Assessment of marine mega-fauna by-catch in the artisanal fishery along North coast Kenya

Abstract

The populations of long-lived marine mega-fauna including elasmobranchs, marine mammals and sea turtles is declining around the world because of their high vulnerability to fishing activities and mortality. Most mega-fauna have been reported as by-catch globally. However, specific information on the magnitude of by-catch is largely lacking in the artisanal, commercial and semi-industrial fisheries. Therefore, by-catch mitigation measures are non-existent in most of these fisheries. The aim of this study was to assess by-catch of elasmobranchs, marine mammals and sea turtles in artisanal bottom-set and drift gillnet fisheries along north-coast Kenya. The study was conducted during May through November 2016 in the small scale fisheries of Old Town and Nyali in Mombasa, Malindi beach and Ngomeni in Malindi and Kiwayuu and Kizingitini in Lamu. Data was collected using structured questionnaires and species guide books were used for identification of species. A total of 92 questionnaires were administered in Old town (n = 4), Nyali (n = 2), Malindi (n = 17), Ngomeni (n = 37), Kiwayuu (n = 20) and Kizingitini (n = 12) landing sites. By-catch incidences were calculated by dividing the number of individual species caught by the number of fishing vessels at the landing sites. Forty seven (47) by-catch species were identified including thirty five (35) species of elasmobranchs, seven (7) species of marine mammals and five (5) species of sea turtles. The most common and most frequently caught species of sea turtles were the green turtle Chelonia mydas (50%), hawksbill turtle Eretmochelys coriacea (18%), olive ridley turtle Lepidochlys o/ivacea (18%) and leatherback turtle Dermochelys imbricata (9%). Among marine mammals, the most common species were the Indian Ocean bottlenose dolphin Tursiops aduncus (42%), common bottlenose dolphin Tursiops truncatus (20%), Risso's dolphin Grampus griseus (13%) and Indo-pacific humpback dolphin Sousa chinensis (11%). Spotted eagle rays Aetobatus narinari (11.9%), honeycomb sting rays Himantura uarnak (10.7%) and cow-tail sting rays Pastinachus sephen (10.2%) were the most frequently caught ray species while hammerhead sharks Sphyrna spp (6.7%), whale sharks Rhincodon typus (5.4%) and black-tip reef sharks Carcharhinus me/anopterus (3.3%) comprised the bulk of the frequent by-catch of sharks. By-catch incidences (BI = 42) were significantly (df = 11; f = 3.21; p < 0.05) higher during north-east monsoon than during south-east monsoon (BI = 29). Drift gillnet fisheries reported higher by-catch incidences of sharks (BI = 4) and marine mammals (BI = 1) and are considered as the biggest threat to these marine mega-fauna along the Kenya coast. Therefore, there is a need to develop defined management strategies for the gillnet fisheries in order to mitigate the by-catch of these mega-fauna. There is also need to promote awareness among artisanal fishers on the importance of protecting these vulnerable marine mega-fauna. The study further suggests that rapid bycatch assessments need be extended to other artisanal fisheries including long-lines, bottom trawls, beach seines, cast nets and other types of nets which present potential threats to marine mega-fauna in Kenya.