Abstract
Successful implementation of an Ecosystem Approach to Fisheries Management
depends on our understanding of and communication about the complex dynamics of
an ecosystem. This study developed a spatially and temporally explicit agent-based
simulation model to examine the dynamics of juvenile Atlantic tarpon in a sub-tropical
near-shore environment. The simulation was a minimally realistic model focused on the
predator-prey dynamic between juvenile tarpon (Megalops atlanticus) and pink shrimp
(Farfantepenaeus duorarum) in Biscayne Bay, Florida.
To effectively model the biophysical linkages between tarpon, their prey and the
environment, a systems approach was utilized by integrating a hydrodynamic model, a
bioenergetic model, a crustacean degree day growth model, a predator-prey interaction
model and several types of movement models. The integrated systems model provided
a visual representation and data about the growth, movement and spatial population
dynamics of both predator (juvenile tarpon) and prey (pink shrimp) in Biscayne Bay
FL, relative to the dynamics of the environment over time.
To quantify the contribution of the abiotic and biotic components of the environment
to tarpon growth and survivorship, a dynamic fitness-scape was defined using juvenile
tarpon life history demographics and metabolic requirements driven by environmental
cues to describe how juvenile tarpon use Florida’s near-shore ecosystems.
Novel empirical data for juvenile tarpon was developed to parameterize a bioenergetic
model. Maximum consumption was found at 30 ºC. Respirometry experiments
performed at ambient water temperature and three salinity profiles; freshwater (6.5 ppt),
brackish (16.5 ppt) and marine (34 ppt) showed a significant relationship between oxygen
uptake and both water temperature and salinity.
The simulation model was used to examine differences in tarpon growth rates with
respect to seasons and environmental conditions. Simulations suggested the highest
rates occurred in marine conditions during summer at a water temperature of 30 ºC,
with the second fastest rate occurring in estuarine conditions at a water temperature of
30 ºC. Interestingly, the third highest growth rate occurred in freshwater conditions at a
much cooler water temperature of 18 ºC. During winter, with estuarine conditions and
water temperatures ranging between 23-31 ºC, juvenile tarpon showed little growth.
While water temperature and salinity significantly influenced growth rates, other
factors such as prey density may play a role in tarpon growth in less optimal environmental
conditions. The interplay between these mechanisms suggest tarpon utilize
movement to maximize growth and minimize mortality rates by taking advantage of
habitat variability. The holistic approach employed in this study could be used to evaluate
impacts of fisheries management decisions, water management strategies and climate
change and to assess ecosystem status relative to management objectives.