Life-history Characteristics of Crangon septemspinosa and Management Implications

Sand shrimp is a widely distributed species in the western North Atlantic Ocean, with a range spanning from Florida to the Gulf of St. Lawrence. Studies of food webs, predator/prey dynamics, and community structures have shown that the sand shrimp is an ecologically important species and is a principal prey for many commercially fished groundfish species. Recently, shrimp fishermen in the Gulf of Maine have requested the Maine Department of Marine Resources (DMR) to allow an experimental fishery for the sand shrimp. A productive fishery exists in the North Sea for a sister species, the brown shrimp. In order to begin a new fishery, more biological and ecological data is needed. The present biological study was conducted in the summer and fall of 2004 and 2005 in the Sheepscot, Kennebec and Damariscotta River estuaries to analyze the population dynamics of sand shrimp. An analysis of length-weight regressions revealed the slopes for males and ovigerous females were statistically different than that of non-ovigerous females. Ovigerous females were heavier in general because length does not change with an increase in weight. An exponential relationship was shown to exist between the length of ovigerous females and the number of eggs a female carries. Population components (juveniles, males, females and ovigerous females) had particular peaks and absences throughout the sampling seasons. Peaks of juvenile abundance in September, and the presence of ovigerous females in June and July inshore in the intertidal and May offshore sub-tidally, is evidence of two separate spawning events. Faster rates of growth were found for those shrimp hatched in the summer (0.42 - 1.25 mm/week) compared to winter (0.31 - 0.83 mm/week). A stomach analysis was conducted on 103 groundfish that contained food items. At least 30 stomachs contained evidence of sand shrimp (~ 29%) including: winter flounder, white hake, silver hake, red hake, winter skate, windowpane, shorthorn sculpin, and longhorn sculpin. Through the investigation of the ecology, biology, and management of the North Sea brown shrimp fishery, as well as other international and U.S. fisheries, several important lessons were learned that could be applied to the potential sand shrimp fishery of the Gulf of Maine. Because of its small size, both geographically and number of potential fishermen, area management, which combines many of the concepts of both community-based and ecosystem management, would be best suited for a sand shrimp fishery. The rules governing the new fishery should be precautionary. A small-sized fishery would need limits on catch and number of boats to prevent unknown biological outcomes. However, in the opinion of the author of this study, there should not be an experimental fishery designed and implemented in the Gulf of Maine. The potential negative consequences of this new fishery far outweigh the benefits.