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

1997 ◽  
Vol 54 (1) ◽  
pp. 211-223 ◽  
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.

scholarly journals Effect of solar ultraviolet radiation (280–400 nm) on the eggs and larvae of Atlantic cod (Gadus morhua)

1999 ◽  
Vol 56 (6) ◽  
pp. 1058-1067 ◽  
Author(s):  
France Béland ◽  
Howard I Browman ◽  
Carolina Alonso Rodriguez ◽  
Jean-François St-Pierre
Keyword(s):  
Water Column ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Outdoor Exposure ◽  
Ultraviolet B ◽  
Solar Ultraviolet Radiation ◽  
Mortality Effect ◽  
Eggs And Larvae ◽  
Very High ◽  
Solar Ultraviolet

In the Gulf of St. Lawrence, Canada, solar ultraviolet B radiation (UV-B, 280-320 nm) penetrates a significant percentage of the summer mixed-layer water column: organisms residing in this layer, such as the eggs of Atlantic cod (Gadus morhua), are exposed to UV-B. In outdoor exposure experiments, Atlantic cod eggs were incubated in the presence versus the absence of UV-B and (or) UV-A (320-400 nm). We tested two hypotheses: H1, UV-B induces mortality in Atlantic cod eggs, and H2, UV-A either exacerbates or mitigates any such UV-B-induced mortality. Hypothesis H1 was supported: there was a significant mortality effect on Atlantic cod eggs exposed to UV-B at the surface and at a depth of 50 cm. Hypothesis H2 was not supported: there was no effect of UV-A. These experiments indicate that Atlantic cod eggs present in the first metre of the water column (likely only a small percentage of the total egg population) are susceptible to UV-B. However, UV-B must be viewed as only one among many environmental factors that produce the very high levels of mortality typically observed in the planktonic early life stages of marine fishes.

scholarly journals On contribution of horizontal and intra-layer convection to the formation of the Baltic Sea cold intermediate layer

2008 ◽  
Vol 5 (4) ◽  
pp. 581-623
Author(s):  
I. P. Chubarenko ◽  
N. Y. Demchenko
Keyword(s):  
Baltic Sea ◽  
Intermediate Layer ◽  
Heat Content ◽  
Field Measurements ◽  
Open Water ◽  
Early Spring ◽  
Cold Intermediate Layer ◽  
The Baltic Sea ◽  
The Baltic ◽  
Fast Increase

Abstract. Seasonal cascades down the coastal slopes and intra-layer convection are considered as the two mechanisms contributing to the Baltic Sea cold intermediate layer (CIL) formation. On the base of TS-diagrams, mean-annual and real-time temperature profiles, the CIL features are re-analyzed. The presence within the CIL of water with temperature below that of maximum density (Tmd) and that at the local surface allows tracing its formation. Field measurements are presented, showing specific features of denser water formation in marine environment. It is argued that such cascades formed during early spring heating (March–April) – before reaching the Tmd – are the source of the coldest waters of the CIL. Fast increase of the open water heat content during further spring heating indicates that horizontal exchange rather than direct solar heating is responsible for that. When the surface is covered with water, heated above the Tmd, the conditions within the CIL become favorable for intralayer convection due to the presence of waters of Tmd in intermediate layer, which can explain the observed increase of its salinity and deepening with time.

Thermoregulatory behaviour in cod: Is the thermal preference in free-ranging adult Atlantic cod affected by food abundance?

2019 ◽  
Vol 76 (9) ◽  
pp. 1515-1527 ◽  
Author(s):  
Björn Björnsson
Keyword(s):  
Growth Rate ◽  
Data Storage ◽  
Gadus Morhua ◽  
Cold Water ◽  
Atlantic Cod ◽  
Vertical Mixing ◽  
Metabolic Energy ◽  
Fat Reserves ◽  
Free Ranging ◽  
Thermoregulatory Behaviour

This study supports the hypothesis that well-fed cod (Gadus morhua) seek higher temperatures to increase growth rate, and poorly fed cod select lower temperatures to save metabolic energy. Depth and temperature of free-ranging adult cod (44–79 cm) were studied with data storage tags as part of a ranching project in an Icelandic fjord. Forage fish were regularly provided at four feeding stations where cod formed distinct “herds” (herd cod) that did not mingle much with the rest of the unconditioned cod in the fjord (wild cod). Several parameters (stomach fullness, liver index (fat reserves), condition factor, and growth rate) indicated that food intake was much greater in herd cod than in wild cod. In August, when the thermocline was well established, the herd cod remained in shallow (15–35 m) and warm water (8–10 °C), whereas the wild cod stayed in deep (80–90 m) and cold water (3–4 °C), but occasionally both groups explored depths and temperatures outside their preferred range. After vertical mixing in autumn when thermoregulation was not possible, the depth difference between the two groups decreased significantly.

Decreased lipid storage in juvenile Atlantic cod (Gadus morhua) during settlement in cold-water eelgrass habitat

2008 ◽  
Vol 154 (5) ◽  
pp. 823-832 ◽  
Author(s):  
L. A. Copeman ◽  
C. C. Parrish ◽  
R. S. Gregory ◽  
J. S. Wells
Keyword(s):  
Gadus Morhua ◽  
Cold Water ◽  
Atlantic Cod ◽  
Lipid Storage ◽  
Eelgrass Habitat

scholarly journals Seasonal variation in the vertical distribution of zone over Oakshin Gangotri, Antarctica

MAUSAM ◽  
2021 ◽  
Vol 42 (3) ◽  
pp. 275-278
Author(s):  
A.L. KOPPAR ◽  
S.C. NAGRATH
Keyword(s):  
Seasonal Variation ◽  
Vertical Distribution ◽  
Early Spring ◽  
The Other ◽  
Late Winter ◽  
Double Peak ◽  
The Vertical Distribution

Ozone soundings made from Dakshin Gangotri, Antarctica during 1987 are presented. The vertical distribution of ozone over Antarctica is characterised by a double peak profile, one around 200-150 hPa and the other around 50 hPa. During late winter-early spring the upper peak is considerably depleted. Tropospheric ozoe remains low and nearly constant throughout the year.  

Movements of Atlantic Cod (Gadus Morhua) Within the Spring Thermocline in Trinity Bay, Newfoundland

1995 ◽  
Vol 75 (2) ◽  
pp. 265-284 ◽  
Author(s):  
J.S. Wroblewski ◽  
Sally V. Goddard ◽  
R. Kent Smedbol ◽  
Wade L. Bailey
Keyword(s):  
Surface Waters ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Antifreeze Protein ◽  
Early Spring ◽  
Subzero Temperature ◽  
Cold Adapted ◽  
Protein Levels ◽  
Trap Fishery ◽  
Trinity Bay

Using depth-telemetering, sonic tags orally inserted into the stomachs of Gadus morhua (Pisces: Gadiformes) found over-wintering in Trinity Bay, Newfoundland, the movements of individual fish were observed as surface waters warmed in early spring. Physiological measurements (antifreeze protein levels in the blood) indicate that many cold-adapted, bay cod change their thermal regime at this time. Fish acclimatized to subzero water temperatures enter the newly-formed thermocline and become available to a cod trap fishery. Most sonically-tagged fish resided in 0–1°C waters along the shoreline. Tracking data confirmed indications from declining antifreeze protein levels that cold-adapted cod, having moved into shallow waters in early spring, do not return to deeper, subzero-temperature waters for any appreciable time. At night some cod swam pelagically near the surface. Fish moved at times in the same direction as the tidal current, but ground speeds were several times greater than current velocities. Nocturnal pelagic swimming was also observed during the summer when temperatures within the thermocline exceeded 10°C.

Temperature and the recruitment of Atlantic cod (Gadus morhua)

1999 ◽  
Vol 56 (11) ◽  
pp. 2069-2077 ◽  
Author(s):  
B Planque ◽  
T Frédou
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Cold Water ◽  
Atlantic Cod ◽  
The Other ◽  
Warm Water ◽  
The North ◽  
The North Atlantic ◽  
Interannual Fluctuations ◽  
The Relationship

Variability in the recruitment of fish has been attributed to either changes in the environment or variations in the size of reproductive stocks. Disentangling the effects of environment and stock has proven to be problematic and has resulted in recurrent controversy between studies supporting either hypothesis. In the present study, we examine the relationship between interannual changes in temperature and variation in recruitment for nine Atlantic cod (Gadus morhua) stocks in the North Atlantic. We show that for individual stocks, the relationship often appears weak and statistically not significant. On the other hand, by combining in a single metaanalysis the results from individual stocks, we demonstrate that recruitment of Atlantic cod is linked to interannual fluctuations in temperature in such a way that for stocks located in warm water the relationship is negative, for stocks located in cold water the relationship is positive, and there is no relationship for stocks located in the middle of the temperature range.

scholarly journals Depth-dependent molecular composition and photo-reactivity of dissolved organic matter in a boreal lake under winter and summer conditions

2013 ◽  
Vol 10 (11) ◽  
pp. 6945-6956 ◽  
Author(s):  
M. Gonsior ◽  
P. Schmitt-Kopplin ◽  
D. Bastviken
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Water Column ◽  
Early Spring ◽  
Boreal Lakes ◽  
Molecular Composition ◽  
Late Winter ◽  
Photochemical Degradation ◽  
Photo Degradation ◽  
Boreal Lake

Abstract. Transformations of dissolved organic matter (DOM) in boreal lakes lead to large greenhouse gas emissions as well as substantial carbon storage in sediments. Using novel molecular characterization approaches and photochemical degradation experiments we studied how seasonal patterns in water column stratification affected the DOM in a Swedish lake under early spring and summer conditions. Dissolved organic carbon (DOC) concentrations were consistently higher above the sediment when compared to surface waters throughout the sampling periods. Photobleaching alone could not explain this difference in DOC because the lake was covered by 40 cm-thick ice during late winter sampling and still showed the same DOC trend. The differences in the molecular diversity between surface DOM in winter and summer were consistent with ongoing photobleaching/decarboxylation and a possible bacterial consumption of photo-products. Additional photo-degradation experiments using simulated sunlight showed a production of highly oxidized organic molecules and low molecular weight compounds in all late winter samples and also in the deep water sample in summer. In the surface summer DOM sample, few such molecules were produced during the photo-degradation experiments, confirming that DOM was already photobleached prior to the experiments. This study suggests that photobleaching, and therefore also the ice cover during winter, plays a central role in surface DOM transformation, with important differences in the molecular composition of DOM between surface and deep boreal lake waters. The release of DOC from boreal lake sediments also contribute to this pattern. Photochemical degradation of DOM may be more extensive following ice-out and water column turnover when non-light exposed and thereby photosensitive DOM is photo-mineralized. Hence, the yearly DOM photo-mineralization may be greater than inferred from studies of recently light-exposed DOM.

Abundance and diurnal vertical distribution of fish larvae in early spring and summer in a fjord at South Georgia

1992 ◽  
Vol 4 (4) ◽  
pp. 405-412 ◽  
Author(s):  
A. W. North ◽  
A. W. A. Murray
Keyword(s):  
Vertical Distribution ◽  
Water Column ◽  
Fish Larvae ◽  
Abundant Species ◽  
Early Spring ◽  
Distinct Pattern ◽  
South Georgia ◽  
Gobionotothen Gibberifrons ◽  
Lepidonotothen Larseni ◽  
Distribution Of Fish

The diurnal vertical distribution and abundance of fish larvae was studied by net samples in the 265 m deep fjord of Cumberland East Bay, South Georgia. In early spring the six most abundant species of fish larvae in the upper 200 m of the water column were Champsocephalus gunnari, Lepidonotothen nudifrons, Pseudochaenichthys georgianus, Chaenocephalus aceratus, Parachaenichthys' georgianus and Electrona antarctica. In summer, the larvae of C. gunnari, Gobionotothen gibberifrons, Lepidonotothen larseni and Trematomus hansoni were most abundant, and the majority were found in the upper 140 m of the water column, with greatest densities in the top 2m. During both seasons most species showed some evidence of diurnal vertical migration. A distinct pattern was found for C. gunnari in summer; they were at 0–20 m during the day and 60–100 m at midnight. Net avoidance by the larvae of most species was greater before sunset in early spring, and during all periods of daylight in summer, than at other times of day.

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