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

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

ICES Journal of Marine Science ◽

10.1006/jmsc.2001.1153 ◽

2002 ◽

Vol 59 (2) ◽

pp. 333-351 ◽

Cited By ~ 33

Author(s):

L Comeau

Keyword(s):

Interannual Variability ◽

Gadus Morhua ◽

Atlantic Cod ◽

Seasonal Migrations

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Is Juvenile Natural Mortality in Marine Demersal Fish Variable?

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f93-180 ◽

1993 ◽

Vol 50 (8) ◽

pp. 1591-1598 ◽

Cited By ~ 40

Author(s):

Ransom A. Myers ◽

Noel G. Cadigan

Keyword(s):

Interannual Variability ◽

Gadus Morhua ◽

Atlantic Cod ◽

Demersal Fish ◽

Independent Component ◽

Melanogrammus Aeglefinus ◽

Natural Mortality ◽

Juvenile Mortality ◽

Merlangius Merlangus ◽

Haddock Melanogrammus Aeglefinus

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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Status and biology of harbour seals (Phoca vitulina) in Svalbard

NAMMCO Scientific Publications ◽

10.7557/3.2671 ◽

2010 ◽

Vol 8 ◽

pp. 47 ◽

Cited By ~ 6

Author(s):

Christian Lydersen ◽

Kit M Kovacs

Keyword(s):

Gadus Morhua ◽

Atlantic Cod ◽

Growth Curves ◽

Reproductive Rate ◽

Time Of Day ◽

Small Population ◽

Polar Cod ◽

Adult Males ◽

Adult Females ◽

Harbour Seals

Harbour seals in Svalbard are the northernmost population of this species. This small population is comprised of ca. 1,000 individuals, most of which reside along the west coast of Prins Karls Forland (78°20’N). Satellite tracking studies have shown that adults are resident. Birthing occurs in the latter half of June. Newborns weigh about 11 kg and gain an average of 0.7 kg/d during the nursing period. Haulout patterns in Svalbard harbour seals are influenced by date (season), time of day, tidal cycle and temperature. Moulting takes place in early fall, first among juveniles, then in adult females and finally in adult males. Feeding studies show that polar cod (Boreogadus saida) is the dominant prey in terms of numbers, while Atlantic cod (Gadus morhua) is the dominant prey based on biomass, at least during the early autumn. Growth curves display significant sexual dimorphism with asymptotic values for standard length and body mass being greater formales. Testosterone levels inmales showed an abrupt increase at 6 years of age, while estradiol levels in females increased abruptly from age 4 years. The reproductive rate for adult females was 0.93. Longevity of Svalbard harbour seals is very short compared with populations from other areas.

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A decade of monitoring Atlantic cod Gadus morhua spawning aggregations in Massachusetts Bay using passive acoustics

Marine Ecology Progress Series ◽

10.3354/meps13219 ◽

2020 ◽

Vol 635 ◽

pp. 89-103 ◽

Cited By ~ 2

Author(s):

PE Caiger ◽

MJ Dean ◽

AI DeAngelis ◽

LT Hatch ◽

AN Rice ◽

...

Keyword(s):

Fish Species ◽

Gadus Morhua ◽

Atlantic Cod ◽

Acoustic Monitoring ◽

Massachusetts Bay ◽

Passive Acoustic Monitoring ◽

Important Species ◽

Spawning Period ◽

Spawning Aggregations ◽

Passive Acoustic

Atlantic cod Gadus morhua populations in the northeast USA have failed to recover since major declines in the 1970s and 1990s. To rebuild these stocks, managers need reliable information on spawning dynamics in order to design and implement control measures; discovering cost-effective and non-invasive monitoring techniques is also favorable. Atlantic cod form dense, site-fidelic spawning aggregations during which they vocalize, permitting acoustic detection of their presence at such times. The objective of this study was to detect spawning activity of Atlantic cod using multiple fixed-station passive acoustic recorders to sample across Massachusetts Bay during the winter spawning period. A generalized linear modeling approach was used to investigate spatio-temporal trends of cod vocalizing over 10 consecutive winter spawning seasons (2007-2016), the longest such timeline of any passive acoustic monitoring of a fish species. The vocal activity of Atlantic cod was associated with diel, lunar, and seasonal cycles, with a higher probability of occurrence at night, during the full moon, and near the end of November. Following 2009 and 2010, there was a general decline in acoustic activity. Furthermore, the northwest corner of Stellwagen Bank was identified as an important spawning location. This project demonstrated the utility of passive acoustic monitoring in determining the presence of an acoustically active fish species, and provides valuable data for informing the management of this commercially, culturally, and ecologically important species.

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Characteristics and vertical distribution of Atlantic cod (Gadus morhua) eggs in the northern Gulf of St. Lawrence, and the possible effect of cold water temperature on recruitment

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f96-297 ◽

1997 ◽

Vol 54 (1) ◽

pp. 211-223 ◽

Cited By ~ 14

Author(s):

P Ouellet

Keyword(s):

Vertical Distribution ◽

Water Column ◽

Intermediate Layer ◽

Gadus Morhua ◽

Cold Water ◽

Atlantic Cod ◽

Early Spring ◽

Ca 125 ◽

Late Winter ◽

Cold Intermediate Layer

In early May from 1993 to 1995 the water column in the northern Gulf of St. Lawrence was weakly stratified, with cold water (<2°C) extending from ca. 125 m to the surface. Cod (Gadus morhua) eggs were distributed throughout the water column, but higher densities were observed in the cold intermediate layer. The vertical distribution of cod eggs was determined by egg size and organic (lipids, proteins) composition. Stage I egg density estimates in May 1994 ranged from 25.0 to 26.0 kg · m-3, which is higher than the water density of the upper mixed layer. Between 1980 and 1989, there was a weak positive relationship between the cold intermediate layer temperature anomalies and cod year-class strength (i.e., abundance of 3-year-old cod). However, it is unlikely that low recruitment levels caused by below-average temperature of the cold intermediate layer alone had a major impact on the recent collapse of the northern Gulf stock. Nevertheless, the poor state of the spawning stock (low abundance, poor fish condition, and less buoyant eggs) and harsh late winter and early spring conditions in the northern Gulf can limit the potential for high recruitment and rapid recovery of the northern Gulf cod stock.

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