Atmosphere–Ocean Coupling and Atlantic Cod Migrations: Effect of Wind-Forced Variations in Sea Temperatures and Currents or Nearshore Distributions and Catch Rates of Gadus morhua

1988 ◽  
Vol 45 (7) ◽  
pp. 1234-1243 ◽  
Author(s):  
G. A. Rose ◽  
W. C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Analysis Model ◽  
Sea Temperature ◽  
The North ◽  
Dual Beam ◽  
Ocean Coupling ◽  
Catch Rates ◽  
Alongshore Wind

Coastal upwellings and downwellings forced by alongshore winds on the north shore of the Gulf of St. Lawrence were associated with variability in onshore movements and inshore daily catches of Atlantic cod (Gadus morhua). Mean cod densities in the zone offshore from the trap sites, determined by hydroacoustic integration scaled by an in situ dual beam determined mean backscatter, ranged from 2.6 to 82.7 fish/105 m3. Cod were located where sea temperatures ranged from −0.5 to 8.5 °C. Catches were nil where temperatures were outside this range. Cod were located at depths which correlated with the strength of alongshore currents (r = −0.55). A path analysis model with predictors alongshore wind stress and current, sea temperature, and cod density accounted for 76% of the variance in catch. Cod abundance in the offshore zone accounted for the most variance independent of other factors (27%). Sea temperature and currents accounted for 15 and 13%, respectively. Peaks in catch (to 1500 kg/d) coincided with maximum rates of decline in sea temperatures and with NE upwelling currents. Low catches coincided with maximum rates of increase in temperatures and with SW currents. In a regression model, four lags of alongshore wind accounted for 83% of the variance in catch.

Effect of environmental change on parasites of Atlantic cod (Gadus morhua) as bioindicators of populations in the north-western Atlantic Ocean

2007 ◽  
Vol 81 (2) ◽  
pp. 129-135 ◽  
Author(s):  
R.A. Khan
Keyword(s):  
Gadus Morhua ◽  
Environmental Changes ◽  
Atlantic Cod ◽  
Metazoan Parasites ◽  
Sea Temperature ◽  
Western Atlantic ◽  
Virtual Absence ◽  
The North ◽  
Over Exploitation ◽  
North Western

AbstractStudies conducted in the 1980s suggested that parasites were useful in distinguishing adjacent populations of Atlantic cod Gadus morhua in the north-western Atlantic. During the mid-1980s, cod populations began to decline, culminating in closure of the fishery in 1992. A marked decrease of cod off the coast of Labrador was coincident with climatic shifts, including a decline of bottom sea temperature, and virtual absence of capelin Mallotus villosus, its main food prey. These changes in some components of the ecosystem were independent of anthropogenic influences. An initial survey of cod parasites in 2000 from coastal Labrador revealed a dramatic decline in abundance of metazoans and also a change in dominance of species of digenetic trematodes compared to 1980–1981. Comparison of metazoan parasites in three other populations of cod inhabiting the Grand (northern and southern) and St. Pierre Banks, where there was no apparent evidence of environmental changes but only commercial over-exploitation, revealed no major alterations in abundance or dominance between 1980–1981 and 2003. The results of this current study suggest that environmental changes in the food web affected the abundance of metazoan parasites only off coastal Labrador but did not influence the use of the parasites to distinguish between cod populations inhabiting the Grand or St. Pierre Banks.

An "experiment" on effort allocation of fishing vessels: the role of interference competition and area specialization

2007 ◽  
Vol 64 (2) ◽  
pp. 304-313 ◽  
Author(s):  
Jan-Jaap Poos ◽  
Adriaan D Rijnsdorp
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Seasonal Pattern ◽  
Interference Competition ◽  
Catch Rate ◽  
The North ◽  
Closed Area ◽  
Fishing Vessels ◽  
The North Sea

A temporarily closed area established to protect spawning Atlantic cod (Gadus morhua) in the North Sea allowed us to study the response of the Dutch beam trawl fleet exploiting common sole (Solea solea) and plaice (Pleuronectes platessa). A number of vessels left the North Sea 1 month earlier than the normal seasonal pattern. The vessels that continued fishing in the North Sea were concentrated in the remaining open areas. In the first week after the closure, the catch rate decreased by 14%, coinciding with an increase in crowding of 28%. Area specialisation affected the response of individual vessels because vessels without prior experience in the open areas showed a larger decline in catch rate compared with vessels that previously fished in these open areas and were more likely to stop fishing during the closed period. The decrease in catch rate in response to the increase in competitor density allowed us to estimate the strength of the interference competition.

Influence of climatic changes on the parasites of Atlantic cod Gadus morhua off coastal Labrador, Canada

2006 ◽  
Vol 80 (2) ◽  
pp. 193-197 ◽  
Author(s):  
R.A. Khan ◽  
C.V. Chandra
Keyword(s):  
North Atlantic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Age Groups ◽  
Climatic Conditions ◽  
Otter Trawl ◽  
Commercial Fishery ◽  
Metazoan Parasites ◽  
Mean Values ◽  
The North

AbstractA study was conducted in 2000 and 2003, following the collapse of the commercial fishery in 1990, to compare metazoan parasites of Atlantic cod Gadus morhua, captured off coastal Labrador, with samples taken in 1980 and 1986. Fish were captured by otter trawl offshore in the North Atlantic Fish Organisation subarea 2J. Parasites were removed from the digestive tract, stained, identified and compared between the different groups. Both the prevalence and mean abundance of trematodes, larval nematodes and E. gadi were significantly lower in fish taken in 2000 and 2003 than in 1980. While mean values of trematodes and nematodes declined in 1986, those of Echinorhynchus gadi remained unchanged in 1986 and 1990. Four-year-old cod sampled in 1990 harboured significantly fewer E. gadi than older age groups. The most commonly occurring trematodes included Podocotylereflexa, Lepidapedon elongatum, Derogenes varicus and Hemiurus levinseni while the larval nematode, Anisakis sp. was predominant. Comparison of offshore samples taken in 2000 and 2003 with others taken in previous years suggests an overall decline of parasites coincident with a change in climatic conditions, the absence of a major food source, namely capelin Mallotus villosus, of cod and ultimately the decline of the Labrador population.

scholarly journals Change in Atlantic cod migrations and adaptability of early land-based fishers to severe climate variation in the North Atlantic

2019 ◽  
pp. 1-11
Author(s):  
Ragnar Edvardsson ◽  
William P. Patterson ◽  
Hlynur Bárðarson ◽  
Sandra Timsic ◽  
Guðbjörg Ásta Ólafsdóttir
Keyword(s):  
North Atlantic ◽  
Atlantic Cod ◽  
Historical Analysis ◽  
Ice Age ◽  
Migration Routes ◽  
Sea Temperature ◽  
The North ◽  
The North Atlantic ◽  
Cod Fisheries ◽  
And Shifts

ABSTRACTWe use biochemical, biological, archaeological, and historical analysis to examine relationships between Atlantic cod migration, sea temperature, and shifts in the distribution and occupancy of historical fishing sites in Iceland during the last millennium. Results support the hypothesis that the cooling climate of the North Atlantic during the period commonly referred to as the Little Ice Age coincided with changes in Atlantic cod migration patterns. Historical analysis shows a concomitant increase in reports of worsening Atlantic cod fishing and a severe decrease in domestic fishing, particularly in north Iceland. We conclude that Atlantic cod fisheries in Iceland originally thrived because of the proximity to cod migration routes. However, despite the mobility of local fishers, fluctuations in fish migrations, coupled with a harsher climate and increased competition for fishing grounds, resulted in a stagnation that lasted until the eventual modernization of the fishery in the mid-nineteenth century.

Mitigation of harbour porpoise (Phocoena phocoena) by-catch in the gillnet fishery in the lower Bay of Fundy

1999 ◽  
Vol 56 (1) ◽  
pp. 113-123 ◽  
Author(s):  
Edward A Trippel ◽  
Michael B Strong ◽  
John M Terhune ◽  
Jeremy D Conway
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Field Testing ◽  
Harbour Porpoise ◽  
Clupea Harengus ◽  
Bay Of Fundy ◽  
Phocoena Phocoena ◽  
By Catch ◽  
Catch Rates ◽  
Wind Sea

Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz every 4 s at a level of 133-145 dB re 1 µPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1-0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.

scholarly journals Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak coast

2018 ◽  
Vol 76 (2) ◽  
pp. 418-429 ◽  
Author(s):  
Henrik Svedäng ◽  
Julia M I Barth ◽  
Anders Svenson ◽  
Patrik Jonsson ◽  
Sissel Jentoft ◽  
...  
Keyword(s):  
North Sea ◽  
West Coast ◽  
Population Genetic ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Early Stage ◽  
Population Genetic Analysis ◽  
Swedish West Coast ◽  
The North ◽  
Spawning Areas

Abstract Dramatic and persistent reductions in Atlantic cod (Gadus morhua) are common in many coastal areas. While offshore cod stocks still were abundant and productive, the Swedish west coast showed signs of diminishing adult cod abundance at the beginning of the 1980s, where the local cod component was considered to be extirpated. To survey the present cod spawning activity and stock composition, we initiated egg trawling over two consecutive years (203 hauls in total) in combination with population genetic analyses (425 individually genotyped eggs). Here, we provide evidence of cod spawning at the Swedish Skagerrak coast, suggesting recolonization or that local cod has recovered from a nearly depleted state. Early stage eggs were found inside fjords too far to have been transported by oceanic drift from offshore spawning areas. The cod eggs were genetically similar in early to late life-stages and cluster mainly with the local adult cod, indicating that eggs and adults belong to the same genetic unit. The cod eggs were genetically differentiated from adult North Sea cod, and, to a lesser degree, also from the Kattegat and Öresund cod, i.e. indicating a possible recovery of local coastal stock. The patterns of the genetic structure in the inshore areas are, however, difficult to fully disentangle, as Atlantic cod in the North Sea-Skagerrak area seem to be a mixture of co-existing forms: local cod completing their entire life cycle in fjords and sheltered areas, and oceanic populations showing homing behaviours. The egg abundances are considerably lower compared with what is found in similar studies along the Norwegian Skagerrak coast. Nevertheless, the discovery of locally spawning cod along the Swedish west coast—although at low biomasses—is an encouraging finding that highlights the needs for endurance in protective measures and of detailed surveys to secure intraspecific biodiversity and ecosystem services.

Partial Recruitment Considerations in Setting Catch Quotas

1993 ◽  
Vol 50 (4) ◽  
pp. 734-742 ◽  
Author(s):  
A. F. Sinclair
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Age Groups ◽  
Combined Effects ◽  
Total Allowable Catch ◽  
Catch Rates ◽  
Fishing Fleets ◽  
The Individual ◽  
Nova Scotian ◽  
Target Fishing

An approach is presented for investigating the interactions between fishing fleets that compete by exploiting different age-groups of the same resource population. The term "partial recruitment" (PR) is used to describe the age-specific exploitation pattern experienced by a population, either from individual fishing fleets or the combined effects of several fleets. Methods are presented to calculate catch quotas for the individual fleets if the management objective is to keep fleet effort constant, or alternatively to predict catch rates by fleet if the allocation rules are based on a percentage sharing of the total allowable catch (TAC) among fleets. Simulations based on an Atlantic cod (Gadus morhua) fishery on the Nova Scotian Shelf is used to illustrate the method. The results indicate the importance of considering differences in PR among competing fishing fleets when setting catch quotas. The relative effort exerted by the fleets will affect target fishing mortalities. The fleet that concentrates on younger fish can intercept recruitment. Since the fleets exploit different age-groups, changes in fishable biomass due to recruitment variation are lagged, and fishing success will vary among fleets. Understanding the dynamics of PR may help explain why certain fleets either exceed or fall short of catch quotas.

Use of Oceanographic Forecasts and Echosounders to Guide and Enhance an Inshore Gillnet Fishery for Atlantic Cod (Gadus morhua)

1993 ◽  
Vol 50 (10) ◽  
pp. 2129-2136 ◽  
Author(s):  
G. A. Rose ◽  
W.C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Shallow Waters ◽  
Gill Nets ◽  
Rule Of Thumb ◽  
Combined Use ◽  
Catch Rates ◽  
Depth Ranges ◽  
High Fish

Vessels fishing with gill nets for Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence in 1985 and 1986 concentrated their fishing effort in shallow waters (<50 m) where cod densities were highest (to 0.5/m3). In both years, seasonal trends (June–August) in mean daily deployment depths of gill nets were positively correlated with mean depths at which cod were surveyed (1985, r = 0.71; 1986, r = 0.51, Ps < 0.05). Daily catch rate variability of individual vessels was accounted for by fish "flux" adjacent to nets (44%), vessel operator skill (19%), and "flux"–skill interaction (8%; total R2 = 0.71). A guided vessel directed to fish at sites predicted to have high fish flux (located down-current from high-density cod aggregations identified by echosounding within depth ranges forecast to be favorable to cod by "rule of thumb" wind-based oceanographic models) had higher catch rates (mean 1.3 t/d) than the fleet average and its own average fishing without guidance (means 0.4 t/d, P's < 0.05). Directed searches were of shorter duration (mean 0.5 h) than searches conducted at random (1.5 h). Combined use of echosounders and air–sea-based forecasts of cod distribution could help stabilize catch rates, especially at times of poor fish availability inshore.

Movements and distribution of cod (Gadus morhua) in the southern North Sea and English Channel: results from conventional and electronic tagging experiments

2007 ◽  
Vol 87 (2) ◽  
pp. 599-613 ◽  
Author(s):  
David Righton ◽  
Victoria Anne Quayle ◽  
Stuart Hetherington ◽  
Gary Burt
Keyword(s):  
North Sea ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
English Channel ◽  
Seasonal Movement ◽  
Southern North Sea ◽  
The North ◽  
Fisheries Policy ◽  
The Uk ◽  
Electronic Tags

The sub-structure of Atlantic cod (Gadus morhua) stocks in the North Sea has important consequences for fisheries management as the Common Fisheries Policy moves towards a more regional approach. We investigated the movements, distribution and behaviour of cod in the southern North Sea (ICES IVc) and English Channel (ICES VIId) by re-analysing historic data from conventional tagging experiments, and by conducting new experiments with electronic tags. Cod tagged and released in IVc showed a northwards shift in distribution during the feeding season consistent with a homing migration away from spawning grounds along the coasts of the UK and the Netherlands. In contrast, cod tagged and released in VIId did not exhibit a consistent pattern of seasonal movement. Many cod released in VIId were subsequently recaptured close to their release position, although some moved out of the Channel and into the southern North Sea. Overlap between the recapture areas of cod released in the different management areas was no more than 25% in either the spawning or feeding season. Behavioural data from electronic tags suggest that cod in IVc make use of tidal streams to migrate northwards and eastwards in spring, whereas selective tidal stream transport was rarely exhibited by cod tagged and released in VIId. Overall, the evidence suggests that there are behavioural differences between cod in IVc and VIId that limit the mixing of cod from these two areas during the feeding and spawning seasons.

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