Petrik
Colleen M.
Petrik
Colleen M.
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PreprintInterannual differences in larval haddock survival : hypothesis testing with a 3D biophysical model of Georges Bank( 2014-06) Petrik, Colleen M. ; Ji, Rubao ; Davis, Cabell S.The ultimate goal of early life studies of fish over the past century has been to better understand recruitment variability. As evident in the Georges Bank haddock (Melanogrammus aeglefinus) population, there is a strong relationship between recruitment success and processes occurring during the planktonic larval stage. This research sought new insights into the mechanisms controlling the recruitment process in fish populations by using biological-physical modeling methods together with laboratory and field data sets. We created the first three-dimensional model of larval haddock on Georges Bank by coupling models of hydrodynamics, lower trophic levels, a single copepod species, and larval haddock. Interactions between feeding, metabolism, growth, vertical behavior, advection, predation, and the physical environment of larval haddock were quantitatively investigated using the coupled models. Particularly, the model was used to compare survival over the larval period and the sources of mortality in 1995 and 1998, two years of disparate haddock recruitment. The results of model simulations suggest that the increased egg hatching rates and higher food availability, which reduced starvation and predation, in 1998 contributed to its larger year-class. Additionally, the inclusion of temperature-dependent predation rates produced model results that better agreed with observations of the mean hatch date of survivors. The results from this biophysical model imply that food-limitation and its related losses to starvation and predation, especially from hatch to 7 mm, may be responsible for interannual variability in recruitment and larval survival outside of the years studied.
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ArticleA simplified age-stage model for copepod population dynamics(Inter-Research, 2008-05-22) Hu, Qiao ; Davis, Cabell S. ; Petrik, Colleen M.Complex 3D biological-physical models are becoming widely used in marine and freshwater ecology. These models are highly valued synthesizing tools because they provide insights into complex dynamics that are difficult to understand using purely empirical methods or theoretical analytical models. Of particular interest has been the incorporation of concentration-based copepod population dynamics into 3D physical transport models. These physical models typically have large numbers of grid points and therefore require a simplified biological model. However, concentration-based copepod models have used a fine resolution age-stage structure to prevent artificially short generation times, known as numerical ‘diffusion.’ This increased resolution has precluded use of age-stage structured copepod models in 3D physical models due to computational constraints. In this paper, we describe a new method, which tracks the mean age of each life stage instead of using age classes within each stage. We then compare this model to previous age-stage structured models. A probability model is developed with the molting rate derived from the mean age of the population and the probability density function (PDF) of molting. The effects of temperature and mortality on copepod population dynamics are also discussed. The mean-age method effectively removes the numerical diffusion problem and reproduces observed median development times (MDTs) without the need for a high-resolution age-stage structure. Thus, it is well-suited for finding solutions of concentration-based zooplankton models in complex biological-physical models.
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ThesisModeling the processes affecting larval haddock (Melanogrammus aeglefinus) survival on Georges Bank(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2011-02) Petrik, Colleen M.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.