Showing papers on "Gadus published in 2003"
TL;DR: It is concluded that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.
Abstract: The Atlantic cod (Gadus morhua L.) has been overexploited in the North Sea since the late 1960s and great concern has been expressed about the decline in cod biomass and recruitment. Here we show that, in addition to the effects of overfishing, fluctuations in plankton have resulted in long-term changes in cod recruitment in the North Sea (bottom-up control). Survival of larval cod is shown to depend on three key biological parameters of their prey: the mean size of prey, seasonal timing and abundance. We suggest a mechanism, involving the match/mismatch hypothesis, by which variability in temperature affects larval cod survival and conclude that rising temperature since the mid-1980s has modified the plankton ecosystem in a way that reduces the survival of young cod.
1,225 citations
TL;DR: The results show that changes in predator populations can have strong effects on prey populations in oceanic food webs, and that the strength of these interactions may be sensitive to changes in mean ocean temperature.
Abstract: Here we present a meta-analytic approach to analyzing population interac- tions across the North Atlantic Ocean. We assembled all available biomass time series for a well-documented predator-prey couple, Atlantic cod (Gadus morhua) and northern shrimp (Pandalus borealis), to test whether the temporal dynamics of these populations are con- sistent with the ''top-down'' or the ''bottom-up'' hypothesis. Eight out of nine regions showed inverse correlations of cod and shrimp biomass supporting the ''top-down'' view. Exceptions occurred only close to the southern range limits of both species. Random-effects meta-analysis showed that shrimp biomass was strongly negatively related to cod biomass, but not to ocean temperature in the North Atlantic Ocean. In contrast, cod biomass was positively related to ocean temperature. The strength of the cod-shrimp relationship, how- ever, declined with increasing mean temperature. These results show that changes in predator populations can have strong effects on prey populations in oceanic food webs, and that the strength of these interactions may be sensitive to changes in mean ocean temperature. This means that the effects of overfishing in the ocean cascade down to lower trophic levels, as has been shown previously for lakes and coastal seas. In order to further investigate these processes, we establish a methodological framework to analyze species interactions from time series data.
511 citations
TL;DR: The study of hybrid zones is central to the understanding of the genetic basis of reproductive isolation and speciation, and using a model‐based clustering method for individual admixture analysis, the existence of intermediate genotypes in all samples from the transition area is demonstrated.
Abstract: The study of hybrid zones is central to our understanding of the genetic basis of reproductive isolation and speciation, yet very little is known about the extent and significance of hybrid zones in marine fishes. We examined the population structure of cod in the transition area between the North Sea and the Baltic Sea employing nine microsatellite loci. Genetic differentiation between the North Sea sample and the rest increased along a transect to the Baltic proper, with a large increase in level of differentiation occurring in the Western Baltic area. Our objective was to determine whether this pattern was caused purely by varying degrees of mechanical mixing of North Sea and Baltic Sea cod or by interbreeding and formation of a hybrid swarm. Simulation studies revealed that traditional Hardy-Weinberg analysis did not have sufficient power for detection of a Wahlund effect. However, using a model-based clustering method for individual admixture analysis, we were able to demonstrate the existence of intermediate genotypes in all samples from the transition area. Accordingly, our data were explained best by a model of a hybrid swarm flanked by pure nonadmixed populations in the North Sea and the Baltic Sea proper. Significant correlation of gene identities across loci (gametic phase disequilibrium) was found only in a sample from the Western Baltic, suggesting this area as the centre of the apparent hybrid zone. A hybrid zone for cod in the ecotone between the high-saline North Sea and the low-saline Baltic Sea is discussed in relation to its possible origin and maintenance, and in relation to a classical study of haemoglobin variation in cod from the Baltic Sea/Danish Belt Sea, suggesting mixing of two divergent populations without interbreeding.
265 citations
TL;DR: DNA recovered from a temporal series of archived North Sea cod otoliths is used to investigate genetic diversity within the Flamborough Head population between 1954 and 1998, during which time the population underwent two successive declines.
Abstract: Despite increasing evidence that current exploitation rates can contribute to shifts in life-history traits and the collapse of marine fish stocks, few empirical studies have investigated the likely evolutionary impacts Here, we used DNA recovered from a temporal series of archived North Sea cod (Gadus morhua) otoliths, to investigate genetic diversity within the Flamborough Head population between 1954 and 1998, during which time the population underwent two successive declines Microsatellite data indicated a significant reduction in genetic diversity between 1954 and 1970 (total number of alleles: 1954, 46; 1960, 42; 1970, 37), and a subsequent recovery between 1970 and 1998 (total number of alleles: 1970, 37; 1981, 42; 1998, 45) Furthermore, estimates of genetic differentiation (F(ST) and R(ST)) showed a significant divergence between 1998 and earlier samples Data are consistent with a period of prolonged genetic drift, accompanied by a replacement of the Flamborough Head population through an increased effective migration rate that occurred during a period of high exploitation and appreciable demographic and phenotypic change Other studies indicate that diversity at neutral microsatellite loci may be correlated with variability at selected genes, thus compromising a population's subsequent recovery and adaptive potential Such effects are especially pertinent to North Sea cod, which are threatened by continuing exploitation and rising sea temperatures
242 citations
TL;DR: The positive effect of the cod condition on their reproductive potential generally implies that the stocks in good condition in the temperate regions of the northeast and west Atlantic can sustain higher exploitation rates than stocks in poor condition in one of the colder regimes of the northwest Atlantic.
192 citations
TL;DR: It is indicated that cod use both glycolytic and oxidative capacities to support endurance swimming, and swimming endurance is linked with the metabolic capacities of red and white muscle.
Abstract: SUMMARY This study evaluated the link between swimming endurance and condition of
Atlantic cod Gadus morhua that had been fed or starved during the 16
weeks preceding the tests, and assessed whether muscle metabolic capacities
explain such links. The condition factor [(somatic mass × fork
length -3 )×100] of starved cod was 0.54±0.1 whereas
that of fed cod was 0.81±0.1. In white and red muscle, we measured four
glycolytic enzymes: phosphofructokinase (PFK), pyruvate kinase (PK), creatine
kinase (CK) and lactate dehydrogenase (LDH), two mitochondrial enzymes:
cytochrome c oxidase (CCO) and citrate synthase (CS), a biosynthetic
enzyme, nucleoside diphosphate kinase (NDPK), glycogen and protein levels and
water content. Muscle samples were taken at three positions along the length
of the fish; starvation affected the metabolic capacities of white muscle more
than those of red muscle. The levels of glycolytic enzymes and glycogen
changed more in white than red muscle during starvation. Both in fed and
starved cod, muscle metabolic capacities varied with position along the fish;
starvation reduced this longitudinal variation more in white than red muscle.
In white muscle of fed cod, the glycolytic enzyme levels increased from head
to tail, while in starved cod this longitudinal variation disappeared. In red
muscle mitochondrial enzyme levels were highest in the caudal sample, but
fewer differences were found for glycolytic enzymes. Swimming endurance was
markedly affected by fish condition, with starved fish swimming only 30% of
the time (and distance) of fed fish. This endurance was closely linked with
the number of burst—coast movements during the test and the activity of
CCO and LDH in white muscle. The number of burst—coast movements was
significantly linked with condition factor and PFK activity in caudal red
muscle and gill arch mass. Our data indicated that cod use both glycolytic and
oxidative capacities to support endurance swimming. Furthermore, swimming
endurance is linked with the metabolic capacities of red and white muscle.
160 citations
TL;DR: A food web model for the Baltic Sea proper is created, using the Ecopath with Ecosim software, to evaluate interactions between fisheries and the food web from 1974 to 2000 and may ultimately provide a basis for estimating community responses to management actions.
Abstract: Because fisheries operate within a complex array of species interactions, scientists increasingly recommend multispecies approaches to fisheries management. We created a food web model for the Baltic Sea proper, using the Ecopath with Ecosim software, to evaluate interactions between fisheries and the food web from 1974 to 2000. The model was based largely on values generated by multispecies virtual population analysis (MSVPA). Ecosim outputs closely reproduced MSVPA biomass estimates and catch data for sprat (Sprattus sprattus), herring (Clupea harengus), and cod (Gadus morhua), but only after making adjustments to cod recruitment, to vulnerability to predation of specific species, and to foraging times. Among the necessary adjustments were divergent trophic relationships between cod and clupeids: cod exhibited top-down control on sprat biomass, but had little influence on herring. Fishing, the chief source of mortality for cod and herring, and cod reproduction, as driven by oceanographic conditions as well as unexplained variability, were also key structuring forces. The model generated many hypotheses about relationships between key biota in the Baltic Sea food web and may ultimately provide a basis for estimating community responses to management actions.
151 citations
TL;DR: Research in Newfoundland has focussed on determining optimal prey densities and light levels to use during larviculture, and survival rates of over 40% from start-feeding to metamorphosis have been achieved.
145 citations
TL;DR: High plasma levels of steroids in male and female cod during spawning serve to promote further development and growth of less advanced stages of germ cells.
Abstract: Gametogenesis in female and male Atlantic cod ( Gadus morhua L.) was investigated by sampling blood plasma and gonadal tissue from 19 to 33-month-old fish. The reproductive cycles of both female and male Atlantic cod are characterized by distinct annual variations in gonadal size and developmental stage and these are associated with changes in sex steroids and liver size. I H did not change during early gonadal development, but both spent females and males had lower I H than late maturing females and spermiating males, respectively. In females I G was correlated to plasma E2 levels and they were highest in spawning females. The lowest levels during the reproductive cycle were observed in spent females. Plasma T levels were low throughout ovarian development, and were at a minimum in spent females. 11-ketotestosterone in plasma of males increased rapidly during spermiation, while T increased at earlier testicular stages and reached maximum during spermiation. High plasma levels of steroids in male and female cod during spawning serve to promote further development and growth of less advanced stages of germ cells.
138 citations
TL;DR: A strong preference of sprat larvae for different developmental stages of Acartia spp.
137 citations
TL;DR: Polychlorinated dibenzo-p-dioxins/dibenzofurans, polychlorinated naphtalenes, Toxaphene and brominated flame retardants in liver of cod from reference sites showed a positive but weak correlation with length, whereas no co-variation was found between PCBs and liver fat.
TL;DR: The results indicate that environmental temperature changes will lead to a distributional change in the different haemoglobin types of Atlantic cod, global warming providing an advantage for HbI-1 cod, however, a combination of increased water temperature and hypoxia could be unfavourable for Atlantic cod stocks.
Abstract: Atlantic cod Gadus morhua has polymorphic haemoglobin, which can be separated into two homozygous types, HbI-1 and HbI-2, and one heterozygous type HbI-1/2. The geographical distribution of Atlantic cod with the different haemoglobin types varies, with the HbI2 allele occurring at high frequency in northern regions, and the HbI1 allele dominant in warmer areas. To determine if temperature is a selective parameter in the distribution of the haemoglobin types, the preferred temperature of the homozygous genotypes HbI-1 and HbI-2 was measured. We found that HbI-2 cod preferred a temperature of 8.2±1.5°C while HbI-1 cod preferred 15.4±1.1°C, and this preference was significant. The effect of hypoxia (35% oxygen saturation) on the preferred temperature was also measured. Previous studies showed that the preferred temperature of fish decreases during hypoxia, and this was the case for HbI-1 cod, which preferred 9.8±1.8°C during hypoxia, whereas HbI-2 cod did not show this effect. The results indicate that environmental temperature changes will lead to a distributional change in the different haemoglobin types of Atlantic cod, global warming providing an advantage for HbI-1 cod. However, since HbI-1 cod prefer a low temperature under hypoxic conditions, a combination of increased water temperature and hypoxia could be unfavourable for Atlantic cod stocks.
TL;DR: Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, and blue-whiting Micromesistius poutassou and other small pelagic fishes were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment.
Abstract: Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua, hake Merluccius merluccius, megrim Lepidorhombus whiffiagonis, whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey (e.g. Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey (e.g. mackerel Scomber scombrus), even though these pelagic prey-fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue-whiting Micromesistius poutassou and other small pelagic fishes (Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density-dependent feeding by predators on mackerel and only hake exhibited density-dependent feeding on horse-mackerel. Hake, cod and megrim consumed more blue-whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.
TL;DR: Profiles of depth and ambient temperature suggest that cod that spawn in the study area select between two alternatives in foraging strategies, i.e., deep- or shallow-water migrations, which appear to follow the seasonal trend in temperature characteristic for the shelf waters.
Abstract: Sixty data storage tags were analysed with respect to depth and ambient temperature and for relationships between depth, ambient temperature, and growth. The fish were tagged and released in April 1996–1999 on the spawning grounds at the southwest coast of Iceland. Profiles of depth and ambient temperature suggest that cod (Gadus morhua L.) that spawn in the study area select between two alternatives in foraging strategies, i.e., deep- or shallow-water migrations. The shallow-water fish appear to follow the seasonal trend in temperature characteristic for the shelf waters. The deep-water fish, however, migrate to deeper and cooler waters outside the spawning season and increase their vertical movement. A significant positive relationship between depth and ambient temperature was observed for the shallow-water fish, and a significant negative relationship was observed for the deep-water fish. Daily variation in depth and ambient temperature showed increasing trends with increase in depth, in particular for...
TL;DR: In this paper, stock assessments were used to compare stock biomass, annual growth (Gs) and surplus production per capita (TSPc) among 15 cod (Gadus morhua) stocks in the North Atlantic.
Abstract: Data from stock assessments were used to compare stock biomass, annual growth (Gs) and surplus production per capita (TSPc) and per unit biomass (TSPb) among 15 cod (Gadus morhua) stocks in the North Atlantic. TSPc ranged from 99 to 1012 g per fish among stocks and averaged 448 g per fish. TSPb ranged from 140 to 469 g kg−1 among stocks and averaged 294 g kg−1. Gs varied considerably with low growth production associated with low surplus production. On average, cod produced 724 g per fish in growth annually with cod in the least productive stock producing 7.2 times less than in the most productive stock. The stocks divided into four clusters reflecting four levels of production. Celtic Sea, Irish Sea and West Scotland cod showed the highest levels of production whereas Eastern Scotian Shelf, Northeast Arctic, Northern Grand Bank, Northern and Southern Gulf of St Lawrence showed the lowest levels. Surface and bottom salinity and temperature differed significantly among clusters in a canonical discriminant analysis. Temperature and salinity correlated with the first and second canonical variates, respectively. The most productive stocks were associated with higher bottom salinity and temperature. None of the stocks, including stocks with a fast growth rate and living at higher temperatures, had a specific growth rate (SGR) close to the maximum rate observed in laboratory experiments. The difference between observed and maximum SGR decreased at temperatures above 6°C. Very cold temperatures resulted in smaller cod also achieving SGR values closer to the maximum. Temperature is a major determinant of stock production.
TL;DR: Habit dimension affected predation risk in juvenile cod via 2 opposing mechanisms and the results stress the importance of considering both habitat areal extent and predator distribution when estimating the effects of habitat fragmentation on predation rates.
Abstract: Eelgrass Zostera marina provides refuge to numerous fish species but is vulnerable to fragmentation through natural and anthropogenic disturbance. In Bonavista Bay, Newfoundland, eelgrass patch size was altered to measure changes in predation risk in Age-0 juvenile cod, Gadus morhua. Artificial eelgrass mats of 5 sizes (0.32, 1.1, 5.5, 11 and 22 m2) were deployed in duplicate at each of 2 sites in Newman Sound in Terra Nova National Park during summer/autumn in 1999 and 2000. Predator distribution was determined using a combination of weekly underwater transect surveys and biweekly seining. Relative predation rates were measured by tethering Age-0 cod at the center of each patch and recording the incidence of predation (n = 1116 tether sets). Predation rates were negatively correlated with patch size during both years, suggesting that larger patches reduce predator foraging ability. However, high predator densities in the largest eelgrass patch resulted in higher than expected rates of predation. Therefore, habitat dimension affected predation risk in juvenile cod via 2 opposing mechanisms. Our results stress the importance of considering both habitat areal extent and predator distribution when estimating the effects of habitat fragmentation on predation rates.
TL;DR: These results suggest that measurements of oxygen isotopes in otoliths can be a reliable tool to estimate ambient temperature since the oxygen isotope seem to be deposited in the Otoliths independently of kinetic and metabolic effects.
TL;DR: The relationship between the growth rate and feeding level (unfed, inter mediate, and maximum rations) of age-0 juvenile cod and haddock Melanogrammus aeglefinus was quantified at different temperatures.
Abstract: The relationship between the somatic growth rate (G) and feeding level (unfed, inter- mediate, and maximum rations) of age-0 juvenile cod Gadus morhua and haddock Melanogrammus aeglefinus was quantified at different temperatures. Laboratory trials were conducted using 2 size- classes of cod (3.6 to 5.6 cm standard length (SL), and 8.1 to 12.4 cm SL) at 5, 8, 12, and 15°C, and 1 size-class of haddock (6.0 to 9.6 cm SL) at 8 and 12°C. The shape of the growth-feeding relationship was well described by a 3-parameter asymptotic function for cod and by a linear function for haddock (R 2 range = 0.837 to 0.966). The growth rate and scope for growth were maximum at 12°C, whereas growth efficiency was greatest (26.0 to 32.2%) at temperatures between 5 and 8°C. Juvenile cod held at 15°C exhibited reduced rates and efficiencies of somatic growth compared to fish at other temper- atures. Biochemical-based growth indicators for age-0 juveniles were calibrated from measurements of the amounts of RNA, DNA, and protein in white muscle samples. A multiple linear regression using RNA:DNA and temperature as independent variables explained a significant portion of the variability observed in G of juvenile cod (R 2 = 0.716) and haddock (R 2 = 0.637). This relationship may be useful in estimating recent growth of age-0 juvenile cod and haddock in the field.
TL;DR: In this paper, the authors measured the connective tissue content from chemical determination of hydroxyproline content, and large differences in percent connective tissues content were found (1 % for pollock viscera to 46% for skin).
Abstract: Individual fish processing waste stream components can be used to make feed ingredients or other products. Waste stream components obtained from commercial fish processing plants included heads, viscera, frames, and skins from Alaska pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus); and heads, and viscera from pink salmon (Oncorhynchus gorbuscha). The protein content of heads from all three species ranged from 13.9 to 16.4%; and the fat content ranged from 0.9 to 10.9%. Viscera protein content ranged from 13.0 to 15.3%, and the fat content from 2.0 to 19.1%. After heating to 85C the percent soluble protein in salmon heads was different (P < 0.05) from pollock or cod heads. Percent soluble protein of pollock and cod skin increased 8 fold (P < 0.05) after the 85C heat treatment. Connective tissue content was calculated from chemical determination of hydroxyproline content, and large differences in percent connective tissue content were found (1 % for pollock viscera to 46% for skin). Estimated rat PER values ranged from a low of 2.1 for skin to a high of 3.1 for viscera and fillet samples (P < 0.05).
TL;DR: Svedang et al. as discussed by the authors explored the temporal and spatial evolution of cod abundance along the Swedish west coast during the past 20-40 years and found that the decline in catches of inshore cod preceded the one in offshore areas at the end of the 1970s.
Abstract: Svedang, H., and Bardon, G. 2003. Spatial and temporal aspects of the decline in cod (Gadus morhua L.) abundance in the Kattegat and eastern Skagerrak. - ICES Journal of Marine Science, 60: 32-37. We explored the temporal and spatial evolution of cod abundance along the Swedish west coast during the past 20-40 years. Analyses of cpue data from the Swedish Nephrops fishery revealed a persistent decline in offshore abundance since the beginning of the 1980s in both the Skagerrak and Kattegat, culminating in extremely low densities in the late 1990s. Owing to a lack of reliable logbook and survey data for the area inside the trawling limit, informal statistics such as records of sport fishing clubs and notes on catches made by a coastal fishermen were used to sketch the development of cod abundance in the coastal zone. These data indicate that the decline in catches of inshore cod preceded the one in offshore areas at the end of the 1970s. The information presented indicates that the depletion of the cod stock in these areas is much worse than suggested by routine annual assessments. 2003 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.
TL;DR: There was strong evidence that the experimental nets would have continued to catch fish beyond the observed 27 months, and nets with a long exposure time seemed to have a tendency of catching smaller individuals than would be implied by their nominal mesh size.
TL;DR: Water temperature and larval R/D explained 37 to 39% of the variability in the observed growth rate and the models are applicable over temperatures ranging from 2.5 to 9.5°C and can be used to determine short-term growth rates of cod larvae collected from both the laboratory and field.
Abstract: The RNA, DNA, and protein content of larval cod Gadus morhua reared in the labora- tory at 3 temperatures and 3 densities of prey was measured. The data were used to define a quanti- tative relationship between RNA/DNA ratio (R/D), water temperature (T), and protein-specific growth rate (SGR, % d -1 ). The nucleic acid content of each larva was determined with both a 2-dye flow-injection fluorometric assay (FIA) and a 1-dye/1-enzyme fluorometric microplate assay (MFA) in order to calibrate each methodology. The resulting equations were: SGR = 3.65 R/D + 1.02 T - 13.05 for FIA, and SGR = 4.03 R/D + 0.88 T - 11.16 for MFA. Measured growth rates ranged from negative (-8% d -1 ) to 20% d -1 . Water temperature and larval R/D explained 37 to 39% of the variability in the observed growth rate. The models are applicable over temperatures ranging from 2.5 to 9.5°C and can be used to determine short-term growth rates of cod larvae collected from both the laboratory and field.
TL;DR: The nature and significance of size preference for fish prey in the diet selection of North Sea cod was analysed and showed that the preferred predator-to-prey weight ratio is an exponentially increasing function of predator size and an exponentially decreasing function of the slope of the number spectrum.
Abstract: The nature and significance of size preference for fish prey in the diet selection of North Sea cod (Gadus morhua L.) was analysed. The analysis combined information on size-specific abundance deri...
TL;DR: Permanent cold adaptation of muscle aerobic metabolism prevails in cod populations at higher latitudes, which is in line with permanently elevated rates of oxygen consumption observed in a parallel study.
Abstract: Activities of citrate synthase (CS), cytochrome c oxidase (CCO) and the electron transport system (ETS) were investigated in white muscle and liver of laboratory-maintained cod, Gadusmorhua, from the North Sea, Norwegian coast and Barents Sea for an analysis of temperature acclimation and adaptation in aerobic metabolism. Cold acclimation within each population led to elevated activities of CS, CCO and ETS in white muscle. In liver, however, only North Sea cod showed cold-compensated CS activities, with CCO and ETS unchanged. In contrast, cold-acclimated Norwegian cod displayed unchanged enzyme activities, and Arctic cod showed elevated activities for CS, but decreased activities for CCO and no change in ETS. Between-population comparisons revealed clear evidence for permanent cold adaptation in white muscle of northern (Norwegian coast and Barents Sea) compared to boreal (North Sea) cod populations, reflected by higher activities of CS, CCO and ETS at the same acclimation temperature. Cold-compensated, mass-specific enzyme activities in liver were found in northern compared to boreal cod for CS and CCO, however, for ETS, after warm acclimation only. When evaluated as capacity in total liver, such activities were only found in northern populations in the case of CS at all temperatures, and for CCO and ETS at 15°C only. Hepatosomatic index (IH) and liver lipid contents were highest in North Sea cod, with similar IH but lower lipid contents in cold- versus warm-acclimated animals. An acclimation effect on IH was found in Norwegian cod only, with higher IH but unchanged lipid contents in the cold. In conclusion, permanent cold adaptation of muscle aerobic metabolism prevails in cod populations at higher latitudes, which is in line with permanently elevated rates of oxygen consumption observed in a parallel study. These differences reflect higher maintenance costs in cold-adapted versus cold-acclimated cod.
TL;DR: The results support previously described associations between juvenile cod and eelgrass, but contradict other published accounts of high site-attachment and restricted movement in G. morhua following settlement.
Abstract: In Bonavista Bay, Newfoundland, we monitored patterns of settlement and distribution of 2 species of gadids, Atlantic cod Gadus morhua and Greenland cod G. ogac, following a large-scale alteration of nearshore eelgrass Zostera marina habitat. Comparisons between control and experimental sites, based on bi-weekly sampling from 1995 to 2001, indicated a significant increase in cod abundance at sites enhanced with simulated eelgrass and a corresponding decrease in cod numbers at sites where eelgrass had been removed. These data supported predictions, demonstrating that: (1) there was a sufficient supply of juvenile cod within the areas that have historically been unoccupied (i.e. sand) and (2) both species preferred to settle in complex habitats. However, G. ogac responded significantly to the removal of eelgrass in more comparisons than G. morhua (70 and 37% respectively), suggesting that G. ogac has a higher affinity for complex vegetative habitats than G. morhua at the scale of manipulation (ca. 800 m2). Furthermore, despite an overall preference for eelgrass habitat, high within-site catch variation of post-settled juvenile cod indicated that both species were not restricted to a seine site. Such variation was occurring well after the settlement period, suggesting that juvenile cod were moving and occasionally aggregating (i.e. shoaling) throughout the study period. Our results support previously described associations between juvenile cod and eelgrass, but contradict other published accounts of high site-attachment and restricted movement in G. morhua following settlement.
TL;DR: Life histories of Atlantic cod from the Gulf of St Lawrence south to Georges Bank differ significantly through time and space, and significant variation in size-specific fecundity is also evident among populations.
Abstract: Life histories of Atlantic cod (Gadus morhua) from the Gulf of St. Lawrence south to Georges Bank differ significantly through time and space. Within the Southern Gulf, fecundity per unit body mass differed by more than 40% over short (2 years) and long (42-45 years) periods of time. Significant variation in size-specific fecundity is also evident among populations: Southern Gulf cod produce almost 30% more eggs per unit body mass than those on Georges Bank, whereas fecundity of Scotian Shelf cod is almost half that of cod in Sydney Bight. Compared with those on Georges Bank, Southern Gulf cod life histories are characterized by high fecundity, late maturity, high gonadosomatic index, and large eggs. Relative to the influence of body size, neither temporal nor spatial differences in fecundity can be attributed to physiological condition, as reflected by liver weight, hepatosomatic index, and Fulton's K. Delayed maturity and higher reproductive allotment among Southern Gulf cod can be explained as selection re- sponses to slower growth, higher prereproductive mortality, and fewer lifetime reproductive events. Patterns of covariation in heritable, fitness-related traits suggest the existence of adaptive variation and evolutionarily significant units at spatial scales considerably smaller than the species range in the Northwest Atlantic. Resume : Les cycles biologiques des morues franches (Gadus morhua) de l'Atlantique, depuis le golfe du Saint- Laurent jusqu'au banc Georges, different significativement dans le temps et dans l'espace. Dans la partie sud du golfe, la fecondite par unite de masse corporelle varie de plus de 40 % sur des periodes courtes (2 ans) et longues (42-
TL;DR: RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well-conditioned larvae in the first 3 weeks.
Abstract: Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m3) under semi-natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m3) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m3 mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well-conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.
TL;DR: The BWF reported in this study were applied to assess the mortality that would result from accumulation of a given CPD load: for both C. finmarchicus and cod eggs, an increased load of 10 CPD Mb−1 of DNA due to UV exposure would result in approximately 10% mortality.
Abstract: In previous work, we evaluated the effects of ultraviolet (UV = 280–400 nm) radiation on the early life stages of a planktonic Calanoid copepod (Calanus finmarchicus Gunnerus) and of Atlantic cod (Gadus morhua). Both are key species in North Atlantic food webs. To further describe the potential impacts of UV exposure on the early life stages of these two species, we measured the wavelength-specific DNA damage (cyclobutane pyrimidine dimer [CPD] formation per megabase of DNA) induced under controlled experimental exposure to UV radiation. UV-induced DNA damage in C. finmarchicus and cod eggs was highest in the UV-B exposure treatments. Under the same spectral exposures, CPD loads in C. finmarchicus eggs were higher than those in cod eggs, and for both C. finmarchicus and cod embryos, CPD loads were generally lower in eggs than in larvae. Biological weighting functions (BWF) and exposure response curves that explain most of the variability in CPD production were derived from these data. Comparison ...
TL;DR: The data reported here are the first showing a relationship between the total arsenic concentration in fish and salinity, and there was a positive linear relationship between arsenic concentration andSalinity for all three species.
Abstract: Total arsenic concentrations were determined in three teleost species (herring Clupea harengus; cod Gadus morhua, and flounder Platichthys flesus) taken from four locations in the Baltic and North Sea with salinities ranging from 8 to 32 psu. Individual arsenic concentrations ranged from 0·04 to 10·9 mg/kg wet mass, and there was a positive linear relationship between arsenic concentration and salinity for all three species (r2 0·44 to 0·72, all P<0·001). Although it is well known that marine fish contain much higher concentrations of arsenic than do freshwater fish, the data reported here are the first showing a relationship between the total arsenic concentration in fish and salinity.
TL;DR: The microbiota in both sterile rehydrated commercially produced and laboratory (aseptically) produced salt-cured cod was dominated by this same bacterium, which seems to mainly originate from the fresh fish itself and not from contamination during processing.