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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Investigating impacts of Hurricane Charley and red tide on dolphin abundance, reproductive rates, distribution, and residency in Charlotte Harbor and Pine Island Sound.

Do major ecological disturbances impact resident dolphin populations? The Sarasota Dolphin Research Program was in a unique position to evaluate this question as both Hurricane Charley in August 2004 and a severe red tide in 2005 impacted Charlotte Harbor and Pine Island Sound. These combined events may have affected habitat health, including prey fish availability, in ways that could have short or long-term implications for the bottlenose dolphins that use this estuary.

Mangrove damage from Hurricane Charley in August 2004 is still evident on Cayo Costa in March 2007, two and a half years later.

The SDRP has been working with the dolphin population in these areas since its start in 1970, with photographic identifications since 1982, and baseline data on dolphin abundance, reproductive rates, distribution, and site fidelity from intensive seasonal surveys immediately prior to the 2004 hurricane. Knowledge of the status of the dolphin population units inhabiting Charlotte Harbor and Pine Island Sound is important for protecting dolphin stocks in the area, and follow-up surveys would provide a unique opportunity to investigate the adaptability of these animals to large scale disturbances.

With funding from Harbor Branch Oceanographic Institution’s “Protect Wild Dolphins” program, we were able to conduct a comprehensive, multi-week, photographic-identification survey in Charlotte Harbor and Pine Island Sound in September 2006, at the same scale as our 2001-2003 September surveys. This allowed us to examine trends in abundance, distribution and reproductive rates pre-and post-Hurricane Charley. These surveys also allowed us to gather additional sighting information on distinctively marked individuals to examine long-term and seasonal site fidelity and reproductive status of females.

“SPKY” has been observed in Pine Island Sound 16 times between 1996 and 2007, both before and after Hurricane Charley.
“SPKY” has been observed in Pine Island Sound 16 times between 1996 and 2007, both before and after Hurricane Charley.

Hurricane Charley devastated the shoreline, terrestrial flora, and man-made structures along its path through Charlotte Harbor. However, two years later, and one year after a major red tide event, we found no indications of impacts on the resident dolphins. The 2006 abundance estimate was within 10% of the range of abundance estimates from previous years, by all measures. Similarly, reproductive rates were within the previously-documented range for the area. Of the 206 identifiable dolphins seen 10 or more times, 94% were found in the same region of Charlotte Harbor two years after the storm as before. The level of resilience documented for the Charlotte Harbor dolphins provides important perspective for evaluating the threats to dolphin populations from a variety of natural and anthropogenic sources. Many additional funding sources contributed to this project and the earlier surveys, including: Mote Scientific Foundation, the Chicago Zoological Society, Mote Marine Laboratory, NOAA’s Fisheries Service, Dolphin Biology Research Institute, and Earthwatch Institute.