摘要:

On-site angler surveys commonly yield data on fish catch, fishing effort, and their variances for a sample of anglers. The ratio of catch to effort, or catch rate, often is multiplied by an independent estimate of total effort to calculate total catch (with its confidence interval) throughout the fishery. The most frequently used measures of catch rate are the ratio-of-means estimator (mean catch per angler divided by mean effort per angler) and the mean-of-ratios estimator (mean angler's catch rate). Bias and misleading confidence intervals are associated with use of ratio estimators, and the best catch rate measure for estimating total catch has been uncertain. We used statistical theory and simulation modeling to demonstrate that the most appropriate estimator (least bias, truest confidence interval) depends on the method of sampling. The ratio-of-means catch rate is better when anglers are sampled with equal probability at the completion of their trips (as in access point surveys). The mean-of-ratios estimator should be used when anglers are sampled, while still fishing, with probabilities proportional to trip length (as in roving surveys). When either estimator is used, confidence intervals around total catch are strongly influenced by skewness in the distribution of catch rates among anglers. At least 100 anglers or angler parties must be interviewed to attain targeted two-tailed ∝-levels; even then, the two statistical rejection areas (ideally, ∝/2) differ between tails of the distribution. Our results clarify the appropriate use of catch rate estimators with survey data, and they show the desirability of larger sample sizes than are customarily used in angler surveys.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0911:POCRUI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Sex ratios for 16 beds of northern quahogsMercenaria mercenaria(N= 22–964 clams/site) from various habitats in the coastal waters of Georgia did not differ significantly from a 1:1 ratio, regardless of habitat. However, there was a trend toward a consistently higher percentage of males occurring farther up the intertidal zone. Northern quahogs collected during the peak of the reproductive period (spring) from the highest intertidal habitat in salt-marsh grassSpartina alterniforashowed no apparent sexual development; however, 4–6 months after transplantation to the lower intertidal zone, gametes developed and the clams could be sexed. For pooled data from all sites (N= 2,637 northern quahogs), the sex ratio was equal for all ages (except for ages 1 and 23) and sizes (except for the 66–70-mm size-class). The sex ratio of the northern quahog population in Georgia was in equilibrium.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0929:SROTNQ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We tested an assumption of the instream flow incremental methodology that depth and velocity preferences are independent of streamflows. We had previously developed depth and velocity preferences (P[d] and P[v]) for juvenile (parr) steelheadOncorhynchus mykissat 0.86 m3/s in Morse Creek, Washington, and found parr distributed in microhabitats with higher combined depth–velocity preference (P[dv] = P[d] × P[v]) at a similar flow (0.69 m3/s). In the present study, we evaluated the relationship between fish distribution and combined depth–velocity preference using an independent data set from a higher flow (2.41 m3/s) in the adjacent stream segment. Most steelhead parr were distributed in microhabitats with high P[dv], consistent with distribution at 0.69 m3/s and significantly different than expected if fish distribution were independent of habitat preference (chi-square,P< 0.02). These results suggest that depth and velocity preferences are independent of flow.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0935:NUODAV>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The number of wild Atlantic salmonSalmo salarthat return to Spanish rivers has steadily decreased because of environmental degradation and overfishing. To alleviate this decline, juvenile salmon obtained from adults returning to Asturian rivers are used in a supplementation program. Gametes from no more than 35 adults are used to create groups of juveniles that are released back into the wild. We examined the effect of parental numbers on the chromosomal patterns found in juveniles produced by this protocol. When less than 20 parental fish were used, the chromosomal patterns found in their offspring were significantly different (P< 0.001) from those found in naturally produced fish. Consequently, in supplementation endeavors, at least 20 parents should be used to create groups of juveniles.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0939:EOPNOC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A morphometric study of the otoliths of a population of Pacific hakeMerluccius productuswas conducted to detect developmental instability (DI) related to parasitism by Myxosporeans,Kudoaspp. We report a link between parasitism and DI, which we measured as fluctuating asymmetry by comparing the right–left differences in otolith shape, width, and weight in the same fish. Otolith shape provided the most sensitive measurement of DI asymmetry. Results suggest thatKudoaspp. could be a strong agent of selection in the Pacific hake.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0943:DIITPH>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effect of the presence of scuba divers conducting visual point count surveys on the abundance and size distribution of fishes estimated with dual-beam hydroacoustics was examined at a petroleum platform in the northern Gulf of Mexico during November 1991 and February, March, and June 1992. Mean density of fishes declined 41–77% for all sampling periods when scuba divers were present. Target strengths also dropped significantly for all sampling periods when scuba divers were present. Our results show that fishes at petroleum platforms avoid scuba divers. Therefore, visual surveys of fish at petroleum platforms and other similar environments should be supplemented with hydroacoustic assessments.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0946:EOSDOF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The three-masted, wooden-hulled steamshipCentral Americasank in 1857 during a hurricane 370 km east of Savannah, Georgia. During a recovery project begun in 1988, the unmanned research submersibleNemoequipped with video and still cameras filmed a 6-m-long, male Greenland sharkSomniosus microcephalusat the 2,200-m-deep wreck site. The depth is 1,000 m deeper than the maximum reported depth for this species. The Savannah location is 440 km further south than the previously known North Carolina records for the Greenland shark.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0950:AGSFTW>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-124.6.954

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-124.6.956

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-124.6.960

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor