- Masses of large ocean-going squid have inundated the
shores of Southern Chile, alarming local fishermen who fear these carnivorous
invaders could threaten fish stocks. Envisat has helped account for their
otherwise mysterious arrival.
-
- These jumbo flying squid - Dosidicus gigas is their Latin
name - are some of the largest known squids on the planet: the ones here
measure between 70 to 150 centimetres in length, although specimens have
been known to reach more than three metres. Making their home in the open
ocean, they rise to the surface at night to aggressively feed on small
fish using barbed suckers. In the final days of February more than 200
of the squid were washed up on the beaches around Ancud, on the northern
coast of the island of Chilo' in southern Chile. Further incursions have
since taken place towards Calbuco, on the inner side of the Chacao channel
and towards the southern part of the island along the coast, up to Castro
in the middle of the big island of 'Los Lagos' region of the country. Strandings
have also been reported in more northerly areas such as Chile's VIII region.
-
- Wondering why these deepwater animals unexpectedly made
it to coastal waters is a matter of more than just scientific interest.
Thousands of Chileans earn their livelihood from fishing in this part of
the country, and these voracious cephalopods are known to prey on commercial
fish including hake, sardines and anchovies. The squid themselves are a
delicacy in some parts of the world but there is no local tradition of
catching or consuming them.
-
- But an explanation for the incursions was available ñ
from 800 km away in space. Envisat's Advanced Along Track Scanning Radiometer
(AATSR) instrument works like a space-based thermometer, taking the temperature
of land and sea as it orbits the Earth. It can measure sea surface temperature
(SST) to an accuracy of 0.3 degrees centigrade at a spatial resolution
of one square km.
-
- A Chilean team is currently working with AATSR SST results
in combination with ocean colour data from another Envisat instrument,
the Medium Resolution Imaging Spectrometer (MERIS). The main goal of the
project is to investigate the feasibility of a satellite-based early warning
system for harmful phytoplankton blooms ñ explosive growths of sometimes
toxic marine algae.
-
- "The AATSR results show the appearance of the squid
was connected with changes in the water mass conditions off the coast of
Southern Chile in recent weeks," says Dr Cristina RodrÌguez-Benito
of oceanography company Mariscope Chilena.
-
- This part of the Chilean coast, like most western continental
coasts, is subject to upwellings - cold, nutrient-rich waters rise from
the oceans depths as prevailing winds blow warmer surface waters away.
The phenomenon supports rich fisheries. But the AATSR data reveal that
a coastal upwelling that typically influencing the waters between ChiloÈ
and the mainland was not seen in the last week of February.
-
- "This caused an influx of warmer water, between
0.5 and 1.5 degrees, and also squid, which are attracted to steep temperature
and salinity gradients in the sea where they find their food," adds
RodrÌguez-Benito. "The squid ended up in a lens of cold water
between warmer masses, and this carried them into the inner Gulf of Ancud
area.
-
- "The decrease in water temperature in the inner
areas can also have a direct effect on aquaculture, because the metabolic
systems of fish species are very sensitive to such changes. Envisat's AATSR
data registered a decrease of up to 3C.
-
- "Even more important than temperature is the indication
of the entrance of a water mass poor in oxygen that could be the reason
for the losses already registered in some aquaculture sites.
-
- "We are interested in such events as part of our
main project because temperature gradients are often where new phytoplankton
blooms occur. But the possibility of being able to predict these phenomena
would be very useful also to the fishing industry."
-
- The team plans to present their experiences of using
Envisat data in this way to a conference this month of the Chilean Civil
Protection Organisation.
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- http://www.sciencedaily.com/releases/2004/03/040323072405.htm
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