The dispersal pattern and behaviour of Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence: results from tagging experiments

2012 ◽  
Vol 69 (1) ◽  
pp. 112-121 ◽  
Author(s):  
Hacène Tamdrari ◽  
Martin Castonguay ◽  
Jean-Claude Brêthes ◽  
Peter S. Galbraith ◽  
Daniel E. Duplisea
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Management Strategies ◽  
Fishing Effort ◽  
Fish Distribution ◽  
Suitable Habitat ◽  
Dispersion Pattern ◽  
Dispersion Index ◽  
Dispersal Pattern ◽  
Centre Of Gravity

We examined how the distribution of Atlantic cod ( Gadus morhua ) is influenced by abiotic (temperature, salinity, depth, suitable habitat) and biotic (stock biomass) factors based on tagging−recapture data collected from 1995 to 2008 by the Department of Fisheries and Oceans Canada in the northern Gulf of St. Lawrence. We calculated a centre of gravity index and a dispersion index using only individuals recaptured more than 1 year after tagging during the summer. The centre of gravity showed a northward expansion and eastward contraction in recent years, reflecting both fish distribution and changes in fishing effort. The dispersion index was significantly related to temperature, habitat suitability, and biomass but not to salinity or depth. These results indicate that interannual fluctuations of temperature and stock abundance both influence the dispersion pattern of cod. This new information could influence spatio-temporal fisheries management strategies for northern Gulf cod.

Fish Distribution and Catchability: What Is the Appropriate Measure of Distribution?

1994 ◽  
Vol 51 (5) ◽  
pp. 1046-1054 ◽  
Author(s):  
D. P. Swain ◽  
A. F. Sinclair
Keyword(s):  
Population Size ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Fish Distribution ◽  
Minimum Area ◽  
Spatial Spread ◽  
Density Dependent ◽  
Absolute Density ◽  
Using Data

Catchability to commercial fisheries has been predicted to be density dependent due to density-dependent variation in stock area. Previous studies have used indices of stock area based on thresholds of absolute density. These indices will increase with abundance even if density increases uniformly over all areas. We show that spatially uniform changes in abundance can affect catchability given certain models for the distribution of fishing effort, but that this effect is slight compared with the effect of changes in the spatial spread of fish distribution. We describe an index of distribution that depends only on spatial spread: the minimum area over which a specified percentage of the population is spread. We tested the density dependence of this index using data on Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence. Results depended on the percentage of the population for which the index was evaluated. The area containing most (90 or 95%) of the population was density dependent, expanding as population size increased. The area of highest cod concentration (i.e., the area containing 50% of the population) did not expand significantly as population size increased.

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

1993 ◽  
Vol 50 (10) ◽  
pp. 2129-2136 ◽  
Author(s):  
G. A. Rose ◽  
W.C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Shallow Waters ◽  
Gill Nets ◽  
Rule Of Thumb ◽  
Combined Use ◽  
Catch Rates ◽  
Depth Ranges ◽  
High Fish

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.

Survey gear calibration independent of spatial fish distribution

2004 ◽  
Vol 61 (4) ◽  
pp. 636-647 ◽  
Author(s):  
Peter Lewy ◽  
J Rasmus Nielsen ◽  
Holger Hovgård
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Survey Design ◽  
Fish Distribution ◽  
Simulation Studies ◽  
Conversion Factors ◽  
The Baltic ◽  
Standard Software ◽  
Track Line ◽  
Stock Abundance

Trawl surveys provide important information for evaluation of relative stock abundance fluctuations over time. Therefore, when survey gears or vessels are changed, it is important to compare the efficiency and selectivity of old and new gears and vessels. A method for estimation of conversion factors is developed based on a survey design where paired hauls are taken in the same trawl track line. The method explicitly accounts for changes in fish density caused by trawling disturbance. A generalized linear model for paired hauls catches is analytically derived and the gear conversion and disturbance parameters with their precision are obtained using standard software. Simulation studies carried out additionally showed that the estimated conversion factors were practically unbiased. Because of the independence of the spatial fish distribution, the new method is preferable to the traditional paired hauls design for which it is generally not possible to obtain the statistical properties of the estimated conversion factors. The paper is concluded with suggestions on how to optimize survey design. The method was used to estimate conversion factors for Atlantic cod (Gadus morhua) from Danish gear calibration experiments in the Baltic Sea.

scholarly journals Seasonal cycles in weight and condition in Atlantic cod (Gadus morhua L.) in relation to fisheries

2005 ◽  
Vol 62 (5) ◽  
pp. 1006-1015 ◽  
Author(s):  
L.G.S. Mello ◽  
G.A. Rose
Keyword(s):  
Gadus Morhua ◽  
Physiological Condition ◽  
Atlantic Cod ◽  
Management Strategies ◽  
Maximum Yield ◽  
Product Yield ◽  
Economic Benefits ◽  
Hepatosomatic Index ◽  
Economic Returns ◽  
Condition Indices

Abstract Seasonal cycle in weight and physiological condition of Atlantic cod (Gadus morhua) influenced productivity and economic impacts of the cod fishery in Placentia Bay, Newfoundland. Condition indices (Fulton's K condition factor and hepatosomatic index – HSI) were lowest during the spawning season (spring) and increased rapidly during the postspawning period, reaching maximum values by fall (K and HSI increased on average 24% and 82% between spring and fall, respectively). Somatic weight and condition indices varied seasonally. Condition indices were correlated with an industry index of product yield. Historically, cod fisheries have been prosecuted during all seasons, but simulations of 1997–1999 fisheries indicate that a fall fishery (period of peak physiological condition) resulted in a 8–17% decrease in the number of cod removed from the stock while maintaining the same weight-based quotas, and profiting from maximum yield and better product quality. Spring and summer fisheries resulted in lower yield (6%) and quality (5–26%) of fish products by weight. Seasonal biological cycles could be used as templates for management strategies that promote fisheries conservation and economic benefits by harvesting fish during periods when biological impacts are minimal and economic returns maximal.

Tracking escaped Atlantic cod (Gadus morhua L.) aggregated around Norwegian farms: Considerations for management strategies

2017 ◽  
Vol 24 (4) ◽  
pp. 265-273 ◽  
Author(s):  
R. D. Hedger ◽  
R. M. Serra-Llinares ◽  
P. Arechavala-Lopez ◽  
R. Nilsen ◽  
P. A. Bjørn ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Management Strategies

Mixing and migration of overwintering Atlantic cod (Gadus morhua) stocks near the mouth of the Gulf of St. Lawrence

1999 ◽  
Vol 56 (10) ◽  
pp. 1873-1881 ◽  
Author(s):  
S E Campana ◽  
G A Chouinard ◽  
J M Hanson ◽  
A Fréchet
Keyword(s):  
Large Scale ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Trace Element Composition ◽  
Eastern Canada ◽  
Management Area ◽  
Elemental Fingerprint ◽  
And Migration ◽  
Southern Flank

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 out each January between 1994 and 1997 documented dense aggregations of cod along both flanks of the Laurentian Channel in each year, with estimated biomasses exceeding 100 000 metric tons. Using the trace element composition of the otolith ("otolith elemental fingerprint") as a natural tag, we found members of four populations to be present on the overwintering grounds in significant numbers, yet large-scale mixing among the populations was minimal. Individual trawl samples were often composed of a single population, suggesting that population integrity was maintained at a scale of <20 km. Cod from the southern Gulf of St. Lawrence dominated the population composition along the southern flank of the Channel, while cod from the northern Gulf dominated the northern flank; the distributions of both of these populations extended well to the east of their summer habitats and were remarkably similar across years. There was no evidence of large-scale mixing across the Channel. In light of the substantive migration of northern Gulf cod into the management area for the southern Newfoundland population, fishing effort off southern Newfoundland has the potential to reduce the size of the northern Gulf population.

Temporal changes in harvesting dynamics of Canadian inshore fisheries for northern Atlantic cod, Gadus morhua

2000 ◽  
Vol 57 (4) ◽  
pp. 805-814 ◽  
Author(s):  
Jeffrey A Hutchings ◽  
Mark Ferguson
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Temporal Changes ◽  
Catch Rate ◽  
Fish Stock ◽  
Small Fish ◽  
Trap Design ◽  
Northern Atlantic ◽  
Unreported Catches

We quantified temporal changes in catch rate, fishing effort, and catch misreporting for two sectors of the fixed-gear fishery for Newfoundland's northern Atlantic cod, Gadus morhua, from 1980 to 1991, the year preceding the stock's commercial fishing moratorium. Over the 12-year period, fishermen reported catch rate declines of 40 and 75% in the trap and gillnet fisheries, respectively, associated with significant increases in nominal fishing effort. Additional changes to effort included smaller gillnet and trap mesh sizes, larger traps, longer soak times, and modifications to trap design to increase catch retention probabilities. Compared with the early 1980s, unreported catches among inshore fishermen may have trebled by the late 1980s and early 1990s due to longer gillnet soak times, increased gear selectivity for small fish, and declining availability of fish of marketable size. These patterns in harvesting dynamics are consistent with the hypothesis that the decline of northern cod was gradual and that increased rates of catch misreporting contributed to increases in fishing mortality. The concomitants of declining fixed-gear catch rate, increasing quantitative and qualitative fishing effort, increased selectivity for smaller fish, and increasing levels of unreported catches may represent general correlates of imminent fish stock collapses.

Growth, condition, and environmental relationships in Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence and implications for management strategies in the Northwest Atlantic

1999 ◽  
Vol 56 (10) ◽  
pp. 1818-1831 ◽  
Author(s):  
J -D Dutil ◽  
M Castonguay ◽  
D Gilbert ◽  
D Gascon
Keyword(s):  
Gadus Morhua ◽  
Cold Water ◽  
Atlantic Cod ◽  
Management Strategies ◽  
Extreme Environments ◽  
Eastern Canada ◽  
Intensive Exploitation ◽  
Growth Production ◽  
Marked Decline ◽  
Size At Age

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 stocks are examined, size-temperature relationships are not as clear if the analysis is restricted to cold-water stocks, possibly because of differences in food availability. Biological production varies from year to year and among stocks and should be taken into consideration when managing fisheries in variable or extreme environments.

Nearshore settlement and localized populations of age 0 Atlantic cod (Gadus morhua) in shallow coastal waters of Newfoundland

1998 ◽  
Vol 55 (6) ◽  
pp. 1317-1327 ◽  
Author(s):  
Scott M Grant ◽  
Joseph A Brown
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Indirect Evidence ◽  
Suitable Habitat ◽  
Site Variation ◽  
Mean And Variance ◽  
Eelgrass Habitat ◽  
The Mean ◽  
Catch Rates ◽  
Density Dependent Habitat Selection

Mark-recapture experiments and seasonal sampling were carried out to examine the nearshore movements, abundance, and behaviour patterns of age 0 Atlantic cod (Gadus morhua) in eelgrass (Zostera marina) and no-eelgrass habitat in Trinity Bay, Newfoundland, during 1994 and 1995. Cod remained localized, not moving further than a few hundred metres in eelgrass and no-eelgrass habitats for several weeks after settling from a pelagic habit, and may remain localized during their first winter. Observations from this study of bulk movements of marked and unmarked cod, high within-site variation in catch rates during the day, and significant day-night differences in the mean and variance of catch data, combined with results from related studies, provide indirect evidence that age 0 cod shoal during the day and disperse at night within the study area. Behaviour patterns exhibited by age 0 cod (restricted nearshore movements, diurnal shoaling, and preference for structurally complex habitat) are mechanisms for predator avoidance, suggesting that predation risk is high in coastal Newfoundland. A significant increase in abundance of age 0 cod in less suitable habitat (no-eelgrass cover) when settlement strength was high is consistent with the hypothesis of density-dependent habitat selection.

What Can Be Learned from the Collapse of a Renewable Resource? Atlantic Cod, Gadus morhua, of Newfoundland and Labrador

1994 ◽  
Vol 51 (9) ◽  
pp. 2126-2146 ◽  
Author(s):  
Jeffrey A. Hutchings ◽  
Ransom A. Myers
Keyword(s):  
Newfoundland And Labrador ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Renewable Resource ◽  
Fishing Effort ◽  
The Past ◽  
Northern Cod ◽  
Population Sustainability ◽  
Catch Rates ◽  
Adult Abundance

Temporal changes in demography, population sustainability, and harvest rates support the hypothesis that overexploitation precipitated the commercial extinction of northern cod, Gadus morhua, off Newfoundland and Labrador in 1992. Annual estimates of realized population growth (r) indicate that the stock was rarely sustainable at the age-specific survival and fecundity rates experienced since 1962. A twofold decline in annual survival probabilities in the 1980s was concomitant with increased inshore and offshore fishing effort, declining catch rate, and spatial shifts in gillnetting effort from areas of low (inshore) to high (offshore) catch rates. We reject hypotheses that attribute the collapse of northern cod to environmental change. Water temperature was associated neither with juvenile nor adult abundance nor with adult distribution by depth. Harvests equivalent to those of the past decade were sustainable in the nineteenth and early twentieth centuries in a considerably colder environment. An updated analysis of previous work indicates that salinity has little effect on recruitment. We conclude that the collapse of northern cod can be attributed solely to overexploitation and that population sustainability indices such as r provide a means by which the susceptibility and resilience of exploited populations can be assessed and their probability of commercial extinction reduced.

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