Conservation and management of the western North Atlantic shark resource based on the life history strategy limitations of sandbar sharks.

摘要

The life history strategy of sharks is very different from most boney fishes and appears to fall in the realm of "K selected species" of classic r/K selection theory. The intrinsic rate of increase (r) for sandbar sharks was estimated from a life history model, in order to define recruitment overfishing. The age-structured population model incorporated age dependent rates of fecundity, maturity and mortality. The model identifies critical life history parameters necessary for an assessment of the effects of fishing. It is believed the existence of the shark fishery and the fleet that depends upon it is threatened by current fishing levels.;Sharks are unique among marine fishes. The life history is characterized by slow growth, delayed maturation, long reproductive cycles and small broods. Compensatory mechanisms have been inferred to be relatively weak and the stock recruitment relationship is strong which explains their low resilience to and long recovery from fishing pressure. Most sharks are predators at the top of the food chain, and so they, in turn, have few predators--except man.;Reported commercial landings grew eight fold in the past five years. On average, for the past 10 years, mortality of sharks exceeded the maximum sustainable yield estimate by 40%.;Incorporating the best potential biological estimates yields an r of 10%. Thus, fishing mortality of around five percent could be sustainable. Yield from a fishery is directly related to the r and the effort applied, thus a low r value has significant effect on the sustainable effort level. Modeling costs, revenues and profits illustrates that the open access fishery will be inefficient, with too much effort, low yield, low biomass and dissipation of all profits. If economic gains are to be obtained and maintained, effort limitation is required.;Management measures, which would allow continuance of a shark fishery, could include: annual quotas with reporting requirements and future property right assignments, recreational bag limits and encouragement of tag and release, finning prohibition, nursery closures, gill net prohibition, expansion of domestic observer program, and encouragement of selective harvesting of males. The life history strategy of sharks dictates a conservative management philosophy.