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.

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.

scholarly journals Histological analysis invalidates macroscopically determined maturity ogives of the Kattegat cod (Gadus morhua) and suggests new proxies for estimating maturity status of individual fish

2006 ◽  
Vol 63 (3) ◽  
pp. 485-492 ◽  
Author(s):  
F. Vitale ◽  
H. Svedäng ◽  
M. Cardinale
Keyword(s):  
Gadus Morhua ◽  
Histological Analysis ◽  
Spawning Season ◽  
Age Classes ◽  
Data Set ◽  
Histological Techniques ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Correct Estimation ◽  
Spawning Biomass

Abstract Assessment and management of fish populations currently rely on correct estimation of the spawning-stock biomass (SSB), which is based on accurate maturity ogives of the population. Although maturity ogives are usually calculated through macroscopic evaluation of the gonads, histology is generally considered to be more accurate. Here we show that the macroscopic analysis consistently overestimates the proportion of mature females for all age classes in Kattegat cod. The resulting bias showed minimum values for all age classes about a month before the spawning season. Consequently, estimation of the incidence of maturation in females several months before or after the spawning season can only be accurate using histological techniques. Further, the observed bias was used to reconstruct a historical data set of maturity ogives of Kattegat cod. The results showed that female spawning biomass (FSB) might have been overestimated by up to 35%. However, as histological analysis is considered a laborious procedure, proxies of maturity status were sought. It was indicated that the gonadosomatic and hepatosomatic indices may serve as robust proxies for discriminating mature females from immature, thus greatly enhancing the accuracy of the macroscopic maturity evaluation of cod gonads when histological analysis is lacking.

Re-evaluating Atlantic cod mortality including lobster bycatch: where could we be today?

2020 ◽  
Vol 77 (6) ◽  
pp. 1049-1058 ◽  
Author(s):  
Robert Boenish ◽  
Yong Chen
Keyword(s):  
Gadus Morhua ◽  
Gulf Of Maine ◽  
Atlantic Cod ◽  
Homarus Americanus ◽  
Small Scale ◽  
Stock Biomass ◽  
Stock Assessments ◽  
Spawning Stock ◽  
Assessment Bias ◽  
Related Mortality

Full accounting of fisheries mortality is one of the most tractable ways to improve stock assessments. However, it can be challenging to obtain in cases when missing catch comes from small-scale nontarget fisheries unrequired to report incidental catch. Atlantic cod (Gadus morhua) in the Gulf of Maine (GoM), USA, once served as a regionally important fishery, but has been serially depleted to <5% of historic spawning stock biomass. Recent management efforts to rebuild GoM cod have largely failed. We test the hypothesis that unaccounted bycatch of Atlantic cod in the Maine American lobster (Homarus americanus) fishery is a substantial missing piece in the GoM Atlantic cod assessment. We integrated multiple scenarios of hind-casted discards into the two accepted regional cod assessment models from 1982 to 2016. Incorporation of discards improved the assessment bias for both models (10%–15%), increased estimates of spawning stock biomass (4%), and decreased estimates of fishing mortality (9%). A novel evaluation of longitudinal model bias suggests that alternative modelling approaches or specifications may be warranted. We highlight the importance of accounting for all fishery-related mortality and the need for methods to deliver more comprehensive estimates from both target and nontarget fisheries.

Potential effects of maternal factors on spawning stock–recruitment relationships under varying fishing pressure

1999 ◽  
Vol 56 (10) ◽  
pp. 1882-1890 ◽  
Author(s):  
Beth Scott ◽  
Gudrun Marteinsdottir ◽  
Peter Wright
Keyword(s):  
Gadus Morhua ◽  
Reproductive Output ◽  
Atlantic Cod ◽  
Reproductive Potential ◽  
Fishing Pressure ◽  
Age Composition ◽  
Standard Population ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Stock Recruitment

The use of spawning stock biomass as a direct measure of reproductive potential may not be valid because of age- or size-specific differences in fecundity and the effect of maternal size and condition on offspring viability. In this study, we examine the potential significance of these effects using modelled Atlantic cod (Gadus morhua) populations. We quantify how changes in the age composition of the spawning stock, due to a range of fishing pressures and under different stock-recruitment relationships, could influence the reproductive output. Quantitative comparisons were made between a "standard" population where all age-classes only suffer natural instantaneous mortality (M = 0.2) and populations that suffer increasing levels of fishing pressure (F = 0.0-1.0). The results of the modelling exercise suggests that if the effects of the loss of more fecund older/larger individuals in the population are not considered, the number of potential recruits produced by populations under higher levels of fishing mortality could be overestimated by as much as 60%. When age/size-related maternal effects on egg viability are also considered, the amount of potential recruits can be overestimated by a further 10% in the heavily exploited populations.

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.

Effects of sex, stock, and environment on the shape of known-age Atlantic cod (Gadus morhua) otoliths

2004 ◽  
Vol 61 (2) ◽  
pp. 158-167 ◽  
Author(s):  
M Cardinale ◽  
P Doering-Arjes ◽  
M Kastowsky ◽  
H Mosegaard
Keyword(s):  
Shape Analysis ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fourier Descriptors ◽  
Faroe Islands ◽  
Stock Identification ◽  
Relative Importance ◽  
Age Classes ◽  
Otolith Shape ◽  
Left And Right

The effects of sex, stock, and environment on the shape of known-age Atlantic cod (Gadus morhua) otoliths from the Faroe Islands were investigated. Moreover, the feasibility of otolith shape analysis for stock identification was evaluated. The shape was described by using several normalized Fourier descriptors and morphometric variables. There were no consistent differences between the left and right otoliths and between sexes within different age classes, stocks, and environments. With our experimental design, we could evaluate the relative importance of genetic and environmental conditions (water temperature and diet regime) on otolith shape and morphometrics. Using otolith shape, cod individuals were significantly separated into Bank and Plateau stocks. Total classification success was between 79% and 85% between stocks and between 85% and 96% between environments for the different age classes. The significant differences in otolith shape between Faroe Bank and Faroe Plateau cod stocks provided a phenotypic basis for stock separation. Stock and environmental influences were substantial in determining the shape of cod otoliths.

Otolith growth and zone formation during first maturity and spawning of Atlantic cod (Gadus morhua)

2020 ◽  
Vol 77 (1) ◽  
pp. 113-123 ◽  
Author(s):  
Christian Irgens ◽  
Arild Folkvord ◽  
Håkon Otterå ◽  
Olav S. Kjesbu
Keyword(s):  
Gadus Morhua ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Somatic Growth ◽  
Otolith Growth ◽  
Zone Formation ◽  
Stock Biomass ◽  
Tank Experiment ◽  
The Individual ◽  
First Maturity

Specific impacts of somatic growth, sexual maturation, and spawning events on otolith zone formation in Atlantic cod (Gadus morhua) were assessed in a 33-month tank experiment, using Barents Sea cod and Norwegian coastal cod. High and low feeding ration combinations were used to mimic environmental stressors in the field. For both stocks, apparent macrostructural “spawning zones” in otoliths are registered in statutory stock monitoring programs to estimate age at maturity, thus adding key information to stock biomass assessments. We found that substantial energy investments in reproduction caused reductions in otolith growth and altered proportional width between translucent and opaque zones. These effects, however, were only statistically significant among individuals with high reproductive investments, while otoliths from individuals with low investments did not differ from the otoliths for immatures. Reproduction may thus not necessarily induce spawning zones, and alternatively, spawning zones may not necessarily reflect reproduction. Altogether, this suggests that the individual energy level, as a premise for metabolic activity, plays a key role in the formation of such zones and thus is related to environmental conditions.

scholarly journals Prerecruit survival and recruitment of northern Gulf of St Lawrence Atlantic cod

2008 ◽  
Vol 65 (6) ◽  
pp. 946-952 ◽  
Author(s):  
Daniel E. Duplisea ◽  
Dominique Robert
Keyword(s):  
Linear Models ◽  
Atlantic Cod ◽  
Information Criterion ◽  
Factors Affecting ◽  
Control Rules ◽  
Strategy Evaluation ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Long Time ◽  
Parsimonious Model

Abstract Duplisea, D. E., and Robert, D. 2008. Prerecruit survival and recruitment of northern Gulf of St Lawrence Atlantic cod. – ICES Journal of Marine Science, 65: 946–952. Recruitment (R) of exploited marine fish populations is usually modelled exclusively as a function of spawning-stock biomass (SSB). A problem arising when modelling over long time-series is that the nature of the R–SSB relationship is unlikely to be stationary. Changes are often interpreted as productivity regime shifts and are linked to alterations in prerecruit survival rate. We examine the role of environment and predation by fish and harp seals as factors affecting the R–SSB relationship in the northern Gulf of St Lawrence cod, by fitting linear models using combinations of covariates to explain cod prerecruit survival. The most parsimonious model (based on a Bayesian Information Criterion, BIC) included cod, mackerel, and temperature, whereas redfish and seals did not appear in any of the best-fit models. Recruitment models derived from this analysis could be used in operating models for management strategy evaluation simulations for northern Gulf cod, so one could develop harvest control rules that are robust to changes in recruitment productivity regimes.

The role of spawning stock in formation of recruitment of northeast atlantic cod Gadus morhua

2006 ◽  
Vol 46 (1) ◽  
pp. 74-82 ◽  
Author(s):  
V. M. Borisov ◽  
A. A. Elizarov ◽  
V. D. Nesterov
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Northeast Atlantic ◽  
Spawning Stock
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