摘要:

All life stages of the bay anchovy Anchoa mitchilli were sampled intensively in Barnegat Bay, New Jersey, during 1975–1981. This species was the most abundant trawl-susceptible fish, accounting for 52% of the catch, with peaks in abundance occurring during May and June and again in September and October. Seasonal movements appeared to be correlated with seasonal changes in water temperature. Adults moved into the estuary in the spring, and an offshore and southerly emigration from the estuary to continental shelf wintering grounds occurred in the fall. Spawning began as early as April and peaked in June and July; some eggs were found as late as November. Larvae first appeared in May of each year, were most abundant in July and August, and were rare after October. Ichthyoplankton samples were dominated numerically by bay anchovy eggs and larvae, accounting for up to 98 and 56% of the annual egg and larval catches, respectively. Significant annual fluctuations in the abundance of all life stages were documented. Population levels of the bay anchovy in New Jersey waters appear to be regulated largely by the survival rate and migratory patterns of the overwintering population and to a lesser degree by events occurring within the estuary during the first few months of life.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<141:LHAPDO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Reproductive success (spawning, egg production, fertilization, hatch, larval survival) of striped bass Morone saxatilis from Cherokee Reservoir, Tennessee, was less in most years from 1979 to 1984 than that for stocks from two other Tennessee reservoirs, Norris and Watts Bar, when captured individuals from all three stocks were spawned in a hatchery. Reduced reproductive performance was expressed largely as reduction in percentage of females that spawned successfully and as poor embryo survival within 1 d postfertilization. Reproduction by Cherokee stock was best in years following those when the reservoir flushing rate was high. Reduced reproductive competence may be related to a decrease in the amount of summer habitat with suitable temperatures and dissolved oxygen concentrations, which stresses fish most severely in Cherokee Reservoir compared with the other two reservoirs. Rigorous testing of this hypothesis is recommended to guide management of striped bass and water quality in fresh and estuarine waters.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<154:PRSOSB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

American eels Anguilla rostrata harvested from weirs by the commercial fisheries of three Nova Scotian rivers differed in life history characteristics. Depending upon their orientation, weirs captured either downstream-migrating silver American eels or upstream-migrating yellow American eels. Mean lengths and weights of downstream-migrating American eels differed among rivers, increasing as the run progressed from late August to mid-November. Sexually maturing (silver) migrants were larger (typically exceeding 400 mm in length) and older than immature nonmigrants and had a higher ovarian gonadosomatic index (proportion of body weight contributed by ovaries; usually above 1.5%). At a given length, silver eels had larger eye-diameter indices (eye width x eye height) than did yellow eels but, for silver eels, eye index was not a predictor of gonadosomatic index. Silver eels migrating later in the run were more mature (had higher gonadosomatic indices) than those migrating earlier. Silver eels from different rivers were similar in age and gonadosomatic index. Male silver eels were smaller, less mature, and migrated earlier than did most females. Skin coloration (yellow-silver) was a fairly reliable guide to sexual maturity (immature-maturing), but histologically detectable maturation may begin one or more years prior to coloration change and participation in the spawning migration.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<161:MAEINS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Oxytetracycline (OTC) injections were used in a mark-recapture study undertaken to validate the otolith method of age determination for yellowtail rockfish Sebastes flavidus. Otoliths from recaptured fish were broken across the focus and burned to enhance the contrast of features in the internal structure. The number of opaque and translucent zones laid down in the otolith after the deposition of the fluorescent OTC mark at the time of tagging agreed with the number of years (up to four) that the fish had been at liberty. These results validate the annual pattern of banding in otoliths of fish of ages 8–34 years. A larger sample of fish aged by this technique indicated an instantaneous natural mortality rate (M) of 0.07, a value only 28% of the estimate presently used for stock assessment and management of yellowtail rockfish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<171:AVARNM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Winter stream conditions at elevations between 2,280 and 3,205 m above mean sea level and the use of winter habitat by adult brook trout Salvelinus fontinalis above 2,990 m were evaluated in 1983–1984 and 1984–1985. Little surface ice was observed at elevations above 2,900 m, which was associated with high snow accumulation; moderate surface ice and anchor ice formation were observed at elevations from 2,550 to 2,900 m; extensive surface ice formation occurred at 2,550 m. Little snow accumulated at 2,550 m and surface ice physically excluded substantial brook trout habitat. In late fall, brook trout at elevations above 2,990 m tended to move into low-gradient areas where they remained active throughout the winter. During winter, brook trout appeared to select for areas with maximum velocities of 15 cm/s or less, measured during summer low flow, and for deeper water, but not for substrate type.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<176:WSCAUO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Summer and winter habitat utilized by age-0 spring chinook salmon Oncorhynchus tshawytscha was assessed in the Red River, an Idaho stream heavily embedded with fine sediment. During summer 1985, chinook salmon used habitats with water velocities less than 20 cm/s, depths of 20–80 cm, and close associations with cover (undercut banks). Densities were greater than 60 fish/100 m2. As the fish became larger they selected faster, deeper water. Eighty percent of the chinook salmon emigrated from the study sites in October when stream temperatures were 4–8°C, apparently because suitable winter habitat was not available. Those fish that remained in the study sites selected areas where submerged sedges and grasses overhanging undercut banks provided cover and where water velocities were less than 12 cm/s. After cobble substrate was added to the streambed (September 1985) beneath undercut banks and in midchannel in a glide and a riffle habitat, eight times more chinook salmon used the cobble substrate in November 1985 as compared with November 1984. Significantly more chinook salmon utilized cobble placed under banks than any other area. By March 1986, cobble piles were embedded with silt and sand, and chinook salmon densities were not significantly different from those found in March 1985.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<185:SAWHSB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A survey of the fish assemblages between river kilometer 283 and 2 of the mainstem Willamette River, Oregon, was conducted in 1983 to evaluate the effects of improved water quality on longitudinal changes in fish assemblages and the usefulness of two indices of fish assemblage quality (index of well being and index of biotic integrity). Physical and chemical habitat quality and fish assemblage quality showed gradual, similar, and expected declines from the upper to the lower river, with only small changes near large point sources of pollution. More fish species, more species intolerant of poor habitat quality, and fewer species tolerant of poor habitat occurred in 1983 than in 1945. Stream order was not a predictor of fish assemblage patterns. A modification of the index of biotic integrity appeared to reflect changes in fish assemblage patterns and habitat quality better than the index of well being.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<196:LCIFAA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Before 1970, yellow perch Perca flavescens grew at similar rates in Lake Erie's western and central basins. At that time, high rates of nutrient loading were causing rapid eutrophication in both areas so that by the mid-1970s the central basin had become mildly eutrophic while the shallow western basin had reached hypereutrophy. From 1970 to 1983, growth rates of yellow perch in the western basin declined sharply while growth rates increased moderately in the central basin. Modeling of bioenergetics suggests that present differences in yellow perch growth rates are due to interbasin differences in food supply and not to temperature. Direct estimation of yellow perch feeding rates in each basin in 1983 supports this inference. Food limitation in the western basin appears related to a reduced size structure of benthic prey associated with advanced eutrophy. In the central basin, larger benthic prey are available and food consumption rates by yellow perch are high. Food limitation is more serious for larger than for smaller yellow perch in the western basin, and this has apparently caused stunting and population degradation. Further evidence from the literature suggests that changes in prey size structure which accompany eutrophication may be a primary cuase of the succession of fish species that occurs as lakes age. Mechanistic understanding of this succession will enhance present capacity to predict fish community responses both to ongoing eutrophication and to the more recent oligotrophication of lakes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<210:EEOPSA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

I used results derived from a bioenergetics model to develop a simplified method of estimating food consumption by largemouth bass Micropterus salmoides and northern pike Esox lucius. Growth data for each of three populations of each species from lakes covering a wide latitudinal portion of their ranges were used together with temperature data to estimate cumulative consumption rates with the model. For each species, a multiple regression with the independent variables of initial mean weight, weight gain, and degree-days accounted for 99% of the variability in estimated consumption rates. Sensitivity analyses were performed to determine the magnitude of errors associated with the assumptions made in using the model. The following assumptions were made: (1) close correspondence existed between simulated temperatures and those experienced by the fish; (2) feeding rates throughout the simulation period were a constant proportion of the maximum consumption rate; (3) gonad losses could be disregarded; (4) average swimming speed was 1 cm/s; and (5) energy densities of predators and prey were similar. In general, the errors associated with these assumptions were ± 10% of the estimated values, suggesting that the predictive equations could provide reasonable approximations of cumulative consumption rates.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<224:SMBOBM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The EM (expectation-maximization) algorithm was used to develop a general procedure for finding maximum likelihood estimates of population proportions when some observations cannot be assigned unambiguously to a population category. The method can be used to estimate the age composition of fish from length frequencies, to adjust biased estimates of age composition (e.g., scale ages that tend to be too low), and to correct biased estimates of unit stock composition. To implement the method, two samples are obtained. In the first sample, the items are cross-classified by their actual identity and by a second (possibly error-prone) surrogate classifying variable. In the second sample, the items are classified by only the surrogate variable. The information in the two samples is then used to estimate the population proportions in the second sample.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1987)116<232:UOALMW>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor