U.S. GLOBEC: An Experimental Evaluation of Biological and Physical Modulators of Foraging Success in Early Cod Larvae on Georges Bank - Turbulence, Prey Motility, Depth, and Light Intensity

Scott M. Gallager
Woods Hole Oceanographic Institution, Woods Hole, MA
Hidekatsu Yamazaki
Tokyo University of Fisheries, Tokyo, Japan

This is a combined field and laboratory study to investigate the effects of turbulence, prey motility, depth, and light intensity on foraging success in young (1 to 20 day) cod larvae. Theoretical studies have shown that these variables are critical to foraging success and recruitment in cod and haddock populations, yet little if any empirical evidence exists to substantiate these predictions. This study addresses Phase II goals of the North Atlantic GLOBEC program by proposing to (1) Measure vital rates of target species (feeding in young cod larvae as a function of light, turbulence, and prey motility); (2) Quantify target species (microplankton including nauplii of Calanus sp.) abundance patterns across Georges Bank and through their growing season; and (3) Determine the interaction between vertical position (migration) and retention and loss of planktonic animals on the Bank (foraging success of cod larvae as a function of depth in the water column).

Our objectives are:

1) To determine the effects of depth, the natural light field, and prey motility on foraging success in early cod larvae feeding on natural assemblages of microplankton prey on Georges Bank.

2) To determine the effects of light (intensity and optical contrast), turbulence intensity, and prey motility on the perceptive volume and foraging success in early cod larvae.

3) To describe the seasonal development of the microplankton prey field in terms of size, abundance, and motility characteristics across Georges Bank and surrounding regions.

4) To integrate the results of these studies into the three- dimensional advective/diffusion and IBM trophodynamics model of larval cod on Georges Bank being developed by Drs. Cisco Werner, Dan Lynch, John Loder, and Chris Naimie.

Quantifying foraging success as a function of turbulence, prey motility, and light intensity in these laboratory and field experiments will advance our ability to predict successful larval recruitment in the field in relation to the seasonally developing microplankton prey field. Data from these studies are critical to the successful modeling of bio-physical coupling and trophodynamics of larval cod and haddock larvae in relation to climate change.