摘要:

Simulations based on the Ricker and Beverton–Holt stock–recruitment models illustrate the difficulties with developing information about the effectiveness of habitat restoration efforts from the relation between measurements of habitat and populations of anadromous fishes. The relation between the two is confounded by density-dependent mortality and variable density-independent mortality and is masked by measurement errors. The simulations are considered in terms of populations of fall-run (ocean-type) chinook salmon Oncorhynchus tshawytscha from the Sacramento–San Joaquin river system of central California, where major federal and state efforts are underway to restore anadromous fish populations, as well as brackish and freshwater ecosystems. The simulations show that to implement effective adaptive management of salmon habitat, these efforts must move beyond a trial and error approach in which efforts to restore salmon habitat will be evaluated by population responses. A more promising alternative is evaluating restoration efforts by identifying and testing hypotheses about the mechanisms or processes that relate the restoration actions to populations.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0329:SDAAMO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Bycatch reduction devices (BRDs) have been mandated for use in the U.S. Gulf of Mexico shrimp fishery to reduce shrimp trawl mortality of juvenile red snapper Lutjanus campechanus. Conditional survival of juvenile red snapper from shrimp trawl bycatch has been estimated to be on the order of 12%. The BRDs have been estimated to reduce shrimp trawl bycatch mortality by more than the 50% reduction that has been estimated as necessary to rebuild the stock by the target date of 2019. Results from analyses in this study that used observer data collected during 1992–1996 do not support this contention. A low fraction of the annual bycatch occurs during times of the year when BRDs effectively exclude juvenile red snapper at the sizes encountered. Maximum potential exclusion of juvenile red snapper with the use of BRDs is only about 25–27%, not 59% as has been previously estimated. If rebuilding requires a 50% reduction in age-0 and age-1 red snapper bycatch mortality to achieve the stock recovery targets, this study's results clearly demonstrate that the BRD by itself will not produce the mortality reductions necessary to meet this objective.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0342:ROJRSB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Stocks of anadromous striped bass Morone saxatilis of the Atlantic coast have supported important fisheries since colonial times. Commercial landings reached a record high in 1973, then declined by almost 90% during the following decade. Juvenile production by the Chesapeake Bay stock, a major contributor to coastal fisheries, was depressed during the 1970s. These patterns prompted efforts to identify why striped bass had declined and to rebuild the Chesapeake Bay stock. We review the history of the striped bass decline and the science, management, and legislation that led to its recovery. Historical data and modeling results indicated that recruitment overfishing was a major factor in the decline. Juvenile production may have been further depressed by water quality problems that reduced survival of early life stages. Mathematical models demonstrated that reducing fishing mortality would immediately increase population growth rate, regardless of the decline's cause. An Interstate Fishery Management Plan (the Plan) was adopted by the Atlantic States Marine Fisheries Commission in 1981 and amended in 1985 to protect females until 95% could spawn at least once, thus increasing age at entry from 2 to 8 years. The Plan was strengthened in 1984 by the Striped Bass Conservation Act (Public Law 98-613), which required states to comply with the Plan or submit to federal moratoria. In 1985, states imposed moratoria or began a progressive increase in minimum size limits scheduled to reach 97 cm (38 in) in total length by 1990. Hatchery-reared striped bass were stocked in the Chesapeake Bay beginning in 1985 and may have accelerated recovery, though the benefits of stocking were far outweighed by the benefits of reducing fishing mortality. Abundance of females on spawning grounds in Maryland doubled between 1985 and 1988, and recruitment began to improve in 1989. Coastwide recreational catches increased more than 400% between 1985 and 1989. Regulations were relaxed in 1990 and an adaptive management scheme was adopted to allow limited harvest while the stock continued to recover. Recruitment continued to improve and the Chesapeake Bay stock was declared fully recovered in 1995, 10 years after stringent management measures were implemented.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0356:ACHOEF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Little is known of the relationship between instantaneous natural mortality rate, M (year−1), and body weight, W (g), for the lake-resident life stages of sockeye salmon Oncorhynchus nerka and kokanee (lacustrine sockeye salmon), despite the importance of the M–W relationship for modeling fishery management options. This study provided estimates of the two parameters of the allometric relationship M = 1.38W−0.19based on nonlinear regression of sockeye salmon egg–fry and egg–smolt survivals on fry and smolt weights reported in the literature. The values of both parameters were low compared with values reported from data sets that included marine iteroparous fish species and larval fish but were similar to values calculated from production–biomass ratios of lake fish populations. The difference suggests that nonpredation mortality plays a minor role in the population dynamics of juvenile sockeye salmon due to their relatively large size at emergence. The M–W relationship provided reasonable predictions of M for juvenile kokanee, based on M calculated from literature reports of kokanee density at age. Predictions of M also appeared reasonable when extrapolated to adult kokanee body weights, based on a comparison with M predicted by four previously published models of adult fish M. The M–W relationship has three potential applications to fishery management: (i) modeling of O. nerka population dynamics; (ii) back-calculating density of age-0 kokanee from density of age-2 kokanee; and (iii) estimating fishing mortality rate of exploited age-classes of kokanee by subtracting predicted M from total mortality rate.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0376:SDONMR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Mark–recapture studies indicated that a pulsed-DC electrical barrier set to a 2-ms pulse width and 10 pulses/s completely blocked the spawning migration of sea lampreys Petromyzon marinus in the Jordan River, Michigan. Capture efficiency of fyke nets averaged 24% for four groups, about 300 tagged sea lampreys each, released upstream of the barrier; no unmarked sea lampreys and none of the 1,194 sea lampreys tagged and released downstream of the barrier were captured in the fyke nets while the barrier was energized. At a lower pulsator setting (1-ms pulse width; 10 pulses/s), 1 of 900 sea lampreys released below the barrier was recaptured in the nets. Sea lampreys from downstream were captured in the fyke nets after the barrier was de-energized, indicating that the barrier should remain in operation later than mid-Jul. Both sea lampreys and teleosts exposed to the electrical field were stunned but exhibited no apparent damage at either barrier setting. The pulsed-DC electrical barrier should help reduce the use of chemical lampricides for controlling sea lampreys in some Great Lakes streams and would be particularly suited for streams where even the smallest low-head barrier would create an unacceptably large impoundment.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0397:EOAEBI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Predation by large northern pikeminnow (formerly northern squawfish) Ptychocheilus oregonensis is a major source of mortality for juvenile salmonids Oncorhynchus spp. in the lower Columbia and Snake rivers. Large-scale, agency-operated fisheries have been implemented in this area since 1990 to harvest northern pikeminnow with a goal of 10–20% exploitation. We used indirect methods to analyze the success of the fisheries, and examined benefits to salmonid populations. From 1991 to 1996, three fisheries (sport-reward, dam-angling, and gill-net) harvested approximately 1.1 million northern pikeminnow that were 250 mm in fork length or longer, with the sport-reward fishery contributing 86.5% of the total catch. Total exploitation averaged 12.0% (range, 8.1–15.5) for 1991–1996 and met program goals in all years except 1993. Gill-net and dam-angling fisheries harvested larger northern pikeminnow (which consume a greater number of juvenile salmonids) than the sport-reward fishery. Modeling results indicate that potential predation on juvenile salmonids by northern pikeminnow has decreased 25% since fishery implementation. The relative benefits of a given exploitation rate decreased with time as the number of large northern pikeminnow was reduced; however, additional reductions in potential predation are probable if exploitation is maintained at mean 1994–1996 levels. We estimate a reduction in potential predation of 3.8 million juvenile salmonids (representing 1.9% of the total population) if exploitation rates are maintained at mean 1991–1996 levels. Continued monitoring of predator populations is prudent, and we recommend that restoration and enhancement of Columbia River basin salmonids not rely solely on any one management approach.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0406:MONPAI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

For a multispecies fishery managed to achieve a harvest rate target for a single species, an early and accurate forecast of an in-season or the end-of-season harvest rate index can assist a manager with a decision to control effort. We present a model for rapidly forecasting an in-season or end-of-season harvest rate index for one species, the species of interest, in a multispecies fishery using catch and effort data collected for that fishery. These harvest rate predictions can be statistically evaluated against harvest rate indices calculated independently from demographic and biological data obtained for the fishery. The model structure was defined such that an estimate of both measurement error and process error could be obtained. The data required are the historical time series of catches for the species caught in the fishery, fishing effort, and harvest rate indices for the species of interest calculated independently of the catch and effort data. We illustrate the model with chinook salmon Oncorhynchus tshawytscha as the species of interest in the west coast of Vancouver Island troll fishery and the Strait of Georgia sport fishery. Other important species caught in these multispecies fisheries are coho salmon O. kisutch, sockeye salmon O. nerka, and pink salmon O. gorbusha.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0421:AEIATF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Approximately 22% of the waters of the Merritt Island National Wildlife Refuge, which encompasses the Kennedy Space Center, Florida, have been closed to public access and fishing since 1962. These closed areas offer an opportunity to test the effectiveness of “no-take” sanctuaries by analyzing two replicated estuarine areas. Areas open and closed to fishing were sampled from Nov 1986 to Jan 1990 with 653 random trammel-net sets, each enclosing 3,721 m2. Samples from no-fishing areas had significantly (P < 0.05) greater abundance and larger fishes than fished areas. Relative abundance (standardized catch per unit effort, CPUE) in protected areas (6.4 fish/set) was 2.6 times greater than in the fished areas (2.4 fish/set) for total game fish, 2.4 times greater for spotted seatrout Cynoscion nebulosus, 6.3 times greater for red drum Sciaenops ocellatus, 12.8 times greater for black drum Pogonias cromis, 5.3 times greater for common snook Centropomus undecimalis, and 2.6 times greater for striped mullet Mugil cephalus. Fishing had the primary effect on CPUE, independent of habitat and other environmental factors. Salinity and depth were important secondary factors affecting CPUE, followed by season or month, and temperature. The importance of specific factors varied with each species. Median and maximum size of red drum, spotted seatrout, black drum, and striped mullet were also significantly greater in the unfished areas. More and larger fish of spawning age were observed in the unfished areas for red drum, spotted seatrout, and black drum. Tagging studies documented export of important sport fish from protected areas to fished areas.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0436:EOAEEN>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, and spotted bass M. punctulatus were sampled by electrofishing in the spring and fall for 6 years in Normandy Reservoir, Tennessee, to assess spatial and seasonal differences in abundance. Bass were collected each season from 40 transects stratified among the following habitats: riprap, rubble, gravel, mixed substrate, and coves. A randomized-block design analysis of variance (ANOVA) was used to partition variation by habitat and year. Abundance was greatest in riprap habitats for largemouth bass and smallmouth bass in spring samples. Abundance was greatest in rubble habitats for spotted bass in spring samples, but in only 2 of 6 years. Abundance of largemouth bass and spotted bass was lowest in gravel habitats and cove habitats, respectively; smallmouth bass abundance was uniform and consistently low in all nonriprap habitats. Abundance trends among habitats in fall samples were similar to spring samples for all three species. Gravel habitats supported the smallest and youngest individuals for all species in both seasons. Catch rates of largemouth bass and spotted bass were lower in fall than spring, whereas catch rates of smallmouth bass were higher in fall than spring. Mean total lengths were smaller in fall samples for all three species. Stratifying samples across habitats identified specific habitats that contributed high variability to overall estimates of density; by allocating more samples to those habitats, variance can be reduced. Managers designing electrofishing surveys to obtain a random sample of black bass should be aware that catch rates from electrofishing surveys vary due to different habitat uses by different sizes and species of black bass.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0454:SATVIE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Much of the knowledge on salmonid ecology is based on electrofishing. Because there is little information on how electrofishing affects the subsequent behavior of fish, some of the salmonid data may be unreliable. Estimates of population sizes of stream fish based on mark–recapture or removal rely to a large extent on electrofishing as well. The population estimates obtained can be affected by high rates of movement suggested among stream-dwelling fish, regardless of whether the movements are natural or sampling induced. The amount of movement before and after electrofishing a closed population of brown trout Salmo trutta was determined by trapping in a small stream during 1994–1996. To assess the influence of movements on mark–recapture estimates and evaluate obtained estimates in relation to removal estimates, four different estimates (removal in summer, removal in autumn, conventional mark–recapture, and mark–recapture considering fish movements) were made for the closed brown trout population. The number of brown trout caught in upstream traps increased following electrofishing. For these fish, mean size was larger and recapture rates were lower compared with the general population in the stream. In all years the conventional mark–recapture method resulted in the highest population estimates and differed from the mark–recapture estimates in which fish movements were accounted for. Mark–recapture estimates accounting for movements did not differ from autumn removal estimates. The results emphasize the importance of minimizing disturbances in connection with studies of the population dynamics of stream fish.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0462:MOBTIA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor