| dc.description.abstract | 1. Trawl fishing for deep sea prawns commenced in Norway in the
autumn of 1898 after Hjort had proved in 1897 the existence of
great quantities of P. borealis in the fjords of East Norway. On
the recommendation of Dr. C. G. JOHS. PETERSEN, HJORT constructed
a serviceable gear for this fishery by modifying the Danish
eel-seine to an otter-trawl. In table 1 and Figures 2, 3 and 4 a
summary is given of the growth of prawn fishing in Norway, Sweden
and Denmark. In 1935 nearly 5 million kilogrammes of prawns
were fished by these three countries altogether, and 2/3 of this
quantity by Norway alone.
2. On the basis of information and charts placed at our disposal, mainly
by two fishermen, a survey is given of the prawning grounds which
are known from the Svenör Bank to the Trondheim Fjord.
3. The development of gear and fishing craft from HJORT's first
trawl and sailing boats to modern gear and motor vessels is described.
4. The statistical value of the prawn fishing in the case of Norway
has amounted in recent years to about 2 million kroner per annum.
From 1908 to 1935 the value of the total yield in the case of Norway
has been more than 22,5 million kroner. The incomes of the
fishermen vary considerably according to their ability. Some
examples show that in good years the gross income has amounted
to about Kr. 20.000,00. The nett income amounts to 35 % - 50
% of the gross.
5. The life history of P. borealis is described on the basis of previous
investigations and those undertaken by us. An account is given
of the growth of the prawn in Norwegian waters and of the probable
number of moultings to which it is subjected.
6. When the prawn fishery commenced an accumulated stock was
fished. After the lapse of a number of years the catches became
dependent on the annual renewals and the intensity of the fishery.
The yield has therefore declined considerably on all the old grounds
until in recent years it has become more constant with minor
fluctuations.
7. The possibility of discovering new prawn grounds in the Norwegian
Channel has been investigated by cruises from the Reef off Kristiansand
S. to the waters off Stadt during the summer of 1934. On
these cruises it was found that the quantity of prawns declined
gradually with the disappearance of detritus from the material of
the sea-bed. From Utsira and northwards the bottom consisted
of pure sand.
8. Similar experience was gained by BIGELOW and HJORT in the Gulf
of Maine (U.S.A.) during the summer of 1936. Quantities of P.
borealis capable of being fished on an industrial scale were found
in waters which had strong points of resemblance with the prawn
grounds in the Norwegian fjords.
9. A comparison between the animal life of the prawn grouncls examined
by bottom sampler (BROCH 1935) and that brought up by the trawl
shows that the trawl only takes up a very small selection of the
bottom fauna, namely, the large forms which live on and over the
bottom. A list of the species of fish caught by trawl in Norwegian
waters is also given here, and the quantities in which they are
takeil.
10. The injurious effects which trawling is said to have on other fisheries
are discussed.
11. The effect of the gear on the size of the stock of prawns is examined.
12. The bearing of our investigation is discussed, and recommendations
for a minimum mesh in the trawl are made in order to bring
the fishery into rational forms and to increase the catches of the
fishermen. | |
