Spatial and temporal changes in the fish communities from a mangrove-dominated creek system near Karachi, Pakistan

Abstract

Summary The objectives of the study were to inventory the fish community, examine how the fish communities changed in these creeks temporally (season), and compare the fish communities between creeks of varying structure (width). During February 1999 to December 2001, a survey was undertaken to monitor the distribution and abundance of fishes in the Korangi-Phitti Creek (KPC) system (24°45′N, 67°20′E) near Karachi, Pakistan. Fish were collected from 123 stations using a combination of monofilament gillnets of 8.9 cm, 5.7 cm, and 3.8 cm stretched mesh sizes. A total of 17 023 fish representing 86 species were collected during the study; Sardinella gibbosa and Nematalosa nasus were the most abundant taxa (in terms of numbers of individuals) collected, accounting for over 60% of the total catch. Physical conditions in the study area were found to have significant seasonal (monsoon) patterns related more to temperature and salinity than to rainfall. Seasonal comparisons indicated that the communities were significantly different between the northeast monsoon (NEM) and southwest monsoon (SWM) seasons. Taxa primarily responsible for distinguishing the NEM were the mullets (Moolgarda cunnesius, Liza carinata, Mugil cephalus). The SWM was characterized by Anodontostoma chacunda, Scomberoides commersonnianus, and the engraulid (Thryssa hamiltonii). The community sampled in wide creeks (shipping channels) was very different in composition than the community in small creeks within this system. Wide creeks were characterized by schooling pelagic species (S. gibbosa, N. nasus), while the smaller creeks were characterized by the presence of mullets (M. cunnesius, M. cephalus, L. carinata) and scat (Scatophagus argus). The KPC system was shown to contain a highly diverse fishery, which in turn contributes to regional offshore fisheries (shad, mackerel, tuna and perches). The various negative natural and anthropogenic events in this region highlight the need for information regarding the fish community, water quality, and the mangrove forest to evaluate ecosystem changes, the effects of disturbances, and for the development and making of sound management decisions.