Juvenile fish surveys on the Scotian Shelf: Implications for year-class size assessments

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

“…Distribution of sets where age 0 haddock were captured and subsequently examined for gut contents, southern Scotian Shelf, eastern Canada, 1982Canada, to 1983 Pelaglc sets; (m) demersal sets entire water column was fished during a 3-step oblique haul of 30 rnin duration, 10 min at each depth. However, based on depth-stratified sampling which indicated that the majority of age 0 haddock were caught in the uppermost 50 m of the water column (Koeller et al 1986), the subsequent cruise sampled only that depth interval. The tow speed during p e l a q c trawls was 3.5 knots and depth was monitored using a headrope transducer.…”

“…In practice, owing to the need to switch from a bottom trawl to a pelagic trawl, this would require more than one vessel or a large number of replicate tows. Due to the costs of such an experiment we have combined the information from 2 sets of surveys, one pelagic, the other demersal, as did Koeller et al (1986).…”

“…In the northwest Atlantic, the pelagic phase lasts about 4 to 5 mo, with fish moving to the bottom in August and September at a length of 9 to 10 cm (Miller et al 1963). The transition from the pelagic to demersal environment appears to be relatively rapid, taking place over a period of about 4 wk in July and August (Koeller et al 1986). Most attempts to explain the high recruitment variability of haddock have focussed on the effects of the environment and food supply during the relatively short pelagic phase.…”

In situ observations of the association between juvenile fishes and scyphomedusae in the Bering Sea

“…), although the intervening period is too brief to draw any definite conclusions. Regardless of their effect on population levels of pollock, the meso-and fine-scale features in the distribution of medusae, such as their propensity to be found in high densities in surface convergences set up by Langmuir circulation in the Bering Sea (Hamner & Schneider 1986), may need to be taken into account in designing studies to determine the horizontal and vertical distribution patterns and assess the abundance of juvenile pollock as well as other pelagic juvenile gadoids (Koeller et al 1986, Hay et al 1990). …”

“…Associations with a wide diversity of fish taxa are also well known (Mansueti 1963, Thiel 1978, Arai 1988, Kingsford 1993. Associations of juvenile North Atlantic gadoid fishes with gelatinous zooplankton are well-documented due to the high abundance and considerable economic importance of gadoids in boreal waters (Dahl 1961, Mansueti 1963, Bailey 1975, Koeller et al 1986, Hay et al 1990). …”