Distribution, abundance and mortality of young and adolescent Norwegian spring spawning herring (Clupea harengus Linné) in relation to subsequent year-class strength

1. The distribution of young and adolescent herring in coastal and offshore waters of northern Norway has been investigated for the 1959- 1965 year-classes by combined acoustic surveys and fishing experiments. 2. In the autumn (August-October) 0-group herring occur pelagically in the upper 50 m of water together with the 0-group of several other species, such as cod, haddock, redfish, capelin and others. This complicates the charting and identification of the sound scatterers, but detailed studies of the echo recordings and frequent sampling in the scattering layer made it possible to determine the distribution of 0-group herring. 3. In 1959, 1960, 1964 and to some extent in 1963 and 1965, 0-group herring had an oceanic distribution, and only a minor part of the 0-group population entered the fjords of northern Norway. In 1961 and 1962 the distribution was more restricted to the coastal areas, and a greater proportion of the total 0-group population was present in the fjords. Herring entering the fjords at the 0-group stage in the autumn emigrate during the I-group stage from March to May. 4. Herring in the northern and eastern Barents Sea had slower growth rates and consequently a longer phase of migration to the spawning areas than did those distributed farther south and west. Herring from nursery grounds in the Barents Sea, therefore, are considerably more reduced in numbers before they reach the spawning grounds off Møre than those which have spent their 0-group stage in the southern nursery areas in Norwegian coastal waters. The growth rate, therefore, may influence the migration pattern and the duration of the adolescent phase. Growth on the other hand is determined by the distribution during the 0-group stage, and the 0-group distribution consequently plays an important role in recruitment mechanism. 5. Abundance estimates of 0-group herring were obtained from three independent sources, i.e. acoustic surveys, catch and effort statistics and tagging experiments. The 1959 year-class, but also that of 1960, were numerous during the 0-group stage and remained abundant throughout the adolescent phase and in the adult stock. Year-classes of low abundance at the 0-group stage, such as the 1962 year-class, remained weak throughout the subsequent stages. The 1963 year-class, which was fairly abundant as 0-group, did not show up in significant numbers in the adult stock in 1968 and 1969. The 1964 and 1965 year-classes have not been studied in their adult phase because they had not attained maturity when the material was compiled. The year-classes of 1963 and 1964 showed about the same relative strengths during the adolescent phase as at the 0-group stage. 6. Mortality estimates obtained from catch and effort data and tagging experiments indicate that the fishing mortality of 0- and I-group herring in Norwegian fjords was relatively high, but because natural mortality was much higher, the exploitation rate was relatively low. Taking into account that the fjord population is only part of the total 0-group population, it is concluded that the fishing mortality generated by the 0- and I-group fishery in Norwegian fjords was too small to be the primary cause of the failure of recruitment to the adult stock. 7. A considerable increase in the exploitation of fat-herring, i.e. I- to IV-group herring took place from 1965 to 1968. The increase in exploitation during the adolescent phase of the 1963 and 1964 year-classes compared with those of the 1959-1961, and a long duration of the migration of the former year-classes from the nursery areas to the spawning grounds may explain why the year-classes of 1963 and 1964 tended to be relatively weak in the adult stock. 8. With the relatively low level of the spawning stock size an intensified fishery on the Norwegian herring should be avoided. An extension of the small- and fat-herring fisheries into the open sea may result in an appreciable reduction in the subsequent abundance in the adult stock, and a reduction of the fishery on young and adolescent herring should be considered to improve the abundance of adult herring

NORFISK - an ecosystem simulation model for studies of the fish stocks off the coast of Norway

A biomass based ecosystem simulation model has been fitted to a restricted area of the Norwegian coastal waters. The model uses a holistic ecosystem approach and data on biomasses and their interaction with each other have been taken from the Møre region, western Norway. The main objective was to study interactions beetween cod, haddock saithe and herring and their prey in this area. lnitial estimation of the biomasses was based partly on acoustic methods and partly on data from the literature. Sampling of stomach contents was conducted to provide data for food composition tables. The calculations in the model were based on biomasses only, but in the analysis each species was treated as eggs and larvae, juveniles and adults to give biomasses with relative homogeneous structure and behaviour. The problems of intergroup recruitment and migration have been discussed. The results indicate that using such a model as a tool to treat data can give a better understanding of the ecosystem

Estimates of stock size and reproduction of the Barents Sea capelin in 1970-1972

DRAGESUND, O., GJØSÆTER, J. and MONSTAD, T. 1973. Estimates of stock size and reproduction of the Barents Sea capelin in 1970-1972. FiskDir. Skr. Ser. HavUnders., 16: 105-139. The distribution and migration of young and maturing capelin during the period 1969-1972 have been investigated by combined acoustic surveys and fishing experiments. The nursery area of the capelin is extensive, but the main grounds are in the central and eastern part of the Barents Sea. The two and three year old fish are distributed farther north and northeast than the younger capelin. Previously, the main part of the spawning stock approached the western part of the Murman coast and the Varanger peninsula, and dispersed westward along the Norwegian coast. During recent years, a major part of the stock also reached the coast of West-Finnmark and migrated farther west and south along the coast for spawning. The capelin mainly become sexually mature when they are four years old. A very heavy postspawning mortality is observed, and most likely very few capelin survive to spawn a second time. At present the Barents Sea capelin is the most important fish resource for the Norwegian purse seine fleet, and Norway has been responsible for more than 90% of the total catch from this resource. Preliminary spawning stock size estimates for 1971 and 1972 are available from acoustic surveys, egg and larval surveys, and tagging experiments. It is tentatively concluded that the spawning stock size in 1971 was at a high level, being somewhat lower both in 1970 and 1972. So far no sign of overfishing has been observed. The increase in catch during the last six years is due to a significantly increased fishing effort, but also for a larger part attributed to a raise in the stock size. A more detailed analysis of the location and time of spawning during the 1971 season is given. Spawning took place along the coast from Vesterålen to Varangerfjord. The major spawning west of North Cape took place during March and off the coast of eastern Finnmark in April. Fertilization and survival of eggs were studied. On the spawning beds the fertilization seemed to be almost 100%. Egg mortality seemed to be low. The distribution of capelin larvae, during the first month after hatching, was studied. The larvae were collected on five surveys in oblique hauls with Clarke Bumpus plankton samplers

NORFISK - an ecosystem simulation model for studies of the fish stocks off the coast of Norway

A biomass based ecosystem simulation model has been fitted to a restricted area of the Norwegian coastal waters. The model uses a holistic ecosystem approach and data on biomasses and their interaction with each other have been taken from the Møre region, western Norway. The main objective was to study interactions beetween cod, haddock saithe and herring and their prey in this area. lnitial estimation of the biomasses was based partly on acoustic methods and partly on data from the literature. Sampling of stomach contents was conducted to provide data for food composition tables. The calculations in the model were based on biomasses only, but in the analysis each species was treated as eggs and larvae, juveniles and adults to give biomasses with relative homogeneous structure and behaviour. The problems of intergroup recruitment and migration have been discussed. The results indicate that using such a model as a tool to treat data can give a better understanding of the ecosystem

Capelin and polar cod investigations in the Barents Sea in August - September 1971

During August-September 1971 two subsequent series of observations were made on distribution and abundance of maturing capelin and Polar cod in the Barents Sea. Abundance estimates for the two species indicated by echo integrator readings in the two periods are presented. Most of the capelin were recorded east of 35 degrees E and north of 76 degrees N. In the western part of the investigated area the abundance was significantly lower than in 1970. In the eastern and northeastern part of the Barents Sea no comparison can be made with 1970 since no investigations were carried out in that region. It is tentatively concluded that between 30 and 40 per cent of the capelin observed in the central and northern part of the Barents Sea will become mature in 1972. Most of the adult Polar cod were observed in the northeastern part of the Barents Sea. The younger fish were mainly recorded in the western area of distribution

Capelin and Polar Cod investigations in the Barents Sea in August - September 1971

During August—September 1971 two subsequent series of observations were made on distribution and abundance of maturing capelin and Polar cod in the Barents Sea. Abundance estimates for the two species indicated by echo integrator readings in the two periods are presented. Most of the capelin were recorded east of 35° E and north of 76° N. In the western part of the investigated area the abundance was significantly lower than in 1970. In the eastern and northeastern part of the Barents Sea no comparison can be made with 1970 since no investigations were carried out in that region. It is tentatively concluded that between 30 and 40 per cent of the capelin observed in the central and northern part of the Barents Sea will become mature in 1972. Most of the adult Polar cod were observed in the northeastern part of the Barents Sea. The younger fish were mainly recorded in the western area of distribution