Recent Developments in Larval Fish Trophodynamic Modeling

Francisco E. Werner, John A. Quinlan Greg Lough, Larry Buckley, Jeff VanKeuren and Christopher E. Naimie

One of our objectives is to explain observed larval distributions and growth rates during the 1995 Stratification Experiment. We will simulate field estimates of light, turbulence, temperature and prey distribution in a trophodynamic model of larval cod and haddock. In particular, we want to see if we can reproduce observed growth rates of 10-15% per day (in weight) for larvae initially 8mm in length (approximately 300 micro-gm in weight). We use a one-dimensional point model (t vs. z; Naimie, 1996) forced by winds and sea-level gradients to obtain turbulent dissipation rates and stratification. The trophodynamic model is based on Laurence's bioenergetic formulation extended to include effects of turbulence on encounter and capture success, preferred prey size range (Werner et al. 1996), temperature effects on metabolism (Laurence, 1981), and light limitation (Huse, 1994; VanKeuren, 1997). We find, using idealized prey and light fields that we can reproduce (and exceed) field derived growth rates of 10-15% per day in certain regions of the water column. Our next step will be to input observed, depth and time-dependent prey fields for May 1995. We will also explore alternative formulations for temperature effect on metabolism and begin to develop behavioral rules based on choices (of position in the water column through active swimming) that optimize growth rates, intake rates, and reduce metabolic costs.