Feeding and Food Consumption by the Barents Sea Skates

Stomach content data were used to study spatial, seasonal and interannual dynamics of feeding of the thorny skate Raja radiata. Data on food composition for other Barents Sea skates ( Northern skate – R. hyperborea, Round skate – R. fyllae, Blue skate – R. batis, Spinytail skateR. spinicauda, Long-nosed skate – R. oxyrhynchus and Sail ray R. lintea) are presented. The diet of thorny skate of different age is analysed. Food consumption by thorny skate is assessed with a special focus on the consumption of commercial species. Introduction The Barents Sea is inhabited by seven skate species (Dolgov, 2000). However, the biology and feeding of most of them still remain largely unknown. Except for a few papers on feeding of thorny and round skates (Zenkevich and Brotskaya, 1931; Antipova and Nikiforova, 1983; Berestovsky, 1989; Dolgov, 1997), data on feeding of other skates are virtually unavailable. This paper summarizes data on feeding of the six Barents Sea skate species registered in catches in the recent decade in order to specify their diet and estimate the effects of their predation on commercial stocks. Materials and Methods The number, length and weight of each prey species occurring in skate stomachs were identified and the biological parameters of predator (length, weight, sex, stomach fullness) were defined. Prey species were classified to the smallest identifiable taxon. A total of 2 192 stomachs of thorny skate, 85 of round skate, 48 of northern skate, 39 of blue skate, 14 of spinytail skate and 5 of sail ray were examined. Percentage by weight (m) (% of the food bolus) and frequency of occurrence (f) (% of feeding fish) were used as feeding indices. Food consumption in the entire Barents Sea was calculated by quarter and by 5 cm age groups. Daily ration of all age groups in all quarters was taken as 0.80% of the body weight (Berestovsky, 1989). The abundance of length groups was calculated as mean abundance of this group based on the trawl survey data for 1994-2001 and was assumed to be the same over the year (Dolgov, 1997; Dolgov et al., 2002). Approximate consumption by other skates was calculated using averaged data on food composition and total stock biomass (Dolgov et al., 2000). Mean daily ration was taken as 1% of the body weight.