Shortfin mako (Isurus oxyrinchus) COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

Mortality from fishing, both directed and incidental, is the principal threat facing shortfin makos. Their slow intrinsic growth rate and low fecundity mean that even low levels of additional mortality could lead to population decline. Internationally there has been insufficient monitoring effort resulting in severe limitations in the quantity and quality of the data used in stock assessments (ICCAT 2005a). The resulting inability to monitor trends in population increases the uncertainty surrounding shortfin mako status. Longline effort in the Atlantic has steadily increased beginning in 1955, indicating that the potential for fishing mortality on shortfin makos has also increased (Figure 12). Under present fishing practices (i.e., gear type, seasons), decreasing catch on this species is only possible by lowering fishing effort for targeted pelagic species (i.e., tunas, swordfish) worldwide. Other threats such as pollution or contamination have not been investigated, but given that shortfin mako feed at a high trophic level, pollution could have long-term health effects on the population.

Figure 12. Trend in effort for the North Atlantic longline fleet (1956-1997). Source: ICCAT 2005a.

Figure 12.  Trend in effort for the North Atlanticlongline fleet (1956-1997). Source: ICCAT 2005a.

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