Northern Grand Bank Research Articles

Age- and Sex-Specific Survival of Northern Grand Bank Capelin (Mallotus villosus)

Age-specific, sex-specific survival rates for immature and mature capelin (Mallotus villosus) were estimated by linear least-squares models, using abundance data derived from annual acoustic/trawl research surveys conducted from 1982 to 1990 on the northern Grand Bank. Survival estimates for age 2 immature fish were comparable between sexes (annual survival equals approximately 40%). Survival estimates for age 4 mature fish differed between sexes, with females having a higher (25–51%) average survival estimate than males (6%). Survival estimates for immature and mature age 3 fish were equivocal; immature males and females had comparable rates (30.3–32.3 and 15.2–26.6%, respectively) whereas a greater proportion of mature females (25–50%) survived than of mature males (2.5–13%). The stated ranges denote survival estimates including and excluding an influential data point, respectively. Higher average survival of mature females than of mature males may be a result of sex-specific behavior during beach spawning. The average annual contribution of surviving mature females to the total number of female spawners was estimated as 24–47%.

Migration of pre-spawning capelin (Mallotus villosus) as related to temperature on the northern Grand Bank, Newfoundland

Migration of pre-spawning capelin (Mallotus villosus) as related to temperature on the northern Grand Bank, Newfoundland

Environmental influences on fish and shellfish production in the Northwest Atlantic

Evidence is reviewed, linking physical oceanographic processes in the marine environment to changes in fish and shellfish stocks in the Northwest Atlantic. A case history study of the cod (Gadus morhua) stock of the northern Grand Banks and Labrador Shelf indicates a long slow amelioration of the environment between about 1945 and 1965, followed by a deterioration in the period 1965–1992. The most important environmental factors for the cod stocks appear to have been salinity and temperature. The trends can be traced back to climatic factors involving the Icelandic Low and the Azores–Bermuda High. When the atmospheric pressure difference in winter tended to be high, there was a progressive increase in the area of sea ice off Labrador and in the volume of cold water at depth. These factors have been shown to affect temperature and salinity conditions on the Grand Banks in spring and summer and are associated with poor growth and recruitment in the cod stocks. A similar case study of lobster (Homarus americanus) stocks indicates that temperature and river discharge are important environmental correlates, but neither can be shown to fully account for the recent trends in the stocks. Evidence is reviewed to show that physical environmental processes also influence recruitment and distribution of stocks of haddock, capelin, and squid. Some of the problems with correlational analysis are also discussed. It is recognized that factors other than the environment are influencing the stocks. Fishing mortality (detailed consideration of which is not included in this review) has clearly been important. Interactions between environmental factors and fishing mortality are probably of major importance.Key words: ocean environment, fish production, recruitment, northern cod, American lobster.

Geographic Variation in the Spawning of Atlantic Cod, Gadus morhua, in the Northwest Atlantic

We analyzed 47 yr (1946–92) of research trawl data and 5 yr (1964–68) of research gillnet data to identify spawning locations of Atlantic cod, Gadus morhua, in the Newfoundland–Labrador region. Offshore, spawners are common on the continental shelf but generally rare on the slope. Relative abundance of spawning individuals on the shelf is comparably high off northeast Newfoundland, within 100 km of the Newfoundland coast from Cape Freels to Cape Race, on central Grand Bank, and on St. Pierre Bank. Slope spawning is largely restricted to the eastern slope of Hamilton Bank, a small section of northern Grand Bank, and Flemish Cap. Inshore spawning is evident in southeastern Labrador and southeastern Newfoundland, particularly in St. Mary's, Placentia, Trinity, and Bonavista bays. Trajectories of satellite-tracked drifter buoys indicate that it is highly improbable that eggs spawned on the slope of Grand Bank and much of the northeastern Newfoundland slope will be transported into shelf and coastal waters. We conclude that cod spawn in areas in which their eggs and larvae are likely to be retained and that inshore spawning populations may provide a considerably larger contribution to cod recruitment in coastal Newfoundland than has previously been believed.

Patterns in Coastal Migration and Stock Structure of Capelin (Mallotus villosus)

Approximately 57 500 mature capelin (Mallotus villosus) were tagged with external tags from 1983 to 1988 along the southeast and east coasts of Newfoundland to determine inshore migration patterns and to reexamine the current belief that two separate capelin stocks spawn on east coast beaches. Capelin released in a particular bay were recaptured from the same bay or locations further north. Upstream migration using the Labrador Current was hypothesized as a directional clue to the prespawning migration. Capelin caught in one stock area were recaptured in another area, indicating that mature capelin from the Northeast Newfoundland – Labrador and Northern Grand Bank – Avalon stocks mix and migrate north together. The distribution and mixture of pre-spawning fish inshore as described by tag returns have implications on how capelin resources should be surveyed, assessed, and managed.

Seasonal distribution of American plaice on the northern Grand Banks

Seasonal distribution of American plaice on the northern Grand Banks

An analysis of fleet numerical oceanographic center winds on the grand banks

Abstract An analysis is made of the errors in the wind field of the Fleet Numerical Océanographie Center (FNOC) over the northern Grand Banks. Observed wind data from an oil rig at the Bonanza site (47° 30'?, 48° 12 ‘ W) are comparedwith wind data obtainedfrom the grid prepared by FNOC. The resulting two time series are found to be strongly correlated at frequencies up to 0.5 cycles d−l (cpd). Most of the error in the FNOC wind field is observed at frequencies above 0.5 cpd. Discrepancies in direction between the two data sets occur most frequently at low wind speeds (less than 10ms−1). There is better agreement for wind direction in the winter than in the summer. Linear interpolation of the FNOC grid data yields the best regression with the observed wind. Wind observed at St John's shows no correlation with the observed wind on the northern Grand Banks.

Distribution and relative abundance of greenland Halibut ( Reinhardtius hippoglossoides (Walbaum)) in the Canadian Northwest Atlantic from Davis Strait to the northern Grand Bank

The catches of Greenland halibut ( Reinhardtius hippoglossoides (Walbaum)) were distributed from Davis Strait to the northern slopes of the Newfoundland Grand Bank with no apparent break in the continuity of the distribution. They were most abundant along the slopes of the continental shelf and in the deep channels around the fishing banks. They were caught in depths less than 200 m to depths greater than 1000 m. However, the preferred depth ranges varied with both latitude and season. For the areas where bottom temperature data were presented, fish were caught in a range of 0.0–6.0°C with a preference for warmer water (5.1–6.0°C) in northern Labrador during summer compared with colder water (< 0.0°C) during autumn in southern Labrador. For all areas examined larger and older fish predominated in the deeper waters and also increased in abundance moving progressively from south to north. An examination of age compositions from the commercial fishery which exists mostly in the more southerly area (Div. 2J, 3K and 3L) shows that it exploits a few younger age groups (6–9-year-olds in particular) while older fish ( > 10 years old) are hardly exploited at all.

On the spatial frequency of linear ice scours on the seabed

In this paper the factors which affect the spatial frequency of linear scours on the seabed are identified through the use of a Monte Carlo simulation model. This identification is followed by analysis leading to various formulas useful for assessing the risk to undesea structures from scouring ice. Specifically, formulas for the conditional probability that a scour will intersect a segment of pipeline or an installation in the shape of a convex geometric figure, expressed in terms of measured scour parameters, are developed. In addition, formulas for the annual probability that a segment of pipeline may be scoured and the expected number of pipeline/scour interactions are obtained. Similarly, it is shown how to calculate the annual probability that a rectangular region will be scoured. Definitions of areal and scour start-point density are presented which precisely delineate the important concepts associated with scour frequency as seen in existing sonogram imagery. The use of these concepts is illustrated by their application to some simulated sonogram imagery. Finally, the methods are applied to recent resurvey results for an area on the northern Grand Banks of Newfoundland to estimate an upper bound on the annual scour rate for the region.

Repeated cluster analysis of stomach contents data: method and application to diet of cod in NAFO division 3L

Data matrices of fish stomach contents frequently contain many zeros, and nonzero values often do not follow usually encountered statistical distributions. Therefore, many common methods of statistical analysis are inappropriate for such data. A method of repeated k-means cluster analysis is proposed for exploratory analysis of data sets on fish stomach contents. Objective rules are proposed for setting the clustering parameters, so the arbitrariness and subjectivity common in interpreting hierarchical clustering methods is avoided. Because the clusters are nonhierarchical, the analysis method also requires much less computer time and memory. Application of the method is illustrated with a data set of 1771 stomachs of cod (Gadus morhua), feeding on 38 different prey types. The results of the clusterings reveal that nine types of prey may account for the systematic information about the diet of cod in this sample from the northern Grand Bank in Spring of 1979. The results are also used to test specific hypotheses about size selectivity of the predator, spatial variation of feeding, environmental influences on diet, and relative preferences among prey taxa.

An Analysis of Morphometric Characters of Greenland Halibut (Reinhardtius hippoglossoides) in the Northwest Atlantic Using a Multivariate Analysis of Covariance

Eleven morphometric characters were measured on samples of Greenland halibut (Reinhardtius hippoglossoides) from eight different areas of high Greenland halibut abundance throughout the Northwest Atlantic from Davis Strait to the northern Grand Bank. These data were then analysed using a multivariate analysis of covariance technique with the aim of using the results to delineate Greenland halibut stocks throughout the study area. The results suggested that each area examined may very well support a separate stock. However, given the state of knowledge of this resource, this was not believed to be truly the case. Alternative explanations for the results are discussed.

Tools for embracing uncertainty in the management of the cod fishery of NAFO divisions 2J+3KL

Algorithms for estimating the effect of spawning-stock biomass on the probability distribution of recruitment are used to answer questions about the cod stock of the northern Grand Banks and southern Labrador Sea, in a way that takes account of intrinsic variability and uncertainty. We re-evaluate prospects for past rebuilding strategies, examine events that occurred in the last decade, speculate about possible events if the stock had been managed differently, and use knowledge of recent stock sizes to estimate the size of year classes not yet seen.

Stock Delineation of Greenland Halibut in the Northwest Atlantic Using a Recently Developed, Multivariate Statistical Analysis Based on Meristic Characters

Meristic characters of Greenland halibut (Reinhardtius hippoglossoides) from eight areas of the Canadian Northwest Atlantic were examined. Using a recently developed multivariate analysis technique, the meristics were analyzed to determine the accurate delineation of Greenland halibut stocks throughout the area investigated. Our findings indicate at least two separate populations of Greenland halibut in the Canadian Northwest Atlantic. These are found in the Gulf of St. Lawrence and from Davis Strait at West Greenland to the northern Grand Bank. There is some evidence, however, of localized spawning stocks in Fortune Bay, Newfoundland and the Labrador area. Based on this analysis, the results tend to agree with those other independent techniques for stock separation of Greenland halibut.

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