Sturgeon in Hillsborough River

Telemetry Study of Habitat Utilization and Success of Hatchery-reared Gulf of Mexico Sturgeon in the Hillsborough River, Florida

Sturgeon conservation research was initiated in the Special Projects Group of the Directors office. The Hillsborough River was selected as a study area where habitat utilization of Gulf of Mexico sturgeon in a coastal urban river system.

The Hillsborough River is unique in that although it flows through a large metropolitan and agriculture area it has been aggressively conserved by maintenance of a "green corridor" of adjacent upland, conservation of some of its groundwater sources, intensive pollution elimination and maintenance of good water quality. There is a dam in the river at the Sulfur Springs fall line that partitions it into two diverse reaches, one tidal the other freshwater.

A conservative program to release, track, monitor and assess hatchery-reared fish in both major reaches of the river was developed in the first half of calendar year 2000.

Data from this project will be used to develop an analysis of sturgeon utilization of both reaches of the Hillsborough River (time series geographical description of distribution), to estimate relative abundance of fishes, to develop survival indices, and to provide data on the status and trends of sub-adult sturgeon after release. These data will provide the Florida Fish and Wildlife Conservation Commission (FWC) and other resource management agencies with information necessary for implementing effective threatened species management measures. These data will also provide relative life history, feeding, health and other information for Gulf of Mexico sturgeon, especially in perturbed river systems.

An important element of this project is that it encourages diversity of scientific approach for sturgeon research. It has an extensive public education component to encourage dissemination of information about the threatened and endangered status of sturgeon to the public. It will educate diverse groups on worldwide status of sturgeons and provide extensive regional information about Gulf of Mexico and other sturgeon of Florida. This study also contributes information to other research groups on mapping, habitat types and distribution, and water quality of the Hillsborough River system. This will complement a large assemblage of research information for the Tampa Bay estuary.

OBJECTIVES
The first objective of the study is to determine initial mortality, if any, and short-term suitability of two reaches of the river to support sub-adult Gulf sturgeon. This objective will test the immediate feasibility of the project concept and allow determination of survival. In addition short-term movements, growth and health of stocked sub-adult sturgeon in freshwater habitat of the river, including the reservoir and the tidal downstream habitat of the river will be assessed along with water quality evaluations and habitat parameters for a period of one year. Feasibility of executing further research will be evaluated.

The second objective is to assess growth, survival, movement, and habitat utilization in the upper reach of the river (above the dam) and the lower reach of the river (below the dam). Multiple stocking sites, stratified over in each of the two reaches of the system and over three habitat types in each reach were used.

Refinement of existing techniques and development of new techniques to monitor, track and recapture released sturgeon for recovery of scientific information will be refined during the course of this project. This will provide scientists and managers with information regarding suitability of the system to support sturgeon and allow conservation decisions based on use of hatchery-reared stock.

GEOGRAPHIC COVERAGE
This monitoring program was initiated in the Hillsborough River Basin, in the main flow of the river between Crystal Springs Park, FL. and Davis Islands, FL. (Figure 1.)

MARKING AND TRACKING ELEMENTS
On October 17 and 18 forty nine Gulf of Mexico Sturgeon (mean weight 2.76 kg and mean total length 877.40 mm) were implanted with acoustic transmitters and passive integrated transponders. For the most part fish survived surgery and recovered to better condition than they were prior to surgery.

Between November 13, 2000 and January 1, 2001 46 sturgeon were released into 6 separate habitat types in both reaches of the river. Fish were stocked over a protracted two-month period in order to closely monitor initial survival and performance of fish. This was necessary in case problems occurred and stocking strategy needed to be modified.

EXPERIMENTAL DESIGN
Fish were released at the Hillsborough River State Park, Dead River County Park, and in the Reservoir in Temple Terrace in the upper reach of the river. Fish were released in the Sulfur Springs area, Lowery Park area and between Hillsborough Avenue and Columbus Drive in the lower reach of the river.

Habitat types in the upper river include: (1)hard bottom/limestone sediments mixed with shell, coarse sand and silt , (2) Riverine (majority of upper river includes mixed hard bottom/limestone, mud flat/coarse shell and sand/clay and rock banks with bars and deep holes/emergent hardwoods and flatwoods, (3) Hillsborough River Reservoir (modified riverine with cypress spoils, fine sand/mudflats, broad shallow areas interspersed with channels and deep holes, fringed with emergent vegetation and low density residential dwellings Habitat types in lower river include: 1) Karst (hard bottom/limestone sediments mixed with shell and coarse sand with ground water sources into the river Sulfur Springs/Hannah's Swirl, (2) degraded riverine habitat with broad mud/sand flats emergent oligohaline vegetation, mixed oligohaline invertebrates/relatively high density residential dwellings with bulkhead shoreline, (3), riverine/mesohaline to brackish water habitat, mixed mesohaline-brackish emergent and submerged vegetation, low density residential dwellings with broad areas of natural shoreline and adjacent urban greenspace.

Released fish will be monitored on a biweekly sampling schedule using a digital reference map with mid-river transect and 250 meter gridlines. When practicable fish will be located from mid-river at intervals of 250 meters. This approach will vary in the upper river where bends in the river and structures alter transmissions of acoustic devices.

A stationary receiver has been set up on a floating dock at the University of Tampa where river width is about 300 meters. A directional hydrophone is connected to a Sonotronics USR 90 stationary scanning receiver interfaced with a Hewlett Packard Palm computer utilizing DOS 5.0 as an operating system. Data is stored on a PCMCIA card and uploaded to an Excell Spreadsheet file for analysis. As of 12/02 no transmission data in the frequency range or transmission intervals for our sturgeon have been logged at this fixed station. The fixed station is about 3000 meters from the mouth of the Hillsborough River.

MOVEMENT OF FISH
Overall, movement of released fish has been diverse. Some have remained near their release sites, some have moved up-river from their release sites, and some have moved down-river. A few have moved long distances from the place of release. Two fish released at the Hillsborough River State Park were found below Harney Canal in the reservoir at Temple Terrace, a distance of well over 30 kilometers. This movement has occurred in less than two months. Sampling the Temple Terrace area on January 2-3, we found 5 of 8 sturgeon up-river, closer to Harney Canal. Sampling the Sulfur Springs and Lowry Park areas on January 4 we found 13 fish. Six of those moved down-river, five moved up-river and two stayed in the same general area of their release. Sampling the river between Hillsborough River State Park and Dead River we found 6 of 8 fish. Tracking has now intensified as most of activities with implantation surgery and release have subsided.