Early growth, lipid composition, and survival expectations of shrimp Pandalus borealis larvae in the northern Gulf of St. Lawrence

Abstract

Shrimp Pandalus borealis larval abundance, early growth, and lipid composition were assessed at 3 sites in the northern Gulf of St. Lawrence, Canada, in May 1990. Physical characteristics (temperature, salinity, beam attenuation) of the water column, zooplankton biomass (80 to 250 pm and 333 pm to 2 mm size fractions) and its taxonomic composition (333 pm to 2 mm size fraction) at each s ~t e , were also investigated. The 3 sampling sites were different environments with distinct water column characteristics and zooplankton community structures. Phospholipids were the most abundant (-80%) lipid class in shrimp zoea 1 and zoea I1 larvae whereas the triacylglycerols (TAG) accounted for an average of 5% of the total lipids. The distribution of TAG wet-weight ratios of shrimp larvae captured in the field was similar to laboratory reared larvae, suggesting that the laboratory-derived TAG condition index can be used to infer the performance of shrimp larvae in different environments and to estimate relative survival expectations among the larval cohorts. In general, shrimp larvae were apparently not suffering from limited food resources in the sectors of the Gulf in 1990. Nevertheless, zoea I1 larvae were larger in size (weight) and length, and showed a higher TAG condition index at the sites where developmental stages of calanoid copepods were more abundant. This supports the proposition that secondary production in the water column influences growth, condition, and surv~val potential of shrimp larvae. It is proposed that survival of the first larval stage and recruitment to the shrimp stocks are influenced by the factors affecting stratification and mixing in the water column, i.e. buoyancy fluxes, through control of phytoplankton and copepod production in the northern Gulf of St. Lawrence.