On the problem of by-catch of juvenile fish in krill fishery

Studies of by-catch of juvenile fish in krill catches by research vessels were conducted during 1985-1988 in the Kosmonavtov and Sodruzhestva seas (Antarctic Indian Ocean sector). Isaacs-Kidd trawl with an opening area of 6.0 m2 was used. Trawls were taken in the 0-200 m surface layer over the bottom depth range from 100 to 5000 m. In 1988, studies included catches taken by a commercial krill trawl with an opening area in a small meshed section of the trawl beg of 100 m2. Catches were mainly taken over depth ranges from 300 to 500 m and from 2 500 to 4 200 m. Most frequently observed species of fish in krill catches were Pleuragramma antarcticum, Electrona antarctica and Trematomus eulepidotus. Other species were observed in catches only occasionally and in small numbers. By-catch of juvenile fish was highest in Prydz Bay and Fram Bank areas. By-catch of juvenile fish in Isaacs-Kidd trawl was usually less than 50 fish per 30 min trawling. By-catch in commercial trawls was from 114 to 1 x 106 fish per tonne of krill caught. Small by-catch of fish was usually observed when krill catches were higher than 2 tonnes (2-12 tonnes) and over the bottom depth less than 1 000 m. Maximum by-catch (up to 1 x 106 fish per tonne of krill) was observed when krill catches were less than 2 tonnes and over the bottom depth from 1 500 to 4 500 m. It was found that areas of maximum concentrations of juvenile fish and krill did not overlap. Therefore, high fish by-catch corresponds to low krill catch and vice versa. It was concluded that krill fishery should be best conducted over the bottom depth more than 1 200 m and on high-density krill concentrations. It was also suggested that in order do avoid large by-catch of juvenile fish, krill fishing should not be conducted in shallow waters over the continental slope