THE SHRIMPING INDUSTRY IN ESSEX
239
It has been mentioned earlier that the brown shrimp is found
all the year round over a great part of the Thames Estuary.
However, the brown shrimps do migrate a little and these move-
ments are connected with salinity and temperature. If the
salinity and temperature drop considerably the animals will move
to deeper and warmer waters, generally to a few miles from the
coast, where the eggs carried by the females will develop further.
There the young larvae will be hatched out in more saline waters,
and when the temperature and salinity rise in the spring the
shrimps make their way to coastal waters. Food is another
factor which induces certain movements which are of a local
character. Sexual impulse again may bring shrimps together,
although special spawning grounds are quite unknown.
(b) The pink shrimp (Pandalus montagui).
The pink shrimp is widely distributed from the extreme north
of Norway to the English Channel. It is abundant over the
whole of the North Sea, and it is found in the Skagerrak, Cattegat
and Baltic. It is common off the English and Scottish coasts,
and it has been recorded from Ireland, Shetlands, the west coast
of Greenland, and off the east coast of North America,
The pink shrimp prefers hard stony bottom and it is found in
deeper water than the brown shrimp. Although a coastal animal,
it is often found at a depth of 20 to 50 fathoms. There is a
record of several specimens being taken off the east coast of North
America, at a depth of 430 fathoms.
The life history of the pink shrimp is of great interest. There
seems to be no doubt that, for a considerable part of its existence,
the species is gregarious and migratory. Pink shrimps disappear
from the fishing grounds in the Thames Estuary by the end of
October or the beginning of November, just before the breeding
season starts. Sometimes, if the weather keeps moderate, the
shoals will stay longer on the grounds. The disappearance, how-
ever, is never complete since some small concentrations of pink
shrimps have been found off Sheerness and Clacton-on-Sea even
in January and February. This movement or migration is corre-
lated with temperature, salinity and breeding. By November and
December the water temperatures drop considerably, and if in
addition there are heavy rainfalls the sea-water close to land
becomes less saline. At that period egg laying commences,
reaching the highest peak in January. It has been found that
during the winter months the population which had remained on
the grounds consisted of young shrimps, and particularly males.
The older groups and mainly the females had decreased markedly
or disappeared completely, and it appeared that they had moved
to deeper water, where higher temperatures and salinities are
beneficial for the development of the egg and the newly hatched
larvae. By the beginning of April the majority of the eggs will
be hatched out, and soon after the shoals would appear over the
grounds, first towards the open sea, and later further west and