Showing papers on "Atlantic cod published in 1999"
TL;DR: Norwegian coastal (NC) and northeast Arctic (NA) Atlantic cod larvae were reared on live zooplankton to investigate temperature- and size-specific growth and a stock-specific difference in mean weight at age was observed, with NC growing better than NA.
Abstract: Norwegian coastal (NC) and northeast Arctic (NA) Atlantic cod (Gadus morhua) larvae were reared on live zooplankton to investigate temperature- and size-specific growth. Larval and juvenile growth ...
303 citations
TL;DR: Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks, and the effects of environment and stock changes are disentangling.
Abstract: Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock ...
292 citations
TL;DR: The conclusion is that, at the level of digestion, trypsin is the only enzyme measured that could be suspected to potentially limit growth rate in cod.
Abstract: The objective of this study was to determine the potential sites of maximal growth limitation in Atlantic cod (Gadus morhua). Forty cod were reared in ten sea water tanks. Fish were randomly divided into 5 groups, a control group (injected with saline solution) and 4 experimental groups that received different levels of recombinant bovine somatotropin (rbST: 1.0, 2.0, 4.0 and 10.0 μg g fish−1 2 weeks−1) by injection in the abdominal cavity. Fish were fed ad libitum 3 times a week during four weeks. We measured individual body mass, growth rate, food intake and food conversion efficiency. At the end of the experiment, we measured the activity of acid proteases in the stomach; trypsin and chymotrypsin in the pyloric caeca; alkaline phosphatase (ALP) and glutamyltransferase (GGT) in the intestine. No significant differences were observed in growth rate, food intake or food conversion efficiency among the five groups. Trypsin, chymotrypsin, ALP and GGT activities when expressed in U g fish−1 were correlated with growth rate. These enzymes were also correlated with food ingestion except for trypsin when expressed in U mg protein−1. Trypsin was the only enzyme that showed a significant correlation with food conversion efficiency. Our conclusion is that, at the level of digestion, trypsin is the only enzyme measured that could be suspected to potentially limit growth rate in cod.
248 citations
TL;DR: Slow growth in low O2 was not due to increased activity, because activity decreased in hypoxia, and in the Gulf of St Lawrence, waters deeper than 200 m usually are <65% saturated in O2, and thus should impact negatively on cod growth.
Abstract: Growth in length and mass, improvements in condition, as well as final condition of c. 700 g Atlantic cod Gadus morhua were significantly less at 45% and 56% O2 saturation than at 65%, 75%, 84% and 93% O2 saturation. Hypoxia decreased food consumption. In turn, food consumption explained 97% of the variation in growth. Conversion efficiency varied slightly, but significantly, with level of dissolved O2, except that the group reared at 93% O2 had a lower than expected conversion efficiency. Slow growth in low O2 was not due to increased activity, because activity decreased in hypoxia. In the Gulf of St Lawrence, waters deeper than 200 m usually are <65% saturated in O2, and thus should impact negatively on cod growth.
240 citations
TL;DR: The effects of environmental temperature on certain humoral immune parameters in Atlantic cod (Gadus morhua L.) were studied in this article, where they found that immunoglobulin and natural antibody levels increased with increasing temperature whereas the total serum protein concentration, anti-protease activity, iron concentration, unsaturated and total iron binding capacity decreased with an increasing temperature.
Abstract: The effects of environmental temperature on certain humoral immune parameters in Atlantic cod (Gadus morhua L.) were studied. Serum samples were collected from captive cod, of wild origin, kept at different temperatures for 12 months. It was found that immunoglobulin and natural antibody levels increased with increasing temperature whereas the total serum protein concentration, anti-protease activity, iron concentration, unsaturated and total iron binding capacity decreased with increasing temperature. Haemolytic activity and percentage iron saturation also tended to decrease with increasing temperature although this was not statistically significant.
202 citations
TL;DR: Individual differences in Atlantic cod reproductive behaviour at a field-reported spawning density under experimental conditions are quantified.
Abstract: We quantified individual differences in Atlantic cod, Gadus morhua, reproductive behaviour at a field-reported spawning density under experimental conditions. Marked individuals (nine females, seve...
183 citations
TL;DR: It is suggested that bathymetric and hydrodynamic/oceanographic structure represents a rational starting point for developing hypotheses aimed at assessing the genetic structure of high gene-flow marine fish species.
153 citations
TL;DR: Alteration of seafloor habitat by fishing activity in the northwest Atlantic could magnify the effects of overfishing by limiting juvenile survivorship in post-settlement juvenile Atlantic cod.
Abstract: Fishing activity can impact fish populations in 2 ways. The first is the immediate effect on population demographics by the removal of fish. Second is the impact of fishing (e.g. bottom trawls and dredges) on the seafloor which can reduce habitat structure and thus increase the vulnerability of juvenile fish to predation by older conspecifics and other predators. We conducted laboratory experiments to investigate the role of variability in seafloor habitat structure on the survivorship of post-settlement juvenile (0-yr) Atlantic cod Gadus morhua. Groups of 0-yr cod were exposed to a foraging predator (3+ cod) over 5 seafloor habitats of varying complexity (sand, cobble, minimum density short sponge, maximum density short sponge, and tall sponge). These habitats were selected to mimic the range of impacts of mobile fishing gear given a gradient in fishing effort. Emergent epifauna resulted in a significant decrease in 0-yr mortality when compared to flat sand, the least complex habitat. Epifaunal density was shown to be more significant than epifaunal height in reducing 0-yr mortality. Predator reaction distance decreased with increasing habitat complexity, presumably due to the obstruction of visual cues by complex relief. Latency to first and second capture did not differ statistically between habitats. Alteration of seafloor habitat by fishing activity in the northwest Atlantic could magnify the effects of overfishing by limiting juvenile survivorship.
131 citations
TL;DR: For example, millions of Atlantic cod (Gadus morhua) migrate distances of up to 500 km each fall to aggregate together in a small overwintering area off eastern Canada as mentioned in this paper.
Abstract: Millions of Atlantic cod (Gadus morhua) migrate distances of up to 500 km each fall to aggregate together in a small overwintering area off eastern Canada. Synoptic research vessel surveys carried ...
130 citations
TL;DR: The condition factors and hepatosomatic indices of cod in spring were low enough to suggest that winter starvation may cause mortality in this stock.
Abstract: Atlantic cod (Gadus morhua L.) were sampled from the southern Gulf of St Lawrence over a 2-year period (1991‐1993) to assess the timing and magnitude of seasonal changes in diet composition, stomach fullness, carcass weight, and organ weights. The proportion of fish (mainly Clupea harengus L. and Mallotus villosus Muller) in the diet of cod was the highest ever reported for this stock. Cod fed very little during the five winter months (December to April) and lost 25‐27% of their carcass weight and 76‐84% of their liver dry weight during this time. Declines in carcass and liver weights occurred steadily throughout winter and were not specifically coincident with the spring and autumn migrations (approximate one-way distance 500 km) performed by this cod stock. Gonad growth occurred primarily between November and January in males and between January and May in females. Depending on gender and body size, 4‐19% of the dry weight lost from the carcass and liver over winter could be accounted for by gonad growth. Therefore, 81‐96% of the loss in carcass and liver dry weight over winter was used to meet metabolic energy requirements. The condition factors and hepatosomatic indices of cod in spring were low enough to suggest that winter starvation may cause mortality in this stock. The yield of marketable product (muscle) varied by 39‐50% (depending on cod body size) over the course of the study; yields were highest in late autumn and lowest in spring. ? 1999 International Council for the Exploration of the Sea
126 citations
TL;DR: Monitoring of food consumption and egg production of 26 adult and 13 male Atlantic cod were monitored during prespawning, spawning and postspawning periods and laboratory results were supported by stomach fullness index values of Georges Bank cod exhibiting different maturity states.
Abstract: The food consumption and egg production of 26 adult (13 female and 13 male) Atlantic cod (Gadus morhua) were monitored during prespawning, spawning and postspawning periods. Females spawned from late January to mid-April. Feeding activity occurred from December to early January and ceased for females, on average, 36 days (15–54 days) before the onset of spawning. The duration of spawning by females was, on average, 42 days (10–61 days) and feeding was suppressed by both sexes during the first three-quarters of each female’s spawning period. Mature females went, on average, 70 days or 19% of the year without eating. An abrupt increase in feeding activity, particularly by females, occurred during the last quarter of spawning or shortly after the release of the last egg batch (on average, feeding started again after 91% of a female’s eggs had been released or 82% of egg batches). Females consumed greater quantities of food than males during both winter and postspawning feeding periods. During spawning, females lost, on average, 29% of their body weight and males 14%. Fecundity ranged from 0.75 to 3.97 million eggs per female. The volume of eggs produced by four individual females (range = 1285–5995 ml in four to 11 batches) ranged from 99 to 195% (mean 150%) of a female’s postspawning body volume. Six immature cod fed throughout the experimental period and gained, on average, 8% of initial body weight. Laboratory results were supported by stomach fullness index values of Georges Bank cod exhibiting different maturity states.
TL;DR: Most of the parameters increased with increasing cod size, except the haemolytic activity which decreased, and higher serum protein levels were seen in cod sampled in the fall than in the spring.
Abstract: The effects of size and gender on several humoral immune parameters in cod were examined under different environmental conditions. Serum samples were collected from wild cod of different sizes. Two samplings were undertaken: In the spring in relatively cold waters off the north west coast of Iceland and in the fall in relatively warm waters off the west coast of Iceland. Most of the parameters increased with increasing cod size, except the haemolytic activity which decreased. Higher serum protein levels were seen in cod sampled in the fall than in the spring. In cod sampled in the spring there was an apparent difference between specimens B 75 cm in length and the larger specimens with respect to haemolytic activity and iron concentration. None of the parameters were influenced by the gender of the cod. © 1999 Elsevier Science Inc. All rights reserved.
TL;DR: The relative fertilization success of males varied depending on which female was the egg donor, suggesting that female "choice" at the gamete level may be occurring in cod.
Abstract: Sperm competition experiments were conducted to test the null hypothesis that sperm quality is not affected by male body size in Atlantic cod (Gadus morhua). Genetic markers (allozymes) were used t...
TL;DR: Cod exposed to a chronic stressor are able to spawn successfully, but there appears to be a negative impact of this stress on their reproductive output, particularly through the production of abnormal larvae.
Abstract: This study imposed stress upon spawning cod Gadus morhua in the laboratory to evaluate the potential effects of trawl avoidance on their reproductive physiology and spawning behaviour. Plasma cortisol levels of stressed fish were significantly higher than controls. Stressed cod initiated fewer courtships and often performed an altered courtship sequence. Both control and stressed fish spawned and there was little difference in the production of eggs, fertilization rate, hatching success or time to starvation of larvae. However, stressed fish produced abnormal larvae more frequently. Cod exposed to a chronic stressor are able to spawn successfully, but there appears to be a negative impact of this stress on their reproductive output, particularly through the production of abnormal larvae.
TL;DR: Data indicate that early urea cycle enzyme expression is not unique to rainbow trout but is also a feature of Atlantic cod development, and possibly other teleosts.
Abstract: For many years, the urea cycle was considered to be relatively unimportant in the life history of most teleost fishes. In previous studies, we were surprised to find that newly hatched freshwater rainbow trout embryos had relatively high activities of the key urea cycle enzyme, carbamoyl phosphate synthetase III (CPSase III), and other enzymes in the pathway, whereas adult trout had much lower or non-detectable activities. The present study tested the hypothesis that urea cycle enzyme expression is unique to early stages of rainbow trout. In marine Atlantic cod (Gadus morhua) embryos, CPSase III, ornithine transcarbamoylase (OTCase), glutamine synthetase (GSase) and arginase activities were all expressed prior to hatching. Urea excretion was detected shortly after fertilization and rates were high relative to those of ammonia excretion (50-100 % of total nitrogen excreted as urea nitrogen; total=ammonia+urea). Urea concentration was relatively constant in embryos, but ammonia concentration increased by about fourfold during embryogenesis. Two populations of cod embryos were studied (from Newfoundland and New Brunswick), and significant differences in enzyme activities and excretion rates were detected between the two populations. In adult cod, CPSase III was not detectable in liver, white muscle, intestine and kidney tissues, but OTCase, GSase and arginase were present. Adult cod excreted about 17 % of nitrogenous waste as urea. Taken together, these data indicate that early urea cycle enzyme expression is not unique to rainbow trout but is also a feature of Atlantic cod development, and possibly other teleosts. The relatively high urea excretion rates underline the importance of urea as the primary nitrogen excretory product in Atlantic cod during early embryogenesis.
TL;DR: Molecular divergences between each of the three endemic Pacific species and their respective closest relatives are similar and consistent with contemporaneous speciation events following the reopening of the Bering Strait ca.
Abstract: Phylogenetic relationships among 14 species of gadid fishes were investigated with portions of two mitochondrial DNA (mtDNA) genes, a 401 base pair (bp) segment of the cytochrome b gene, and a 495 bp segment of the cytochrome oxidase I gene. The molecular data indicate that the three species of gadids endemic to the Pacific Basin represent simultaneous invasions by separate phylogenetic lineages. The Alaskan or walleye pollock ( Theragra chalcogramma) is about as closely related to the Atlantic cod ( Gadus morhua) as is the Pacific cod (Gadus macrocephalus), which suggests that T. chalcogramma and G. macrocephalus represent separate invasions of the Pacific Basin. The Pacific tomcod (Microgadus proximus) is more closely related to the Barents Sea navaga (Eleginus navaga) than to the congeneric Atlantic tomcod (Microgadus tomcod), which suggests that the Pacific species is derived from the Eleginus lineage and that Eleginus should be synonymized with Microgadus. Molecular divergences between each of the three endemic Pacific species and their respective closest relatives are similar and consistent with contemporaneous speciation events following the reopening of the Bering Strait ca. 3.0-3.5 million years BP. In contrast, the Greenland cod (Gadus ogac) and the Pacific cod have essentially identical mtDNA sequences; differences between them are less than those found within G. morhua. The Greenland cod appears to represent a contemporary northward and eastward range extension of the Pacific cod, and should be synonymized with it as G. macrocephalus. Resume : Les relations phylogenetiques ont ete etudiees chez 14 especes de gadides a l'aide de segments de deux
TL;DR: Smaller sizes-at-age in the 1980s were not associated with changes in the fishery or increased fishing mortality, nor were they consistent with the density-dependence hypothesis, but slopes were always positive, suggesting higher growth rates at higher temperatures.
Abstract: Northern Gulf of St. Lawrence Atlantic cod (Gadus morhua) is one of several stocks that collapsed in eastern Canada following a long period of intensive exploitation. Surplus and net production per capita became nil or negative in the mid-1980s so that any level of exploitation would have caused a decline of the stock. This was partly explained by a marked decline in growth production and is consistent with smaller sizes-at-age but also lower condition factor values during the same period. Correlations between size-at-age and temperature were not significant when corrected for autocorrelation, but slopes were always positive, suggesting higher growth rates at higher temperatures. Smaller sizes-at-age in the 1980s were not associated with changes in the fishery or increased fishing mortality, nor were they consistent with the density-dependence hypothesis. Lengths at age 8 decreased by more than 10 cm as the stock decreased 10-fold in abundance. While size-at-age and temperature covary in cod when all stoc...
TL;DR: In this article, the authors advocate the inclusion of a time-dependent detectability coefficient in the scaling of acoustic backscatter to abundance for semi-demersal fish and conclude that diel change in acoustic density resulted from variations in detectability caused by cod vertical movements and habitat preferences.
Abstract: A major source of bias and imprecision in acoustic abundance estimates of semi-demersal fish is detectability, defined here as the proportion of the true abundance of a target species within the ensonified volume (surface to bottom) that is detected by an echosounder and included in integration. In autumn 1996 and 1997, acoustic surveys for Atlantic cod (Gadus morhua L.) in inshore Placentia Bay, Newfoundland, Canada, indicated mean daytime densities (e.g. 0.016 fish m −2 in 1997) an order of magnitude higher than at night (0.001 fish m −2 ). A corresponding downward shift in vertical distribution at night was also observed. At the same site in 1996,in situ video censuses of cod from a submersible showed equivalent cod abundance by day (n=3) and night (n=1). Submersible observations indicated that at night cod were located nearer to bottom, and preferred rocky and boulder-strewn substrates and not open sandy bottoms (p<0.001). Acoustic densities measured from the submersible cruising 20m above bottom, and from the surface vessel, were similar. Submersible acoustic estimates and video census indices were positively associated during daytime. The sole night-time acoustic estimate was near zero while the corresponding video index was the highest recorded. We conclude that diel change in acoustic density resulted from variations in detectability caused by cod vertical movements and habitat preferences. A broad-scale springtime inshore and offshore survey of cod in the same stock area confirmed the trend of higher acoustic density estimates during the day than at night. We advocate the inclusion of a time-dependent detectability coefficient in the scaling of acoustic backscatter to abundance for semi-demersal fish.
TL;DR: In this article, sound was recorded at five stations at and near the main spawning grounds of the northeast Arctic cod (Gadus morhua L.) off the Lofoten Islands, Norway.
Abstract: Sound was recorded at five stations at and near the main spawning grounds of the northeast Arctic cod (Gadus morhua L.) off the Lofoten Islands, Norway. Recordings were carried out during April 1997 when large numbers of cod aggregated to spawn, and were repeated in September when the cod were no longer spawning and, in fact, most had emigrated. The analysis revealed differences between the two time periods with April showing sound of a transient character with 7-18 dB increased sound level between 50 and 500Hz. Sound from single cod in captivity has been reported to be located in this frequency range. We argue that the sound recorded is produced by spawning cod and discuss acoustic communication as a potential mechanism in cod mate assessment.
TL;DR: In this article, age-by-age changes in the distribution of Atlantic cod (Gadus morhua L.) with respect to depth, temperature, and latitude in the northern Gulf of St Lawrence (Canada) in both winter (1978−1994 and summer (1984−1995) in relation to a water cooling event were examined.
Abstract: Research vessel trawl survey data were examined to investigate age-by-age changes in the distribution of Atlantic cod (Gadus morhua L.) with respect to depth, temperature, and latitude in the northern Gulf of St Lawrence (Canada) in both winter (1978‐1994) and summer (1984‐1995) in relation to a water cooling event. We used a cumulative distribution function method that statistically compares distributions of sampled variables with those occupied by fish. There was no evidence that the ambient temperatures occupied by cod changed with the cooling. On average, cod occupied waters with temperatures of 4.4‐5.9)C in winter and of 1.4‐3.5)C in summer, with no temporal trend. However, major distribution shifts occurred in winter: the median latitude of the geographic distribution in 1993 was 2) (220 km) south of that in 1985, and cod were also distributed 200 m deeper in the 1990s. Even though stock abundance decreased drastically during the time period considered, abundance in the deepest stratum surveyed (>365 m) increased. The median latitude of distribution in winter was correlated with an index of temperature anomaly in the cold intermediate layer during the previous summer (r=0.85, p<0.05, corrected for autocorrelation). This indicates that the cooling at mid-depth influenced cod distribution and resulted in an earlier wintering migration. Cod responded to a change in their habitat by changing their migration and distribution patterns. ? 1999 International Council for the Exploration of the Sea
TL;DR: Maturation data collected by Northeast Fisheries Science Center research bottom trawl surveys from 1970–98 were examined to determine if the rate of sexual maturation of Atlantic cod varied in response to fluctuations in stock density, growth, or ambient temperature.
Abstract: Stocks of Atlantic cod, Gadus morhua, off the coast of New England have been heavily exploited by distant water fleets in the 1960s and 1970s and by domestic fisheries in recent years and abundance has declined. Maturation data collected by Northeast Fisheries Science Center research bottom trawl surveys from 1970–98 were examined to determine if the rate of sexual maturation of Atlantic cod varied in response to fluctuations in stock density, growth, or ambient temperature. Median age and length at maturity by sex for the 1970– 96 year-classes was estimated by using logistic regression. Both age and length at maturity have significantly declined during the past 25 years. Mean length at age did not show significant trends for the time series. Stepwise logistic regression with interaction was used to determine if such factors as cod stock biomass and bottom temperature explain variation in maturation rates. Regressions were performed by aggregating all year-classes for each sex. Both stock biomass and temperature explained a significant amount of the variation (P<0.05) in sexual maturation. The influence of stock biomass was similar for both stocks, but bottom temperature had a slightly greater and opposite influence on maturation for Gulf of Maine cod than for Georges Bank cod. The sensitivity analysis of biological reference points to regime shifts in maturation and partial recruitment illustrated more variation in spawning stock numbers per recruit and F20% than in spawning stock biomass per recruit.
TL;DR: Shifts in cod distribution during the feeding season in the southern Gulf appear to be more closely linked todensity-dependent changes in environmental preferences than to density-independent responses to changing environmental conditions.
Abstract: Density-independent redistribution in response to changing temperature conditions and density-dependent redistribution in response to changing temperature preferences are two contrasting hypotheses to explain changes in the distribution of cod populations. I tested these hypotheses using survey data on the distribution of cod during the feeding season in the southern Gulf of St Lawrence. These tests used indices of cod distribution as the dependent variable and indices of cod abundance and bottom temperature as explanatory variables. Both hypotheses were often supported in univariate tests that ignored confounding between the two explanatory variables. Tests that accounted for this confounding indicated an effect of cod abundance on distribution for ages 4–8+ years, and 3+, but provided no support for an effect of environmental conditions on distribution except for age 3. Variation in the temperature distribution of cod was consistent with an effect of abundance on interannual variation in distribution and with no effect of environment except for age 3 cod. Age 3 cod were consistently under-represented in areas of very cold bottom water but older cod were not. As predicted by bioenergetic considerations, cod tended to occupy colder water at high levels of abundance, suggesting a mechanism for density-dependent shifts in distribution. Shifts in cod distribution during the feeding season in the southern Gulf appear to be more closely linked to density-dependent changes in environmental preferences than to density-independent responses to changing environmental conditions.
TL;DR: The results indicate that the cod in south and south-east Icelandic waters do not belong to one panmictic population.
Abstract: Significant differences were found at the synaptophysin (Syp I) locus between two groups of Icelandic cod Gadus morhua; Loftstaoahraun (spawning ground), Reykjanesgrunn and Eyrabakkabugur (feeding grounds) on the one hand and Kantur (spawning ground) and Austfjaroadjup (feeding ground) on the other. There was also a considerable genetic heterogeneity within the former group. The results indicate that the cod in south and south-east Icelandic waters do not belong to one panmictic population.
TL;DR: It is concluded that as long as 0-group cod are above a “safe” level of condition their body length can still increase even when condition is declining, a pattern similar to that of larger juveniles and adults.
Abstract: Demersal 0-group Atlantic cod (Gadus morhua L.) were collected in Trinity Bay, Newfoundland, Canada, between August 1993 and January 1994. Diet composition and simple indices of condition (hepato-somatic index, condition factors and body ash content) were determined. Laboratory experiments were also conducted to determine whether simple indices of condition reflect differences in energy intake (ration level) and to determine minimum index of condition values, assessed from 0-group cod that died due to exhaustion of their energy reserves. Determination of lower critical indices of condition provided a meaningful interpretation of field data on feeding, condition and survival of 0-group cod. In the wild, indices of condition reflecting variation in liver and muscle energy reserves of cod increased rapidly with the consumption of Calanus finmarchicus, which exhibited a high incidence of oil sacs, and declined abruptly when this lipid-rich prey was no longer consumed. Liver and muscle condition of 0-group cod from the field varied seasonally, but their condition was consistently above that of cod that died in the laboratory. Laboratory studies, using three ration levels, revealed that condition indices differed over time and among ration levels. Indices of condition representing variation in muscle energy reserves exhibited a steady decline once the hepato-somatic index fell below about 2.0. We interpret this as evidence for depletion of lipids first and then proteins, a pattern similar to that of larger juveniles and adults. We conclude that as long as 0-group cod are above a “safe” level of condition their body length can still increase even when condition is declining.
TL;DR: Critical swimming speed performance between treatments was found to be nonsignificant between groups, suggesting that tagged juvenile cod are capable of similar physical performance to that of untagged cod when released 24 h after surgery.
Abstract: Short-term and long-term effects of intraperitoneal implantation of dummy acoustic transmitters (1.9–4.6% of the fishes' body weight) in wild juvenile Atlantic cod Gadus morhua were investigated. Short-term effects were examined by comparing critical swimming speeds 24 h after surgery for implanted, sham-implanted, and control groups using a Blazka-style swim tube. Additionally, comparative growth rates, mortality, and tag expulsion by cod in the same three groups were determined during a 220-d period. Critical swimming speed performance between treatments was found to be nonsignificant between groups, suggesting that tagged juvenile cod are capable of similar physical performance to that of untagged cod when released 24 h after surgery. During the long-term study, no significant difference in growth between groups, no increase in mortality associated with the tagging procedure, and no incidents of transmitter expulsion occurred. This study suggests that intraperitoneal implantation of acoustic t...
TL;DR: A study to determine the survival rate of sub-legal cod caught in the longline fishery using 11/0 circle hooks found that sea bird predation should be included when estimating the survival of fish caught by a long-line.
Abstract: Longline fishing has often been promoted as a clean, low impact fishing method. Some longline fishermen and biologists have expressed concern that there is a high mortality rate for cod and haddock that pass through a dehooking device prior to release. The device, aptly called the crucifier, usually consists of two steel cylinders placed vertically on the gunwale of the vessel. During hauling, the gear passes through the opening between the cylinders while the fish, too large to pass through the narrow opening, is excluded. This process pulls the hook from the mouth of the fish and can inflict severe injuries such as torn and broken jau's. A study was conducted to determine the survival rate of sub-legal cod caught in the longline fishery using 11/0 circle hooks. The focus of the research was to assess the rate of mortality of sub-legal catch after the cod were placed in cages for 72 hours. The results of the study showed that there was high mortality (69%) associated with capture using the 11/0 circle hook when the fish were injured by the process of having the hooks removed from their mouths by the crucifier. Furthermore, sublegal cod that had wounds from the dehooking process and were under 39 cm were statistically more likely to die as compared to cod between 38 and 49 cm. An ancillary set of observations on the predation by sea birds of released sublegal cod was included. Despite low numbers, the,findings from these observations show that sea bird predation should be included when estimating the survival of fish caught by a long-line.
TL;DR: It is found that prey density, turbulence, and temperature ranges typical of the peak spawning season are variable enough to be limiting to larval growth.
Abstract: Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus ) on Georges Bank are subjected to a high degree of variability in temperature, turbulence, and prey densities, depending on when they are spawned and where they are advected. We have developed an individual-based model that includes the effect of varying prey density, turbulence, and temperature. Temperature effects were included by using a Q10-type adjustment to the standard metabolic rate as well as a second temperature-dependent term added to the overall ingestion ability of our model fish, a function of the swimming speed, capture efficiency, and "liveliness" of a fish. Three cases were analyzed: (i) constant food and temperature conditions, (ii) variable temperature cycles, and (iii) variable temperature cycles plus turbulence. We found that prey density, turbulence, and temperature ranges typical of the peak spawning season are variable enough to be limiting to larval growth. The timing and location of spawning are crucial to the survival of the larvae. Increasing the average temperature cycle by 1°C, as might occur due to climatological change or interannual variability, increased growth for larvae that were not growing well previously. The increased temperature failed to increase larval growth in areas where larvae were already growing at rates close to their maximum. Resume : La morue franche (Gadus morhua) et l'aiglefin (Melanogrammus aeglefinus ) du banc Georges sont exposes
TL;DR: Size selection of otter trawls equipped with square or diamond mesh codends with mesh sizes of 130–155 mm was examined for Atlantic cod, haddock and pollock in 14 cruises with research or commercial fishing vessels conducted off the Canadian Atlantic coast in 1988–1991.
01 Jan 1999
TL;DR: In this article, a study of 22,000 Atlantic cod tagged with T-bar tags and released in the Gulf of Maine area in 1984-97 and 2400 recovered tags were used to interpret movement of tagged fish.
Abstract: Over 22,000 Atlantic cod, Gadus morhua, were tagged with T-bar tags and released in the Gulf of Maine area in 1984-97 and 2400 recovered tags were used to interpret movement of tagged fish. Most of the releases were of adult fish made during the winter cod spawning season from aggregations found on known spawning banks. Re- captures by NAFO divisions were weighted with an annual index of fish- ing effort to account for probability of recapture. At the division level, very little exchange between the area east of 4X and the Gulf of Maine was evi- dent. However, within the Gulf of Maine an exchange of about 15% be- tween 4X and 5Z and somewhat higher between 4X and 5Y was apparent. Cod tagged on Browns Bank and Georges Bank during the spawning season showed widespread dispersal both within their respective division and to adjacent divisions. The seasonal distri- bution of recaptures in 4X indicates aggregation for spawning followed by postspawning dispersal. The seasonal pattern for Georges Bank is less clear but there are indications of net loss to the 4X area. Distribution of recaptures from Georges Bank releases in 1994 was similar to those observed for re- leases made in 1984-85. Results of the study were consistent with results from earlier tagging experiments and dem- onstrate substantial interaction of cod from different management areas. These findings may have implications for stock assessment models and man-
TL;DR: The results are consistent with those from studies of several other fish species, and are discussed in relation to the ecology of age-0 cod, and their potential use in aquaculture in Newfoundland.
Abstract: This study examined the effects of body size and food ration on over-winter survival of age-0 Atlantic cod Cod were divided into two groups based on standard length (large=7695±110 mm SL; small=5765±102 mm SL; mean±1 SE) and wet weight (large=402± 021 g; small=152±009 g) Replicate tanks (n=2) of 10 large and 10 small cod were exposed to one of two food rations (025% and 10% body weight day-1) for the entire experiment (December to June) Tanks were examined daily for mortalities and feeding was adjusted accordingly The experiment was run under ambient light and seawater conditions All but large age-0 cod exposed to the low food ration grew over the course of the experiment The specific growth rate (SGR) of small cod was significantly higher (02425% wet weight day-1) than that of the large fish (00443% wet weight day-1) Food ration had no significant influence on SGR or over-winter survival Significantly more of the large age-0 cod survived the winter (585% of those originally introduced) compared to the smaller fish (14%) Our results are consistent with those from studies of several other fish species, and are discussed in relation to the ecology of age-0 cod, and their potential use in aquaculture in Newfoundland