AMERICAN PLAICE
Growth, Quotas,
Stock Status & Timeframe,
Conservation, Production
& Survival
Environmental Conditions
PHYSICAL DESCRIPTIONS
American Plaice belongs to the flatfish group of
fishes. These fish
possess laterally compressed bodies and lie and
swim on one side. When the
young fish hatch from the egg, at or near the
surface, they have the normal
fish form. During development, as they settle to
the bottom of the ocean, a
change occurs in the body structure. The head
becomes twisted so that the
fish now swims and lies on its side. The upper
side (which now has eyes) has
normal pigmentation as compared to the lower
side which lacks pigmentation.
Plaice almost invariably have their eyes on the
right side of their body.
The fish has a large mouth that extends at least
below the middle of the
eye. The body is covered with relatively small
scales, the tail fin is rounded,
and the line that runs along the side of the
body is slightly curved just behind
the gill openings. The color is normally reddish
to grayish brown on the upper
pigmented side and white on the lower side.
COMMON NAMES
American plaice, Canadian plaice, plaice, sand
dab, dab, rough dab, long
rough dab (British Isles), flounder, grey sole.
SWIMMING PATTERNS
They swim on their side to which their head is
twisted. They also lie
on their side.
BREEDING & FEEDING HABITS
For most of their distribution, female plaice
begin to spawn at eight or nine
years of age when they are about 30 cm in length
(depending on location).
However, most female plaice do not reach the
spawning stage until at least
11 years of age (40- 45 cm). Some males, on the
other hand become sexually
mature at three years of age when they are 15-20
cm in length (depending on
the locality). However, all male plaice are
usually mature after the age of
6 (25-30cm). Plaice produce large quantities of
eggs, thus, a 40cm plaice,
on the average, produces 250,000 to 300,000 eggs
and a 65-70 cm plaice
produces nearly 1,500,000 eggs. Spawning and
fertilization of the eggs occur
at or near the bottom and the fertilized buoyant
eggs float to the surface layer
where hatching occurs. While no specific
spawning grounds for this species
have been recognized, certain localities offer
environmental conditions such
as bottom type, temperature and depth that are
particularly favorable for
spawning activity.
American plaice are spring spawners with
spawning occurring from as
early as the first part of April on the Flemish
Cap and on the southern half
of the Grand Banks, to late May or early June
off Labrador. The length
between fertilization and hatching of the eggs
varies considerably depending
on the water temperature in the upper layers.
Hence, developing eggs and
larvae could drift a considerable distance
before the young fish finally settle
to the bottom.
Feeding:
Larval plaice feed on minute plants and animals
that are present in the upper
water layers. When they settle to the floor of
the ocean their diet gradually
changes as they grow and the mouth size
increases to accommodate
a wider variety of prey. Adult plaice feed on
such things as sand dollars,
brittle stars, shrimp-like animals, marine worms
called polychaeters, and
fish, primarily capelin and lance. As a matter
of fact, the latter make up most
of the diet of plaice in some localities.
Although the normal habitat is at or near the
ocean floor, plaice frequently
move off the bottom, usually at night, possibly
in pursuit of prey species such
as capelin.
HABITAT
This species is distributed on both sides of the
Atlantic, although the European
type probably is a subspecies of the North
American fish. In the Northwest
Atlantic they occur from West Greenland to the
Gulf of Maine. The general
distribution is off the east coast of Canada. As
indicated, the occurrence of the
species is widespread throughout the area and it
is probably the most abundant
flatfish in the Northwest Atlantic. The area of
highest abundance is the Grand
Banks, especially the northern half.
While American plaice is considered to be a
"cold" water species, it nevertheless
appears to have a fairly wide temperature
tolerance. It occurs in temperatures
ranging from about -1.5 degrees Celsius
temperature above 5 degrees Celsius
and from inshore localities down to 700m.
However, the preferred temperature
for this species appears to be in the range of
just below 0 degrees Celsius to
about 1.5 degrees Celsius and principally in the
90 to 250m depth range. It is
worth noting that the largest catches are
normally taken between 125 and 200m
in temperatures of -0.5 degrees Celsius to 1.0
degrees Celsius.
GROWTH
Plaice are relatively slow growing fish. Age is
determined by counting rings on
the ear bones (otoliths). The dark rings are
probably formed when environmental
conditions and food supplies are unfavorable and
growth is slow. The lighter
rings probably reflect favorable conditions and
periods of more rapid growth.
Because of differences in environmental
conditions and food supplies
throughout the region, there is considerable
variability in the rate at which these
fish grow. Plaice on the northeast part of the
Grand Banks at 10 years of age are
on the average 32cm in length whereas on the
southwest part of the Grand Banks
they are approximately 45cm in length. Male
plaice are slightly smaller than female
plaice, after about six years of age, and
usually have a shorter life span. American
plaice from the Gulf of St. Lawrence (4T) and
the Scotian Shelf (4V,W,X) have a
growth rate slightly below the average on the
southwest part of the Grand Banks.
Plaice up to at least 25 years of age have been
caught, but in heavily exploited
stocks 20 years of age is usually the maximum recorded.