Seasonal distribution and abundance of the common carangid fishes found in Unguja island (Zanzibar) coastal waters, Tanzania

The study was carried out to investigate seasonal distribution and abundance variations, growth type and size structure of carangid fish species in Unguja Island coastal waters, Tanzania from April 2013 to March 2014. Sampling was done using catch assessment survey for adult and beach seining for juveniles. A total of 20 carangid species were identified, of which only 7 composed of sub-adult and adult fish and 4 of juveniles dominated. The most abundant species was Carangoides bajad with a composition of 31.2% with the highest peak in November, which coincides with North-East monsoon season and the least common species was Gnathanodon speciosus with 3.2% with highest peak in October. Juvenile Trachinotus blochii occurred year round and were found in sandy and sandy beach with some rockly outcrops whilst other carangid species were found seasonally in the sandy beaches and sandy-muddy habitats near the mangroves with peaks during the rainy seasons. The coefficient b of the length-weight relationships indicated negative allometric growth (b˂3) (p˂0.05) for juveniles, sub adults and adults of major species, except juvenile Caranx sexfasciatus which showed isometric growth (b=3). The overall sex ratios for seven major carangids were not significantly different from the expected value of 1:1 (p˃0.05). the length frequency distribution showed that six species were numerically dominated with fish sized ˂49 cm TL except C. sexfasciatus which is dominated with size ˃60 cm TL. These results will be convenient for fishery biologists and ecologists to recommend suitable guidelines for sustainable in the Zanzibar coastal waters, Tanzania and neighbouring countries.