Solveig Thorkildsen

Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus)

Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries. Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed. According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q10 effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.

Genotype distributions of cod from the Norwegian Skagerrak coast

Abstract The genotype distributions for cod, Gadus morhua L., from the southeastern coast of Norway are studied as part of a more extensive study on cod enhancement and the possible effects of mass liberation of 0-group cod on endemic cod populations. This paper focus on possible geographical variation in allele frequencies, temporal variations in haemoglobin type frequencies and mean length of age of various genotypes. Twelve samples were analysed for genotype distribution of haemoglobins and the tissue enzymes LDH, PGI, IDH, PGM, and GPD by agar-gel and starch gel electrophoresis. Some inters ample variations were found indicating heterogeneity of the total cod stock structure in the area. The haemoglobin-controlling genes occurred with similar frequencies in this material as in corresponding material analysed more than 25 years earlier. Possible associations between life history traits and individual genotypes were investigated, and genotype-dependent growth rate was indicated.

Identification keys to halosaurs and notacanthids (Notacanthiformes, Elopomorpha) in the subarctic Atlantic Ocean including three new distributional records and multiple molecular OTUs of Notacanthus cf. chemnitzii

As part of an ongoing effort to monitor the fish diversity in Greenland waters using morphological and molecular taxonomy, and construct pragmatic identification keys, we here update distributions of all known halosaurs (Halosauridae) and notacanthids (Notacanthidae) in the subarctic Atlantic Ocean. New distributions are included for Aldrovandia oleosa, Halosauropsis macrochir, and Notacanthus bonaparte, all caught once in the Denmark Strait off SE Greenland. We also present the first observation of luminous tissues in halosaurs. Photo, illustrative and text identification keys are included for pragmatic identification corroborated by molecular barcoding data, produced as part of the Greenland Fishes Barcoding Project (GLF) introduced in this study. Barcoding data revealed five operational taxonomic units (OTUs) of Notacanthus cf. chemnitzii present, including three distinct haplotypes observed off SE Greenland alone, within this species complex currently described as one circumglobal species.