Research Document - 2006/091

Assessment of the Recovery Potential of Shortfin Mako Sharks in Atlantic Canada

By Campana, S., J. Brazner and L. Marks

Abstract

International indices indicate that shortfin mako (Isurus oxyrinchus) population abundance in the North Atlantic has declined since the 1970s, but has been relatively stable since the late 1980s. Catch rate statistics from the Canadian pelagic longline fleet also indicated relatively stable bycatch rates since the late 1980s, but analysis of median size trends suggests there has been a decline in the abundance of larger shortfin makos in the Canadian fishery since 1998. Reference points to characterize recovery have not been developed for shortfin mako, but one half the virgin spawning stock biomass (SSB₀) is proposed as a potential target. Canadian catch accounts for only a small percentage (at most 2-3%) of the North Atlantic catch, indicating that bycatch by foreign fleets in the North Atlantic is the most significant source of mortality for the population. Thus, international efforts will be needed to reduce cumulative impacts and promote recovery. Live release of makos and a maximum annual catch limit of 100t are precautionary measures that could be used to reduce mortality. Uncertainty around estimates of the current population size and trajectory is the main reason that population abundance relative to the recovery target is poorly estimated. Monitoring shortfin mako population status in Canadian waters through a fishery-independent shark survey is recommended as a means for obtaining more accurate population estimates.

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