Long-term trends in a coastal northern Gulf of Mexico bottlenose dolphin population in the wake of the Deepwater Horizon oil spill

The Deepwater Horizon blowout and oil spill began on 20 April 2010 and resulted in the largest oil spill in the history of the U.S., contaminating approximately 800 kilometers of coastline and nearshore waters along the northern Gulf of Mexico, including Louisiana, Mississippi, Alabama, and the Florida panhandle.  The oil spill was an additional stressor to bottlenose dolphins in a region that had already been impacted by a series of four Unusual Mortality Events (UMEs) since 1999.  Studies to assess the potential impacts to bottlenose dolphins in the Northern Gulf were initiated as part of the Deepwater Horizon Natural Resource Damage Assessment, which included photo-identification surveys to estimate abundance for three estuarine dolphin stocks in the region.

One of these study sites was St. Joseph Bay, along Florida’s northern Gulf of Mexico coastline. St. Joseph Bay was impacted by three prior UMEs, and was the geographic focus of the 2004 UME in which more than 100 dolphins stranded during March and April.  Since 2004, SDRP researchers have led and/or been involved with multiple projects (health assessments, photo-identification, remote biopsy sampling, and telemetry) focusing on the health and population structure of dolphins within this region.  The results of these studies have provided insight into abundance and distribution patterns, identified baseline concentrations of persistent chemical pollutants, and established health parameters for dolphins in the St. Joseph Bay area.  Photo-identification surveys conducted during the summer of 2010, when oil was still gushing from the Deepwater Horizon wellhead, identified the highest abundance, greatest number of new individuals sighted, and highest coastal dolphin density for any season surveyed in the St. Joseph Bay region since 2004.  Prior to 2010, an influx of coastal dolphins into the region had been observed during the spring and fall, with summer abundance typically lower and primarily consisting of resident dolphins that remained in St. Joseph Bay throughout the year.

Ultimately, significant oiling from the Deepwater Horizon oil spill was not observed along the St. Joseph Bay coastline.  However, the bottlenose dolphins in this region are one of the best-studied groups in the Northern Gulf and much was learned by assessing their status during the months following the Deepwater Horizon spill.  The presence of oil in nearshore waters west of St. Joseph Bay as well as in offshore waters may have prompted temporary movement of dolphins from oiled sites to those that had less oiling.  Comparisons of dolphins sighted during the summer of 2010 to other photo-identification catalogs along the Northern Gulf are necessary to determine if individuals sighted during these surveys were from other sites, and to track potential shifts in ranges as ecological conditions change.

This material is based upon work supported by BP and NOAA.  Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of BP and/or state or federal natural resource trustees.


This article was published on pages 6-7 in the January 2013 Nicks n Notches.


The SDRP Turns 43; Dolphin Surveys Continue

The Sarasota Dolphin Research Program entered its 43rd year in October, 2012.

Regular monthly photo-identification dolphin surveys continue in Sarasota Bay. We complete 10 surveys per month, and these records form the backbone of our data on the behavioral ecology of bottlenose dolphins.

After each 4-8 hour boat survey, the team logs the sighting data, including data sheets and photographs.  And during spare moments later, they spend lots and lots of time looking at photos of dorsal fins trying to make or verify dolphin identifications.

Our photo identification catalog currently includes over 7,500 images, including over 4,800 distinct individual dolphins (alive and dead), plus some of their calves (young animals are often not individually distinctive).

More than 480,000 dolphin photographs from 1970 to the present are currently archived by the SDRP.  They have been collected during more than 41,000 dolphin group sightings.

The sighting database with the photographic records has more than 113,000 sightings of identifiable dolphins.  Some individuals have been identified more than 1,400 times, and a few have only been seen once.

 Read more at: http://sarasotadolphin.org/what-we-do/surveys/


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A Gulf-wide photographic identification catalog for bottlenose dolphins

The Deepwater Horizon oil spill and several Unusual Mortality Events (UMEs) in the Gulf of Mexico have shown that knowledge of bottlenose dolphins in much of the Gulf is insufficient to meet the mandates of the federal Marine Mammal Protection Act.

In much of the Gulf, stock boundaries have been assigned arbitrarily based on geography rather than on dolphin biology.

Abundance estimates for putative stocks are out of date for most of the Gulf and are unusable for stock assessments. These problems have precluded assessment of the impacts of large scale environmental or mortality events, and inadequate baselines exist for accurately evaluating recovery.

Research Assistant Carolyn Cush
Research Assistant Carolyn Cush performing photo-identification analyses.

With a pledge of 3-years of support from the Disney Worldwide Conservation Fund, we are developing a long-term, broad scale conservation tool to begin rectifying these issues and to meet the urgent need to monitor dolphins following the oil spill.

We are compiling a Gulf-wide photographic identification catalog involving contributing researchers from Texas to Key West. Photo-identification of individual dolphins allows for abundance estimation and provides opportunities to determine residency and transience. By accurately assigning specific individuals to specific areas, biologically based stocks can be defined, and exposures to threats can be evaluated. Had these kinds of efforts occurred before the oil spill and UMEs, it might have been possible to evaluate which specific stocks were impacted, to what extent, and to focus resources for monitoring recovery.

In response to the oil spill, increased bottlenose dolphin photographic identification efforts are underway along much of the northern Gulf of Mexico coastline (including and in addition to the efforts described elsewhere in this newsletter).

While it is too late to develop pre-spill baselines, it is worthwhile to establish current patterns of residency and abundance and to begin to look for movements of individuals outside of the oil-impacted area as ecological effects of the spill may begin to occur.

To detect larger-scale individual movements between the study areas of different investigators, a central clearinghouse for identification photographs and associated meta-data will be helpful.

In addition to developing and maintaining a Gulf-wide bottlenose dolphin photographic identification catalog, we will implement an updated and standardized database system for dolphin sighting data and identification images to facilitate data sharing. This database will be based on the Finbase system developed and currently maintained by NOAA.

Photographic identification leads to the compilation of individual animal histories. As another goal of the project, we plan to apply the histories of “real dolphins” to develop “dolphin stories” that can exemplify aspects of their biology and conservation issues and to disseminate these stories to elementary schools and the general public.


2011 International Training Perspective

I have been very lucky to participate once again in the Sarasota Dolphin Research Program, but this time working on my senior thesis, which will allow me to get my degree when I go back to Argentina.

Yamila Rodriguez returning
Yamila Rodriguez returning from a hard day of purse seining.

I’ve always been attracted to how a simple algal cell could cause such a big change in the ecosystem. This is one of the reasons that I have focused my research on investigating how severe red tide blooms (caused by the toxic dinoflagellate Karenia brevis) affect the activity patterns and group size of the local dolphin community.

In order to study this, I used the data from regular  photo-identification surveys conducted for the SDRP during the 2000-2009 period in Sarasota Bay.

After the analysis I found that the activity patterns of Sarasota dolphins show changes during severe red tide events that mirror recent findings which focused on juvenile dolphins during a shorter time period.

More specifically, foraging activity decreased, which might be related to changes in fish abundance and community structure.

I also noticed an increase in social activity and group size during the red tide years, perhaps related to a shift in their diet which maybe requires different foraging strategies.

Finally, I observed that the dolphins’ interaction with boats became higher in those years with K. brevis blooms. This suggests that some animals may turn to anglers and boaters as a potential source of food or that they may bow or wake ride to save energy.

In conclusion, these results indicate that several red tide events have induced changes in the activity patterns of bottlenose dolphins over that time, showing that this species can change their habitual routine to adapt to the new conditions that K. brevis induces.

I’m very grateful for all the help I have received from my advisor Randall Wells and the SDRP’s dedicated staff. Without their support my thesis wouldn’t be possible.

Working with the SDRP has been a wonderful opportunity for me to learn from the best, and I’m certain that all the knowledge and skills that I have acquired are going to be very helpful in this magical career for which I’m just beginning.


Field and laboratory methods available on-line

The 2006 SDRP “Manual for Field Research and Laboratory Activities,”  is available as a downloadable pdf file.

This 62-page document provides detailed documentation of our protocols used for field operations and data processing. It includes chapters on:

1) Field survey protocols,

2) Post-survey lab protocols,

3) Photo-identification protocols,

4) Database entry, verification, and management, and

5) Operations protocols.

The accessibility of these protocols to colleagues and students promotes and facilitates standardization of methodologies across research sites.  The manual provides incoming students and interns with background materials prior to their arrival.

This is considered to be a “living document” that will be constantly evolving as we improve and refine our approaches.