Smalltooth Sawfish Research in Southwest Florida
Sawfish are modified rays with a shark-like body. Sawfish get their name from their “saws”, which are used for defense and to locate, stun, and kill prey; mostly fish. The earliest sawfish arose about 200 million years ago. These sawfish were distant cousins of the ones we see today which appeared about 65 million years ago. At one time sawfish were abundant; however, they have experienced significant declines due to decades of unintentional overfishing, mostly the result of entanglements in fishing gear. Sawfish saws (scientifically called rostrums) have also been popular trophy items, but when they’re removed, they don’t grow back and sawfish are unable to feed normally or defend themselves. Today, all sawfish species (five) are endangered, including the smalltooth sawfish which occurs in our area. The smalltooth sawfish historically ranged from around North Carolina to central Brazil, and along the western coast of Africa. Now, smalltooth sawfish are only found in south and southwest Florida, and the Bahamas. With few remaining, it is important to learn about their life history, biology, and ecology so that conservation efforts will be successful.
In Southwest Florida, smalltooth sawfish research began in the early 2000s with most research efforts focused in the Caloosahatchee and Peace rivers; research data and angler observations indicate these areas still support juvenile sawfish. Last month I accompanied FWC-Fish and Wildlife Research Institute (FWRI) researchers on a directed sawfish trip in the Caloosahatchee River. FWRI’s sawfish research includes both random and directed sampling using a variety of net gear. We sampled in areas where anglers and shore observers had reported sawfish sightings (hence directed sampling).Sampling involved deploying a net and letting it soak for one hour. We had to check the net whenever anyone saw movement or after a half hour, whichever came first. Our first set resulted in nothing. We then cruised the shoreline looking for sawfish before setting a second net. We thought we were skunked a second time but finally at the end of our set, we got a sawfish!
When FWRI catches a sawfish they do a quick health assessment before the animal is tagged and released. Tagged and released sawfish have been between about two feet (newborn) and seven feet long, including the saw. FWRI researchers use three primary types of tags on each captured sawfish. The first is a PIT tag. This is similar to the tags that are put in dogs and cats. It’s injected under the skin and is about the size of a grain of rice. The tag is picked up by researchers during recapture using a scanning device. These tags are the most permanent of the three. The second tag is a roto tag. This tag is brightly colored with identification numbers and contact information on it. These tags, located on the 1st dorsal fin, are used for angler reports. Reporting information is at the end of this article. The last tag is an acoustic tag. These small tags are located on the 2nd dorsal fin. Acoustic tags transmit at a specific frequency to a series of moored hydrophones that record activity 24 hours a day. The information obtained using this method provides a general picture of sawfish movement patterns. The sawfish we caught on my trip was a baby male estimated to be between two weeks and a month in age. He is now sporting all three of the tags mentioned. Hopefully he will provide many years of valuable information to scientists.
Although scientists still have much to learn about smalltooth sawfish, they do know that adult females generally reproduce every other year and that they return to the same nurseries to give birth. Babies are born in the spring and grow very fast, doubling their length in one year. Juvenile sawfish stay in the estuary for 2-3 years before heading offshore; and at this age they are about seven feet long. In southwest Florida, scientists have identified sawfish hotspots within the Peace and Caloosahatchee rivers and core use areas within these hotspots. Understanding where these areas are and knowing how and why sawfish use them is essential for the long term survival of this species. Other important research findings to date include quantifying movement patterns based on salinity and flow, particularly in the Caloosahatchee, understanding temperature and dissolved oxygen thresholds, prey preferences, and patterns of habitat use particularly as it relates to early juvenile growth.
Smalltooth sawfish are listed as endangered under the Endangered Species Act, which makes it illegal to harm, harass, or handle them. If you happen to catch a sawfish while fishing for other species, keep it in the water at all times. If you can do so safely, untangle any line that is wrapped around the saw and remove as much line as possible. Cut the line as close to the hook as possible then immediately release the sawfish.
If you do see or catch a sawfish, you can help conservation efforts greatly by reporting your encounter to: firstname.lastname@example.org, (941) 255-7403.
Notice to Recreational and Commercial Fishers Sign. Sawfish safe release guidelines.
Poulakis, G.R. 2016. Personal Communication.
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