Environmental influences on the recruitment of Newfoundland/Labrador Cod*

Helbig, J.; Mertz, G.; Pepin, Pierre

doi:10.1111/j.1365-2419.1992.tb00024.x

Cited by 38 publications

(32 citation statements)

References 22 publications

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“…It may have taken several years of this distributional shift to have a significant effect on population biomass. Helbig et al (1992) and Hutchings et al (1993) suggested that deep spawning habits would be detrimental to recruitment since the currents over deeper water would tend to transport the larvae away from the shelf and thus reduce survival. The present study provides further evidence that spawning concentrations during the 1980s and 1990s did change their distribution and behaviour significantly.…”

Section: Resultsmentioning

confidence: 99%

“…Their data from deeper waters may not have been adequate to reflect the extent of the spawning distribution along the edge of the north-east Newfoundland Shelf, and so the spawning distribution that we observed during the 1980s and 1990s may have been quite different from earlier years. Helbig et al (1992), using numerical simulations of particle drift, suggested that reproductive activity of cod on the Labrador Shelf is separate from that of the Grand Banks. It is entirely possible that the spawning behaviour and distributions of the two areas are quite different, with the Labrador component occurring along the edge.…”

Section: Resultsmentioning

confidence: 99%

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Recent changes in the winter distribution and movements of northern Atlantic cod (Gadus morhuaLinnaeus, 1758) on the Newfoundland-Labrador Shelf

Kulka

Wroblewski

Narayanan

1995

ICES Journal of Marine Science

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S. 1995. Recent changes in the winter distribution and movements of northern Atlantic cod (Gadus morhua Linnaeus, 1758) on the Newfoundland-Labrador Shelf. -ICES J. mar. Sci., Using catch data collected by fishery observers from the otter trawl fleet, we describe changes in the winter distribution of cod on the Newfoundland-Labrador Shelf between 1980 and 1992. We determined the relative abundance of cod in three areas of winter aggregation: south-east of Hamilton Bank, south-east of Belle Isle Bank and south-east of Funk Island Bank. The principal finding was that the cod, during their reproductive period, exhibited significant changes in distribution and behaviour, well before the stock showed signs of collapse. There were three indicators of these changes. First, there was a progressive disappearance of fish from the north with time. Most of the biomass was located in the Hamilton Bank area before 1984. By 1989, most of the fish were found at the Belle Isle Bank and south-east of Funk Island Bank locations and by 1991, only to the south (Funk Island Bank). Second, movements of the prespawning/spawning schools became more limited. Compared with the extensive along-shelf migrations, often covering distances of about 100 km, observed in earlier years, the fish schools after 1989 exhibited less movement to the north. Density of fish in the schools was highest in 1990. By 1991, the schools remained nearly stationary around 49 30 N, near the southern end of their distribution. Third, the schools spread over an increasingly greater range of depths. The greatest density of fish as reflected by high catch rates was generally observed no deeper than 600 m between 1980 and 1988 . By 1989, substantial catch rates were observed as deep as 1100 m, particularly to the north although catches continued to be considerable at the shallower depths. These changes in distribution and behaviour were generally coincident with the occurrence of anomalously cold ocean temperatures and heavy ice conditions, but no direct link between these changes and the environment was evident.1995 International Council for the Exploration of the Sea

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Recent changes in the winter distribution and movements of northern Atlantic cod (Gadus morhuaLinnaeus, 1758) on the Newfoundland-Labrador Shelf

Kulka

Wroblewski

Narayanan

1995

ICES Journal of Marine Science

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“…and larval drift (Helbig et al 1992) and adult movements between spawning and feeding areas (Rose 1993). Such cod groups have diverse population sizes and ranges.…”

Section: Atlantic Cod Migrations D Robichaud and G A Rosementioning

confidence: 99%

Migratory behaviour and range in Atlantic cod: inference from a century of tagging

2004

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A century of tagging experiments on 174 Atlantic cod (Gadus morhua) groups is reviewed and the frequency and spatial distribution of four migratory behaviours documented. Of all cod groups, 41% were categorized as sedentary, 18% as accurate homers, 20% as inaccurate homers and 20% as dispersers (ranging over large areas without recognizable return migrations). All behaviours occurred over the full spatial range of cod. Coastal groups did not differ significantly from offshore (shelf) groups in the relative frequency of migratory behaviours. However, the north-east Atlantic had more sedentary and accurate homing groups than did the north-west Atlantic, which had more dispersing groups. Overall, sedentary cod groups had lower maximum historical biomass than did other groups, confirming that migration/dispersal begets abundance. Maximum historical biomass was strongly related to the area occupied [log (biomass, tonnes)] ¼ 1.58 log (range, km 2 ) + 1.529; r 2 ¼ 0.9), irrespective of migratory type (for 23 major groups a total of 22 million tonnes over 3.3 million km 2 with an average density of 7 tonnes km )2 ). Historical densities were not related to area occupied, although all large groups exhibited high densities (10-12 tonnes km )2 ; smaller groups had a wide range of density). The four migratory strategies in cod enable entrainment by diverse physical, oceanographic and biological ecosystem properties, and is key to cod success in the North Atlantic.

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“…Recruitment at ages 3 and 4 fluctuated by a factor of 9 during the 30-year period from 1962 to 1987 (Baird et al, 1991). A number of hypotheses explored to explain recruitment in northern cod include salinity, temperature, dispersal of eggs and larvae, and shifts in spawning location affecting egg dispersal and survival (Sutcliffe et al, 1983;Helbig et al, 1992;Myers et al, 1993;deYoung and Rose, 1993). These hypotheses have focused exclusively on the egg and larval stages prior to the juvenile stages, and the results have been largely inconclusive.…”

Section: Introductionmentioning

confidence: 98%

Factors regulating survival of northern cod (NAFO 2J3KL) during their first 3 years of life

Anderson¹

2000

ICES Journal of Marine Science

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Mean instantaneous mortality was estimated for northern cod (NAFO Divisions 2J3KL) during the first 3 years of life for the period 1962-1987. Mortality was a density-dependent function of the adult population, increasing non-linearly with abundance. Residual mortality reached maximum values in 1970-1971, in association with cold, low salinity water of the Great Salinity Anomaly. Juvenile cod c2 years old were distributed towards the inshore and did not migrate offshore seasonally with larger juvenile cod (d3 years) and adults. Geographic distributions of 1-and 2-year-old cod were density-dependent, where the distribution expanded in direct proportion to year-class abundance. There were no local increases in density as year-class abundance increased. These results imply a spatial limit on preferred seabed habitats for small cod. When 2-year-old cod were more abundant and distributed more widely onto the shelf they experienced a significant increase in cannibalism. Older juvenile cod, age 4, did not expand their geographic range with increasing year-class abundance, but did increase in density within local areas of high abundance, implying that this age group was not dependent on seabed habitats. The offshore persistence within local areas of high abundance may be associated with other factors, such as prey availability. Three-year-old cod appeared to be in transition between the habitat-dependent distributions of younger cod and the habitat-independent distribution of older cod. We hypothesize that increased cannibalism occurs at higher adult population sizes during their summer feeding migration to the inshore. In addition, increased cannibalism occurs on cod c2 years old belonging to more abundant year classes owing to a wider geographic distribution into less preferred habitats that overlap with the overwintering distribution of adults and large juveniles. Our results are consistent with the hypothesis that recruitment in cod is largely established during the egg and larval stages linked to environmental effects, while density-dependent processes operate to moderate survival during subsequent juvenile stages prior to recruitment. International Council for the Exploration of the Sea

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Environmental influences on the recruitment of Newfoundland/Labrador Cod*

Cited by 38 publications

References 22 publications

Recent changes in the winter distribution and movements of northern Atlantic cod (Gadus morhuaLinnaeus, 1758) on the Newfoundland-Labrador Shelf

Recent changes in the winter distribution and movements of northern Atlantic cod (Gadus morhuaLinnaeus, 1758) on the Newfoundland-Labrador Shelf

Migratory behaviour and range in Atlantic cod: inference from a century of tagging

Factors regulating survival of northern cod (NAFO 2J3KL) during their first 3 years of life

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