Lough, G.1, E. Broughton1,
J. Manning1, L. Buckley2,
L. Incze3, N. Wolf3,
F.E. Werner4, K. Pehrson Edwards4,
R. Converse4, and A. Aretxabaleta4
1Northeast Fisheries Science Center, NMFS, NOAA,
Woods Hole, MA 02543, USA
2
University of Rhode Island/NOAA CMER Program, Graduate School of Oceanography,
Narragansett, RI 02882, USA
3
Bioscience Research Institute, U. Southern Maine, Portland, ME 04104 USA
4
Marine Sciences Department, University of North Carolina, Chapel Hill,
NC 27599-3300, USA
Cruises were conducted in spring 1999 to describe the
interaction between tidal-front processes and the transport,
retention and growth of cod and haddock larvae and their prey during
the transition to stratified-water along the southern flank of
Georges Bank. The project implemented a modeling component, where a
three-dimensional circulation model was used in near real-time
aboard ship to help guide the field program, as well as in
hindcasting mode to integrate all the physical and biological
observations in coupled circulation-trophodynamic simulations. Data
assimilation methods were used in the circulation model to achieve
the cell-like secondary circulation associated with the tidal front;
downwelling on the stratified side and weak upwelling on the mixed
side of the front. Passive drifter trajectories showed accumulation
of particles in the front due to surface convergence, and cross
isobath, on-bank, near-bottom flow under the tidal-front jet. A
larval cod biophysical model (IBM) was used to consider
trophodynamic effects on the growth and survival of larval cod and
haddock. Prey fields were specified for mixed and stratified water
columns from net and pump profiles and allowed to mix in the
circulation model. Encounter and ingestion rates of larvae are
functions of prey concentration, larval search patterns, sensitivity
to light, swimming speeds of predator and prey, and turbulence.
Model outputs provide hourly depth-dependent estimates of growth,
prey biomass ingested, larval length and weight. Simulations were
conducted to test the relationship among temperature, water-column
structure, food availability, and larval growth. Observed larval
growth, based on RNA-DNA, had higher mean growth rates from the
upper 20m at the front and stratified stations. Simulations
indicated that larval growth can be maximized at the tidal-mixing
front due to near optimal temperature, turbulence, light, and given
a surface convergence zone, high food availability.
Click here for an attached image.