摘要:

We constructed a simulation model for Redfish Lake, Idaho, using water budget and nutrient loading measurements, to predict the dependence of lake production on nutrients from the watershed, precipitation, lake fertilization, and marine-derived nutrients from sockeye salmonOncorhynchus nerkawhich historically have reared in the lake. We also used the model to simulate different management scenarios to help restore the endangered Snake River sockeye salmon. The model and other empirical evidence indicated that even before hydropower dams were present in the migration corridor, marine-derived nutrients were not of major importance to lake production, contributing only about 3% of the annual phosphorus load of the lake. This contribution was partially removed by the quick flushing rate (3 years) of the lake and phosphorus export by smolts. The model predicted annual adult sockeye salmon returns to be 3,800 fish under predam conditions, 370 fish under modern conditions, 780 fish when watershed nutrient loading was doubled (simulating lake fertilization), and 750 fish when smolt-to-adult survival was doubled. Although fertilization should stimulate sockeye salmon production, the effect would be transitory. The model predicted that 8 years after the end of a 3-year fertilization period, adult returns would be only 5% greater than those for unfertilized conditions. Our analysis suggests that to restore self-sustaining anadromous sockeye salmon populations to Redfish Lake, increased smolt-to-adult survival must be achieved; however, lake fertilization should be considered an important short-term tool for decreasing continued erosion of the stock.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0001:TROASS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Snake River sockeye salmonOncorhynchus nerkalisted under U.S. law as endangered in 1991 in response to a decline in anadromous adult numbers, spend their first 1–2 years in Redfish Lake, Idaho, before migrating to the sea. To determine how nutrient enhancement might influence phytoplankton, zooplankton, and fish production, we performed fertilization experiments in large enclosures in this oligotrophic lake using juvenile kokanee (lacustrineO. nerka) as analogues for endangered sockeye salmon. Fertilization of the metalimnion substantially increased chlorophylla(150%), phytoplankton biovolume (75%), primary productivity (250%), and zooplankton biomass (200%), and moderately increased fish growth (12%) over our control enclosures. Community composition of phytoplankton and zooplankton changed little, and water transparency declined less than 15% compared with controls. Thus, we concluded that metalimnetic fertilization could maintain the aesthetic value of these lakes while increasing zooplankton food resources for juvenile salmon. Our results suggest that whole-lake fertilization would aid in the recovery of Snake River sockeye salmon.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0019:ANTETG>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Our investigations into the effects of the 1989Exxon Valdezoil spill in Prince William Sound, Alaska, suggest that chronic damage occurred to some populations of pink salmonOncorhynchus gorbuscha.Significantly elevated embryo mortalities were observed from 1989 through 1993 in populations inhabiting streams previously contaminated by oil. No statistically detectable difference in embryo mortality was observed in 1994 and 1995. We assessed the possible influence of the natural environment on these findings by collecting gametes from adults returning to contaminated and to uncontaminated streams, transporting the gametes to a hatchery where intrastream crosses were made, and incubating the resulting embryos under identical environmental conditions. Significantly increased embryo mortality was detected for embryos originating from the oil-contaminated lineages in 1993 but not in 1994, which indicated that the significant differences detected in the field in 1989–1993 were not induced by naturally occurring environmental variables.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0035:EODTPS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The absolute number of individuals and survival of juvenile gagsMycteroperca microlepisin a 15.4-km2shallow sea grass meadow in St. George Sound, Florida, were estimated by the Jolly–Seber mark–recapture method. Abundance was estimated within three sampling stations (150 m × 150 m) by means of standard (150 m, 1.8 km/h) tows with a 5-m otter trawl. The average densities (95% confidence limits), based on three stations sampled every 1–2 weeks from June to mid-September 1991, were 496 (251–744), 424 (210–670), and 549 (165–1,773) juveniles/ha. Trawl capture efficiencies and the effects of sea grass habitat conditions and size of juvenile gags were estimated so that absolute numbers could be determined outside the sampling stations. We estimated absolute abundance outside the sampling stations by trawling and dividing gag captures per standard tow by trawl capture efficiency estimates. The estimated absolute abundance of juvenile gags for the entire 15.4-km2area was 943,615. Survival of juvenile gags in sea grass was near 100%, as estimated from trawl capture rates over the sampling period. Survival estimates were generally variable but were confounded by emigration from the sampling areas. The small-scale spatial pattern of juvenile gags was random. The results of this work provide the basis for establishing a juvenile recruitment index by providing quantitative estimates of juvenile abundance.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0044:AAASOJ>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Distribution and growth of young-of-the-year striped bassMorone saxatiliswere determined at the northern edge of the species' range in the Miramichi River, Gulf of St. Lawrence, between May and December 1992, from samples obtained from ichthyoplankton, beach seine, trawling, and bycatch surveys. Shortly after yolk absorption, catches declined in offshore plankton surveys, and young-of-the-year appeared in nearshore areas. As summer progressed, young-of-the-year striped bass moved downstream into more saline waters. Downstream migration appeared to be size related. A logistic growth model closely fit field observations. Growth was relatively slow in spring (June: 0.32 mm/d), rapid in summer (July, August, and September: 0.75–1.15 mm/d), and reduced in fall (October and November: 0.17–0.46 mm/d). Growth was faster and length attained before winter was greater than reported for populations in the center of the species' geographic distribution.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0056:DAGOYO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Either gizzard shadDorosoma cepedianumor bluegillsLepomis macrochirusdominate prey assemblages in many small (<100 ha) Ohio reservoirs. Because gizzard shad spawn early in the spring and their offspring grow rapidly, age-0 gizzard shad may be invulnerable to age-0 largemouth bassMicropterus salmoidesthereby compromising this piscivore's growth and, potentially, recruitment. To test this hypothesis, we quantified growth, abundance, and diets of age-0 largemouth bass in reservoirs dominated by age-0 bluegills (one reservoir) or age-0 gizzard shad (two reservoirs) during June through early October 1992–1994. In the bluegill-dominated reservoir, age-0 largemouth bass grew slowly (about 0.04 g/d) during June through mid-August. Though age-0 bluegills became abundant after mid-August, contributing to rapid growth (about 0.2 g/d) of age-0 largemouth bass, these age-0 largemouth bass only reached small to moderate sizes by fall (range of mean wet weights, 3–7 g). In the reservoirs dominated by gizzard shad, summer growth and fall sizes of largemouth bass varied among systems and years. During one summer in one shad-dominated reservoir, an early rise in temperature plus small age-0 gizzard shad probably contributed to rapid growth (∼0.12 g/d) and large fall size (mean wet weight, 10.8 g) of age-0 largemouth bass. More commonly, age-0 largemouth bass grew slowly or moderately (∼0.06 g/d). However, fall sizes of largemouth bass always were equivalent to or exceeded those in the bluegill-dominated reservoir (range of mean wet weights, 3–11 g). Our results suggest that growth of age-0 largemouth bass should vary more in systems dominated by gizzard shad than in bluegill-dominated ones. Management efforts that increase gizzard shad vulnerability during early summer may reduce this variability, thereby enhancing first-summer growth and, potentially, recruitment success of largemouth bass.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0070:LBAGSP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Piscivores can control prey populations in north temperate lakes, leading to increased zooplankton and reduced phytoplankton. In reservoirs with gizzard shadDorosoma cepedianuman omnivorous planktivore, this cascade occurs with lower probability because while this fish is shorter than 60 mm in total length (TL) it readily consumes zooplankton but also switches to phytoplankton and detritus. Prospects for gizzard shad control probably hinge on piscivore consumption of age-0 individuals. Hence, we quantified capture efficiency of hybrids of striped bassMorone saxatilis× white bassM. chrysops(small: 190–250 mm, TL; large: 310–360 mm, TL) when combined with three gizzard shad size-groups (of five possible, ranging 40–120 mm) in a 500-L aquarium. Small hybrid striped bass selected 40-mm gizzard shad but preferred neither 60-mm nor 80-mm prey. Large hybrid striped bass demonstrated no selection for 40–120-mm gizzard shad. We incorporated these data into a bioenergetics model to evaluate whether hybrid striped bass could sufficiently reduce abundance of age-0 gizzard shad in Ohio reservoirs to permit increased zooplankton, thereby improving the potential for resident sport fish recruitment in reservoirs. Hybrid striped bass potentially increased larval sport fish occurrence only when they were stocked at high densities (≥350 fish/ha or ≥22 kg/ha) coupled with age-0 gizzard shad suffering low natural mortality and occurring at an intermediate peak density of 25 fish/m3or less. We believe gizzard shad are largely immune to control by hybrid striped bass in Ohio reservoirs. Hence, managers must consider combining watershed management with predator stocking to regulate gizzard shad.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0084:PROAGS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The endangered razorback suckerXyrauchen texanusis endemic to the Colorado River system in western North America and is threatened with extinction because of limited recruitment. To assist in management and recovery efforts, we developed methods for the cryopreservation of sperm, evaluated the influence of various factors on motility of thawed sperm, and examined the effect on fertilization of cooling rate and the addition of caffeine. Sperm samples cryopreserved with 10% methanol (MeOH) had significantly higher postthaw motility than did samples preserved with 5% or 20% MeOH or with 5% or 10% dimethyl sulfoxide,N, N-dimethylacetamide, glycerol, propylene glycol, or ethylene glycol. Sperm samples cryopreserved in 0.5-mL and 2.5-mL straws had significantly higher postthaw motility than did samples cryopreserved in 0.25-mL straws. Exposure to 10% MeOH for up to 30 min did not significantly influence sperm motility before freezing or after thawing. Cooling rate (−21°C/min or −91°C/min) did not significantly influence sperm motility. Samples thawed in a water bath at 20°C, 30°C, or 40°C had significantly higher motility than did samples thawed on the laboratory bench (19°C). Refrigerated sperm had significantly higher motility after the addition of 0.005 M caffeine; however, caffeine did not increase the motility of thawed sperm. Fertilization percentage was 41 ± 31% for the egg quality control treatments (fresh sperm) in the freezing rate study. The freezing rate of −91°C/min yielded 66% fertilization relative to the control (actual value, 27 ± 26%), which was significantly higher than the 12% fertilization (actual, 5 ± 3%) yielded by the freezing rate of −21°C/min. Fertilization percentage was 25 ± 24% for the egg quality control treatments in the caffeine study. Caffeine-treated sperm yielded 60% fertilization relative to the control (actual, 15 ± 13%), which was significantly higher than the 16% fertilization (actual, 4 ± 4%) yielded by sperm without caffeine treatment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0095:COSOTE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Otolith microstructure of endangered Colorado squawfishPtychocheilus luciuswas investigated to determine patterns of otolith growth and to validate daily deposition of increments. Sagittae and lapilli formed prior to hatching. After fish hatched, otolith increments were deposited daily whether larvae were reared at a constant 22°C temperature or subjected to fluctuating temperatures (±2.5°/d) centered at 18, 22, or 26°C. Otolith increments were clearer and counts of increments were more accurate for fish reared at fluctuating than at constant temperatures. Otolith growth was lower at 18°C than at 22 or 26°C, but evidence of a direct effect of temperature on otolith growth was inconclusive. Lapillus diameters of slow-growing Colorado squawfish were larger than those of similar-sized but fast-growing fish, indicating that fish and otolith growth rates were not proportional. When larvae were starved, growth in body length generally ceased immediately but otolith growth continued for up to 15 d. Otolith growth was reduced for up to 5 d after starved fish began to feed. Timing of starvation and reduced growth may not be accurately recorded by reduced otolith increment spacing. Low-contrast otolith increments in wild fish may indicate periods of low food abundance and starvation. Increased otolith growth early in life could reflect the start of exogenous feeding by Colorado squawfish larvae, a habitat shift to warmer water, or both. Otolith analysis will be useful for elucidating age, growth, and recruitment patterns of young Colorado squawfish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0105:EFADID>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Behavior and passage rate of smolts of Atlantic salmonSalmo salarand juvenile American shadAlosa sapidissimawere compared between a standard (sharp-crested) and a modified surface bypass weir that employs uniform flow velocity increase (1 m·s−1·m−1of linear distance). Within the first 30 min after release, significantly more smolts passed the modified weir than the standard weir, but no differences in passage rate between weir types were noted for juvenile American shad. More Atlantic salmon smolts and juvenile American shad were passed by the modified weir in groups of two or more than were passed by the standard weir. Mean lengths of passed and nonpassed smolts were not significantly different between weir types, but American shad passed by the sharp-crested weir were significantly smaller than nonpassed fish. Most individuals of both species that passed the modified weir maintained positive rheotaxis and strong swimming throughout the length of the weir. In addition to acceleration, visual cues may be an important factor in avoidance behaviors near bypass entrances. The observed reduction of delay time before passage and maintenance of school integrity may facilitate appropriate timing of emigration and enhance passage survival.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0118:EOWAOD>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor