摘要:

In some lakes, first-year growth of walleyesStizostedion vitreumhas been identified as an important factor governing recruitment of juveniles to the adult population. We developed a regression model for walleye recruitment in western Lake Erie by considering factors such as first-year growth, size of the spawning stock, the rate at which the lake warmed during the spring, and abundance of gizzard shadDorosoma cepedianum. Gizzard shad abundance during the fall prior to spring walleye spawning explained over 40% of the variation in walleye recruitment. Gizzard shad are relatively high in lipids and are preferred prey for walleyes in Lake Erie. Therefore, the high degree of correlation between shad abundance and subsequent walleye recruitment supported the contention that mature females needed adequate lipid reserves during the winter to spawn the following spring. According to the regression analysis, spring warming rate and size of the parental stock also influenced walleye recruitment. Our regression model explained 92% of the variation in recruitment of age-2 fish into the Lake Erie walleye population from 1981 to 1993. The regression model is potentially valuable as a management tool because it could be used to forecast walleye recruitment to the fishery 2 years in advance. First-year growth was poorly correlated with recruitment, which may reflect the unusually low incidence of walleye cannibalism in western Lake Erie. In contrast, first-year growth was strongly linked to age at maturity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0821:FYGRAM>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Survival of the 1963–1982 year-classes of stocked yearling lake troutSalvelinus namaycushdeclined significantly over time in Lake Superior. To investigate possible causes of this decline, a Ricker model of stock–recruitment was used to describe the catch per effort (CPE) of age-7 stocked lake trout in the Michigan, Minnesota, and Wisconsin waters of Lake Superior as functions of the numbers of yearlings stocked 6 years earlier (an index of density dependence), the density (CPE) of wild adult lake trout (an index of predation), and large-mesh (≥114-mm stretch-measure) gill-net fishing effort (an index of fishing mortality). Declining CPE of stocked lake trout in Michigan and Wisconsin was significantly associated with increasing large-mesh gill-net fishing effort. Declining CPE of stocked lake trout in Minnesota was significantly associated with increasing density of wild lake trout. Declining survival of stocked lake trout may therefore have been caused by increased mortality in large-mesh gill-net fisheries in Michigan and Wisconsin, and by predation by wild lake trout that recently recolonized the Minnesota area. We recommend that experimental management be pursued to determine the relative importance of large-mesh gill-net fishing effort and of predation by wild lake trout on the survival of stocked lake trout in U.S. waters of Lake Superior.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0831:CODSOL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Humpers are one of at least three morphological variants of wild lake troutSalvelinus namaycushthat maintain self-sustaining populations in Lake Superior. In an early study, bumpers from Isle Royale were shown to have a sharply truncated age distribution that was attributed to high mortality after age 11, but we suspected that these fish were underaged. In August of 1989 and 1992 we collected spawning humper lake trout from the same area and estimated their ages using both scales and sagittal otoliths. Humpers in our sample ranged from 5 to 13 years, based on scale annuli, but counts of sagitta annuli revealed ages of 8 to 28 years. Individual discrepancies between ages from scales and sagittae varied from –2 to 20 years, but differences between scale and otolith ages did not increase with individual age. We applied the von Bertalanffy growth model to the humper length-at-age data to indirectly assess the accuracy of aging estimates. The model significantly overestimated mean asymptotic length when scale ages were used, but the mean asymptotic length estimate was more similar to observed lengths when sagitta ages were used. Our results corroborate evidence that bumpers in Lake Superior grow more slowly and mature at a smaller size than lean lake trout; however, the age composition of bumpers is more diverse than previously thought. This particular population experiences little or no exploitation; the presence of older fish provides one standard by which the success of lake trout rehabilitation programs can be evaluated and emphasizes the need for accurate aging techniques.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0844:ORADAS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Little is known about the stock structure of lake herringCoregonus artediin Lake Superior, and recent increases in harvestable stock sizes has led to expanded exploitation in some areas. Research on marine teleosts has demonstrated that chemical differences in sagittal otoliths can be used for identification of fish stocks. We used plasma emission spectrophotometry to measure the concentrations of 10 trace elements in the sagittal otoliths from lake herring captured at eight spawning sites in Lake Superior and from Little Star Lake. an inland lake outside the Lake Superior basin. Discriminant function analysis indicated that elemental concentrations provided site-specific information but that considerable overlap existed among some locations, especially those in western Lake Superior. Correct classification rates varied from 12.0% to 86.1% and were generally higher for spawning locations from embayments in eastern Lake Superior and for the outgroup population from Little Star Lake. The results presented here demonstrate the potential usefulness of this technique for strictly freshwater species, especially those that live in highly oligotrophic waters such as Lake Superior.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0852:DASCOL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Size-selective mortality of age-0 inland silversidesMenidia beryllinawas assessed by using otolith microstructure analysis and the biological intercept back-calculation procedure. Back-calculated size-frequency distributions were compared with the size-frequency distributions of field collections to determine if and when size-selective mortality occurred. These analyses indicated that in both 1990 and 1992, size-selective mortality occurred and was directed at the larger members of the inland silverside cohort. The timing of size-selective mortality varied between the 2 years. In 1990, size-selective mortality occurred during the juvenile stage, whereas in 1992, size-selective mortality occurred during the late larval and early juvenile stages. These results conflict with the prevailing hypothesis that larger individuals have higher survival probabilities than smaller individuals but support our previous finding that juvenile bluefishPontatoinus saltatrixprefer to prey on the larger members of the inland silverside cohort.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0860:SSMOIS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We have developed a computer-aided system (Bony Parts) to analyze periodic bands in fish otoliths (or other structures) for age estimation. The image analysis program first scans the image of a thin otolith section, perpendicular to the bands specified by the user. Adjacent scans are averaged and filtered with Fourier transformation or spatial domain convolution. Bands of higher density are detected and are marked and summed on the screen. We evaluated this new technique using subsamples of thin-sectioned otoliths from the bank rockfishSebastes rufus. The time and effort for cleaning, preparation, sectioning, and mounting are the same for both traditional and computer-aided techniques. The computer-aided technique reduced the time and tedium of counting bands, yet still allowed the user to interactively make subjective decisions about aging criteria. Both approaches produced similar readings, but computer-aided estimates were more precise than traditional readings and required less analysis time. Thus, this new technique allows sample size and precision to be increased for a given amount of effort. Use of this new technique to age 1,897 sections produced von Bertalanffy growth equations that indicate female bank rockfish grow to a larger theoretical maximum size than males (L∞= 500.7 mm versus 438.1 mm total length) but grow at a slightly slower rate (K= 0.054 for females versus 0.073 for males).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0874:DOACAA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We compared three proportional back-calculation methods for scales using data sets for pumpkinseedsLepoinis gibbosusand golden shinersNotemigonus crysoleucasfrom 10 southern Quebec lakes, and we validated back-calculations by comparing them with observed lengths at time of annulus formation. Ordinary least-squares regression (OR) was compared with geometric mean regression (GMR) for describing body–scale relationships. Although minor differences were detected in body–scale regressions among lakes, pooling data across lakes yielded linear body–scale relationships with very highr2. Differences between OR and GMR body–scale relationships were negligible in both species. Likewise, all back-calculation methods produced equivalent results. Back-calculated lengths generally corresponded well with observed lengths in all pumpkinseeds age-classes and in golden shiners older than l year. Observed lengths were often greater than back-calculated lengths for age-1 golden shiners. Our results, indicating little or no difference among methods, contradict recent reviews claiming substantial disagreement among methods. Tighter body–scale relationships in our data sets than in previous studies appear to explain this contradiction. We suggest that tight body–scale relationships are attainable for many species, obviating concern over which proportional back-calculation method is chosen.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0889:BCOFLF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

From 1986 to 1995, over US$2.5 million has been spent or allocated for projects to modify channel conditions to improve spawning habitat for Chinook salmonOncorhynchus tshawytschain the Merced, Tuolumne, and Stanislaus rivers, tributaries to the San Joaquin River, California. We evaluated the planning, design and performance of the Riffle 1 B reconstruction on the Merced River. This is typical of the nine individual riffle reconstructions completed to date, involving excavation of the existing channel bed (here, to 0.6 m) and back-filling with smaller gravels believed to be more suitable for salmon spawning. We reviewed project documents, interviewed agency staff, and conducted field surveys to document channel conditions in 1994 for comparison with the project as constructed in 1990. The project planning and design did not consider the site's geomorphic context nor processes of erosion and sediment transport under the current flow regime. As a consequence, spawning-sized gravel placed in the channel was scoured and transported through the site at a flow with a return period of 1.5 years. The need for spawning habitat enhancement in the Merced River is questionable, but if such projects are to be built, we recommend that the project planning and design consider the site's geomorphic context and acknowledge the need for and provide funds for project maintenance, and that the performance of completed projects be systematically monitored and evaluated.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0899:SSHROT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

I assessed the effects of a devastating spate upon the populations of brown troutSalmo trutta, Atlantic salmonS. salar, and European eelAnguilla anguillaof the Esva River basin in northern Spain. Numbers and lengths were determined for fish sampled with electrofishing techniques at nine sites along three streams before and after the spate. In addition, brown trout and Atlantic salmon that had been marked in two streams prior to the spate permitted a direct evaluation of the immediate effects. Because the spate occurred at the spawning time and destroyed reproductive habitats, I also determined its effects upon the recruitment of that year-class of brown trout. There was no evidence of negative effects of the spate upon the variables examined. The persistence of the site-specific populations after the spate was independent of site characteristics and the corresponding numbers and sizes of fish. The recruitment of brown trout was successful and similar to that of previous years. I hypothesize that mechanical responses related to microhabitat use permit brown trout and Atlantic salmon to withstand spates.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0913:ROASFA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In 1990 and 1991, we collected larval smallmouth bassMicropterus dolomieu7–25 d after swim-up and juveniles 5–9 weeks after swim-up. Using otolith analysis, we compared the size distributions of larvae and juveniles at identical life stages (6, 12, and 24 d after swim-up). In both years, there was little evidence to suggest that the individuals that survived to become juveniles were statistically larger than the average larvae at any stage. Larval smallmouth bass in this system were probably most susceptible to predators that were not gape-limited and therefore did not experience size-selective mortality.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0920:AOSSMA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor