Abstract
The fishery, biology, growth and stock structure of Euthynnus affinis is studied in detail. Hooks and lines, gillnets and purse seines are the major equipment used to exploit the fish. Fisheries are sustained mainly by 1-2 year old fishes (34-50 cm). Spawning was observed around the year with peaks during July-August and November-January. The length-weight relationship is 0.0254 L2.889 with no significant difference between males and females. Age and growth are estimated using length based methods. The maximum sustainable yield estimated was higher than the average annual catch, indicating scope for further exploitation. Elevated levels of heavy metals in Euthynnus affinis may be a good indication of pollution of an aquatic ecosystem due to anthropogenic influences. A total of 278 fishes were collected from Karachi coast, Fish Harbor West Wharf, Karachi, for metal (Cd, Pb, Zn and Cu) analysis in the organs of the fish. The metal levels in the sample fishes are in descending order of toxicity Cd>Pb>Zn>Cu. In the risk assessment, we assessed potential human health risks associated with consumption of fish, incorporating information gathered during a year-long, intercept-style creel angler survey and representative heavy metal concentrations in fish tissue. Fishing operations can cause ecological impacts of different types, e.g. by the catches, damage of the habitat, mortalities caused by lost or discarded gear, pollution, and generation of marine debris. Periodic reassessment of the tuna potential is required, with adequate inputs from exploratory surveys as well as commercial landings; this may prevent any unsustainable trends in the development of the tuna fishing industry in the Arabian Sea.