摘要:

Fishery managers have long been troubled by phenotypic variation within and among Colorado PlateauGila.The problem is twofold. From an historical perspective, there was reticence to investigate fishes long considered as “undesirable.” In a taxonomic sense, there is confusion over within- and among-species variability. We document the former, then clarify the latter by applying discriminant analysis to meristic and morphometric data collected from museum specimens. We test three hypotheses: roundtail chubG. robustahumpback chubG. cyphaand bonytailG. elegansare morphologically indistinguishable; juveniles are assignable to species based upon adult characters; and putative hybrids are morphologically intermediate between parental forms. Through the use of meristic characters in a nonparametric discriminant analysis, over 95% of all adults were segregated to species. By using morphometric characters, 97% could be allocated to species.Gila robustawas easily separated fromG. cyphaandG. elegans.The latter were most difficult of all species-pairs to discriminate, yet field characters still segregated them at better than 95%. A discriminant function, based upon five morphometric characters, will allocate unknowns to species. JuvenileG. robustawere easily discriminated (>97%), but juveniles ofG. cyphaandG. eleganswere often misidentified asG. robusta.Putative hybrids were generally assigned to one or the other parental form; thus, hybrid intermediacy could not be rejected. However, paucity of hybrids weakened the test. We conclude that factors most important in segregating these species are character selection, adequate analyses, and “the art of seeing well.”

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0163:MDOCPG>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We used an individual-based modeling approach to study the consequences of cannibalism and competition for food in a freshwater fish population. We simulated the daily foraging, growth, and survival of the age-0 fish and older juvenile individuals of a sample population to reconstruct patterns of density dependence in the age-0 fish during the growth season. Cannibalism occurs as a part of the foraging process. For age-0 fish, older juvenile fish are both potential cannibals and competitors of food. We found that competition and cannibalism produced intraclass and interclass density dependence. Our modeling results suggested the following. (1) With low density of juvenile fish and weak interclass interactions, the age-0 fish recruitment shows a Beverton–Holt type of density dependence. (2) With high density of juvenile fish and strong interclass interactions, the age-0 fish recruitment shows a Ricker type of density dependence, and overcompensation occurs. (3) Interclass competition of food is responsible for much of the overcompensation. (4) Cannibalism intensifies the changes in the recruitment that are brought about by competition. Cannibalism can (a) generally reduce the recruitment, (b) particularly reduce the maximum level of recruitment, (c) cause overcompensation to occur at lower densities, and (d) produce a stronger overcompensation. (5) Growth is also a function of density. Cannibalism generally improves average growth of cannibals. (6) Variation in the lengths of age-0 fish increases with density and with a decreased average growth. These results imply that cannibalism and competition for food could strongly affect recruitment dynamics. Our model also showed that the rate of cannibalism either could be fairly even through the whole season or could vary dramatically. The individual-based modeling approach can help ecologists understand the mechanistic connection between daily behavioral and physiological processes operating at the level of individual organisms and seasonal patterns of population structure and dynamics.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0174:COCACF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Starvation can directly affect energy levels and mortality rates in fish and may have indirect influences on behaviors essential to survival. We examined physiological and behavioral effects of food deprivation for larval (8–24 mm) and juvenile (small, 45–70 mm; medium, 80–120 mm; and large, 140–230 mm) walleyesStizostedion vitreumencompassing critical periods in their early life history. Juvenile walleye size ranges encompass important ontogenetic diet shifts (small and medium) and the overwinter period (large). The direct effects of starvation on total body energy (J/g wet weight) and mortality rates of larval and juvenile fish were assessed in both laboratory tanks (420 L) and pond (0.4 ha) experiments. Temperature (15–25°C) affected mortality rates and the depletion of energy reserves. During the overwinter period (4°C), initial energy losses were observed that did not affect mortality through 150 d. A “point of no return” was observed for larval fish after 6–8 d of starvation. Larval and juvenile fish (all sizes) survived longer at low energy densities when temperatures were reduced. We also assessed the indirect effects of starvation on foraging efficiency and vulnerability to predation in laboratory experiments. Capture efficiency and handling time was affected for larval fish after 5 d and for juveniles after 21 d of starvation, but no effects were observed for overwintering fish. Starved fry were more vulnerable to predation than fed fish were after 6 d, and juveniles were more vulnerable after 21 d of starvation. Direct effects of starvation were more important to survival than indirect behavioral effects, but for both direct and indirect effects, the length of the period to critical starvation levels increased with fish size.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0192:RIODAI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effect of water temperature on the incidence of metamorphosis in sea lampreysPetromyzon marinuswas evaluated in a laboratory study to determine the optimal temperature and the temperature extremes for metamorphosis. The experiment began on June 4, 1996, and involved lampreys larger than 120 mm and 3.0 g in size. The incidence of metamorphosis was 0% at 9°C, 80% at 21°C, and 58% at 25°C. By August, the median stage of metamorphic development for each temperature was stage 4 at 17°C and 21°C, stage 3 at 25°C, and stage 2 at 13°C. Based on the incidence of metamorphosis and the rate of development, we conclude that 21°C is near optimum for metamorphosis of sea lampreys and that the lower thermal limit for metamorphosis in sea lampreys is between 9°C and 13°C. An upper thermal limit could not be determined from our data. Our results support the hypothesis that spring temperature is an important cue for metamorphosis in lampreys, and they also demonstrate that temperature exposure in the month immediately prior to metamorphosis (June) is critical for normal commencement of this event.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0206:EAOTFM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Thermal habitat selection and behavior by young-of-year brook troutSalvelinus fontinaliswas studied in a lake in central Ontario, Canada. In May, trout foraged actively within 2 m of shore in the warmest water available (∼15°C). In early June, trout foraged near the bottom within 4 m of shore, where bottom water temperatures were near, or at, the upper thermal tolerance, for trout, of 20°C. In July, when ambient water temperatures ranged from 23°C to 27°C, trout lay on the bottom in the coldest water available (18–20°C) in discrete areas 3–8 m from shore. Flow rate of cold groundwater accounted for 87% of the variance in trout density in these areas, and the data suggest that a minimum flow rate of 125 mL·m−2·min−1is required for trout to take up station. When trout were displaced from holding positions, sites with greater groundwater flow were more quickly reoccupied by trout than sites with lower flow. Experimentally created trough-like depressions at these sites attracted higher densities of trout than the same sites with their natural topography and restricted trout distribution to within each depression. Preliminary behavioral observations suggest that trout lie on the bottom and defend cool microhabitats at the expense of daytime feeding. These results suggest that areas with cold groundwater may be a limiting resource for young-of-year brook trout in the littoral zone during summer, and resource managers should consider protecting such areas from lakeshore development and logging.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0212:SCBTDS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We used radiotelemetry and underwater observation to assess fall and winter movements and habitat use by bull troutSalvelinus confluentusand westslope cutthroat troutOncorhynchus clarki lewisiin two headwater streams in the Bitterroot River drainage, Montana, that varied markedly in habitat availability and stream ice conditions. Bull trout and cutthroat trout made extensive (>1 km) downstream overwintering movements with declining temperature in the fall. Most fish remained stationary for the remainder of the study (until late February), but some fish made additional downstream movements (1.1–1.7 km) in winter during a low-temperature (⩽1°C) period marked by anchor ice formation. Winter movement was more extensive in the mid-elevation stream where frequent freezing and thawing led to variable surface ice cover and frequent supercooling (<0°C). Habitat use of both species varied with availability; beaver ponds and pools with large woody debris were preferred in one stream, and pools with boulders were preferred in the other. Trout overwintered in beaver ponds in large (N= 80–120), mixed aggregations. In both streams, both species decreased use of submerged cover following the formation of surface ice. Our results indicate that (1) continued activity by trout during winter is common in streams with dynamic ice conditions and (2) complex mixes of habitat are needed to provide suitable fall and winter habitat for these species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0223:ROSIOF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Lake troutSalvelinus namaycushin nearshore waters of Lake Michigan grow faster than lake trout residing offshore on Sheboygan Reef, which is in midlake. We examined the stomachs of lake trout, spanning ages 1 through 16, caught in both nearshore and offshore environments of Lake Michigan during 1994 and 1995 to determine whether diet differences may be responsible for the difference in growth rate. A comparison of the diets, coupled with bioenergetics modeling, indicated that juvenile lake trout on Sheboygan Reef experienced slow growth due to low food availability rather than to cold water temperatures. The availability of appropriate-size prey appeared to regulate lake trout growth. Small prey fish were probably not readily available to small (200- to 399-mm total length) lake trout on Sheboygan Reef, a substantial portion of whose diet consisted of invertebrates; in contrast, nearshore juveniles had a nearly 100% fish diet. Growth rate on the reef remained slow through intermediate lake trout sizes (400–599 mm total length), presumably due to low availability of rainbow smeltOsmerus mordaxon the reef. Once lake trout achieved total lengths of approximately 600 mm, they grew slightly faster on Sheboygan Reef than near shore, indicating that large (>170-mm total length) prey fish were readily available to lake trout in the reef area. On a wet-weight basis, alewifeAlosa pseudoharengusdominated the diet of large (≥600 mm total length) lake trout from both the nearshore and offshore regions of the lake, although bloaterCoregonus hoyicomposed over 30% of the diet on Sheboygan Reef and in southeastern nearshore Lake Michigan. Size of alewife prey increased with lake trout size. The bloater population currently represents the bulk of the biomass of the adult prey fish community, so our diet analysis suggests that large lake trout are continuing to select alewives.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0236:OASPID>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Spatiotemporal distributions and microhabitat use of pink salmonOncorhynchus gorbuschaand sockeye salmonO. nerkawere studied in Lake Creek, southeast Alaska, during three spawning seasons. Sockeye salmon migrated approximately 1 week earlier than pink salmon and spawned 250–350 m upstream from pink salmon. Habitat overlap measured with proportional similarity index monotonically increased with increasing spawner densities. Multidimensional niche spaces measured with water depth, current velocity, and channel gradient at redds were significantly different between pink and sockeye salmon (P< 0.005, Hotelling'sT2-test). However, classification of the redds into individual species was subjected to large error rates; 33% of 70 pink salmon redds and 34% of 125 sockeye salmon redds were misclassified. Competitive interaction between pink and sockeye salmon was not demonstrated.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0253:SHSOSS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We investigated some of the ecological impacts to rainbow troutOncorhynchus mykissthat could occur by supplementing spring chinook salmonO. tshawytschain the upper Yakima River basin, Washington. Controlled field experiments conducted in three different streams indicated that presence of wild juvenile spring chinook salmon did not adversely affect growth of wild rainbow trout in high-elevation tributaries. Experiments at two spatial scales, habitat subunit and stream reach scales, were used to detect impacts. In small-enclosure experiments conducted in two tributaries to the Yakima River in 1993 and 1994, specific growth rates (SGRs) of wild rainbow trout paired with wild juvenile spring chinook salmon were not significantly lower than SGRs of their unpaired counterparts (1993:P= 0.360; 1994:P= 0.190). Stream reach experiments in another Yakima River tributary in 1995 also indicated that introductions of wild juvenile spring chinook salmon into 100-m-long enclosures, at a numerical density equal to the preexisting wild rainbow trout, did not adversely affect rainbow trout growth or abundance. The mean fork length (FL) and instantaneous growth rate (IGR) of age-0 wild rainbow trout in stream reach enclosures were unaffected by introduced spring chinook salmon after 7 (FL:P= 0.318) and 14 weeks (FL:P= 0.387, IGR:P= 0.265) in sympatry. Mean fork lengths and IGRs of age-1 rainbow trout were also unaffected by the addition of the spring chinook salmon after 7 weeks (FL:P= 0.553, IGR:P= 0.124) and 14 weeks (FL:P= 0.850, IGR:P= 0.084) of cohabitation. Furthermore, the stream reach experiment showed that spring chinook salmon introduction did not affect rainbow trout abundance (P= 0.298) or biomass (P= 0.538). Site elevation in the stream reach tests appeared to influence rainbow trout size more than the addition of juvenile spring chinook salmon. Site elevation was negatively correlated with length of wild age-0 (P< 0.001) and age-1 (P< 0.001) rainbow trout in October 1995. It appears that rainbow trout and spring chinook salmon partitioned the resources so that impacts were not detected. Our work suggests that rainbow trout have a refuge from interactions with juvenile spring chinook salmon in high-elevation portions of tributaries (e.g., over 700 m).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0261:EOWJSC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We field tested the hypothesis that predation by piscivorous fish is reduced in turbid compared with clear water. The Harrison River (⩽1 nephelometric turbidity units, NTU) is a clear tributary of the naturally turbid Fraser River (27–108 NTU), in British Columbia, Canada. Age-0 juveniles of Harrison River stocks of Pacific salmonOncorhynchusspp. migrating seaward in spring obligately pass through turbid and clear reaches of these rivers. To test the hypothesis, we compared predation on salmonids by potential predators caught by beach seine and by the rate of predator attack on tethered juvenile chinook salmonO. tshawytschain these two rivers. Of 491 predators examined, 30% of Harrison River piscivores had recently consumed fish compared with only 10% of Fraser River piscivores. Of those that ate fish, fish prey per predator was significantly lower in the Fraser River (mean = 1.1,N= 21) than in the Harrison River (mean = 1.7,N= 66). In a clear-water side channel of the Fraser River—Nicomen Slough (1–6 NTU)—both incidence of predation (37%) and number of fish prey per predator (mean = 2.4,N= 19) were similar to values for the Harrison River. Loss of prey from tethers was significantly higher in the Harrison River (23–61%) than in the Fraser River (10–24%). The loss of prey from tethers was highest at dusk and near the bottom in the Harrison River; no spatial or temporal difference occurred in the turbid Fraser River. Therefore, our data support the hypothesis. During their seaward migration in the Fraser River system, age-0 Pacific salmon were less likely to encounter and be consumed by fish piscivores in turbid water than in clear water.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0275:TRPOMJ>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor