Feeding Habits of Mesopelagic Species of Fish and Estimation of Plankton Graze in the Northwest Atlantic

NAFO Sci. Coun. Studies, 19:79-85

S. G. Podrazhanskaya

All-Union Research Institute of Marine Fisheries and Oceanography (VNIRO)
17, V. Krasnoselskaya, 107140, Moscow, Russia

The feeding habits of lanternfishes of the family Myctophidae was investigated in one of the most productive regions in the Northwest Atlantic, where the oceanographic regime and character of bioproductive processes are formed under the influence of the Labrador, North Atlantic and Gulf Stream Currents. A total of 344 stomachs from 11 species of adult myctophids ranging from 30 to 135 mm in size were examined. The most representative data were on Benthosema glaciale, Myctophum punctatum, Ceratoscopelus maderensis and Notoscopelus elongatus. Benthosema glaciale is an arcto-boreal species endemic to the North Atlantic while the other three species are immigrants that are brought in with warm currents. The average volume of food in the stomachs examined was low and there were many empty stomachs (up to 82.5% in B. glaciale). The mean-value of the feeding index was also low, from 28.6 o/ooo in B. glaciale to 173.3 o/ooo in Protomyctophum arcticum. Copepods were the main food item found in the stomachs of B. glaciale, Hygophum benoiti, Lobianchia dolfeni, Electrona risso and P. arcticum whereas M. punctatum, Diaphus rafinesque, N. elongatus and Notoscopelus bolini fed mainly on euphausiids, and hyperiids dominated in the food of C. maderensis. The food spectra showed the spatial distribution and vertical structure of the main water masses, played an important role. The most favourable feeding conditions for myctophids were on the North Atlantic water mass with high values of the feeding index and narrow spectrum of food species. The investigation focusing on the summer-autumn season showed the diurnal diet was moderate ranging from 0.3 to 1.5%. The grazing rate of the known biomass of myctophids ranged widely and suggested that the availability of food in the area in the summer-autumn period may be a limiting factor. This and the hydrographic regime seemed responsible for the absence of fishable concentrations of myctophids in July-October, 1983.