Search

Fish stocks represent fundamental units in fisheries management, and their identification, especially in mixed-fisheries, represents one of the primary challenges to sustainable harvest. Here, we describe the first “real-time” genetic management program used to manage a mixed-stock fishery of a non-salmonid and commercially significant marine fish, the Atlantic cod ( Gadus morhua L). Based upon the analysis of >18 000 fish sampled from the commercial catch in Lofoten (Norway), which represents the largest remaining cod fishery in the Atlantic, we estimated the fraction of North East Arctic cod (NEAC), and Norwegian Coastal cod (NCC), just 24 h post-landing. These estimates, based upon the analysis of the Pantophysin gene, were performed weekly in the winter and spring of each year in the period 2007–2017. The program has successfully permitted the Norwegian Directorate of Fisheries to actively manage the commercial exploitation of the highly abundant NEAC stock, while simultaneously limiting exploitation of the fragile NCC stock, both of which overlap at the spawning grounds. Data from this program have also revealed a distinct temporal increase in the fraction of NEAC on the spawning grounds in this region, which is consistent with the overall increased abundance of this stock as estimated by ICES. [ABSTRACT FROM AUTHOR]

• Combining eDNA and trawl data increases the detected biodiversity. • Good reference databases are of vital importance for correct taxonomic classification. • We advocate that a combined sampling effort is a good strategy for future monitoring of biodiversity in the Arctic including the Barents Sea. Managing natural resources in a sustainable manner requires understanding the complexity of ecosystems and the species that are associated with the different parts of the ecosystem. Much of this knowledge is derived from traditional sampling methods (e.g., different types of trawls). The analysis of environmental DNA (eDNA) can provide increased knowledge, complementary to the traditional methods. In the present pilot study, we sampled eDNA from two geographical areas, north and west of Svalbard (NWS) and in the southwestern Barents Sea (SWBS). The combination of trawling, visual identification of mammals and eDNA collection facilitated a robust analysis of fish and marine mammal diversity and species composition. Through 12S MiFish metabarcoding of the eDNA samples, we found that incorporating eDNA data provided an additional level of information on both the diversity of fish and marine mammals in the study areas. By adding eDNA data to the trawl data, we found that richness increased from 32 to 49 fish taxa. Significant differences in diversity and composition of the fish communities were detected by eDNA between the two study areas. Considering degradation and dilution factors it is postulated that the results represent resident species to the Barents Sea and that long -transported DNA from other areas are less likely. [ABSTRACT FROM AUTHOR]

In management of fisheries, knowledge about the species is crucial due to differences in life history traits. The first step is therefore species identification. For many species this task is straightforward, however for some species e.g. the two species of Atlantic redfish Sebastes mentella and Sebastes norvegicus , it can be difficult for an untrained eye. With the goal to separate the two species, we analysed otolith shape variation of S. mentella and S. norvegicus caught on the continental slope of East Greenland using the R package “Shape R”. Results were evaluated against genetic analysis of the same fish, and compared to results of both a visual identification of the two species and a separation based on a linear discriminant analysis on standardised values of fish length, fish weight and otolith weight. It was concluded that the objective otolith shape analysis using the Shape R package analysis achieve a reasonable classification success, however with a clear bias towards S. mentella . Classification using the otolith weight achieved a slightly higher success than the shape analysis making it a promising method. Furthermore, the method is at the same time both objective, less time consuming than the otolith shape analysis and less expensive than genetic analysis. However, the visual classification method of the whole fish had the highest success rate of the three tested methods, which despite the need for trained technicians makes it the most successful method. [ABSTRACT FROM AUTHOR]

In a preliminary study, 121 individually tagged juvenile Atlantic cod (Gadus morhua) were classified according to their haemoglobin genotypes into four groups, i.e., two main haemoglobin genotypes [Hb-I(1/2), Hb-I(2/2)] and two sub-types [Hb-I(1/2b), Hb-I(2/2b)], and reared for 3 months at 10 °C, 13 °C and T-step (fish reared at 16 °C and then subsequently moved to 13 and later to 10 °C). Overall growth rates across temperatures were 10% and 19% higher in the Hb-I(2/2b), Hb-I(1/2b) sub-types compared to corresponding Hb-I(2/2) and Hb-I(1/2) main types, respectively. Individual growth rate trajectories varied between the genotypes at all temperatures studied. Our study indicates that under certain environmental conditions higher growth in the two sub-types compared to the main genotypes could be expected. This may indicate difference in other physiological characters not studied here, but seen in previous studies, i.e., oxygen affinity and competitive performance. [Copyright &y& Elsevier]