摘要:

Current practices for computing maximum sustainable yield (MSY) from fisheries result in yields that are rarely maximized and never sustainable. We recast MSY determination as the maximization of constant catch, which is subject to the risk of stock depletion below levels necessary to generate the target constant catch. Monte Carlo yield models with stochastic recruitment functions were used to examine the effects of constant-catch policies on fishing mortality, catch, and stock size. Three additional output variables and their statistical properties were developed as indices of fishery variability and risk: delta catch, the change in catch between successive years; length of run, the number of successive years the target constant catch was attained; and the proportion of years in which the target constant catch was not taken. We constructed two stochastic yield models to account for different stock-recruitment relationships. The first used a statistical distribution of recruitment values in which recruitment was independent of spawning-stock biomass; the second used a stochastic form of the Shepherd stock-recruitment relationship. For the parametric stock-recruitment model, the ability to sustain moderate yields was critically dependent on rehabilitation strategies for years when total stock size dropped below that necessary to support the constant-catch target. Depending on specific stock dynamics, fluctuations in annual yields can be damped by accumulating harvestable stock and setting constant-catch targets that, on average, result in low to moderate fishing mortality. Target constant catches thus defined represent a stochastic analog of MSY and estimate the long-term potential catch from the stock. The desirability of such strategies is determined by the relative value of averting the risk of undesirable stock and catch fluctuations versus the costs of foregone yields due to natural mortality and density-dependent processes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0349:YSUCPA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In second- to fifth-order streams that drain old-growth timber in western Washington, characteristics and function of woody debris changed in relation to stream size. Average diameter, length, and volume of pieces of wood increased as stream size increased, whereas the frequency of occurrence of woody debris decreased. In streams with channel widths less than 7 m, 40% of the pieces of debris were oriented perpendicularly to the axis of flow; in streams with channel widths over 7 m, more than 40% of the pieces were oriented downstream. The types of pools most commonly associated with pieces of wood changed from plunge pools in small streams (42%) to debris scour pools in larger systems (62%). Pool area was correlated with the volume of the piece of wood forming the pool in streams of all sizes. However, this relationship was most evident in larger channels. Nearly 40% of the pieces of wood in channels less than 7 m wide were associated with sediment accumulations. Less than 30% of the pieces retained sediment in channels from 7 to 10 m wide, and less than 20% retained sediment in channels greater than 10 m wide. Surface area of sediment accumulations and the volume of the piece of wood forming the accumulation were related in all streams, but the relationship was clearest in the larger channels. Accumulations of particulate organic matter associated with woody debris were more frequent in small streams but were larger in large streams. No relationship was observed between the volume of fine particulate organic matter accumulated by a piece of wood and the piece of wood's volume.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0368:CICAFO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

To measure the changes in substrate composition produced by spawning brook troutSalvelinus fontinalis, we collected 187 freeze-core samples, both before and after spawning, from egg pockets, inside redds but excluding egg pockets, and outside redds. In the upper strata of reddassociated samples, we found that the proportions of particles 0.85–1.70, 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were significantly lower in egg pockets than outside redds, and the proportions of particles 0.425–0.85, 0.212–0.425, and less than 0.212 mm in diameter were also lower in egg pockets than in other areas inside redds. Samples collected outside redds were similar to samples collected before spawning. We observed no significant correlations between the proportion of fine sediment in samples from outside redds (and presumably the proportion present before spawning) and the proportion of fine sediment in egg pockets. In vertically stratified samples, the lower strata contained a greater proportion of the smaller substrate particles than the upper strata. Spawning brook trout removed fine sediment from the substrate during redd construction, and this removal was most apparent in the egg pocket. Thus, egg pockets, rather than entire redds, should be the focus of studies of survival to emergence.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0379:SABSBT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

When exposed to a range of pH from 7.0 to 4.0 in soft water (1 mg Ca2+/L), juvenile rock bassAmbloplites rupestris, black crappiePomoxis nigromaculatus, and largemouth bassMicropterus salmoidesshowed a capacity to osmoregulate and survive for up to 30 d at pH 4.5 and above. Juvenile yellow perchPerca flavescensmaintained osmoregulatory control through 58 d at pH 5.0. All four species lost osmoregulatory control at pH 4.0, and death of fish ensued within a few days after blood osmolality declined to about 200 mosmol/kg or less (normal values, about 300 mosmol/kg). After 58 d of exposure to pH 4.0, mean blood osmolality of yellow perch was 218 mosmol/kg, and these fish were severely emaciated and moribund. Rock bass, black crappie, and largemouth bass all died by days 29, 16, and 9, respectively, when exposed to pH 4.0. However, when exposure to pH 4.0 was halted and pH was raised to 7.0 before death, blood osmolality returned to near-initial values within 15 d. Cessation of feeding also was noted at pH 4.0. Examination of gills showed progressively increased pathology with longer exposures to lower than normal pH. Among fish exposed to low pH, gill hyperplasia was present most often, but epithelial hypertrophy, chloride-cell proliferation, chloride-cell degeneration, edema, and vacuolization of the tissues also were observed. Morphological changes that were observed in the three centrarchids at pH values above pH 4.0 suggested that gill pathology may be a more sensitive indicator of potentially lethal acid stress than blood osmolality.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0386:SBOAGM>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Red shinersNotropis lutrensis(weight, about 1 g each) from the selenium-affected areas of Belews Lake, North Carolina, a cooling reservoir for an electric power plant, were fed to striped bassMorone saxatilis(about 250 g each) in a laboratory experiment. Consumption of red shiners (whole-body selenium concentration, 9.6 μg Se/g wet weight) by striped bass was followed by modified behavior, little increase in weight, a reduced condition factor (105·weight/length3), an elevated selenium concentration in muscle (3.8 ug Se/g wet weight), histological damage to the liver and trunk kidney, and the death of all fish within 78 d. Striped bass fed a comparable, uncontaminated diet of golden shinersNotemigonus crysoleucas(about 1 g each) gained weight, increased their condition factor, had muscle selenium concentrations averaging 1.1 μg Se/g wet weight, and exhibited no histological abnormalities or reduced survival during the 80-d experiment. Toxicity and death induced by selenium-contaminated prey fish may contribute to the absence of piscivorous game fish in selenium-affected regions of Belews Lake.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0400:DTOSRS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Salinity preferences of adult and young-of-the-year largemouth bassMicropterus salmoidesfrom a freshwater lake and a brackish marsh in south-central Louisiana were tested at 22°C in salinity-gradient chambers (0, 3, 6, 9, and 12‰ salinity) under a photoperiod of 12 h light 12 h dark. Young largemouth bass from both collection sites preferred 0‰ salinity. Although adult marsh and freshwater largemouth bass preferred 3‰ salinity, differences in salinity selection were noted: mean number of observations at 0‰ salinity was significantly greater for freshwater fish, whereas mean number of observations at 3‰ salinity was significantly greater for marsh fish. Salinity preferences were not affected by prior acclimation of fish to salinities of 0 or 5‰. Salinities of less than 5‰ did not influence short-term (daily) movements of marsh fish implanted with ultrasonic transmitters. Although no tagged largemouth bass could be located in the marsh after salinities exceeded 5‰, marsh largemouth bass smaller than tagged individuals were still present. Salinity is only one component of the biologically and physicochemically complex marsh environment, but it does appear to be an important factor that influences seasonal abundance and movement patterns of marsh largemouth bass.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0409:BAMOLB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Biomass of aquatic macrophytes, densities of benthic and epiphytic macroinvertebrates, and the food consumed by bluegillsLepomis macrochirus75 mm in total length and longer were quantified and compared in different macrophyte communities in February, April, June, and August 1983 in two Florida lakes (referred to as community-date comparisons). Densities of benthic macroinvertebrates ranged from 88 to 1,933 individuals/m2. Densities of epiphytic macroinvertebrates ranged from 721 to 34,379 individuals above 1 m2of bottom and were 30–99% of the total macro-invertebrates in and above the bottom. The composition of the bluegill diet was positively related (P≤ 0.05) to the epiphytic macroinvertebrate assemblages in 13 of the 15 possible community-date comparisons but not related to the benthic macroinvertebrate assemblages in any community-date comparisons. The greater similarity of the bluegill diets to the epiphytic than to the benthic macroinvertebrate assemblages suggested that bluegills obtained most of their macroinvertebrate prey in the vegetation and little from the benthos. Linear selectivity indices indicated positive selection for chironomids, caddisflies, mayflies, odonates, hemipterans, andPalaemonetesspp. Except forPalaemonetesspp., these taxa generally were more abundant among the epiphytic than among the benthic assemblages. Because of the abundance of epiphytic macroinvertebrates and their consumption by bluegills, management for macrophytes can enhance the prey resource for adult bluegills.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0416:EMAAFR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Families of channel catfishIctalurus punctatusof the 1982 and 1983 year classes were maintained in separate ponds. Fish from 4 to 26 months of age were evaluated for weight, length, and sex during seven sampling periods. Sex did not influence the growth of fish weighing less than 50 g at 10 months of age. Subsequently, sex had an increasing influence with increasing age: by 26 months, males were 37% heavier and 10% longer than females. Fish whose sex was reversed from male to female with steroid hormones grew like normal females through the time of sexual maturity. Growth and reproductive characteristics were typical of the phenotypic sex rather than of the genotype. Monosex populations of male channel catfish could increase production in commercial aquaculture operations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0427:IOSOGO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We examined the relationships between two hatchery and two wild populations of the endangered Colorado squawfishPtychocheilus luciusby use of starch gel electrophoresis of 44 presumptive locus products. Samples of fish from the Green and Colorado rivers were found to be very similar to two hatchery stocks established in 1973 and 1978 (unbiased genetic identity = 0.99; Nei 1978). At least 9 of the 44 loci were polymorphic. Average heterozygosities were high (2.6–5.3%) for an endangered species but were similar to those for nine other cyprinid genera. The proportion of polymorphic loci ranged from 9.1 to 13.6%, which was also high when compared with reported values of 4% for a congener. Genotypes deviated from Hardy–Weinberg proportions at two loci (EST-1*,GPI-2*) in the Colorado River samples and at one locus (EST-1*) in the Green River samples. Also, as a secondary objective we resolved five of the nine polymorphic loci from samples of fin tissue.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0435:BGOECS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We used starch gel electrophoresis to assay 24–28 presumptive gene loci in captive and natural populations of three species of endangered fishes held at the Dexter (New Mexico) National Fish Hatchery. The species included two cyprinodontids, the Leon Springs pupfishCyprinodon bovinusand Comanche Springs pupfishC. elegans, and a poeciliid, the Pecos gambusiaGambusia nobilis. Hatchery stocks had been founded with 30–80 wild fish and subsequently held in captivity for 6–8 years in 0.1–0.2-hectare ponds where spawning has occurred spontaneously. Heterozygosity and polymorphism of the hatchery stocks were similar to those of the populations from which they were derived. However, the captive populations apparently had lost some rare alleles, probably due to the small sizes of the founding populations. Managers should avoid complacency with small species that spawn spontaneously in hatcheries and, superficially, seem to require little special attention. Minimum requirements for management of such species include initiating captive stocks with hundreds of individuals from natural populations, monitoring genetic status and population size of captive stocks, and, where possible, periodically inoculating genetic material from natural populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1989)118<0441:GCOHAN>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor