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.

scholarly journals Cod recruitment is strongly affected by climate when stock biomass is low

2005 ◽  
Vol 62 (3) ◽  
pp. 339-343 ◽  
Author(s):  
Keith M. Brander
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Environmental Variability ◽  
Atlantic Cod ◽  
Management Strategies ◽  
Pooled Analysis ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The North Atlantic

Abstract Stocks of Atlantic cod (Gadus morhua) have been declining over much of the North Atlantic for the past 30 years, owing to a combination of overfishing and adverse changes in their environment. In a previous study, environmental effects were introduced as an extra parameter in the stock-recruit relationship, where they act as a multiplier, independent of the level of spawning-stock biomass (SSB). Using a non-parametric pooled analysis of all cod stocks on the European Shelf south of 62°N, it is shown here that environmental variability (as represented by the North Atlantic Oscillation) only has a significant effect on recruitment when the spawning stock is low. This has implications for fisheries management strategies, and for rates of stock recovery, which will be very dependent on environmental conditions.

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.

Influence of climatic changes on the parasites of Atlantic cod Gadus morhua off coastal Labrador, Canada

2006 ◽  
Vol 80 (2) ◽  
pp. 193-197 ◽  
Author(s):  
R.A. Khan ◽  
C.V. Chandra
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Age Groups ◽  
Climatic Conditions ◽  
Otter Trawl ◽  
Commercial Fishery ◽  
Metazoan Parasites ◽  
Mean Values ◽  
The North

AbstractA study was conducted in 2000 and 2003, following the collapse of the commercial fishery in 1990, to compare metazoan parasites of Atlantic cod Gadus morhua, captured off coastal Labrador, with samples taken in 1980 and 1986. Fish were captured by otter trawl offshore in the North Atlantic Fish Organisation subarea 2J. Parasites were removed from the digestive tract, stained, identified and compared between the different groups. Both the prevalence and mean abundance of trematodes, larval nematodes and E. gadi were significantly lower in fish taken in 2000 and 2003 than in 1980. While mean values of trematodes and nematodes declined in 1986, those of Echinorhynchus gadi remained unchanged in 1986 and 1990. Four-year-old cod sampled in 1990 harboured significantly fewer E. gadi than older age groups. The most commonly occurring trematodes included Podocotylereflexa, Lepidapedon elongatum, Derogenes varicus and Hemiurus levinseni while the larval nematode, Anisakis sp. was predominant. Comparison of offshore samples taken in 2000 and 2003 with others taken in previous years suggests an overall decline of parasites coincident with a change in climatic conditions, the absence of a major food source, namely capelin Mallotus villosus, of cod and ultimately the decline of the Labrador population.

The influence of spatially variable and connected recruitment on complex stock dynamics and its ecological and management implications

2019 ◽  
Vol 76 (6) ◽  
pp. 937-949 ◽  
Author(s):  
Lisha Guan ◽  
Yong Chen ◽  
James A. Wilson ◽  
Timothy Waring ◽  
Lisa A. Kerr ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Temporal Trends ◽  
Substantial Reduction ◽  
Management Implications ◽  
Agent Based ◽  
Stock Biomass ◽  
Spawning Stock ◽  
The Individual

To evaluate the influence of spatially variable and connected recruitments at spawning component scale on complex stock dynamics, a typical agent-based complex stock was modeled based on the Atlantic cod (Gadus morhua) stock in the Gulf of Maine. We simulated three scenarios with different degrees of connectivity (i.e., individual exchange) between the spatially variable recruitments of 36 spawning components within four subpopulations under the stock. Subsequently, the temporal trends were compared for different scenarios in age-1 recruitment, spawning stock biomass, and local depletion proportion of the overall complex stock and the individual subpopulations. Results show that increased recruitment connectivity from 0.1–0.2 to 0.6–0.8 between various components tends to increase the productivity and stability of a complex stock at local and global scales and reduce the proportion of depleted components due to overfishing. Moreover, depletions of less productive components may occur without a substantial reduction in the overall complex stock biomass and recruitment.

Greenland halibut (Reinhardtius hippoglossoides) in the North Atlantic are genetically homogeneous

1997 ◽  
Vol 54 (8) ◽  
pp. 1813-1821 ◽  
Author(s):  
M L Vis ◽  
S M Carr ◽  
W R Bowering ◽  
W S Davidson
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Genetic Distances ◽  
Greenland Halibut ◽  
Western Atlantic ◽  
Grand Banks ◽  
The North ◽  
Greenland Halibut Reinhardtius Hippoglossoides ◽  
The North Atlantic ◽  
Reinhardtius Hippoglossoides

Greenland halibut (Reinhardtius hippoglossoides) have become of great importance to the Canadian fishery since the moratorium on northern cod (Gadus morhua), and an understanding of stock relationships among populations at the northern and southern extremes of their commercial range is crucial for proper management. We compared mitochondrial DNA sequence variation among fish taken from thoughout the Northwest Atlantic (Flemish Pass, the Grand Banks, Davis Strait, and Northwest Greenland) with samples from the Gulf of St. Lawrence, Iceland, and Norway. Within a 401 base pair portion of the cytochrome b gene, 22 genotypes were identified. Three of these occur at frequencies >10% and in the same relative abundances in all samples (except the Gulf of St.Lawrence). Genotype proportions do not differ significantly among samples, and genetic subdivision among samples (measured by the coancestry coefficient theta ) is nil. Genetic distances among samples are not related to geographic distribution: pairwise differences between the Gulf sample and other western Atlantic samples exceed those for trans-Atlantic comparisons. These data suggest that there is sufficient mixing of Greenland halibut, not only within the NAFO regulatory area, but among sites in the North Atlantic generally, to prevent the development or maintenance of genetically independent stocks.

A reanalysis of North Sea plaice spawning-stock biomass using the annual egg production method

2009 ◽  
Vol 66 (9) ◽  
pp. 1999-2011 ◽  
Author(s):  
Cindy J. G. van Damme ◽  
Loes J. Bolle ◽  
Clive J. Fox ◽  
Petter Fossum ◽  
Gerd Kraus ◽  
...  
Keyword(s):  
North Sea ◽  
Egg Production ◽  
Stock Assessment ◽  
Population Analysis ◽  
Spatial Dynamics ◽  
Production Method ◽  
Southern Bight ◽  
The North ◽  
Stock Biomass ◽  
Spawning Stock

Abstract van Damme, C. J. G., Bolle, L. J., Fox, C. J., Fossum, P., Kraus, G., Munk, P., Rohlf, N., Witthames, P. R., and Dickey-Collas, M. 2009. A reanalysis of North Sea plaice spawning-stock biomass using the annual egg production method. – ICES Journal of Marine Science, 66: 1999–2011. Uncertainty about the quality of current virtual population analysis-based stock assessment for North Sea plaice (Pleuronectes platessa) has led to various abundance indices. We compared biomass estimates from the annual egg production (AEP) method with current stock assessments based on catch-at-age to validate the current and historical perception of exploitation. The AEP method was also used to investigate the dynamics of the spatial components of plaice in the North Sea. We corrected for fecundity down-regulation and changes in sex ratio. Estimates from both methods were similar in trend and absolute biomass. On the Dogger Bank, there was a dramatic decline in biomass from 1948 and 1950 to 2004, and in the Southern Bight, the stock appeared to increase from 1987 and 1988 to 2004, although not reaching the historically high levels of 1948 or 1950. The timing of spawning of North Sea plaice does not appear to have changed throughout the period of high exploitation. We conclude that the AEP method is a useful way to hindcast the spatial dynamics of heavily exploited flatfish stocks.

Comparison of the performance of age-structured models with few survey indices

2018 ◽  
Vol 75 (6) ◽  
pp. 2016-2024
Author(s):  
Hiroshi Okamura ◽  
Yuuho Yamashita ◽  
Momoko Ichinokawa ◽  
Shota Nishijima
Keyword(s):  
Stock Assessment ◽  
Population Analysis ◽  
Assessment Model ◽  
Sufficient Information ◽  
Abundance Estimates ◽  
Virtual Population ◽  
Stock Biomass ◽  
Abundance Indices ◽  
Spawning Stock ◽  
Age Structured

Abstract Age-structured models have played an important role in fisheries stock assessment. Although virtual population analysis (VPA) was once the most widely used stock assessment model for when catch-at-age information is available, (hierarchical) statistical catch-at-age analysis (SCAA) is about to take that position. However, the estimation performance of different age-structured models has not been evaluated sufficiently, especially in cases where there are few available abundance indices. We examined the performance of VPA and SCAA using simulation data in which only the abundance indices of spawning stock biomass and recruitment were available. The simulation demonstrated that VPA with the ridge penalty selected by minimizing retrospective bias provided near-unbiased abundance estimates without catch-at-age error and moderately biased estimates with catch-at-age error, whereas SCAA with random-walk selectivity suffered from problems in estimating parameters and population states. Without sufficient information on abundance trends, naïvely using SCAA with many random effects should be done cautiously, and comparing results from various age-structured models via simulation tests will be informative in selecting an appropriate stock assessment model.

Gear-independent patterns of variation in catch of juvenile Atlantic cod (Gadus morhua) in coastal habitats

1998 ◽  
Vol 55 (6) ◽  
pp. 1430-1442 ◽  
Author(s):  
David A Methven ◽  
David C Schneider
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Cohort Size ◽  
Spatial And Temporal Patterns ◽  
Age Classes ◽  
Coastal Habitats ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Depth Gradients ◽  
Spatial Depth

Habitat and size of juvenile Atlantic cod (Gadus morhua) change substantially during the first 3 years after settlement, and hence, cohort size cannot be followed using a single gear. We investigated whether catch could be calibrated across gear types by deploying pairs of gears repeatedly in the same habitat. As expected, size selectivity differed substantially among gears. Trawls and seines generally collected individuals <200 mm. Gillnets and jiggers collected individuals >150 mm. Size modes, corresponding to age-classes, were common to catches of most gears. Highest catches were taken by trawls and seines. Gillnet catches were orders of magnitude lower. Standardized catches could not be calibrated across pairs of gears deployed in the same habitat at approximately the same time. However, it was possible to identify spatial depth gradients and diel changes in catch that were independent of gear. Consistent spatial and temporal patterns across gears were interpreted as characteristic of fish populations, not just of gears. Density in coastal habitats was higher at night and was higher at 4-7 m than at greater depths. These results, in conjunction with other studies, establish that coastal depths of 4-7 m represent the centre, and not the edge, of the distribution of age 0 cod in Newfoundland during autumn. Hence nursery areas during the early 1990s, a time of historically low spawning stock biomass, must be identified as the coastal zone, not offshore.

Temperature and the recruitment of Atlantic cod (Gadus morhua)

1999 ◽  
Vol 56 (11) ◽  
pp. 2069-2077 ◽  
Author(s):  
B Planque ◽  
T Frédou
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Cold Water ◽  
Atlantic Cod ◽  
The Other ◽  
Warm Water ◽  
The North ◽  
The North Atlantic ◽  
Interannual Fluctuations ◽  
The Relationship

Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock has proven to be problematic and has resulted in recurrent controversy between studies supporting either hypothesis. In the present study, we examine the relationship between interannual changes in temperature and variation in recruitment for nine Atlantic cod (Gadus morhua) stocks in the North Atlantic. We show that for individual stocks, the relationship often appears weak and statistically not significant. On the other hand, by combining in a single metaanalysis the results from individual stocks, we demonstrate that recruitment of Atlantic cod is linked to interannual fluctuations in temperature in such a way that for stocks located in warm water the relationship is negative, for stocks located in cold water the relationship is positive, and there is no relationship for stocks located in the middle of the temperature range.

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