Southern Grand Banks Research Articles

Commercial fishing practices on offshore juvenile flatfish nursery grounds on the Grand Banks of Newfoundland

Analyses of the 1985 to 1989 juvenile flatfish survey data from the Grand Bank off the east coast of Newfoundland has delimited two major areas of juvenile American plaice, Hippoglossoides platessoides, concentrations: one on the northern slope and one on the southern edge of the bank. A major concentration of juvenile yellowtail flounder, Limanda ferruginea, was distributed in the area of the Southeast Shoal on the southern Grand Bank. Juveniles of both species shared their distribution with their adult population and there was some overlap by juveniles of both species on the southern Grand Bank. These areas of concentrations are hypothesized to be oceanic nursery sites for both Grand Bank species. The northern plaice nursery area is fished heavily by the Canadian otter-trawler fleet because the majority of the adult population is located in this area. The southern nursery area for plaice is fished heavily by many otter-trawl fleets of other nations since it is located outside of Canada's 200-mile fishing boundary. The southern nursery area for juvenile yellowtail flounder straddles the 200-mile boundary and, consequently, is fished heavily by Canadian (inside) and non-Canadian (outside) fleets. The implications of these dual fisheries on the southern Grand Bank is discussed in terms of discarding of under-sized fish by the Canadian fleet inside the 200-mile boundary and the directed effort on juveniles outside the boundary.

Application of section-balancing techniques to deep seismic reflection data from offshore eastern Canada: preliminary observations

The application of section-balancing techniques to the analysis of deep seismic sections requires account be taken of isostasy and ductile-deformation processes. Structures imaged by deep seismic reflection profiling across the southern Grand Banks, offshore eastern Canada, are analyzed in this way. Correlations of dipping events in the deep crust, interpreted as shear zones, with faults recognized in the shallow part of the section are tested by attempting to restore the sections to their undeformed state by reversing the displacements on the faults. This process tests the geometric compatibility of the interpreted fault and the structures in its hanging wall. Our models suggest that the faults bounding the Whale and Horseshoe basins detach at the Mohorovičić discontinuity. In contrast, the fault bounding the Jeanne d'Arc Basin detaches within the lower crust.

Variation of Vertebral Numbers with Fish Length in Atlantic Cod (Gadus morhua) of the Eastern Newfoundland Area, 1947-71

Means of vertebral numbers in cod samples collected in 1947-71 from the eastern Newfoundland and Labrador area were compared by length-ranges. In NAFO Div. 2GHJ and 3KL, the northern-type high-vertebral means (usually over or slightly below 55) were usually present at the length-ranges of lesser length, declining toward lower means at greater sizes. The high-vertebral-type mean extended to higher length-ranges northward than southward. In coastal areas of Div. 2GHJ and 3K, the means at the same length-ranges tended to be somewhat lower than offshore. Means at the same length-ranges for the above areas were usually a little higher in the earlier period, 1947-55, than in the later period, 1958-71. Throughout the area (not including Div. 3M) offshore and inshore vertebral means at the same length-range and period were typically lower in the southern than in the adjacent northern area. The vertebral means of the relatively isolated cod stock on Flemish Cap (Div. 3M) were intermediate between the northernand the southern-types, and on the southern Grand Bank (Div. 3NO) the means (usually below 54) were typically the lowest in the eastern Newfoundland area. Within each of these areas (Div. 3M and 3NO), means did not differ greatly by length-range and from the earlier to the later

Crustal structure beneath the southern Grand Banks: seismic-refraction results and their implications

A seismic-refraction profile was shot on the southern Grand Banks using large air-gun sources and an array of ocean-bottom seismograph receivers. A sediment column 1–2 km thick directly overlies Paleozoic basement with velocity structure similar to that of the Meguma Zone of Nova Scotia. The main crustal layer is 27 km thick, with seismic velocity of 6.3 km/s increasing to about 6.5 km/s in the lowest few kilometres. Complexity is apparent in the crust–mantle transition around 32 km depth. Comparison with deep multichannel reflection data suggests that the increased velocity in the lower part of the crust may be associated with a reflective zone and shows the Mohorovičić discontinuity to be delineated by a well-defined reflection. The absence of a major lower crustal layer of intermediate velocity (> 7 km/s) is consistent with observations elsewhere in the region.

Crustal structure across the Southwest Newfoundland Transform Margin

A seismic-refraction survey providing deep crustal structure information of the continent–ocean boundary across the South-west Newfoundland Transform Margin was carried out using large air-gun sources and ocean-bottom seismometer receivers. Continental crust ~30 km thick beneath the southern Grand Banks (P-wave velocity = 6.2–6.5 km/s) thins oceanward to a 25 km wide transition zone. In the transition zone, Paleozoic basement of the Grand Banks (5.5–5.7 km/s) is replaced by a basement of oceanic volcanics and synrift sediments (4.5–5.5 km/s). Seaward of the transition zone the crust is oceanic in character, with a velocity gradient from 4.7 to 6.5 km/s and a thickness of 7–8 km. Oceanic layer 3 is absent. No significant thickness of intermediate-velocity (>7 km/s) material is present at the continent–ocean transition, indicating that no under-plating of continental crust has taken place. The continent–ocean transition across the transform margin is much narrower than across rifted margins, supporting the theory that formation of the transform margin is by shearing of continental plates.

Movements of Atlantic Halibut (Hippoglossus hippoglossus) in the Canadian North Atlantic

The results of Atlantic halibut (Hippoglossus hippoglossus) tagging experiments conducted in Northwest Atlantic Fisheries Organization (NAFO) Subareas 3 and 4 between 1958 and 1973 were reexamined. Data from the 230 recaptures indicated a tendency for fish released on the Scotian Shelf to move to the northeast, while fish released on the Newfoundland Grand Bank showed no preferred direction of movement. The Laurentian Channel does not appear to be a barrier to migration for this species. Small (<75 cm) fish moved further than larger fish. The seemingly limited movement by larger fish may be due to acyclic annual migration between feeding and spawning grounds, similar to that suggested for Pacific halibut (Hippoglossus stenolepis). The extensive movement of Atlantic halibut throughout most of the Canadian Northwest Atlantic suggests that a single area would be the most feasible management unit, encompassing the Scotian Shelf and southern Grand Bank regions.

Canada's East Coast Offshore Exploration And Development

Abstract Canada's east coast offshore continental shelf is extensive and has excellent oil and gas potential. Numerous Mesozoic sub-basins have been explored, and the principal targets are Late Jurassic to Early Cretaceous clastic reservoirs found in a variety of plays and trapping modes. Exploration activity has only taken place over the past 20 years, with approximately 250 wells drilled. Some 41 discoveries have been made containing an estimated total recoverable resource of about 1.3 billion barrels of oil and 10.0 TCF of gas. The Hibernia oil discovery, offshore Newfoundland, and the Venture area gas Discoveries, offshore Nova Scotia, are the accumulations most likely to be developed in the near future. Introduction This paper gives a generalized overview of the geological setting, the exploration history and the hydrocarbon development potential of Canada's east coast offshore. There have been several excellent papers written over the past 15 years describing Canada's east coast offshore geology. This paper attempts to summarize the major findings of these earlier works in a generalized overview. Although references are not quoted, readers are referred to a recent publication by Grant, McAlpine and Wade (AAPG Mem. 40, 1986, pp. 177–205) for an excellent geological synthesis of the Atlantic offshore margin of eastern Canada. The subject area (Fig. 1) encompasses the offshore continental margin of Atlantic Canada from northern Labrador to southern Nova Scotia, a distance of over 3500 km. The continental shelf out to the 1000-m isobath covers a vast area readily drillable with modern technology. This accessible shelf can be subdivided into four regions, each with its unique physiographic setting, underlying geology and exploration history. These are the Labrador Shelf, the northern Grand Banks/northeastern Newfoundland Shelf, the southern Grand Banks and the Scotian Shelf. Common to each of these areas is a wedge of Mesozoic/Cenozoic sediments that expands seaward from a zero edge to thousands of metres in thickness in specific Mesozoic sub-basins or depocentres. These Mesozoic sub-basins or "thicks " tend to be elongated, fault controlled and separated by basement-cored shelf areas or arches. The Mesozoic sub-basins have been the focus of exploration activity, and are the areas where practically all the significant discoveries have been made. Surrounding the sub-basins, structurally monotonous shelf areas and arches are covered by a much thinner veneer of Mesozoic sediments and are only marginally prospective. Offshore areas such as the Gulf of St. Lawrence, Bay of Fundy and Baffin Bay have been less intensely explored and are only briefly mentioned. The petroleum industry has been seriously exploring the east coast offshore for only the past 20 years. During that time there have been approximately 250 wells drilled and over 800 000 km of seismic shot. This has resulted in a tremendous increase in the geological understanding of the area. The discovery of significant accumulations of oil and gas has confirmed its hydrocarbon potential. Canada's east coast offshore is, however, an extremely hazardous and costly frontier in which to explore. The rewards have not always justified the finding costs and interest and activity levels have fluctuated over the past two decades.

Basement Extension and Salt Mobility, Southern Grand Banks, Newfoundland: ABSTRACT

Basement Extension and Salt Mobility, Southern Grand Banks, Newfoundland: ABSTRACT

Atlantic Salmon (Salmo salar) On and East of the Grand Bank

Exploratory fishing with surface gillnets on the Grand Bank and eastward of the Bank over oceanic depths in May of 1979and 1980 revealed the presence of Atlantic salmon (Sa/rna safar L.) at most stations where surface temperatures ranged from 3.8° to 7.5° C. These temperatures were more prevalent in the oceanic area and salmon were found in greater abundance there than on the Grand Bank. Of 341 salmon which were caught, 169 were tagged and released after scales were taken for ageing. Information on tagging locations of three salmon which were caught with tags attached and the distribution of recaptures of 12 salmon from the offshore tagging indicated that the offshore population consisted of migrants from Newfoundland, Nova Scotia, New Brunswick and Maine rivers. The sea-age composition of the catch and the gonad condition of the sampled catch indicated that some of the salmon were maturing to spawn as grilse which had spent only one winter at sea. Apart from their capture in coastal fisheries, this is the first record of grilse being caught in offshore areas of the Northwest Atlantic. Analysis of sea-surface temperature charts for 1978-83 indicated that favorable conditions (4° to 8° C water) persist for salmon in January and April, implying that the eastern and southern Grand Bank region may represent not only the route by which maturing salmon migrate from the Labrador Sea to their home rivers in eastern Canada and northeastern United States but also a major feeding and overwintering area. Comparison of catch rates of salmon from commercial and research fishing off West Greenland and in the Irminger Sea with those of the Grand Bank region implies that the feeding population east of the Grand Bank was quite large in 1980.

Continental Margin of Eastern Canada--Geologic Framework and Petroleum Potential: ABSTRACT

The Atlantic-type continental margin of eastern Canada is underlain by a series of Mesozoic-Cenozoic sedimentary basins separated by basement highs or areas of thinner sediments. Regional and/or salt tectonics have structured the Mesozoic sequence, which is masked by a less-deformed wedge of prograding uppermost Cretaceous and Cenozoic sediments. The basins have been targets of active hydrocarbon exploration for over 2 decades. Data from 138 exploratory wells and over 680,000 km (420,000 mi) of multichannel seismic coverage have indicated four major geologic/geochemical regions: Scotian Shelf, southern Grand Banks, northeastern Grand Banks, and Labrador-Southeast Baffin Shelf. On the Scotian Shelf, 13 significant gas/condensate discoveries have been made out of 62 wildcats drilled since 1967. Five of the discoveries, including the Venture field, are in an overpressured zone that has been explored only since 1979. No commercial hydrocarbon accumulations have been found in the southern Grand Banks where 28 wildcats were drilled between 1966 and 1975. The northeastern Grand Banks region has been actively explored since 1971. The 22 wildcat wells drilled through late 1983 have yielded six significant light oil discoveries, including the giant Hibernia oil field. Labrador-Southeast Baffin Shelf exploration has yielded six gas/condensate discoveries in 26 exploratory wells drilled since 1971. The Geological Survey of Canada has developed hydrocarbon-generation models to explain the regional variation in oil and gas occurrence and to assess future potential in terms of the nature and thermal maturity of the source rocks, type of organic material, and time of trap formation. These factors are related to the geologic history of the margin, which is characterized regionally by diachronism in major basin inception and in the resultant stratigraphic record. We predict an exciting future for this vast petroleum province. End_of_Article - Last_Page 1203------------

Tectonic control of Triassic sedimentation in southern New Brunswick: Local and regional implications

Both regional and local tectonics controlled the sediment distribution in the Fundy half-graben during the Triassic. Locally, alluvial fans built out into the basin from the western boundary fault along what is now the south shore of New Brunswick. The alluvial fan red beds of the Honeycomb Point Formation are covered by fluvial conglomerates of the Quaco Formation, which in turn are buried by a resurgence of alluvial fan deposition represented by the Echo Cove Formation. Pollen recovered from the upper part of the Echo Cove Formation indicates that, regionally, the system of Triassic-Jurassic grabens along the eastern seaboard is composed of two separate graben systems; one stretching from South Carolina to Connecticut, the other from the Gulf of Maine to the southern Grand Banks. Initial graben formation began at the southern end of each system, followed by successive grabens opening toward the north. The areal distribution of both graben systems appears to have been controlled by four large transform-fault systems from the Middle Triassic through the Jurassic. The age and overall distribution of sediments within the Fundy Basin confirm the existence of a hot spot along the Kelvin Seamount chain and refines determination of the position and timing of the initial rifting that led to the formation of the present Atlantic Ocean.

Prevalence of a Trypanosome in Atlantic Cod (Gadus morhua) Especially in Relation to Stocks in the Newfoundland Area

A study was initiated to ascertain the prevalence of a trypanosome in Atlantic cod (Gadus morhua) especially in relation to stocks in the Newfoundland area and as an aid in management and conservation. Highest prevalences were recorded in fish taken off the Labrador coast (ICNAF divisions 2J and 3K, 94 and 90%, respectively). Trypanosomes were not as prevalent in fish collected from the northern Grand Bank (46%, division 3L) or from the southern Grand Bank (13 and 16%, divisions 3N and 3O, respectively). A further decrease in prevalence occurred among fish collected on the Flemish Cap (10%,, division 3M) and St. Pierre Bank (8%, subdivision 3Ps), while the lowest levels (4%) were apparent in cod taken from the Gulf of St. Lawrence (divisions 4R and 4S). Fish sampled at inshore localities reflected prevalences corresponding to some extent to offshore localities. Cod taken on coastal Labrador and from northern Newfoundland have a high prevalence of trypanosome infections while in the more easterly bays, intermediate levels occur. A conspicuous decrease in prevalence was apparent in a sample taken from the most easterly inshore locality (Portugal Cove) and from two others on the south coast of Newfoundland. Lowest prevalences were noted among fish taken at four inshore localities in the Gulf of St. Lawrence. These results, based on prevalences of infection, support conclusions from other studies that there are at least six stocks of cod in the Newfoundland area with some degree of mixing.Key words: trypanosome, prevalence, cod stocks, Newfoundland–Labrador, ICNAF

The canadian atlantic margin: A passive continental margin encompassing an active past

The continental margins of Atlantic Canada described in this paper show the effects of plate tectonic motions since Precambrian time and thus represent an ideal natural laboratory for geophysical studies and comparisons of ancient and modern margins. The Grenville Province shows vestiges of Helikian sedimentation on a pre-existing continental block beneath which there may have been southeastward late-Helikian subduction resulting in collision between the Grenville block and the continental block comprised of the older shield provinces to the north. The Grenville block was subsequently split in Hadrynian time along an irregular line so that the southeastern edge of the Grenville exhibited a series of promontories and re-entrants similar to those seen at the present Atlantic continental margin of North America. That margin, which had a passive margin history perhaps comparable with that of the present Atlantic margin, was separated by the lapetus ocean from the Avalon zone whose Precambrian volcanism has been attributed both to that associated with an island arc and with intra-cratonic rifting. However, the lapetus ocean appears to have been subducted in early Paleozoic time with a southeastward dip beneath the Avalon zone, leaving exposures of oceanic rocks in place as in Notre Dame Bay, or transported onto Grenville basement as at Bay of Islands. Plate motions proposed for Devonian and Carboniferous time are numerous, but resulted in the welding of the Meguma block to the Avalon zone of New Brunswick and northern Nova Scotia, extensive faulting within Atlantic Canada which can be correlated with contemporaneous European faulting and extensive terrestrial sedimentation within the fault zones. Graben formation, continental sedimentation and basaltic intrusion in the Triassic represent the tensional prelude to the Jurassic opening of the present Atlantic Ocean. This Jurassic opening produced a rifted margin adjacent to Nova Scotia and a transform margin along the southern Grand Banks. The width of the ocean-continent transition across the transform margin (approx. 50 km) is narrower than for the rifted margin (approx. 100 km). The eastern part of the transform margin is associated with a complex Cretaceous (?) volcanic province of seamounts and basement ridges showing evidence of subsidence. The western portion of the transform margin is non-volcanic, adjacent to which lies the 350 km wide Quiet Magnetic Zone floored by oceanic crust. Development of the margin east of Newfoundland was more complicated with continental fragments separated from the shelf by deep water basins underlain by foundered and atypically thin continental crust. Although thin, the crust appears unmodified, the similarities between the crustal sections of the narrow Flemish Pass and the wide Orphan Basin suggesting that the thinning is not simply due to stretching. The Newfoundland Basin shows evidence for two-stage rifting between the Grand Banks and Iberia with both lateral separation and rotation of Spain, leaving a wide zone of transitional crust in the south. The overall pattern of variations in crustal section for the margin east of Newfoundland is comparable with that of the British margin against which it is located on paleogeographical reconstructions. The major sedimentary unconformities on the shelves (such as the Early Cretaceous unconformity on the Grand Banks) reflect uplift accompanying rifting. Tracing of the sedimentary horizons across the shelf edge is complicated by paleocontinental slopes, which separate miogeocline and eugeocline depositional environments. The subsidence of the rifted margins is primarily due to cooling of the lithosphere and to sediment loading. The subsidence due to cooling has been shown to vary linearly with (time) 1 2 , similar to the depth—age behaviour of oceanic crust. The consequent thermal history of the sediments is favourable for hydrocarbon generation where other factors do not preclude it.

Geophysical evidence for the extent of the Avalon zone in Atlantic Canada

Precambrian volcanic rocks exposed in structural highs of the Avalon zone of Newfoundland are marked by high magnetic anomalies whose continuity offshore permits recognition of the extent of the Avalon zone, particularly on the Grand Banks. South of Newfoundland and in the Gulf of St. Lawrence, where the magnetic pattern is less well defined, the Avalon platform can also be recognized by the existence of seismic velocities of the order of 6.6 km s−1, which are apparently associated with volcanic rocks. The magnetic Collector Anomaly running eastwards from Cape Breton across the southern Grand Banks is the southern limit of these Avalonian markers, while the northern boundary follows a serrated path (the offsets apparently caused by a series of northwest-trending faults) from the Belle Isle Fault in New Brunswick to the Hermitage and Dover Faults in Newfoundland, thence to the western end of the Charlie Fracture zone. These Avalonian boundaries provide markers for the constraint of pre-drift continental reconstructions.

Oceanic heat flow measurements over the continental margins of eastern Canada

Sixteen heat flow measurements have been obtained on the continental rise and slope off Nova Scotia and off the southern Grand Banks of Newfoundland. The mean of the 14 most reliable values is 48 ± 4 mW m−2 (1.15 ± 0.09 μcal cm−2 s−1), which is in agreement with the mean for previous measurements on ocean floor of age greater than 100 m.y. However, the heat flux from the crust indicated by the new values is significantly lower because of the heat produced in the some 5 km of terrigenous sediments underlying the stations. The low values could represent an edge effect between continent and ocean. Two lines of stations across the Nova Scotia rise show large heat flow variations. Numerical models indicate that the variations could arise from thermal refraction by high thermal conductivity salt, which probably constitutes the 'sedimentary ridge complex' outlined by deep seismic reflection profiles. The salt or evaporites formed in the restricted basin that was parallel to this rifted margin during the first phase of opening of the Atlantic Ocean. The heat flow variations measured on a profile perpendicular to the southern edge of the Grand Banks are smaller. This margin was a transform fault between Newfoundland and northwest Africa during the early ocean opening, so that the seafloor in the region of the profile was produced after the restricted basin phase of evaporite formation.

Migrations and Intermingling of Atlantic Cod (Gadus morhua) Stocks of the Newfoundland Area

Commercial recaptures of 26% (22.5% in years after the tagging year) of 18,822 Atlantic cod (Gadus morhua) 50 cm or more in length that were tagged mainly in the feeding season at 13 localities in the Newfoundland area in 1954–55 elucidated migrations and intermingling of cod of various stocks or stock complexes. Cod of the northern Gulf of St. Lawrence stock migrated southward from the Strait of Belle Isle to winter on the northern side of Cabot Strait and vicinity, mingling there with the Burgeo Bank stock. Cod of the Newfoundland–Labrador complex tagged at three sites mingled along the east coast of Newfoundland and off southern Labrador and with cod of the northern Gulf stock near the Strait of Belle Isle, of the Avalon–Burin stock complex off the Avalon peninsula, and of a Grand Bank stock on the northern part of the bank. Though cod tagged off the Avalon peninsula and on St. Pierre Bank were recaptured mainly near the tagging sites, some moved as far north as Labrador, to the southern Grand Bank, and to Cabot Strait. Fish tagged on the northwestern Grand Bank were recaptured mainly at the tagging site but also elsewhere on the bank and off the east coast of Newfoundland. Those tagged on the Southeast Shoal of the Grand Bank were recaptured mainly on the southeastern part of the bank though some moved as far as southeastern Newfoundland. Those tagged on Burgeo Bank mingled with the Avalon–Burin stock complex, including the St. Pierre Bank component, but mainly with the Northern Gulf stock in winter–spring near Cabot Strait.Cod 90–129 cm long at tagging were recaptured at shorter distances from the tagging sites than 50–89-cm cod. Tagging–recapture distances also increased with increasing age for cod of the smaller length ranges on tagging. In their vertical movements, most tagged cod moved to shallow water in late spring or early summer and retreated gradually to deeper water from late summer to early spring. Some remained in deep water throughout the year.Recapture rates at different size ranges varied with area but were not greatly different at length ranges from 50–59 to 80–94 cm, which included 95% of the tagged cod.

Vertebral and Other Meristic Characteristics of Greenland Halibut, Reinhardtius hippoglossoides, from the Northwest Atlantic

Vertebral averages were not useful in separating Greenland halibut stocks of the northwest Atlantic, apart from the possible separation of the Gulf of St. Lawrence population.Mean numbers of vertebrae did not differ significantly at the 5% level within the main areas in samples collected between 1950 and 1968 from Baffin Bay to the southern Grand Bank. Mean numbers of vertebrae for each of these main areas also were, with one exception, not significantly different. Mean vertebral numbers of Greenland halibut from the northern Gulf of St. Lawrence (61.850 ± 0.057 SE) differed (P < 0.001) from the overall mean for the remainder of the northwest Atlantic (61.575 ± 0.014).The similar means were associated with similar temperatures at depths of 800 m and over, where eggs and early larvae are presumed to develop. Means of vertebral numbers of males and females were not significantly different.Precaudal and caudal vertebral numbers were negatively correlated. Fused vertebrae were not numerous and did not show much localization except toward the posterior end of the vertebral column, especially in the two most posterior whole vertebrae. The numerical value of each fused partial vertebra was very close to one.Anal and dorsal fin-ray numbers were highly correlated but were not correlated significantly with vertebral numbers. The means of dorsal and anal fin-ray numbers in a few samples from west Greenland to the southern Grand Bank were not significantly different.

Distributions and Comparisons of Centrolophus niger (Gmelin) and Centrolophus britannicus Günther (Centrolophidae) from the North Atlantic

The general distribution of Centrolophus niger in the North Atlantic is reviewed including the first two records from the Canadian area and two additional records off the New England coast to add to the four previously recorded from this area. Two new records from the Dana collections extend the distribution of this species westward in the oceanic area between Iceland and the Azores. All known records of the rarely captured Centrolophus britannicus are presented. These include 34 previously published records from the northeastern Atlantic, eight new records from the northeastern Atlantic and the first seven records from the northwestern Atlantic, from Flemish Cap and the southern Grand Bank to North Carolina.In separating C. niger and C. britannicus some meristic characters are useful: C. niger, D. 35–41, A. 23–25, P. 20–23, gill-rakers on lower limb 1st arch, 13–15; C. britannicus, D. 44–51 (one, 55), A. 27–33 (one, 25), P. 18–21 (one, 16), gill-rakers on lower limb 1st arch, 11–13. Some body proportions are also important: the bases of the dorsal and anal fins are longer in C. britannicus and the distance from the snout to the anterior base of the dorsal fin usually greater. The length of the caudal peduncle is distinctly greater in C. niger.In C. niger the flesh is firm and the skin tough whereas in C. britannicus the flesh is flabby and the skin delicate. The peritoneum of C. britannicus is usually dark and that of C. niger usually light.

Age, Growth and Sexual Maturity of Cod (Gadus morhua L.) in the Newfoundland Area, 1947–1950

Samples of cod were collected from fishing gears in the coastal areas of Newfoundland and Labrador and from research otter-trawlers on the neighbouring banks from 1947 to 1950. Collections for the most part were from early summer to early autumn. Ages were determined using otoliths. Calculations of growth were based on average lengths and weights of the different age-groups in the samples.The growth rates of cod from various parts of the area were found to differ widely. Labrador cod had the slowest growth rate, much slower than cod from other parts of the area. Cod from the east coast of Newfoundland and the northeastern part of the Grand Bank were also slow-growing. Cod from the southwestern part of the Grand Bank had the fastest growth rate. Though cod from St. Pierre Bank and southwestern Newfoundland were fast-growing, also, they exhibited a somewhat slower growth rate than those from the southwestern part of the Grand Bank. Cod from the west coast of Newfoundland grew faster than cod from the east coast, but slower than those from southwestern Newfoundland.Though differences in growth rate were small between the sexes, the females generally grew at a slightly faster rate.The influence of differences in temperature and in food supply on the growth of cod in the area is discussed.Comparable growth data for the area published by several investigators are discussed. It is suggested that differences in these data were the result of variation in sampling locality, different sampling gears, different combination of individual samples and differences in age estimation.Both the size and age at which all fish were sexually mature varied throughout the area of investigation. Labrador cod matured at an earlier age and smaller size than cod from other parts of the area, whereas cod from the southwestern part of the Grand Bank generally matured at a later age and larger size than cod from other parts of the area. Cod from the east coast of Newfoundland, the northeastern part of the Grand Bank, St. Pierre Bank and the southwest and west coasts of Newfoundland were intermediate between cod from Labrador and the southwestern part of the Grand Bank in age and size at maturity, fish from the east coast generally maturing at an earlier age and smaller size than fish to the south on the Grand Bank and St. Pierre Bank and from the southwest and west coasts.The age, growth and sexual maturity relationships of cod from various parts of the area, when analyzed in the light of tagging experiments, meristic studies, parasite studies and hydrographic information, suggest the existence of at least four relatively distinct divisions in the cod population of the area, between which there is only limited intermingling. These are the Labrador, the Newfoundland east coast, the southern Grand Bank and the Newfoundland west coast divisions, with areas such as St. Pierre Bank and the Strait of Belle Isle being mixing areas of cod from adjacent divisions.