ATLSS Fish Functional Group Dynamics Model ALFISH Holly Gaff, Rene’ Salinas, Louis Gross, Don DeAngelis, Joel Trexler, Bill Loftus and John Chick

Fish biomass is one of the most important components of the Everglades system. For example, fish provide the prey-base for wading bird species such as Great Egret (Casmerodius albus). To produce projections of fish biomass, ATLSS uses a spatially explicit group dynamic simulation model, ALFISH. ALFISH

ALFISH Overview ALFISH simulates the number and biomass densities of “small fish” and “large fish” functional groups in the freshwater marsh on 5-day time steps. This represents the temporally and spatially varying food base for wading birds. ALFISH has been compared to data at some sites in Shark Slough and WCA3.

Objectives Provide estimates of effects of alternative water management scenarios on spatial and temporal distribution of food resources for upper trophic level consumers (wading birds). Provide method to evaluate hypothesized impact of hydrologic changes on fish functional group dynamics.

A size-structured population model for fish functional groups (large and small fish) that operates with a 5-day time step on a 500x500m spatial cell basis with movement between cells and between habitats within cells. Approach

Fish Cell Layout Pond areas assumed permanently wet, marsh areas periodically dry

Landscape Layout and Movement White - movement from low water to high water areas Red - movement from high fish density to low density areas

ALFISH Restudy Output Maps of the Small Fish functional group total number density (#fish/m 2 ) in the marsh areas within cells over the entire region modeled at a 500 m x 500 m cell resolution generated for a single day at different days of the year. This allows comparisons for years with a high, average, and low level of rainfall

Average Fish density on February 15 from

ALFISH Restudy Output Maps generated for a single day at several times during wading bird breeding season in cells with appropriate water depth for wading bird foraging). Again, these allow comparisons of fish availability to wading birds for years with a high, average, and low level of rainfall.

Average Fish Available as Prey on January 1, 1977

ALFISH Restudy Output Graphs of average Small Fish functional group total number density (# fish/ m 2 ) in the marsh areas within cells over the entire 31 year scenario for particular days of the year. Graphs of average Small Fish functional group total number density of fish of certain sizes in certain water depths.

Total Fish Densities through 31- year Model Run

Average Fish Available as Prey during Breeding Season for Wading Birds

ALFISH Evaluation A start on evaluating the fish landscape model, ALFISH, has been made, using data from Shark Slough and WCA sites for 1995 and one site for This has so far involved Comparisons of output statistics (fish densities) of three alternative models with empirical data Correlation analysis of model and fish density data

WCA 2A WCA 3A WCA 3B Shark River Slough km Everglades National Park Data Sites

Evaluation of fish functional group dynamics model Three models, with different assumptions concerning “density of ponds” and “consumption” parameters, were compared with both the long time series from the single site and the spatially explicit sites for Model 1 – original Restudy parameters Model 1.1 – increased number of ponds Model 2.5 – increased consumption of prey

Results of ALFISH Evaluation WCA 3A

Results of ALFISH Evaluation Shark River Slough

Results of ALFISH Evaluation Correlation analysis shows that ALFISH explains only 25-35% of the field data when comparing data from different spatial sites and years. But this is consistent with the available fish data showing that hydrologic differences account for only 20-40% of the variation in fish densities (Chick 1998).

Results of ALFISH Evaluation Shark River Slough Site 6

Conclusions Continued improvements as new data becomes available Currently being used to test different hypotheses Will be linked to lower trophic level model