Modeling the Processes Affecting Larval Haddock (Melanogrammus aeglefinus) Survival on Georges Bank

Colleen Petrik, Ph.D., 2011
Cabell Davis, Advisor

The ultimate goal of early life studies of fish over the past century has been to better
understand recruitment variability. Recruitment is the single most important natural
event controlling year-class strength and biomass in fish populations. As evident in
Georges Bank haddock, Melanogrammus aeglefinus, there is a strong relationship
between recruitment success and processes occurring during the planktonic larval stage.
Spatially explicit coupled biological-physical individual-based models are ideal for
studying the processes of feeding, growth, and predation during the larval stage. This
thesis sought new insights into the mechanisms controlling the recruitment process in fish
populations by using recent advances in biological-physical modeling methods together
with laboratory and field data sets. Interactions between feeding, metabolism and
growth, vertical behavior, advection, predation, and the oceanic environment of larval
haddock were quantitatively investigated using individual-based models. A mechanistic
feeding model illustrated that species-specific behavioral characteristics of copepod prey
are critically important in determining food availability to the haddock larvae.
Experiments conducted with a one-dimensional vertical behavior model suggested that
larval haddock should focus on avoiding visual predation when they are small and
vulnerable and food is readily available. Coupled hydrodynamics, concentration-based
copepod species, and individual-based larval haddock models demonstrated that the
increased egg hatching rates and lower predation rates on larvae in 1998 contributed to its
larger year-class. Additionally, results from these coupled models imply that losses to
predation may be responsible for interannual variability in recruitment and larval
survival. The findings of this thesis can be used to better manage the haddock population
on Georges Bank by providing insights into how changes in the physical and biological
environment of haddock affect their survival and recruitment, and more generally about
the processes significant for larval fish survival.