Preliminary assessment of shark bycatch from Kenya’s nascent industrial tuna fisheries

The offshore tuna fisheries in Kenya are still nascent, with two longliners in operation from 2016 after a lull of about 6 years. These longliners are normally targeting tuna, swordfish, marlin and sharks. However, sharks are as well caught as by-catch, regardless of the target fishery. Major problems with compliance exist in this fishery, as the lack of constant deployment of scientific observers hinders adequate biological data collection.
In order to assess the shark bycatch in the tuna longline fisheries of Kenya, data provided by the skippers from the logbooks and recorded as catch from one longliner fishing vessel (FV. Shang Jyi) from the period of July 2017 to September 2017 was used.
Preliminary results indicate general substantial catches of sharks at 10.9%, with the hammerhead sharks (Sphyrna lewini) constituting 6.5%, blue sharks (P. glauca) 3.1%, and blacktip sharks (Carcharhinus melanopterus) at 1.2%. Hammerhead sharks were predominantly caught in the months of July, August and September, but none was caught in October and November. The Blue sharks were predominantly caught in November while the blacktips were mainly caught in October. This clearly points to a species-specific segregation which could have been due to seasonality and lunar periodicity effects, or differing fishing locations. However, more data is required for conclusive recommendations.