Human-related Impacts to Manatees
Manatee Entanglement/Ingestion Impacts – Keep fishing line and other debris out of the waterways!
Humans, for whatever reason and for many years, have either accidentally dropped, intentionally discarded or gleefully thrown items into water. Accidentally or intentionally introduced into rivers, bays or oceans, human-generated trash becomes marine debris, which can be a big problem for aquatic wildlife and habitats. Entanglement in and ingestion of marine debris by marine life can be fatal, and manatees are no exception.
- For example, discarded plastic packing straps or even bicycle tires can encircle an animal’s body and, if not removed from the animal, will imbed into flesh as the animal grows.
- Shredding fishing line from reels when returning to the marina or throwing a “bird’s nest” of snarled fishing line overboard not only creates problems for wildlife that swim into this mess, it may even impact other boaters (prop damage), divers and others recreating on or in the water who may also get entangled in the line.
- Some manatees unintentionally wrap their flippers with fishing line and lines from anchors or crab trap buoys. Manatees seem to be intrigued with items in their environment and often explore these items with their flippers or mouths. Their sense of touch or innate curiosity often gets manatees into trouble when the exploration leads to swallowing the object or when the animal is unable to remove the entangled item. The loss of a flipper or flippers is possible if the entangled animal is not discovered in time. Experienced rescuers are often able to remove the entanglement and either release the animal or send it to a rehabilitation facility to recover.
- Monofilament fishing line and other plastics (bags, deflated balloons, etc.) can drift into seagrass beds or snag onto floating vegetation—a sure path to a slow death if a manatee ingests any of these items and is not able to pass it through its digestive system (manatee intestines are over 100 feet long!). During necropsies, monofilament fishing line is the most common foreign object discovered in manatee digestive systems.
According to researchers, in over 6,500 manatee necropsy reports from a 20-year dataset (1993 to 2012), over 11% of the animals that died either ingested or showed evidence of entanglement in marine debris (or both). (Reinert, et al. 2017)
Rehabilitated manatees that survive these entanglements often develop scar tissue at the site where the entanglement occurred. Like scars received from boat propellers, these entanglement scars aid researchers in identifying individual animals as some manatees become entangled in similar ways more than once. Researchers think that the scarring and mutilations make the animal more susceptible to snagging items, which increases their chances for future entanglements.
How to identify a Crab Trap Buoy from a Manatee Research Tag:
People sometimes confuse crab trap buoys and research tags. Please look closely at these images or on the research link to learn how to identify the differences. The crab trap buoy is a small, usually round, Styrofoam float that has a line attached to a crab trap. The braided polyethylene line will show knots and the buoy will have numbers pressed into the float. While a manatee will still be able to travel with the entangled crab trap, the weight of the crab trap can cause self-amputation of a manatee’s flipper(s) if it is not removed. Contact FWC via the Wildlife Alert Hotline if you see movement of a small buoy and a manatee nearby.
The research tag has a small rigid antenna that protrudes out of the top of a floating housing unit that contains a GPS unit, and satellite and radio transmitters. The multi-colored tag is attached to a flexible tether that is then attached to a belt secured around the manatee’s tail (peduncle). The tether is built with safety features, called weak links, which will break if the tag gets stuck during the animal’s travels. The animal is able to move freely without the tag unit affecting its behavior. Researchers are interested in manatee behavior and encourage you to call the Wildlife Alert Hotline with information about any tagged manatees you see: Manatee Radiotelemetry and Tracking.
Note: Please do not touch or attempt to remove the crab trap or the research tag. Take a picture, if possible, and contact FWC with information about your sighting and the location of the animal.
You can help
Whenever you are out on the water or near any of Florida’s waterbodies:
- Secure items on your vessel or in your recreation area that may blow into the water.
- Bring a container with a lid to store plastic bags or used fishing line (e.g., tennis ball canister or coffee can).
- Collect any plastic items or fishing line you see.
- If you see an entangled manatee or one that may be towing a small buoy, please contact FWC via the Wildlife Alert Hotline 1-888-404-3922.
Most plastic can be recycled. Fishing line can be recycled, too. Look for the large white PVC tubes to put your fishing line in and take other plastic items home to your recycle bins or to community collection centers. Recycled fishing line is made into tackle boxes and fish habitat structures
Thank you for protecting Florida’s fish and wildlife resources.
Links for References and Information:
Entanglement in and Ingestion of Fishing Gear and other Marine Debris by Florida Manatees, 1993-2012, “Manatee Interactions with Marine Debris” Thomas R. Reinert, Ann C. Spellman, Brandon L. Bassett, 2017