SCIENCE REVIEW 1987 - Bedford Institute of Oceanography

which takes approximately 40-90 days to
complete one revolution (Figure 1). However,
this gyre is not a closed system and
water is continually added to and lost from
the Bank by radial exchange processes all
times of the year. Because of strong tidal
currents and storm-generated waves,
sediments on the Bank tend to be coarse,
primarily sand and gravel. Georges Bank
has not always been a marine environment.
During the last glacial period when sea
level was about 100 m lower, most of it
was exposed and populated by terrestrial
organisms.
Management Issues
As Georges Bank includes waters under the
jurisdiction of both Canada and the United
States, the transboundary fish stocks
located there are exploited by both nations,
thus complicating their management.
Finfish stocks of major significance to
Canada with historical landings in excess of
1000 tonnes per year include Atlantic cod
(Gadus morhua), haddock (Melanogrammus
aeglefinus), pollock (Pollachius
virens) and herring (Clupea harengus).
Recent nominal landings are shown in
Figure 2. The exact causes for the fluctuations
observed are not understood but both
physical and biological factors are thought
Fig. 2. Nominal Canadian landings of major finfish
resources from Georges Bank between 1968 and
1987.
to be important. Other fisheries include
yellowtail flounder (Limanda ferruginea),
cusk (Brosme frosme) and Atlantic halibut
(Hippoglossus hippoglossus).
Overfishing is the central management
issue. For example, recent stock abundance
Fig. 1. Map of Georges Bank showing bathymetry, the Canadian-US international boundary and major physical
oceanographic features during summer. Arrows indicate the approximate direction of average residual currents.
estimates for Georges Bank haddock are
amongst the lowest observed since 1963
(Gavaris, 1987). In recent years, the
haddock stock has been exploited at about
twice the level recommended by scientists
and recruitment has been variable, but
generally poor. For Atlantic cod, abundance
has shown a steady decline from
95,000 tonnes in 1978 to 34,000 tonnes in
1986. The current recommended exploitation
level is less than 15,000 tonnes per
year (Hunt, 1987). In the case of haddock
and probably cod, limitation of fishing
mortalities to acceptable levels will require
joint management by both Canadian and
US authorities.
A multinational fishery for herring on
Georges Bank began in 1961 and yielded
2.7 million tonnes before crashing in 1977
after a classic “boom and bust” pattern
brought about by overfishing. For several
years, there was virtually no sign of a
population that had once been estimated at
1.14 million tonnes in total biomass. The
loss was felt not only in the collapse of the
large fishery on adults but also in the
decrease of the coastal weir fihery for
juvenile herring (sardines) in Maine and
New Brunswick which is assumed to have
been partially dependent on emigrants
from Georges Bank. Recently there have
been signs of recovery of Georges Bank
herring, including the occurrence of spawning
and of larvae in both 1986 and 1987
(Stephenson et al., 1987). Management
issues regarding this stock again focus on
the need for consistent regulatory measures
on both sides of the international boundary
and improved understanding of the relationship
between herring populations on
the Bank and along the coast.
The most valuable invertebrate fishery
on Georges Bank is the sea scallop
(Placopecten magellanicus). A management
plan, developed in consultation with
the fishing industry, ensures the conservation
and prudent management of this
resource while providing reasonable access
for fishermen. In 1987, over 55,000 tonnes
were caught with a landed value of
approximately $60 million. As a management
measure meat counts, which regulate
the size of scallops harvested, have not only
proven to be a useful conservation measure
but they have also allowed better use of
different age groups of scallops. The
industry has endorsed a Total Allowable
Catch (TAC) Enterprise Allocation (EA)
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