Stock status indicators of mako sharks in the western North Atlantic Ocean based on the US pelagic longline logbook and observer programs

Two stock status indicators were examined for mako sharks (Isurus spp.) encountered by the US pelagic longline fleet. First, standardized indices of relative abundance were developed from data in the US pelagic longline logbook (1986-2015) and observer (1992-2015) programs. Indices were calculated using a two-step delta-lognormal approach that treats the proportion of positive sets and the CPUE of positive catches separately. Observations affected by fishing regulations (time-area closures or bait restrictions) were subsequently excluded in a restricted analysis. The logbook time series showed a concave shape from the beginning of the series in the mid-1980s to 2009-2010, followed by a downward trend thereafter. The observer time series also showed a concave shape from the beginning of the series in the early 1990s to 2011, followed by a declining trend thereafter. Overall, the logbook index did not show a substantial change in relative abundance since the late 1990s and the observer index showed a generally increasing tendency since the mid-1990s. No discernible trends in size were detected, suggesting that no specific segment of the population is being disproportionately affected.