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.

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.

scholarly journals Regional variation in otolith geochemistry of juvenile Atlantic cod (Gadus morhua) in coastal Newfoundland

2016 ◽  
Vol 73 (10) ◽  
pp. 1507-1519 ◽  
Author(s):  
Ryan R.E. Stanley ◽  
Claudio DiBacco ◽  
Simon R. Thorrold ◽  
Paul V.R. Snelgrove ◽  
Corey J. Morris ◽  
...  
Keyword(s):  
Gadus Morhua ◽  
Environmental Variability ◽  
Atlantic Cod ◽  
Environmental Influence ◽  
Spatial Scales ◽  
Early Life History ◽  
Otolith Chemistry ◽  
Geographic Patterns ◽  
Assignment Success ◽  
Scale Classification

We examined spatial variation in otolith geochemistry as a natural tag in juvenile Atlantic cod (Gadus morhua) to resolve geographic patterns during early life history. Individuals from 54 inshore sites spanned five embayments in eastern Newfoundland. Otolith composition differed at all spatial scales and related inversely to spatial scale. Classification analysis revealed increasing discrimination at coarser spatial scales: site (26%–58%), bay (49%), and coast (76%). Assignment success declined by ∼10% per added site with increasing sampling sites per bay, demonstrating fine-scale (<100 km) variation. When we partitioned environmental variability from observed otolith chemistry using predictive models, assignment success improved by 56%, 14%, and 5% for site, bay, and coast, respectively. Our results demonstrate environmental influence on spatial structure of otolith chemistry and illustrate the importance of resolving baseline variability in otolith chemistry when conducting assignment tests. Collectively, our results describe the potential utility of juvenile otolith composition in evaluating contributions of subpopulations to the Northwest Atlantic cod stock and highlight important limitations imposed by environmental variation at scales less than 100 km.

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

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 Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stock–recruit theory and management

2006 ◽  
Vol 63 (5) ◽  
pp. 980-994 ◽  
Author(s):  
C Tara Marshall ◽  
Coby L Needle ◽  
Anders Thorsen ◽  
Olav Sigurd Kjesbu ◽  
Nathalia A Yaragina
Keyword(s):  
Egg Production ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Reproductive Potential ◽  
Threshold Level ◽  
Systematic Bias ◽  
Stock Status ◽  
Relative Fecundity ◽  
Time Period ◽  
Spawning Stock

Stock–recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs·g–1 and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (1980–2001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.

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.

Maternal age, fecundity, egg quality, and recruitment: linking stock structure to recruitment using an age-structured Ricker model

2012 ◽  
Vol 69 (10) ◽  
pp. 1631-1641 ◽  
Author(s):  
Andrew O. Shelton ◽  
Stephan B. Munch ◽  
David Keith ◽  
Marc Mangel
Keyword(s):  
Age Structure ◽  
Maternal Age ◽  
Gadus Morhua ◽  
Egg Quality ◽  
Atlantic Cod ◽  
Natural Populations ◽  
Ricker Model ◽  
Icelandic Population ◽  
Spawning Stock ◽  
Age Structured

Understanding the process of recruitment is fundamental to fisheries biology and management. However, recruitment in natural populations is highly variable and rarely well described by classical stock–recruitment relationships (SRRs). Recent analyses suggest that the age composition of the spawning biomass may play an important role in the mismatch between SRRs and data. Here we develop a generalization of the Ricker SRR that incorporates age structure by allowing mortality and fecundity rates to depend on maternal age. We provide a flexible SRR with biologically interpretable parameters that can be estimated from existing fisheries time series and use a Bayesian framework that enables parameters to be informed by experimental data. We apply our method to the Icelandic population of Atlantic cod ( Gadus morhua ) and show models that include age structure effects outperform the classical Ricker SRR that ignores age structure. Our results indicate a strong effect of spawning stock age structure on recruitment dynamics in this population. Our approach provides a biologically interpretable and immediately applicable method for investigating the consequences for spawning stock age structure on recruitment.

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.

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