Interim Report 

on the 

Bottlenose Dolphin (Tursiops truncatus) 

Unusual Mortality Event 

Along the Panhandle of Florida 

March-April 2004

 
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

TABLE OF CONTENTS 

I. Executive Summary 

II. Introduction 

A. Unusual Mortality Event (UME) Program and the Working Group on 

Marine Mammal Unusual Mortality Events 

B. Historic UMEs in the Gulf of Mexico and Florida Panhandle 

C. Historical Knowledge of Bottlenose Dolphin Populations and 

Strandings Along the Florida Panhandle 

III. Methods and Results 

A. Dolphin Sampling 

1. Gross Necropsy Findings 

2. Stomach Content Analyses 

3. Virology 

4. Histopathology 

5. Organochlorines 

6. Biotoxins 

7. Genetic Analyses 

B. Environmental Sampling 

1. Satellite Imagery 

2. Harmful Algal Bloom (HAB) Monitoring and Toxin 

Analyses 

3. Mortality Reports in Addition to Dolphins 

4. Shellfish Monitoring for Harmful Algal Bloom Species 

IV. Discussion and Future Plans 

A. Comparison with Other UMEs 

B. Insights into Dolphin Behavior and Feeding in the Florida Panhandle 

C. Continuing Studies 

D. Future Studies 

E. Evaluation of UME Response 

V. Acknowledgements 

VI. References 

VII. Tables and Figures 

VIII. Appendices 

A. Criteria for Determining an Unusual Mortality Event 

B. Fact Sheet on Brevetoxin and Red Tide 

C. Fact Sheet on Domoic Acid 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

I. EXECUTIVE SUMMARY 

This interim report outlines the initial findings and the ongoing analyses in the 

investigation of the bottlenose dolphin (Tursiops truncatus) mortality event that began in 

March 2004. One hundred and seven (107) bottlenose dolphins stranded dead along the 

Florida Panhandle between March 10 and April 13, 2004. Hundreds of dead fish and 

marine invertebrates were also discovered in the area. The National Marine Fisheries 

Service formally declared the dolphin deaths an “Unusual Mortality Event” (UME) after 

consulting with the Working Group on Marine Mammal Unusual Mortality Events. A 

multi-agency investigation was initiated and is being conducted by federal and state 

marine wildlife officials working in partnership with private research organizations and 

universities. 

Analyses conducted to date found brevetoxins (see Appendix B), naturally occurring 

neurotoxins produced by Karenia brevis, the Florida red tide, at high levels in the 

stomach contents of all dolphins examined to date and at variable levels in the tissues of 

these animals. Metabolite concentrations in tissues of fish or dolphins are not yet 

completed. The concentrations of brevetoxins observed in the analyzed subsample of the 

stomach contents are greater than or equal to those observed in previous marine mammal 

mortality events associated with Florida red tides (Karenia brevis blooms) in the Gulf of 

Mexico. In most of the dolphins, the first chamber of the stomachs was gorged with large 

amounts of fish, some of which were partially whole and undigested indicating recent 

feeding. Fish (planktivorous, herbivorous, and omnivorous fish species) collected from

St. Joseph Bay on March 18 tested positive for brevetoxins in stomach contents and in 

muscle, liver, and gill tissues whereas fish collected on March 28-31 also tested positive 

for brevetoxin but at much lower levels (except in sea trout). Satellite imagery of the 

northern Gulf of Mexico indicated elevated chlorophyll levels in the UME area March 9-

11, 2004 but water samples collected March 11 and later in the area of the UME did not 

contain significant quantities of Karenia brevis, although low levels of brevetoxins were 

detected. Thus, the source of the brevetoxins involved in this event remains uncertain, 

but the presence of toxic fish and water suggests that there was an undetected bloom

somewhere either in the bay itself or in waters in which the fish or dolphins were feeding. 

A similar dolphin UME occurred in 1999-2000 in the same area of Florida and was 

correlated with a Karenia brevis bloom. 

In addition to brevetoxin, low levels of domoic acid (see Appendix C) were detected in 

the stomachs, urine and feces of some dolphins. Further, Pseudo-nitzschia delicatissima, 

a diatom that can produce domoic acid was present at low to moderate levels in water 

samples. However, the levels of domoic acid detected were 1-2 orders of magnitude 

lower than those found in domoic acid related marine mammal mortalities on the 

California coast. Therefore, its role in the current event would appear to be secondary to 

brevetoxin if, in fact, it is involved at all. 

The evidence based on gross and histological findings does not indicate an infectious 

process and viral testing has ruled out morbillivirus, a virus known to cause high 

morbidity and mortality in dolphin populations. The lack of evidence of infectious 

disease, the wide age class spread of the mortalities, and the fact that most animals had 

recently fed (demonstrated by full stomachs) does implicate a toxin of some type as one 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

of the causes of the event. The Investigative Team is continuing to look at all potential 

causes of the mortality event and will conduct further analyses of the brevetoxin 

metabolites, prey and stomach contents, and genetic identification of the Florida 

Panhandle population. Additional work includes quantification of the estimated dose of 

toxins received by the animals, examination of any predisposing factors, and searching 

for evidence of any other toxicants that might be in dolphin prey species. The fact that 

southwest Florida has significant blooms of Karenia brevis almost annually without 

unusual numbers of bottlenose dolphin mortalities makes this investigation even more 

perplexing. In order to fully understand what is happening in these dolphin mortalities, 

the investigation will continue to work with an interdisciplinary team of scientists using 

an ecosystem approach to understand the factors that contributed to this mortality event. 

II. INTRODUCTION 

Between March 10 and April 13, 2004, 107 bottlenose dolphins (Tursiops truncatus) 

stranded dead along the Florida Panhandle coastline from Escambia to Franklin counties. 

The majority of the animals (70%) stranded in St. Joseph Bay and surrounding areas of 

Gulf County (Figure 1). On March 12, approximately 26 dolphins had stranded within a 

3-day period. The annual average of dolphin strandings along the Florida Panhandle is 

eight (8) animals per year, so the high number of dolphin strandings in March 2004 

prompted the National Marine Fisheries Service (NMFS) to initiate consultation with the 

Working Group on Marine Mammal Unusual Mortality Event (Working Group). The 

Working Group reviewed the available stranding data as well as historical records from

the area for comparison, and recommended that NMFS declare the die-off an official 

“Unusual Mortality Event” (UME). 

A. Unusual Mortality Event (UME) Program and the Working Group on 

Marine Mammal Unusual Mortality Events 

Title IV of the Marine Mammal Protection Act (MMPA) established the “Marine 

Mammal Health and Stranding Response Program” (16 U.S.C. 1421 et seq.), and section 

404 of the MMPA specifically directs the Secretary of Commerce (through NMFS) to 

administer responses to UMEs. The MMPA characterizes UMEs as mass mortalities 

and/or strandings of marine mammals that are: (1) unexpected; (2) involve a significant 

die-off of any marine mammal population; and (3) demand an immediate response. 

Additional considerations include strandings of unusual species, locations, time of year, 

etc. 

Section 404 of the MMPA also established the Working Group whose role is to: (1) 

determine whether or not a UME is occurring; (2) determine if/when a UME has ended; 

and (3) help develop a contingency plan for UME response. The Working Group is 

composed of 12 scientific experts with experience in marine mammal science, marine 

mammal veterinary science and husbandry, biomedical specialties, and/or marine 

conservation. There are seven criteria that the Working Group uses to determine if a 

marine mammal mortality event is “unusual” (see Appendix A). A single criterion or 

combination of criteria may indicate the occurrence of an unusual mortality event. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

B. Historic UMEs in the Gulf of Mexico and Florida Panhandle 

Since 1992, eight marine mammal unusual mortality events have been investigated in the 

Gulf of Mexico. Three of those involved manatees and were associated with Karenia 

brevis blooms and brevetoxins in tissues and gut contents. The remaining five UMEs 

involved bottlenose dolphins, and two of those occurred in the Florida Panhandle 

counties. In 1993-1994 an UME of bottlenose dolphins started in the Florida Panhandle 

and spread west with most of the mortalities occurring in Texas. That mortality event 

was caused by a morbillivirus epidemic. Between August 1999 and February 2000, the 

Florida Panhandle experienced a second UME of at least 120 bottlenose dolphins 

coincident with Karenia brevis blooms and fish kills. In both the 1999-2000 and 2004 

UMEs other species of marine life such as fish, invertebrates and birds died. The current 

UME and the 1999-2000 UME both started in the same location (St. Joseph Bay) and 

extended along the seven counties of the Florida Panhandle (Escambia, Santa Rosa, 

Okaloosa, Walton, Bay, Gulf and Franklin Counties). The 1999-2000 UME persisted 

over a long period of time (9 months) and was spatially and temporally concurrent with a 

K. brevis bloom that moved from east to west. Brevetoxicosis was implicated as the 

cause of the 1999-2000 UME, but carcass condition limited the investigation and no 

definitive diagnosis was made. 

 

C. Historical Knowledge of Bottlenose Dolphin Populations and Strandings 

Along the Florida Panhandle 

The historical average of bottlenose dolphin strandings for the Panhandle counties over 

the last 10 years is eight (8) animals per year excluding years when a UME occurred. 

However, little is known of bottlenose dolphin behavior, ecology, and stock structure in 

the Florida Panhandle, including the region in and around St. Joseph Bay. To the best of 

our knowledge, no systematic research was performed prior to the 2004 UME to 

determine the daily or seasonal patterns of use of St. Joseph Bay by bottlenose dolphins, 

or their broader ranging patterns or genetic composition as these might relate to stock 

structure. 

At other sites around the southeastern United States, a variety of techniques have been 

applied to determine stock structure, including among others: (1) biopsy darting to obtain 

small skin samples for genetic marking; (2) capture, sample, and release efforts to obtain 

genetic samples and apply tags or other markings; (3) photographic identification and resighting using distinctive natural markings on dolphin dorsal fins; and (4) radio-tagging 

and tracking. In the absence of specific empirical data identifying stocks of dolphins in 

the coastal waters of the panhandle, NMFS has used the approach of designating each of 

the 33 bays, sounds or estuaries in the US Gulf of Mexico as separate putative stocks, 

until such time as better data become available clarifying stock identification. The 

NMFS U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments - 2000

(using 1993 survey data) reports that no dolphins were observed in St. Joseph Bay and 

surrounding waters during aerial surveys, so it was not designated as a putative stock. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

The appearance of two die-offs of over 200 animals in the last five years, as well as the 

recent biopsy darting and photographic identification work with dolphins in St Joseph 

Bay and vicinity, indicate clearly that the 1993 aerial survey findings of no dolphins 

present in the Bay are out of date and do not provide sufficient information to determine 

impacts of these mortality events on coastal populations or stocks. 

III. METHODS AND RESULTS 

A. Dolphin Sampling 

The dolphin strandings were initially clustered temporally (at least 30 dolphins within the 

first four days from March 10-13) and spatially along the Florida Panhandle, with the 

majority of strandings (70%) in St. Joseph Bay (Figure 1). The first three dolphins were 

reported on March 10 and the last two dolphins were reported on April 13. All of the 107 

dolphins involved in the UME were discovered dead and no live strandings were 

reported. A variety of samples were collected and analyzed by several collaborators 

(Table 1). 

The demographics of the strandings indicate that both sexes and most age classes were 

involved. The sex distribution of the stranded animals was approximately equal: 36 

females and 46 males, with 25 carcasses of unknown sex. Age estimates based on 

growth layer groups of teeth have not been completed, therefore for this report age 

estimations are based on length to age curves for bottlenose dolphins in the Gulf of

Mexico (Fernandez and Hohn, 1993; Read et al., 1993). Carcass measurements of 100 

animals (not including two fetuses) show that length ranged from 76 cm (premature 

parturition) to 280 cm (adult) (Figure 2). Comparing the results of length classes with 

historic stranding records for this region (n=51, over 7 years), it is clear that a higher 

number of animals over 210 cm are represented in this die-off. 

Gross Necropsy Findings: 

Of the 107 dolphins involved in the UME, gross necropsies were conducted on 46 

animals, some samples (e.g., teeth and skin) were collected from 44 animals, and the 

remaining animals (n=17) were located and recorded but not sampled due to logistical 

constraints and/or carcass condition. Blubber, liver and kidney were collected from four 

mildly decomposed animals for the National Marine Mammal Tissue Bank. 

Carcass decomposition was classified into five categories: Code 2 - fresh (19 animals); 

Code 3 - mildly decomposed (39 animals); Code 4 - moderately decomposed (46 

animals); Code 5 - severely decomposed (2 animals); and unknown (1 animal). No live 

stranded animals (Code 1) were found during the event. Most of the fresh animals were 

detected in the first half of the event, and the last known Code 2 animal was recovered on 

April 1. 

Most animals were found to be in good nutritional condition, however a few animals 

were considered to be thin for this season as compared to winter season dolphin ranges in 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Sarasota, Florida. Studies have shown that blubber thickness is affected by season in 

bottlenose dolphins in the Gulf of Mexico. Blubber thicknesses ranged from a low of 0.8 

cm in a 268 cm male to a high of 2.3 cm in a 205 cm female using the mid-lateral 

measurement position from 19 animals. Gross findings varied with each animal, but 

pulmonary changes suggestive of pneumonia were noted in a number of animals which 

was further characterized histologically. Some animals possessed mild to moderate 

parasite infestations which was characterized by individuals with pterygoid sinus 

trematodiasis, pulmonary nematodiasis, gastric trematodiasis and enteric cestodiasis. 

There was evidence in a few animals of sediment in the trachea and primary and 

secondary airways, a characteristic that is seen in some animals that strand live but die on 

the beach. Many animals had evidence of generalized lymphoid stimulation, which was 

characterized by multiple enlarged lymph nodes. A number of animals had empty 

urinary bladders or contained a scant amount of opaque, pasty material with few 

containing collectable urine for analysis (10 urine samples collected). The majority of 

animals demonstrated a distended stomach with partially digested contents. Many 

animals had intestines which contained scant ingesta (n=11). 

Stomach Content Analyses: 

Stomach contents from 28 of 50 dolphins have been analyzed to date through the 

identification of fish remains and hard parts. Gastric subsamples were collected for 

biotoxin analyses from all 28 dolphins. Semi-digested fish found in the dolphin stomachs 

were collected for toxin analyses: menhaden from 16 dolphins; a puffer fish from 1 

dolphin; and spot, silver perch, kingfish, pinfish and others from 11 dolphins. Two 

preliminary findings stand out: 

(1) Dolphins appear to have gorged on food prior to death, as most stomachs were 

packed to capacity. Mean stomach content values were 773 g, with 10 samples 

weighing > 1 kg (maximum: 2.258 kg). These figures are significantly higher 

than those obtained from the 2001 bottlenose dolphin UME that occurred in the 

Indian River Lagoon (IRL) system on the east coast of Florida. During the 2001 

IRL event, dolphins were generally emaciated and had very little food matter in 

their stomachs (mean of 36 g, n= 14) comprised mostly of fleshless fish bones. In 

addition, several of the IRL animals had empty stomachs. Compared with other 

studies in the southeastern U.S. (Figure 3), the 2004 UME dolphins from the 

Florida Panhandle stranded with considerably fuller stomachs than stranded 

dolphins in other areas. Data obtained from stranded dolphins in Texas (1987-

1988) also showed high stomach mass values, but dolphins in that area are 

believed to gorge on fish discards from shrimp boats. 

(2) Menhaden was the dominant prey species in at least 14 of the 28 (50%) dolphins 

examined, judging by the large number (dozens) of semi-digested fish found in 

each stomach. A sub-set (n= 19) of the undigested menhaden ranged from 9.5 to 

16 cm, with most in the 14-15 cm size class. Sciaenid fish (e.g., silver perch, 

spot, kingfish) were dominant in 11 (39%) of the other samples. A few dolphins 

had undigested shrimp remains in their stomachs, and others had hundreds 

(possibly thousands) of fish ear bones (otoliths) of very small fish, mostly 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

croakers of the family Sciaenidae. These findings are similar to those found for 

Texas dolphins, where feeding in association with shrimpers is known to occur. 

Virology: 

Tissues obtained from 26 dolphins have been analyzed to date to determine pathogen 

presence using polymerase chain reaction (PCR) and reverse transcription PCR (RTPCR). To date, all samples have been negative for morbillivirus (50 samples from 24 

animals), influenza A virus (14 samples from 8 animals), and influenza B viruses (14 

samples from 10 animals) as well as calicivirus (26 samples from 15 animals), cetacean 

poxvirus (3 samples from 3 animals), herpes virus (10 samples), and parapoxvirus (3 

samples from 3 animals). 

Histopathology:

Histopathological examinations were performed on partial to complete necropsy 

submissions from 38 dolphins (14 females and 24 males). No cause of death was evident 

histologically, and there was no histological evidence of infectious disease. Autolysis 

and postmortem bacterial overgrowth ranged from moderate to advanced, occasionally 

limiting the histological evaluations. 

The vast majority of the dolphins appeared to be in good nutritional condition with mild 

to moderate fat atrophy only present in 6 of the 38 animals (16%) examined. Common 

histological lesions included prominent eosinophilia within multiple tissues (34/38), 

parasitic pneumonia (28/38), angiomatosis (20/38), mild myocardial fibrosis (11/38) and 

mild hepatic fibrosis (9/38). Less common lesions included mild perivascular brain 

edema (4/38), mild chronic interstitial nephritis (4/38), lymphocytic laryngitis (2/38), 

lymphoid hyperplasia (2/38), mild cerebral gliosis (1/38), mild lymphocytic meningitis 

(1/38), multifocal chronic myocarditis (1/38), and a pleural adhesion (1/38). 

The prominent eosinophilic inflammation within multiple tissues is most likely associated 

with parasitism, a common finding in wild marine mammals. The changes within the 

liver are suggestive of a previous parasitic infection. Angiomatosis, a common 

proliferative lesion that occurs in the lungs and lymph nodes of dolphins, is thought to be 

clinically insignificant. Mild myocardial fibrosis is a fairly common finding in adult 

dolphins, and is usually clinically insignificant. The mild perivascular edema seen in a 

few dolphins is a common, nonspecific finding in the brains of stranded dolphins. 

Lymphoid hyperplasia is a nonspecific finding in response to antigenic stimulation. The 

significance of the myocarditis is uncertain since the inflammation was not associated 

with degenerative changes within the myocytes. The causes of the remaining lesions 

were not evident. They were all mild, and not likely associated with the death of the 

dolphins. Gross and histological lesions of brevetoxicosis are not well established or are 

nonspecific except in the case in inhalation brevetoxicosis. Gross lesions from the 

manatees with inhalation brevetoxicosis included nasopharyngeal and pulmonary edema 

and hemorrhage. Histological lesions in manatees with inhalation exposure included the 

above plus catarrhal rhinitis. No such gross or histological lesions were seen in the 

current investigation. 

 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Organochlorines: 

Concentrations of persistent organic pollutants (“POPs”, i.e., polychlorinated biphenyl 

(PCB) congeners, DDT and its derivatives, and other organochlorine insecticides) in 

bottlenose dolphin blubber samples collected from these animals were determined and 

compared to those observed in free-ranging Sarasota Bay dolphins captured during health 

assessment work. Only juvenile animals were used in this comparison because it has 

been shown that POP concentrations in juveniles are not statistically different between 

genders and juvenile animals can be identified by their length. The use of juveniles was 

also an attempt to control for age since that can influence POP levels in cetaceans. 

Eighty PCB congeners, DDT and metabolites (DDE and DDD), oxychlordane, dieldrin 

and mirex were determined in full depth blubber biopsies from 23 juvenile dolphins 

collected from Sarasota Bay (collection interval: 2000 to 2004) and seven full depth 

blubber biopsy samples collected from Code 2 dolphins that stranded during the UME 

event. Samples were analyzed by gas chromatography with mass spectrometry at the 

NIST Charleston Laboratory. Total PCBs (sum of all measurable congeners) and total 

DDT (sum of 2,4’- and 4,4’-DDD, -DDE, and DDT) were not statistically different 

between the UME and Sarasota animals. The geometric mean of total PCBs was 18.5 

mg/kg wet wt. (range 6.4 to 52.5 mg/kg wet wt.) and 16.5 mg/kg (range 12.3 to 24.7 

mg/kg wet wt.) for the Sarasota and UME animals, respectively. The geometric mean of 

total DDT was 9.7 mg/kg (range 3.7 to 25.9 mg/kg wet wt.) and 9.6 mg/kg (range 6.3to 

21.8 mg/kg wet wt.) for the Sarasota and UME animals, respectively. Based on the 

scientific literature, these levels are above those thought to have toxicological 

significance in delphinids (e.g., immunosuppression). Other organochlorine pesticides 

tended to be much lower in the UME animals than in the Sarasota animals. For instance, 

concentration (geometric mean) of dieldrin in blubber was 0.71 mg/kg (range 0.26 to 2.3 

mg/kg wet wt.) in the Sarasota animals versus 0.097 mg/kg the UME animals (range 

0.065 to 0.13 mg/g wet wt). Lipid content in blubber was not significantly different 

between the Sarasota dolphins and the six juvenile males from the UME analyzed to date, 

suggesting that these 6 animals were not thin at the time of their deaths. 

Biotoxins: 

Tissue and fluid samples from 38 dolphins along the Florida Panhandle (Figure 4) were 

analyzed for brevetoxins using multiple methods (competitive ELISA, 

Radioimmunoassay, Receptor Binding Assay, LC/MS, and reversed phase 

chromatography coupled to tandem mass spectrometry). All dolphins tested had high 

levels of brevetoxins in their stomach contents and/or feces (Figure 5). Significantly 

lower concentrations were present in tissues. The pattern of metabolites in tissues has not 

been completed but will provide insights into metabolism and potential toxicity. 

Brevetoxins were also measurable in the urine of most of the few animals tested (n=10). 

Brevetoxin concentrations varied widely between individual animals and between tissues 

but had a narrower range of values in 2004 than observed in the 1999-2000 dolphin UME 

along the Florida Panhandle. In addition, the levels found in stomachs of the 2004 UME 

dolphins were greater than those measured in the 1996 and 2003 manatee mortalities on 

the west coast of Florida (Figure 6). Although the toxic effect level of brevetoxin and its 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

metabolites remains poorly defined, its presence at high levels in all animals tested 

supports brevetoxicosis as a differential diagnosis for this mortality event. 

Trace levels of domoic acid (using receptor binding assay, ELISA and LC tandem mass 

spectroscopy) were found in the stomach contents and feces of some, but not all, of the 

stranded dolphins tested. Pseudo-nitzschia is not uncommon in the waters along the 

Florida Panhandle coast and, as there is no data on the natural levels of domoic acid in 

the food web from this part of the Gulf of Mexico, it is unclear if the trace amounts of 

domoic acid in the stomach contents and feces of these animals are significant to this 

mortality event. 

Genetic Analyses: 

Genetic analyses were performed on 64 sampled dolphins to determine whether the UME 

animals belonged to coastal or offshore stocks of bottlenose dolphins using DNA 

sequencing of a portion of the mitochondrial DNA genome (methods described in Rosel 

et al. 1999). Results indicate that all 64 animals were of the coastal morphotype. 

B. Environmental Sampling 

Satellite Imagery: 

Satellite ocean color imagery has been used effectively for over four years as part of a 

monitoring program for Karenia brevis to support state and federal activities. The 

primary sensor is on the Sea-viewing Wide Field-of View Sensor (SeaWiFS). Data and 

analyses are typically provided to the state as a monitoring and forecasting tool for the 

blooms. These analyses have aided with other blooms, such as Pseudo-nitzschia, but are 

most effective with Karenia blooms. Detection is limited to about 50,000 cells L-1 of 

Karenia, which is much higher than that required for shellfish closures, but about the 

minimum at which human respiratory impacts occur. Images of total chlorophyll 

concentration and images showing the presence of new blooms are normally used as part 

of the analyses (Figures 7-12). 

On February 28, a chlorophyll feature (2-4 μg/L) occurred about 12 nautical miles SouthSouthwest of Cedar Key (Figures 8-9). In January 2004, a bloom of Karenia appeared 

near Clearwater Florida. Analyses of imagery and winds indicates that the bloom

originated south of Cedar Key, making it possible that a K. brevis bloom was present in 

the Cedar Key area. This region is problematic, with many frequent blooms. 

On March 2, an area was flagged for new blooms from Cape San Blas to near Tyndall Air 

Force Base. Extreme elevated chlorophyll and a new bloom was evident in St Joseph 

Bay on March 9-11 (Figure 10). This characteristic of a bloom only in the Bay was 

observed in 1999 when a bloom of K. brevis occurred in St. Joseph Bay in August. Cell 

counts from water samples collected on March 11 contained Pseudo-nitzschia but not 

Karenia brevis (see HAB Monitoring), so it was assumed that the elevated chlorophyll 

was the result of a Pseudo-nitzschia bloom. The presence of brevetoxins in water at low 

levels (March 12, see Toxicity Testing) and fish from St. Joseph Bay suggest that 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

K. brevis may also have been present but was gone by the time samples were collected 

for phytoplankton counts. By March 18, slightly elevated chlorophyll levels were 

observed from the east end of St. George Island, offshore St. Joseph Bay and from Cape 

San Blas to 30 N. 

Between April 12-15, a front passed through the UME area. Strong southerly winds 

followed by strong North-Northwesterlies caused mixing in the St. Joseph Bay area and 

resuspension of benthic material. This resulted in a rapid increase in chlorophyll that 

persisted for a few days and then diminished (Figures 11-12). Between April 16-18, two 

bloom patches were observed offshore and fish kills that were reported in St. Joseph Bay 

and 20 miles to the south of Cape San Blas. 

Harmful Algal Bloom (HAB) Monitoring and Toxin Analyses: 

HAB monitoring

Two dedicated cruises, one of which was funded by the CSCOR HAB Event Response 

Program and one cruise of opportunity, were conducted and water samples were collected 

at over 115 stations (Figure 13) from March 11 to May 5, 2004. Microscopic (both light 

and electron microscopy) identification and enumeration of phytoplankton and toxin 

analyses were conducted on the samples. During the event, as often as was feasible, 

water samples were collected in areas flagged by NOAA satellite imagery as potential 

HAB events. 

No significant populations of Karenia brevis, were observed in 233 counts of samples 

from St. Joseph Bay and the surrounding offshore region in surface waters or at depth. 

Pseudo-nitzschia delicatissima was observed at low concentrations (0 to 1.7 x 104

 cells L1

) outside St. Joseph Bay, and at moderate concentrations (0 to 4.6 x 105 cells L-1) inside 

the Bay. All stations measured had dissolved oxygen concentrations >7.2 mg L-1, ruling 

out the involvement of low oxygen concentrations in the event. 

Toxin Analyses

Brevetoxins: 84 water samples and 60 fish (both live-caught and from fish kills, total of 

128 samples) were analyzed for brevetoxin by competitive ELISA. All water samples 

collected outside of St. Joseph Bay were negative, while those collected inside the bay 

contained low levels of brevetoxin (0.72 – 1.1 μg/L on March 12) in the absence of any 

apparent Karenia brevis cells. 

Several species of fish were collected live and from fish kills in St. Joseph Bay. Most 

contained elevated levels of brevetoxin. Fish tissues examined included gill (64-798 

ng/g), liver (865-4,655 ng/g), stomach contents (51-9,000 ng/g) and muscle (nd-473 

ng/g). Fish collected live in St. Josephs Bay on March 18 contained variable levels of 

brevetoxin in their stomach contents. Burrfish (carnivores), spot (omnivores), and pinfish 

(herbivores) had high levels of toxin in their stomach contents (>1000 ng/g), whereas 

Gulf flounder and sardine collected at the same time were negative. Whether this reflects 

feeding habits of these species or individual variation is uncertain based on the small 

number of samples analyzed to date. Live fish collected on March 28 and 31 (n=47) 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

included Spanish mackerel, pinfish, flounder, southern codling, spot, sea trout, bluefish, 

and thread herring. Brevetoxins were measurable but below 1000 ng/g in the stomach 

contents of all fish except for the sea trout, which contained 4,000 ng/g. In addition 

brevetoxins were found in the flesh of some fish. 

Domoic Acid: Eighteen water samples were analyzed for domoic acid by ELISA. 

Although Pseudo-nitzschia was present and identified as P. delicatissima, all water 

samples were below the level of detection of the ELISA kit for domoic acid. 

Mortality Reports in Addition to Dolphins 

Fish kills and other animal mortalities were reported in St. Joseph Bay as follows: 

03/11/04 Limited number of dead fish and horseshoe crabs were reported 

03/14/04 Report of many dozens of lightning whelk at the Bay entrance (may have 

been empty shells) 

03/18/04 Hundreds of dead horseshoe crabs; hundreds of dead jellyfish, one dead 

cormorant; dead red drum; numerous baitfish were swimming in circles at 

the surface; one sick laughing gull and cormorant exhibited neurologic 

signs 

03/23/04 Fish kill involving spot, bay anchovy, cowfish, and striped burrfish. 

Additionally horseshoe crabs 

04/02/04 Red drum, hundreds of dead adult horseshoe crabs, two dead pelicans, one 

egret, and one loon 

04/12/04 Red drum

04/19/04 Red drum

05/06/04 From Pig Island, SW corner of the Bay - red drum, Gulf killifish, spotted 

sea trout 

20 miles south of Cape San Blas: 

04/14/04 Red drum and thread herring 

These reports were not necessarily verified in every case, nor are they necessarily 

separate events, nor were necropsies conducted on all animals. Biotoxin analyses have 

not been completed for all the samples. General field observations and behavioral 

symptoms of moribund or sick animals are typical of exposure to Karenia brevis blooms. 

Shellfish Monitoring for Harmful Algal Bloom Species 

The only shellfish harvesting area in the immediate vicinity of the UME is the St. Joseph 

Bay Shellfish Harvesting Area. The area was temporarily closed at sunset on November 

19, 2003 due to the detection of K. brevis. Therefore, no commercial or recreational 

harvesting of shellfish was allowed following November 19, 2003 including the time that 

the UME occurred. Waters surrounding the St. Joseph Bay Shellfish Harvesting Area are 

unclassified and commercial and recreational shellfish harvesting is never allowed. 

12
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Results from samples of shellfish meats for brevetoxins continued to be above the 

established regulatory level until April 29, 2004 (even though Karenia brevis cells were 

not present). The area was reopened to harvest at sunrise, on April 30, 2004 due to 

nontoxic bioassays for brevetoxin. Results from shellfish samples collected from the area 

showed that domoic acid concentrations were well below the established regulatory limit 

for public health protection. Therefore, recognized shellfish public health concerns were 

and continue to be adequately and appropriately addressed. 

IV. DISCUSSION AND FUTURE PLANS 

A. Comparison with Other UMEs 

In the last decade there have been several UMEs of marine mammals that have been 

attributed to or correlated with harmful algal blooms. The most common harmful algal 

bloom in the Gulf of Mexico is caused by the red tide organism Karenia brevis, known to 

cause Neurotoxic Shellfish Poisoning and respiratory irritation in humans. The biotoxin 

brevetoxin and its metabolites produced by Karenia brevis were implicated in manatee 

mortality events in Florida in 1963, 1982, 1996, 2002, and 2003. Also, brevetoxin and its 

metabolites were suspected as a possible cause for bottlenose dolphin die-off events in 

Mississippi during 1996 and along the Florida Panhandle during 1999-2000. Although 

Pseudo-nitzschia spp. blooms are known in the Gulf of Mexico, no marine mammal 

mortality events have been attributed to these blooms or domoic acid (the related 

biotoxin) in this region. We must note that this is the first time that domoic acid has been 

analyzed in tissues from marine mammals that have stranded in the Gulf of Mexico, 

therefore no baselines exist for this biotoxin in marine mammals in the Gulf of Mexico. 

However, Pseudo-nitzschia blooms and subsequent domoic acid intoxication have been 

associated with sea lion and dolphin mortalities in California (1998 to 2003) and 

humpback whale mortalities on George’s Bank (2003). The concentrations of domoic 

acid found in the bottlenose dolphin samples that were collected during this event were 

much lower than those found associated with previously documented marine animal 

mortalities. Therefore domoic acid intoxication is not considered as a primary cause of

the 2004 dolphin UME, but has not been ruled out as a contributing factor. 

B. Insights into Dolphin Behavior and Feeding in the Florida Panhandle 

During Chicago Zoological Society/Florida State University biopsy sampling in AprilMay 2004, dolphins were frequently observed feeding on fish discarded from shrimp

trawlers, while anchored or drifting and culling fish in St. Joseph Bay. Active trawlers 

were not observed in the bay -- it appeared that they trawled elsewhere and culled their 

catch in the sheltered waters of the bay prior to offloading their product at Port St. Joe. 

Croakers (Sciaenidae) are the predominant finfish by-catch group in the Gulf of Mexico 

shrimp fishery, which targets organisms (e.g., shrimp, bottom fish) living on or near the 

bottom. It has been suggested that the fact that some dolphins in St. Joseph Bay obtain at 

least part of their daily diet from the fish caught outside of the bay by shrimp trawlers and 

provided to the dolphins in the bay may have potential implications for evaluating the 

source of toxins in the stomach contents of dolphins dying during the UME. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Menhaden, on the other hand, are caught in large numbers in purse-seine nets. The biopsy 

darting team also observed purse-seine vessels returning to Port St. Joe, but the boats 

were neither fishing nor culling in the bay at the time they were observed. 

C. Continuing Studies: 

Acoustic/Blast Trauma -- Local citizens reported that the Department of Defense was 

conducting military exercises off the coast of the Florida Panhandle in March 2004. 

Based on the gross examinations, there was no physical evidence of blast or acoustic 

trauma in the 22 freshest dolphin carcasses. However, heads and ears collected from a 

subset of these animals will be examined specifically for blast and acoustic trauma using 

CT scanning methodology and histopathology. NMFS is working with the US Navy to 

determine what types of activities were conducted, and when and where they occurred, to 

compare with stranding data. 

Life History – Demographics and life history parameters are essential components of 

UME investigations and provide tremendous insights into the real epidemiology of the 

event. Life history factors that will be critical to this investigation include such factors 

as: age determination, prey or feeding strategies (what do the animals eat?), and 

population or stock identification and assessment (who are the animals and where do they 

go). Stable isotope analyses will be conducted to determine historic feeding habits. 

Age Determination -- Age estimations of the dolphins involved in the UME will be 

obtained by analyzing growth layer groups of teeth and reproductive organs. 

Reproductive status will also be determined. 

Feeding (Stomach Content Analyses) -- Detailed dietary studies will be completed for all 

available UME samples (n= 50), including the contribution by biomass of the most 

important prey species. In addition, samples obtained from the 1999-2000 UME (n= 70 

to 80) will be analyzed for comparative purposes. 

Genetics -- Subsequent to the die-off, genetic samples from 30 live bottlenose dolphins in 

St. Joseph Bay and vicinity were sampled via biopsy darting. These samples will be 

compared to the UME animals using mitochondrial DNA sequencing and microsatellite 

analyses to help determine the origins of the dead dolphins. In addition, samples from

the 1999-2000 event will also be analyzed and compared to the current mortalities. 

Trophic transfer and metabolism -- There is increasing evidence that animals can be 

exposed to brevetoxins by multiple routes (inhalation and ingestion), though different 

vectors (prey, feeding habits, or directly consuming the harmful algae), and under 

different time scales. The mechanisms and timing of movement of biotoxins through the 

ecosystem and food web are critical to understanding risks of exposure and risks to 

populations. In addition to examining prey types and biotoxin levels in prey, metabolism

of brevetoxins through the various levels of the food web will also be examined. 

Biotoxin Dosage Determination -- Additional work will be conducted to quantify the 

estimated dose of toxins received by the animals and search for evidence of any other 

toxicants that might be in dolphin prey species and to compare the results with previous 

14
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

UMEs. The toxicity of multiple biotoxin exposures in marine organisms using animal 

models will be useful to evaluate as part of long range studies. 

D. Future Studies 

This section outlines specific studies that need to be conducted to better understand this 

UME , the role of brevetoxins in UMEs, and the impacts of repeat UMEs in this 

geographic area. Although needed, there is no identified funding specific for these 

investigations. 

Stock Structure -- To date the stock structure of coastal and estuarine bottlenose dolphins 

in the northern Gulf of Mexico has not been rigorously investigated using genetic and 

photo identification techniques. This should be a priority. Since so much is unknown 

about stock structure in this area, it will take some time to understand the impacts of 

these mortality events on a specific population(s) and risks from an increasing frequency 

of harmful algal blooms.

Health Assessments -- Health assessment indices should be developed and monitored 

through the use of live captures, sampling and release exercises in specific areas where 

anomalous mortality events have occurred (i.e., in St. Joseph Bay). Studies through live 

capture will be critical in determining risk factors in populations and which populations 

may be at risk. These studies will be essential in understanding any contributing or 

predisposing factors in the population that puts this population more susceptible to 

biotoxins, infections or other morbidity or mortality factors. This also includes 

assessment of strandings that occur to obtain more baseline information on mortalities 

and life history in this area. 

Feeding Ecology -- Understanding the trophic ecology of wild dolphins is crucial in the 

monitoring of UMEs in which feeding is suspected to play an important role, particularly 

in areas where algal blooms are known to occur. A recommendation is made that samples 

(dolphin stomachs) be collected from stranded animals, so that baseline data on feeding 

and biotoxin concentrations can be obtained for the Florida Panhandle area. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

E. Evaluation of UME Response 

What went right? 

• Long-term stranding response data were available and identified the unusual level 

of mortality almost immediately

• The response by the stranding network and colleagues was more organized and 

complete than during the 1999-2000 event 

• Multiple federal and state agencies and outside partners worked cooperatively on 

a comprehensive investigation 

• Appropriate expertise for various analyses had been previously identified, 

resulting in efficient dissemination of samples for various analytical tests 

What challenges were faced? 

• Current efforts to monitor blooms are guided primarily by the need to protect 

humans from Neurotoxic Shellfish Poisoning, not to protect marine mammals 

from Neurotoxin Fish Poisoning. Understanding the links between marine 

mammal mortality events in this area and the occurrence of HABs is not adequate 

to provide guidance for future monitoring to predict marine mammal events. 

Resources and equipment for the immediate response were limited 

• Baseline information on the health, distribution, demographics, and abundance of 

dolphins in the area of the UME was limited, making interpretation of results 

more uncertain and tentative 

• Baseline information with regard to concentrations of biotoxins (brevetoxin, 

domoic acid, and combinations of the two) in plankton, food items, digestive tract 

contents, body fluids, and tissues consistent with morbidity and mortality in 

bottlenose dolphins was, for the most part, limited or non-existent 

• Baseline information on the levels of man-made environmental contaminants in 

this dolphin population and information on how these may interact with natural 

toxins was not available 

• Currently we continue to be limited in biotoxin detection and quantification (for 

metabolites) by the state of the science and the limitations on standards and 

techniques 

• Training and maintaining professional teams to respond to increasingly more 

complex investigations anywhere in U.S. waters is difficult and requires 

substantial resources 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

V. ACKNOWLEDGEMENTS 

NOAA/National Marine Fisheries Service 

Marine Mammal Health and Stranding Response Program: Angela Collins-Payne, Teri 

Rowles, Trevor Spradlin, Janet Whaley, Sarah Wilkin 

Southeast Fisheries Science Center, Miami: Laura Engleby, Ruth Ewing, Sarah Gomez, 

Jenny Litz, Blair Mase-Guthrie 

Southeast Fisheries Science Center, Beaufort, NC: Aleta Hohn, Gretchen Lovewell, 

Karen Sayles 

Southeast Fisheries Science Center, Lafayette, LA: Sarah Kingston, Patricia Rosel 

Southeast Fisheries Science Center, Panama City, FL: Nancy Evou, Pete Sheridan 

NOAA/National Ocean Service 

Center for Sponsored Coastal Ocean Research: Quay Dortch, Marc Suddleson, 

Center for Coastal Monitoring and Assessment: Richard Stumpf, Michelle Tomlinson 

Center for Coastal Environmental Health and Biomolecular Research, Marine 

Biotoxins Program, Charleston, SC: Greg Doucette, Kristin King, Tod Leighfield, Jen 

Maucher, Brad Mitchell, Steve Morton, John Ramsdell, Fran Van Dolah, Zhihong Wong, 

Ricky Woofter 

Center for Coastal Environmental Health and Biomolecular Research, Marine Mammal 

Group, Charleston, SC: Leslie Gilroy-Burdett, Wayne McFee, Jessie Stenftenagel, Eric 

Zolman 

Florida Fish and Wildlife Conservation Commission/Florida Marine Research 

Institute 

Ken Arrison, Alex Costidis, Elsa Haubold, Jessica Lightsey, Tom Pitchford, Tanya 

Pulfer, Butch Rommel, Leslie Ward 

Jay Abbott, Susan Cook, Leanne Flewelling, Matt Garrett, Cindy Heil, Ryan Pigg, Bill 

Richardson, Paula Scott, Earnest Truby, Jennifer Wolny 

Ann Forstchen, Jan Landsberg, Emilio Sosa, Christy Stephenson 

Stephanie Fahrny, Dayle Flint, Chad Hanson, Kelly Hooper, Ed Matheson, Stephanie 

McGrath, Bob McMichael, Missy Millender, Sky Rudloe, Sherri Thourot, Troy Tuckey, 

Jeff Wren 

Allison Bozarth 

Armed Forces Institute of Pathology 

Dale Dunn, Michelle Fleetwood, Tom Lipscomb

Chicago Zoological Society, Sarasota Dolphin Project 

Jason Allen, Brian Balmer, Spencer Fire, Larry Fulford, Randall Wells 

Florida Department of Agriculture and Consumer Services 

Richard Davis, David Heil, Joe Shields 

Florida Department of Environmental Protection 

Tammy Summers, Kim Wren

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Florida State University 

Doug Nowacek

Gulf World Marine Park 

Ron Hardy, Cheryl Joyner 

Harbor Branch Oceanographic Institute 

Greg Bossart 

Hubbs-SeaWorld Research Institute 

Teresa Mazza, Wendy Noke 

Mote Marine Laboratory 

Nélio Barros, Mike Henry, Rich Pierce 

National Institute of Standards and Technology 

Charleston Lab: Michael Ellisor, Jennifer Keller, John Kucklick, Rebecca Pugh, Bob 

Swarthout, Stacy Vander Pol

Sea World – San Diego 

Judy St. Leger

University of Florida 

Carlos Romeros 

Working Group on Marine Mammal Unusual Mortality Events 

Val Beasley, University of Illinois 

Sylvain De Guise, University of Connecticut 

Dale Dunn, Armed Forces Institute of Pathology 

Frances Gulland, The Marine Mammal Center 

Ailsa Hall, NERC Sea Mammal Research Unit/University of St Andrews. 

Linda J. Lowenstine, University of California-Davis 

Pamela A. Tuomi, Alaska SeaLife Center 

Frances Van Dolah, NOAA National Ocean Service 

Michael Walsh, Sea World-Orlando 

Randall Wells, Chicago Zoological Society and Mote Marine Laboratory 

Sharon Young, Humane Society of the United States 

Federal Agency Representatives: 

Teri Rowles, National Marine Fisheries Service 

Diane L. Bowen, U.S. Fish and Wildlife Service 

Tim Ragen, Marine Mammal Commission 

John Heisler, U.S. Environmental Protection Agency 

International Participants: 

Canada: Ole Nielsen, Department of Fisheries and Oceans Canada 

Mexico: Lorenzo Rojas-Bracho, Programa Nacional de Mamíferos Marinos, Instituto 

Nacional de Ecología 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

VI. REFERENCES 

Bossart, G.D., D.G. Baden, R.Y. Ewing, B. Roberts and S.D. Wright. 1998. 

Brevitoxicosis in manatees (Trichechus manatus latirostris) from the 1996 epizootic: 

gross, histologic and immunohistochemical features. Toxicol. Pathol., 26: 276-282. 

Ch’ng, M.M., T.A. Leighfield, M.A. Busman, F.M. Gulland, K. Matassa, M. Chechowitz, 

T. Rowles and F.M. Van Dolah. 2002. Analysis of domoic acid involvement in marine 

mammal morbidities and mortalities on the west coast of the U.S.: February-Aug 2000. 

Report to the Working Group on Marine Mammal Unusual Mortality Events. 18 pp. 

Fernandez, S. and A.A. Hohn. 1998. Age structure, growth, and calving season of 

bottlenose dolphins stranded along the coast of Texas. Fish. Bull. 96(2):357-365. 

Gulland, F.M. 2000. Domoic acid toxicity in sea lions (Zalophus californianus) stranded 

along the central California coast, May-October 1998. Report to the National Marine 

Fisheries Service Working Group on Marine Mammal Unusual Mortality Events. NOAA 

Tech. Memorandum NMFS-OPR-17, 45 p. 

Landsberg, J.H. and K.A. Steidinger. 1998. A historical review of Gymnodinium breve

red tides implicated in mass mortalities of the manatee (Trichechus manatus latirostris) 

in Florida, USA. Pages 97-100 in B. Reguera, J. Blanco, M.L. Fernández and T. Wyatt, 

eds. Harmful Algae. Xunta de Galicia, IOC, Paris, France. 

O'Shea, T.J., G.B. Rathbun, R.K. Bonde, C.D. Buergelt and D.K. Odell. 1991. An 

epizootic of Florida manatees associated with a dinoflagellate bloom. Mar. Mammal Sci., 

7: 165-179. 

Read, A.J., R.S. Wells, A.A. Hohn and M.D. Scott. 1993. Patterns of growth in wild 

bottlenose dolphins, Tursiops truncatus. J. Zool., London, 231:107-123. 

Rosel, P.E., S.C. France, J.Y. Wang and T.D. Kocher. 1999. Genetic structure of 

harbour porpoise, Phocoena phocoena, populations in the Northwest Atlantic based on 

mitochondrial and nuclear markers. Mol. Ecol., 8:S41-S54. 

Scholin, C.A., F. Gulland, G.J. Doucette, S. Benson, M. Busman, F.P. Chavez, J. 

Cordaro, R. Delong, A. De Vogelaere, J. Harvey, M. Haulena, K. Lefebvre, T. Lipscomb, 

S. Loscutoff, L.J. Lowenstine, R. Marin, III, P.E. Miller, W.A. McLellan, P.D.R. 

Moeller, C.L. Powell, T. Rowles, P. Silvagni, M. Silver, T. Spraker, V. Trainer and F.M. 

Van Dolah. 2000. Mortality of sea lions along the central California coast linked to a 

toxic diatom bloom. Nature, 403: 80-84. 

Van Dolah, F.M., G.J. Doucette, F. Gulland, G. Bossart and T. Rowles. 2003. Impacts 

of algal toxins on marine mammals. Pages 247-269 in J. Vos, G.D. Bossart, M. Fournier 

and T. O’Shea, eds. Toxicology of Marine Mammals. Taylor and Francis, New York, 

NY. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Van Dolah, F.M., E.L. Finley, B.L. Haynes, G.J. Doucette, P.D. Moeller and J.S. 

Ramsdell. 1994. Development of Rapid and Sensitive High Throughput Pharmacologic 

Assays for Marine Phycotoxins. Nat. Toxins, 2:189-196. 

Woofter, R.T. et al. Environmental Health Perspectives, October 2003, volume 111, 

number 13, pages 1595-1600. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

VII. TABLES AND FIGURES 

Table 1. Samples collected for analysis during the 2004 Florida Panhandle Unusual 

Mortality Event 

Analyses Purpose Investigator/Laboratory No. of 

Animals 

Sampled 

Status 

Gross Examination

and Necropsy

Identification of

gross causes of 

mortality and

tissue sample 

collection 

Various field investigators Level 3* - 46 

Level 2 – 44 

Level 1 – 9 

No Exam - 8 

107 Completed 

Acoustic trauma To determine 

morphology and 

pathology of 

acoustic tissues 

Woods Hole Oceanographic 

Institute 

8 8 Pending

Aging and Life 

History

Estimate age and 

reproductive 

status 

NOAA Fisheries, Southeast 

Fisheries Science Center, 

Beaufort, NC 

51 51 Pending

Bacteriology Bacterial Purdue University 2 2 Pending 

identification to

examine 

infectious

processes and 

cause of death 

Hubbs Sea World Orlando 2 2 Pending 

Florida Marine Research 

Institute Florida Fish and

Wildlife Conservation

Commission

Brevetoxin/ 11 11 Completed

Domoic acid 

Tissue 

examination to

identify and

quantify

biotoxins Marine Biotoxin Program

NOAA/NOS 

Charleston, SC

54 21 Completed

33 Pending 

Genetics DNA analysis to 

determine stock 

identity 

NOAA/NOAA Fisheries 

Southeast Fisheries Science 

Center Baton Rouge, LA 

65 65 Completed

Histopathology Tissue

examination to

identify disease 

processes 

Armed Forces Institute of

Pathology

38 38 Completed

Immunoperoxidase Examination to

identify 

presence and 

distribution of 

brevetoxin in

tissue samples 

Harbor Branch 

Oceanographic Institute 

TBD Pending

Stomach Contents

(Fish Species ID) 

To evaluate diet Mote Marine Laboratory 50 28 Completed 

Initial Analysis; 

22 pending 

(plus 1999-2000 

animals) 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

National Institute of

Standards and Technology

Charleston, SC

33 26 Pending

7 completed for 

POPs 

Toxicology Identification 

and 

quantification of 

toxins including 

pesticides, 

organochlorides 

and heavy

metals 

National Ocean Service 

Center for Coastal 

Environmental Health and 

Biomolecular Research 

5 1 Completed for 

water pesticides 

4 Pending 

Virology Viral

identification/

isolation to

examine 

infectious

processes 

Carlos Romero, Ph.D. 

University of Florida 

31 21 Completed

10 Pending 

* Level 3: full examination including necropsy and sample collection; Level 2: no 

necropsy, but some samples collected (typically skin, blubber, muscle and/or teeth); 

Level 1: basic data collected including length, sex and location.

22
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Figure 1. Map of the Florida Panhandle indicating locations where the 107 reported 

bottlenose dolphins were recovered. Insert depicts Gulf County and Bay County 

including St. Joseph Bay where the majority of animals stranded from March 10 - April 

14, 2004. 

23
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280

length (cm)

proportion of total animals

97-03

(n=51)

2004

(n=80)

Newborns or 

within a few

months of birth

Predicted length at

1 year of age

Juvenile (2-4 

years)

Subadult Adult

(> 8-10 years

for females; 

>10-12 years

for males)

 

Figure 2. Standard length distribution (in cm) of 80 stranded dolphins recovered during 

the Florida Panhandle UME March-April 2004, divided into age categories based on 

length, and compared to length data from stranded animals reported in historical data 

(1997-2003). 

24
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Bottlenose Dolphin Stomach Content Biomass

0

500

1000

1500

2000

2500

UME 2004 PAN UME 2001 IRL NON-UMEIRL (1993-

2004)

NON-UME IRL (1976-

1992)

UME 1990 TEXAS NON-UME TEXAS

(1987-1988)

SARASOTA BAY

(1984-1996)

Mean Sto

mach Content W

et W

eight (g)

28

14

102

22

37

33

15

 Figure 3. Stomach content biomass comparison.

25
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

 

Dolphin carcass, brevetoxins confirmed in tissues (n=31)

Dolphin carcass, tissues not tested (n=76) 

Gulf of Mexico

See Inset Inset 

GULF 

BAY

ESCAMBIA 

SANTA 

ROSA OKALOOSA 

WALTON 

HOLMES 

WASHINGTON 

BAY

GULF 

JACKSON 

CALHOUN 

LIBERTY

FRANKLIN 

WAKULLA 

GADSDEN

LEON 

Gulf of 

Mexico 

St. Joseph Bay 

Figure 4. Dolphin Carcass Recovery Locations (n =107) in the Panhandle Region of 

Florida (March 10 – April 13, 2004) 

26
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

0

200

400

600

800

1000

1200

1400

1600

1800

stomach contents (27)

feces (7)

urine (10)

blood (12)

liver (13)

kidney (13)

lung (13)

cerebellum (13)

Figure 5. Brevetoxin concentrations found in stranded bottlenose dolphins. 

Concentrations in ng/g (tissues and feces) or ng/ml (urine and blood). 

27
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

0.1

1

10

100

1000

10000

04 dolphin 

99 dolphin 

03 manatee 96 manatee 

'04 dolphin 

99 dolphin 

03 manatee 96 manatee 

04 dolphin 99 dolphin 

03 manatee 96 manatee 

04 dolphin 99 dolphin 

03 manatee 96 manatee 

PbTx (ng/g)

Stomach Liver Kidney Lung

Figure 6. Ranges of brevetoxin concentrations found in tissues of bottlenose Panhandle 

dolphins (’99 and ’04 mortality events) and manatees (’96 and ’03 mortality events). 

Bars reflect high and low values for PbTx in ng/g. 

28
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

 Figure 7. Map of Florida Panhandle indicating locations referenced in report.

29
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Figure 8. February 28, 2004, chlorophyll image. Yellows and reds show high 

chlorophyll (1-5 μg/L). High chlorophyll does not indicate the presence of harmful 

algae. 

Figure 9. February 28, 2004 image showing new blooms in red. HAB events are more 

common as new blooms. 

30
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Figure 10. March 9, 2004 image showing the bloom in St. Joseph Bay. 

Figure 11. April 14, 2004 showing the apparent blooms all along the coast caused by 

the resuspension event. These apparent blooms occur because algae at the bottom in 

shallow areas are resuspended with the sediment. 

31
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

Figure 12. April 14, 2004, chlorophyll image. 

32
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

 

Stations Sampled During Dolphin Mortality Event (March-April 2004)

Area Shown

Gulf of

Mexico

Atlantic

Ocean

Pensacola

Gulf of Mexico

St. Joseph Bay

Panama City

3/11-3/19 (FDACS, FDEP, FMRI)

3/20, 4/9, 4/28 (volunteer)

4/7-4/8 cruise (FMRI)

Sample date

3/22-3/24 cruise (NOAA CSCOR HAB Event Response Fund, FMRI)

3/25, 3/31 (FDEP, FMRI)

4/13, 4/16, 4/19 (FDACS, FDEP, FMRI)

Beasley Park

4/25-4/29, 5/6 (FMRI)

Stations Sampled During Dolphin Mortality Event (March-April 2004)

Area Shown

Gulf of

Mexico

Atlantic

Ocean

Pensacola

Gulf of Mexico

St. Joseph Bay

Panama City

3/11-3/19 (FDACS, FDEP, FMRI)

3/20, 4/9, 4/28 (volunteer)

4/7-4/8 cruise (FMRI)

Sample date

3/22-3/24 cruise (NOAA CSCOR HAB Event Response Fund, FMRI)

3/25, 3/31 (FDEP, FMRI)

4/13, 4/16, 4/19 (FDACS, FDEP, FMRI)

Beasley Park

4/25-4/29, 5/6 (FMRI)

Figure 13. Stations sampled by FMRI or associated personnel during the dolphin 

mortality event, including the stations sampled during the NOAA CSCOR HAB Event 

Response Program sponsored RV Seminole Cruise (red dots).

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

VIII. APPENDICES 

A. Criteria for Determining an Unusual Mortality Event 

1. A marked increase in the magnitude of strandings when compared with prior 

records. There is no set formula for determining what magnitude would trigger a 

response. The NMFS Southeast Region has used a formula of the historic mean 

plus two times the standard deviation to determine a threshold level. The 

Working Group stated that magnitude must be weighed against other knowledge. 

As a pragmatic method, it was suggested that if a pulse in strandings is spread 

over an area or time frame that strains the capacity of the Stranding Networks to 

respond, it should be cause for concern. 

2. Animals are stranding at a time of the year when strandings are unusual. 

3. An increase in strandings is occurring in a very localized area (possibly 

suggesting a localized problem), is occurring throughout the geographical range 

of the species/population, or spreads geographically with time. 

4. The species, age, or sex composition of the stranded animals is different than that 

of animals that normally strand in the area at that time of the year. 

5. Stranded animals exhibit similar or unusual pathologic findings or the general 

physical condition (e.g., blubber thickness) of stranded animals is different from

what is normally seen. 

6. Mortality is accompanied by behavior patterns observed among living individuals 

in the wild that are unusual, such as occurrence in habitats normally avoided or 

abnormal patterns of swimming and diving. 

7. Critically endangered species are stranding. Stranding of three or four right 

whales, for example, may be cause for great concern whereas stranding of a 

similar number of fin whales may not. 

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Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

B. Fact Sheet on Brevetoxin & Florida Red Tides 

Source of Brevetoxin (BTX): Red tides in Florida are caused by annual blooms of the 

dinoflagellate Karenia brevis which have been recorded since at least the mid 1800s. 

Karenia brevis is principally distributed throughout the Gulf of Mexico, with occasional 

red tides occurring along the mid and south Atlantic coast. The State of Florida 

continuously monitors for K. brevis, which produces nerve toxins (neurotoxins) known 

as brevetoxins that can cause serious public health effects and significant animal 

mortalities. 

Toxin/Mode of Action: 

Brevetoxins are polyether ladder 

neuro-toxins that bind to voltagesensitive sodium channels, an

important protein structure of cell

membranes. Binding results in persistent activation of neuronal cells, 

skeletal muscle cells and cardiac cells.

Karenia brevis Source: FWCFlorida Marine Research Institute

Brevetoxin Structure

Source. http://www.cfsan.fda.gov/~mow/ 

brevotox.html

Human Health Syndrome: Neurotoxic Shellfish Poisoning (NSP) is 

caused by human consumption of molluscan (e.g. oysters, clams) 

shellfish contaminated by brevetoxins. NSP is characterized by 

paresthesia (tingling), reversal of hot-cold temperature sensation, 

myalgia (muscle pain), vertigo, ataxia (loss of coordination), abdominal

pain, nausea, diarrhea, headache, bradycardia (slow heart rate), and 

dilated pupils. 

Syndrome Distribution: Although shellfish poisonings were known in Florida since the 1880s, the cause was not identified 

as K. brevis until 1960. Shellfish monitoring to protect the public from NSP is successfully managed by the State of Florida 

and there have been no human fatalities attributed to NSP. New NSP cases may rarely occur when people consume 

unregulated shellfish species, when shellfish are illegally harvested, or when blooms expand to other unmonitored geographic 

areas. For example, in 1987, an entrained K. brevis red tide that originated off the Florida west coast was transported to

North Carolina waters, causing 48 NSP cases. 

Other Human Health Effects: People can suffer from respiratory effects when brevetoxins become aerosolized through the 

disruption of K. brevis cells by breaking waves, surf or onshore winds. The first written report of respiratory irritation caused

by a Florida red tide was in 1917.

Effects on Other Organisms: Karenia brevis red tides are responsible for the annual mass mortalities of thousands of fish. 

In some years, notable mass mortalities of marine mammals, birds, and sea turtles have been reported. During 1946-1947, 

one of the largest K. brevis red tide events on record occurred in Florida waters and was associated with catastrophic 

mortalities of bottlenose dolphins, sea turtles, and numerous fish species from Tarpon Springs to Key West (150 miles). 

Other marine mammal and bird mortality events with red tide links include: 

• Brevetoxin involvement suspected in the unprecedented die-off of more than 740 bottlenose dolphins, Tursiops 

truncatus, from June 1987-February 1988 along the eastern USA. 

• During August 1999-February 2000, over 120 bottlenose dolphins stranded along the Florida panhandle during a cooccurring red tide. 

• During an October 1973-May 1974 red tide, large numbers of birds were found moribund or dead, particularly

double-crested cormorants, red-breasted mergansers, and lesser scaup. 

• Substantial numbers of sick and dying cormorants co-occurred with red tide outbreaks along the west Florida coast

during 1995-1999. 

• K. brevis was implicated in mass mortalities of the endangered Florida manatee, Trichechus manatus latirostris, in 

1963, 1982, 1996, 2002, and 2003 when hundreds of animals died during the winter-spring in southwest Florida. 

35
Interim Report on the Bottlenose Dolphin (Tursiops truncatus) Unusual Mortality Event, March-April 2004 

C. Fact Sheet on Domoic Acid 

Source of Domoic Acid (DA): Pseudo-nitschia, a diatom genus, can be found 

worldwide. Diatoms are microscopic marine plants with silica shells. Several 

species of Pseudo-nitschia produce the toxin DA. These toxic species have been 

found on the east and west coasts of the US, as well as the Gulf of Mexico. 

Toxin/Mode of Action: DA is a 

tricarboxylic acid that acts as a 

neurotoxin. It binds to glutamate 

receptors, which are involved in 

memory processing. When receptors 

are excessively activated, as occurs 

with DA, damage to neurons leads to

permanent loss of neurological

function.

Human Health Syndrome: DA causes 

the syndrome known as Amnesic Shellfish Poisoning (ASP). Mild cases arise 

within 24 hours of consumption of contaminated shellfish. Symptoms include

nausea, vomiting, diarrhea, and abdominal cramps. In more severe cases neurological symptoms occur which include 

headaches, hallucinations, confusion, short-term memory loss, respiratory difficulty, seizures, coma, and in extreme cases, 

death. 

Chains of Pseudo-nitzschia 

multiseries Source: http://www.nwfsc.noaa.gov 

/hab/HABs_Toxins/HAB_Species/PseudoN/index.htm

Domoic Acid Structure 

Source: http://www.cfsan.fda.gov/

~mow/domoic.html

Syndrome Distribution: ASP was recorded for the first 

time off the Atlantic coast of Canada in 1987 when three 

deaths and over 100 confirmed cases of acute

intoxications followed the consumption of cultured 

mussels. Milder cases have subsequently been reported. 

Effects on Other Organisms: Since the 1987 human 

outbreak, DA has been identified as the causative agent 

in the mass mortality of pelicans and cormorants off of

California, extensive die-offs of sea lions, dolphins, and 

otters off of California and whale deaths near Georges 

Bank. The toxin is transferred to higher trophic level

carnivores via the food chain, usually from filter feeding 

fish or bivalves. 

Pseudo-nitzschia and DA in the Gulf of Mexico: 

Pseudo-nitzschia spp. are present, sometimes at very 

high abundance, in coastal waters of the Gulf of Mexico. 

There is evidence that their abundance has increased as a 

result of eutrophication from increased nutrient supply to

some coastal areas. Although DA has been detected in

natural plankton samples and in cultures of Pseudonitzschia isolated from the Gulf, no cases of human or animal illness or death due to DA have been documented in the Gulf 

of Mexico.

Source:http://www.whoi.edu/redtide/HABdistribution/ICESmap/USASP93-02.jpg

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