Dolphins face risks of injury because they frequently approach sport fishing vessels and piers in Sarasota Bay, as well as at offshore reefs and coastal fishing piers along the Gulf coast. Interactions include scavenging of fish that are required to be released and depredation of caught fish from angler’s lines. We are studying tools to reduce interactions between dolphins and recreational anglers. Our tests focus on devices used by anglers to return live fish to depth and the application of a modest tackle enhancement called a Depredation Mitigation Device (DMD).
We evaluated two descender devices: one is a simple barbless hook that resembles a large bobby pin, called the Shelton Fish Descender® (SFD). The SFD is attached to a weighted line and the pin is inserted through the lip of a live fish, which is then lowered quickly down to depth and released with a tug on the descent line. The SFD is best suited for shallow water use with smaller size fish. Several other devices are commercially available that use a spring-loaded grip to hold the fish, the most practical of which is the Seaqualizer®. It grips the fish by the lip and will not release until reaching a preset depth. This device is best suited for offshore reef fishing in depths of 70-150 ft, where scavenging by dolphins is a common problem. We employ underwater cameras to observe the effectiveness of these fish releases near dolphins; one camera is mounted close to the device to view the fish descent/release, another is hung below the boat to capture a wide angle view of any dolphins that are attracted to the descended fish.
During April-May 2016, we conducted field trials in Sarasota Bay to test if SFD devices are practical around dolphins interacting with inshore anglers. A series of fish-release trials were conducted near dolphins that were known depredators. At each trial, we recorded dolphin identities, distance, movements, and whether animals appeared to respond to the fish descent. In total, 22% of 18 trials occurred while animals were actively patrolling, The SFD worked successfully on 50% of trials, but proved unreliable since fish often wiggled free at the surface or did not release as intended. The results suggest that a different type of device that securely holds the fish would be a better solution. We were somewhat encouraged by the fact that under most circumstances nearby dolphins were not attracted to released fish, but on one occasion a patrolling dolphin did chase a fish that came off at the surface.
Since 2014, we have tested Seaqualizer with over 30 sport fish released during the course of 16 deep-sea fishing trips at reefs offshore of Destin and Pensacola, FL. Dolphins only approached our boats on two trips, and we did not observe any interactions with them during the fish descents. We find the Seaqualizer easy to deploy and reliable. Testing will continue until a sufficient number of observations are made to determine effectiveness of using fish descents to reduce scavenging, and we are optimistic this method has great promise.
Part two of the project is to test a DMD prototype design. Prior studies showed that metal wires and chains attached near hooks on fishing tackle may decrease depredations, since metal is acoustically obvious to dolphin sonar and they avoid wires and hard fishing tackle. We created an inexpensive prototype affectionately called a “Porpoise Popper” that will release metal chains when pulled on suddenly. The device is placed just before the baited fishing hook, but does not “pop” until either a large fish takes the bait, or the hooked fish is grabbed by a larger animal. Once triggered, chains fall from the barrel and flail around the fish. Our testing suggests no difference exists in catch rate between normal hooks vs with a popper, and that the devices are easy to use and reload. Trials will continue until sufficient observations in the presence of dolphins are made to determine whether the poppers are effective, with a goal to distribute them to anglers and gather their feedback on the DMD performance and potential improvements. Sport anglers that have reviewed the prototype are very supportive of our concept.
In addition, we are conducting angler surveys on three shoreline fishing piers in Fort Walton Beach, Navarre, and Pensacola where dolphin interactions are commonly reported. We record their experience level, attitudes about dolphins around the piers, if they have encountered dolphins, and if they follow “Dolphin Friendly Fishing Tips.” The survey results will be used to guide future consideration if other tips can be added specific for Gulf pier fishing. Due to the frequency of dolphin interactions at these piers, we believe most anglers will eagerly welcome any type of approved mitigation device to reduce dolphin depredations.
In summary, we are encouraged that fish descending may discourage dolphin scavenging of discarded catch, and that a simple DMD prototype might be effective in reducing dolphin interactions with fishing lines. While no simple solutions exist to reduce dolphin-fishery interactions, we hope testing and promoting new device concepts will eventually produce valuable tools for sport fishing and dolphin conservation.
Assisting this project are Hannah Roth, Christina Toms, Courtney Nelson-Seely, and Gisele Nieman, along with a multitude of volunteer anglers and dolphin observers. We thank Chris Verlinde and Laura Tiu of Florida SeaGrant/IFAS for helping with fishing trips and devices. This study is funded by a grant from the Mississippi-Alabama Sea Grant Consortium and support from the Chicago Zoological Society.
This article appeared on pages 7-8 of the 2017 SDRP Annual Report, Nicks n Notches.