Shortfin Mako in the north and the south Atlantic constitute genetically distinct groups (Heist et al. 1996). Casey and Kohler (1992) hypothesized from tag-recapture data that western north Atlantic makos form a separate population from those in the eastern Atlantic although limited intermixing is possible as shown by crossings to the Azores and Europe. Mitochondrial DNA data indicate separation of female makos between the western and eastern north Atlantic, but a lack of differentiation in nuclear DNA suggests male mixing across the North Atlantic (Heist et al. 1996, Schrey and Heist 2003). For fishery assessment purposes, mixing between the western and eastern north Atlantic is considered minimal.

Mature males were occasionally caught in the western English Channel in the 1960s and 1970s but are now rarely encountered (J.D. Stevens, pers. comm.), suggesting possible range contraction in the north-east Atlantic.

Analyses of CPUE from US pelagic longline fishery logbooks reported that Isurus species may have declined by about 40% in the northwest Atlantic between 1986 and 2000 (Baum et al. 2003). A more recent assessment of observer data for the same fishery found a similar instantaneous rate of decline of 38% between 1992 and 2005 (Baum et al. in prep). A similar analysis of the same dataset and species grouping that restricted the areas of analysis to account for unbalanced observations, resulted in an overall decline of 48% from beginning to end of the time series (1992-2005; Cortes et al. in press). A 2004 ICCAT stock assessment workshop reported that stock depletions for North Atlantic shortfin mako are likely to have occurred based on CPUE declines of 50% or more. Demographic model results varied widely, with one approach suggesting present stock size is about 80% of virgin level, and another approach suggesting reductions to about 30% of virgin biomass (1950s) (Cortes et al. in press).

In the south Atlantic, the magnitude of decline appears to be smaller than in the North Atlantic and the stock size appears to lie above MSY, although only one modeling approach could be applied to the available data and assessments results were more uncertain than for the North Atlantic.

For both north and south Atlantic populations, uncertainties about demographic parameters and catches, and the uninformative nature of available catch data indicate that further analysis is necessary to properly delineate stock status. If historical Shortfin Mako catch is higher than the estimates in this report, the likelihood of the stock being below the biomass at MSY will surely increase (ICCAT 2005). A standardized catch rate index from the commercial large pelagic fishery off Canada suggested a decline in the 1970s and stable abundance since 1988 (Campana et al. 2005). However, the analysis did not have the statistical power to detect anything less than a severe decline and these sharks represent the margins of the population. The most heavily fished areas lie outside of Canadian waters. The median size of mako sharks in the commercial catch has declined since 1988, possibly indicating a loss of larger sharks (Campana et al. 2005).

Off Brazil, the highest and lowest catches of Shortfin Mako from Santos longliners were 235 and 29 t from 1971–2001. The CPUE and average weight decreased from 4.5 to 4.1 kg/1,000 hooks and 60 to 37.3 kg respectively (Amorim et al. 2002). About 20 t/yr were caught by gillnetters in southern Brazil between 1993–94 (Jorge Kotas, pers comm, CEPSUL-IBAMA, Brazil). The unstandardised CPUE in the Uruguayan longline fleet was low and stable (average 35 kg/1000 hooks) from 1983 to 1998 and has increased steadily to 2004 (185 kg/1,000 hooks), lower in 2005 (90 kg/1,000 hooks) (ICCAT data). According to Mourato et al. (in press), based on the landings records and logbooks from the Sao Paulo fleet operating off Southern Brazil, the standardized CPUE for the period 1971–2006 was fluctuating but showed a slight decline. In contrast, the standardization of the CPUE of 29 years in the Brazilian tuna longline fleet showed a slight upward trend (Hazin et al. in press). In Uruguay, the total captures oscillated through the years, mainly in low values (8 to 21 tons per year), and reached maximum values in 2003–2005 (up to 200 tons per year) (Domingo 2002, Domingo et al. 2008). The standardization of the mako shark CPUE in the Uruguayan pelagic longline fleet for the period 1981-2006 show a slight increase between 1989 and 2003, and a decreasing trend towards 2006 (Pons and Domingo in press).

Shortfin Mako contribute some 9.5% to 10% of the pelagic sharks caught by Spanish longline fleets (targeting sharks and swordfish) in the Atlantic and Pacific Oceans (Mejuto et al. 2002, 2005, 2006, 2007).

Decreasing