Tore Haug

Biology of the Atlantic Halibut, Hippoglossus hippoglossus (L., 1758)

Publisher Summary The Atlantic and Pacific halibut (Hippoglossus hippoglossus and H. stenolepis, respectively) are two morphologically similar flatfish forms inhabiting the boreal and subarctic waters in their respective oceans. Until recently, there were disagreements as to the taxonomic status of these two forms. More recent studies, however, using genetically determined electrophoretically detectable protein variants to test for genetic differences, have revealed a genetic difference between Atlantic and Pacific halibut of a magnitude that confirms the treatment of the two taxa as separate species. Pleuronectiform flatfishes are thought to have evolved in the Pacific Ocean in the early Tertiary period because of their greater present-day diversity in the Pacific Ocean. This chapter presents an account of the biology, fishery, and potential for aquaculture of the Atlantic species.

Lipid class and fatty acid composition of eggs from the Atlantic halibut (Hippoglossus hippoglossus)

Abstract Lipid class and fatty acid analyses were carried out on ripe roe of halibut caught in North Norway. The percentage of neutral lipids was c. 30% while the main polar lipids were phosphatidylcholine (62%) and phosphatidylethanolamine (7%). The phospholipids were very unsaturated, with high concentrations of ( n −3) polyunsaturated fatty acids (PUFA), especially 20:5 ( n −3) and 22:6 ( n −3).

Lipids in atlantic halibut (Hippoglossus hippoglossus) eggs from planktonic samples in Northern Norway

Fertilized Atlantic halibut (Hippoglossus hippoglossus L.) eggs in different developmental stages (Days 0 to 18) were sampled from plankton in North Norway in February 1986 and analysed for lipid classes and fatty acid content. In unfertilized ovulated eggs taken from ripe fish caught in 1983/1984, polar and neutral lipids comprised ca. 71 and 30% of the total lipids, respectively, decreasing and increasing to 67 and 33%, respectively, in Stage III (11 to 18 d old) fertilized eggs. Of the polar lipids, phosphatidylcholine decreased markedly from 62% in unfertilized ovulated eggs to ca. 40% in Stage I (0 to 3 d old) fertilized eggs, while phosphatidylethanolamine increased from ca. 7 to 33%. Triacylglycerols, the major neutral lipids, increased from ca. 13% in unfertilized ovulated eggs to 16% in Stage III fertilized eggs. The total lipid in Stage I fertilized eggs had relatively low levels of polyunsaturated fatty acids (PUFA), with (n-3) PUFA accounting for only ca. 25% of the total fatty acids. The (n-3) PUFA increased to ca. 40% of the total fatty acids in Stage III, while the (n-3): (n-6) ratio increased from 4.1 to 7.0.

Feeding habits of harp seals (Phoca groenlandica) during early summer and autumn in the northern Barents Sea

The feeding habits of harp seals (Phoca groenlandica) in the Barents Sea were examined in studies conducted during June 1991, September 1990 and 1991, and October 1992. Analyses of stomach and intestinal contents were carried out and concurrent estimates of prey abundance were made using trawl gear. Harp seals appeared to feed at low intensity in the pack ice belt during the first half of June. There was little potential prey in the water column, but prawns (Pandalus borealis), capelin (Mallotus villosus) and polar cod (Boreogadus saida) were abundant close to the bottom. In September, the seals sampled in the northern pack ice areas of the Barents Sea fed on the pelagic amphipod Parathemisto libellula, krill (Thysanoessa spp.), prawns and, to a lesser extent, on fish species such as polar cod, sculpins (Cottidae) and snailfish (Liparidae). Trawling revealed that large quantities of Parathemisto libellala were present in the upper layers of the water column. Fish, mainly capelin and polar cod, were less abundant and occurred in deeper waters. In mid-October, the diet of seals in the northern Barents Sea consisted mainly of amphipods (Parathemisto sp.). Later in October, when increasing pack ice cover forced the harp seals to move south, the diet seemed to change from amphipods to fish prey, predominantly capelin and polar cod.

Growth, sexual maturation, and spawning season of Atlantic halibut, Hippoglossus hippoglossus, in Faroese waters

Abstract Biological data on Atlantic halibut, Hippoglossus hippoglossus, caught in an exploratory bottom trawl fishery in November–February 1983–1986 in a recently discovered deep water spawning area and in other both coastal and bank areas in Faroese waters, are presented. Studies of increases in length and weight confirmed the sex-dependent growth patterns found in earlier works, i.e. a higher growth rate in females than males especially after sexual maturity. The data show that Faroese halibut grow much more rapidly and mature at lower average ages (c. 4.5 years in males and slightly above 7 years in females) than in any other area investigated in the North Atlantic. Average length and round weight at sexual maturity were slightly above 55 cm and c. 1.7 kg in males, while the corresponding values in females were 110–115 cm and c. 18 kg. Spawning in the area appeared to commence in January and intensify in February. The peak in spawning activity was apparently not attained during the study period (November–February), and most probably occurred later in winter or early in spring.

Occurrence and size/age relations of polar cod, Boreogadus Saida (Lepechin), in Spitsbergen coastal waters

Abstract The polar cod were common in catches with bottom and pelagic trawl in Spitsbergen coastal waters. O-group polar cod were found in the upper echo-layers (15–80 m), while adults were confined to the deeper layers. A size/depth segregation was noted in the bottom layers with smaller individuals occurring mostly in the shallower areas and larger ones at greater depths. In general, pelagic hauls were dominated by fish smaller than 10 cm. Polar cod from Spitsbergen coastal waters were generally smaller and apparently grew more slowly than their counterparts in the central and eastern Barents Sea.

Changes in size- and age-distributions and age at sexual maturity in Atlantic halibut, Hippoglossus hippoglossus, caught in North Norwegian waters

Abstract There has been a decrease in the percentage of old, but not of large, fish in the catches of mature Atlantic halibut, Hippoglossus hippoglossus , taken in gill nets during the period 1981–1985, compared with catches taken in Northern Norway during the period 1956–1960. This change is associated with increases in size at age and a substantial reduction in average age at first spawning between the two periods. The changes in these population parameters may point to a drop in halibut density due to exploitation.

Panmictic population structure in the hooded seal (Cystophora cristata)

Two putative populations of hooded seals (Cystophora cristata) occur in the North Atlantic. The Greenland Sea population pup and breed on the pack ice near Jan Mayen (‘West Ice’) while the Northwest Atlantic population is thought to pup in the Davis Strait, in the Gulf of St. Lawrence (the ‘Gulf’), and off southern Labrador or northeast Newfoundland (the ‘Front’). We used microsatellite profiling of 300 individuals at 13 loci and mitochondrial DNA sequencing of the control region of 123 individuals to test for genetic differentiation between these four breeding herds. We found no significant genetic differences between breeding areas, nor evidence for cryptic nor higher level genetic structure in this species. The Greenland Sea breeding herd was genetically most distant from the Northwest Atlantic breeding areas; however, the differences were statistically nonsignificant. Our data therefore suggest that the worlds hooded seals comprise a single panmictic genetic population.

Summer vocalisations of adult male white whales (Delphinapterus leucas) in Svalbard, Norway

Abstract. The principal aim of this study was to describe the vocalisations produced by the largely unstudied white-whale population in Svalbard, Norway. It was found that Svalbards white whales produced most of the vocalisations that have been documented in other populations, but they also displayed minor vocal novelties and differences. A subjective classification suggested 21 call types, which were dominated by a variety of whistles. A statistical classification (cluster analyses) produced 11 groupings (after exclusion of general pulsed call types), which contained fairly logical grouping of the subjectively determined call types. However, neither method of classification employed was considered ideal for classifying white-whale vocalisations because of the highly graded nature of the calls. The white whales in this study were most vocal during milling and joining behaviours. A surprising result in this study was how little time white whales in this area spent vocalising. Their relative silence could possibly be: (1) an anti-predator strategy in response to killer whales (Orcinus orca); (2) a result of the type of schools encountered during this study (all-male grouping); (3) a by-product of the presence of the research boat in an area where whales are not accustomed to boat traffic; or (4) a result of the limited behavioural repertoire covered in this study. More extensive studies of acoustic behaviour of this population, which include various age and sex classes, with broader seasonal coverage that includes more potential behavioural contexts, are required before firm conclusions can be made regarding geographic trends in white-whale acoustic behaviour.

Population substructure of North Atlantic minke whales (Balaenoptera acutorostrata) inferred from regional variation of elemental and stable isotopic signatures in tissues

Abstract Information on population structure is essential for estimating population demographics and managing the impacts of exploitation of North Atlantic minke whales ( Balaenoptera acutorostrata ). New approaches including assessment of geochemical signatures in tissues can assist in defining such structure. This study determined regional variations in long-term elemental diagnostics of stock differences among 159 minke whales harvested in West Greenland, the Northeast Atlantic Ocean and the North Sea in 1998. The diagnostics tested included mercury (Hg), selenium (Se) and cadmium (Cd) in various tissues, and the trace and major element composition of baleen. Supporting data was also gathered on δ 15 N and δ 13 C and stable lead isotope ratios. For female whales, significant differences in at least one long-term diagnostic element occurred between several areas. Existence of the following population substructure was inferred: (a) West Greenland, (b) a central group represented by whales from Jan Mayen, (c) a northeastern stock encompassing the Barents Sea, Svalbard and coastal Norway, and (d) the North Sea. These groups were consistent with those defined genetically by Andersen et al. [Mar. Ecol., Prog. Ser. 247 (2003) 263]. Males appeared to fall into similar groupings to females but because of smaller sample sizes fewer significant differences occurred between areas. Stable-isotopic values in minke whales suggested lower trophic-level feeding in this species than hitherto suspected, with significant dietary differences between areas. Variations in feeding habits appeared to explain part of the geographical variation in tissue Cd, but not tissue Hg or Se. Differences among elements with a relatively long biological half-life in specific tissues suggested that groups of minke whales have fidelity to certain summer feeding areas at least for several years.