Tuesday, November 29, 2011

More crab megalopae? Larger fisheries, but only when it rains.

Scientists have known that increases in numbers of juvenile blue crabs can lead to increases in adults and associated fishery harvests. It has been less clear whether the number of megalopae (postlarvae) returning to the coast each year regulates the number of juveniles and adults.

My latest paper, published recently in the journal Fisheries Oceanography, describes a pattern in which higher numbers of megalopae arriving at the coast in Beaufort, North Carolina result in higher fishery landings and a greater number of fishing trips in the Pamlico Sound 2 years later when those crabs have matured. This pattern was only true for years in which salinity was relatively low (rainy years) in Pamlico Sound. In dry years, when salinity was relatively high, an increase in the number of megalopae only resulted in small increases in the catch of crabs per fishing trip, but did not affect the total number of landings or fishing trips. During dry years, fishery landings appear to remain low regardless of the number of megalopae because fishing is never good enough for part-time fishers to put much effort into fishing.

It appears, then, that good and bad years for blue crab fishing in the Pamlico Sound are determined by the number of megalopae arriving at the coast, but fishing will only be very good if you have both high numbers of megalopae and low salinity (high rainfall).