摘要:

Experiments monitoring the egg and larval production of captive northwest Atlantic codGadus morhuaindicated that first-time spawners perform poorly compared to second-time spawners. They breed for a shorter period, produce fewer egg batches, exhibit lower fecundity, and produce smaller eggs with lower fertilization and hatching rates; moreover, their larvae are less likely to hatch in environmental conditions favorable for survival. Batch-average egg diameters of first-time spawners underwent a continuous rapid decline between initial and terminal batches, whereas second-time spawners commonly exhibited a parabolic curve (slight increase followed by a decrease). Seasonal composite hatching rates of all eggs spawned by first- and second-time spawners were 13 and 62%, respectively. Larval production per maternal gram was an order of magnitude greater for second-time than for first-time spawners (200 versus 20 larvae/g). Batch-average egg diameter declined 11% and larval dry weight declined 29% from initial to terminal batches when data were pooled over both spawner types. Egg diameter correlated positively with larval dry weight, yolk dry weight, and ratio of yolk to larval dry weight. Additional monitoring of individuals between the first and second breeding year confirmed results obtained on 12 cod pairs monitored during the same year at constant temperature. These results have a direct bearing on the development of mathematical models of spawner–recruitment relationships, and they suggest that conventional approaches may overestimate the reproductive potential of age-truncated populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0339:ESAVAS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Previous studies have shown that juvenile chinook salmonOncorhynchus tshawytschafrom a contaminated estuary of Puget Sound, Washington, are immunosuppressed. Immunosuppressed fish may be more susceptible to disease and ultimately experience an increase in mortality. To evaluate this possibility, differences in susceptibility to a marine pathogen in outmigrating juvenile chinook salmon from an urban estuary and a nonurban estuary in Puget Sound were assessed. Juvenile chinook salmon were sampled from hatcheries before their release and subsequently from their respective estuaries as the population outmigrated from freshwater to the saltwater environment during the springs of 1993 and 1994. The study was repeated during a 3-month period to assess the duration of the effect after the fish were removed from the source of contaminants and was replicated during a 2-year period to examine interannual variation. Bile, liver, and stomach contents were collected from fish after capture to determine exposure to organic chemical pollutants. Examination of these tissues demonstrated that juvenile salmon from the urban estuary were exposed to higher concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls than juveniles from the nonurban estuary or hatcheries. Juvenile salmon were challenged with serial doses of a marine pathogen,Vibrio anguillarum(serotype 1575), and mortality was measured daily for 7 d. In both years, salmon from the urban estuary challenged withV. anguillarumexhibited a higher cumulative mortality after exposure to the pathogen than salmon from the hatcheries or the nonurban estuary. Our results together with our previous findings support the hypothesisthat contaminant-associated immunodysfunction in juvenile chinook salmon may lead to increased susceptibility to infection by a virulent marine bacterium.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0360:ISOJCS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The objective of this study was to determine if exposure to aromatic hydrocarbons (AHs) or polychlorinated biphenyls (PCBs) was associated with altered ovarian development or reduced spawning success in rock solePleuronectes bilineatus. This objective was addressed in two separate phases. In the first study, concentrations of AHs and PCBs were measured in individual fish from four sites in Puget Sound, Washington (Eagle Harbor, Sinclair Inlet, Yukon Harbor, and Pilot Point) with different levels of AH and PCB contamination in sediments and their ovarian development was monitored during the 1989–1991 spawning seasons. In these fish, egg weight was negatively correlated with levels of PCBs in the liver. However, contaminant exposure levels were not significantly associated with the probability of entering vitellogenesis or with gonadosomatic index, plasma estradiol concentrations, or fecundity. In the second study, gravid female soles were taken from Eagle Harbor, Sinclair Inlet, Yukon Harbor, and University Point (known spawning areas for rock soles), and hormonally induced to spawn in the laboratory. Eggs were fertilized with pooled sperm from reference males. Consistent with the first study's findings, fish from Sinclair Inlet, where sediments contain elevated concentrations of PCBs, produced eggs with significantly reduced weight. Furthermore, the overall spawning success of fish from the site with the highest level of AH contamination (Eagle Harbor) was significantly impaired. These findings suggest that environmental exposure to AHs and PCBs may reduce reproductive success in female rock soles, but this species appears to be more resistant to such effects than other Puget Sound flatfish species, such as the English solePleuronectes vetulus.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0375:CEOODA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We conducted an allozyme survey of genetic variation at 33 gene loci in smallmouth bassMicropterus dolomieufrom 57 localities encompassing most of the range of the species, but with an emphasis (51 samples) on the Interior Highlands (Ozark and Ouachita uplands). Samples exhibited a moderate amount of total genic diversity (HT= 0.068), but high genetic heterogenity (FST= 0.383). Phylogenetic analyses supported recognition of three clades from the Interior Highlands: (1) the previously recognized Neosho smallmouth bass in Ozark tributaries of the middle Arkansas River; (2) the Ouachita smallmouth bass in the Little and Ouachita river drainages of the Ouachita Highlands; and (3) a clade that included populations from the White, Black, Missouri, and other streams in the northern and eastern Ozarks. This third clade was very similar to populations from the Ohio and upper Mississippi river basins, and, on the basis of allele frequency parsimony, more closely related to them than to the Neosho and Ouachita smallmouth basses. To preserve genetic diversity and the options that divergent native stocks represent for future management, stock transfers of smallmouth bass should take into account potential effects on native forms of the species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0393:GSASOS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The invasion of the Sacramento–San Joaquin estuary by the wakasagiHypomesus nipponensisposes threats of competition and hybridization with the endemic delta smeltHypomesus transpacificus, a species listed as threatened by federal and state agencies. Small individuals of these species are difficult to distinguish morphologically, but correct identification is extremely important to avoid mistaking delta smelt for wakasagi under the limited take provisions of the federal endangered species act. Allozyme markers were used to identify 280 individual fish from several sites across the range ofH. transpacificus.We used these results to document the current level of invasion byH. nipponensis, quantify levels of misidentification based on morphological characters, identify hybrid individuals, and estimate levels of gene flow inH. transpacificus.Wakasagi have spread throughout the Sacramento–San Joaquin estuary, and further monitoring will be necessary to determine the long-term consequences of their invasion on the native delta smelt. Our data suggest that when the level of uncertainty in morphological identification is high, biochemical identification is the safest way to identify fish. We identified only two F1hybrid individuals, suggesting that although hybridization does occur, it is not a serious threat to delta smelt at the present time. Finally, estimates of θ based on four variable allozyme loci indicate that gene flow between our four sampled locations is very high inH. transpacificus.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0417:BIAAOP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Karst topography is a unique and distinct landscape and its geology may have important implications for salmon productivity in streams. The relationship between salmonid communities and water chemistry and the influence of habitat was examined in a set of streams on north Prince of Wales Island, southeast Alaska. Streams in karst landscapes showed higher alkalinities (1,500–2,300 μeq/L) than streams not influenced by karst landscapes (750–770 μeq/L). A significant, positive relationship was observed between alkalinity and density of coho salmon parrOncorhynchus kitsutch.Backwater pools supported higher densities of coho salmon than did other habitat units. Both coho salmon fry and parr tended to be larger in most karst-influenced streams than in nonkarst streams. Although past timber harvest practices in the riparian areas of several of the streams appeared to influence stream habitat and water temperature, streams flowing through karst landscapes had a distinct water chemistry. Furthermore, these streams appeared to support more fish than nonkarst streams.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0425:CSPITK>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Lowest distributional elevations for brook troutSalvelinus fontinalisin 25 streams in east Tennessee were determined during 1991–1995 to evaluate changes related to encroachment and possible replacement by rainbow troutOncorhynchus mykisssince surveys conducted during 1978–1984. No efforts to remove rainbow trout or enhance brook trout populations were made in these streams during the 7–16-year intervals between surveys. Compared with the earlier surveys, brook trout distributions receded (lower elevation increased) in nine streams (36%), advanced (lower elevation decreased) in eight streams (32%), and did not change in eight streams (32%). The average total change in stream length occupied by brook trout was a 109-m downstream increase (SE = 82) with a mean annual increase of 8 m (SE = 6). Neither average total change nor annual change was significant (P> 0.19). Additionally, the highest elevations at which rainbow trout were present (determined in 10 streams) increased in four streams but decreased in six. The average total change in stream length occupied by rainbow trout was a 158-m decrease in elevation (SE = 151) with a mean annual change of −14 m (SE = 13). Neither average total change nor mean annual change was significant (P> 0.30). We concluded that rainbow trout were not affecting the downstream limit of most brook trout populations where the two species occurred sympatrically in Tennessee. Further, after examining published data from Great Smoky Mountains National Park, we found no evidence that the downstream limits of brook trout distribution in most streams were affected by the presence of rainbow trout between the 1950s and 1970s. These data support an emerging theory that the distributional limits of brook trout and rainbow trout in sympatry in the southern Appalachian Mountains will ebb and flow upstream and downstream over time.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0434:NNLOBT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

PaddlefishPolyodon spathulawere sampled by boat-mounted electrofishing and gill netting in the Tallapoosa and Cahaba rivers and in oxbow lakes of the Alabama River floodplain, Alabama, during January–June of 1992 and 1993. Tagging studies, characterization of spawning migrations, and comparative analyses of catches suggested that paddlefish in the Tallapoosa and Cahaba rivers represented functionally discrete populations that reside in the adjacent reservoirs. Variation in population characteristics appeared to be related to differences in the hydrologic and thermal regimes of the two study rivers and to differences in historical exploitation of populations in the two resident reservoirs. Growth (calculated via back-calculated body length at age) differed between populations in the upper and lower Alabama River, probably reflecting the relatively lentic (upper) and lotic (lower) nature of habitats in these two reaches. Life history characteristics of paddlefish in the Alabama River drainage differed from fish in the Mississippi River drainage. Growth, fecundity, spawning frequency, and age at maturity all were advanced for Alabama River fish relative to Mississippi River fish, whereas maximum age and size of Alabama River fish were less than had been previously reported for populations in the Mississippi River drainage. Differences between populations in the two drainages may reflect geographic variation in biotic and abiotic variables as well as long-term geographic and reproductive isolation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0441:PITARD>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Assessing potential effects of flow regulation on southeastern warmwater fish assemblages is problematic because of high species richness and poor knowledge of habitat requirements for most species. Our study investigated relationships between availability and temporal persistence of key habitats and fish assemblage structure at regulated and unregulated sites in the Tallapoosa River system. Fish assemblage characteristics at seven sites were quantified based on 1,400 electrofishing samples collected during 1994 and 1995. Physical Habitat Simulation (PHABSIM) programs were used to model availability and persistence of key habitats at regulated and unregulated sites. Associations between fish assemblages and availability or persistence of key habitats were identified via regression and analysis of variance. We found that hydropeaking dam operation reduced the average length of time that shallow-water habitats persisted and also reduced year-to-year variation in the persistence of shallow-water habitats compared with unregulated sites. Across sites and years, proportional representation of catostomids was positively correlated with persistence of shallow and slow-water habitats during spring. Proportion of individuals as cyprinids was positively correlated with median availability of deep–fast habitat whereas proportion of percids was inversely related to median availability of deep–fast habitat. Mean fish density was positively correlated with the persistence of shallow and slow-water habitats. Comparisons of key-habitat measures and fish abundances between 1994 and 1995 at each site indicated that higher abundances of percids, catostomids, and cyprinids were associated with increased availability and persistence of shallow and slow-water habitats in 1995. These findings demonstrate that the temporal and spatial availability of key habitats could serve as useful measures of the potential effects of flow alteration on lotic fish assemblages and suggest that both short-term persistence of key habitats as well as annual variation in key-habitat availability are important for maintaining diverse fish assemblages.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0455:EOGHCF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The Wisconsin Department of Natural Resources has carried out a complete creel census on Escanaba Lake, Wisconsin for more than 40 years. We used this creel census data set as the basis for simulations of a stratified random three-stage creel survey (stages were days, shifts, and count times) in which harvest was estimated as the product of effort and harvest rate. Effort was estimated from instantaneous counts of anglers, and harvest rate was estimated from completed-trip interviews. We evaluated the bias and precision of estimators of annual angler effort and harvest with creel census data from 3 years of varying angler effort and harvest. This creel survey method resulted in excellent estimates of annual effort. There was no evidence of bias, and coefficients of variation were less than 0.10 even though the standard errors of estimates were somewhat too large, resulting in conservative 95% confidence intervals (97–99% coverage). We found no evidence of bias for a stratum estimator of harvest in which harvest rate was estimated across all interviews in a stratum before multiplying by effort to estimate harvest. Coefficients of variation were less than 0.20, and confidence interval coverage was close to the targeted 95% level. An advantage of estimating harvest rate across all interviews in a stratum is that the sample size on which harvest rate estimates are based is then relatively large. We did find evidence for bias in a daily estimator of harvest in which harvest rate estimates were based only on interviews obtained each day.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0469:BACICO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor