Investigating capture rates of Neritic tuna species in the tuna gillnet fisheries of Pakistan; results from four tuna gillnet vessels

Neritic tuna are extremely important resource for Pakistan, although poorly managed, remains a source of animal protein sustaining livelihoods of fishers. Among neritic tuna, long tail, kawakawa, frigate, bullet and striped bonitos are caught in tuna gillnet fisheries. Here we investigate the capture rates of the neritic tuna in four gillnet vessels and provide a snapshot on how different gear setting impact catch composition of neritic tuna. The different gear settings have proven to be a useful measure without compromising capture rates of tropical tuna species, in addition to reduced bycatch. However, the impact of different gear setting on neritic tuna species has not been determined. This paper therefore, aims to assess capture rates and discusses the catch composition variance by area of fishing and method using the data collected by four trained skippers (on 15-20 m vessels) during January 2013 – December 2017. During this period, a total of 3,430 sets were observed, using two different gear settings viz., surface and sub-surface (2 m below surface) multifilament gillnets. A total of 193,309 neritic tuna were captured equaling to 300,266 Kg representing Long tail (Thunnus tonggol), Kawakawa (Euthynnus affinis), Bullet tuna (Auxis rochei), and Frigate tuna (Auxis thazard thazard). The dominant catch based on data collected from four observer vessels belonged to Long tail tuna 52,353 (181,580 Kg), followed by Kawakawa 33,564 (75,035 Kg), Frigate tuna 93,454 (38,273 Kg) and Bullet tuna 13,938 (5,377 Kg). Capture rates were calculated for all neritic tuna species caught for both gear settings. Narrow-barred Spanish mackerel (Scomberomorus commerson) catch data was also recorded for the same period.

The results from the study suggest no significant impact on target catch, however, holds promising results as the different gear settings result in positive impact on incidentally caught species. We are encouraged by the results of the study and recommend coupling of technologies such as the use of electronic monitoring systems for triangulating observer data and expanding studies elsewhere, in addition to also studying the gear behavior. Sub-surface gear settings in tuna directed gillnet fisheries provide trade-off among target and non-target catch and may be considered as a potential conservation and management measure in gillnet fisheries.