Published Date: 2004-06-17 23:50:00
Subject: PRO/AH> Dolphin die-off - USA (FL)(04): domoic acid
Archive Number: 20040617.1615
DOLPHIN DIE-OFF - USA (FL)(04): DOMOIC ACID
A ProMED-mail post
ProMED-mail, a program of the
International Society for Infectious Diseases
Date:16 Jun 2004
From: Barbara D. Graeber <BDGraeber@aol.com>
Source: National Marine Fisheries Service website and Associated Press [edited]
[Though the previous posting on Dolphin die-off - USA (FL)(03): Domoic
acid, 20040323.0806 suggested the cause might be domoic acid, the latest
report seems to implicate red tide. However, Dr Rowles is quoted as saying
that the case has not been closed.. This information can be found at:
However, the NOAA website on strandings has posted the following report
explaining that, while domoic acid was found, it is not believed to be the
sole cause of death.
2004 Bottlenose Dolphin Unusual Mortality Event Along the Florida Panhandle
This interim report outlines the initial findings and the ongoing analyses
in the investigation of the bottlenose dolphin (_Tursiops truncates_)
mortality event that began in March 2004. 107 bottlenose
dolphins stranded dead along the Florida Panhandle between 10 Mar and 13
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, 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. [Analysis of] 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 1st
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 18 Mar 2004 tested positive for brevetoxins in
stomach contents and in muscle, liver, and gill tissues; whereas fish
collected on 28-31 Mar 2004 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 9-11 Mar 2004, but water samples
collected 11 Mar 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 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 marine
mammal mortalities related to domoic acid 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 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.