Bottlenose dolphins interact frequently with recreational fishing, resulting in potential harm to the animals and to fish stocks.
Our current study is designed to test if modifications to fishing techniques and gear can reduce these adverse interactions.
Some dolphins have become skilled at taking fish directly off hook and line gear while an angler is trying to reel in their catch, which can lead to line entanglement or gear ingestion. Secondly, dolphins scavenge on fish that sport anglers are required to release, which may result in dolphins engaging in this activity as an alternate form of foraging, and which also defeats the purpose of discarding fish to recover depressed stocks. Both types of interaction can cause dolphin injury and deaths.
Studies have shown that stiff wires and streamers attached to fishing tackle could decrease depredation of hooked fish, and coined the term Depredation Mitigation Devices (DMDs). Descender tools have recently become a focus area in fisheries research for recompressing fish suffering from barotrauma, which is caused by the sudden change in pressure as a reef fish is quickly reeled up from depth. By rapidly lowering a caught fish back to depth using a descender on a weighted line, an angler is able to improve fish survival by alleviating barotrauma, while potentially decreasing the opportunity for dolphins to chase down these compromised fish. A number of devices are now available for purchase in tackle stores and outdoor suppliers, such as the Seaqualizer and Shelton Fish Descender, yet their broad public acceptance as essential fishing tools remains to develop. We will be testing the applicability and effectiveness of using these devices aboard recreational fishing vessels as a means to reduce dolphin interactions, which will have long-term benefits if accepted by the sport angler.
Our study will evaluate: 1) use of DMDs attached to fishing tackle to deter depredation; 2) the effectiveness of fish descender tools to reduce dolphin scavenging of released fish; 3) application of using such devices in inshore fishing to alleviate dolphin interactions; and 4) practicality of using these tools by sport anglers. In addition, we will build on our previous study to further characterize the nature of dolphin interactions with recreational fishing using photo-ID and mark recapture methods.
A necessary element in conducting this research will be to collect data in the presence of dolphins that predictably engage in fishing interactions. To accomplish this, we are collaborating with charter captains that can identify hot spots where dolphin interaction problems are common at deep-sea Gulf reefs near Destin, FL and Orange Beach, AL. The Sarasota Bay dolphin community will be the site for experiments to improve fishing tackle modifications to evaluate mitigation potential over time. Underwater video will be used to record the success of DMDs to discourage depredation and descender tools for reducing scavenging. DMD effectiveness will also be measured through observation of fish landing success. Recreational anglers will be enlisted in the later stages of testing to evaluate mitigation device acceptability aboard typical for-hire reef fishing trips. We anticipate that improvements to the devices and techniques will evolve as anglers are given the opportunity to assist with the study and provide feedback. The results of this project will benefit resource managers conducting outreach to encourage use of mitigation techniques that reduce dolphin interactions, and ultimately will enhance conservation of both dolphins and reef fish stocks. This study is funded by a grant from the Mississippi-Alabama Sea Grant Consortium and support from the Chicago Zoological Society.
This article was published on page 6-7 in the November 2014 issue of Nicks n Notches