FWC Smalltooth Sawfish Research Project
Smalltooth sawfish research is being conducted by scientists with the FWC's Fish and Wildlife Research Institute.
Scientists with the Florida Fish and Wildlife Conservation Commission’s (FWC) Fish and Wildlife Research Institute are studying the smalltooth sawfish in state waters. The location of the current research project is southwest Florida, specifically in the Charlotte Harbor estuarine system.
Research and Monitoring of Smalltooth Sawfish in Charlotte Harbor
The study is funded by the National Oceanic and Atmospheric Administration’s (NOAA), National Marine Fisheries Service (NMFS), Southeast Region’s Office of Protected Resources and the National Fish and Wildlife Foundation.
There is a general lack of biological and ecological information on the endangered smalltooth sawfish. This fact makes assessment of recovery of this species difficult. As a result, the Florida Fish and Wildlife Conservation Commission (FWC) initiated a sampling program to collect needed data on this species. For research purposes, anglers and boaters are encouraged to call the sawfish hotline or e-mail the sawfish researchers to report any encounters they have had (see Report Sawfish Sightings link at bottom of page).
Reports from anglers who have encountered sawfish have indicated that the fish are regularly found in the Charlotte Harbor area. The purpose of this project is to monitor smalltooth sawfish in the Charlotte Harbor estuarine system and characterize habitat use, relative abundance (number of sawfish), juvenile recruitment (number of smalltooth sawfish born each year), and temporal and spatial distributions (seasonal movement and habitat) of the species. Depending on their size, captured sawfish may be fitted with several different tags: 1) bright yellow fin tags, 2) small, subdermal (below the skin) passive integrated transponder tags (similar to microchips used to identify pets), 3) acoustic tags, or 4) satellite tags.
Research Methods
Random Sampling
Monthly random sampling (to ensure broad sampling coverage of the study area) is conducted year-round using a large center-bag haul seine. The seine is deployed by boat, set in a rectangular shape along the shoreline, and retrieved by hand. A total of 27 hauls per month are conducted throughout the bay during routine monthly random sampling (eight of these are concentrated in the lower Caloosahatchee River). The lower Caloosahatchee River is an area where anglers have reported seeing and catching sawfish.
Directed sampling
Monthly directed sampling (specifically targeting smalltooth sawfish) is conducted year-round using a multi-gear approach. We conduct up to four directed sampling trips per month, primarily in the Caloosahatchee River. The type of gear for directed sampling varies depending on location, habitat, and season in order to optimize the likelihood of collecting smalltooth sawfish. Sampling gear includes the large haul seines described above as well as gill nets, smaller seines, and longlines. Gill nets are set primarily in creeks, canals, and embayments where haul seines are less effective. When water clarity is favorable, we actively search for sawfish and use both gill nets and seines to catch visually detected animals.
Sample processing
A variety of measurements are taken on all sawfish. They are examined for overall health (e.g., external surface condition, broken rostral teeth), and a fin clip is taken for DNA analysis. Photographs and video are used to document the health of the animals as well as the normal sawfish tagging, handling, and release procedures. The FWC has a special research permit issued by the federal government to conduct this type of sawfish research.
A variety of environmental variables are recorded with each sample. For example, location, time, salinity, water temperature, pH, dissolved oxygen, and water depth along the shoreline and at the bag of the net (if applicable) are recorded at each sampling site. Observations of shoreline inundation (or rising and spreading of the water), tidal level, and shoreline and bottom vegetation descriptions are also recorded.
Tagging
Captured sawfish are tagged with a variety of tag types and released at or near the site of capture. Rototags are printed with the FWC tagging hotline information on one side and a unique tag number on the other (Figure 1 top). Passive integrated transponder (PIT) tags are injected beneath the skin at the base of the first dorsal fin. These tags are about the size of a grain of rice and contain a uniquely numbered microchip that is detected by an electronic reader that is carried by researchers. Most sawfish are also tagged with acoustic tags (Figure 1 bottom). Acoustic tags are used to track sawfish movements. Other tags are used to report information such as water depth where the sawfish swim or report their locations using satellites. Anglers who encounter these tags are asked to call the sawfish hotline and report the information.
Fig. 1. Examples of tags applied to smalltooth sawfish:
(top) Rototag ® attached to the first dorsal fin,
(bottom) acoustic tag attached to the second dorsal fin.
Acoustic monitoring
To examine large scale movements of smalltooth sawfish in the Caloosahatchee River area, a system of 42 acoustic monitors is used in the main stem of the river (Figure 2a) and in a canal system adjacent to the river (Figure 2b). These “listening stations” are located from the mouth of the river to the Franklin Lock about 30 kilometers upstream. Researchers studying sawfish as well as other species such as bull sharks and snook maintain the listening stations. In late 2007, the listening stations were re-distributed in the lower portion of the river and will monitor more canals and creek systems adjacent to the river. The goal is to determine the extent of movements between the river and the adjacent habitats. Listening stations are set up to continuously record signals emitted by the acoustic tags that are attached to the sawfish. Each time a sawfish with an acoustic tag is within the detection range of a listening station, the station records the date, time, and tag number 24 hours a day.
Figure 2. a: Location of acoustic monitors in the main stem of the lower Caloosahatchee River, Florida (map courtesy Mote Marine Laboratory). b: Location of acoustic monitors in a canal
system near the Cape Coral Yacht Club.
Acoustic tracking
To examine small scale movements of smalltooth sawfish, we use a tracking receiver with omni-directional (can detect movements from all directions), and directional hydrophones. We follow individual sawfish from the boat after their release for 1–2 hours to determine short-term, post-release behaviors. We also follow some sawfish while wading if visibility permits. Each time an acoustic tag is within the detection range of the hydrophone, the receiver records information such as the location of the receiver, time, tag number, and signal strength.
Preliminary Results
Field sampling
Between November 2004 and December 2006, 55 sawfish were collected, including 13 recaptures. A variety of data were taken on all sawfish (e.g., lengths, rostral tooth counts or the number of teeth on the sawfish’s snout) and each animal was tagged and released. Sawfish have been captured in all months. Maximum total lengths ranged from 800 to 1,931 mm (mean = 1,438 mm) for males and from 690 to 2,120 mm (mean = 1,351 mm) for females (Figure 3); all of the male sawfish were immature based on clasper (male reproductive organ) shape and size as well as lack of calcification (calcium deposits in the cartilage).
Fig. 3. Length frequency of smalltooth sawfish collected between
November 2004 and December 2006. Recaptures are included.
Although extensive random sampling occurred throughout the estuarine system (598 Charlotte Harbor samples as part of normal FWC fisheries sampling; 208 Caloosahatchee River samples funded by sawfish grants), sawfish captures from all sampling techniques occurred primarily in three areas of the Caloosahatchee River: Iona Cove, Glover Bight, and the Cape Coral canals (Figure 4). Reports of sawfish encounters by anglers and boaters also indicate that these areas contain important sawfish habitats.
Figure 4. Directed sampling and capture sites in the
Caloosahatchee River (November 2004–December 2006)
Marine pollution and notable catches
Marine pollution has affected several sawfish encountered during our field sampling. One sawfish caught on March 29, 2005 had three types of monofilament fishing line, including one bead (“bobber stop”); braided fishing line; and part of a cotton trot line, including a 15.6 g (0.5 oz) lead egg sinker, wrapped around the entire length of the rostrum (Figure 5). These items were removed from this animal before it was released with the exception of a small amount of braided line that had become incorporated into the rostrum during the healing process. This sawfish was recaptured on June 2, 2006 and was well-healed. The only noticeable effect from the presence of the marine pollution was a curvature near the tip of the rostrum where the small amount of braided line had become incorporated prior to the original capture. The fish also had a missing rostral tooth. A sawfish caught on August 1, 2006 had evidence of being previously entangled by marine pollution (Figure 6). The overall effects that marine pollution has on sawfish are unknown, but should be monitored.
Other sawfish catches were notable. Several sawfish had recurved rostral teeth (Figure 7). The prevalence and possible function of recurved rostral teeth is unknown, but as more sawfish are captured (and recaptured) we may learn more about this phenomenon (e.g., genetic basis, relation to development). On April 17, 2006, a sawfish was caught with a parasitized clasper (Figure 8). To date, this is an unusual occurrence.
Figure 5. A 1.6 m (about 5 feet) smalltooth sawfish that was entangled
by a variety of marine pollution. This animal was caught in the Caloosahatchee
River in March 2005 and recaptured with well-healed
wounds in the same location in June 2006
Figure 6. A 1.1 m (about 3.5 feet) sawfish that had previously been
entangled by some form of marine pollution. Note the indentations
on the head (a: dorsal view; b: ventral view).
Figure 7. (a) 1.6 m (about 5 feet) female with typical rostral
teeth perpendicular to the axis of the rostrum, and (b) 1.7 m
(about 5.5 feet) female from the same sample with atypical curved rostral teeth.
Figure 8. Parasitized clasper of a 1.5 m (about 5 feet) sawfish
Through this monitoring effort, we are beginning to identify habitats and environmental variables that are important during the early life history of this endangered species. Most of the locations where sawfish were collected are characterized by mangrove shorelines, tidal creeks, and shallow non-seagrass covered sand flats—all of which are near deeper water. During the first two years of sampling, sawfish were only collected when the water temperature was at least about 19°C (66°F). This is approximately the temperature that triggers the movement of some sharks to offshore waters. More data are needed to support the hypothesis that smalltooth sawfish are behaving similarly; however, the absence of sawfish in our collections from October to January during the first two years of sampling suggest that this type of migration may occur, at least in some years. Sawfish were collected in a wide range of salinities and dissolved oxygen levels, but these factors may nevertheless be influencing the movement of smalltooth sawfish.
Acoustic monitoring and tracking
Between November 2004 and December 2006, 36 smalltooth sawfish were fitted with acoustic tags and were monitored in the Caloosahatchee River and an associated canal system with an array of listening stations dispersed along the river up to the Franklin Lock. The tagged sawfish typically stayed within the 9 km2 area of the lower river. Sawfish have been collected in salinities ranging from 3.2 to 29.8 percent salinity units (ocean water is 35 psu), but more data and analyses are needed to determine whether these animals are selecting a particular salinity range or whether other environmental factors are influencing their movement patterns to a greater extent. Acoustic monitoring of sawfish and analysis of movement data is an ongoing collaborative effort between scientists at FWC and Mote Marine Laboratory.
A subset of smalltooth sawfish have been tracked to assess short-term, post-release movements (see examples in Figure 9). Sawfish were tracked with acoustic tags from the boat for up to two hours or visually while wading for up to 20 minutes. The sawfish in Figure 9b moved along a path of ca. 0.83 miles and a straight line distance of 0.77 miles. The sawfish in Figure 9c moved along a path of ca. 0.59 miles and a straight line distance of 0.48 miles.
Figure 9. Examples of tracks where the sawfish moved from the
capture/release locations (b: female 5.5’, 11/15/06; c: male 5’, 12/1/06).
Post-hurricane sampling and assessment
On August 13, 2004, Hurricane Charley, a compact Category 4 storm, passed over the Charlotte Harbor estuarine system, including the Peace River area as it made landfall in Florida. Maximum-recorded wind speeds were in excess of 150 mph, and extensive damage to the environment occurred. Within about one month, the physical conditions of much of the aquatic area had recovered to pre-hurricane conditions, with the normal fish population returning. Above-water habitats such as fringing mangroves were damaged and will take many years to recover. Since the smalltooth sawfish is an endangered species and data from public encounters with sawfish in the region indicate that this is an area where smalltooth sawfish regularly occur, there were concerns that damage from the storm may have affected the ability of these habitats to support sawfish, and hence hindered recovery efforts.
Sampling techniques described above and encounter reports from the public were used to determine the effects of the hurricane on smalltooth sawfish. Prior to Hurricane Charley, a compact Category 4 storm that passed over the Charlotte Harbor study area, public and angler encounter report data revealed the presence of smalltooth sawfish in Florida from Charlotte Harbor to the Florida Keys. Encounter data collected after the storm were collected for comparison. These data indicate that the large scale distribution of sawfish remains unchanged and suggests that this hurricane had little if any long-term effects on the ability of smalltooth sawfish to reside in the areas most affected by the storm, including upper Charlotte Harbor (Figure 10).
The future
As mentioned above, this report summarizes some preliminary data from a year-round, ongoing long-term sampling program designed to collect data on the endangered smalltooth sawfish. Scientists with the FWC will continue their research from 2007 to 2009 with monies provided by the National Marine Fisheries Service/ National Oceanic and Atmospheric Administration, Southeast Region's Office of Protected Resources. Sampling for smalltooth sawfish in successive years in the Charlotte Harbor estuarine system will help determine whether tagged sawfish use the estuary for multiple years and if so, whether they are using the same habitats year after year. Multi-year sampling will also provide insight into which environmental variables influence the movements of this species.
Collaborations with scientists from other institutions exist (e.g., Mote Marine Laboratory, Rookery Bay National Estuarine Research Reserve, Pew Institute, Chicago Field Museum) and these relationships are important to ensure maximum protection and conservation of the species. For example, a collaborative analysis on growth rates of juvenile smalltooth sawfish was published recently (Simpfendorfer et al. 2008; see Selected Sawfish References link at bottom of page). Analyses of sawfish genetics are also being conducted in an effort to answer a variety of important questions which include overall population structure, genetic diversity, maternal philopatry (or a fish returning to a specific location to breed), multiple paternity, and passive integrated transponder (PIT) tag retention.
Figure 10. Sawfish encounter reports between 2002 and 2006 in the Charlotte Harbor area
(ca. 2.5 years before and after Hurricane Charley). Red line approximates the path of
the center of the eye of the storm.
Report Sawfish Sightings
Unless noted otherwise, all photographs are credited to G.R. Poulakis, Florida Fish and Wildlife Conservation Commission (FWC).
