Biology of the Northern Shrimp, Pandalus borealis, in the Gulf of Maine

Northern shrimp from offshore waters in the Gulf of Maine were studied to determine their occurrence and to learn some major features of their life history. The area sampled extends from Nova Scotia, Canada, to Long Island, New York. Northern shrimp were found only in the western portion of the Gulf of Maine, where they were present throughout the year, and at two isolated localities southeast of Nova Scotia. Abundance was highest in moderate depths in the vicinity of Jeffrys and Cashes Ledges and southeast of Mount Desert Island, Maine, and lowest in the deeper, offshore areas in the west-central part of the Gulf. High water temperatures appear to limit the southward extension of this species off New England. Within the Gulf of Maine this shrimp occurs on fine-grained bottom sediments, such as clay, silty sand, and glacial till, which contain relatively large amounts of organic matter. Average life span is about 3 1/2 years and may extend to 4 1/2 years for a small portion of the population. Northern shrimp are protandric hermaphrodites, functioning first as males. Spawning is in August and September. Most of the shrimp spawn only once as females—about 20% at 2 1/2 years of age, 70% at 3 1/2 years, and 10% at 4 1/2 years. The eggs remain attached to the pleopods for about 6 months and hatch in the spring (March and April). Egg-bearing females migrate from the deeper (offshore) waters to shallow (inshore) areas during the maturation period. It is the egg-bearing females, which are concentrated near the mouths of estuaries and other nearshore areas, that make up the bulk of the commercial catch. The number of eggs per clutch increases with shrimp size and averages 2,400 (range, 800 to 3,400). Length-weight relations are similar for males and nonovigerous females; ovigerous females are about 1.4 g heavier for any given length than the nonovigerous ones. Growth rate of the Gulf of Maine population is faster at ages of 2 years and older than that of any other population of this species reported to date.