Catch per unit effort (CPUE) was computed from fisheries‐independent monitoring data collected from 1996 through 2013 in the lower Peace River and Charlotte Harbor, Florida. Seasonal habitat suitability modeling (HSM) based on delta‐gamma generalized additive models was prepared for eight fish and invertebrate species life stages with affinities for either low or moderate salinities. Using a geographic information system, habitat maps were created from monitoring data for temperature, salinity, dissolved oxygen, depth, and bottom type in the study area. Gear‐corrected CPUEs derived from HSM were applied to corresponding habitat grid cells. Seasonal HSM maps were then created, depicting the spatial distribution and relative abundance for early juvenile, juvenile, and adult life stages. By overlaying Optimum abundance zones from each HSM map onto corresponding salinity grids, the preferred ranges of salinity were found to be similar between seasons for each of six estuarine‐resident species life stages. This implies that each resident species occupies a unique salinity range in the river and estuary, which varies little between seasons. During the summer wet season, the geographic ranges occupied by each resident species life stage expanded in response to increased inflow, while the preferred salinity ranges occupied were similar between seasons. However, this was not the case for the two estuarine‐transient species (Red Drum Sciaenops ocellatus and Spot Leiostomus xanthurus), which tended to utilize different salinity ranges between seasons. Habitat‐based population estimates were prepared for each species life stage by using the predicted CPUE grids used to create the HSM maps. The demonstrated methods support ecosystem‐based fishery management and management of freshwater inflow to tidal rivers.
In this article, we present an approach based on generalized additive models (GAMs) to predict species’ distributions and abundance in Florida estuaries with habitat suitability modeling. Environmental data gathered by fisheries‐independent monitoring in Tampa Bay from 1998 to 2008 were interpolated to create seasonal habitat maps for temperature, salinity, and dissolved oxygen and annual maps for depth and bottom type. We used delta‐GAM models assuming either zero‐adjusted gamma or beta‐inflated‐at‐zero distributions to predict catch per unit effort (CPUE) from five habitat variables plus gear type for each estuarine species by life stage and season. Bottom type and gear type were treated as categorical predictors with reference parameterization. Three spline‐fitting procedures (the penalized B‐spline, cubic smoothing spline, and restricted cubic spline) were applied to the continuous predictors. Two additive, linear submodels on the log and logistic scales were used to predict CPUEs >0 and CPUEs = 0, respectively, across environmental gradients. The best overall model among those estimated was identified based on the lowest Akaike information criterion. A stepwise routine was used to omit continuous predictors that had little predictive power. The model developed was then applied to interpolated habitat data to predict CPUEs across the estuary using GIS. The statistical models, coupled with the use of GIS, provide a method for predicting spatial distributions and population numbers of estuarine species’ life stages. An example is presented for juvenile pink shrimp Farfantepenaeus duorarum during the summer in Tampa Bay, Florida. Received February 10, 2015; accepted August 11, 2015
The effects of potential reductions of freshwater inflow were evaluated for the lower Peace River and its largest tributary, lower Shell Creek, which flow into the Charlotte Harbor estuary in southwest Florida. Habitat suitability modeling (HSM) and mapping of fish and invertebrate species life stages were used to seasonally predict changes in spatial distributions and population numbers associated with simulated freshwater withdrawals. Seasonal salinity grids and temperature grids derived from values predicted by hydrodynamic modeling (2007-2014) were similar between baseline (i.e., flows not affected by water withdrawals) and minimum flows (flows associated with water withdrawals). Depth grids, bottom type grids, and seasonal dissolved oxygen grids were held constant between the two scenarios. Seasonal habitat suitability models were applied to 28 fish and invertebrate species life stages with affinities for low or moderate salinity. Salinity was the most significant factor in seasonal models for species life stages. The seasonal HSM maps produced showed that spatial distributions were similar between baseline and minimum flows for each species life stage. Most seasonal estimates of population numbers under minimum flows were less than the estimates for the baseline condition, indicating some effect on population numbers associated with flow reductions. Reductions in population numbers under minimum flows ranged from 0.3% to 21.0%, with 3 out of 28 seasonal comparisons indicating losses >15% and 12 comparisons indicating losses between 5% and 15%. Although other factors related to freshwater inflow can also influence species abundance and distribution, these results demonstrate how output from hydrodynamic modeling can be applied to HSM analyses and mapping to estimate spatial changes in habitat areas and population numbers for the life stages of selected fish and invertebrate species in relation to changes in salinity distributions, which can be used to identify areas of an estuary that are particularly susceptible to the effects of inflow reductions. The assessment and management of freshwater inflow to estuaries have received increased emphasis in recent decades to account for the important ways in which freshwater inflow affects physical, chemical, and biological processes and the resources of estuaries, including relationships with the productivity of sport and commercial fish
Research was undertaken to model and map the spatial distributions and abundances of pink shrimp Farfantepenaeus duorarum on the West Florida Shelf (WFS) using habitat suitability modeling (HSM). Data loggers and electronic logbook systems on three shrimp boats were used to gather catch and effort data along with bottom temperature, salinity, and depth data at the fishing locations. Vessel monitoring system (VMS) data supplied by the fishing company helped delineate areas with high fishing activity. For the vessels participating in this study, significantly higher mean catch per unit effort (CPUE) of pink shrimp was realized on the WFS during June–September 2004 and October–December 2004 than during January–March 2005 and April–June 2005. Suitability functions were created to predict CPUE in relation to depth, aspect, bottom type, bottom temperature, current speed, current direction, and VMS zone. Oceanographic modeling was conducted monthly from March 2004 to June 2005. Bottom current speed and direction indicated marked upwelling onto the WFS during 2004 and downwelling during 2005. The HSM linked to GIS was used to predict the spatial distributions and abundances of pink shrimp monthly from March 2004 to June 2005. While seven factors contributed to the HSM, current speed and current direction appeared to be most important during June–December 2004. The areas with the most pronounced upwelling were also the areas that the HSM predicted would have the highest mean CPUEs. This relationship was verified by overlaying the observed CPUE from the fishing vessels onto the suitability zones predicted by the HSM. Received January 6, 2015; accepted August 1, 2015
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