Diet changes in Scotian Shelf haddock during the pelagic and demersal phases of the first year of life

Abstract

The diet of haddock Melanograrnmus aeglefinus from the southern Scotian Shelf was studied during their first year of Me. WMe haddock were pelagic, copepods were the numerically dominant component in the diet, with a significant benthic contribution (amphipods, polychaetes) first occurring in late summer. Examination of gut contents indicated that the transition from pelagic to demersal Life occurred relatively suddenly. Catch rates did not vary with die1 periodicity and gut contents of demersal fish had few occurrences of pelagic prey, indicating that diel migration was likely not an important aspect of the ecology of age 0 fish. Dietary changes during the months subsequent to the pelagic-demersal transition were minor relative to those associated with the transition itself, although some trends in importance of dietary items were observed, notably with copepods and mysids. Such trends did not appear to be related to the size of age 0 haddock.

Spatial and temporal variability in feeding and condition of age-0 walleye pollock (Theragra chalcogramma) in frontal regions of the Bering Sea

“…The prey found in association with the bottom (e.g., harpacticoid copepods, caprellid amphipods, cumaceans) may indicate an ontogenetic transition in vertical distribution and food dependencies of these juveniles. In the Gulf of Alaska, juvenile pollock in their first winter show a marked shift toward bottom-oriented prey (Krieger, 1985;Brodeur and Wilson, 1996a), which is similar to that observed for other gadoid fishes in the Atlantic Ocean (Mahon and Neilson, 1987;Perry and Neilson, 1988). Table 2.…”

Food resource utilization by juvenile Baltic cod Gadus morhua:a mechanism potentially influencing recruitment success at the demersal juvenile stage?

“…In both groups (5 to 50 and 50 to 150 mm) cod fed initially on prey of presumably optimal size, but the size of the prey consumed did not increase with increasing fish size. Pelagic juveniles are known to continue feeding on small prey items such as copepods to the size of settlement unless larger prey items are available (Palsson 1973, 1980, Robb & Hislop 1980, Bowman 1981, Robb 1981, Mahon & Neilson 1987. However, in no other region was the size of food items of demersal juveniles reported to be as small as those from this study.…”

“…Abrupt transition to the demersal habitat has previously been observed for gadoids by Koeller et al (1986) and Mahon & Neilson (1987). Through the utilization of stomach content analysis, these authors concluded that the transition period for juvenile Scotian Shelf haddock is of short duration.…”

“…These groups represent the prey item's habitat attachment, which was specified as pelagic, benthic or intermediate, accorde.g. mysids, amphipods and molluscs, only their weight ing to Gosner (1971) and Mahon & Neilson (1987). The was considered.…”

“…Koeller et al (1986) found that the transition to the demersal life for a whole cohort took 27 d. Mahon & Neilson (1987) estimated this period to be of approximately 4 wk duration. Juvenile cod in the present study were observed to settle in a 30 mm size interval, with most of the settlement taking place within a 10 mm size interval.…”