Populations of the deep-sea shrimp (Pandalus borealis Krøyer) in the Barents Sea

Three populations of P. borealis were identified in the open part of the Barents Sea. In the (4-1) population the females spawn each year and sex-change occurs 4 years old. This population was found in the soutwestern part of the sea and mostly in water masses with a temperature of approximately 2°C. In both the (5-2) and (6-2) populations the females spawn biennially, and in these populations sex-change takes place 5 and 6 years old respectively. The (5-2) population was found in the central part of the sea in water masses with a temperature a little below 1°C, while the (6-2) population was found in the northern part of the ocean in water masses with a temperature a little above 0°C. Von Bertalanffy growth curves, total mortality estimates and estimates of maximum age are given for each population. The (4-1) population, having the fastest growth, had the highest total mortality and the shortest lifespan, while the very slow-growing (6-2) population had the lowest total mortality and attained the highest age. Egg hatching was found to take place in May. The (4-1) population spawns markedly later than the two other populations, and the duration of the egg-carrying period is therefore regulated mainly by differences in the time of spawning. Length-fecundity relationships are given for the populations. Vertical migration was observed to take place over a depth interval of more than 300 meters. The youngest individuals participated in this migration to the greatest extent. A horizontal migration of the (4-1) population, probably caused by changes in the hydrographical conditions, is described. A grand total of 0.2% of the individuals were infected by the bopyride isopode Phryxus abdominalis (Krøyer)