Several species of wrasse (Labridae) are used as cleaner fish to remove salmon lice from farmed Atlantic salmon. We estimated the fishery and use of wrasse in Hardangerfjord. The estimated numbers of labrids used on salmon and rainbow trout farms varied between 86,000 and 251,000 from 2002Á2006, but increased to as much as 1.1 million in 2009 and 2010. A total of 93,500 kg (around 1.54 million) labrids were reported landed during 2000Á2010. Corkwing wrasse (Symphodus melops) was by far the most important wrasse species: 52% by weight and 56% by number. Ballan wrasse (Labrus bergylta) made up 34% by weight but only 14% by number (due to its larger size). The relative proportion of species between the different sampling locations in the fjord was significantly different, as was the condition factor of some species. Goldsinny wrasse (Ctenolabrus rupestris) had the slowest growth of the labrids in this study, and did not reach the minimum commercial catch size (11 cm) before they were 4Á5 years old. Very few goldsinny caught were over that size. Corkwing reach commercial size in 1Á2 years. The results of this study indicate that wrasse should be protected during the spawning season. Species such as goldsinny grow so slowly that they will most likely be collected several times in heavily fished areas but discarded because they are smaller than the minimum allowable size. This could be avoided through the use of modified traps with escape routes for undersized fish. This study represents a first step towards establishing a knowledge-based management plan for the wrasse fishery.

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Genetic studies on populations of Atlantic herring (Clupea harengus L.) in Norwegian seawaters have revealed a number of genetically distinct fjord populations. One population in Balsfjord in northern Norway was nearly fixed for several alleles that were very rare in the Atlanto-Scandian herring stock. A comparison with a sample of Pacific herring (Clupea pallasi) from British Columbia demonstrated that these alleles were identical to the more common alleles in this species. Genetic distance estimates based on six polymorphic loci demonstrated that Balsfjord herring were more similar to Pacific herring. Balsfjord and Pacific herring were also similar in vertebrae number and spawning behaviour. Restriction fragment analyses of mitochondrial DNA using five restriction enzymes revealed distinct clones that separated different herring groups. Nucleotide sequence divergence among groups was small.

Survival and growth of two strains of Atlantic cod (Gadus morhua) were compared through the larval and juvenile stages in a marine pond in western Norway in 1990 and 1991. Strain A was homozygous for the genetic marker allele GPI-1*30 at the glucose phosphate isomerase (GPI) locus expressed in white muscle, and Strain B possessed other GPI-1* genotypes, in 1990 the frequency of Strain B increased significantly from the larval to the juvenile stage; however, in 1991 the frequency of Strain A increased slightly but not significantly from the larval to the juvenile phase. Larval mortality did not differ significantly between strains any year, but juvenile mortality was significantly lower in Strain B in 1990 and Strain A in 1991. Average growth rates in length estimated from regressions were not significantly different between strains during the larval and juvenile period any year, but initial length was significantly larger in Strain B in 1990 and Strain A in 1991. Our results indicated that food limitation during the early juvenile stage induced differential size-selective mortality among the strains due to small differences in body size and actual age between strains. Body size did not become important for survival until the food-limited regime had occurred.

T. SVASANDIn the spring of 1995, 18 million genetically marked yolk-sac cod larvae Gudus morhuu were released into a 2,9-kmz, nearly land-locked fjord in western Norway. Four quantitative surveys were conducted, 11, 33, and 63 days, and 1 year after the first release. Almost 100% of the collected cod larvae were successfully identified to GPZ-1* genotype. The marked cod larvae constituted 18% of all sampled cod larvae in the first survey and 9% in the two next. The average rate of mortality was estimated to be 23% day-' for the first 10 days after release and 12% day-' during the next month after release. After 1 year (April 1996), the number genetically marked I-group cod in the fjord was estimated to be <120. The effect of the historical programme of large-scale releases of yolk-sac larvae on recruitment were evaluated and found to be small. 3; 1991 The Fisheries Society of' the Bntiab Isles

A genetically marked Atlantic cod (Gadus morhua L.) strain was used to identify escapes from commercial cod farms, and to investigate the potential interbreeding between farmed and wild cod. This farmed cod was homozygote for a rare allele (30) in the GPI-1 locus expressed in white muscle tissue. Juveniles were produced from this strain in 2007 and 2008, and 500 000 individuals of each year class were transported to a cod farm in western Norway, where they were raised under commercial conditions. A monitoring fishing program was established from spring 2007 to detect escapees during the farming period. The first farmed cod escapees, identified to the 2007 year class through the genetic mark, age and body size, were detected during the fishing survey in November 2008. The second escape of the same year class was detected during the natural spawning season in early April 2009. A third escape was detected in November 2009, and this time the farmed cod were identified to the 2008 year class. The escapees were spreading through the whole fjord system, including local spawning sites for wild cod. Detailed examination of the escaped cod revealed a substantial degree of sexual maturation, and nearly 1000 cod larvae and early juveniles were therefore collected through spring 2009. The genetic analyses identified eight of these as genetically marked, demonstrating successful reproduction either in the cage or after escape. Interbreeding between escaped and wild cod may also have occurred, but cannot be proven from our material. In all years after the three identified escapes, genetically marked cod were found in the fjord area. In addition, several specimens were observed in adjacent fjord systems, demonstrating long-term survival in the local spawning areas as well as substantial spread over larger distances.

Four larvae of Atlantic halibut (Hippoglossus hippoglossus) were collected during a larval survey for Atlantic cod (Gadus morhua) in true inshore and shallow locations in the Norwegian fjord system Skjerstadfjorden. This observation contributes to the previous 57 larval specimens ever found for Atlantic halibut and is in accordance with earlier findings from aquaculture research on an ontogenetic change in phototaxi during larval development in this species. The catch sites indicate that shallow water in fjord systems may be of importance as nursery areas for early life stages of Atlantic halibut along the Norwegian coast.