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International Council for the Exploration of the Sea

C,M. 1976/F:39 Derner sal Fish (N) Committee

PRELIMINAR Y RESULTS OF SAITHE TAGGING EXPERIMENTS ON THE NORWEGIAN COAST IN 1973

by

Tore Jakobsen

Institute of Marine Research Box 1870-72, 5011 Bergen, Norway

INTRODUCTION

The Norwegian saithe tagging experirnents carried out on the Norwegian west coast south of 62⁰N in 1972 wer e the fir st of any significance in that area. Preliminary results were presented last year (Jakobsen 1975) showing an extensive migration of irn.m.ature saithe into the North Sea.

From the coastal area between 62⁰N and Lofoten results of Norwegian experiments carried out in the M!Z5re (Svin!Z5Y) area (62⁰ - 63⁰ 30 ' N) have been published (Ols en 1959, Anon. 1965), indicating a basically north- ward trend in the migration pattern although a few recaptures were also made in the North Sea. This substantiates the common opinion (Anon. 1965) that the borderline between the North Sea and the North- East Arctic stocks of saithe is most conveniently set at 62⁰N.

However, three tagging experiments at M!Z5re in 1971 and 1972, which unfortunately produced very few recaptures (Jakobsen 1976), gave slight indications that the migration of immature saithe from the area might be more frequently directed towards the North Sea than previously suspected.

In June 1973 five saithe tagging experiments were carried out on the Norwegian west coast, two of these north of 6ZoN.

with the results up to and including 1975.

This paper deals

MA TERIAL AND METHODS

In 1973 saithe tagging was carried out at five localities on the west coast of Norway. Hydrostatical tags of Lea's type were used, fastened to the fish with a nylon gut through the flesh in front of the anterior dorsal fin. The release data were: 13 June, 59⁰27'N - S005'E, 600 saithe, 31 - 51 cm. 12 June, 59°59'N - SOOS'E, 300 saithe, 24 - 40 cm.

7 June, 610

56'N - S007'E, 600 saithe, 32 - 54 cm. 5 June, 630

29'N - SOOO'E, 600 saithe, 32 - 51 cm. 4 June, 64°Z0'N - 10026'E, 600 saithe, 36 - 52 cm.

The tagged saithe were predQminantly 2. - 4 yea.r s old and accordingly most of the recaptures made by 1975 were inlITlatnre fish. The saithe had been caught by purse or beach seine and had been kept in a net for a few days.

RESULTS

Fig. 1 - 5 show the geographical distribution of the recaptures in 1973 - 75 for which the locality was reported. Tag returns without locality or position are ommitted. They generally amount to less than ten per cent of the total number of tags returned.

The figures show the recoveries made during the first two and a half year after release and may give the irnpression that some of the

tagged fish still remain near the tagging localities. However, as was clearly demonstrated in the more detailed presentation of the 1972 tagging experiments (Jakobsen 1975, 1976), rnuch of the saithe migrate away from the coast already during the first year after tagging and recaptures near the tagging localities after two years are very few if any.

The three experiments south of 620

N (Figs 1 - 3) all show a basic migration pattern towards the North Sea from where 69 recoveries were made (including Skagerrak). Eleven recoveries were rnade just

- 3 -

north of 63 N and three tags were returned from northern Norway. o In addition, there were three returns from the Faroe Islands and one from Iceland.

The experiment at M~re (Fig. 4) indicate that the immature saithe from that area also basically migrate to the North Sea. Thus, of the recaptures outside the release area, only 12.5 per cent were made to the north. The recoveries from the North Sea were more concen- trated in the northern part than those from the experiments south of

6Z^oN.

From the northernmost experiment, at Tr~ndelag (Fig. 5), there were seven recoveries north of 66^b30'N and six from the North Sea. Most of the recoveries on the Norwegian coast near the release area were to the south.

There have been reported seven recoveries near the Faroe Islands and two at Iceland from these experiments. This demonstrates what is known from earlier tagging experiments (Anon. 1965), that there is some degree of mixing between the different saithe stocks.

DISCUSSION

The recoveries will be influenced by the fishing intensity in the different areas. For saithe, however, the exploitation is fairly equally distributed on the different stocks (Anon. 1976) and with the exception of local variations, especially along the Norwegian coast, the recoveries should give a useful picture of the migration patterns, also with regard to quantity.

The tagging experiments have so far given little direct information about what spawning grounds the immature saithe from. the different parts of the Norwegian west coast finally migrate to. However, it would seem natural that immature saithe once having m.igrated to the North Sea also will prefer chiefly the North Sea spawning grounds.

If this assumption is correct, there is at present obviously a high degree of recruitment to the North Sea stock also from the areas north of 6Zo

N. From the M~re area (Fig. 4) it seems that a clear

majority of the saithe migrate to the North Sea, whereas from Tr~ndelag

(Fig. 5) the number s of saithe migrating to the south and north re- spectively seem to be about equal. Thus, the coastal ar ea around 64⁰N appears to be approximately the middle of a mixing zone between the two stocks as far as recruitment to the spawning stocks is con-

cerned. The extension of this mixing zone is largely a question of definition since some degree of mixing seems to occur all along the coast.

The tagging experiments on immature saithe carried out at M~re in 1955 - 58 indicated a basically northward migration, although a few recoveries were also made in the North Sea (Olsen 1959, Anon. 1965).

Accordingly, the migration pattern of the saithe at M~re have changed during the last 15 years. At present, the borderline between the North Sea and North-East Arctic stocks at 6ZoN is set too far south as far as immature saithe is concerned and 64°N seems to be more suitable. However, the M~re shelf at about 63⁰N is one of the major spawning grounds for the North-East Arctic stock and it is not possible to fully divide the stocks geographically. Besides, the border area between the stocks is apparently unstable and it seems recommendable that routine, tagging experiments should be carried out to keep a con- tinuous record of the recruiting migrations to the two stocks from the Norwegian coast.

SUMMARY

In June 1973, Z 700 young saithe were tagged on the Norwegian west coast. Of these, 1 ZOO were tagged north of 6Zo

N which is the

commonly set borderline between the North Sea and North-East Arctic stocks of saithe.

The saithe tagged south of 6Zo

N mo stly migrated out into the North Sea.

- 5 -

The saithe tagged north of 62⁰N were also to a large extent re<::aptured' in the North Sea, a.lthough some also migrated northwards.

The results indicate that the borderline at 62⁰N is at present too far south as far as the recruitment of immature saithe to the spawning stocks is concerned. However, the border area between the stocks is apparently unstable.

REFERENCES

ANON. 1965. Report of the ,Coal£ish Working Group. Co-~. Res.

Rep. into Coun. Exp1or. Sea, Ser. A, ~~ 1 - 23.

ANON. 1976. Report of the Saithe (Coal£ish) Working Group.

Coun. Meet. into Coun. Exp1or. Sea_L._1976 (F 2): 1 - 34.

JAKOBSEN, T. 1975. Preliminary Results of Saithe Tagging Experiments on the West Coast of Norway in 1972. Coun. Meet. into Coun.

Exp1or. Sea, 1975 (F 35): 1 - 9.

JAKOBSEN, T. 1976. Fore1~pige resu1tater av merkefors~k med sma~

sei pa Vest1andet i 1971 og 1972. Fiskets Gang, 62: 222 - 226.

Fi sk en 0 g Ha vet, 1 976 (1): 29 - 3 3.

OLSEN, S. 1959. Preliminary Results of the Norwegian Coal£ish taggings 1954 - 58. Coun. Meet. into Coun. Exp1or. Sea,

1959 (114): 1 - 7.

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