Timing of Atlantic cod (Gadus morhua L.) seasonal migrations in the southern Gulf of St Lawrence: interannual variability and proximate control

We test the hypothesis that the interannual variability of the density-independent component of juvenile natural mortality is a major source of variability in abundance of marine demersal fish. Our tests use data on populations for which there are research surveys consisting of two simultaneous estimates of abundance of young juveniles soon after settlement and two more simultaneous estimates of the same cohort a year later. We applied our test to 14 populations of Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), plaice (Pleuronectes platessa), and sole (Solea vulgaris). We conclude that, in all populations examined except North Sea sole, there was very little or no interannual variability in the density-independent component of juvenile mortality.

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Risk of oil contamination of fish eggs and larvae under different oceanic and weather conditions

ICES Journal of Marine Science ◽

10.1093/icesjms/fsz035 ◽

2019 ◽

Vol 76 (6) ◽

pp. 1902-1916 ◽

Cited By ~ 1

Author(s):

Annette Samuelsen ◽

Ute Daewel ◽

Cecilie Wettre

Keyword(s):

Interannual Variability ◽

Oil Spill ◽

Gadus Morhua ◽

Oil Spills ◽

Atlantic Cod ◽

Weather Conditions ◽

Oil Contamination ◽

Drift Model ◽

High Risk Situation ◽

Eggs And Larvae

Abstract An oil drift model is applied to determine the spread of oil spills from different locations along ship lanes off southern Norway every month for 20 years. These results are combined with results from an egg- and larvae drift model for Atlantic cod (Gadus morhua) to determine their risk of being impacted by oil. The number of eggs and larvae exposed to oil contamination is connected to environmental conditions. The highest risk of overlap between an oil spill and cod in early life stages occurs during March and April when the eggs and larvae concentrations are highest. Spills off the west coast pose a greater risk because of the ship lanes’ proximity to the spawning grounds, but there is large interannual variability. For some spill locations the interannual variability can be explained by variability in wind and ocean currents. Simultaneously occurring onshore transports lead to a high-risk situation because both oil and larvae are concentrated towards the coast. This study demonstrates how results from oil drift and biological models can be combined to estimate the risks of oil contamination for marine organisms, based on the location and timing of the oil spill, weather/ocean conditions, and knowledge of the organisms’ life cycle.

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Effect of changes in reproductive potential on perceived productivity of three Northwest Atlantic cod (Gadus morhua) stocks

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2004.10.003 ◽

2005 ◽

Vol 62 (1) ◽

pp. 65-74 ◽

Cited By ~ 29

Author(s):

M. Joanne Morgan ◽

John Brattey

Keyword(s):

Sex Ratio ◽

Interannual Variability ◽

Egg Production ◽

Gadus Morhua ◽

Atlantic Cod ◽

Relative Rate ◽

Reproductive Potential ◽

Basic Information ◽

Northern Cod ◽

Spawning Stock

Abstract Variation in maturity-at-age, sex ratio, and potential egg production (through changes in length at age) were examined for northern cod (NAFO Division 2J + 3KL), southern Grand Bank cod (3NO), and southern Newfoundland cod (3Ps). All showed significant interannual variability in each stock. Estimates of reproductive potential were produced by sequentially incorporating estimates of proportion mature at age, sex ratio at age, and potential egg production. The estimates of reproductive potential produced by each method were broadly similar, but there were important differences. This leads to differing perceptions of stock productivity, as measured by relative rate of recruitment of a stock and in the spawning stock produced per recruit. These differing perceptions can have a major impact on expectations for the recovery of depleted stocks and the sustainability of various levels of fishing. Efforts should be made to improve estimates of reproductive potential by further exploring the impacts of changes in the spawning characteristics of populations, and by collecting such basic information as fecundity data.

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The drift-retention dichotomy on Browns Bank: a model study of interannual variability

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f00-234 ◽

2000 ◽

Vol 57 (12) ◽

pp. 2506-2518 ◽

Cited By ~ 15

Author(s):

Charles G Hannah ◽

Jennifer A Shore ◽

John W Loder

Keyword(s):

Interannual Variability ◽

Gadus Morhua ◽

Atlantic Cod ◽

Retention Indices ◽

Melanogrammus Aeglefinus ◽

Vertical Position ◽

Mean Flow ◽

Model Study ◽

Level Data ◽

Mean Circulation

Interannual variability in drift and retention in the Browns Bank region in spring was investigated by tracking particles in numerical-model estimates of the seasonal mean circulation and monthly mean flow anomalies computed using wind and sea-level data. The circulation changes associated with the variable forcing tend to reinforce either drift to the Bay of Fundy or retention in the vicinity of Browns Bank. Regular spring spawning can lead to widely different distributions of 1-month-old larvae, supporting the concept of a drift-retention dichotomy for Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) larvae in the region. Analysis of interannual variability indicates that retention has bounded properties that must be accounted for when relating retention variability to forcing indices. As well, the nonlinearities associated with calculating particle trajectories from velocity fields contribute about 10% of the variance in retention indices. Comparison with biologically based indices of haddock survival indicates that circulation variability alone is not the dominant influence on survival to ages 1 and 2 years. However, it can be expected to have a significant influence in conjunction with biological factors such as the location and timing of peak spawning and the variable vertical position of eggs and larvae.

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Evidence of near year-around spawning in Atlantic cod off southern Newfoundland: implications for management

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2020-0206 ◽

2020 ◽

Vol 77 (12) ◽

pp. 1969-1976

Author(s):

George A. Rose ◽

Sherrylynn Rowe

Keyword(s):

Interannual Variability ◽

Linear Model ◽

Gadus Morhua ◽

Atlantic Cod ◽

General Linear Model ◽

Late Winter ◽

Random Factor ◽

Spawning Aggregations ◽

Adult Females ◽

Composite Data

Management of Atlantic cod (Gadus morhua) off southern Newfoundland (Northwest Atlantic Fisheries Organization (NAFO) Subdivision 3Ps) entails allocated quotas and restrictions on fishing during late winter and springtime to protect presumed spawning aggregations. We present data collected from research trawls and handlines (1995–2014) indicating spawning inshore may occur near year-around with limited resting from December to February and with more contracted spring spawning possible offshore. A mixed general linear model with binomial error, using year as a random factor, recognized month and length as significant impacts on proportions of females spawning, but not gear or inshore–offshore location. Composite data indicated that females in spawning condition may be present inshore (∼10%–20% of adult females) from March to October. During 1997–1999, with 8–9 months sampled each year, protracted annual spawning schedules and interannual variability were evident. At present, the fishery primarily employs gillnets inshore and otter trawls offshore, with spring spawning closures offering only partial and inconsistent protection. Behavioural interference might be reduced by employing less intrusive longlines, as historically practiced in this fishery.

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Using tagging experiments to evaluate the potential of closed areas in protecting migratory Atlantic cod (Gadus morhua)

ICES Journal of Marine Science ◽

10.1093/icesjms/fsp281 ◽

2009 ◽

Vol 67 (5) ◽

pp. 1024-1035 ◽

Cited By ~ 10

Author(s):

Sigfus A. Schopka ◽

Jon Solmundsson ◽

Stefan Aki Ragnarsson ◽

Vilhjalmur Thorsteinsson

Keyword(s):

Spatial Distribution ◽

Marine Protected Areas ◽

Gadus Morhua ◽

Atlantic Cod ◽

Unit Area ◽

Fishing Effort ◽

Fishing Gear ◽

The Third ◽

Reference Length ◽

Seasonal Migrations

Abstract Schopka, S. A., Solmundsson, J., Ragnarsson, S. A., and Thorsteinsson, V. 2010. Using tagging experiments to evaluate the potential of closed areas in protecting migratory Atlantic cod (Gadus morhua). – ICES Journal of Marine Science, 67: 1024–1035. About 5200 cod (Gadus morhua) were tagged on three fishing grounds and within two marine protected areas (MPAs) northwest of Iceland. Two of the fishing grounds were closed to otter trawling, and the third was open to all fishing gear. Tagged fish were divided into two size classes, below (small) and above (large) a reference length of 55 cm, and the following variables were estimated: (i) proportion of the recaptured small cod that did not reach the reference size, (ii) size increase from tagging to recapture, (iii) time at liberty, and (iv) spatial distribution of recaptures. For the small cod, the results suggest that not only protection status but also the distance to areas of intense fishing mainly account for differences in the variables among tagging areas. No differences were observed for the large cod among tagging areas. The results show that immature cod are relatively stationary, but perform seasonal migrations between feeding and spawning grounds after reaching maturity. The estimated distribution of tagged cod generally changed after standardizing the recapture data with fishing effort (catch per unit area). Our results suggest that area closures on nursery grounds can be useful in protecting immature cod, but the MPAs studied are of little use in protecting highly migratory adults.

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