Title

Impacts of water management on roseate spoonbills and their piscine prey in the coastal wetlands of Florida Bay

Date of Award

2000

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Samuel C. Snedaker, Committee Chair

Abstract

In its pristine state, the Everglades delivered large volumes of freshwater to Florida Bay. To provide flood control to urban and agricultural areas, southern Florida's extensive man-made canal system diverted Everglades flow, resulting in shorter hydroperiods and higher salinities in northeastern Florida Bay. Roseate Spoonbills are good indicators of ecosystem "health" because they nest throughout the northeastern bay and primarily forage in the proximal estuarine wetlands while raising their young. An examination of 65-years of spoonbill nesting patterns showed that the anthropogenic impacts to foraging grounds had a major effect on the spoonbill nesting patterns, presumably by altering prey availability. The small, demersal fishes that make up the majority of the spoonbill diet are also excellent bio-indicators of perturbations to the ecosystem. Statistical analyses of 10-years of fish collections from spoonbill foraging grounds indicated that fish density increased with both short-term and longer-term increases in water levels. Fish biomass also increased with water level, however, biomass was also negatively influenced by increases in the frequency, magnitude and duration of saline periods. A natural experiment examined the effect of an unusually long freshwater period on fish community composition. Results indicated that a restoration of natural salinity patterns might revert the prey base back to pre-canal production levels. However, spoonbill nesting failed during the low salinity period, indicating that other parameters besides salinity impact wetland function. Nesting failure was probably due to anthropogenic alterations to seasonal water level patterns. During high water periods prey fishes exploited ephemeral wetlands and increased in overall abundance. During dry periods, ephemeral wetlands dried, forcing fish to become highly concentrated in the remaining wetted areas. When spoonbill nesting failed, water levels were found to be higher and prey less available than during successful nesting attempts. Out-of-season pulse-releases of water from the canal system raise water levels on spoonbill foraging grounds thereby dispersing prey and making it difficult for spoonbills to capture enough prey to meet the energetic demands of their young. In conclusion, water management practices have reduced the abundance and availability of prey base fishes in the estuarine wetlands, resulting in a decline of nesting Roseate Spoonbill population in northeastern Florida Bay.

Keywords

Biology, Ecology; Environmental Sciences; Agriculture, Fisheries and Aquaculture

Link to Full Text

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