SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

Long term changes in the Labrador Current
J.R.N. Lazier
Summary
J.R.N. Lazier
FISH catches in the waters east of
Newfoundland vary from year to year but
so do the temperature, salinity and speed of
the water. We are trying to find connections
between the abundance of fish and
the changing environment.
Introduction
The Labrador Current flowing down the
east coast of Canada is famous for ice and
cold water, the biggest cod fishery in the
world, the birds, whales and seals that feed
in it and the natural gas and oil that lie
beneath it (Figure 1). Humans have
exploited the living resources for eighty
centuries, but not always wisely. Many bird
species for instance are gone to supply the
needs of bygone fashions and overfishing in
the 1960’s severely depleted some fish
stocks.
To protect these resources Canada
declared, in 1977, a 200 mile limit. This
meant the country would manage all the
resources in and under the ocean up to 200
nautical miles (370 km) from the land. The
new boundary includes most of the Labrador
Current.
Good management needs accurate information.
Back at the time of the 200 mile
declaration we knew as much about the
Labrador Current as any other part of the
ocean around Canada. This knowledge
came from observations collected in the
late 1920’s and early 1930’s following the
loss of the Titanic to a Labrador Current
iceberg. Since 1977 however, Canada has
become the world’s largest exporter of fish
Figure 1 Ocean currents east of Canada: the
Labrador Current arises from the Baffin Island
and Greenland currents, plus the outflow from
Hudson Bay.
and fish products and the sixty year old
oceanographic knowledge is not adequate
for managing these precious resources
which are coming under even more pressure
as the demand for Canada’s fish
increases.
One thing we eventually must understand
about the fish is why there is so much
variation from one year to the next in the
number that grow up to be adults. Is it
because one year is colder than another or
because the wind blew from the wrong
direction at the wrong time or because too
many fish were caught? There are many
possible reasons but before answers can be
found we must have a thorough understanding
of why the environment varies
from year to year. These long term changes
are well known to be large in and near the
Labrador Current. The whalers, over one
hundred years ago, knew how the weather
off west Greenland could be bitterly cold
Figure 2 Temperature measured in July 1985 in
a section across the continental shelf and slope
at Hamilton Bank. Note the cold layer over the
shelf compared to the warmer water in the deep
ocean. The main part of the Labrador Current
lies over the upper part of the slope, where the
temperature changes rapidly from -1.5°C to
3.0° C at 100m depth.
one year and relatively mild the next. The
amount of ice off Newfoundland varies
greatly from winter to winter and has been,
for years, an indicator of the severity of the
winter. The iceberg that sank the Titanic in
1912 at 42°N was much further south than
icebergs normally get because that was an
unusually severe year for ice.
Measuring the Current
The only way we are going to get the data
we require is to go and start measuring the
temperature, salinity and speed of the
current in some key locations (Figure 2).
The temperature and salinity data are
important because the fish avoid water that
is too cold or too salty. The data are also
used to calculate the current’s speed in
regions where we can’t afford to put the
instruments that measure the speed directly
and to find the relationships between the
changing weather in the atmosphere and
the changing environment in the sea.
Continuous records of the speed of the
current are compared with wind over the
ocean and runoff from the land to determine
the main forces that determine the
strength of the current and the variations
over seasons and longer.
We began this measuring program in
1978 by placing four continuously recording
current meters at important locations in
the current near Hamilton Bank on the
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