Southwest Nova Scotia Research Articles

Anatomy of an Apparent Year-Class Failure: The Early Life History of the 1983 Browns Bank Haddock Melanogrammus aeglefinus

Abstract We analyzed ichthyoplankton data from six cruises off southwest Nova Scotia, spanning the spawning and early life history period (February-June), to determine the stage(s) at which the apparent failure of the 1983 haddock year class occurred. Egg production over the season did not differ significantly from that expected, but the abundance of larvae was 1–2 orders of magnitude lower than in recent years. Instantaneous egg mortality rates (M) calculated from catch curves were very high: 0.21–0.54 for the six cruises. The lowest egg mortality rates (M = 0.21–0.22) occurred during peak spawning (April), but no surviving larvae were obtained from this period, which indicates sharply increased mortality at or near the point of hatch. There appeared to be a weak relationship between wind displacement and diffusion rate of the egg mass, but drift rates were low, and wind speeds generally below average during the study period. Temperatures in the upper 50 m over the spawning ground, where the eggs predomi...

Condition of larval cod (Gadus morhua) off southwest Nova Scotia in 1983 in relation to plankton abundance and temperature

In our study of the condition of larval cod (Gadus morhua) collected off southwest Nova Scotia in winter-spring, 1983, we (1) examined relationships between larval condition and ambient environmental conditions, and (2) compared the use of simple morphometric indices of larval condition and of multivariate statistics to obtain information relevant to larval condition. Twelve indices of relative condition were obtained, based upon seven measurements made on each larva, and a principal component (PC) analysis was performed on these condition indices. Most condition indices and the first PC were significantly correlated with numbers of nauplii and of zooplankters per m3 in the water column, which are direct measures of food available to the larvae, but not to less direct measures of environmental quality for the larvae, such as plankton displacement volume or chlorophyll concentration. Conventional indices based upon relations of dry weight or body height at the anus to length were most sensitive to environmental conditions. There was no apparent advantage in performing a multivariate analysis based upon a larger series of measurements.

Work Satisfaction and Community Attachment among Fishermen in Southwest Nova Scotia

Social scientists have examined the problem of attachment to the New England fisheries in terms of two interacting influences: work satisfaction, based on questionnaire interviews, and attachment to kin and community, based on ethnographic field research. There is a paucity of equivalent information for the Maritimes. This study replicates the New England work satisfaction studies, and includes additional questions concerning community attachment. We demonstrate that fishermen in southwest Nova Scotia are, in contrast with their New England counterparts, satisfied with all questions about their work (save for the common dissatisfaction with government officials found in both the Nova Scotia and New England samples). In particular, although offshore fishermen in southwest Nova Scotia tend to be somewhat less satisfied than those who fish inshore or both inshore and offshore, they have, by comparison with the New Bedford fishermen, scores that are over the "neutral value" on all time and adventure questions. The underlying factors of job satisfaction are comparable with those in the New England studies, except that the factors in our data are more numerous and simpler to interpret. High job satisfaction is combined with strong community attachments in southwest Nova Scotia.

Molting rates and cohort development of Calanus finmarchicus and C. glacialis in the sea off southwest Nova Scotia

Species of Calanus were sampled at stations off southwest Nova Scotia during an 8-d cruise in June, 1982. A simple model using shipboard measurement of molting rates of predominant copepodite stages accurately predicted the changes in cohort structure that occurred at stations along a transect at the beginning and end of the cruise. The combined durations of C. finmarchicus (Gunnerus) stages CIII and CIV, calculated from the inverses of molting rates corrected for presence of diapausing C. glacialis Jaschnov, corresponded well with development times based on laboratory rearing experiments. We conclude that our molting rate measurements accurately reflected processes in nature. This methodology is useful for analyzing the dynamics and production of copepod populations.

Molting rates and cohort development of Calanus finmarchicus and C. glacialis in the sea off southwest Nova Scotia : Runge, J.A., I.A. McLaren, C.J. Corkett, R.N. Bohrer and J.A. Koslow, 1985. Mar. Biol., 86(3):241–246. Dept. of Oceanogr., Dalhousie Univ., Halifax, NS B3H 4J1, Canada

Molting rates and cohort development of Calanus finmarchicus and C. glacialis in the sea off southwest Nova Scotia : Runge, J.A., I.A. McLaren, C.J. Corkett, R.N. Bohrer and J.A. Koslow, 1985. Mar. Biol., 86(3):241–246. Dept. of Oceanogr., Dalhousie Univ., Halifax, NS B3H 4J1, Canada

Variability of Chlorophyll a off Southwestern Nova Scotia in Late Fall and Its Relationship to Water Column Stability

Chlorophyll a, nitrate, and physical variables collected during December 1978 and November 1979 off southwest Nova Scotia show two distinct patterns in phytoplankton abundance. In December 1978, conditions were similar to those expected in late fall over temperate North American shelves. The water was well mixed and chlorophyll was at background level (~0.5 mg/m3). By contrast, in November 1979, both inshore and offshore regions were stratified, and chlorophyll levels were, in some places, 5 times above background. Two explanations are offered for this bimodal chlorophyll distribution. Offshore, temporary stratification resulted from the intrusion of warm saline water from either the slope or the Gulf of Maine. This may be a temporary condition that eventually deteriorates with seasonal cooling and convective mixing. Inshore, stratification results from the influx of a shallow layer of relatively low-salinity water carried by the Nova Scotia current. The onset and seasonal vagaries of this current help to explain differences observed in 1978 and 1979.

Reproduction, recruitment and mortality in two species of Laminaria in southwest Nova Scotia

In a southwestern Nova Scotia kelp forest the average density of Laminaria longicruris Pyle. remained constant through 1 yr at ≈1.2 plant·m −2. The density of L. digitata (Huds.) Lamour. was more variable through time, but averaged 3.2 plants·m −2. At these densities those plants which reproduced developed 8.9 × 10 9 and 20.02 × 10 9 spores·m −2·yr −1, respectively for L. longicruris and L. digitata. From the spores produced, 8.89 × 10 6 ( L. longicruris) and 0.98 × 10 6 ( L. digitata) microscopic benthic stages were recruited per m 2 per yr. From this bank of microscopic stages, one sporophyte of L. longicruris and two of L. digitata grew to visible size per m 2 per yr. Recruitment of visible sporophytes was enhanced ten-fold by removal of a red algal turf. Removal of macroscopic kelp plants had no effect on recruitment of visible stages. The rate of mortality among macroscopic individuals of L. longicruris (but not of L. digitata) was related to initial plant size and distance to nearest congeneric neighbour. Mortality rates of both species were unrelated to type and size of substratum or season of the year.

Political Efficacy and Political Activity Among Fishermen in Southwest Nova Scotia: A Research Note

This paper reports briefly on the political attitudes and behaviour of fishermen in southwest Nova Scotia. On the basis of some recently gathered survey data, we show that these fishermen are considerably more alienated than a comparable sample of workers in the Maritimes, and that they are also somewhat more likely to be politically active. In this context, we discuss some recent conflicts between the fishermen and the federal Department of Fisheries and Oceans, and speculate about comparative differences in involvement in policy processes between Canada and the United States.

Bankrupt Government Policies and Belligerent Fishermen Responses: Dependency and Conflict in the Southwest Nova Scotia Small Boat Fisheries

Despite massive federal/provincial government financial and policy interventions in the Atlantic Canadian Fisheries, relations between small boat fishermen and various levels of the state are rife with a pervasive alienation, distrust and conflict. This essay examines attributes and consequences of state intervention in the fisheries. Small boat fishermen’s increasing dependence on state-controlled resources and the non-consultative bureaucratic style of government are considered to be primary factors intensifying alienation, distrust and conflict. Two cases of conflict in Southwest Nova Scotia are described and discussed in order to illustrate the attributes and processes associated with this condition.

Microsetella norvegica: a rare report of a potentially abundant copepod on the Scotian Shelf

Fine mesh (0.080 mm) zooplankton samples were collected along an onshore-offshore transect during three cruises (February to May, 1983) off southwest Nova Scotia, Canada. The small harpacticoid copepod Microsetella norvegica was numerically the dominant copepod during the winter (February) cruise, where it composed up to 50% of the total zooplankton, and was consistently among the three most abundant copepods during the spring cruises. Due to its small size (<0.45 mm in length), M. norvegica has rarely been reported from plankton surveys of the northwest Atlantic. However, existing reports indicated it varies interannually from being a rare to an abundant member of the zooplankton community in the northwest Atlantic.

The Mean and Seasonal Circulation off Southwest Nova Scotia

Long-term measurements off southwest Nova Scotia reveal the following features of the mean circulation: (a) a westward longshore coastal current (4–10 cm s−1, (b) an anticyclonic gyre around Brown Bank (5–15 cm s−1, and (c) an upwelling circulation off Cape Sable (1–2 cm s−1, at bottom). The gyre circulation appears permanent but the coastal current and upwelling exhibit annual variations of the same order as the means. There is a distinct annual signal in the longshore transport at Cape Sable (maximum westward in winter), whereas the mean transport (0.14 × 106 m4 s−1) is consistent with both geostrophic estimates and budget requirements in the Gulf of Marine. Strong seasonal cycles are also found in the salinity and density fields at Cape Sable which appear to be controlled both by buoyancy input from the coastal current and local mixing effects. A linear diagnostic model indicates that the primary dynamical balance for the circulation is between a longshore pressure gradient and longshore mean density and stratification gradients which have summer maxima. Lesser contributions arise from longshore wind, offshore density gradient and centrifugal upwelling. Tidal rectification, deduced from coherent modulations of the semidiurnal tidal streams and low-frequency currents, supports the Browns Bank gyre circulation and drives both westward and offshore components of the near-bottom flow off Cape Sable. Thus the “centrifugal upwelling” hypothesis fails and the main driving force for Cape Sable upwelling appears to be the longshore density variations maintained by tidal mixing.

Growth and Maturation of Southwest Nova Scotia Atlantic Herring (Clupea harengus harengus)

Juvenile and adult growth rates, and the maturation schedule, for the southwest Nova Scotia herring stock (NAFO SA 4WX) were investigated over the period 1968–78. The variance in juvenile (age 2) summer growth is not well accounted for by initial weight, juvenile population abundance, and temperature unless a discontinuity in growth pattern starting in 1970 is accounted for. Length at maturity and at recruitment to the adult schools appears to be inversely related to the population abundance experienced during juvenile growth. However, at very low juvenile population size, maturation appears to be inhibited. Somatic growth rate and its year-to-year variability decreases close to an order of magnitude with the onset of maturation. Because of this decrease with age and the radical shifts in age, composition with time, population growth rate fluctuates markedly. Because high population abundance parallels downward shifts in age composition, there is a clear, positive relationship between population growth rate and population abundance. There is a dome-shaped relationship between cohort somatic growth rate and cohort size at intermediate ages, suggesting that over a broad range in population size, adult growth rate is not density-dependent. This growth response is interpreted in relation to planktivorous feeding in a patchy environment. Strong year-class strength variability coupled with a marked decline in somatic growth rate with age results in non-steady state population production. When the age composition is biased towards older ages, catch (defined by F0.1 guidelines) exceeds population production resulting in rapid stock declines. The growth characteristics of herring are discussed in relation to the literature and "analytical" yield models.Key words: Atlantic herring, growth, maturation, production

Fire and Stability in the Postglacial Forests of Southwest Nova Scotia

Fire has been a major source of instability in the postglacial forests surrounding Everitt Lake in southwest Nova Scotia. Time series analyses of preserved pollen and charcoal reveal the processes involved. Correlograms and pollen sequence splits confirm that prior to 6000 years BP repeated widespread fires maintained the forest in constant disequilibrium. Each fire triggered rapid, major forest composition changes, especially the proliferation of invading tree species that had previously been excluded by competition. The absence of such widespread fires is shown to have left most tree populations in near-equilibrium for much of the last 6000 years. Power spectra for different pollen sections suggest the changing ecological 'strategies' and affinities of tree taxa through time and imply that much forest change occurred by piecewise replacement of individual stands in the forest mosaic.

THE FOODS OF GREAT AND SOOTY SHEARWATERSPUFFINUS GRAVISANDP. GRISEUSIN EASTERN CANADIAN WATERS

SummaryThe foods of Great and Sooty ShearwatersPuffinus gravisandP. griseusare described from birds collected off eastern Canada. There was a broad overlap in diet, but Great Shearwaters tended to take more squid and tough‐bodied fish such as mackerelScomber scombruswhile Sooties took more euphausiidsMeganyctiphanes norvegicaand soft‐bodied fish such as HerringClupea harengus. These differences are apparently related to differences in bill structure and in the degree of adaptation to underwater swimming.The birds appeared to feed opportunistically on whatever prey was locally available in the size‐range between euphausiids and small fish and squid:Meganyctiphanesoff southwest Nova Scotia, spawning and post‐spawning capelinMallotus villosusoff eastern Newfoundland, and migrating squidIllex illecebrosuson the Grand Bank. Possible factors influencing prey selection are discussed. It is suggested that the timing and routes of the birds' migrations in the North Atlantic are related to the exploitation of such local concentrations.Despite the overlap in diets, differences in the distributions of the two species rule out the possibility of significant competition for common food resources.

The Geochemistry and Origin of the Devonian Granitic Rocks of Southwest Nova Scotia

The Geochemistry and Origin of the Devonian Granitic Rocks of Southwest Nova Scotia

The geochemistry and origin of the Devonian granitic rocks of southwest Nova Scotia: Summary

INTRODUCTION Approximately one-third of southwest Nova Scotia (7,000 km 2 ) is underlain by Devonian granitic rocks (Malcolm, 1912; Sage, 1954; Fairbairn and others, 1960, 1964; Leech and others, 1963; Lowdon, 1960; Lowdon and others, 1963; Cormier and Smith, 1973; Reynolds and others, 1973), penetrating a conformable pile of lower Paleozoic meta-sedimentary and metavolcanic rocks at least 12 km thick (Taylor and Schiller, 1966; McKenzie and Clarke 1975). These stratified rocks were compressed into a series of tight upright folds during the Acadian orogeny and show no evidence of deformation during the Taconic orogeny. Most of the metasediments and metavolcanics have been recrystallized in the greenschist facies and rocks characteristic of the almandine-amphibolite facies are known only from the southernmost part of Nova Scotia (Taylor and Schiller, 1966, Fig. 1).

The Geochemistry of the Granitic Rocks of Halifax County, Nova Scotia

Studies of part of a large batholith in southwest Nova Scotia show that granitic rocks of two different ages penetrate the Lower Palaeozoic metasediments of the Meguma Group. They are distinguished by their field relationships, mineralogy, and petrology from an older series, varying from biotite granodiorite through quartz monzonite to muscovite biotite granite, which is penetrated by younger large dikes, up to 1.5 km wide, of alaskite. Rb–Sr whole rock isochron ages show that the older series was emplaced approximately 415 m.y. ago and that the younger alaskite dikes were emplaced about 350 m.y. ago. Major and trace element chemistry shows that the older series of granitic rocks were formed by differentiation of a calc-alkali magma in situ. The younger dikes are all highly silicic, show limited major element variation, and have been affected by hydrothermal metasomatism.

Observations on Herring Spawning off Southwest Nova Scotia

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