2007 Texas Unusual Mortality Event - 1st Quarter 2007
Here at TMMSN, we
are always prepared for Stranding Season (January-March) as it rolls
around every year.
Stranding Season is the time period over which we experience a
significant increase in deceased marine mammal strandings across the
state in comparison to the rest of the year.
However, this year handed us something that we were
definitely not expecting…..
During the months
of January and early February, we saw a slight increase in
strandings, but it was not anything out of the ordinary for our
stranding season. It
was during the last week in February that the report of a deceased
bottlenose dolphin on the beach became a daily event.
As we responded to the reports it was not unusual for us to
find additional deceased dolphins en route to the initial animal
reported. Some of these
deceased dolphins were even found within several yards of each other
or actually seen washing onto the beach as we were engaged in
another recovery. As we
experienced the sharp increase in strandings, we of course began to
investigate further. It
seemed that the only two geographic regions throughout the state
that were experiencing an increase were the Galveston and Sabine
Pass Regions (Northeastern Texas).
NMFS/NOAA was
notified of the increase and the “Unusual Mortality Event” (UME)
process was launched.
The first step was to begin a close look at historical data for the
areas. Historical data showed that the mean average for the past
five years of strandings in both the Sabine Pass and Galveston
Regions had already been met or exceeded by early March.
The second step in the process was to submit a breakdown of
data on the current 2007 strandings, such as species, age classes,
and condition codes of the dolphins.
Also included in the initiation package was any information
on unusual meteorological, environmental, and anthropogenic
conditions in the surrounding and affected areas.
This UME Initiation Package was then submitted to the
National Marine Fisheries Service’s Marine Mammal Health and
Stranding Response Program which consults with the “Working Group”,
a group of individuals with extensive experience in different fields
pertinent to the investigation process.
After consideration of the information submitted, the Working
Group made their recommendation to NMFS that this be declared an
Unusual Mortality Event based on 2 of 7 criteria:
1) There was a marked increase in the magnitude or a marked
change in the nature of morbidity, mortality or strandings when
compared with prior records and (2) the species, age, or sex
composition of the affected animals is different than that of
animals normally affected.
Limited sample
collection was initially taken due to the advanced state of
decomposition of the animals.
However, after the die off event was suspected, protocols
were implemented for sample collection for biotoxin, virology, life
history (including genetics), toxicology, and blast trauma analysis.
The bottlenose dolphins affected (Tursiops
truncatus) were suspected to be from the off-shore population
due to their robust body size and presence of Xenobalanus. All but three of the dolphins included in the UME washed
ashore in a moderate or advanced state of decomposition. While all age classes were recovered, there was a
preponderance of calves with fewer animals found larger than 200cm. The adult animals that were examined were found to be in good
body condition (robust, not emaciated) with full stomachs.
Satellite imagery
in the areas did not indicate the presence of red tide.
A high chlorophyll image obtained suggested only a
non-harmful algal bloom off of Texas.
There was an unidentified bloom noted offshore Louisiana and
we worked closely with the HAB departments conducting further
studies on water samples collected during this time period to
identify it.
Among our initial
hypotheses were the following:
Due to the fact that the animals were stranding in such an
advanced state of decomposition, we suspected that the animals
affected were being transported by winds/currents potentially from
further offshore or farther north.
The adequate body condition of the adult animals recovered
suggested an acute process resulting in death.
Additionally, the high percentage of neonates and fetuses
recovered suggested premature labor.
To date, a cause
of the strandings has not been found from the analyses of samples
collected from the deceased marine mammals.
Again, the state of decomposition was a key factor to whether
or not we are able to get any answers as to the cause of this
Unusual Mortality Event. As
you will see on the graph, unfortunately 44% of all UME causes are
unknown due to various factors. The UME investigation remains open at this time and the
investigation team will consider a suite of information before a
final decision is made by the Working Group to close the UME with or
without a known cause.
As you can see
from the statistics included in this article, TMMSN was very busy
during the first quarter of 2007 and recovered nearly 100 animals in
only one month’s period of time with 80 percent of the strandings
occurring in the northeastern portion of Texas.
These recoveries
could never have been accomplished without the willingness of so
many hardworking volunteers.
It was very encouraging to see so many volunteers from the
Galveston region join in the recoveries even though many times they
were under very unpleasant conditions.
We have very admirable volunteers and agencies alike that
truly believe in the research work that we do to benefit marine
mammal conservation and it’s remarkable to see them in action.
I just cannot thank you enough for all of your assistance and
hard work during this time!
Heidi R. Watts
State Operations Coordinator
TMMSN