Capelin and polar cod investigations in the Barents sea in August-September 1970

In the period 26 August to 11 September a joint Soviet-Norwegian 0-group fish survey was carried out in the Barents Sea (ANON. 1970). During this survey observations were also made on the distribution and abundance of adult capelin and polar cod, especially in the area covered by R. V. «G. O. Sars» (Fig. 1). Echo integrator readings in the investigated area are given in Fig. 3 and 4. Age and length compositions of capelin indicated that the 1967 year-class dominated in the northern part of the Barents Sea. Farther southeast in the investigated area younger fish showed up in the catches (Tables I and 2). Length distributions of polar cod are shown in Table 3

Density‐ and size‐dependent mortality in fish early life stages

The importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density‐ and size‐dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruitment to the population. We applied a statistical state‐space modelling approach to analyse time series of abundance and mean body size of larval and juvenile fish. The focus was to identify the importance of abundance and body size for growth and survival through successive larval and juvenile age intervals, and to quantify how the dynamics propagate through the early life to influence recruitment. We thus identified both relevant ages and mechanisms (i.e. density dependence and size dependence in survival and growth) linking recruitment variability to early life dynamics. The analysis was conducted on six economically and ecologically important fish populations from cold temperate and sub‐arctic marine ecosystems. Our results underscore the importance of size for survival early in life. The comparative analysis suggests that size‐dependent mortality and density‐dependent growth frequently occur at a transition from pelagic to demersal habitats, which may be linked to competition for suitable habitat. The generality of this hypothesis warrants testing in future research.publishedVersio

Småsildundersøkelsene i Nord-Norge 1960/61

1. During the autumn of 1960 the distribution of the 0- and I-groups of herring was investigated along the coast of Northern Norway, in the northeastern part of the Norwegian Sea, and in the Barents Sea. At the beginning of October the 0-group was numerous just outside the entrance of the fjords in the Røst-Torsvåg area. Off the northernmost district, Finnmark, the herring were a mixture of the 0- and I-groups, which were also observed around Bear Island and in the Barents Sea, especially in the eastern and southeastern part of the sea. During the second half of October schools, mainly of the 0-group, which were located near the coast, migrated into the fjords and became available to the fishing fleet. 2. The temperature was high just outside the entrances of the fjords, decreasing inwards. During the immigration the herring thus moved towards lower temperature. During the winter 1960-61 the herring stayed in the fjords, being found in areas with low temperatures, except in some fjords in Troms ( e. g. Ullsfjord), where the herring were found in a warm, intermediate layer. During the spring the herring left the fjords, earlier in Troms than in Finnmark. 3. In seven localities (Table 1) a total of 7800 herring (6800 of the 0-group and 1000 of the I-group) was tagged with internal steel tags. No recaptures have been reported from the taggings in the Barents Sea (Sørdjupet and Skolpenbank NW) and off Bear Island. The recaptures from taggings in the Ullsfjord-Lyngenfjord and Varangerfjord areas were all taken near the tagging localities, the fishing mortalities of the tagged herring being 20.6 % and 15.5 % respectively

Sildeundersøkelsene i Nord-Norge 1962/1963

A progress report of the herring investigations in Northern Noway from September 1962 to May 1963 is presented. l. In autumn 1962 only small concentrations of the 0-group were recorded in the open sea off Northern Norway (the area around Bear Island and in the Barents Sea). Even though the herring were more abundant along the coast than in the open sea the 1962 year-class as a whole is expected to be rather poor compared to the 1959 and 1960 year classes. During the period of investigation fat herring of the 1959, 1960 and 1961 year-classes were observed several places on the banks along the coast. The best concentrations were recorded in the Lofoten-Vesterålen area, off the coast of West-Finnmark and on the Skolpenbank. 2. The migration from the coastal waters into the fjords took place in September-October and the herring consisted almost entirely of the 0 and 1-groups. In some areas, however, the herring were mixed up with the 1960 and 1959 year-classes. During the immigration the herring moved from warmer to colder water, the temperature decreasing inwards 1-1.5°C in the surface layer. During the winter 1962/63 no distinct warm intermediate water-layer existed in Ullsfjord (Troms). The water was warmest near the bottom where also the herring were observed. The herring left the fjord from March to May. In Porsangerfjord (West-Finnmark) the herring remained in the coldest water throughout the winter and no emigration had taken place when the investigations were finished. 3. In five localities a total of 6400 herring were tagged with intemal steel tags (Table 1). No recaptures of the fat herring tagged off Torsvåg have been reported. The recaptures of the 0-group (mussa) were all taken near the tagging localities, the fishing mortality of the tagged herring being 12.1 % in Vesterålen, 21.0 % in Malangen and 23.9 % in Ullsfjord-Lyngenfjord. If the Lyngenfjord is excluded from the fishing area the mortality is estimated to 26.5 %

Småsildundersøkelsene i Nord-Norge 1960/61

1. During the autumn of 1960 the distribution of the 0- and I-groups of herring was investigated along the coast of Northern Norway, in the northeastern part of the Norwegian Sea, and in the Barents Sea. At the beginning of October the 0-group was numerous just outside the entrance of the fjords in the Røst-Torsvåg area. Off the northernmost district, Finnmark, the herring were a mixture of the 0- and I-groups, which were also observed around Bear Island and in the Barents Sea, especially in the eastern and southeastern part of the sea. During the second half of October schools, mainly of the 0-group, which were located near the coast, migrated into the fjords and became available to the fishing fleet. 2. The temperature was high just outside the entrances of the fjords, decreasing inwards. During the immigration the herring thus moved towards lower temperature. During the winter 1960-61 the herring stayed in the fjords, being found in areas with low temperatures, except in some fjords in Troms ( e. g. Ullsfjord), where the herring were found in a warm, intermediate layer. During the spring the herring left the fjords, earlier in Troms than in Finnmark. 3. In seven localities (Table 1) a total of 7800 herring (6800 of the 0-group and 1000 of the I-group) was tagged with internal steel tags. No recaptures have been reported from the taggings in the Barents Sea (Sørdjupet and Skolpenbank NW) and off Bear Island. The recaptures from taggings in the Ullsfjord-Lyngenfjord and Varangerfjord areas were all taken near the tagging localities, the fishing mortalities of the tagged herring being 20.6 % and 15.5 % respectively

Lodde- og polartorskundersøkelser i Barentshavet august-september 1970

In the period 26 August to 11 September a joint Soviet-Norwegian 0-group fish survey was carried out in the Barents Sea (ANON. 1970). During this survey observations were also made on the distribution and abundance of adult capelin and polar cod, especially in the area covered by R. V. «G. O. Sars» (Fig. 1). Echo integrator readings in the investigated area are given in Fig. 3 and 4. Age and length compositions of capelin indicated that the 1967 year-class dominated in the northern part of the Barents Sea. Farther southeast in the investigated area younger fish showed up in the catches (Tables I and 2). Length distributions of polar cod are shown in Table 3

Småsildundersøkelsene i Nord-Norge 1961/62

A progress report of the small herring investigations from September 1961 to May 1962 is presented. 1. During the autumn of 1961 rather small concentration of the 0-group were ecorded in the area around Bear Island and in the Barents Sea. Even though the herring were more abundant along the coast than in the open sea, the 1961 year-class as a whole is expected to be rather poor compared with the two previous ones. Fat herring were observed in different areas at a distance of 20-100 nautic miles of the coast from Vestfjord to Varangerfjord. 2. The migration from the coastal waters into the fjords took place in late October and the herring consisted almost entirely of the 0-group. During the immigration the herring moved from warmer to colder water, the temperature decreasing inwards l-1.5°C in the surface layer. From October to February the herring were observed in the warm intermediate water layer, which usually exists in the fjords of Troms and West Finnmark during the autumn and early winter. An exception was the Porsangerfjord, where such intermediate water layer was not observed. The herring left the fjords in February-March when the warm water layer disappeared. In Porsangerfjord the herring remained in the coldest water throughout the winter and immigrated in May. 3. In six localities a total of 6150 herring were tagged with internal steel tags. (Table 1). No recaptures of the tagged fat herring have been reported nor of the 0-group tagged in Varangerfjord.. The recaptures from the taggings in the Ullsfjord-Lyngenfjord and Senja areas were all taken near the tagging localities, the fishing mortality of the tagged herring being 11.30 % and 0.27 % respectively