|Patterns of Movement of Florida Gar (Lepisosteus platyrhincus) in the Everglades Revealed by Radio Telemetry
Lawrence F. Wolski, Joel C. Trexler
Florida International University, Miami, FL
Washington University, St. Louis, MO
Carl Ruetz III
Annis Water Resources Institute, Muskegon, MI
William F. Loftus
U.S. Geological Survey, Center for Water and Restoration Studies, Miami, FL
To build credible simulation models for the Everglades fish community for use in the restoration process, information on fish movement patterns and habitat use is a critical need. In this pilot project, we are testing the feasibility of using implanted radio transmitters to trace the movements of Florida gar across the open Everglades landscape. Beginning in March 2002, we monitored the movements of Florida gar (fig. 1) in the Everglades Wildlife Management Area, Conservation Area No. 3A (WCA-3A). An initial group of 20 was monitored from March to July and monitoring of the second group of 20 began in August and is ongoing. We collected gar using standard electrofishing techniques from an airboat, weighing and measuring each gar as it was collected. Fish were anesthetized in a solution of MS-222 for surgical implantation of transmitters (SB-2, Holohil Systems, Ltd.). Transmitters were inserted into the body cavity of the gar through a ventral incision posterior to the pelvic girdle, which was closed with three to five sutures and SuperGlue (fig. 2). The transmitter size maximizes the range and lifespan of the transmitter but cause no harm or mechanical interference to the fish. Each fish was released at the point from which it was captured and was monitored for the lifetime of the transmitter (approximately 3 months for the first group of fish). We captured the fish in two widely separated areas of WCA-3A, one short-hydroperiod area to the west (site 3; 26.014 N, 80.82 W), and a second, longer hydroperiod area in central 3-A (site 1; 25.86 N, 80.73 W). We tracked the gar using a Wildlife Systems receiver from an airboat. Fish that were unable to be located from the airboat were tracked by helicopter or airplane.
We tracked gar from the first group an average of 52 days between transmitter insertion to the time of last field record (Max. = 128, Min. = 1). Fish tracked at site 1 were monitored for an average of 50.5 days (Max. = 128, Min. = 3) and moved an average of 2.62 kilometers from the point of release (Max. = 7.339, Min. = 0.010). The majority of fish moving long distances swam to the southeast (fig. 3).
At site 3, the shorter hydroperiod site, the average tracking duration was nearly the same (54.8 days), but the average distance travelled was much less (0.913 km; Max = 2.96, Min. = 0.004). There was no trend in the direction of movements at that site, in contrast to the fish marked at site 1. This difference in movement may be related to local hydrology. At site 3, the gar travelled the greatest distances during the periods of March 12 – 24 and June 16 – July 1. Water depth at site 3 dropped substantially between March 24 and June 16 as the dry season progressed. Between May 6 and June 14, site 3 was unreachable because of low water levels. There was also a decrease in the distance per day travelled during this period (fig 4), which was probably related to the declining water depths.
We are presently monitoring a second group of gar at sites 1 and 3 that were tagged at the height of the 2002 wet season. We are tracking 14 individuals, of which four have moved beyond the range of our equipment. We believe this is a result of the deep, wet-season water depths that enable the gar to move longer distances than in the dry season.
In addition to long-term monitoring of the gar, we collected intensive diel movement and habitat-use data at both study sites by locating all fish at each site every 2 hours during a 24-hour period. As of November 2002, two diel studies have been completed from site 1 and two from site 3. Both diurnal sampling events from site 1 involved the most recent group of tagged gar, while at site 3, we collected one diurnal data set from each group. Preliminary analysis indicates that for 3 of the 4 tracks, there was no directional pattern to the movement of gar and no change between day and night movements. However, in one case (site 3, Group 1) the fish became more active at night and traveled longer distances. This coincided with shallow water depths at site 3; gar were found in alligator holes and deeper areas of the marsh during the day, moving into shallower areas during the night. This variation indicates that hydroperiod, and weekly variation in water depth at a particular site, play an integral role in the movement of gar. This study demonstrates the feasibility and effectiveness of using radio transmitters to describe movement patterns of large, mobile fishes across the wetland landscape. By collecting and analyzing movement data, we aim to develop a deeper understanding of survival, dispersal, and habitat use by these and other aquatic predators in the Everglades.
This research was funded by a cooperative agreement between the U. S. Geological Survey and FIU, under the CESI initiative (CA 1445-CA09-95-0112, Sub-agreement No. 1). Mention of specific manufacturers does not imply endorsement.
Lawrence, Wolski, Department. of Biological Sciences, Florida International University, University Park, Miami, FL 33199, Phone: 305-348-4032, Wolskil@fiu.edu, Ecology and Ecological Modeling