摘要:

Since 1934 when Fridriksson originated the age–length key, it has been widely used by fisheries biologists to estimate age distributions of populations. In recent years, there has been a general recognition that often the key has little value, or even worse, gives biased results. The analysis presented here indicates why the age–length key is so susceptible to bias. More importantly, a criterion is presented for determining whether the age–length key should be used in a particular situation. If the key is to be used, results from examples indicate that random age subsamples (i.e. the number of specimens aged from each length category proportional to the number in each length category) are superior to fixed age subsamples (i.e. a constant number of specimens aged from each length category). Generally, small increases in the age sample will likely increase the accuracy of an age-distribution determination more effectively than relatively large increases in the length sample.

ISSN:0706-652X    

DOI:10.1139/f77-052

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Echinorhynchus salmonisMüller was the dominant intestinal parasite infecting 14 species of southwestern Lake Michigan fishes. New host records are reported for chinook salmon,Oncorhynchus tshawytscha, and slimy sculpin,Cottus cognatus. Infections were heaviest in members of the Salmonidae. Host–parasite relationship in smelt was most closely analyzed. No pronounced seasonal periodicity in the rate and intensity of infection or worm maturation was observed. Recruitment and maturation occurred throughout the year but were, however, enhanced by colder and warmer temperatures, respectively. Sex ratio was nearest to even in winter. Fifty percent or more of worms were localized in the posterior-most region of host intestine and posterior migration with maturation was indicated. Heavier infections were noted in larger (older) fishes. Alternative routes of infection of the larger piscivorous salmonids via transfer hosts are suggested. Female hosts were more heavily infected than males.Echinorhynchus salmoniswas not shown to seriously threaten its host's health or survival.

ISSN:0706-652X    

DOI:10.1139/f77-053

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Daily rings formed on otoliths of known-age, laboratory-raised pumpkinseed (Lepomis gibbosus), green sunflsh (L.cyanellus), bluegill (L.macrochirus), and mozambique mouthbrooder (Tilapia mossambica) for at least 176, 170, 125, and 60 days, respectively. Subdaily rings found in young laboratory and wild fish were easily distinguished from daily rings. Width of daily rings on otoliths of green sunfish was linearly related to daily increase in length of fish, but the number of rings was a product of age of fish only, not length of fish or otolith radius. Growth and daily ring formation on otoliths in wild bluegill and largemouth bass (Micropterus salmoides) appeared to be similar to those in laboratory-raised fish. Otoliths of green sunfish held under simulated winter conditions ceased to produce daily rings, but did form an annulus. Two kinds of otolith tissue were present in most of the larger laboratory fish and wild bluegill but were not observed in wild largemouth bass. The first type, present in all areas of the otolith except the extreme posterior end, was translucent and had well-defined daily rings. The second type, present only in the posterior end, was opaque and had poorly etched daily rings that were difficult to discern. Both tissues were calcium carbonate in the aragonite form. Daily rings were found on otoliths offish held at constant temperature. Results of experiments with young mouthbrooders held under various light–dark and feeding cycles suggested that a 24-h light–dark cycle that entrained an internal, diurnal clock was required for daily ring production.

ISSN:0706-652X    

DOI:10.1139/f77-054

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The upstream orientation and frequency of upstream movement of prespawning common shiners,Notropis cornutus, in response to a water current simulated by moving a striped background past the fish were observed at three temperatures (10, 15, 20 °C) and two photoperiods (12L: 12D and 16L: 8D). The greatest frequency of upstream movement was induced by a combination of spring day lengths and warm water temperatures. Further increases in the frequency of upstream movement followed immediate 5 °C increases in water temperature. Neither temperature nor photoperiod had a major effect on the frequency of upstream orientation. The significance of environmental regulation of rheotropism as a mechanism of upstream migration is discussed.

ISSN:0706-652X    

DOI:10.1139/f77-055

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Concentrations ofn-alkanes ranged from <20 ng/ℓ to about 1 μg/ℓ at depths of 2 and 50 m. Estimated oil concentrations based on fluorescence analyses ranged from 0.2 to 9.3 μg/ℓ. The highest concentrations occurred in Bedford Basin; the similarity of fluorescence contour plots to petroleum products and the presence of unresolved envelopes in chromatograms suggest that a large portion of the hydrocarbons in the Basin are derived from oil. Hydrocarbons in other regions appear to be principally biogenic in origin.Key words: Oil detection, northwest Atlantic, gas–liquid chromatography, fluorescence spectr

ISSN:0706-652X    

DOI:10.1139/f77-056

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Returns of Atlantic herring (Clupea harengus harengus) tagged internally with magnetic tags along southwest Newfoundland and in the southern Gulf of St. Lawrence in 1970–71 were analyzed for biases due to initial tagging mortality and to tag extrusion during the reproductive act. Initial tagging mortalities calculated by two methods ranged from 4 to 49% and increased with the duration of impoundment of the fish prior to tagging. Estimates of tag loss during the spawning season indicated that most of the tags inserted in ripening herring were extruded with the reproductive products, whereas those applied to recently spent or recovering herring had sufficient time to become attached to internal organs and hence had a high retention rate. The results indicate that the effectiveness of tagging herring internally will be greatly improved if conducted on recovering or spent fish impounded for only short periods of time before tagging.

ISSN:0706-652X    

DOI:10.1139/f77-057

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The patterns of habitat utilization in the littoral zone fish community of two small southern Michigan lakes were examined. Abundance and habitat use of the fish were quantified by underwatertransect censuses. The sunfishes (Centrarchidae) dominated the communities numerically and by weight, with two species, the bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) accounting for 85% of the community biomass. Spatial (habitat) segregation of species was evident along gradients of depth (distance from shore), vertical height in the water column, and vegetational structure. Several species showed intraspecific differences in the spatial distribution of size-classes. Comparative analyses of habitat use in the two lakes suggest that small size-classes are confined by predation to areas of dense cover and that within these areas competition determines space utilization by different species. The patterns of habitat use are discussed in relation to the food habits and morphology of species in this community. Only one clear case of segregation of two species by food size occurs (bass and bluegill); most other species segregate predominantly by habitat. The rarer centrarchids show strong niche complementarity with the codominant bass and bluegill.

ISSN:0706-652X    

DOI:10.1139/f77-058

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A reexamination of white sucker populations originally used to document the subspecies validity and biology of a dwarf white sucker,Catostomus commersoni utawana, provided no evidence of two separate populations of different-sized individuals. Small mature white suckers and larger or normal-sized white suckers still were present, but there was a continuous range of sizes after maturity. After maturity males grew slower than females and had a higher rate of annual mortality. If the size separation originally used to separate the two forms was applied to this study, then all normal-sized white suckers in this study were females and would have had to reproduce with smaller males. Also, no meristic or morphological evidence for justification of a subspecies designation for the dwarf form of white sucker in this lake was found. Because it was also known that considerable variation in the size of white suckers at maturity occurs throughout the range of this species, it was concluded that the existence of a distinct dwarf subspecies has not yet been demonstrated.

ISSN:0706-652X    

DOI:10.1139/f77-059

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Annual lobster landings (1912–74) at the Magdalen Islands can be represented with the Box and Jenkins method, by a first order autoregressive model which explains 41.9% of the total variance. Analysis of fishing effort and surface temperature yields, through a regression on principal components, a linear model that includes the first and makes use of the December temperatureago and that of the winterago. This prediction model explains 84.4% of the total variance. The biological interpretation is as follows: annual landings depend on available stock, on the influence of temperature on the survival probability of larvae and possibly, on a similar influence on the probability of access to sexual maturity of the 5-yr-old class.

ISSN:0706-652X    

DOI:10.1139/f77-060

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Oysters,Crassostrea virginica(Gemlin), were taken from a low- and an intermediate-salinity habitat. Males from each population were crossed with females from both populations and the offspring were raised at three salinities. Observations on survival during the larval period indicate that there are genetic differences between the two populations with regard to their tolerance to high and low salinity.

ISSN:0706-652X    

DOI:10.1139/f77-061

出版商:NRC Research Press    

年代:1977

数据来源: NRC