Atlantic Cod Gadus Morhua Research Articles

Effect of turbulence on the energetics of foraging in Atlantic cod Gadus morhua larvae

A net energy gain (NEG) model was used to assess the effects of turbulence on the energy budget of Atlantic cod Gadus morhua larvae, feeding on copepod nauplii at different concen- trations. The geometry of their prey search space was parameterised as either a sphere, hemisphere (the most commonly applied in analogous studies), or wedge. Observed distributions in behaviour (e.g. move duration, pause duration, turn angles) were used as model input, and 2 facets of this behaviour (move duration and move speed) were varied to examine how parameterised changes in foraging behaviour can affect the NEG of the predator. At a prey concentration of 100 l -1 , and in sta- tic water, NEG is an order of magnitude higher for a hemispherical shape relative to a wedge-shaped search volume. This difference decreases with increasing prey concentration (600 l -1 ), but always remains considerable. When parameterised turbulence was added, prey capture rates for a larva with a hemispherical search space increases 3 times as much as for a larva with a wedge-shaped search space (typically a 50% increase using the hemisphere vs 15% using a wedge). Thus, when this one key assumption (the search volume shape) of current turbulence-effects models is more realistically parameterised, the theorized advantage of turbulence is greatly reduced (at the level of the animal's prey capture and NEG). This result demonstrates the need to carefully reassess the underlying assumptions of current turbulence-effects models and, therefore, the conclusions that have been based upon those models. Our NEG model also demonstrates the energetic benefits of certain changes in larval behaviour — such as shorter move durations — which lead to a more thorough and cost-effective search of the surrounding water for larvae with a wedge-shaped search volume. This latter effect is not observed for predators with spherical or hemispherical search volumes. These results indicate that it would be prudent to reconsider the conclusions of any previous study that was based upon over-simplified search space geometries.

Temporal and spatial variation in reproductive investment of Atlantic cod Gadus morhua in the northern North Sea and Scottish west coast

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 276:237-248 (2004) - doi:10.3354/meps276237 Temporal and spatial variation in reproductive investment of Atlantic cod Gadus morhua in the northern North Sea and Scottish west coast Michio Yoneda1,2,*, Peter J. Wright1 1Fisheries Research Services Marine Laboratory, PO Box 101 Victoria Road, Aberdeen AB11 9DB, UK 2Present address: Tohoku National Fisheries Research Institute, Shinhama, Shiogama, Miyagi 985-0001, Japan *Email: myoneda@fra.affrc.go.jp ABSTRACT: The recent decline in many fish stocks has been accompanied by marked changes in age at maturity. However, there is little information on whether other components of reproductive investment have changed and the relative roles of phenotypic plasticity or genetic selection in such change. This study explored how reproductive investment in cod Gadus morhua from different regions around Scotland has changed between a period of high (1969, 1970) and low (2002, 2003) spawning-stock size. Maturity ogives indicated that inshore North Sea cod now mature at a smaller size and younger age than they did around 1970. The relationship between potential fecundity and size indicated that cod in the inshore region are now more fecund than 30 yr ago. Cod from the inshore region of the North Sea now have a higher fecundity at a given size and age than cod from the offshore region and the west of Scotland. There was no such spatial trend around 1970. Similarly, whilst the relative fecundity of cod in recent times is positively correlated with age, no such relationship was evident in 1969 and 1970. Nutritional influences on maturity and fecundity, particularly liver condition, were also evident from the recent study. However, the temporal and spatial differences in fecundity-size relationships were not consistent with a change in growth conditions, as there has been a significant decrease in body condition in recent times. Our findings regarding the temporal change in reproductive investment in the inshore North Sea region appear consistent with genotypic changes in life-history traits predicted to arise from intense periods of size-selective mortality. KEY WORDS: Cod · North Sea · Maturity · Fecundity · Nutritional status · Population dynamics · Life-history traits Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 276. Online publication date: August 02, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Development and validation of a bioenergetics model for juvenile and adult burbot

Oxygen consumption of juvenile and adult burbot Lota lota was measured in an intermittent‐flow respirometer to determine the effect of temperature and fish body mass on metabolic rate. These results were combined with data from earlier experiments and the ‘Wisconsin bioenergetics’ model was constructed. The model was validated under laboratory conditions by comparing observed and predicted food consumption and growth of burbot fed on dead vendace Coregonus albula. There was a good correspondence between observed and estimated growth and food consumption under experimental conditions: the mean absolute per cent errors of growth and food consumption were 4·8 and 24·0%. Estimated values with the new model were an improvement over the Atlantic cod Gadus morhua model previously used for burbot. In the field, the reliability of food consumption estimates was verified by using polychlorinated biphenyls (PCB) accumulation as an indirect indicator of the food consumption rate. The total PCB concentration of nine out of 13 burbot was estimated accurately. Thus, the burbot model produced good estimates of food consumption, even under field conditions.

Mating systems and the conservation of commercially exploited marine fish

Unprecedented declines of marine fish have revealed our inability to predict the susceptibility of populations to collapse and their capacity for subsequent recovery. Lack of knowledge about the behaviour and ecology of exploited species has hindered our understanding of how exploitation influences the resistance of marine fish to catastrophic decline and their resilience thereafter. Based on available data, particularly on the Atlantic cod Gadus morhua, we argue that the breeding behaviour of marine fish is considerably more complex than was believed previously. Mate competition, mate choice and other components of mating systems can affect population growth rate deleteriously during and after periods of intense exploitation. There is a pressing need to incorporate knowledge of mating systems in population assessments, to undertake field research on spatial and temporal scales of reproduction, and to initiate laboratory manipulation experiments to test hypotheses about marine fish mating systems, Allee effects and correlates of individual reproductive success.

Prostaglandins.

Prostaglandins.

Modifying Thyroidal Status in Atlantic Cod by Osmotic Pump Delivery of Thyroid and Antithyroid Agents

The objective of this study was to determine whether osmotic pump delivery of 3,5,3′-triiodo-L-thyronine (T3), thyroid inhibitors (potassium iodide, methimazole, and thiourea), or gonadal hormones (estradiol-17β and testosterone) could modify the thyroidal status of wild Atlantic cod Gadus morhua. Osmotic pumps implanted intraperitoneally delivered on average 3% (SE = 0.5%) of their initial volume per day under the experimental conditions (depth, 25 m; temperature, 5.2–7.6°C). The administration of T3 significantly increased serum levels of both T3 and L-thyroxine (T4). Treatment with either methimazole or thiourea significantly depressed serum T3 levels to about 55% of control values, whereas treatment with testosterone significantly reduced T4 levels to about 35%. We conclude that the delivery of thyroid or antithyroid agents by osmotic pumps is an effective means for creating experimental hyper- or hypothyroidism in wild Atlantic cod.

Temperature‐dependent changes in energy metabolism, intracellular pH and blood oxygen tension in the Atlantic cod

The effect of acute increase in temperature on oxygen partial pressure (Po2) was measured in the gill arches of Atlantic cod Gadus morhua between 10 and 19° C by use of oxygen microoptodes. Oxygen saturation of the gill blood under control conditions varied between 90 and 15% reflecting a variable percentage of arterial or venous blood in accordance with the position of each optode in the gill arch. The data obtained suggested that arterial Po2 remained more or less constant and arterial oxygen uptake did not become limiting during warming. A progressive drop in venous Po2, however, was observed at >10° C indicating that excessive oxygen uptake from the blood is not fully compensated for by circulatory performance, until finally, Po2 levels fully collapse. In a second set of experiments energy and acid–base status of white muscle of Atlantic cod in vivo was measured by magnetic resonance (31P‐NMR) spectroscopy in unanaesthetized and unimmobilized fish in the temperature range between 13 and 21° C. A decrease in white muscle intracellular pH (pHi) with temperature occurred between 10 and 16° C (ΔpH per ° C = −0·025 per ° C). In white muscle temperature changes had no influence on high‐energy phosphates such as phosphocreatine (PCr) or ATP except during exposure to high critical temperatures (>16° C), indicating that white muscle energy status appears to be relatively insensitive to thermal stress if compared to the thermal sensitivity of the whole animal. The data were consistent with the hypothesis of an oxygen limitation of thermal tolerance in animals, which is set by limited capacity of oxygen supply mechanisms. In the case of Atlantic cod circulatory rather than ventilatory performance may be the first process to cause oxygen deficiency during heat stress.

Variability in condition and growth of Atlantic cod larvae and juveniles reared in mesocosms: environmental and maternal effects

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.

Temperature and developmental plasticity during embryogenesis in the Atlantic cod Gadus morhua L.

Atlantic cod (Gadus morhua L.) embryos were reared at 4 °C, 7 °C, and 10 °C, and the relative timing of developmental events was characterized, with particular reference to myotomal muscle. Embryos started to feed at an apparently equivalent stage of development, so comparisons were made between temperature groups on the basis of percentage of time to first feeding and somite stage. No differences were found in the time of hatching or timing of appearance of the otic placode, unpaired median fin fold, gut lumen, otic vesicle, lens of the eye, otoliths, first muscular contractions, swim bladder, and hindgut, or in the rate of development of somites, myotubes, myofibrils, and acetylcholinesterase activity over the temperature range studied. In contrast, closure of the blastopore occurred late with respect to segmentation at higher temperatures, at the 3-somite, 10-somite, and 12-somite stages at 4 °C, 7 °C, and 10 °C respectively. Muscle cellularity was also markedly altered in the 10 °C group relative to the 4 °C and 7 °C groups. Larvae reared at 10 °C had significantly more (+14%) deep white fibers at hatch (P <0.001), whereas numbers of superficial red fibers remained unchanged. It is suggested that differences in muscle cellularity might be related to changes in the relative timing of epiboly, through differential proliferation of presomitic myogenic cells and/or their relative exposure to inductive signals.

The blood volumes of the primary and secondary circulatory system in the Atlantic cod Gadus morhua L, using plasma bound Evans Blue and compartmental analysis.

The volume of the primary (PCS) and secondary (SCS) circulatory system in the Atlantic cod Gadus morhua was determined using a modified dye dilution technique. Cod (N=10) were chronically cannulated in the second afferent branchial artery with PE-50 tubing. Evans Blue dye was bound to harvested fish plasma at a concentration of 1 mg dye ml(-1) plasma, and injected at a concentration of 1 mg kg(-1) body mass. Serial sampling from the cannula produced a dye dilution curve, which could be described by a double exponential decay equation. Curve analysis enabled the calculation of the primary circulatory and total distribution volume. The difference between these volumes is assumed to be the volume of the SCS. From the dilution curve, it was also possible to calculate flow rates between and within the systems. The results of these experiments suggest a plasma volume in the PCS of 3.42+/-0.89 ml 100 g(-1) body mass, and in the SCS of 1.68+/-0.35 ml 100 g(-1) body mass (mean +/- S.D.) or approximately 50% that of the PCS. Flow rates to the SCS were calculated as 2.7% of the resting cardiac output. There was an allometric relationship between body mass and blood volumes. Increasing condition factor showed a tendency towards smaller blood volumes of the PCS, expressed as percentage body mass, but this was not evident for the volume of the SCS.

Spatial pattern and patchiness during ontogeny: post-settled Gadus morhua from coastal Newfoundland

We tested the hypothesis that patchiness increases after settlement to the bottom in a marine broadcast spawner, the Atlantic cod Gadus morhua. Patchiness P=1+1/k was estimated from the dispersion parameter k of the negative binomial distribution. Estimates were based on length frequency distributions of fish from 18–330 mm that were seined from shallow nursery areas ( 200 mm depends on a shifting balance between establishment of home ranges (tending to reduce patchiness) and schooling behaviour (tending to increase patchiness). Patchiness generally increased for G. morhua between 25–200 mm SL when examined at different spatial (major bays along the northeast coast of Newfoundland) and temporal (years) scales suggesting processes responsible for these patterns may be consistent among the bays and years examined. Our results show that more is learned about the distribution of fish by examining the zeroth, first, and second moments (presence/absence, mean abundance and patchiness) than by examining only one measure. We hypothesize that patchiness continues to increase for larger juvenile and adult G. morhua that were not examined in this study. We propose that patchiness may then decrease for the very largest cod, ‘‘mother fish’’ that may not undergo extensive annual spawning migrations. 2003 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Condition, prolonged swimming performance and muscle metabolic capacities of cod Gadus morhua.

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 x fork length(-3))x100] 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.

RNA–DNA Ratio in Scales from Juvenile Cod Provides a Nonlethal Measure of Feeding Condition

Abstract We removed scales from juvenile Atlantic cod Gadus morhua, extracted RNA and DNA from tissue associated with the scales, and found that the ratio of RNA to DNA (R/D) reflects the feeding condition and growth of the fish. Moreover, R/D was found to be a more sensitive indicator of feeding condition than either weight or length. We performed a series of experiments in which the diets of juvenile cod (mean total lengths, 10.4–18.8 cm) were manipulated. At regular intervals, the fish were weighed and measured, and scales were removed from each individually marked fish. In fish that were either fed or starved for 49 d, R/D was significantly correlated with growth in length for individual fish (r 2 = 0.27, P < 0.0001) and tank means (r 2 = 0.59, P < 0.0001). The ratio of RNA to DNA was also sensitive to changes in feeding condition. Fish that were initially starved had significantly (P < 0.05) higher R/D after 2 d of feeding, and fish that were initially fed had significantly (P < 0.05) lower R/D after...

Microhabitat use of juvenile Atlantic cod in a coastal area of Newfoundland determined by 2D telemetry

A location-finding acoustic telemetry system (resolution ±1 m) was used to map ocean substrates and to continuously monitor the habitat associations (substrate, water temperature, and depth) of 58 Age 2 to 3 juvenile Atlantic cod Gadus morhua from 11 August to 20 December 1999. Substrate use was studied in 2 stages to determine if it differed from the pattern expected given an absence of selectivity (substrate use proportional to substrate availability). The first level compared the proportions of substrate in the study-area home ranges of Atlantic cod to those of the entire study site. The second assessed if the time spent over specific substrates was proportional to the substrate availability within the study-area home ranges. Boulder substrate was incorporated into the home ranges of juvenile Atlantic cod more than would be expected given its availability within the study area. Kelp substrates were included in these home ranges less than expected while sand and gravel were used in proportion to availability. Time spent over substrates within study-area home ranges varied over the diel and seasonal periods. Within study-area home ranges, juvenile cod occurred in boulder substrates at levels greater than or equal to availability. Conversely, the proportion of time spent over open substrates (e.g. sand and gravel) was either less than or not different from those of substrate availability. Kelp substrates were used less than expected in August and December and more than expected in September and October. Over the diel period, it was found that nocturnally, associations with structure diminished except during September and December when boulder habi- tats were still used to a greater degree. Unlike younger conspecifics, Age 2 to 3 cod in Buckley Cove were not strictly associated with structurally complex substrates, which suggests that these fish expe- rience less vunerability to predation. Also, unlike younger conspecifics, the distribution of Age 2 to 3 cod did not shift inshore nocturnally and therefore they did not benefit metabolically by moving through the thermocline that existed from August to mid-November. This study indicates that sub- strate use by juvenile cod is dynamic and the strength of associations with structural complexity varies over diel and seasonal temporal scales.

Relationship of RNA/DNA ratio and temperature to growth in larvae of Atlantic cod Gadus morhua

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 262:229-240 (2003) - doi:10.3354/meps262229 Relationship of RNA/DNA ratio and temperature to growth in larvae of Atlantic cod Gadus morhua Elaine M. Caldarone1,*, Jeanne M. St. Onge-Burns1, Lawrence J. Buckley2 1National Oceanic and Atmospheric Administration National Marine Fisheries Service, Northeast Fisheries Science Center, Narragansett Laboratory, 28 Tarzwell Drive, Narragansett, Rhode Island 02882-1199, USA 2URI/NOAA CMER Program, Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA *Email: elaine.caldarone@noaa.gov ABSTRACT: The RNA, DNA, and protein content of larval cod Gadus morhua reared in the laboratory at 3 temperatures and 3 densities of prey was measured. The data were used to define a quantitative 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. KEY WORDS: RNA/DNA ratio · Growth · Cod · Larvae · Temperature effects Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 262. Online publication date: November 07, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Growth and mortality patterns evaluated from otolith microstructure in Atlantic cod Gadus morhua larvae reared on different feeding regimes in mesocosms

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 264:95-107 (2003) - doi:10.3354/meps264095 Growth and mortality patterns evaluated from otolith microstructure in Atlantic cod Gadus morhua larvae reared on different feeding regimes in mesocosms Terje van der Meeren1,*, Erlend Moksness2 1Institute of Marine Research, Austevoll Aquaculture Research Station, 5392 Storebø, Norway 2Institute of Marine Research, Flødevigen Marine Research Station, 4817 His, Norway *Email: terje.van.der.meeren@imr.no ABSTRACT: The objective of this work was to test the hypothesis that in a situation where predators are excluded growth and mortality rates of cod larvae should be independent. This was evaluated from distributions of otolith increments in larvae sampled at different times of development. The mesocosm experiment was carried out in four 5.2 m3 plastic-bag enclosures placed along a raft system in a 20000 m3 seawater pond used for zooplankton production. Two different feed regimes (low and high ration, each in 2 enclosures) were set up on the basis of a fixed specific growth rate (SGR) applied in a bioenergetic model. Cod larvae showed a very dynamic relationship to food availability and larval growth. An increase in prey size after Day 20 had profound effects on otolith growth, which responded rapidly to availability of suitable prey. Thus, a short-term change in feeding conditions seems to be easily tracked in otoliths of cod larvae. The overall relationship between otolith radius and larval length was not linear, indicating a certain degree of decoupling between otolith and somatic growth. In a situation with adequate feeding conditions and exclusion of predators, mortality was not clearly dependent on otolith growth or size. This indicates that no strong inherent mechanisms in the larvae are responsible for growth- or size-dependent mortality. KEY WORDS: Cod larvae · Otolith dynamics · Selective mortality · Feeding regimes · Growth history · Larval rearing · Mesocosms Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 264. Online publication date: December 15, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Effects of food consumption and temperature on growth rate and biochemical-based indicators of growth in early juvenile Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 251:233-243 (2003) - doi:10.3354/meps251233 Effects of food consumption and temperature on growth rate and biochemical-based indicators of growth in early juvenile Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus Myron A. Peck1,5,*, Lawrence J. Buckley2, Elaine M. Caldarone3, David A. Bengtson4 1Graduate School of Oceanography, University of Rhode Island, South Ferry Road, Narragansett, Rhode Island 02882, USA 2URI/NOAA CMER Program, Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA 3National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Narragansett Laboratory, 28 Tarzwell Drive, Narragansett, Rhode Island 02882, USA 4Department of Fisheries, Animal, and Veterinary Science, University of Rhode Island, Kingston, Rhode Island 02881, USA 5Present address: Institute of Hydrobiology and Fisheries Research, University of Hamburg, Olbersweg 24, 22767 Hamburg, Germany *Email: myron.peck@uni-hamburg.de ABSTRACT: The relationship between the somatic growth rate (G) and feeding level (unfed, intermediate, 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 (R2 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 temperatures. 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 (R2 = 0.716) and haddock (R2 = 0.637). This relationship may be useful in estimating recent growth of age-0 juvenile cod and haddock in the field. KEY WORDS: Age-0 juvenile · Cod · Haddock · Feeding · Growth · RNA:DNA Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 251. Online publication date: April 11, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

The return of cod transplanted from a spawning ground in southern Newfoundland

To investigate the navigation mechanisms used by Atlantic cod (Gadus morhua) to locate spawning grounds we conducted a biotelemetric study in which 23 large (74-98 cm) spawners were displaced in small groups up to 35 km from a coastal Newfoundland spawning ground at Bar Haven, Placentia Bay. Overall, approximately 60% of the transplanted fish returned to the grounds, most within a few days. The data derived from this exercise allow the development of hypotheses regarding the navigatory mechanisms used by cod during movements on a small scale spatially. The return success was negatively related to distance of the release sites from the spawning ground (p<0.05) but was higher when fish were released along a known migratory pathway, or when released upcurrent of the spawning site. There was no support for the hypotheses that cod conducted contra-natant spawning migrations or tracked water-borne chemical-olfactory signals respectively. Transplanted groups did not stay together but a group transplanted near a large cod aggregation stayed there for some time, although 50% eventually returned to Bar Haven. Finally, our data suggest that cod moved towards an omnidirectional “attractor”, such as a characteristic sound or geophysical signature, that dissipates with distance perhaps in combination with spatial memory of bathymetry or current structures and the presence of maturing conspecifics.

Regime Shift Signatures from Stable Oxygen Isotopic Records of Otoliths of Atlantic Cod (Gadus morhua)

The sudden collapse of Atlantic cod (Gadus morhua) may relate to ocean climate, or regime shifts as demonstrated in production of Pacific salmon. This paper reports the results of stable oxygen isotope ratio analyses (18O/16O or δ18OA) from 91 otoliths of cod over a period of about 20 years. Seasonal δ18OA variations of individual otoliths started at an initial value of about −0.5 to 0‰ VPDB, and then reached a stable level in the range of +2.5 to +3.5‰ VPDB after 4–5 years. The initial low values correspond to the natal sources of mature cod, while the higher δ18OA values represent the water conditions before the cod was caught. This pattern of δ18OA variation was observed over the life history of all cod examined. Furthermore, the calculated isotopic temperatures agreed with those obtained from summer bottom trawl survey, indicating that δ18OA of otoliths could be used as a thermometer in determining the ambient seawater temperature where the cod lived. Comparison of long-term δ18OA records and biological and meteorological observations suggested that decadal-scale ecosystem changes did occur in the late 1970s and early 1990s in Atlantic Canada, comparable to regime shifts occurred in the North Pacific.

Enhancing the reproductive potential of local populations of coastal Atlantic cod (Gadus morhua)

We investigate the feasibility of enhancing the reproductive potential of northern Atlantic cod (Gadus morhua L.) populations resident in Newfoundland and Labrador bays by "catch, grow out, and release". This entails trapping juvenile and young adult fish from the local population, increasing their growth, maturation rate, and potential fecundity by feeding them a natural diet in net pens, and then returning the fish to their natal bay habitat to spawn. To determine whether multiyear farming affects spawning success, we determined the spawning period and egg quality of cod held in captivity for three growth seasons. Farmed cod spawned in a net pen concurrently with wild cod in Trinity Bay during 1995 and produced fertilized eggs from which viable larvae hatched. Sonic tracking showed that cod farmed for 3 years and then released reintegrated with wild cod aggregations over known spawning grounds. Recaptures of tagged fish several years after release suggest that farmed fish remained in the bay as members of the resident population. Fishing mortality (bycatch in coastal fisheries for lumpfish (Cyclopterus lumpus) and winter flounder (Pseudopleuronectes americanus)) of released farmed cod was not negligible, emphasizing that any enhancement effort must be carried out under a complete fishing moratorium.