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**Cooperators Continue to Track Sea Squirt off Georges Bank**

WOODS HOLE, MA, September 2006 -- Two NISC member agencies, the National
Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological
Survey (USGS) along with non-federal scientists have begun their fourth
year of tracking and surveying the growth of the invasive Georges Bank
sea squirt, *Didemnun* sp. This non-native sea squirt, which may
actually be more than one species, continues to proliferate off of
Georges Bank and increasingly dense colonies have been found over an 88
square-mile area.

The non-native sea squirt may potentially devastate and dominate
underwater ecosystems, suppress indigenous fish and shellfish species,
and can harm economically important fisheries in the region. So far that
hasn't happened, according to Dr. Page Valentine of the USGS, who tracks
occurrences of the species off the northeastern U.S., and elsewhere in
the world "no doubt this is having an impact on certain kinds of
aquaculture, but we haven't seen an affect on the fishing grounds yet,"
he said.

Sea squirts, also referred to as tunicates because of their primitive
spinal cord and outer sheath or "tunic", expand outwardly by budding new
millimeter-sized individuals through both sexual and asexual
reproduction to form circular mats up to a foot in diameter. The mats
coalesce with neighboring colonies to form a tough, barren layer of
interwoven colonies that attach to hard surfaces including gravel, wood,
metal and plastic.

The underwater mats they create cover the seafloor and can prevent fish
from feeding on the worms and crustaceans that live in and on the gravel
bottom. They have no known enemies. Periwinkle snails have been observed
nibbling on the tunicate in tidal pools, but only after the mat has
died. Live sea squirt is very acidic.

Sea squirts spread in several ways: by larvae that swim for only a few
hours before settling, by colonies that hitchhike onto surfaces such as
boat hulls, moorings, fishing gear, and other manmade objects, and by
fragments of colonies that are broken up by human activities such as
scallop dredging.

"The area of seabed covered by the colonies has doubled at 75 percent of
the sites we observed in both 2005 and 2006," said Dr. Valentine.
Greater density of colonies observed during the survey is evidence that
the infestation is persistent, and not a short-lived phenomenon.

Scientists have noted that this non-native sea squirt has not yet spread
to nearby Canadian waters and they are continuing to monitor the
expansion of new colonies.

U.S. Federal officials from NISC member agencies and scientists continue
to be concerned about the affects of the expansion of *Didemnum* at
Georges Bank and stress that it is vitally important to continue
surveillance efforts of the current areas and of other susceptible
coastal waters to ensure that other sites are not infested with
unaccounted for tunicate communities.

***[Note to Stakeholders:]{.underline}*** This stakeholder's
announcement is based on a recent NOAA press release, which can be
viewed at <http://www.nefsc.noaa.gov/press_release/2006/nr0613.htm>. For
additional information on this topic, contact Lori Williams at (202)
354-1875 or <Dean_Wilkinson@ios.doi.gov>.