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Ålesund, Norway

Helle K.,Norwegian Institute of Marine Research | Pennington M.,Norwegian Institute of Marine Research | Hareide N.-R.,Runde Environmental Center | Fossen I.,Moreforsking Marin
Fisheries Research

Ling is an important species for the Norwegian longline fishery. Motivated by an apparent steep decline in a catch per unit of effort (CPUE) series for ling based on commercial longline data during the periods 1971-1993 and 2000-2003, ling was classified as Near Threatened and placed on the Norwegian Red List, which caused difficulties for the marketing of ling. To examine the validity of the conclusion that this CPUE series indicated that the ling stock was Near Threatened, we estimated CPUE series for the period 2000-2012 based on extensive logbook data available since 2000. The Norwegian longline fishery is a mixed-species fishery: therefore, we constructed three different CPUE series based on; (1) all catches including zeros, (2) selected catches that appeared to have target ling and (3) selected vessels for each year that seemed to have often targeted ling during that year. It was concluded that these CPUE series indicated that the abundance of ling in Norwegian waters has been fairly stable or increasing since at least 2000, and hence there was no compelling evidence that the abundance of ling was declining. Based on our analysis, ling was removed from the Norwegian Red List. Even though all three series indicated increasing abundance, their precision varied, and estimates of how much the ling stock has increased depended on the subset of the commercial data on which the CPUE series was based. © 2015 Elsevier B.V. Source

Silva F.F.G.,University of Bergen | Silva F.F.G.,Norwegian Institute of Marine Research | Slotte A.,Norwegian Institute of Marine Research | Johannessen A.,University of Bergen | And 2 more authors.
Fisheries Research

In this study the reproductive investment of six populations of Atlantic herring (Clupea harengus) in Norwegian waters was contrasted in relation to trade-offs with body growth (relatively slow-relatively fast) and migration distance (stationary-migratory). Down-regulation of fecundity through the process of atresia as well as standardisation of fecundity to the prespawning stage were included as process-oriented reproductive factors, applying both histological and image analysis techniques. The further analysis included historic information on body growth as well as published information on fecundity from several stocks in the North Atlantic. The Norwegian spring-spawning (NSS) herring could be split into three sub-components: migratory (oceanic), likely semi-stationary (coastal) and stationary. The latter one as well as three other populations were sampled in relatively isolated semi-enclosed areas (pond, " lake" or fjord). The study documented clear signs of trade-offs: migratory herring had a significantly higher growth rate and lower relative fecundity while stationary populations grew slower and presented higher values of relative fecundity. So these traits appeared highly plastic and for the first time explicitly demonstrated in the three types of NSS herring: stationary NSS herring had high fecundity and body condition while the truly migratory counterpart was low in both while the intermediate version was low in fecundity but high in condition. The literature-based analysis of other Atlantic spring-spawning herring populations seemed to corroborate the finding that slow-growing herring is relatively more fecund than the faster-growing populations. © 2012 Elsevier B.V. Source

Kennedy J.,Moreforsking Marin | Hedeholm R.B.,Greenland Institute of Natural Resources | Gundersen A.C.,Moreforsking Marin | Boje J.,Greenland Institute of Natural Resources | Boje J.,Technical University of Denmark
Fisheries Research

When estimating reproductive potential (RP), correct interpretation of the maturity status is essential. It has now become apparent the presence of vitellogenic oocytes within the ovary of Greenland halibut (Reinhardtius hippoglossoides) does not necessarily indicate they will spawn within the next twelve months. This has led to a revision of the interpretation of the maturity scale where fish which contain only a developing cohort (DC) of oocytes are considered immature. Comparisons were made of estimates of L50 of female Greenland halibut in East Greenland using the previous interpretation of maturity status where the leading cohort (LC) and DC oocytes are not differentiated with the new interpretation where they are. Differentiation led to an increase from 63.8 to 80.2cm and from 61.2 to 74.1cm for the northern (between 63°40'N and 67°00'N) and southern area (between 61°45'N and 62°40'N), respectively. Combining the maturity data with abundance data of Greenland halibut in East Greenland, spawning stock biomass (SSB) and total egg production (TEP) was estimated in four quadrants between 1998 and 2012 using both the previous and current interpretation of the maturity scale. Using the new interpretation of the scale led to a decrease in SSB estimates of 28-92% in specific areas and years, with an average of 56%. Estimates of TEP were directly proportional to SSB so this approach did not offer any advantages over SSB as a measure of reproductive potential. Length composition of Greenland halibut caught by Norwegian fishing vessels fishing in East Greenland indicate that 85 and 57% of the females caught by the trawl and longline fleet respectively in the northern area and 46% caught by the longline fleet in the southern area were immature. © 2014 Elsevier B.V. Source

Kennedy J.,Moreforsking Marin | Gundersen A.C.,Moreforsking Marin | Hoines A.S.,Norwegian Institute of Marine Research | Kjesbu O.S.,Norwegian Institute of Marine Research
Canadian Journal of Fisheries and Aquatic Sciences

Ovary development in Greenland halibut (Reinhardtius hippoglossoides) is complex, with several cohorts of developing oocytes present during vitellogenesis; this is unusual for a determinate spawner. There are also speculations that Greenland halibut are not capable of spawning every year. To investigate this possibility, ovaries from Greenland halibut caught throughout the year were examined histologically, and successive cohorts of oocytes were tracked through development. Results showed that the initial maturation of the ovaries from immature to spawning takes more than 1 year. The ovary initially develops as far as early vitellogenesis; however, the time scale for this is unclear. During the final year of development, the cohort of vitellogenic oocytes splits to form two cohorts; the larger cohort increases in size and is spawned in the coming spawning season. The smaller cohort also continues to develop, but at a much lower rate, in preparation for development for spawning in the following year. Within each month, there is a large range of oocyte sizes between fish; this leads to the extended spawning season that is known in many populations of this species. This complicates the assessment of maturity, and a more accurate microscopic maturity scale is proposed. Source

Woll A.K.,Moreforsking Marin | Larssen W.E.,Moreforsking Marin | Fossen I.,Moreforsking Marin | Fossen I.,MonAqua As
Journal of Shellfish Research

Knowledge of the brown crab's (Cancer pagurus Linnaeus 1758) tolerance to emersion related to air temperatures and duration is scarce. In the current study, the condition of the brown crab was examined during emersion in laboratory experiments simulating dry storage and transport at air temperatures between 220°C. Samples of hemolymph were taken at different intervals simultaneously as the crab was classified using a vitality index based on behavior and responses. Individual variances in hemolymph pH, total ammonia (TA), lactate, and glucose were large; but, in general, pH decreased and TA and lactate increased during emersion, most at the highest temperatures. When hemolymph samples were grouped according to vitality index, deterioration was found for pH, TA, and lactate as the vitality dropped, whereas no trend was found for glucose. Vitality of crabs was reduced during emersion, with the greatest reduction being crabs exposed to high temperatures. To secure strong and healthy crabs, exposure at 20°C and 15°C should not exceed 5 h and 10h, respectively. For crabs exposed at 10°C and 5°C, emersion for 36 h and 72 h, respectively, did not seem to have negative consequences for the animals. A general increase in vitality occurred when crabs were reimmersed. Delayed mortality occurred for weak and moribund crabs, highest during the first 24 h of reimmersion, and continuing over the next day, suggesting that such crabs should not be transported in the live value chain. Source

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