摘要:

Northern pike (Esox lucius) were sampled periodically from Lac Ste. Anne, Alberta, between March 1976 and September 1978. The yearly cycle of production and depletion was determined for individual 3-yr-old fish. Body growth in length was similar for both sexes, and occurred during the summer. Somatic caloric growth was completed during the summer by females, while male somatic growth continued over winter. Gonad growth began in August; testicular growth was completed by September while ovarian growth occurred mainly during winter. There was no loss of somatic energy during ovary growth. Energy requirements for testicular growth appeared to come from liver stores. Both sexes lost considerable somatic energy between March and May, the spawning period; this loss appeared to be due to spawning activity and not late gonad growth. Young-of-year fish did not mature sexually and all of their energy accumulation went into somatic tissue. Total production in females from May to March was twice as high as production in males. Both sexes had similar yearly somatic production, while females had approximately 15 fold higher gonadal production than males.Key words: calories, growth, liver, gonad, somatic,Esox lucius, production, spawning depletion

ISSN:0706-652X    

DOI:10.1139/f79-071

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Theories of food chain dynamics have important implications for the management of marine resources. As yet, however, there are few empirical studies of the food chain dynamics of resource species against which these theories can be judged. This paper compares the food requirements of juvenile chum salmon (Oncorhynchus keta) in the Nanaimo Estuary with the productivity of their principal food species. Chum were present in the estuary from March until June and the estuary population ranged up to 4.1 million in May 1975 and 2.4 million in April 1976. The average weight of chum was 0.66 g in 1975 and 0.65 g in 1976, and their rate of growth averaged ~6% body weight per day in both years. Food intake estimated by three independent methods ranged 4.4–18% body weight per day and was assumed to average 15% body weight per day. Annual fry production was 2381 kg in 1975 and 1122 kg in 1976. Food intake was 6184 kg in 1975 and 2815 kg in 1976. The principal dietary item in both years was harpacticoid copepods. In 1975Harpacticus uniremismade up 50% of the diet overall, and >80% of the diet when fry were most abundant. The seasonal pattern of abundance of fry andH.uniremison the estuary was the same, and the fry consumed most of the estimated production ofH.uniremis. Juvenile chum production was potentially limited by food supply. Food chain dynamics were, therefore, important in the productivity of the chum population, but since both chum and its chief food were rare and ephemeral elements of the estuarine fauna, their interaction probably had little impact on the dynamics of the estuary as a whole.Key words: chum salmon, estuaries, food chains, populations, feeding rates

ISSN:0706-652X    

DOI:10.1139/f79-072

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The meiofauna of the Nanaimo Estuary are briefly described. Nematodes and harpacticoid copepods were the numerically dominant taxa and reached their maximum population densities in late summer.Harpacticus uniremiswas very important to the early diet of juvenile chum salmon (Oncorhynchus keta) but was one of the least common harpacticoid copepods in the estuary. The productivity ofH.uniremiswas found to be only slightly greater than the calculated food requirement of the chum salmon fry; there was close coupling between prey and predator. The role of detritus and bacterially processed carbon in the feeding ofH.uniremisare discussed.Key words: harpacticoid copepods, secondary production, detritus,Harpacticus uniremis, turnover ratios, meiofauna

ISSN:0706-652X    

DOI:10.1139/f79-073

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Sources of autotrophic and allochthonous organic carbon available to the Nanaimo Estuary delta, British Columbia, were studied from 1974 to 1978. Annually, benthic microalgae produce 4–55 g C∙m−2, phytoplankton ~7.5 g C∙m−2, and macroalgae 0.9–7.5 g C∙m−2.Zostera marina(26.8 g C∙m−2∙yr−1) and Carex (~564 g C∙m−2∙yr−1) are productive but enter the food web as detritus. Allochthonous sources are most important with organic matter from the river, especially dissolved organic carbon (~2000 g C∙m−2∙yr−1) and fine particulates (56 g C∙m−2∙yr−1), contributing greatest amounts. The standing crop of organic detritus in the top 5 cm of sediments averages from 58 to 233 g C∙m−2, depending upon the station. The timing of organic inputs are important, however. Seventy to 93% of total annual river inputs occur during autumn freshets,Zosteraenters the food web during winter,Carexmay contribute in early spring, and algae are productive over summer months. Activity and biomass of microbes are high most of the year in surface sediments but in the water column microbes are relatively active only during warmer months. Surface sediment ATP concentrations range seasonally from 3 to 36 μg∙g sediment−1; and concentrations in the water column range from < 0.2 to 1.5 μg∙L−1. Microbial activity, measured with14C-glucose, ranges seasonally from 4 to 20% uptake per hour for surface sediments and from < 1 to nearly 40%∙h−1in the water column. These results are compared with those from other studies and coupled to concurrent studies of meiofauna and salmon ecology to show a link between detritus, microbes, harpacticoid copepods, and the food, growth, and production of juvenile chum salmon (Oncorhynchus keta).Key words: detritus, Nanaimo Estuary, primary production, carbon, microbes, salmon, a

ISSN:0706-652X    

DOI:10.1139/f79-074

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

This paper documents net entrapments of baleen whales in the inshore waters of Newfoundland and Labrador. The species involved are principally minke whales (Balaenoptera acutorostrata) and humpback whales (Megaptera novaeangliae). Finback whales (Balaenoptera physalus) are also caught in nets but far less frequently. The timing of these entrapments corresponds with the spawning season for capelin (Mallotus villosus) on the beaches around the province. The magnitude and implications of this problem, both to the whales and the fisherman, are assessed.Key words: baleen whales, net entrapments, mortality assessment, capelin,Balaenoptera acutorostrata,B.physalus,Megaptera novaeangliae

ISSN:0706-652X    

DOI:10.1139/f79-075

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A detailed examination of the sediment in a small area of St. Margaret's Bay revealed it to be composed of two main types of particles, mineral particles and particles of organic debris. Debris was also adsorbed onto the mineral particles. Particles generally had relatively low numbers of bacteria associated with them indicating that most of the organic carbon in the sediment is refractory. Variation in size distribution of the component particles with depth in the sediment was found to be minimal, but a slight decrease in the proportion of debris particles was seen. Variation in size distribution along a transect was also limited, but where the mineral particles became coarser the size range of the debris particles remained constant. The relative amount of debris particles along the transect varied little but values for total organic carbon (by weight) changed dramatically.Key words: sediment, particle composition, size distribution, organic carbon

ISSN:0706-652X    

DOI:10.1139/f79-076

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Various predation techniques used by rock crabs,Cancer irroratus, and American lobsters,Homarus americanus, to open sea scallop,Placopecten magellanicus, prey are reported. Adult rock crabs and lobsters successfully fed on sea scallops up to 72 and 76 mm in height, respectively. Juvenile lobsters were capable of preying on scallops whose height exceeded their own carapace length. Daily predation rates on a range of scallop sizes by various sizes of predator were obtained. Given a choice, both rock crabs and lobsters showed distinct and constant preferences for certain size scallops. This preferred prey size increased with predator size. These laboratory studies demonstrated that both rock crabs and lobsters are potential scallop predators.Key words: sea scallops, crabs, lobsters, predation techniques, prey selectivity

ISSN:0706-652X    

DOI:10.1139/f79-077

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

In experimentally reared winter steelhead trout (Salmo gairdneri) fry, mean weights, lengths, and condition factors of three isozyme phenotypes of lactate dehydrogenase (LDH) enzyme differed significantly. Time of emergence from the gravel was unrelated to LDH phenotype. Relative mortality of the phenotypes between eyed-egg stage and emergence was unaffected by different subgravel conditions of temperature and dissolved oxygen. Differential tolerance to acute challenges of high temperature and low dissolved oxygen was observed between phenotypes of isocitrate dehydrogenase (IDH) enzyme and LDH in juvenile trout. Parental effects may have biased the result for LDH. Differences between IDH phenotypes may be related to intrinsic properties of variant isozymes.Key words: isozymes, lactate dehydrogenase, isocitrate dehydrogenase, temperature, dissolved oxygen, adaptive significance,Salmo gairdneri

ISSN:0706-652X    

DOI:10.1139/f79-078

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A mathematical model that simulates the effect of selective fishing on the size distributions of populations of trout is presented. The model assumes that the growth rate is genetically controlled by a small number of major genes. Empirical numbers for the growth and mortality rates of brown trout (Salmo trutta) in the Au Sable River of Michigan are used as input data. A computer is used to calculate the changes in the population subject to various degrees of fishing pressure for various size limits. Results are presented for periods of time ranging from 5–30 yr. The observed changes in the population over the period 1959 to 1977 in a test stretch of the Au Sable River agree quite well with the computations.Keywords: fish, trout, genetics, growth, size limit, population,Salmo trutta

ISSN:0706-652X    

DOI:10.1139/f79-079

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

An infectious pancreatic necrosis (IPN) carrier population of brook trout (Salvelinus fontinalis) planted in an isolated natural lake was tested for virus over a period of 6 yr. The initial isolation rate of 90% had decreased to 50% during this period indicating that there is a prolonged persistence of virus in infected animals of this species. The ceca with the associated pancreatic tissue of these fish yielded virus most frequently during the early years but the virus then decreased to low levels. Kidneys were the most consistent organs to yield virus throughout the study period. The feces yielded little virus at first but later increased for several years and then decreased. The spleen and liver yielded virus infrequently. Surgically removed gonads were the least frequent yielders of virus. The low virus isolation rate from progeny of the carrier population and from other planted fish indicated that transmission in the wild is probably infrequent. Other lakes with normal angling that had plantings with IPN carrier fish but subsequently planted annually with disease-free fish had populations whose carrier rate had decreased to undetectable levels within a 6-yr period. These findings indicated that the practice of planting IPN-free fish into areas where carriers were previously introduced may lead eventually to a carrier-free state.Key words: infectious pancreatic necrosis virus,Salvelinus fontinalis, virus persistence, carrier fish, virus isolation rate

ISSN:0706-652X    

DOI:10.1139/f79-080

出版商:NRC Research Press    

年代:1979

数据来源: NRC