A general biophysical model of larval cod ( Gadus morhua) growth applied to populations on Georges Bank

• Published in: Fisheries Oceanography
• Main Authors: LOUGH, R. G., BUCKLEY, L. J., WERNER, F. E., QUINLAN, J. A., PEHRSON EDWARDS, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2005
• Subjects: Gadus morhua
• Online Access: http://dx.doi.org/10.1111/j.1365-2419.2005.00330.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2419.2005.00330.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2419.2005.00330.x

Abstract Field‐derived growth rates (RNA‐DNA based) of cod ( Gadus morhua ) larvae collected on the southern flank of Georges Bank were higher on average in May 1993 than May 1994, despite the apparent higher abundance of potential prey in 1994. A biophysical modeling study is presented here in which factors are examined that may have led to the difference in population mean growth. A one‐dimensional physical model, forced by winds and tides, was used to simulate the vertical structure (of currents, temperature field, and turbulent kinetic energy dissipation rate) following a column of water in a Lagrangian sense at a site on the southern flank of Georges Bank over 5‐day periods in late May of 1993 and 1994. The biophysical model and observed zooplankton abundance allowed us to explore the vertical structure and temporal (hourly) evolution of feeding and growth for cod larvae in relation to environmental conditions. Our trophodynamic model is improved over previous versions and now includes the effect of light on larval feeding response, as well as the effect of temperature on larval metabolic costs, ingestion, and digestion. Larval prey profiles, comprising four copepod species, were used from a time series of 1/4‐m 2 MOCNESS tows to define the prey field. Data from a collateral time‐series of larval gut contents (1‐m 2 MOCNESS tows) was used to define maximum ingestion (satiation level) and prey selection. Model outputs provide depth‐dependent estimates of growth, prey biomass ingested, larval length, and larval weight. Water‐column growth‐rate profiles were made for four size classes of larvae (5, 6, 7 and 9 mm) under the environmental conditions observed in May 1993 and 1994. A weighted‐mean growth rate based on the mean vertical distribution of larvae was estimated for each size class. In all cases, when using all available potential prey, the model‐derived 1994 growth rates were higher (by 3–6% day −1 ) than those for 1993. However, simulations in which 7‐mm larvae followed the field‐derived weighted mean ...