Standardized catch rates of shortfin mako caught by the Brazilian fleet (1978-2012) using a Generalized Linear Mixed Model (GLMM), with a Delta Log Approach

In the present paper, catch and effort data from 91,831 sets done by the Brazilian tuna longline fleet, including both national and chartered vessels, in the equatorial and southwestern Atlantic Ocean, from 1978 to 2012, were analyzed. The fished area was distributed along a wide area of the equatorial and South Atlantic Ocean, ranging from 3ºW to 52oW of longitude, and from 011ºN to 40ºS of latitude. The CPUE of the shortfin mako shark was standardized by a Generalized Linear Mixed Model (GLMM) using a Delta Lognormal approach. The factors used in the model were: year, fishing strategy, quarter, area, sea surface temperature, and the interactions year:area and year:quarter. The standardized CPUE series of the shortfin mako showed a gradual increasing trend, particularly after the year 2000 (Table 4 and Figure 7). The reason for such a trend is not clear and could result from a number of factors, including: an actual increase in abundance, an increase in catchability, a change in the fishing strategy or an improvement in data reporting.