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 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.

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.

Predicting the recruitment strength of an annual squid stock: Loligo gahi around the Falkland Islands

2000 ◽  
Vol 57 (12) ◽  
pp. 2479-2487 ◽  
Author(s):  
David J Agnew ◽  
Simeon Hill ◽  
John R Beddington
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Negative Relationship ◽  
Sea Surface ◽  
Falkland Islands ◽  
Factors Affecting ◽  
Model Combining ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Faster Development

Two cohorts of Loligo gahi recruit to the fishery around the Falkland Islands, the first in summer and the second in autumn-winter. We investigated factors affecting recruitment to these cohorts using 13 years of data (1987-1999). The first evidence for density-dependent effects on recruitment in a squid population is reported, with very high spawning stock biomass leading to a reduction in recruitment in both cohorts. October sea surface temperature was negatively correlated with recruitment to the second cohort 6 months later, and a linear model explained 66% of the variance in recruitment strength. A model combining sea surface temperature and spawning stock size explained 77% of the variance. Thus, low October temperatures and moderate stock sizes lead to higher recruitment the following year than high October temperatures and high stock sizes. A strong negative relationship was also found between sea surface temperature in May and the timing of recruitment to the first cohort the following January-February, suggesting that higher temperatures lead to faster development of embryos or paralarvae and earlier recruitment to the fishery. A predictive model of recruitment size and timing should enable better management of L. gahi.

Factors affecting frog density in the Solomon Islands

2016 ◽  
Vol 22 (3) ◽  
pp. 223 ◽  
Author(s):  
Patrick Pikacha ◽  
Chris Filardi ◽  
Clare Morrison ◽  
Luke Leung
Keyword(s):  
Forest Type ◽  
Solomon Islands ◽  
Distance Sampling ◽  
Information Criterion ◽  
Forest Types ◽  
Lowland Forest ◽  
Factors Affecting ◽  
High Conservation ◽  
Parsimonious Model ◽  
Species Being

This paper identifies some important factors affecting the density of frogs in the Solomon Islands. Distance sampling was used to estimate frog density in all major frog habitats across 13 islands. A total of 109 transects, covering five forest types (coastal, freshwater marshes, lowland forest, hill or ridge, and montane forest) were used, with 16 species being sampled. Estimated densities ranged from 2 ha–1 to 675 ha–1. Akaike’s Information Criterion (AIC) was used to select the most parsimonious model of frog density. Factors identified in the selected model to predict density of Batrachylodes elegans, Batrachylodes vertebralis, Ceratobatrachus guentheri, Discodeles bufoniformis, Discodeles guppyi, Discodeles malukuna, Litoria thesaurensis, Palmatorappia solomonis, Platymantis guppyi, Platymantis neckeri, Platymantis solomonis, Platymantis sp., Platymantis weberi, and Rana kreffti were island, landform, and forest type. Additional factors such as disturbance, leaf litter, shrub, and understorey were also described by the regression model as predictors of density for B. vertebralis, C. guentheri, D. guppyi, D. malukuna, Pal. solomonis, P. guppyi, and R. kreffti. These findings have important management implications for the conservation of frogs in the Solomon Islands. High densities of most species were strongly related with forest type and low disturbance. Preservation of rainforest, in especially high conservation value old-growth forests, is imperative to protecting these species.

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.

scholarly journals A review of early life history dynamics of Barents Sea cod (Gadus morhua)

2014 ◽  
Vol 71 (8) ◽  
pp. 2064-2087 ◽  
Author(s):  
Geir Ottersen ◽  
Bjarte Bogstad ◽  
Natalia A. Yaragina ◽  
Leif Christian Stige ◽  
Frode B. Vikebø ◽  
...  
Keyword(s):  
Early Life ◽  
Gadus Morhua ◽  
Barents Sea ◽  
Atlantic Cod ◽  
Prey Availability ◽  
Life Stage ◽  
Early Life History ◽  
Sea Temperature ◽  
Spawning Stock ◽  
Long Time

Abstract The Barents Sea stock of Atlantic cod (Gadus morhua) is currently the world's largest cod stock. It is also a stock for which long time-series are available and much research has been carried out. With this review, we wish to present an overview and evaluation of the knowledge on Barents Sea cod early life dynamics. The focus is on the effects of the biotic and abiotic drivers, which jointly determine the strength of a year class. A stage-by-stage approach is employed. We summarize and assess the significance of the different processes described in the literature to be at play during each specific life stage, from spawning stock, through eggs, larvae, and pelagic juvenile, to demersal juvenile and recruitment at age 3. Also Russian work is included, some of which until now has not been available to non-Russian readers. Physical drivers examined include sea temperature, advection and dispersal, wind-induced turbulence, and light. Biotic mechanisms studied range from maternal effects and skipped spawning in the adult stock through egg quantity and quality, to prey availability for the larvae and effects of cannibalism on the juveniles. Finally, we evaluate the main hypotheses put forth by Johan Hjort a hundred years ago in the light of our synthesis of present knowledge. A main conclusion is that it is unlikely that there is any one single life stage during which recruitment with any generality is determined.

scholarly journals Large scale, synchronous variability of marine fish populations driven by commercial exploitation

2016 ◽  
Vol 113 (29) ◽  
pp. 8248-8253 ◽  
Author(s):  
Kenneth T. Frank ◽  
Brian Petrie ◽  
William C. Leggett ◽  
Daniel G. Boyce
Keyword(s):  
Marine Fish ◽  
North Atlantic ◽  
Large Scale ◽  
Atlantic Cod ◽  
Spatial Scales ◽  
Ocean Dynamics ◽  
Fish Populations ◽  
Fishing Mortality ◽  
Stock Biomass ◽  
Spawning Stock

Synchronous variations in the abundance of geographically distinct marine fish populations are known to occur across spatial scales on the order of 1,000 km and greater. The prevailing assumption is that this large-scale coherent variability is a response to coupled atmosphere–ocean dynamics, commonly represented by climate indexes, such as the Atlantic Multidecadal Oscillation and North Atlantic Oscillation. On the other hand, it has been suggested that exploitation might contribute to this coherent variability. This possibility has been generally ignored or dismissed on the grounds that exploitation is unlikely to operate synchronously at such large spatial scales. Our analysis of adult fishing mortality and spawning stock biomass of 22 North Atlantic cod (Gadus morhua) stocks revealed that both the temporal and spatial scales in fishing mortality and spawning stock biomass were equivalent to those of the climate drivers. From these results, we conclude that greater consideration must be given to the potential of exploitation as a driving force behind broad, coherent variability of heavily exploited fish species.

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 Evaluating the parameters of a MSY control rule for the Bristol Bay, Alaska, stock of red king crabs

2007 ◽  
Vol 64 (5) ◽  
pp. 995-1005 ◽  
Author(s):  
M. S. M. Siddeek ◽  
J. Zheng
Keyword(s):  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Stochastic Simulations ◽  
Bristol Bay ◽  
Control Rule ◽  
Single Sex ◽  
Control Rules ◽  
Stock Biomass ◽  
Spawning Stock ◽  
Spawning Potential Ratio

Abstract Siddeek, M. S. M. and Zheng, J. 2007. Evaluating the parameters of a MSY control rule for the Bristol Bay, Alaska, stock of red king crabs. – ICES Journal of Marine Science, 64: 995–1005. A maximum sustainable yield (MSY) control rule, which defines the level of overfishing, and determines the control rule parameters based on an age-, sex-, and size-structured assessment for Bristol Bay red king crabs (Paralithodes camtschaticus) is developed. Fx% (F corresponding to x% spawning potential ratio) is used as a proxy for FMSY and a minimum spawning-stock biomass (to open the fishery) for incorporation into the MSY control rule. The performance of the selected MSY control rule and the associated target control rule is evaluated using stochastic simulations. F50% is a reasonable proxy for FMSY when effective spawning biomass is used as the stock biomass in the stock-recruitment relationship. This method with appropriate modifications might be used for determining biological reference points and developing control rules for any crustacean stock with discrete growth, complex reproductive dynamics, and single sex exploitation.

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