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

Hannah Roth prepares to lower a reef fish
Hannah Roth prepares to lower a reef fish using a Seaqualizer recompression device equipped with an underwater camera

Our study is underway in the Florida Panhandle, designed to test if modifications to fishing techniques and gear can reduce adverse interactions between dolphins and recreational anglers. Anglers report that dolphins frequently remove bait and catch from their fishing gear, which can result in injury due to line entanglement and gear ingestion. In our past study, many dolphins were resighted frequently around fishing vessels over a two year period, and routinely scavenged on fish that sport anglers are required to release. This problem is common on offshore “deep-sea” fishing reefs near Destin, Pensacola, and Orange Beach, AL and it causes anglers to develop deep dislike of dolphins. Surveys we conducted in 2010-11 showed that the more experienced the fisherman, the more interest they have in finding ways to discourage dolphins from depredating (stealing bait and catch from lines) and scavenging their released fish. Our goal is to find promising and easily applied mitigation techniques, and then promote them for everyday use by the sport fishing community.

Studies in other locations have shown that stiff wires and streamers attached to fishing tackle may decrease dolphins’ interest to depredate hooked fish, and various fish release tools now available commercially may allow anglers to return discarded fish back to the reef with sufficient vigor to avoid being scavenged by dolphins. Starting in October 2014, we began testing the applicability and effectiveness of using tackle modifications and fish descender devices aboard charter fishing vessels on deep-sea reefs. We have spent the majority of our effort to date developing data collection protocols and easy-to-deploy remote camera setups for observing dolphins underneath the fishing vessels. By summer 2015, we took six charter fishing trips to collect data on fish release devices such as the Seaqualizer recompression tool. Our preliminary findings indicate that commonly caught reef fish that were discarded during the trips visibly regained vigor and appeared to have good survival odds once recompressed and released at a depth of 50 feet (15 m). We did not observe any dolphins approaching or scavenging discarded fish during those fishing trips but we will increase our observations through 2015 and the coming year.

red snapper being descended on a Seaqualizer device
Underwater image of a red snapper being descended on a Seaqualizer device, with depth in feet indicated on the dial.

In addition to offshore reef trips, we are working with students from the Navarre Marine Science Station on a survey project to solicit feedback from anglers on the Gulf fishing pier at Navarre Beach, billed as the longest on the Gulf coast, located between Destin and Pensacola. This new pier opened to anglers in summer of 2010 after a five year period of reconstruction with no fishing at this site, making it an ideal location to monitor changes in dolphin activity over time. By comparison, the piers at Destin and Pensacola Beach have well known dolphin interaction problems. We ask anglers about their experience level, if they have encountered dolphins, and if they are familiar with “Dolphin Friendly Fishing Tips” that are widely available to the local fishing community. The survey results may help determine if “Fishing Tips” can be more effectively applied in a Gulf pier fishing scenario.

A third component to the project will be to implement our approach at inshore fishing spots in Sarasota Bay. Dolphin interactions with sport fishing are well documented in this area and we will explore fishing tackle modifications to evaluate mitigation potential in the shallow inshore waters and inlets. The results of our project will benefit outreach efforts encouraging use of mitigation techniques that reduce dolphin interactions, and ultimately will enhance conservation of both dolphins and sport fish stocks.

We appreciate the assistance of Hannah Roth, Christina Toms, and Savannah Koontz, and Chris Verlinde of Florida SeaGrant/IFAS. Funding for this project is being provided by Mississippi-Alabama Sea Grant Consortium.

This article appeared on page 7-8 in the December 2015 issue of Nicks n Notches.

Dolphin Photo Identification Explained

Individual bottlenose dolphins can be identified by their dorsal fins. But how exactly is that done? And why bother?

A new report published by NOAA, with SDRP staff members Brian Balmer and Randy Wells as co-authors, explores the use of photo identification as a tool for making abundance estimates of inshore populations of bottlenose dolphins.

Abundance estimates are critical for dolphin stock assessments along the Atlantic Coast and the Northern Gulf of Mexico, because they inform management policy decisions.

You can’t manage the conservation a dolphin population unless you know how many dolphins there are. Right?

Using results from repeated photographic surveys from boats, scientists can estimate abundance with calculations comparing the identifiable dolphins with unknown dolphins.

We pioneered the use these techniques in the SDRP in1975-6, and the process undergoes continuing refinement.

The NOAA report, from a workshop attended by marine mammal experts, statisticians, and population biologists, sought to develop agreement on best practices for fieldwork, photo processing and analytical practices for estimating abundance.

For more information the report is available for downloading as a pdf, or from NOAA.


Rosel, P.E., K.D. Mullin, L. Garrison, L. Schwacke, J. Adams, B. Balmer, P. Conn, M.J. Conroy, T. Eguchi, A. Gorgone, A. Hohn, M. Mazzoil, C. Schwartz, C. Sinclair, T. Speakman, K. Urian, N. Vollmer, P. Wade, R. Wells and E. Zolman. 2011. Photo-identification Capture-Mark-Recapture Techniques for Estimating Abundance of Bay, Sound and Estuary Populations of Bottlenose Dolphins along the U.S. East Coast and Gulf of Mexico: A Workshop Report. NOAA Technical Memorandum NMFS-SEFSC-621. 30 p.


Dolphin Survey Update: 9 New Calves in 2011

To date, 9 calves have been born to Sarasota Bay resident dolphins, and 3 more to mothers seen frequently around the periphery of the Sarasota home range.

While these are encouraging numbers, calf mortality averages about 50% during their first year of life, so we’ll have to wait and see how well they do.

Happily, all but one of the 17 calves born in 2010 have been seen with their mothers in recent months.

The missing calf, C797, apparently died from fishing line entanglement injuries in June 2011.

Calves typically stay with their mothers 3-6 years. Data on calves are collected as part of our 10 dolphin surveys each month.




Deepwater Horizon Oil Spill: Natural Resource Damage Assessment (NRDA) of the St. Joseph Bay bottlenose dolphin community

By Brian Balmer, MS, PhD Student, Chicago Zoological Society and University of North Carolina Wilmington

In response to the Deepwater Horizon oil spill, we were contracted to perform a Natural Resource Damage Assessment (NRDA) on the St. Joseph Bay bottlenose dolphin community. The overall goals of the NRDA process, which is part of NOAA’s Damage Assessment, Remediation, and Restoration Program (DARRP), are to:

1) Identify the extent of resources that were damaged

2) Determine methods for resource restoration

3) Assess the amount of restoration required to bring the

resources back to levels pre-oil spill

Although it was uncertain if the Deepwater Horizon oil spill would reach St. Joseph Bay, the bottlenose dolphins in this region are one of the best-studied communities along the northern Gulf of Mexico coast. Since 2004, there have been two health assessments and follow-up radio tracking on 29 individuals, 103 remote biopsy samples collected, and 165 photo-identification surveys performed on the St. Joseph Bay bottlenose dolphin community, with a catalog of over 350 individuals. Thus, the bottlenose dolphins in St. Joseph Bay could provide insight into possible effects that the oil spill might have on other coastal bottlenose dolphin communities in the more affected regions of the northern Gulf coast.

“X23” with “X29” and calf
“X23” with “X29” and calf travelling past oil containment booms in Crooked Island Sound, along the northern Gulf coast of Florida.

The goals for this particular NRDA assessment were to monitor the St. Joseph Bay (and vicinity) bottlenose dolphins before, during, and after the oil spill. Specifically, remote biopsy samples from individual dolphins were to be collected and analyzed for contaminants before oil reached the region as well as if/when oil actually entered St. Joseph Bay. Seasonal abundance estimates utilizing mark-recapture, photo-identification surveys were to be performed during the same time periods as the above mentioned biopsy sampling, as well as an additional set of surveys planned for February 2011. The St. Joseph Bay research is part of a larger study by NOAA that includes similar efforts in Barataria Bay and Chandeluer Sound in Louisiana, and Mississippi Sound.

The “pre-oil” surveys for this assessment were conducted during 17 – 30 June 2010. During this survey effort, 21 remote biopsy samples were collected, and 123 distinctive dolphins were identified. In addition, 14 of the 29 individuals that were captured during health assessments in 2005 and 2006 were re-sighted, of which 6 females had new calves that had not been sighted until these surveys. No oil was observed in the region, but remediation efforts were apparent, with oil containment booms positioned along much of the coastline surrounding St. Joseph Bay. Abundance estimates are typically low during the summer and winter, with year-round residents (approximately 120 individuals) inhabiting the St. Joseph Bay region. During spring and fall, a two to three fold increase of animals is observed in which the majority of individuals are suspected to be seasonal residents or transients to St. Joseph Bay. Interestingly, the abundance estimates generated from these June 2010 surveys were much higher than expected and more similar to the spring and fall time periods when an influx of animals is observed in the region.

At the beginning of August 2010, when it was evident that the oil spill was not going to come into direct contact with the St. Joseph Bay region, the second round of remote biopsying and photo-identification surveys for NRDA was performed. During this survey effort, an additional 17 biopsy samples were obtained and 18 of the 29 individuals that were captured during previous health assessments were sighted. Although photo analysis is not complete for this portion of the project, preliminary data suggest that the abundance estimates for August 2010 will be similar to “typical” summer estimates in St. Joseph Bay, with a lower number of individuals sighted, primarily those with long-term residency patterns to the region. No oil was observed during this survey period and our field crew was able to observe the oil containment booms along the St. Joseph Bay coastline being removed by the hard working remediation crews; an encouraging sight to witness when just a few months earlier the ecosystem of St. Joseph Bay was under threat from the worst marine oil spill in history.

Funding for this research was provided by NOAA’s Damage Assessment, Remediation, and Restoration Program.

Sarasota Bay dolphin monitoring program

We have been able to continue our year-round monthly monitoring of the Sarasota dolphin community thanks to support from 15 Earthwatch Institute volunteers and NOAA’s Fisheries Service (NMFS). The Sarasota bottlenose dolphin community is one of the most thoroughly studied free-ranging dolphin populations in the world. We continue to address increasingly refined questions about the lives of these animals with the benefit of information gained through our intensive year-round studies of their distribution, social and reproductive patterns.

Some pleasure boaters get a surprise show from “FB 127,” March 2007.  It is important that boaters remember that they are a guest in the dolphins’ home and safely admire them from a distance of at least fifty yards
Some pleasure boaters get a surprise show from “FB 127,” March 2007. It is important that boaters remember that they are a guest in the dolphins’ home and safely admire them from a distance of at least fifty yards
Three generations together, May 2007. “Scooter” and her yearling swim toward “Scooter’s” mother, “FB 79.”
Three generations together, May 2007. “Scooter” and her yearling swim toward “Scooter’s” mother, “FB 79.”

Photo-identification surveys were conducted on 117 days from November 2006 through October 2007 with the assistance of Earthwatch volunteers and undergraduate interns. These volunteers contributed over 2,500 hours to our project. We had 813 group sightings that totaled 2,459 dolphins (including resighted animals). Monthly values varied (Figure 1), but overall we averaged about seven sightings and 21 dolphins per day. These values have remained fairly consistent over the past several years. We had a high of 20 sightings with 56 dolphins on 25 October 2007, the last survey day during this time period.

“Casper” catches a mullet, March 2007.
“Casper” catches a mullet, March 2007.

We documented 11 newborn calves during the spring/summer of 2007. “Lightning” and “Killer” both had their seventh calves, “FB 79” her sixth, and “Tramp” her fourth. Other 2007 mothers included “FB 55”, “Lizzie”, “Annie”, “ Big Shout”, “C99-1” and “Hawk”. “ Annie’s” calf, her second, is a fifth generation resident of Sarasota Bay. Its great-great-grandmother (“Cathy”) is still seen in Sarasota Bay almost every month. Unfortunately, “Lightning”, “Killer”, “Lizzie” and “Square Notch’s” calves have not survived. During 2007, carcasses were recovered for three other dolphins with sightings and medical histories: “Remo”, “Beaker”, and “F230”. Of these, “Beaker” was not considered to be a resident of Sarasota Bay due to an extensive sighting history to the south, and “Remo” had emigrated to waters near St. Petersburg several years ago. In addition, “F201”, a yearling seen frequently in southern Sarasota Bay during December 2006 – January 2007, was rescued, treated for severe monofilament injuries, and tracked following release, but was only seen for about one month following release.

“Annie” surfacing with her second calf less than two weeks after it was born, July 2007
“Annie” surfacing with her second calf less than two weeks after it was born, July 2007

Through our Earthwatch and NMFS-sponsored surveys, we have accounted for 145 recognizable dolphins using Sarasota Bay on a regular basis. Another 17 dolphins seen in 2006 were not seen in 2007; if they are not seen in 2008, they will be scored as permanent disappearances, which could include death, emigration, or changes to identifying features. Thus, 90% of the expected residents were found during 2007 surveys.

We would like to thank all of our Earthwatch Institute volunteers for their interest in, and support of, the Sarasota Dolphin Research Program over the past 26 years. The August 2007 team was our final team through the Earthwatch program.

Table 1: Births, additions, deaths, and disappearances of well-known dolphins from Sarasota Bay and vicinity over the past year.
Table 1: Births, additions, deaths, and disappearances of well-known dolphins from Sarasota Bay and vicinity over the past year.

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