Nutrient Flex onto the Labrador Shelf from Hudson Strait and its Biological Consequences

1983 ◽  
Vol 40 (10) ◽  
pp. 1692-1701 ◽  
Author(s):  
W. H. Sutcliffe Jr. ◽  
R. H. Loucks ◽  
K. F. Drinkwater ◽  
A. R. Coote
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Population Analysis ◽  
Water Discharge ◽  
Nutrient Supply ◽  
Fish Abundance ◽  
Residual Circulation ◽  
Yearly Variation ◽  
Commercial Fish ◽  
Time Required

Fish abundance, based upon commercial fish catches and numbers offish-feeding birds, is shown to increase southward along the Labrador Shelf from Hudson Strait. Also, yearly abundance of Labrador Atlantic cod (Gadus morhua) using virtual population analysis is shown to be closely correlated with salinity changes at Station 27 off St. John's, Newfoundland. We suggest these observations are related to physical oceanographic events originating within Hudson Strait. Analysis of available data indicates nutrient enrichment of the surface waters through physical mixing in Hudson Strait. These waters are carried by the residual circulation onto the northern Labrador Shelf. Our interpretation of the southward increase in fish abundance is that fish production develops downstream of the area of nutrient injection due to the southward flow of the Labrador Current coupled with the time required for food chain development. The yearly variation of cod is interpreted as arising from the variation of the nutrient supply, which is itself correlated with salinity. The fresh water discharge into Hudson Bay which eventually flows out through Hudson Strait and onto the Labrador Shelf appears to suppress mixing and hence years of higher discharge would tend to decrease the nutrient supply.

Large effective population size and temporal genetic stability in Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

2010 ◽  
Vol 67 (10) ◽  
pp. 1585-1595 ◽  
Author(s):  
Nina Overgaard Therkildsen ◽  
Einar Eg Nielsen ◽  
Douglas P. Swain ◽  
Jes Søe Pedersen
Keyword(s):  
Genetic Variability ◽  
Population Size ◽  
Effective Population Size ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Population Decline ◽  
Allelic Diversity ◽  
Estimation Methods ◽  
Effective Population ◽  
Commercial Fish

Worldwide, many commercial fish stocks have experienced dramatic declines due to overfishing. Such fisheries-induced population reductions could potentially erode the genetic diversity of marine fish populations. Based on analyses of DNA extracted from archived and contemporary samples, this paper compares the genetic variability at nine microsatellite loci in a Canadian population of Atlantic cod ( Gadus morhua ) over 80 years, spanning from before the fishery intensified to now when the population is at historically low abundance. Extensively validated genetic data from the temporally spaced samples were used to estimate the effective population size. Over the period, we observed no loss of either heterozygosity or allelic diversity. Several of the estimation methods applied could not distinguish the effective population size from infinity, and the lower 95% confidence limit on estimates was generally >500, suggesting that the effective population size is probably considerably larger than this. Hence, it appears that the southern Gulf of St. Lawrence cod stock has maintained genetic variability to sustain future evolution despite a dramatic population decline.

Covariation between grey seal (Halichoerus grypus) abundance and natural mortality of cod (Gadus morhua) in the southern Gulf of St. Lawrence

2005 ◽  
Vol 62 (9) ◽  
pp. 1991-2000 ◽  
Author(s):  
G A Chouinard ◽  
D P Swain ◽  
M O Hammill ◽  
G A Poirier
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Population Analysis ◽  
Halichoerus Grypus ◽  
Natural Mortality ◽  
Grey Seal ◽  
Synthetic Populations ◽  
Time Period ◽  
Abundance Indices

More than 10 years after the collapse of Atlantic cod (Gadus morhua) fisheries in Canada, the role of increased seal populations in the decline and lack of recovery of the stocks continues to be discussed. Using removals and abundance indices from synthetic populations, we found that sequential population analysis can uncover trends in natural mortality. We used this approach to examine variation in natural mortality (M) of southern Gulf of St. Lawrence cod. M increased from the late 1970s to the mid-1990s but declined slightly recently. Results were consistent with previous work indicating that M increased in the 1980s. Changes in estimated M for this cod stock matched fluctuations in grey seal (Halichoerus grypus) abundance. The increase in grey seal abundance from the late 1970s to the mid-1990s corresponded with the increase in estimated M of cod over this time period. The correspondence between seal abundance and M of cod supports the hypothesis that seal predation may be a cause of increased M. However, the diet information available suggests that seals consume mainly juvenile cod, whereas our evidence for an increase in M is for larger cod (ages 3 years and older).

scholarly journals Effects of photoperiod and exercise on growth, liver size, and age at puberty in farmed Atlantic cod (Gadus morhua L.)

2006 ◽  
Vol 63 (2) ◽  
pp. 355-364 ◽  
Author(s):  
Ø. Karlsen ◽  
B. Norberg ◽  
O.S. Kjesbu ◽  
G.L. Taranger
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Continuous Light ◽  
Gonadal Development ◽  
Natural Light ◽  
Food Conversion ◽  
Liver Size ◽  
Time Required ◽  
Loss Of Appetite ◽  
Food Conversion Efficiency

Abstract Sexual maturation in Atlantic cod (Gadus morhua) results in loss of appetite and weight during spawning, leads to increased production time required to reach desired harvest size, and results in greater mortality and reduced food conversion efficiency. Thus, methods to stop or delay maturation are urgently needed. In the present study, the effect of continuous light (LL) treatment on maturation was tested in combination with different exercise levels in seawater tanks compared with controls under natural light. LL treatment in lightproof tanks arrested gonadal development for at least 8 months. Exercising Atlantic cod by forcing them to swim with 0, 0.5, or 1 body length per second from the summer solstice had no effect on incidence of maturation either under natural light or under LL. Growth was enhanced in the LL groups compared with the NL groups, mainly as a result of the weight loss of the NL groups during spawning.

scholarly journals Estimating catch-at-age by combining data from different sources

2005 ◽  
Vol 62 (6) ◽  
pp. 1377-1385 ◽  
Author(s):  
David Hirst ◽  
Geir Storvik ◽  
Magne Aldrin ◽  
Sondre Aanes ◽  
Ragnar Bang Huseby
Keyword(s):  
Gadus Morhua ◽  
Ad Hoc ◽  
Atlantic Cod ◽  
Data Types ◽  
Commercial Fish ◽  
Bayesian Hierarchical ◽  
Length Relationship ◽  
Setting Process ◽  
Combining Data ◽  
Almost All

Estimating the catch-at-age of commercial fish species is an important part of the quota-setting process for many different species and almost all countries with a fishing fleet. Current procedures are usually very time-consuming and somewhat ad hoc, and the estimates have no measure of uncertainty. We previously developed a method for catch-at-age of Norwegian Atlantic cod (Gadus morhua), but this only considered aged fish sampled randomly from random hauls. In most countries, the sampling scheme is not so simple. There are usually a very large number of length-only samples from which the age must be estimated using an age–length relationship, and often some or all of the age samples are collected from data that are first stratified by length. This adds considerably to the difficulties in the estimation. In this paper, we model the three different kinds of data simultaneously using a development of our earlier Bayesian hierarchical model. This enables us to obtain estimates of the catch-at-age with appropriate uncertainty and also to provide advice on how best to sample data in the future. The data types are random samples of age, length, and weight; age and weight stratified by length; and length only.

Salinity and Recruitment of Atlantic Cod (Gadus morhua) in the Newfoundland Region

1993 ◽  
Vol 50 (8) ◽  
pp. 1599-1609 ◽  
Author(s):  
Ransom A. Myers ◽  
Kenneth F. Drinkwater ◽  
Nicholas J. Barrowman ◽  
James W. Baird
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Population Analysis ◽  
Grand Banks ◽  
The North ◽  
Virtual Population ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Recruitment Time

Recruitment predictions for Atlantic cod (Gadus morhua) in the North Atlantic, based upon a previously published regression with salinity, are found to be well correlated with recent recruitment estimates from both virtual population analysis and those derived from research surveys. The addition of spawning stock biomass in the regression significantly increased the percentage of the variance accounted for in the recruitment time series. A similar relationship between recruitment and salinity was found for two nearby stocks (southern Grand Banks and St. Pierre Bank). Oceanographic and food chain mechanisms that might be responsible for a link between salinity and recruitment are discussed.

Measuring changes in the direction and magnitude of size-selective mortality in a commercial fish population

2002 ◽  
Vol 59 (2) ◽  
pp. 361-371 ◽  
Author(s):  
A F Sinclair ◽  
D P Swain ◽  
J M Hanson
Keyword(s):  
Gadus Morhua ◽  
Slow Growth ◽  
Atlantic Cod ◽  
Fish Population ◽  
Disruptive Selection ◽  
Commercial Fishery ◽  
Fishing Mortality ◽  
Selective Mortality ◽  
Commercial Fish ◽  
Size Selection

A 28-year time series (1971–1998) of backcalculated length-at-age was used to investigate changes in the direction and magnitude of size-selective mortality of prerecruit and adult Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence, Canada. Size selection changed from favouring fast growth in the 1970s to favouring slow growth in the late 1980s and 1990s. There was an intervening period of disruptive selection where fast and slow growth was favoured while intermediate growth rates were selected against. The intensity of size selection declined at the end of the study period following the closure of the commercial fishery. These different forms of selection (positive directional, negative directional, and disruptive selection) can all be accounted for by the sharply dome-shaped curve of fishing mortality against length observed in the fishery.

scholarly journals Increased environmentally driven recruitment variability decreases resilience to fishing and increases uncertainty of recovery

2014 ◽  
Vol 71 (6) ◽  
pp. 1507-1514 ◽  
Author(s):  
Anna Kuparinen ◽  
David M. Keith ◽  
Jeffrey A. Hutchings
Keyword(s):  
Gadus Morhua ◽  
Environmental Variability ◽  
Atlantic Cod ◽  
Major Effect ◽  
High Productivity ◽  
Spawning Stock ◽  
Recruitment Variability ◽  
Alternative Scenarios ◽  
Time Required ◽  
Population Resilience

Abstract Independent of the effects of spawning-stock biomass (SSB), environmental variability in juvenile production, driven by factors such as temperature and food supply, have considerable potential to influence population resilience to fishing and depletion. Here, we analyse 18 time-series of Atlantic cod (Gadus morhua) stocks and empirically estimate this “environmental variability” in recruit-per-spawner (RPS) ratios. We then investigate the role of environmental recruitment variability on population resilience to fishing and ability to recover following depletion. To this end, cod population dynamics are simulated through a period of fishing, followed by a period of recovery, with alternative scenarios of recruitment variability and autocorrelation within it. The major effect of environmental recruitment variability is manifested through uncertainty. Firstly, the higher the recruitment variability, the shorter and less variable the time required for the population to decline below 15% of its carrying capacity, K. Secondly, higher variability leads to higher uncertainty in recovery time. Both these patterns are further strengthened by autocorrelation. Our findings suggest that increased environmental recruitment variability decreases resilience to fishing and increases uncertainty in recovery, thus challenging some traditional views that variability confers high productivity and rapid ability to recover from collapse.

A Novel Method for Predicting Anisakid Nematode Infection of Atlantic Cod Using Rough Set Theory

2018 ◽  
Vol 81 (3) ◽  
pp. 502-508
Author(s):  
Barbara Wąsikowska ◽  
Ewa Sobecka ◽  
Iwona Bielat ◽  
Monika Legierko ◽  
Beata Więcaszek
Keyword(s):  
Set Theory ◽  
Rough Set ◽  
Fish Species ◽  
Gadus Morhua ◽  
Rough Set Theory ◽  
Atlantic Cod ◽  
Production Chain ◽  
Commercial Fish ◽  
Pseudoterranova Decipiens ◽  
Parasite Infections

ABSTRACT Atlantic cod (Gadus morhua L.) is one of the most important fish species in the fisheries industries of many countries; however, these fish are often infected with parasites. The detection of pathogenic larval nematodes is usually performed in fish processing facilities by visual examination using candling or by digesting muscles in artificial digestive juices, but these methods are both time and labor intensive. This article presents an innovative approach to the analysis of cod parasites from both the Atlantic and Baltic Sea areas through the application of rough set theory, one of the methods of artificial intelligence, for the prediction of food safety in a food production chain. The parasitological examinations were performed focusing on nematode larvae pathogenic to humans, e.g., Anisakis simplex, Contracaecum osculatum, and Pseudoterranova decipiens. The analysis allowed identification of protocols with which it is possible to make preliminary estimates of the quantity and quality of parasites found in cod catches before detailed analyses are performed. The results indicate that the method used can be an effective analytical tool for these types of data. To achieve this goal, a database is needed that contains the patterns intensity of parasite infections and the conditions of commercial fish species in different localities in their distributions.

Spatial scales of variability in cod recruitment in the North Atlantic

1995 ◽  
Vol 52 (9) ◽  
pp. 1849-1862 ◽  
Author(s):  
R. A. Myers ◽  
G. Mertz ◽  
N. J. Barrowman
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Spatial Scales ◽  
Population Analysis ◽  
Estimation Error ◽  
Commercial Catch ◽  
The North ◽  
The North Atlantic

We reexamine the hypothesis that there are large-scale (thousands of kilometres) patterns of recruitment of Atlantic cod (Gadus morhua) in the North Atlantic. Previous analyses have used sequential population analysis to reconstruct population histories; however, these methods are subject to a variety of biases and rely on the accuracy of commercial catch-at-age data. Several different studies have arrived at conflicting interpretations using virtually the same data. Here we analyze alternative data from research surveys using statistical methods that explicitly account for estimation error and we also employ detrended sequential population analysis. We conclude that the spatial scale of recruitment correlations generally does not exceed 500 km.

Is spawner biomass a sensitive measure of the reproductive and recruitment potential of Northeast Arctic cod?

1998 ◽  
Vol 55 (7) ◽  
pp. 1766-1783 ◽  
Author(s):  
C Tara Marshall ◽  
Olav Sigurd Kjesbu ◽  
Nathalia A Yaragina ◽  
Per Solemdal ◽  
Øyvind Ulltang
Keyword(s):  
Egg Production ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Population Analysis ◽  
Reproductive Potential ◽  
Fish Stocks ◽  
Virtual Population ◽  
Individual Scale ◽  
The Individual ◽  
The Relationship

The assumption that spawner biomass is directly proportional to total egg production by fish stocks underlies most spawner-recruit relationships. Despite its importance, this assumption is largely untested. Data describing the reproductive potential of Northeast Arctic (NEA) Atlantic cod (Gadus morhua) were used to test the proportionality assumption for a period showing strong variation in condition and abundance of spawners. At the individual scale, relative fecundity varied with length and condition. This decreases the likelihood that the proportionality assumption is valid. At the stock level, total egg production was estimated (1985-1996) using acoustic estimates of total abundance and demographic information from trawl sampling in combination with year-specific fecundity-length relationships. For NEA cod, spawner biomass estimated by virtual population analysis (VPA) was not proportional to total egg production. Compared with VPA-based estimates of spawner biomass, total egg production is an improved index of recruitment potential because (i) the magnitude of variation observed in total egg production was closer to that observed in recruitment and (ii) the relationship between recruitment at age 1 and total egg production approaches the origin. The results suggest that further progress in explaining recruitment variation will be achieved using more sensitive measures of the true reproductive potential of the stock.

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