| The biological and behavioural characteristics of spawning populations of Atlantic herring (Clupea harengus) have frequently been inferred from the composition of commercial gillnet catches on the spawning ground. This thesis examines the suitability of fishery-generated data for such purposes, and details the daily fluctuations in spawning shoal composition through analysis of multiple daily samples. Observations were made in 1990 and 1991 at Fisherman's Bank, a fall spawning ground in the south-eastern Gulf of St. Lawrence.; Nearly all biological characteristics of the commercial gillnet catch at this site varied significantly from those estimated from the composite catch of research gillnets. Differences were chiefly due to the under-recruitment of herring {dollar}<{dollar}270 mm total length into commercial gillnets. Spawning shoals varied markedly in length, age, length at a given age, gonad maturity stage composition, sex ratios and body condition, both within and among days. Catch rates (catch per net, catch per boat, and daily fleet landings), gonad maturity stage, length and age composition showed no predictive relation with the number and timing of spawning events. (Abstract shortened by UMI.)... |
