Gadoid Species Research Articles

Annual Variation in the Diet of Breeding European Shag (Phalacrocorax Aristotelis) in Central Norway

Abstract. The diet of breeding European Shag (Phalacrocamx aristotelis) was studied at Sklinna, one of the world's largest colonies, during 2007–2010. Regurgitated pellets were collected regularly throughout the chick rearing period and hard parts used to identify prey items to the lowest possible taxonomic level. The length and width of otoliths were used to estimate fish body length and mass. Shags' diet was varied and contained at least 17 different species of fish. Gadoid species, including saithe (Pollachius virens), cod (Gadus morhua) and Poor Cod (Trisopterus minutus), were the main prey and contributed approximately 90% of the diet during the study period. Saithe dominated the diet by numerical frequency, biomass and frequency of occurrence in all study years. Sandeels (Ammodytidae) contributed little to shag diet. The numerical frequency and percentage saithe biomass was lower in 2010 than in the other years. However, this was compensated by a higher frequency of cod and poor cod, making the tota...

Effect of age and temperature on spawning time in two gadoid species

Large inter-annual differences in spawning time and duration have been reported in a number of fish stocks. This study considers the relative importance of age and temperature on this variability in cod (Gadus morhua) stocks from both sides of the Atlantic and haddock (Melanogrammus aeglefinus) in the North Sea. Age related differences in spawning time were evident from the proportion of spawning or spent fish. These effects were not linear but resembled a step function. The effect of age was opposite between the Northeast and Northwest side of the Atlantic, with younger fish spawning later than older fish in the North Sea and the opposite occurring in the Northwest Atlantic. Such differences in regional trends may be related to differences in energy acquisition and allocation. Temperature effects were considered both as an effect on the developing gonad and as cue to spawning. There was significant inter-annual variation in spawning time but there was little evidence of an effect of temperature on this variation. In Div. 3L and Div. 3NO, cod spawned later in recent years. The fact that mean age of spawners has declined in both these areas and young fish in these regions tend to spawn earlier than old fish suggests that the later spawning in recent years is unlikely related to changes in age structure. Analyses by age suggest fish of all ages are now spawning later than in previous years in these stocks. Such findings point to the underlying complexity of the processes governing spawning time.

Size selection of haddock ( Melanogrammus aeglefinus) in square mesh codends: A study based on assessment of decisive morphology for mesh penetration

In the past, experimental fishing with square mesh codends was conducted with the expectation that this would lead to a better defined size selection indicated by a smaller selection range (SR) of haddock ( Melanogrammus aeglefinus) and other gadoid species compared to that provided by traditional diamond mesh codends. However, experimental results demonstrated considerable between-haul variations in the selection parameters (L50 and SR). It was speculated that these results could be linked to differences in morphology of individual haddock of the same length. In the present study we assessed which measures of haddock morphology are important for size selection through meshes. We quantified between-individual variation in morphology and used simulation techniques to estimate that this variation can account for less than 28% (range 15–28%) of the SR values found during experimental fishing. By including a realistic range of mesh openings when simulating the fishing process of a square mesh codend, we were able to explain most of the experimental results. Additionally, we used our method to better understand the seasonal variation in size selectivity reported in the literature and to predict the basic selective properties for haddock for other mesh shapes. Finally, we found that the conditions of our model, which describes mesh penetration for haddock based on assessment of morphology, is very similar to the conditions previously applied in the literature to study size selection of haddock in diamond mesh codends.

Sexual dimorphism of drumming muscles in European hake (Merluccius merluccius)

Dissections of mature and non-mature European hake males and females (N = 142) collected in waters off the western coast of Norway and in the Bay of Biscay (France) in 2004–2006 demonstrate for the first time that this gadoid species contains drumming muscles. There were differences in drumming muscles weight with body length, sex and maturity stage. This study shows that the difference between females and males is primarily manifested during the spawning season, seen both in the French and Norwegian samples. For the mature females the drumming muscles dry weight increases only slightly, if at all, with increase in total length. For mature males there is a corresponding rapid increase. There does not seem to be any consistent difference between the average dry weight of the drumming muscles in immature male and immature and mature female hake of the same length, tested on the Norwegian samples. Our results suggest that male hake, like the males of other gadoids studied, may produce sounds in the context of spawning.

Factors that accelerate dimethylamine formation in dark muscle of three gadoid species during frozen storage

We investigated factors that accelerate dimethylamine formation in gadoid dark muscle. The degradation rate of trimethylamine-N-oxide into dimethylamine and formaldehyde during frozen storage was compared between ordinary muscle and dark muscle from walleye pollock, southern blue whiting, and hoki. Dimethylamine was generated faster in dark muscle than in ordinary muscle in each species, and it was produced most abundantly in hoki dark muscle compared with the other two species. We investigated the mechanism that caused dimethylamine to be generated more abundantly in dark muscle during frozen storage, and found that the amount of dark muscle nonheme iron, which catalyzes trimethylamine-N-oxide degradation, was higher than that in ordinary muscle in each species, and hoki dark muscle in particular contained the highest levels of nonheme iron among these three species. Moreover, dark muscle in all three fish species had a higher taurine content (known to accelerate dimethylamine formation) than ordinary muscle. These data suggested two candidate factors, namely nonheme iron and taurine, that may accelerate dimethylamine generation during frozen storage. In addition, gel filtration results suggested that walleye pollock dark muscle contains as yet unidentified low-molecular-weight agents that stably accelerate dimethylamine generation.

Long-term exposure of Atlantic cod (Gadus morhua) to components of produced water: condition, gonad maturation, and gene expression

Effects related to offshore contamination have been observed in gadoid species in the North Sea, but uncertainties regarding exposure conditions have led to the need for environmentally relevant exposure studies. In the current study, Atlantic cod ( Gadus morhua ) were sampled at regular intervals during an 11-month continuous or pulsed water-borne exposure to a mixture of produced water components. There was variation in time to female maturation between and within treatment groups; although differences were not significant, there was a tendency towards delayed maturation in intermittently exposed females not seen in continuously exposed females. Physiological parameters such as condition factor, liver somatic index, gonadosomatic index, or hematocrit did not appear to be affected by the treatments. A range of toxicologically relevant genes were differentially expressed in the exposed fish, including AhR-responsive genes (CYP1A, UDP-GT) and genes relevant to immune function (complement C3, MHC 1, CYP27B), apoptosis (PERP), and oxidative stress (hepcidin, serotransferrin, glutathione peroxidase). Although powerful in their depiction of the complexity of cellular responses to environmental stressors, the use of molecular tools should be accompanied by biochemical and physiological endpoints, and results should be holistically interpreted in terms of individual health and function.

Timing of the maturation transition in haddock Melanogrammus aeglefinus

The timing of maturation in haddock Melanogrammus aeglefinus was examined using changes in gonad development, follicle stimulating hormone β (FSH-β) transcript expression profile, growth and condition of 1 year old females held under a common environment between the summer and winter solstices. The circumnuclear ring, cortical alveolus and vitellogenic oocyte stages were first observed in August, October and November, respectively. FSH-β transcript levels did not change significantly until September but increased markedly thereafter in maturing fish. A combined analysis of the mean oocyte diameter of the leading cohort, histological staging and FSH-β transcript profile provided evidence of a commitment to maturation by October or November. Contrary to that previously proposed for gadoid species, histological analysis of field-caught immature M. aeglefinus during the spawning season indicated that cortical alveolar, rather than circumnuclear ring, stage oocytes provided definitive evidence of maturation. A decrease in relative liver size following the summer solstice suggested a possible link between energy status and maturation.

The Fate of Atlantic Bluefin Tuna

For several years, nongovernmental organizations (NGOs) have made Atlantic bluefin tuna (BFT) the archetype of overfishing and general mismanagement of the world fisheries. There are good reasons for this, as BFT crystallizes most of the problems of many fisheries: severe overcapacity, open access in international waters, high market value, and deficient governance at both the international and national levels. Because of this situation, Monaco has proposed that BFT be listed under Appendix 1 (the “most endangered” category) of the Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, it is unclear whether current BFT stock status really meets the biological listing criteria for CITES; the media has sometimes exaggerated the threat to BFT, and BFT management has changed for the better during the past two years. From a strict scientific standpoint, current scientific knowledge does not unequivocally support BFT listing under Appendix 1 (which bans international trade), but it fully supports Appendix 2 (which does not ban fishing in international waters or trade, but mandates monitoring by CITES and the International Commission for the Conservation of Atlantic Tunas). If Monaco's proposal is adopted at the March CITES meeting in Doha, Qatar, BFT will become the first commercially exploited marine species to be listed under Appendix 1. This could generate a revolution in fisheries management, as more than 100 exploited marine species are currently equally or more overfished than BFT—these include many species of sharks, rays, billfishes, sturgeons, salmons, eels, groupers, snappers, flat fish, deep-sea fish, gadoids, shrimps, and clams. This could finally lead to the implicit substitution of current management fisheries organizations by CITES. Is CITES ready to manage the world fisheries in near future, and is it the right multilateral organization to do it?

Development of 10 microsatellite loci in the ling (Molva molva)

We developed primers for two dinucleotide and eight tetranucleotide microsatellite loci in a marine fish, the ling (Molva molva). All markers were obtained from partial genomic DNA libraries and characterized in 55 unrelated individuals from one putative population. The number of alleles ranged from five to 24 (average 10.5) per locus, and the observed heterozygosity ranged from 0.218 to 0.981 (average 0.643). No loci amplified in two other gadoid species tested, the Atlantic cod (Gadus morhua) and the tusk (Brosme brosme).

Application of DNA-based Techniques for Intraspecies Differentiation of Hake Fish

Fish species identification is important as the interest of consumers in sea-fish meat is increasing. The aim of this study was to determine hake species distribution on the Czech market by the PCR-RFLP and sequencing of mt cyt b, and to develop and optimise an alternative system for determination of hake species by sequencing and/or PCR-RFLP using Pan I sequence. Among 20 samples of hake obtained on the Czech market three species were identified: North Pacific hake (Merluccius productus), Argentine hake (Merluccius hubbsi) and South Pacific hake (Merluccius gayi). The approaches tested in our study represent a significant tool either for the differentiation of hake species from other gadoid species (PCR) or for intraspecies identification of different hake species (PCR-RFLP, sequencing). This knowledge can be applied in detection of fish species substitution within the consumers' rights protection.

Identification of Gadoid Species in Fish Meat by Polymerase Chain Reaction (PCR) on Genomic DNA

Identification of fish species is significant due to the increasing interest of consumers in the meat of sea fish. Methods focusing on fish species identification help to reveal fraudulent substitution among economically important gadoid species in commercial seafood products. The objective of this work was to develop a conventional PCR method for the differentiation of the following gadoid fish species in fish products: Alaska pollack ( Theragra chalcogramma), blue whiting ( Micromesistius poutassou), hake spp. ( Merluccius spp.), Atlantic cod ( Gadus morhua), saithe ( Pollachius virens), and whiting ( Merlangius merlangus). The species-specific primer pairs for gadoid species determination were based on the partial pantophysin I ( PanI) genomic sequence. Sequence identification was confirmed by cloning and sequencing of the PCR products obtained from the species considered. For the simultaneous detection of Alaska pollack, blue whiting, and hake spp., a quadruplex PCR system was constructed. Other gadoid species were detected in separate PCR reactions. After optimization of the reactions, the developed PCR systems were used for the analysis of codfish samples obtained from the Czech market and the customs' laboratories. This method represents an alternative approach in the use of genomic DNA for the identification of fish species. This method is rapid, simple, and reliable without the need for further confirmative methods. Furthermore, the identification of a mixture of more than one species is possible. The PCR system has been optimized for routine diagnostic purposes.

An abundance estimate of ling ( Molva molva) and cod ( Gadus morhua) in the Skagerrak and the northeastern North Sea, 1872

Fisheries management may suffer from historical myopia, because most stock assessments are based on time series which are ca. 30–40 years long. This investigation examines changes in population dynamics of two gadoid species in the Skagerrak- northeastern North Sea on a century scale, and argues that long-term, historical abundance estimates are relevant to the determination of biomass reference points in fisheries management. Situated within the field of historical ecology, this paper presents findings on the abundance of ling and cod in 1872. Calculations are based on historical CPUE and catch data. Ling abundance was ca. 100–200 million individuals aged 4+ and probably exceeded cod abundances (ca. 3 million individuals aged 3+) in the Skagerrak and in the northeastern North Sea in 1872. Current ling abundances are unknown but probably lower than in 1872, as reflected in declining landings during the late 1990s–early 2000s. Dominating ling size has also declined since the late 19th century. The estimated historic abundance of cod in the Skagerrak and northeastern North Sea is similar to present abundance of cod in these areas but its spatial distribution has contracted. These changes in the ling and cod populations are consistent with effects of fishing on populations and should be considered when setting fishery management plans for population recovery and sustainability.

Distribution and migration of saithe (Pollachius virens) around Iceland inferred from mark-recapture studies

Abstract Armannsson, H., Jonsson, S. Th., Neilson, J. D., and Marteinsdottir, G. 2007. Distribution and migration of saithe (Pollachius virens) around Iceland inferred from mark-recapture studies. – ICES Journal of Marine Science, 64: 1006–1016. Knowledge of the distribution and migration of populations is necessary to identify and conserve stock components and therefore genetic variability. Compared with other gadoid species, little is known about the life history of saithe (Pollachius virens) (known as pollock in the Northwest Atlantic) or its stock components. About 15 800 saithe were tagged near Iceland from 2000 to 2004 to estimate population parameters, to describe saithe dynamics on the Icelandic shelf, and to monitor long-distance migrations, should they occur. A multiplicative model was used to standardize fishing effort to describe the distribution of the tagged population, based on tag returns from the fishery. Saithe have a high affinity to their tagging area, but move considerably within that area. Because of variability in fishing effort among areas, tagged fish exhibit different area-specific catchabilities. The results also indicate seasonal offshore–inshore migrations during summer and variability in migratory routes among different tagging areas related to affinities to different feeding grounds. This could indicate a more complex stock structure than previously thought. Finally, results to date do not indicate large-scale emigration of saithe from Icelandic fishing grounds.

Isolation and characterization of microsatellite loci in a marine fish species, the tusk (Brosme brosme)

AbstractWe developed polymerase chain reaction primers for nine dinucleotide microsatellite loci in the marine deep‐sea fish, the tusk (Brosme brosme). All markers were obtained from a partial genomic DNA library, and characterized in 100 unrelated individuals from one putative population. The number of alleles ranged from two to 60 with an average of 15/locus. The observed heterozygosity ranged from 0.020 to 0.826 (average 0.438). Several of the markers amplified multiple alleles from the two other gadoid species tested.

Identification of gadoid species (Pisces, Gadidae) by sequencing and PCR–RFLP analysis of mitochondrial 12S and 16S rRNA gene fragments

We applied PCR–RFLP (Polymerase Chain Reaction – Restriction Fragment Length Polymorphism) analysis to identify seven gadoid species of different biogeographical origin and commercial relevance, namely Gadus morhua (Atlantic ocean); Trisopterus minutus capelanus, Trisopterus minutus minutus, Molva elongata, Phycis blennoides, Micromesistius poutassou (Atlantic ocean and Mediterranean sea); Theragra chalcogramma (Pacific ocean). Two DNA fragments belonging to mitochondrial 12S and 16S rRNA genes of about 430 and 630 bp, respectively, were isolated by PCR amplification. Their direct sequencing showed a significant genotypic diversity among gadoid species, useful for species identification. Digestion of 16S rRNA gene PCR fragment with MvaI or Bsh1285I restriction enzymes, followed by agarose gel electrophoresis of the cleaved products, yielded specific restriction profiles that enabled direct, visual identification of the species analyzed. This PCR–RFLP method allowed a clear and rapid discrimination of the gadoid species studied.

Habitat associations and diet of young-of-the-year Pacific cod (Gadus macrocephalus) near Kodiak, Alaska

The influence of environmental variables and habitat on growth and survival of juvenile gadoid species in the Atlantic has been clearly demonstrated; conversely, in the North Pacific little is known about the habitat and ecology of juvenile Pacific cod (Gadus macrocephalus Tilesius). The hypothesis that density of young-of-the-year (YOY) Pacific cod in nearshore habitats is predicted by shallow depth and the presence of eelgrass and macroalgae was tested in a variety of nearshore habitats adjacent to commercial fishing grounds near Kodiak Island, AK. From 10 to 22 Au- gust 2002, a beach seine and small-meshed beam trawl were used to capture YOY Pacific cod (n = 254) ranging from 42 to 110 mm fork length. Depth, water temperature, salinity, sediment grain size, and percent cover by emergent structure (i.e. tube-dwelling poly- chaetes, sea cucumber mounds, macroalgae) were measured prior to fishing. Density of YOY Pacific cod was highest in areas of moderate depth (15-20 m) and positively and linearly related to percent cover by sea cucumber mounds and to salinity. No previous studies have documented fish utilizing sea cucumber mounds as habitat. Furthermore, eelgrass and macroalgae were inconsequential to cod distribution. Diets consisted mainly of small calanoid copepods, mysids, and gammarid amphipods and were significantly related to cod length and depth. This work provides important information on previously undocumented factors that affect distribution and feeding of YOY Pacific cod, which ultimately influence growth and survival in this species.

Prey partitioning between cod (Gadus morhua) and minke whale (Balaenoptera acutorostrata) in the Barents Sea

Stomach samples of minke whale (Balaenoptera acutorostrata) and cod (Gadus morhua) were collected on the northeastern parts of the Finnmark coast, northern Norway, in 1998 and 1999 to investigate prey preference, niche overlap and niche width for the two species. A survey to estimate prey abundance was also conducted. Prey preference, niche overlap and niche width were described using Manly's alpha (α), Pianka's index (Ojk) and Levin's index (B), respectively. The diet of cod consisted mainly of capelin, deep-water shrimp, gadoids and krill. The smallest cod (≤64 cm length) preferred capelin, whereas the largest cod (>64 cm length) preferred gadoid species, including cod. The minke whale diet consisted mainly of capelin (Mallotus villosus), herring (Clupea harengus) and krill, and showed a particular preference for herring and capelin. Krill were consumed in large quantities, but did not seem to be a preferred food item for either cod or minke whales. In contrast to cod, which fed very little on herring, the minke whale fed heavily on herring in some areas. The niche widths for both cod and minke whales were relatively low, and the diet overlap between minke whale and cod was low.

Worldwide status and perspective on gadoid culture

Abstract Currently, Atlantic cod (Gadus morhua) is the primary species being developed for commercial culture, with activities concentrated around the North Atlantic. In addition, closed life cycles have been established for haddock (Melanogrammus aeglefinus), pollock (Pollachius pollachius), and hake (Merluccius australis), but production of these species (in Canada, Spain, and Chile) is rather modest. In the short- to medium-term, Atlantic cod will be the dominant gadoid species in culture, and it is believed that production can reach levels similar to those of farmed salmon within the next 15–20 years. This development is possible because methods for year-round production of juveniles and significant hatchery capacity have been established. Also, there is a demand for farmed cod to fill the gap between increasing market needs and diminishing supply from fisheries. However, challenges must be met if cod farming is to reach its anticipated potential. Juvenile production must become more reliable in terms of survival and quality. For the on-growing phase, the supply of cost-efficient feeds produced from sustainable raw materials is of utmost importance. Consumer markets need to be developed with an emphasis on quality and food safety. Relatively little is known about health management for gadoid species.

Distribution and onshore migration behaviour of burbot larvae in Lake Constance, Germany

Larval abundance of burbot Lota lota in the pelagic zone of Lake Constance, Germany, peaked during April and remained at a constant but lower level until mid‐June. From the end of May onwards a significant diel vertical migration pattern was observed: while burbot larvae were distributed above as well as below the thermocline in the daytime with the highest percentages of abundance at water depths of 30 and 50 m (below the thermocline) on 5 and 25 June, they were concentrated from 2 to 15 m (above the thermocline) during the night. This migration pattern coincided with a significant decline in the food items preferred by burbot at this life stage, cyclopoid copepods. This phase of diel vertical migration lasted for c. 4 weeks until the burbot larvae suddenly disappeared from the pelagic zone. This indicated a short phase, lasting only a few days, of larval settlement into profundal benthic habitats. This was supported by a significant, abrupt decrease in the absolute growth rates of the larvae at day 56 after hatching. The day–night pattern of vertical migration observed could be assumed to be a transition phase from a pelagic to a benthic lifestyle, as reported for juveniles of several other, marine gadoid species.

Using knowledge from fishers and fisheries scientists to identify possible groundfish ‘Essential Fish Habitats’

Fishers have often complained that standard fisheries survey data do not adequately reflect the grounds targeted by commercial fishers and hence scientists tend to make over-cautious estimates of fish abundance. Such criticisms are of particular importance if we are to make a creditable attempt to classify ‘Essential Fish Habitat’ using existing large-scale standard trawl surveys. Nevertheless, these data sets provide a powerful tool to examine consistent patterns in the temporal abundance of fish on a spatial scale. Here, we report a questionnaire survey of fishers that invited them to indicate the location of grounds of key importance for gadoid fishes. In addition, fishers were asked to indicate whether they had noticed key habitat features that might indicate the characteristics of EFH. A comparison of such areas as highlighted by fishers with data from standard groundfish surveys were broadly compatible for all three species of gadoids examined. Many sampling stations of these surveys fell outside areas highlighted by fishers as key fishing grounds/habitats. Fishers were able to provide usable biological observations that were consistently cross-referenced by several independent sources, for example the occurrence of haddock over brittlestar beds. We conclude that fishers’ knowledge is an invaluable supplement to existing data sets that can help to better focus more detailed studies of EFH.