Long-term impact of incidental catches by tuna longlines: the black escolar (Lepidocybium flavobrunneum) of the southwestern Atlantic Ocean

We analyze intra and inter-annual harvesting patterns of the black escolar Lepidocybium flavobrunneum (Gempylidae), an important component of the incidental catch of the Uruguayan tuna fleet (UTF) at the southwestern Atlantic Ocean (SAO), based on daily information of catch, fishing effort and individual weight of all the specimens caught during 16 years (1981–1996). The analysis also compares the activities of two fishing fleets that operated in two different periods of fishery development: category A, which comprises Japanese vessels that operated between 1981 and 1991, and category B, consisting of American and Spanish vessels that operated between 1992 and 1996. The relative representation of the total incidental catch significantly increased during the 16-year period of activity of the UTF, reaching 43% of the total catch in 1995. A recurrent seasonal pattern in fishing effort, catch and catch per unit of effort (CPUE) was observed, peaking in austral winter and spring. The daily number of hooks and total catch were significantly higher for category A, which exerted 2.7 times higher number of hooks and obtained catches 3.33 times higher than category B. Differing with the above trends, mean daily CPUE of a category B vessel was 16% higher than category A, which can be attributed to the increase of fishing power. The mean individual weight decreased almost 40% in 15 years, i.e., from 23.2 kg in 1982 to 14.1 kg in 1996, suggesting overexploitation risks of this incidental species. The effect of increasing fishing power and the effectiveness of management measures for large pelagics at the SAO are discussed. [Copyright &y& Elsevier]