Testing tackle modifications and fish descender tools for reducing dolphin depredation and scavenging of sport fish

End Date: 09/30/16

Steve Shippee of Emerald Coast Wildlife Refuge and Reandall Wells and Katie McHugh, both of Mote Marine Lab, will test mitigation devices to see if they deter dolphins from depredating on rod and reel fishing gear or from scavenging discarded fish. The team will evaluate practical use of the gear in offshore sport-fishing and inshore fishing. Tackle on the end of the fishing line (terminal tackle) and descender tools (used to help fish return to deep water) will be tested. The team will also collect observational data on dolphin behavior and how often the marine mammals interact with anglers. These observations will help characterize the nature of depredation and scavenging of rod-and-reel fisheries. 


Bottlenose dolphins interact frequently with recreational fishing at offshore reefs in the northern Gulf of Mexico, resulting in potential harm to the animals and to fish stocks. Anglers complain that dolphins approach fishing vessels on offshore reefs as a reliable source of food, depredating fish off hooks being reeled up from depth, and scavenging on fish they are required to discard. Several depredation mitigation devices (DMDs) designed for attachment to terminal fishing tackle have been suggested as deterrents to discourage dolphins from taking hooked fish. Descender tools may offer a means to reduce dolphins’ scavenging on discarded fish that are being returned to the seafloor. We propose to test the applicability and effectiveness of using these devices aboard recreational fishing vessels as a means to reduce dolphin interactions that might have long-term effectiveness if accepted by the sport angler.

This study will evaluate:

  1. DMDs (wires, shrouds, etc. attached to fishing tackle) to deter depredation;
  2. effectiveness of fish descender tools to reduce dolphin scavenging of released fish;
  3. applicability of using such devices in inshore fishing to alleviate dolphin interactions; and
  4. acceptability of using these tools by sport anglers. In addition, we propose to further characterize the nature of dolphin interactions with recreational fishing.

We will partner with sport anglers in Destin, Florida, and Orange Beach, Alabama, to conduct testing on deep-sea Gulf reefs. The Sarasota Bay dolphin community will be a resource for experiments to improve fishing tackle modifications to evaluate mitigation potential over time. Underwater video will be used to observe the success of DMDs to mitigate depredation, and fish descender tools for reducing scavenging. DMD effectiveness will also be measured through observation of fish landing success. We propose to enlist recreational anglers in the later stages of testing to evaluate mitigation device acceptability. The results of this study will benefit resource managers conducting outreach to encourage use of mitigation techniques that reduce dolphin interactions and enhance conservation of both dolphins and reef fish stocks. 


  1. To determine the success of terminal tackle modifications with Depredation Mitigation Devices (DMDs) for reducing dolphin depredation of hooked fish.
  2. To determine the success of descender tools to reduce dolphin scavenging on discarded sport fish.
  3. To refine methods, improve device performance, and test applicability in inshore fishing situations.
  4. To evaluate the acceptability of using fish descenders and DMDs by sport fishing patrons, if these prove to be effective in reducing scavenging and depredation.
  5. To consider suggestions and test alternative methods that might be proposed by sport anglers, captains, and crewmates that will participate in this study.
  6. Further characterize the nature of dolphin depredation and scavenging from rod and reel fisheries, by building on past and ongoing work off the Florida panhandle and in Sarasota Bay as funded previously by MASGC, and monitor long-term trends.


We intend to measure incidences of dolphin interactions with hook and line fishing gear during deep-sea and inshore fishing trips.

  1. We will test device modifications designed to reduce dolphin depredation of the gear and scavenging of discarded fish
  2. Experimental trials in the presence of free-ranging dolphins will test mitigation device effectiveness
  3. Observation of dolphin interactions with typical fishing activity will serve as a control
  4. Video cameras will be used to acquire underwater images of the DMDs and the fish descenders
  5. Observation of dolphins at the surface around the boat will characterize whether use of DMDs and descender rigs changes their behavior compared to other times
  6. Refinement and testing of these and additional modifications will be conducted in Sarasota Bay with known dolphin communities that engage in fishery interactions
  7. Sport anglers will be surveyed on their enjoyment or dissatisfaction of using these methods on fishing trips
  8. Angler input will guide improvements to gear designs and techniques


This project will study the effectiveness and applicability of fishing tackle modifications and fish release devices to reduce the incidences of bottlenose dolphins interacting with recreational fishing along the Gulf Coast. Several mitigation devices intended for bottom fishing rigs will be evaluated as deterrents to depredation, and descender tools will be tested as a means to reduce scavenging of released fish by dolphins. Acceptability of these devices for use by sport anglers will be assessed. The results of this study will benefit resource managers conducting outreach to encourage use of mitigation techniques that reduce dolphin interactions and enhance conservation of both dolphins and reef fish stocks.


Final Technical Report

Interactions between bottlenose dolphins (Tursiops truncatus) with recreational fishing at offshore reefs and in estuaries can be harmful to the animals, and cause angler complaints that dolphins use fishing vessels as a source of food by depredating catch from their hooks and scavenging on the fish they are required to discard. Our project explored methods to reduce dolphin interactions on offshore reefs and inshore areas where dolphins interfere with sport fishing.

We evaluated if fish descenders could be used to discard fish back to depth without dolphins scavenging them, and tested prototype Dolphin Mitigation Devices (DMDs) designed to discourage dolphins from taking fish off hook and line. During 19 fishing trips to offshore reef sites near Destin, Florida, 66 fish releases using pressure-activated descenders were video recorded to observe if fish were able to evade being scavenged. Dolphins were observed around the vessels on 5 occasions, with no interactions noted with descender-released fish.

Testing of fish descenders during inshore catch-and-release fishing in Sarasota Bay were inconclusive, although dolphins typically were not attracted to descender devices during our trials. Prototype DMDs attached to hook and line tackle used by reef anglers showed no difference between fish landing success of treated hooks compared to untreated hooks, and no depredations of DMD rigs were observed.

Creel surveys conducted with 220 anglers at three Gulf fishing piers showed general adherence to recommended tips for “dolphin friendly fishing,” although angler dislike of dolphins directly correlated with fishing experience. Pier anglers expressed interest in our DMD concepts, leading to a modified design specifically for use at coastal piers. Continued outreach and promotion of simple mitigation methods can encourage recreational anglers to adopt fishing strategies that reduce the frequency of dolphin interactions. This project included 48 coastal and inshore photo-identification surveys to monitor human-dolphin interactions, and recorded survival progress of two young dolphins that were entangled in fishing gear.