Årsyngel av brisling i fjordene på Vestlandet og i Trøndelag høsten 1975

Prognoses for catch of sprat in 1976 in different fjords of western Norway are presented. The prognoses are based on indices of abundance of 0-group sprat calculated from echo recordings obtained on a survey in October-November 1975 by R. V. "Johan Hjort". The echo signals are processed by a computer system, and a relative measure of sprat density per distance travelled, combined with the area of each fjord, provides the abundance index. This index reflects the abundance of sprat available to the fishery 6 -8 months later

Influence of hydrographical and meteorological factors on catch and recruitment strength of the sprat stock in western Norway

The dependence of recruitment strength on hydrographical conditions has been studied, i. e., possible relationship between the transport of sprat larvae from the Skagerak to the stock in western Norway and the thickness of Skagerak water in the coastal current. The material consists of data from 23 years of hydrographical observations and catch statistics. A correlation analysis gave the correlation coefficient r=0.4713 (P≈0.02). which means that good catches seem to be conditioned by a great thickness of Skagerak water the previous year. The validity of the material is discussed, especially the use of catch statistics as numerical expression of recruitment strength. An analysis of the influence of prevailing winds on the hydrographical conditions and on the catch distribution has been carried out. Weak northerly winds during summer seem to give the southernmost county in western Norway a greater proportion of the total sprat catch the following year. The results of this investigation indicate that the majority of the sprat in western Norway originate from spawning in the Skagerak and the Kattegat

Distribution and abundance of 0-group sprat (Clupea sprattus) in western Norway in autumn 1974

An echo survey for 0-group sprat was carried out in October -November 1974 in fjords of western Norway. Charts of sprat distribution are presented together with indices of abundance calculated from mean echo integrator reading per nautical mile and area of each fjord system. The indices reflect the year class strength, and as the fishery is based on the one year old sprat, a clear relationship is found between indices determined in autumn and catch the following year. This is demonstrated by data from the echo survey in 1973 and catch in 1974

Distribution and abundance of sprat (Clupea sprattus) in October 1971 in fjords of western Norway

An echo survey for sprat was carried out in late October 1971 in the fjords of western Norway. Echo recordings were identified by samples obtained with pelagic trawl. The recorded distribution of sprat within the investigated area is indicated. Attempts were made to obtain relative estimates of abundance in the different fjord systems by the use of an echo integrator. Length distributions showed that most of the sprat belonged to the 0-group, Compared to 1971 higher catches are predicted for the summer fishery in 1972. Abundance and distribution in autumn 1971 resemble the conditions of autumn 1969

Sprat (Clupea sprattus) in fjords of western Norway in autumn 1970

Havforskninginstituttet begynte i 1968 undersøkelser av brislingens utbredelse i de vestnorske fjordene om høsten (Dahl og Sangolt 1969). Disse undersøkelsene fortsatte året etter (Bakken 1970). Hovedformålet var ved hjelp av ekkolodd å kartlegge forekomstene av 0-gruppen, dvs. brisling som om høsten er ca 6 måneder gammel. Denne brislingen utgjør hovedtyngden i fangstene som taes den påfølgende sommer og høst. Samtidig har det vært arbeidet med å finne kvantitative mål for mengden av brisling som registreres. Til dette har ekkointegrator (Bodholt 1969, Nakken og Vestnes 1970) vært benyttet. Undersøkelsene høsten 1970 var en fortsettelse av dette arbeidet, og de tok særlig sikte på å kartlegge utbredelsen, måle brislingens akustiske refleksjonsstyrke og å undersøke sammenhengen mellom ekkoloddregistreringene og integratoravlesningene. Disse undersøkelsene er supplert med observasjoner av forandringer i brislingens utbredelse i et enkelt fjordsystem i løpet av vinteren 1969 — 1970

Abundance estimates of sprat (Clupea sprattus) by echo integrator in fjords of western Norway in autumn 1972

An echo survey for O-group sprat in the fjords of western Norway was carried out in late October 1972. An outline of the distribution is given together with relative estimates of abundance. Measures of abundance are compared with similar data from the previous year. A comparison is also made between indices of abundance obtained by an echo integrator in October 1971 and catches of sprat in June—October 1972. Correlation analyses demonstrate a fair relationship, but the index of abundance for some areas seems to be underestimated. Length distributions of sprat indicate that the O-group only is present in most areas. This group will support the 1973 sprat fishery in the fjords, and from the estimates of abundance the yield is predicted to be about the same as in 1972