Occurrence and vulnerability of a giant sea catfish, Arius thalassinus (Rüppell, 1837) (Siluriformes: Ariidae) in Mafia Island, Tanzania

Abstract

The distribution and some biological characteristics of commercially important giant sea catfish, Arius thalassinus (Rüppell, 1837) were studied in Mafia Island from October 2010 to October 2011. Samples were collected from artisanal fishing gear, mainly longlines, sharknets and ringnets, which yielded a total of 2,723 kg comprising 756 A. thalassinus individuals with the largest specimen measuring 1,000 mm TL. The species occurred only on the western coast of Mafia Island with the highest catch rate of 19.3 kg/fisher/day in March when murky water predominates. The reproductive biology of A. thalassinus was investigated to infer its vulnerability to fishing. A. thalassinus reached size-at-first maturity at (L_M50 = 520 mm TL) and exhibited lower mean (± s.e.) batch fecundity of 65.6 ± 3.37 eggs per female of size range 605 – 970 mm TL comprising large-sized hydrated oocytes with mean (± s.e.) diameter of 15.2 ± 0.12 mm. A. thalassinus spawned once in a year during February and April under heavy precipitation conditions (124 - 499 mm). We therefore conclude that restricted distribution, large-bodied size, lower fecundity, late maturation, and reported high trophic level signify that A. thalassinus is potentially vulnerable to fishing pressure. It is therefore recommended to restrict fishing A. thalassinus during spawning season for its sustainability.