Distribution Of Cod Research Articles

Use of Oceanographic Forecasts and Echosounders to Guide and Enhance an Inshore Gillnet Fishery for Atlantic Cod (Gadus morhua)

Vessels fishing with gill nets for Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence in 1985 and 1986 concentrated their fishing effort in shallow waters (<50 m) where cod densities were highest (to 0.5/m3). In both years, seasonal trends (June–August) in mean daily deployment depths of gill nets were positively correlated with mean depths at which cod were surveyed (1985, r = 0.71; 1986, r = 0.51, Ps < 0.05). Daily catch rate variability of individual vessels was accounted for by fish "flux" adjacent to nets (44%), vessel operator skill (19%), and "flux"–skill interaction (8%; total R2 = 0.71). A guided vessel directed to fish at sites predicted to have high fish flux (located down-current from high-density cod aggregations identified by echosounding within depth ranges forecast to be favorable to cod by "rule of thumb" wind-based oceanographic models) had higher catch rates (mean 1.3 t/d) than the fleet average and its own average fishing without guidance (means 0.4 t/d, P's < 0.05). Directed searches were of shorter duration (mean 0.5 h) than searches conducted at random (1.5 h). Combined use of echosounders and air–sea-based forecasts of cod distribution could help stabilize catch rates, especially at times of poor fish availability inshore.

Maccullochella ikei, an endangered species of freshwater cod (Pisces: Percichthyidae) from the Clarence River system, NSW and M. peelii mariensis, a new subspecies from the Mary River system, Qld

The eastern freshwater cod, Maccullochella ikei, from the Clarence River system, NSW, is described and M. peelii mariensis is described as a new subspecies from the Mary River system, Qld. The Murray cod, M. p. peelii and the trout cod, M. macquariensis, are indigenous to the Murray-Darling River system. Using electrophoretic data for 19 presumed loci, the coefficient of genetic identity between M. p. peelii and M. ikei was 0.72 and the banding-patterns of the muscle general protein, liver esterases and five other enzymes, were species-specific. A high proportion of abnormal and inviable hybrid larvae in a cross-breeding experiment indicate that post-zygotic isolating mechanisms have evolved between M. p. peelii and M. ikei. The coefficient of genetic identity between M. p. peelii and M. p. mariensis was 0.85 and banding patterns of muscle general protein were diagnostic. Canonical variates analysis using 18 morphological and nine meristic characters, clearly separated both spccies and the subspecies. Maccullochella ikei is distinguished from M. p. peelii by having longer pelvic fins, larger orbit length, and larger and morphologically distinct sagittalotoliths. Maccullochella p. mariensis differs from M. p. pee/ii by the combination of a deeper and shorter caudal peduncle, longer pelvic fins, larger sagittal otoliths and lesser extension of the first anal pterygiophore towards the first caudal vertebra, and from M. ikei by the combination of a deeper caudal peduncle, greater postorbital head length, smaller orbit, larger interorbital width, fewer scale rows below the lateral line, shorter fifth-sixth dorsal spine and lesser extension of the first anal pterygiophore. Although each species has distinctive colouration and mottling, there is some intra-specific variation. Maccullochella macquariensis is distinct from the other species by having a straight head profile, jaws of similar length, 14 precaudal vertebrae and distinctive colouration. There was a dramatic reduction in the distribution and abundance of cod in the eastern drainage during the early 1900s and cod were probably extinct in the Richmond and Brisbane River systems by the end of the 1930s. Maccullochella ikei and M. p. mariensis are each represented by one, small population. Possible causes of the decline, and the management strategies taken to conserve the endangered M. ikei are discussed.

Influences of mean advection and simple behavior on the distribution of cod and haddock early life stages on Georges Bank

ABSTRACTResults of a modeling study designed to explore the influences of physical advection and certain biological mechanisms on the distribution of cod (Gadus morhua) and haddock (Melarwgrammus aeglefinus) early life stages on Georges Bank are described. Using a late‐winter/early‐spring 3‐D circulation field driven by the M2 tidal current, mean wind stress and Scotian Shelf inflow, we examine the distribution of cod and haddock larvae spawned on the Northeast Peak of the Bank. The sensitivity to a March‐April baroclinic field is also explored. Results indicate that larvae remaining in the surface Ekman layer are generally advected off‐bank. However, downwelling associated with Ekman layer convergence near the shelf break provides a mechanism for larvae to exit from the off‐bank surface drift. Larvae below the surface layer are transported south‐westward along the southern flank of Georges Bank and are retained on the Bank if their position immediately upstream of the Great South Channel is shoalward of (roughly) the 70 m isobath. Within the Great South Channel region and between the 50 and 70 m isobaths, retention can depend on the phase of the tide. Spawning shoalward of the 50 m isobath on the Northeast Peak greatly increases the chances of retention. These results apply to passive larvae and to those with specified vertical distributions and migration based on observations. Directional on‐bank swimming at rates of 0.5 to 1 body length per second would substantially enhance shoalward displacement, resulting in larval distributions during the first 2 months that are consistent with field observations.

Density-Dependent Geographic Distribution of Atlantic Cod (Gadus morhua) in the Southern Gulf of St. Lawrence

We tested effects of population size on the geographic distribution of Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence for age groups 3–8+ over the period 1971–90. Distribution was density dependent for all six age groups. Geographic range or stock area increased with abundance for each age group. Variation in abundance explained 63–94% of the variation in stock area. During periods of low abundance, the highest cod densities occurred in western regions of the southern Gulf for all age groups. Geographic distribution during these periods was more restricted for younger cod than for older cod. Density of age-3 cod was relatively high in only one of three western regions whereas densities of older cod were relatively high in two or all of these regions. As abundance increased, density increased slowly in the regions where cod were concentrated at low population sizes and more rapidly in surrounding regions. The greatest densities were found in the same area at low and high levels of abundance for younger cod but in different areas at these two abundance levels for older cod. We discuss this variation in geographic distribution in terms of density-dependent habitat selection and note its implications for stock assessment.

The distribution of cod (Gadus morhua) in relation to temperature and oxygen level in the Gulf of St. Lawrence

ABSTRACTBottom temperature and oxygen level were measured in the northern Gulf of St. Lawrence during a ground‐fish trawl survey held in August and September 1991. Cumulative relative frequencies of temperature and oxygen level and cumulative relative frequencies of temperature x cod and oxygen X cod were computed with consideration of the random stratified sampling scheme. A total of 84‐3% of temperature x cod frequency cumulated from 2oC to 4oC, but only 25% of the frequency of temperature alone cumulated from 2oC to 4oC. At an oxygen level of 3.4 mg/1, only 2.6% of the oxygen X cod frequency had cumulated, while 24.3% of the cumulative frequency of oxygen alone was already observed at the same oxygen level. A comparison of the cumulative relative frequencies of temperature and of temperature X cod indicates that cod choose intermediate temperatures in the available range. A comparison of the cumulative relative frequencies of oxygen and of oxygen x cod indicate that cod avoid water with an oxygen level below 3.4 mg/1. This oxygen level is known to cause physiological stress in captivity. Data from the stations with oxygen levels ± 3.4 mg/1 were ignored, and the cumulative relative frequency of temperature was recomputed. As a result, the avoidance of cold water by cod was emphasized: 23% of the cumulative frequency of temperature alone was below 2oC, and 47.8% was above 4oC, in contrast to 17.2% and 57.5%, respectively, prior to removal of data from hypoxic stations.

Physiological Response of the Atlantic Cod (Gadus Morhua) to Hypoxia at Various Environmental Salinities

ABSTRACT Atlantic cod (Gadus morhua L.) acclimated to water salinities ranging from 28 ‰ to 7 ‰ were exposed to mild (8.0 kPa) or severe (4.0 kPa) hypoxic conditions for 6h. In each experiment, respiratory, acid–base, ionic, haematological and metabolic disturbances were analyzed. During mild hypoxia, a strong hyperventi-latory response was observed, resulting in a respiratory alkalosis that persisted throughout the 6-h trial. Plasma Cl− and pyruvate levels were the only other variables to display significant changes: they both increased. In more severe hypoxic conditions, although the ventilatory response was the same, a weak metabolic acidosis was superimposed. The haematological response (increased haematocrit and decreased mean cellular haemoglobin content) suggested that catecholamines were released into the blood. Both Na+ and Cl− concentrations increased significantly. Metabolic perturbations occurred: plasma lactate, pyruvate and glucose concentrations increased markedly. Though lactate concen-trations in liver, heart and white muscle increased, the concentrations of pyruvate, glucose and glycogen did not change significantly. Water salinity affected the amplitude of the ionic responses during hypoxia: the amplitude decreased with decreasing salinity. Irrespective of water salinity, 23 of 29 fish survived the severe hypoxic conditions. This relatively good tolerance of low water oxygenation, as compared with other marine bottom-feeders, suggests that this species may face poorly oxygenated waters in the wild. Together with temperature and salinity, water oxygen content may thus be an important variable to take into account in the study of the distribution and migration patterns of Atlantic cod.

Seasonal distribution, abundance, and life-history traits of Greenland cod, Gadus ogac, at Wemindji, eastern James Bay

Greenland cod populations near Wemindji, eastern James Bay, were studied in 1987 and 1988 to describe the species' general ecology and life-history characteristics. During the summer, they principally occupied shallow (2–5 m) coastal waters. This habitat was characterized by a belt of eelgrass (Zostera marina) at depths of 1–3 m, salinities between 20 and 23‰, and temperatures of 3–20 °C. Daily trap catches were highly variable, and more fish were caught at night than during the day. In winter, more cod were found inshore, in the estuary, than in coastal waters. This movement corresponds to the completion of sexual maturity; spawning occurs in April to June. Growth rate was linear for males and females. The age at maturity was 3 years and no trade-off was observed between growth and reproduction. Greenland cod spawned every year, and the maximum age was 9 years. Life-history variables for Greenland cod differ from those of most arctic benthic fishes; this species shows rapid growth, high fecundity, low age at maturity, and high mortality. These characteristics may represent important adaptations allowing cod to sustain life in James Bay coastal waters, where environmental conditions are different from those in arctic waters.

The selectivity for cod ( Gadus morhua L.) in two experimental trammel-nets and one gillnet

The present study analyses the selectivity for cod in two trammel-nets (three-wall nets) and one gillnet (single-wall net) used during an experimental cod fishery conducted monthly from october 1985 to December 1988 in a Norwegian fjord. It is part of a cod enhancement experiment conducted in the fjord. The three nets were grouped and utilized to sample the wild cod population. In addition, the gillnet and one trammel-net were utilized to sample a tagged group of cod with a known length composition. Relative selectivity curves were estimated indirectly for the two trammel-nets by comparing the catches of each length class within the length range 18–58 cm. Absolute selectivity curves were estimated directly for the gillnet and one trammel-net for the length range 15.0–22.0 cm. These were utilized to verify the indirectly estimated curves. The trammel-net selectivity curves obtained were used to provide an estimate for the true length-frequency distribution of cod in the fjord. Finally, it was tested whether a group of the three nets may be utilized as a unit effort to provide approximate random samples from the population.

Numerical simulation model for quantitative management of mariculture

A numerical model is developed for mariculture management, which consists of four parts: (1)current simulaton model which calculates tidal and wind induced currents, (2)COD diffusion model which calculates spatial distribution of COD using simulated current, (3)DO diffusion model which calculates spatial distribution of dissolved oxigen, and (4)accumulation model which calculates distribution of deposits from mariculture of fish. Our model is capable of (1) calculating the detailed spatial distribution of COD and DO by dividing the bay area in to many grid points, (2) taking into consideration the effects of feed and fish in each raft, and the loading of COD from rivers. Using this model, we can assess the influence of the location or the area of the mariculture rafts on the ecological and/or environmental system. It is also of practical use in order to obtain a better distribution of rafts in bay areas, or to calculate the basic data for the renewal of licenses. Application is made to Mikame Bay in Ehime Pref., west part of Japan, as a case study.

Spatial Comparison of Recent Growth in Postlarval Atlantic Cod (Gadus morhua) off Southwestern Nova Scotia: Inferior Growth in a Presumed Nursery Area

Spatial variation in distribution, age, and recent growth of postlarval cod (Gadus morhua) were examined off southwestern Nova Scotia during the early summer of 1985 and 1986. Ages ranged between 40–120 d posthatch throughout the sampling area, from the spawning grounds on Browns Bank, to nearshore (<55 m depth) and offshore regions 150 km north. The hatch-date distributions during 1986 between cruises 3 wk apart were significantly different in the nearshore, contrary to the age structure on the Bank which appeared more stable. These observations are consistent with retention of cod in the Browns Bank gyre, coupled with episodic leakage and northerly advection in the residual current. Recent growth determined from otolith increment widths was significantly less for those cod sampled at nearshore stations than for cod offshore and on the Bank. Recent growth was significantly correlated with Zooplankton biomass in a size range suitable for postlarval cod, while sea temperature was correlated in only one cruise. Nearshore areas had on average 25% of the Zooplankton biomass found on the Bank. Recent growth indices of the third and fourth week precapture were not significantly different between the nearshore and offshore, implying that the cod had shared a common environment, and common origin such as Browns Bank.

Interactive Effects of Geophysically-Forced Sea Temperatures and Prey Abundance on Mesoscale Coastal Distributions of a Marine Predator, Atlantic Cod (Gadus morhua)

Geophysically-forced sea temperatures and prey abundance interactively regulated mesoscale (10's to 100's of km) inshore Atlantic Cod (Gadus morhua) distribution patterns in the northeastern Gulf of St. Lawrence, in both 1985 and 1986. Cod were located most often at temperatures within the range 0–5 °C. However, when mean densities of their chief prey (capelin, Mallotus villosus) were high (> 100/105m3) within the coastal zone, cod frequented waters having temperatures similar to those at which this prey were aggregated, within the broader range of temperatures −0.5 to 8.5 °C. The proportions of cod occupying sea temperature strata were significantly and positively correlated with those of capelin (r = 0.64, slope = 0.6, df = 86), in both 1985 and 1986, under two conditions: (1) sea temperatures within the range 1–9 °C; and (2) mean capelin densities > 100/105m3. Under conditions of lower mean capelin densities, cod distributions were independent of those of capelin. At temperatures outside the range 1–9 °C, cod and capelin densities were not correlated, regardless of capelin densities.

Metathesis “rainbow” polymerizations--a systematic route into polyene sequences

Metathesis polymerization of 1,3,5,7-cyclooctatetraene (COT) yields an intractable, silvery conducting polymer (polyacetylene). Metathesis polymerization of 1,5-cyclooctadiene (COD) affords a rubbery, transparent insulating polymer (poly-butadiene). What material results upon co -polymerization? Since COD and COT undergo metathesis polymerization at similar rates, the resulting copolymer should have a random distribution of ring-opened COD (CCCCCCCC) and and ring-opened COT(CCCCCCCC) units along the polymer backbone. The greater the concentration of COD in the COD/COT monomer mixture, the more sites of saturation randomly inserted in the polymer backbone. By controlling the COT/COT ratio, copolymers with varying conjugation lengths are produced. Raman spectroscopy, UV-Vis, NMR, electrical conductivity, and non-linear optical measurements all indicate a progression of conjugation length in the copolymer with increasing mol fraction COT in the COD/COT mixture. As an important control study, copolymers formed from norbornene (NBE) and COT-- which undergo metathesis polymerization at very different rates--have also been investigated.

Ecology and distribution of juvenile cod and haddock in relation to sediment type and bottom currents on eastern Georges Bank

Recently-settled 0-group juvenile cod Gadus morhua and haddock Melanogrammus aeglefinus were observed by submersible dives and research bottom trawls to inhabit primarily a large pebble-gravel deposit located on the northeastern edge of Georges Bank at 70 to 100 m water depth. Pelagic juvenile gadids are widespread on the bank in late spring, but by late July, they have become demersal and are abundant only on the gravel bed. Coloration of the juveniles mimics the appearance of the pebble bottom, possibly making them less vulnerable to predation there than on the Light-colored sand bottom of most areas of the bank. On the basis of these observations, we hypothesize that the gravel habitat favors their survival through predator avoidance and, possibly to a lesser extent, through increased prey abundance. In particular, the pebble-gravel deposit on northeastern Georges Bank supports the largest aggregations of demersal juveniles, and it may be essential to the recruitment success of the Georges Bank gadid population. By September, the young fish are no longer present on the gravel bed because night-time feeding forays off the bottom result in their transport southeastward in the clockwise current gyre on the bank. The study area is characterized by strong, rotary tidal currents. During the day, demersal juveniles remain withn a few centimeters of the bottom in the boundary layer where currents are somewhat reduced and where they maintain their position by swimm~ng continually into the current. At night, regardless of the current, they rise off the bottom to feed on invertebrates in the near-bottom water column. Abundance estimates of demersal juvelules based on research bottom trawls show variability related to fish s u e and time of day. When compared with estimates of juvenile abundance based on submersible observations, the trawl data underestimate the numbers of juvenile fish present. We expect a knowledge of the die1 behavior, geographic location, and most favorable habitat of demersal 0-group juveniles wdl aid in the assessment and management of the Georges Bank gadid population.

Analysis of Arctic Cod Movements in the Beaufort Sea Nearshore Region, 1978-79

A study was conducted to investigate distribution and abundance of arctic cod in the nearshore region of the Beaufort Sea. Data collection methods included 3 m otter trawl and hydroacoustic surveys. Temperature and conductivity measurements were taken throughout the study area on a regular basis. The results indicated that arctic cod are associated with a transition layer between a surface water mass, characterized by low salinity and high temperature, and a bottom water mass, characterized by high salinity and low temperature. Arctic cod apparently oriented to the shoreward edge of the marine water mass and redistributed themselves depending on the location of the shoreward edge. It is hypothesized that the transition layer concentrates food organisms, and this abundance of food may be one factor that induces shoals of arctic cod to utilize this transition layer. Key words: arctic cod, Alaskan Beaufort Sea, nearshore movements, temperature/salinity association, coastal habitat use, Boreogadus saida

Experiences with Polishing Lagoons

For upgrading of overloaded biological plants the addition of polishing lagoons is feasible. Operational results of eleven polishing lagoons are reported. In addition, one plant has been intensively studied in respect to the cumulative distribution of BOD5, COD, and phosphorus. Design recommendations are given.

Distribution, growth, and foods of Arctic Cod (Boreogadus saida) in the Bering, Chukchi, and Beaufort seas

Distribution, growth, and foods of Arctic Cod (Boreogadus saida) in the Bering, Chukchi, and Beaufort seas

Finite Element Analysis on the Tidal Current and Cod Distribution in Mikawa Bay

This paper deals with computer simulation of the non-stationary advective diffusion of organic matter with biochemical reaction in Mikawa Bay. A new COD model is proposed. The computational techniq...

On Spent Liquor of Semichemical Pulping (III)

This paper describes species variation of pulping timbers in color and COD of spent liquors from neutral sulfite pulping in connection with water pollution problems. Thorough investigation were made with certain hardwood species like Shii (Castanopsis cuspidata), Shide (Carpinus sp..) and Kagonoki (Actinodaphne lanciforia), common in Japan and certain southern tropical wood species like Red lauan (Shorea sp.), White lauan (Pentacme sp.) and Kapur (Dryobalanops sp.).Spent liquor from the cooking of both individual species and species mixture were analysed in each stage of the pulping processes. The digested chips were separated from cooking liquors (black liquor) and washed with one liter of distilled water (washings). And they were refined on a laboratory defibrator in three steps (defibration liquors) and each spent liquor was subjected to the routine spent liquor analysis searching for the main features of pollution characteristics.As a summary of the tests carried out, it may be stated that the effect of the species variation of pulping timbers in color and volume of the black liquor is considerably of high value, but there are no great differences in COD. Especially, volume of the black liquor has been found to be highly proportional to the apparent specific gravity of timber species. The distribution of solid, total color and COD in each stage of the pulping processes differed among timber species, because of the diffence of the apparent specific gravity of wood species. In the case of Lauan species, for example, color and COD were chiefly originated from the washings and the first defibration liquor rather than black liquor.On all wood species used, the contribution of black liquor reaches at most 50% of total color and COD of over all spent liquors produced, and the recovery of black liquor and especially the first defibration liquor are very important for the treatment of water pollution problems. It should also be mentioned that color of spent liquors and the pulp yield increase, as the pH of black liquors of hardwood cooking increases. Southern tropical wood, however, dose not show this relationship. Under the constant pulp yield, variation of the maximum temperature of digestion dose not influence on color and COD of spent liquors. But bark removal has the effect of lower coloration and higher COD of spent liquors. In the case of cooking of species mixture, the volume, color and COD of black liquors are manifestly represented as the mean values of those obtained from the individual cooking of each species.

On Spent Liquor of Semichemical Pulping (I)

This paper describes species variation of pulping timbers in color and COD of spent liquors from neutral sulfite pulping in connection with water pollution problems. Thorough investigation were made with certain hardwood species like Shii (Castanopsis cuspidata), Shide (Carpinus sp..) and Kagonoki (Actinodaphne lanciforia), common in Japan and certain southern tropical wood species like Red lauan (Shorea sp.), White lauan (Pentacme sp.) and Kapur (Dryobalanops sp.).Spent liquor from the cooking of both individual species and species mixture were analysed in each stage of the pulping processes. The digested chips were separated from cooking liquors (black liquor) and washed with one liter of distilled water (washings). And they were refined on a laboratory defibrator in three steps (defibration liquors) and each spent liquor was subjected to the routine spent liquor analysis searching for the main features of pollution characteristics.As a summary of the tests carried out, it may be stated that the effect of the species variation of pulping timbers in color and volume of the black liquor is considerably of high value, but there are no great differences in COD. Especially, volume of the black liquor has been found to be highly proportional to the apparent specific gravity of timber species. The distribution of solid, total color and COD in each stage of the pulping processes differed among timber species, because of the diffence of the apparent specific gravity of wood species. In the case of Lauan species, for example, color and COD were chiefly originated from the washings and the first defibration liquor rather than black liquor.On all wood species used, the contribution of black liquor reaches at most 50% of total color and COD of over all spent liquors produced, and the recovery of black liquor and especially the first defibration liquor are very important for the treatment of water pollution problems. It should also be mentioned that color of spent liquors and the pulp yield increase, as the pH of black liquors of hardwood cooking increases. Southern tropical wood, however, dose not show this relationship. Under the constant pulp yield, variation of the maximum temperature of digestion dose not influence on color and COD of spent liquors. But bark removal has the effect of lower coloration and higher COD of spent liquors. In the case of cooking of species mixture, the volume, color and COD of black liquors are manifestly represented as the mean values of those obtained from the individual cooking of each species.

Effects of Salinity, Temperature, and Dissolved Oxygen on Early Development of the Pacific Cod (Gadus macrocephalus)

Effects of various combinations of levels of salinity, temperature, and dissolved oxygen on incubation of Pacific cod (Gadus macrocephalus) eggs were investigated in the laboratory. Quantitative relations were determined, by response surface analysis, between the environmental variables and four criteria used to estimate success of egg development. Larval size at mean hatching time, and percentages of total hatch, viable hatch, and postmature eggs that failed to hatch were optimized at intermediate salinities (about 15‰), low temperatures (3–5 C), and over a wide range of dissolved oxygen concentrations. Pacific cod eggs are judged to be euryhaline, euryoxic, and stenothermal. As long as temperatures are within the range of about 3–5 C, the developing egg is tolerant of a wide range of salinities, and of dissolved oxygen levels to a minimum of about 2 or 3 ppm. Below 3 C developmental success decreases precipitously; above 5 C it attenuates more slowly.Distribution and abundance of Pacific cod are reviewed in light of the experimental results. Temperature is suggested to be of major importance to successful egg development in the natural environment; the temperature range associated with reasonable egg viability and incubation success is estimated to extend from about 2.5 to 8.5 C.The distribution of cod in the spawning season appears associated with water temperatures between 2.5 and 8.5 C in Asian waters. Near the southern limit of cod distribution on the North American coast the following associations are suggested in relation to temperatures of the upper mixed layer of coastal waters in the spawning period: limit of commercial abundance, 9 C; extent of limited commercial landings, 10 C; limit of occurrence, 13.5 C.