Distribution and Growth of Pre-Recruit Cohorts of the Northern Shrimp ( Pandalus borealis ) in the Western Gulf of St. Lawrence as Related to Hydrographic Conditions

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Simard, Yvan, Brunel, Pierre, Lacelle, Johanne
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1990
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; northern shrimp; Pandalus borealis
• Online Access: http://dx.doi.org/10.1139/f90-171; http://www.nrcresearchpress.com/doi/pdf/10.1139/f90-171

Samples collected with a suprabenthic sled from May to October were analysed to determine the number of pre-recruit cohorts in the northern shrimp population of the Gulf of St. Lawrence and to estimate their growth and distribution. An unexpected cohort was found with carapace lengths of 4.5–9.5 mm. This appeared to be cohort I, thus indicating three pre-recruit cohorts: cohorts 0 (2.5–4.5 mm), I (4.5–9.5 mm), and II (9.5–14.5 mm). The comparatively slow growth rate of 4–5 mm per year was attributed to the low temperatures (0.5–2.0 °C) in the bottom water inhabited by the pre-recruits, immediately below the intermediate cold water mass of the Gulf of St. Lawrence. Growth rates peaked in August–September, reaching 1 mm per month. Benthic settlement of the postlarvae also appeared to occur in August–September, at an age of 4–5 mo. Sexual differentiation in males started at an age of 16 mo and maturity was reached by 30–37 mo. Two strata were sampled, 0.3–0.7 m and 1.0–1.4 m above the bottom. More than 70% of the shrimps were concentrated in the first 0.3–0.7 m stratum. Maximum density observed for one single cohort was 67 individuals per 100 m 2 . Large spatial and temporal variations of densities occured daily, semimonthly, and seasonally, and are thought to be partially related to horizontal transport of water masses. Densities in the strata sampled were significantly lower at night, as a result of vertical migrations in the water column.