specific biomass estimates at age of 50% maturity were then compared to available abundance estimates of Channichthyidae and Nototheniidae species at a family level, and at a species level for C. gunnari and N. rossii.
This methodology takes account of explanatory variables that are significantly associated with presence/absence of finfish bycatch in estimates of finfish bycatch rates in the Saga Sea krill fishery. The methodology can also provide quantitative analysis of the impact of the krill fishery on finfish species at a family level, as well as for individual species.