Distribution, abundance and biological interactions of the cutlassfish Trichiurus lepturus in the southern Brazil subtropical convergence ecosystem

The distribution, abundance and biological interactions of the cutlassfish Trichiurus lepturus in the southern Brazil subtropical convergence ecosystem were studied from demersal trawl surveys conducted along the continental shelf and upper slope from Cape Santa Marta Grande (28 °36′S) to Chui (34 °45′S) between 1981 and 1987. Trichiurus lepturus was more abundant at bottom water temperatures of over 16 °C and in the 40–120 m depth range. From late spring to fall, juveniles of 5–30 cm total length (TL) were found in coastal waters, subadults (TL 30–70 cm) mainly in inner shelf waters and adults (TL > 70 cm) in coastal, inner and outer shelf waters. Higher catches of subadults and adults were found associated with thermal fronts in the western boundary of the Subtropical Convergence or with a shelf break upwelling observed in summer. The standing stock in a 58 000 km² shelf area estimated by the swept area method, ranged from 3066 t (±46% CI) in September 1981 to 37814 t (±22% CI) in January 1982. Correlation between occurrences of different size groups of cutlassfishes and other fishes caught in 250 bottom trawl hauls was analyzed. A positive correlation between cutlassfish and juvenile weakfish, Cynoscion guatucupa, was associated with similar spatial distribution but also indicated trophic competition.