The Deep-Sea Prawn (Pandalus Borealis) in Icelandic Waters
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17. The Deep-Sea Prawn (Pandalus borealis) in Icelandic Waters By A b a l s t e in n S ig u r d s s o n a n d I n g v a r H allgrimsson Atvinnudeild Håskolans, Fiskideild, Reykjavik Commercial prawn fisheries first began in Area 4, Age and growth Isafjaröardjüp (see Figure 1) in 1936, and a few years Since the autumn of 1959, samples of deep-sea prawn later in Arnarfjöröur, Area 3. from Area 4 have been collected and carapace length The deep-sea prawn is very common in Icelandic and sexual development determined. waters, although it has not yet been found in com The spawning season in this area is September- mercial quantities outside Isafjardardjiip (Area 4), October and hatching takes place mainly in March and Arnarfjöröur (Area 3) and Ingölfsfjöröur (Area 5). April. If 1. April is chosen as the time of hatching for The prawn fisheries in Ingölfsfjöröur have, however, the deep-sea prawn, the individuals will be 9 months been almost negligible. old at the beginning of the following year. • TRAWLING STATION PRAWN GROUNDS • a Figure 1. 106 22 Table X. 20 FEBRUARY 5 I960 Sexual development A few males s p a w n .................................. 1 x/2 years old Most of the males spaw n ....................... 21/2 years old A few males spawn for the first or the second tim e ............................................. 3 1/2 years old A few females spawn............................... 21/2 years old Most of the females spaw n .................... 3 x/2 years old A few females spawn for the first or the second tim e ............................................. 4 1/2 years old 22 OCTOBER 27 I960 SÉo 5 I I I960 1961 1962 Figure 3. Area 4 (fsafjaröardjüp). Figure 2. Length distribution and estimated age distribution of 600 the deep-sea prawn in Älftäfjöröur, Area 4, in 1960. A l and Bj_: A2 and B2: a* 500 o immature males ------------ length distribution < 20 0CL —. — . — .— mature males of total sample --------------- intersexes 1x 400 --------------- immature females — estimated division UJ X ------------------m a tu re fem ales betw een year- classes (/> O5 Figure 2At and Bj shows the length distribution of CD OU. 2 0 0 < immature males, mature males, intersexes, immature m females and mature females from two samples col 53 lected in Area 4, on 5. February 1960 and 27. October z 1960, respectively. Figure 2A2 and B2 shows the length distribution SASASASASASASAS (solid lines) of the total samples (see Figure 2 Aj and 1955 1956 1957 1958 1959 I960 1961 1962 Bj, respectively) and a suggested division between Figure 4. Area 4 (fsafjaröardjüp). year-classes (broken lines). S = Spring season. A = Autumn season. Fluctuations in catch (a) Area 4 (Isafjaröardjüp) Figure 4 shows the fishing effort from the years Unfortunately there is no information on catch per 1955-1961 and the total catch in metric tons. In 1957 trawling hour in Area 4 until October 1959, and con the boats were inactive part of the season because of tinuous information exists only from January 1960 unfavourable markets, so the total catch was com (see Figure 3). The catch is evidently decreasing, since paratively low. in October 1959 it was 273 kg, but in April 1962 it Up to the autumn of 1959 all prawns were shelled had reached as low as 47 kg. by hand. Up to that time a shortage of labour pre- 107 1200 3 160 140 1100 300 COO AND HADDOCK 100- 2 50 1000 80- 200 OTHER SPECIES S 60 150 4 0 100 9 0 0 20 ' 50 8 0 0 1953 1954 1955 1956 1957 1958 1959 I960 1961 q3: o Figure 5. Area 3 (Arnarfjöröur). X 700 Z vented the prawn stock from being overfished. In the _J I winter of 1959-1960 two canning factories began to <e I- 6 0 0 use machines to shell the prawns. The effort was Id immediately increased in order to get sufficient raw Q. CE material for the machines. Up to this time the maximal 500 catch per boat per day was limited because otherwise =32 Z the canning factories were unable to process the catch. After 1959 there were no limits on the quantity of the 4 0 0 daily catch per boat and more boats went in for prawn fishing. 3 0 0 From 1960 to 1961 the total yearly catch decreased from 1143 to 1079 metric tons, in spite of the in creased effort, and the total catch in the spring season 200 of 1962 was only 186 metric tons, which is extremely low. Considering the increased effort, the decrease in 100 catch per trawling hour from autumn 1959 up to spring 1962 (see Figure 3) plus the decrease in total catch in 1961 and in the spring season of 1962 (see I 2 3A 3B 4 5 6 7 8 9 10 II 12 Figure 4), it is evident that the prawn stock in Area 4 "R E A NUMBER has been overfished these last few years. Figure 6. (b) Area 3 (Arnarfjöröur) maximal catch per year or some other factors. Should Figure 5 shows the average catch per trawling hour the former be the case, it shows that the prawn stock in kg, total catch per year in metric tons and the in this area cannot support more effort, and it is number of boats fishing in Arnarfjöröur, Area 3, in evident from the 1953-1955 data (see Figure 5) that the years 1953-1961. the fishing of 10 boats was too high an effort. What The number of prawn trawlers in Arnarfjöröur happened in 1953 was likely to recur in the winter of rose from 4 in 1952 to 10 in 1953. The increase in 1962/63 as an increase in effort was imminent. fishing effort resulted in a decrease in catch per Consequently, it was decided to permit a total yearly trawling hour from 150 kg in 1953 to 63 kg in 1954, catch based on the average catch during the period which again cut down the number of boats fishing 1956-1961, i.e. ca. 180 metric tons. for prawns, 5 being active in 1955 and 4 in 1956. Since The low total catch in 1961 was due to a labour then the catch per trawling hour has increased and dispute during a considerable part of the autumn has been fluctuating from 86 to 107 kg, with the season. number of boats from 3 to 5. The catch per year reached a maximum in 1959 and The by-catch 1960. During these years the catch per trawling hour It has been used as an argument against prawn fish decreased a little. This decrease is so slight that it is ing by trawl that other commercial species, especially impossible to decide whether it can be ascribed to the young fish, would be caught as well as the prawns. We 108 have tried to solve the by-catch problem by collecting According to this, it is obvious that the loss of cod data both from commercial and research catches. and haddock caused by the prawn fisheries in Area 4 Figure 1 shows stations worked on six trips, two of is negligible compared with the yield of prawns, since which were made by commercial boats in Area 4 at the time when these investigations were carried out, during the period October 1959 to M arch 1962. The the prawn catch per trawling hour in this area was waters around Iceland are divided into 12 areas (see 140-270 kg. Figure 1). The average number of fish per trawling hour from each area is shown in Figure 6. Résumé of discussion on the paper The histogram in Figure 6 shows both the total Dr. L i n d q u i s t described the reduced abundance number of fish and then specifically the number of cod and, in one case, complete disappearance, of Pandalus and haddock (the black part of the columns) per from certain fjords in Sweden. This was attributable trawling hour in Areas 1 to 12. to hydrographic changes. He asked the speaker if the Icelandic fishermen have developed a new type of changes at Iceland, referred to in the paper under prawn trawl in order to avoid catching other fish. discussion, might not similarly have been due to en The Icelandic prawn trawl was the only gear used in vironmental factors rather than to the effect of fishing. all areas, except Area 3, where a Danish prawn trawl M r. Sigurbsson thought that the decreasing catch was also used (see Figure 6, where 3 A shows the was not attributable to any hydrographic change and number of fish per trawling hour caught by the Ice emphasized that it had been accompanied by in landic prawn trawl, and 3B the catch by Danish creased effort. prawn trawl). A comparison of columns 3A and 3B Dr. C o l e asked if the stocks in individual fjords in Figure 6 will thus give an idea of the difference in were isolated or if they could be recruited from outside. efficiency between the two types of trawl as far as M r. Sigurbsson replied that he was not certain on other fish are concerned. this point; fishermen say that there is an influx in late Non-commercial species, as for instance the Norway winter. Returning to the question Dr. C o l e said he pout (Gadus esmarki Nilsson), form the greatest part of felt that in the particular circumstances the stocks the by-catch where it is outstandingly high.