Standardized catch rates of shortfin mako sharks caught by the Brazilian tuna longline fleet (1978-2016) using generalized linear mixed models (GLMM)

Catch and effort data from the Brazilian tuna longline fleet (national and chartered) in the equatorial and southwestern Atlantic Ocean from 1978 to 2016, including more than 90,000 sets, were analyzed. The CPUE of Shortfin Mako was standardized by a Generalized Linear Mixed Models (GLMM) using a Delta Lognormal approach. The factors initially considered in the models were: quarter, year, area, length of boats, hook per basket, sea surface temperature, bathymetry and fishing strategy. The final model, however, included only quarter, year, area, and fishing strategy. The standardized CPUE series shows an oscillation over time, but with a relative stability, with a few peaks (1993, 2009) and drops (2006). Except for these extreme values, however, the scaled index has fluctuated from 0.5 to 1.5 throughout almost the entire period. In the most recent years, the standardized CPUE has been unusually stable, around 1.5 (1.4 to 1.6), with a drop, however, in 2016, back to a value a bit lower than 1 (0.85).