An overview of the bycatch landed by local and foreign tuna longliners in Mauritius for the period 2009 to 2012

This paper presents by-catch estimates landed by national and foreign longliners fishing inside and outside the EEZ of Mauritius for the period 2009 to 2012. Some 100 licences are issued annually to foreign longliners to fish in the Exclusive economic zone (EEZ) of Mauritius. The average annual landing from these vessels during the period under report amounted to 3 102 tonnes of albacore tuna which is the targeted species followed by 796 tonnes of yellowfin tuna (Thunnus albacares), 360 tonnes of big-eye tuna (Thunnus obesus) and 1106 tons of by-catch comprising billfish, other tuna-like species and sharks. A total of 21 196 tonnes of tuna and tuna-like species was transhipped in Port-Louis by non-licensed fishing vessels targeting albacore (Thunnus alalunga), from 2008 to 2012. The proportion of by-catch landed during this period varied between 28.9% and 39.4%. The total catch landed by non-licensed longliners targeting big-eye tuna has increased over the years from 3495 tonnes in 2008 to 8125 tonnes in 2012. The proportion of by-catch in the total catch seems to be the same (33.1%-47.0%) as compared to the level of by-catch of albacore-targeting fishing vessels (37.9%-39.4 %). The proportion of by-catch landed by longliners targeting swordfish (Xiphias gladius) varied between 37.2% to 49.6%. A comparison of shark landings by tuna longliners and swordfish-targeting longliners was carried out: the levels of sharks in the total catch of longliners targeting big-eye tuna are higher (7.9%-20.2%) than those targeting albacore (3.6%-8.03%). However, the catch of sharks was very significant in swordfish-targeting vessels varying between 24.3%-39.1% of the total catch in comparison to albacore-targeting fleets and big-eye targeting fleet. Sharks landed by swordfish-targeting vessels consisted mainly of blue shark (Prionace glauca) (74.2-84.2%) followed by moro (Isurus oxyrhinchus) (7.1-20.0%) and mako shark (Isurus paucus) (4.6-9.2%). Moreover, Mauritius has a small number of national boats targeting swordfish that operate in its EEZ. These boats also land a considerable amount of non-targeted tuna and tuna-like species including sharks. The by-catch levels for national boats targeting swordfish was higher (50.8%- 52.7% of the total catch) as compared to the FAD fishery whose by-catch varied between 27.9%- 42.9%.