摘要:

A 39-year series of samples (1947–1985) was obtained with gill nets and trawls from a discrete population of lake whitefish Coregonus clupeaformis within the innermost basin of South Bay, Manitoulin Island, in northern Lake Huron. Back-calculations based on scales allowed growth in weight to be estimated for 47 year classes of lake whitefish. Growth of young fish prior to entry into exploited sizes was slow in the mid-1930s, increased to a maximum in the early 1950s, declined again to a minimum in the late 1960s, and increased again during the 1970s and early 1980s. Trend analyses with Fourier transformations provided cyclic sine wave models with a 32-year period that fit growth trends better (higher r2) than either linear or polynomial models. Long-term cycles in water level and temperature correlate significantly with the observed growth cycle. These two environmental factors account for 88% of the variation in lake whitefish growth, leaving 12% to be accounted for by community interactions. Based on observations in South Bay and fishery studies in other areas of the province, a hypothesis is suggested that long-term fluctuations in the hydrological cycle and other climatic factors interact to control long-term fluctuations in fish production throughout Ontario.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<787:LCTIGO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A multispecies model of a demersal fish assemblage on Georges Bank was constructed to investigate the causes of major changes in species composition and relative abundances that occurred during 1963–1978. In particular, we investigated whether simulations of competition, predation, and prey turnover rate could mimic historic population trends. Results suggest that competition and predation, especially acting in concert, could account for some of the variability in fish biomass and abundance in this assemblage. Because the model was developed with a priori hypotheses, the findings suggest that interspecific interactions may be important in determining fish population abundance in assemblages of marine demersal fishes. However, neither the sharp decreases in biomass that occurred in some demersal species in the early 1970s nor the magnitude of increase in others could be accounted for with these hypotheses. This model provides a good first step at organizing and investigating the complex processes that drive this type of marine demersal assemblage, but subsequent models that include different interspecific mechanisms and structures or environmental influences appear to be justified.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<805:AESMOC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Catchability may be expressed as the catchability coefficient, q = F/g, or the “specific catchability,” c = F/f where F is the instantaneous catch rate, g is total fishing effort, and f is fishing intensity or effort per unit area. The latter will usually be most appropriate for analysis of recreational fisheries in relatively small, homogeneous, inland waters, particularly for comparisons between waters that differ in area, and for incorporation in predictive models for general use. Data from large waters may yield overestimates of catchability if total area, rather than the area utilized by the fish stock and the fishery, is used. These conclusions are supported by analysis of published data on stocked rainbow trout in 23 California waters.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<818:IOAWCI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Adult chinook salmon Oncorhynchus tshawytscha that had returned to the University of Washington, Seattle, hatchery were exposed for 1 h to either whole Prudhoe Bay crude oil, a chemical dispersant, or chemically dispersed oil in fresh water. The oil exposure concentrations were higher than under oil spill conditions measured in the field. Members of the treatment groups and similarly handled controls were held for 1 d after exposure and then displaced downstream. Neither frequency of homing (72% overall) nor days to return to the hatchery (mean = 3.2 d) were affected by the treatments. Retention of some treated fish at the hatchery determined that longevity was sufficient to prevent significant bias in estimates of homing. Later in the season, homing speed increased and longevity decreased, but homing frequency remained relatively constant.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<823:HOACSA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We determined the effects of rearing conditions on the physiological development of coho salmon Oncorhynchus kisutch during smoltification. Combinations of various levels of both rearing density and water inflow rate were used in this study. The experiments were performed at a production hatchery and at our laboratory. High rearing density resulted in reduced levels of plasma thyroid hormones in the fish, but no effect of water inflow rate on these hormones was recognized. Although rearing density and water inflow rate affected plasma cortisol and gill Na,K-ATPase activity, their effects on these physiological variables seemed to vary through time producing different developmental patterns of physiology during smoltification. Measurements of plasma corticosteroid clearance and in vitro activity of interrenal cells suggested that rearing density affected plasma cortisol levels primarily by altering the submaximal activity of the interrenal cells. Lowering the rearing density of fish from high to low 2 weeks before sampling resulted in cortisol levels similar to those of fish reared at low density throughout the experiment; however, plasma thyroxine and gill Na,K-ATPase activity were not affected. The relationships observed among experimental rearing conditions, water quality, and physiological status of the fish suggested that crowding stress itself may be an important factor by which high rearing density affects the physiology of coho salmon.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<828:EORCOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Triploid rainbow trout Salmo gairdneri produce spermatozoa with DNA contents intermediate between haploid and diploid values. This confirms that these spermatozoa are aneuploid and explains why progeny produced from the fertilization of haploid eggs with such sperm are not viable. Triploid males have significantly lower spermatocrit and smaller testes than diploids, but still develop normal secondary sexual characteristics and exhibit postspawning mortality.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<838:FCOAIS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

When injected with carp pituitary, triploid male grass carp Ctenopharyngodon idella produced milt that contained sperm of abnormal shape and variable size. Flow cytometry of this milt revealed three types of cells based on DNA content: 1.5n “haploid,” triploid, and hexaploid. Hexaploid cells were interpreted to be spermatogonia in which premeiotic chromosome doubling had occurred; the coefficient of variation (CV = 100˙SD/mean) of DNA content in hexaploids was not different from the CV of DNA in other somatic cells. Meiotic triploid and 1.5n haploid cells from milt had CVs for DNA about 6–7% higher than those of somatic cell populations. This increase was consonant with the theoretical distribution expected from random segregation of the extra chromosomes of triploids. Therefore, both mean and relative variation of DNA content in aneuploid cells support the hypothesis that the third homologous chromosome segregates randomly during anaphase I of meiosis. Because the segregation of chromosomes follows the expected theoretical distribution, it is possible to estimate the probability that competent sperm types will be produced. This estimate can, in turn, be used as one component in estimating the likelihood that triploids will produce diploid offspring, which themselves will reproduce. The probability that a competent sperm from a single triploid male will unite with a normal egg and produce a reproductively capable offspring is conservatively estimated to be 4 × 10−11for every meiotic reduction of hexaploid spermatogonia.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<841:CEOTLT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Cohort analysis of catch-at-age data derived from the angler harvest of walleyes Stizostedion vitreum vitreum under a complete creel census in Escanaba Lake yielded estimates of the number of walleyes at various ages for the 1956–1974 year classes. These estimates of the number-at-age were highly correlated with mark-recapture estimates, indicating the validity of the cohort analysis technique. Where long-term catch-at-age data are available, the cohort analysis method to determine number-at-age of previous year classes may be used in lieu of costly mark-recapture experiments.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<849:CAAAIO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Grass carp Ctenopharyngodon idella and genetic derivatives are widely used as biological control agents for aquatic macrophytes. The results of bioenergetic comparisons of three types of commercially available grass carp are reported. Empirical relationships were developed for consumption rate, metabolic rate, and assimilation efficiency as functions of temperature and size. Summary energy balances are presented for each type of fish. Diploid and triploid grass carp had similar standardized energy balances: 12–13% of the energy ingested was used in metabolism, 74% was egested or excreted, and 13–14% went into growth. Hybrid grass carp (female grass carp x male bighead carp Hypophthalmichthys nobilis) metabolized a greater proportion of the energy intake (16%) and egested 81%, leaving only 3% available for growth; they also ingested food at a significantly lower rate. Thus, intergeneric triploid hybrids appear to be energetically handicapped. Their low consumption rate and reduced assimilation efficiency, coupled with elevated metabolic costs, leave little energy available for somatic growth. High rates of growth of diploid and triploid grass carp are attributed to their “low efficiency-high volume” energetic strategy, which is quite successful as long as food supplies allow them to feed ad libitum.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<853:EBODTA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Each summer between June and September, elvers (6.4–9.0 cm total length) and a small number of yellow (12–26 cm) European eels ascend the Imsa River. In fresh water, the mean annual length increment from the elver stage to age 8 years was 6.2 cm. Males grew more slowly than females in the corresponding year classes. The male:female ratio was approximately 1:20. Male and female yellow European eels transformed into silver eels at lengths of about 40 cm and 62 cm, respectively. Rapidly growing eels of both sexes transformed into silver eels at younger ages than more slowly growing individuals. Length was more important than age for the onset of transformation. Length-weight relationships indicated that growth was allometric and that silver eels were heavier than yellow eels of the same length. Gonad weight of the females increased exponentially with body length, whereas the mean gonadosomatic index, gonad weight/(total weight - gonad weight), did not vary with length.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<864:LCOTEE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor