摘要:

Brook troutSalvelinus fontinalisfrom 21 unstocked waters, 3 naturalized lakes, and 4 hatcheries in New York and Pennsylvania were analyzed electrophoretically for allozyme expression. Thirty-two of the 68 loci examined were polymorphic. Average heterozygosity of samples from populations classified as wild–unstocked was 0.050 (range, 0.026–0.076). Differences (P< 0.05) occurred among the 21 wild–unstocked samples at 25 of 31 possible locus comparisons. All wild–unstocked samples were significantly different from each other and from hatchery samples (P< 0.01). A high fixation index (FST= 0.375) indicated that the wild–unstocked samples represented highly differentiated populations. A considerable portion of the gene diversity was found among major river basins (22.5%); the remainder was due to differences among minor river drainages within basins (10.0%) and among samples within minor drainages (5.0%). Cluster analysis of genetic distances organized samples into three main groups that were also associated by river basins. Management strategies for conserving the genetic variability of wild brook trout should focus on individual lake and stream populations within river basins as primary management units. Data indicated that naturalization had varying success in preserving the gene pools of the progenitor populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0515:HBTINU>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0533:GDAHBS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We investigated relationships between the diet and morphology of what appeared to be two undescribed species and intermediate morphs of the threespine sticklebackGasterosteus aculeatuscomplex living in a closed-basin, coastal lake in British Columbia during 1969 and 1970. One “species” was without a pelvic girdle and lateral plates and the other had a complete pelvic girdle, pelvic spines, and five or more lateral plates per side. For convenience, the former species was referred to as “benthic” because of its association with the lake bottom and the other as “limnetic” because of its pelagic distribution. The two species and intermediate morphs were divided into four groups based on girdle condition (none, partial, complete with incomplete pelvic spine development, and complete with long pelvic spines). Each group was divided into four subgroups based on lateral plate number (0, 1–2, 3–4, and 5 or more) on one side. Plateless morphs of each group fed mostly on bottom prey. Consumption of pelagic prey was associated with an increase in plate number for all groups in 1969. For a given plate number, however, the percentage of pelagic food in the diets was higher as girdle condition increased. In 1970, when there was intense predation on the threespine sticklebacks by introduced coho salmonOncorhynchus kisutchonly individuals in subgroups with complete girdles continued the trend of greater consumption of pelagic prey with an increase in plate number. Although the sample sizes were very small for some subgroups, the results suggested that higher numbers of lateral plates, in combination with girdle condition, were associated with pelagic feeding behavior of all groups in absence of coho salmon predation in 1969. In 1970, the pelvic girdle and lateral plate armor were important in maintaining pelagic feeding behavior in the presence of coho salmon predation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0543:FHODPO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Sockeye salmonOncorhynchus nerkaspawn in many streams and along lake beaches of the Kvichak River system in Alaska, but fry from the distinct spawning areas reside in a common nursery habitat, Iliamna Lake. In addition, Kvichak River subpopulations have similar dates of adult entry into fresh water, similar migration distances, and similar spawning dates. These similarities in rearing environments and migratory timing enabled us to test the hypothesis that differences in spawning and incubation habitat alone can promote differentiation in traits associated with reproductive success. River-spawning sockeye salmon tended to be larger at age and older than those spawning along island beaches. Females from rivers were more fecund but had smaller eggs than the beach-spawning females. Males from beaches were deeper-bodied and (in one comparison) had relatively longer lower jaws than males from rivers. The tendency of river-spawning females to mature later than beach spawners may be related to a higher marine growth rate and greater increase in fecundity with length. Differences in male morphology may reflect the countervailing pressures of natural and sexual selection. We conclude that these patterns of variation reflect, in part, adaptations to spawning and incubation conditions of the populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0550:VILHCA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We used a remotely operated submersible vehicle equipped with a color video camera to videotape the lake bed and document the distribution and abundance of burbotLota lotaon a 156-hectare portion of Julian's Reef in southwestern Lake Michigan. The substrates and bathymetry of the study area had been mapped recently by side-scan sonar. Burbot density determined from videotapes covering 6,900 m2of lake bed at depths of 23–41 m averaged 139 individuals/ hectare (range, 0–571/hectare). This density was substantially higher than the highest burbot density (59–95/hectare) reported in the literature. Burbot were present on the lake bed at depths of 23–36 m, but were most abundant near the crest of the reef at 23–28 m, where the water temperature was 8–13°C, their preferred summer temperature range. Substrates in that temperature range on the reef were bedrock, bedrock ridges, and bedrock and rubble. Burbot were most abundant on the bedrock and rubble. Small fish and macroinvertebrates typically eaten by burbot elsewhere in western Lake Michigan were distributed on the reef according to their summer preferred temperatures and were not seen in abundance where burbot density was highest. We saw no lake troutSalvelinus namaycushon Julian's Reef, although large numbers of juvenile lake trout have been stocked there annually and temperatures on the reef were in the preferred summer temperature range for lake trout.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0560:DAARMO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Seasonal shifts in the microhabitats used by feeding brown troutSalmo truttain a northern Spanish river were related to changes in habitat availability. At higher flows, mean water column velocities, focal velocities, and depths occupied by brown trout were greater and focal elevations above the substratum were less, but no changes in substratum use were detected. Cover use differed between dates, apparently according to the presence of suitable materials. In May, a lower proportion of the observed fish were holding feeding positions than in July, October, or January. Total metabolic costs associated with holding feeding stations were primarily determined by swimming costs, and both costs varied substantially between dates, mainly as a consequence of the different swimming speeds of brown trout on the different dates. Standard metabolism was less important than swimming cost in total energy expenditure and showed no obvious relationship with total metabolic rate. Brown trout exhibited considerable individual variation in swimming costs, which seemed not to be related to fish size.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0575:MUBSRB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Annual production by smallmouth bassMicropterus dolomieuin Bear Creek, Minnesota, was 43.8 and 24.1 kg wet weight per hectare in 1985–1986 and 1987–1988, respectively. Corresponding annual production/biomass ratios were 1.6 and 0.9. Densities and standing stocks changed little between years. Twenty-five additional fish species were present in Bear Creek. Age-0 smallmouth bass (shorter than 11 cm total length) fed most heavily on corixids, whereas older, larger fish fed most heavily on other fishes. Annual production by smallmouth bass was much lower than trout production in similarly fertile streams in southern Minnesota and Wisconsin. This lower production may be attributable to the many more coexisting fishes with which the smallmouth bass must share the food resources of its habitat. More-restrictive creel regulations may be needed for smallmouth bass than for trout, even in streams of similar basic productivity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0588:PDOSBI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

I investigated interactions between native and nonnative fishes in the upper Muddy River system to add insight into (1) the mechanism causing the decline of the Moapa daceMoapa coriaceaafter the introduction of the shortfin mollyPoecilia mexicana, (2) the reason Moapa White River springfishCrenichthys bailevi moapaewere less affected by the introduction, and (3) the reason interactions between natives is relatively benign. I investigated the hypothesis that the shortfin molly caused the decline of the Moapa dace through competition or predation on larvae, pressures not experienced by the Moapa White River springfish. Relative interspecific competition was analyzed by contrasting the ranges of spatial and dietary overlap among larval, juvenile, and adult life stages. There appeared to be moderate to low spatial overlap between the various life stages of native and nonnative fishes. Overlap in diet was highest between adult Moapa White River springfish and shortfin mollies. Laboratory experiments suggested that shortfin mollies prey vigorously upon fish larvae. In terms of spatial habitat use, Moapa White River springfish larvae were less available to adult shortfin mollies for consumption than were Moapa dace larvae. When predation on larvae is the mechanism by which nonnative fish reduce native forms, aggressiveness of the predator and the degree to which the predator overlaps in habitat with the prey may influence the degree to which a native fish population is affected.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0599:IBNANF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We videotaped Arctic graylingThymallus arcticusfeeding on largeDaphnia middendorffianadrifting at different water velocities in an experimental stream with and without stream debris. The angle and distance at which fish first located each prey was determined from the videotapes. Both measures were affected by stream velocity and added debris. Location distance was unchanged at the lower velocities (11.6 and 32.3 cm/s) but declined at higher velocities. However, prey encounter rate increased up to water velocities of 45.8 cm/s, and thus water velocity compensated for reduced search area. Added debris always shortened location distance and decreased location angle. These findings have implications for position choice in streams and search strategies.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0609:EOCVAS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Brook troutSalvelinus fontinalis, mottled sculpinsCottus bairdi, and slimy sculpinsCottus cognatusoccur in many Pennsylvania streams that have depressed pH and elevated aluminum concentrations during episodes of high stream discharge (acidic episodes). We performed 20-d in situ cage exposures with these species to determine their relative sensitivities to field conditions. We also exposed fish in the laboratory to synthetic soft water, without added Al, to elevate possible effects of Al on sodium flux rates and pH toxicity. Exposures were in five streams: Two with high pH (>5.60) and low Al concentrations (<80 μg/L) and three with low pH (usually between 5.0 and 5.5) and high Al levels (124–294 μg/L). Exposures were during two low-discharge fall periods, when pH tends to be seasonally higher and Al concentrations lower, and two relatively high-discharge spring seasons, when lower pH and higher Al concentrations are typical. Few fish died (generally < 10%) in the two streams that had higher pH and lower Al concentrations, whereas mortalities typically exceeded 20% and were as high as 100% during spring exposures in the streams with lower pH and elevated Al concentrations. All three species had higher mortality rates in spring, 20–100%, than in fall, 0–29%. Mottled sculpins and slimy sculpins had similar mortality rates and both had lower mortality rates than brook trout when exposed to similar conditions. We compared Na flux rates of mottled sculpins to those of brook trout in laboratory exposures at pH 4.0, 5.0, and 6.0 to determine if low pH alone could account for mortality rates in the field. Because Na flux rates at pH 5.0, without added Al, were similar to flux rates of the controls for both species, high Al levels were believed to have contributed to the increased mortality observed in streams.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1993)122<0616:MOBTMS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor