Showing papers in "Journal of Northwest Atlantic Fishery Science in 1989"

The Influence of Temperature on Some Fish Population Parameters in the Barents Sea

Abstract: At the beginning of this century it was clear that in the Barents Sea, variations in the physical conditions have a great influence on the biological conditions of fish. The cold period during 1977-82 initiated new investigations on the influence of oceanographic conditions on recruitment, distribution and growth of commercial fish species in the Barents Sea, both by Norwegian and USSR scientists. A review of some of the most important results achieved so far is presented. Rich year-classes of cod occur only in years with relatively high temperature on the spawning grounds and the areas of their distribution during the first half-year of their lives. Feeding distributions of cod, haddock and capelin depend on the climatic conditions in the Barents Sea with more easterly and northerly distributions noted in warm years than in cold ones. The growth of fish also seems to depend on the environmental temperature, but the temperature-growth relationships are probably not simple. The climatic fluctuations also influence the plankton production and thereby the food conditions for all plankton feeders. Temperature effects linked to the variability of food may therefore be as important as the direct effect of temperature on the biological conditions of fish.

Swept Area Variation with Depth and its Influence on Abundance Indices of Groundfish from Trawl Surveys

Abstract: Norwegian stratified-random bottom trawl surveys are carried out under the assumption that a constant area is swept by the trawl during a standard haul to generate abundance indices. Results from measurements of trawl geometry during a trawl survey in the Svalbard area, showed that there was a considerable depth dependency, and to a lesser extent, area/bottom stratum dependency of wingspread. Assuming that the swept area was linearly related to the wingspread, it was found that the currently applied method relatively underestimates the younger ages of cod (1-3 years) in the Svalbard area. The use of instruments for monitoring trawl geometry during all tows is one way to diminish variability in bottom trawl survey indices.

Icelandic Groundfish Survey Data Used to Improve Precision in Stock Assessments

Abstract: The main objective of this study was to improve the precision of stock assessments of demersal fish in Icelandic waters, with particular emphasis on cod. Sampling was carried out on approximately 600 stations in the Iceland shelf area in March 1985 and again in March 1986. Stations were distributed in the survey area through a semi-randomly stratified process. A standardized bottom trawl was designed for the sampling and the data collected included length measurements, otolith samples and sex determination, as well as information onthe environment and fishing gear. Results are presented for cod, haddock, saithe, redfish, catfish and long rough dab. The distributions of the different species indicate common nursery grounds in the northern part of the survey area. The youngest age-groups were generally not fully represented in the survey. Pronounced diurnal catch variations were observed for catfish and redfish. Age disaggregated stock indices of the gadoid species are well correlated with virtual population analysis (VPA) values. However, the total stock indices differ in their proportion of the VPA stock size. In comparison with previous surveys, the precision of stock indices has been increased markedly through this survey for all species except saithe. This is basically the result of an increased number of stations. Skipper-selected stations (non-random) generally gave higher aggregated indices than random ones, although statistically significant differences are exceptional. On a length disaggregated basis, however, a highly significant difference was observed for all species.

Density-dependant Growth in the Northwest Atlantic Stock of Atlantic Mackerel (Scomber scombrus)

Abstract: Density-dependent growth relationships in the Northwest Atlantic stock of Atlantic mackerel (Scomber scombrus) were investigated with regression and. non-parametric statistical procedures. Mean weight at ages 1-3 for research survey caught and ages 2-4 for commercially caught fish were found to be significantly and negatively correlated with stock density. Weight-at-age of fish from the 1978-82, and 1984 cohorts were significantly different at ages 1,2 and 3. The 1982 cohort was found to be one of the slowest growing on record; it is also one of the largest recruiting year-classes that has been observed. Results suggested that a two stage growth model that accounts for different distribution of juvenile and adult fish may be appropriate forthis stock. Early growth r.naybe related to year-class size, whereas stock size may be more influential after juvenile fish join the adult stock further offshore.

Growth of Juvenile Pollock (Pollachius virensL.) Along the Atlantic Coast of Canada with Inferences of Inshore-offshore Movements

Abstract: Data collected from tagging studies along the coast of Nova Scotia and offshore ichthyoplankton surveys were used to investigate growth and inshore-offshore migrations of juvenile pollock. Age zero pollock from 0.3 to 4.2 cm in length were found in the offshore plankton between November and June and small pollock at lengths of 7-11 cm were caught inshore in July. These small pollock appear to have moved inshore after leaving the offshore pelagic community at 3-6 months of age. They remain inshore until they reach approximately 30+ cm during their second year. Tagged inshore pollock were observed to grow 17-18 cm during their first year of life, an annual instantaneous growth rate (G) of4.1, and 27-30 cm by the end of their second year (G =1.8). Seasonal variability in growth was also observed in juvenile pollock. Mean absolute growth from May until August was 1.75 cm per month, from August until October 1.50 cm per month, and from November until April about 0.5 cm per month. A tagging related mortality experiment using winter tagged juveniles indicated a 11% mortality during the first 3 months after tagging.

Comparison of the Growth of Northern Shrimp (Pandalus borealis) from Four Regions of the Northwest Atlantic

Abstract: Modal analyses of carapace length frequencies and interpretation of biological data for the northern shrimp (Panda/us borealis) indicate variation in both age at sex change and growth rate for some Northwest Atlantic populations. The first female age (the species is protendrous) varied from 6 in the southernmost area to 7 and possibly 8 in more northerly areas. The observed differences could not be related to differences in environmental temperature. Overlapping of modes in the length frequency data was severe in many cases, possibly obscuring an additional mode (age group) in the Davis Strait data. The assumption that sex change occurs at a specific age and the choice of appropriate models and statistical analyses to describe growth require further study.

Environmental Conditions off West Greenland, 1980-85

Abstract: The observations and changes in the hydrographic parameters temperature, salinity and oxygen during the 1980s off West Greenland are described and discussed in the light of a climatic cooling, which occupied the Davis Strait area during the period 1982-84. The analysis which includes time-series data from 1963 has revealed great negative anomalies in the temperaturesalinity characteristic due to the atmospheric influence, which has led to changes in the circulation pattern as well as the sea ice distribution in the Davis Strait. In 1980, recognizing the importance of the physical environment to the Iiving conditions of marine species, 60° 55° 50° 45° Map showing major banks of West Greenland where annual cruises were carried out during 1980-85. -10 During the annual autumn groundfish survey conducted by the Institut fur Seefischerei, Hamburg, hydrographic observations along NAFO standard sections off West Greenland are carried out. The timeseries of these measu rements began in 1963. (/) .~ ro E o c co Q) ~ -2 ~ -4 a. § -6 4: -8 This paper summarizes some of the main features of the hydrographic conditions in the West Greenland area during the period 1980-85, when a drastic change -12 '-'--__..L...-__..L...-__...L-__....L...-__-'---__\"\"\"'-~ 198

Patterns of Exploitation and Biological Status of Pollock (Pollachius virensL.) in the Scotian Shelf, Georges Bank and Gulf of Maine Area

Abstract: Commercial exploitation of pollock in NAFO Divisions 4VWX and Subareas 5 and 6 has increased considerably over the past two decades as abundance of traditional groundfish species has declined. Total pollock landings from this area increased from less than 30,000 (metric) tons per year during the late-1960s to over 60,000 tons since 1985; USA recreational catches have contributed between 1,000 and 2,000 tons to the annual totals. Since 1977, when both the USA and Canada extended uni-Iateral jurisdiction over their fishery resources to 200 miles, domestic management programs for pollock have been either non-existent or ineffective in restricting total landings. Assessment and management advice for pollock has traditionally been predicated on the assumption of a single unit stock within the region. Tagging studies and morphometric and meristic measurements, however, suggest a possible separation of Gulf of Maine pollock from those on Browns Bank and Emerald Basin on the Scotian Shelf. The distribution of pollock eggs and larvae also indicates the presence of several spawning sites on the Scotian Shelf in addition to previously documented locations in the western Gulf of Maine. Sexual maturation and growth rates for pollock are similar throughout the region. Growth rates of males and females do not differ significantly, although the median size at maturity is slightly larger for males. The majority of pollock of both sexes become sexually mature during their third year. Recruitment has been consistent since the late-1960s with one or more relatively strong year-classes appearing throughout the region every 3-4 years. Pollock become fully recruited to the fishery between ages 6 and 7, although partial recruitment declines again after age 7. Estimates of total stock size (age 2+), derived from virtual population analysis (VPA), increased from 102 million fish in 1974 to 145 million in 1977, but declined to 97 million in 1980. Following recruitment of the 1979 year-class at age 2 in 1981, stock size increased to 168 million before declining to 113 million in 1988. Instantaneous fishing mortality (F) has exceeded Fo.i (0.29) but remained at or below Fm a, (0.57) throughout the 1970s. Fishing mortality has been close to Fm a" however, in 4 of the 6 years since 1982. Analyses of research vessel survey data generally agree with results obtained from the VPA, indicating a recent decline in stock abundance and biomass, and an increase in instantaneous total mortality. Equilibrium calculations suggest that fishing at Fa' would provide a long-term yield of 53,600 tons from a stock biomass of 317,700 tons, while fishing at Fm a, would provide a yield of 58,100 tons from a stock biomass of 204,600 tons. Corresponding spawning stock biomass levels at Fa' and Fm a, are 260,400 and 149,800 tons respectively. Although long-term yields are approximately 8% greater at the Fm a, level, fishing at Fa' provides for a 55% increase in total stock and 74% increase in spawning stock biomass over those allowed under Fma, . 'Present address: Max Planck Institute, 1A Marconi Strasse, Julich D-5170, Federal Republic of Germany. 14 J. Northw. Atl. Fish. Sci., Vol. 9,1989

Comparison of Species Composition in a Bottom Trawl Calibration Experiment

Abstract: The species composition in a comparative trawl fishing experiment on the Scotian Shelf was analysed to determine if two ships using different gear resulted in different pictures of assemblage structure. A multiple regression technique was used with an index of biological dissimilarity as the dependent variable, and dummy variables to control day-n ig ht differences, sam pi ing stratu m and location. T he analysis showed that the dissi milarity index val ues between vessels were not significantly larger than those within vessels. Pairs of tows by the different vessels and gear at the same location, were significantly less dissimilar than pairs of tows by the same vessel in the same sampling stratum (i.e. nearby). The study shows that it is valid to compare assemblage structure on the basis of surveys by these two vessels. The results also suggest that there are spatial patterns in the demersal fish assemblages on the Scotian Shelf at a scale between the area covered by a trawl tow and the area of a stratum.

Slope Water Intrusion to the Great South Channel During Autumn, 1977-85

Abstract: Measurements of water properties in the Great South Channel (GSC) made on 35 surveys between 1977 and 1985 indicate an intrusion of high salinity water in the autumn of most years. The intrusion represents an influx of slope water. It is most evident near bottom, but high salinity values are found throughout the water column. In some years the intrusion can be traced through the channel to the north side of Georges Bank. Larvae of offshore, warm-water fish species found in the high salinity intrusion support reports that the presence of these larvae is associated with an influx of slope water through the channel. The influx is likely to be associated with the seasonal shelfward movement of the shelf/slope front during the autumn. While the extent of the influx may be modified by Gulf Stream rings located south of the channel region, the phenomenon does not appear to be caused by rings. The influx of slope water across the shelf and to GSC suggests a seasonal reduction in the transport of Georges Bank water westward past Nantucket Shoals.

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

Abstract: 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

Seasonal Distribution of Sharp-beaked Redfish (Sebastesspp.) in Northeastern Grand Bank

Abstract: Sharp-beaked redfish (Sebastes spp.) are distributed widely in northeastern Grand Bank, NAFO Div. 3L, during all of the year. There appears to be a partial separation between northern and southern distribution in the vicinity of 47° 15'N for all but the third quarter of the year. They move westward along and up the continental slope between the second and third quarters then back easterly during the fourth and first. There may also be some movement between the northern part of the Division and more northern waters (Div. 3K) during the year. The redfish are distributed deepest during the second quarter, then they move into shallower waters in the third quarter before beginning to move deeper again in the fourth and first quarters. Females predominate at depths of 400-449 m during the first quarter and 250-349 m during the third. There is very little geographic separation of the sexes in the second and fourth quarters. The largest fish are generally found in intermediate depths, associated with bottom temperatures of about 2.0° to 4.9°C. 51° 50° 49° Longitude (0W) Materials and Methods 54° 46° 50° r------r-----r--.,...-----r-~----r--_r_-__r_-___, 50° I 1 I Quarter I 1 I I ~ : : ~~~~;t~' ---i-1~tt-t I 1,12, I 2,20, I 6,32, I 0,0, 1 1 Div.3K _ ~ _1~,~ _:_1~~ _:_ 2~,.1_8 :__3~ _ ~ J (49°15'N) ~ ~ 490 113,37, 112,43, I 6,61, 2,12, 1 I Div.3L ~ ~ 25,28 1 28,24 I 40,41 I 15,14 1 1 ~ ~ Z I 11~~1~~~i()'4~-10,601\~16,-i-6~,-Toio 4,7, 1(/ 3,8 V 48°' -t'l-.l_~ -.1_ -1-~ _1~L L 48° "0 0,1, I I I 200~13,51,'-l..14,70, I 2,0, B I 0,0 I : 1 1 26,16 1 30'15~1 3,2 j -~----1----:----:---~1254 t--. I I 1 1 1 21'17' 4]0 . _.J -_1_L L -\4]0 I I 1 1 5,37, I ___ L 1_ ~r~nj ~a~~ _: : :_ ~8~9 L _ I I 1 I 1 1 11 52 I 01 I 1 I 1 I I 37',13' 1 0',0' 460