Growth and breeding of meso- and bathypelagic organisms of the Rockall Trough,northeastern Atlantic Ocean and evidence of seasonality

Seasonality of growth and reproduction of a variety of epimeso-and bathypelagic organisms living in the Rockall Trough is examined in samples collected between 1973 and 1978. Rates of growth change seasonally. Epipelagic and shallow-living mesopelagic migrators tend to grow most rapidly in the spring and summer while deeper-living mesopelagic migrators tend to accelerate their growth in the summer and autumn when seasonal water temperatures at these depths are at their seasonal maxima. Mesopelagic migrators all breed seasonally. Rates of growth of bathypelagic non-migrating species could not be determined through analyses of body length/frequency histograms because of the continuous (aseasonal) breeding and recruitment of juveniles to the adult populations. An exception was the mysid crustacean Boreomysis microps that had a seasonal period of spring recruitment of juveniles to the population. Several of the mesopelagic crustaceans and fish have extended periods of approximately linear growth in body length. There is no evidence that organisms living in the mesopelagic or bathypelagic environments have rates of growth that are markedly slower than those of congeners in shallower environments.