摘要:

Rainbow smelt Osmerus mordax were introduced into Horsetooth Reservoir, Colorado, in 1983 to increase prey availability for walleyes Stizostedion vitreum. The introduction was highly successful. Rainbow smelt abundance reached at least 0.4 fish/m3within 6 years, and walleye growth improved by 50%. Zooplankton sampling provided the first clues that the Horsetooth Reservoir food web was undergoing dramatic changes in response to the rainbow smelt introduction. During 1989–1994 the abundant rainbow smelt population apparently reduced April and May crustacean zooplankton concentrations from historical levels of 40–80 organisms/L to less than 1.0 organism/L, and a switch occurred in the cladoceran species composition. Standardized sampling with beach seines and gill nets indicated that after 1988 walleye recruitment ceased. Efforts to bolster walleye recruitment by fry stocking in 1992 and 1993 also failed. A recent decrease in rainbow smelt density allowed a resurgence of zooplankton and a shift in predominance back to a large-bodied cladoceran (Daphnia pulex) in 1995 and 1996. Fish sampling in subsequent years corroborated declines in rainbow smelt abundance and walleye condition. Although hybrids of striped bass Morone saxatilis × white bass M. chrysops have been stocked in recent years, in part to control an overabundant rainbow smelt population, hydroacoustic surveys and bioenergetics modeling suggested that, during 1994–1996, walleye predation alone could have been a significant mortality factor limiting the rainbow smelt population biomass. Thus, we expect further declines in rainbow smelt biomass with possible negative consequences for piscivore growth rates and predation rates on prey-sized sport fish. To manage for balance of prey supply and predator demand, regular estimates of the zooplankton, rainbow smelt, and piscivore populations must be obtained.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0629:FWCOFY>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A bootstrap procedure was used to estimate the precision of biological reference points from stock–recruitment data. A Beverton–Holt model was used for the Georges Bank stock of yellowtail flounder Limanda (= Pleuronectes) ferrugine and a Ricker model was used for the northwest Atlantic stock of Atlantic mackerel Scomber scombrus. Results indicate the bootstrap approach should be useful in developing management strategies and control laws to allow for sustainable harvests of marine fish stocks. Results also illustrate the potential benefits of using the spawning stock biomass that produces maximum sustained yield as a limit reference point and not a target reference point for fish stocks. Statistics and estimates of precision from bootstrap results can be used to (1) develop risk-averse management strategies, (2) identify thresholds for recruitment overfishing, (3) examine the utility of limit and target reference points, and (4) investigate sustainable yield levels. A current goal of many fisheries management organizations is the development of robust target and limit biological reference points. Findings from this study are relevant to providing advice on this topic.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0643:PAUOBR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Northern Refuge in Lake Michigan was established in 1985 as part of a rehabilitation program to stock yearling lake trout Salvelinus namaycush in areas with the best potential for success. Stocking of hatchery-reared lake trout within the refuge began in 1986 at three reefs: Boulder Reef, Gull Island Reef, and Richards Reef. On each reef from 1991 to 1997 we conducted gill-net surveys during the fall spawning season to evaluate performance of adult lake trout, and we conducted beam trawl surveys for naturally reproduced age-0 lake trout in the spring. Criteria to evaluate performance included spawner density, growth, maturity, and mortality. We found no evidence of natural reproduction by lake trout from our surveys. Nevertheless, density of spawning lake trout on Boulder Reef (69 fish/305 m of gill net/night) and Gull Island Reef (34 fish/305 m of gill net/night) appeared to be sufficiently high to initiate a self-sustaining population. Growth and maturity rates of lake trout in the Northern Refuge were similar to those for lake trout stocked in the nearshore region of Lake Michigan. In the Northern Refuge, growth rate for the Marquette strain of lake trout was slightly higher than for the Lewis Lake strain. Annual mortality estimates from catch curve analyses ranged from 0.46 to 0.41, and therefore, these estimates approached a level that was considered to be sufficiently low to allow for a self-sustaining population. Thus, it appeared that the lack of evidence for natural reproduction by lake trout in the Northern Refuge should not be attributed to inability of the population to attain a sufficiently large stock of spawners.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0658:SOLTRI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Hatchery-reared salmon have been reported to be inferior to wild fish in some studies and competitively superior in others. We examined the influence of early rearing environment (hatchery versus natural) on the summer survival, movement, and growth of genetically similar juvenile coho salmon Oncorhynchus kisutch in streams. In each of 2 years, 5,000–10,000 fry from a hatchery cohort were placed above barrier falls in each of two streams to rear naturally at low density. The rest were reared at high density in hatchery raceways. After 3 months (late spring), we electrofished the streams, marked the naturally reared salmon caught, and then added equal numbers of marked hatchery-reared salmon to the streams. The streams were electrofished again in the summer to monitor survival, movement, and growth. Hatchery-reared and naturally reared juveniles survived equally well (about 90% survived each summer), and few fish of either rearing type emigrated from the study streams. Hatchery fish were about 10% larger than naturally reared fish at the time of introduction, but there was no evidence for size-related survival in the streams. When adjusted for size, hatchery fish grew at faster rates than naturally reared fish. Our results suggest that hatchery-reared coho salmon perform similarly to naturally reared salmon when introduced into streams in low numbers and with a relatively small size advantage.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0670:CPOGSH>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We evaluated the use of nonlethal sampling of bony fin tissue to obtain allozyme data for Pacific salmonids Oncorhynchus spp. Enzyme activity was detected for 53 loci, including many polymorphic loci, in caudal fin tissue sampled from chinook salmon O. tshawytscha, chum salmon O. keta, coho salmon O. kisutch, sockeye salmon O. nerka, and steelhead O. mykiss. This represents 61% of all the loci (N = 87) routinely analyzed using eye, heart, liver, and muscle tissue. Anal, dorsal, caudal, pelvic, and pectoral fin tissues all expressed the same loci with approximately the same strength of activity. Fin tissue sampled from adult salmonids yielded a slightly greater number of loci than did juvenile samples. Sufficient allozyme activity was observed for 9 mg of juvenile chinook salmon and steelhead fin tissue for some loci; however, the minimal amount of tissue needed to obtain all detectable loci was 54 mg. We performed computer simulations to test the feasibility of using allozyme data from fin tissue in mixed-stock analyses. The simulations showed that using the loci expressed in fin tissue samples, we were able to accurately estimate the stock composition of adult steelhead migrating up the Columbia River. Fin tissue sampling will be useful for collecting allozyme data when other tissues are not available or when lethal sampling is not desirable and will complement mitochondrial and nuclear DNA techniques that also use nonlethal sampling.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0678:ASOPSW>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Logs of standard dimensions from five species of trees were submerged in a stream to evaluate changes in strength and decomposition over a period of 5 years. Changes in structural properties occurred only for wood near the outer surface of the logs. Nearly all bark was removed from the logs within 12 months. Diameter loss for the five species ranged from 10.6 mm (western hemlock Tsuga heterophylla) to 21.8 mm (bigleaf maple Acer macrophyllum) after 5 years. Decreases in the density of surface wood for the five species ranged from 23% (red alder Alnus rubra) to 31% (western hemlock). Modulus of rupture, modulus of elasticity, and wood density did not change for wood more than 12 mm from the log surface for any of the species. Bigleaf maple exhibited the highest resistance to rupture, and western redcedar Thuja plicata exhibited the lowest. Western redcedar was also the most easily flexed. Microbial activity on the surface of the logs was highest at the start of the experiment and decreased rapidly with time of immersion. The two hardwood species (bigleaf maple and red alder) generally had higher levels of microbial activity than the conifer species (Douglas fir Pseudotsuga menzesii, western hemlock, western redcedar) from 12 months through 60 months of immersion. Differences in the rate of decomposition between conifer and hardwood logs were much less than in terrestrial environments. Our results suggest that hardwood logs can be used in stream enhancement projects where the wood will be submerged.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0687:EOIIWO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We developed an efficient sampling design-based approach using fishery-independent surveys to estimate population abundance of pink shrimp Penaeus duorarum over time in Biscayne Bay, Florida. We initially implemented quarterly stratified random sampling (StRS) using nine habitat strata and determined that average pink shrimp density (numbers/m2) was highest in late fall and lowest in spring and late summer. Coefficient of variation of the quarterly surveys, expressed as percent standard error/mean density, ranged from 5.8% to 14.3%. We found StRS to be more efficient (i.e., with lower variance) than simple random sampling (SRS) in most seasons. Statistical analyses suggested that pink shrimp densities were dependent on the biophysical habitat variables of bottom substrate, depth, and salinity. We also noted ontogenetic shifts in these relationships that were particularly pronounced at the onset of sexual maturation. Poststratification analysis was used to further evaluate several alternative habitat-based sampling schemes. Results showed that a five-strata composite design that used all three habitat variables was similar in performance, but less complex, than the original nine-strata design. In addition, the composite design outperformed both SRS and all other StRS designs indexed on single habitat variables. The new five-strata composite design was implemented in late summer 1997 and achieved a significant reduction in coefficient of variation compared with the late summer 1996 survey. This new design did not perform as well as expected in late fall 1997, which we attribute to a mismatch between our seasonal sample allocation strategy and the timing of pink shrimp recruitment into Biscayne Bay in 1997. Finally, we show how statistical sampling designs that use stratifications based on relevant habitat covariates can yield high-precision abundance estimates at low costs and provide a robust quantitative methodology for identifying habitat essential to fisheries production.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0696:AESSDT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Five surveys of coastal shrimp abundance and distribution were conducted aboard a commercial shrimp trawler between 25 Aug and 4 Nov 1997 to evaluate the potential for a commercial shrimp fishery in Chaleur Bay, southern Gulf of St. Lawrence. The net was equipped with a fish exclusion grate (25-mm bar spacing) to reduce fish bycatch. The initial target species was sevenspine bay shrimp Crangon Sepemspinosa, but very few were captured in the depths fished (20–82 m). The principal shrimp species captured were Aesop shrimp Pandalus montagui and Arctic argid Argis dentata. The catch rates of shrimp were too low to support a commercial shrimp fishery in Chaleur Bay. Average catch rates for Aesop shrimp ranged between 0.5 and 3.2 kg/h (whole animals, wet weight), and catch rates for Arctic argid ranged between 0.5 and 9.3 kg/h. Bycatch of fish was low (usually <10 kg/h) from late Aug to Oct but were excessive during early Nov when an average of 102 kg/h of Atlantic herring Clupea harengus and rainbow smelt Osmerus mordax were caught.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0713:ROAESF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Regional economic impact assessments (EIAs) of recreational fisheries reveal how anglers' expenditures affect economic activity such as sales, income, and employment in a particular region. Unfortunately, most EIA studies report only the final impacts of the EIA, without describing the economic interdependencies that produced the impacts or how the results should and should not be used to guide management decisions. This is particularly troublesome because most resource managers only vaguely understand how EIA models work and how to interpret the results in a fisheries management framework. The purpose of this article is to provide a starting point toward establishing consistent and defensible techniques for conducting regional EIAs of recreational fisheries and to explore the appropriate uses of EIA outputs as they relate to the growing needs of natural resource managers. Using marine recreational party and charter boat fishing in Maine in 1996 as an example, an EIA was conducted with the IMPLAN (Impact analysis for Planning) input–output system. Economic impacts were analyzed separately for Maine residents and nonresidents, and a linear production function that represented average for-hire operating expenditures was developed and integrated into the input–output model. Direct, indirect, and induced economic impacts were estimated for sales, income, and employment. In total, the US$1.12 million spent in Maine by nonresident party and charter anglers in 1996 resulted in $1.04 million in sales that remained within the state, $393 thousand in additional income, and supported approximately 37 jobs. Resident expenditures in 1996 totaled $276 thousand and generated $225 thousand in instate sales, $82 thousand in income, and approximately 10 jobs. The impacts of nonresident expenditures were generally five times greater than that of their resident counterparts. However, the actual economic impact of resident expenditures depends on assumptions regarding the absence of the marine for-hire fishery in Maine. Although the model's multipliers may be used to predict the total impacts of changes in expenditures by party and charter boat anglers, it is important to understand their limitations. The procedures and data sets applied here, if used in conjunction with future versions of IMPLAN, can serve as a foundation for updating the Maine input–output model provided in this study and for developing economic impact assessments of recreational fisheries in other states.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0724:REIAOR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The large number of lakes covering 10% of Finland's surface area provide an opportunity for both full-time and part-time professional fishing. However, the development of the fishing industry is hindered by unpredictable fluctuations in fish stocks, by the elaborate hierarchy of the fisheries system, as well as by certain features of Finnish professional fishing, such as the small size of fishing enterprises, the scattered pattern of production, and long transportation distances to the core demand areas. According to Finnish catch statistics, the stock of vendace Coregonus albula has clearly diminished since the mid 1980s. Our results show that full-time professional fishermen differ from part-time professional fishermen in their adaptation to diminished fish stocks: they increase their fishing efforts, they try to extend their fishing grounds, and they switch to or supplement with a new species. Moreover, their desire to develop their fishing is stronger than that of part-time professional fishermen, and they can be regarded as active agents in the fishing industry. When a fishing enterprise has adequate access to fishing grounds and is allowed to use different kinds of gear effectively, it may develop and expand its operations (i.e., use its entrepreneurial capacity). An important policy implication of resource use would be to ensure the availability of fishing licenses to full-time professional fishermen, in the hope that the most active would also lead the continued development of inland professional fishing as a whole.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0737:TAOPFT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor