Temporal variation of shark catches in the islands and central coast of Nayarit, Mexico, based on official landing statistics

Shark landings are not registered by species in Mexico, preventing their use for population assessments and fishery management. In the present studytemporal variations of landings in the islands and central region of Nayarit are determined based in the official records, analyzing their usefulness and deficiencies. Total monthly catches were estimated by adding the landings of all shark categories registered in the San Bias Fisheries Office during 1992-2010. The seasonality of official landings was compared with the relative abundance of the main shark species registered during field samplings carried out during 2007-2011. Shark landings are registered using several categories, related to the diversity of species, common names and variety of products, making difficut its analysis. No significant differences were found among monthly total catches (ANOVA(11, 224) F = 1.291, p > 0.05), but were found among the seasonal ones (ANOVA(3,224)F = 4.227, p < 0.01), being larger in winter than in spring and summer (monthly average catches per season = 19.24, 10.08 and 7.68t, respectively). Contrary to the national tendency, the total annual catch in the region showed a positive trend during the last two decades (T de Kendall = 0.699, S = 107, p < 0.0001), with a peak during 2009 (605 t). Enforcement of the existing Mexican laws is urgent to develop a specific landing system, allowing its future use for population assessments and effective management measures development.