摘要:

Populations of lake trout Salvelinus namaycush in the main basin of Lake Huron collapsed in the 1940s because of predation by sea lampreys Petromyzon marinus and commercial fishing. Efforts to rehabilitate lake trout have emphasized reduction of mortality and the stocking of hatchery-reared lake trout to reestablish populations. We fit a statistical catch-at-age model for lake trout in the southern main basin of Lake Huron using a maximum likelihood approach to estimate mortality rates and abundance during 1984–1993. This represents the first such analysis for lake trout in the Great Lakes, and a flexible application of the approach proved useful for integrating diverse information and assessing population and mortality trends. Sea lamprey-induced mortality and recruitment of lake trout to age 1 were calculated external to model fitting. Recruitment was based on numbers of lake trout stocked because natural recruitment is negligible. Sea lamprey-induced mortality rates were based on observed wounding data on lake trout. Other mortality rates were estimated during model fitting. Mortality rates have varied from year to year but do not show trends over time and are currently well below target maximum levels. Lake trout abundance has declined from a peak spawning biomass of 412,000 kg in 1988 to a low of 295,000 kg in 1993. This decline is a result of lower stocking levels since the mid-1980s. Sea lamprey predation was the dominant source of mortality for lake trout older than age 4. During 1984–1993, we estimated that sea lamprey predation caused 48% and fishing accounted for 16% of deaths of lake trout older than age 2. Although our estimates of sea lamprey-induced mortality are uncertain, current estimates of lethality of sea lamprey attacks would need to be greatly overestimated to overturn our conclusion that sea lamprey mortality has exceeded fishing mortality in southern Lake Huron.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0881:LTMAAI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In 1973 two sections of a small headwater stream containing allopatric nonanadromous coastal cutthroat trout Oncorhynchus clarki were subjected to two types of streamside logging: (1) clear-cut to the streambank with all existing wood and logging debris left in the channel and on adjacent hill slopes (section B; 4.2% gradient), and (2) clear-cut to the streambank with all logging debris and existing instream wood removed from the channel and adjacent hill slopes (section A; 0.8% gradient; termed scarified). A third upstream reference section was undisturbed (section C; 4.8% gradient). The hill slopes of both treatment sections were burned in 1974. Instream habitat (large woody debris and pool percentage), water temperature, and fish populations were assessed intermittently during the following 25 years. Instream habitat, water temperature, and trout density in section B were in all years similar to the upstream reference section, C. In section A, summer maximum stream temperatures reached 30°C immediately after logging but had moderated by 1975 and were similar to the reference section by 1983; the proportion of wetted area that was in pools was 14% in 1975, 33% in 1985, and 49% in 1997; trout density was low (0.05 fish/m2) after logging but had returned to the reference level (0.21 fish/m2) by 1983 and was double (0.49 fish/m2) the reference level in 1997. The recent increase in fish density in section A may have been influenced by instream habitat enhancement and riparian thinning conducted in 1985. Trout density in section A is presently similar to that found in a nearby low-gradient stream with an undisturbed riparian zone. Our results suggest that large pieces of wood that are left in and over small streams after logging, although a contravention of current logging regulations in British Columbia, may help protect resident trout populations following riparian logging.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0901:SORCCT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Literature describing spawning habitat used by fall-run chinook salmon Oncorhynchus tshawytscha is lacking for populations using large, main-stem rivers. A stable spawning flow regime in the Snake River below Hells Canyon Dam and enhanced survey capabilities using remote underwater videography allowed us to accurately describe spawning habitat used by fall chinook salmon within this large river. Water depth measured at 205 fall chinook salmon redds ranged from 0.2 to 6.5 m. Mean water column velocity at 145 redds ranged from 0.4 to 2.1 m/s, and substrate- level water velocity at 164 redds ranged from 0.1 to 2.0 m/s. Substrate size classifications from 112 redds indicated that areas having particle sizes that are relatively homogenous with diameters of 2.5–15.0 cm are used for spawning. During our study, spawning generally began as water temperatures dropped below 16.0°C, and concluded as temperatures approached 5.0°C. Our results corroborate earlier observations of fall chinook salmon spawning in deep, fast-velocity water in the Hanford Reach of the Columbia River and significantly expand current criteria used to model spawning habitat availability for these fish within large rivers.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0912:SHUBFC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The influence of electrofishing on egg mortality of Arctic grayling Thymallus arcticus was investigated. The hypothesis that electrofishing affects egg mortality was supported by two experiments. Experiment 1 examined the mortality rate of Arctic grayling eggs from parents that were electroshocked before spawning, and experiment 2 examined mortality rates of eggs that were electroshocked after fertilization. For experiment 1, egg mortality rates were significantly higher than the control group. The difference in mean mortality rates was 0.016 (SE = 0.005) compared to the control (P = 0.022). For experiment 2, mean egg mortality varied significantly (P < 0.001) by parents (electroshocked or not electroshocked), level of electroshock, and egg developmental stage. The largest difference in mean mortality rates compared with that of controls was 0.086 (SE = 0.017) for eggs electroshocked at the highest voltage gradient (1.30–1.50 V/cm), at 70 temperature units postfertilization, and from parents that were electroshocked before spawning. Under normal field conditions, only eggs in close proximity to an electrode would experience the highest level of electroshock used in this study. At other stages of development and at lower voltage levels (equivalent to being farther away from the electrodes), egg mortality rates were considerably less (typically <0.05). Arctic grayling eggs experienced less mortality before and after 70 temperature units postfertilization. The results of this study suggest that even in situations when the probability of exposure to electroshock is high, the cost to the population from using electrofishing to sample Arctic grayling is low.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0923:IOEOTO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two strains of anadromous rainbow trout Oncorhynchus mykiss, naturalized steelhead and “kamloops” (not the pure Kamloops strain from British Columbia, hence not capitalized) currently inhabit the Minnesota waters of Lake Superior and may have the potential to hybridize. This could compromise the genetic integrity of the naturalized steelhead population. Both strains are supplemented by annual stocking, despite the fact that the steelhead population reproduces naturally. Egg viability and fry behavior experiments were undertaken to evaluate the potential for hybridization and to provide information for future management of the two strains. The kamloops eggs were slightly smaller, but sizes overlapped substantially with steelhead egg sizes. Mortalilty of kamloops eggs from spawning to hatching was greater than steelhead eggs. Steelhead fry exhibited a greater fright response (wariness) than kamloops fry when startled by movement over their tanks. Hybrid egg survival and wariness traits were intermediate to those of the pure strains, but more closely resembled those of the maternal strain. These traits appeared to be heritable. Reevaluation of steelhead and kamloops management will be necessary in the future, taking into account the popularity of the kamloops fishery and the potential for degradation or elimination of the naturalized steelhead strain.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0930:STONHA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We found that a noninvasive procedure that used total body electrical conductivity (TOBEC) failed to estimate lean mass and whole body lipid content of brook trout Salvelinus fontinalis. We explored two approaches using TOBEC, the inverse-regression approach, in which lipid mass is predicted from the relationship between TOBEC, and lean mass and the multiple-regression approach, in which lipid is predicted directly from TOBEC and morphological measurements. With the inverse-regression approach, TOBEC was a good estimator of lean mass but did not predict lipid mass. With the multiple-regression approach, length and mass alone explained lipid mass best; TOBEC did not add significant explanatory power. We conclude that TOBEC was not a sensitive or cost-effective tool for determining lipid content of brook trout and urge caution in its use with other fish species.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0942:FOTBEC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The potential for hatchery fish to negatively impact wild fish has been identified as a concern for dwindling stocks of naturally produced anadromous salmonids in the Pacific Northwest. Using a control–treatment approach, we performed a multiscale examination of potential behavioral impacts of releases of hatchery-produced steelhead Oncorhynchus mykiss (anadromous rainbow trout) on preexisting wild populations of O. mykiss (anadromous and potamodromous) over a 4-year period. We released approximately 33,000 conventionally reared hatchery steelhead smolts (treatment) into an upper Yakima River tributary in 1991, 1992, 1993, and 1994 and investigated behavioral interactions and small-scale displacement (0.2–5.0 m). Snorkelers conducted behavioral observations and observed small-scale displacements in treatment and control streams for approximately 1 month following releases. Hatchery steelhead were generally larger than wild O. mykiss and dominated most (68%) contests. The types of behavioral interactions observed differed between control and treatment streams (P < 0.01). Behavioral interactions involving physical contact (e.g., nips) were observed more frequently in treatment streams than in control streams, whereas those involving nonphysical contact displays (e.g., threats and chases) were more frequent in control streams. Contrary to our expectations, total behavioral interaction rates were generally higher in control streams than in treatment streams, though the difference was not statistically significant (P = 0.07). Hatchery steelhead displaced wild O. mykiss in 79% of the contests observed between these groups. Our results indicate that the behavior of hatchery steelhead can pose risks to preexisting wild O. mykiss where the two interact. Strategies to minimize undesirable risks associated with behavior of released hatchery steelhead should be addressed if protection and restoration of wild O. mykiss stocks is the management goal.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0948:BIAHRS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We evaluated the effectiveness of airboat electrofishing for sampling large fishes (standard length, SL ≥8 cm) in shallow, vegetated habitats. Concurrent block-netting (0.1 ha) and airboat electrofishing were conducted at 11 sites in freshwater marshes of the Florida Everglades. We found significant positive relationships between log-transformed electrofishing catch per unit effort (CPUE) and both fish density (number/0.1 ha) and biomass (grams dry weight/0.1 ha) estimates from block nets. Analysis of covariance revealed that estimates of species richness were similar for electrofishing and block-net samples after accounting for differences in the total number of individuals sampled. Nevertheless, length-frequency and species-composition data differed between airboat electrofishing and block-net samples. Relative abundance of yellow bullheads Ameiurus natalis, Seminole killifish Fundulus seminolis, sunfishes (Lepomis spp.), and small size-classes of all species, were lower for electrofishing than for block-net samples. Florida gars Lepisosteus platyrhincus, largemouth bass Micropterus salmoides, and large size-classes of all species, had greater relative abundances in the electrofishing samples than in the block-net samples. Despite these differences, CPUE from airboat electrofishing was positively related to fish density in block nets for two size-classes (from 8 to <12 cm SL and ≥12 cm SL). Residuals from the CPUE–fish density regression were unpatterned with respect to water depth, conductivity, and floating-mat volume but were positively related to emergent-stem density. This suggests that electrofishing was less effective in sparsely vegetated habitats, possibly because fish were better able to detect and flee from the airboat. Our study suggests that airboat-electrofishing (log10CPUE) provides a useful index of the abundance of large fishes in shallow, vegetated habitats, but length-frequency and species-composition data should be interpreted with caution. Additionally, emergent-stem density should be included as a covariate in statistical analyses of airboat electrofishing CPUE.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0957:EOAEFS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Three types of barriers were evaluated in Lake Seminole (13,158 ha) to determine the success of confining triploid grass carp Ctenopharyngodon idella in two embayments (250 and 350 ha) that were almost entirely covered with submersed macrophytes. In 1995, two different physical barriers that permitted boat passage were constructed. One had tandem V-shaped weirs placed at the entrance of a cove, and the other had two gated barriers that confined an embayment connecting two arms of the reservoir. Grass carp were radio-tagged, stocked into the confined areas (N = 119 for the V-shaped barrier and N = 69 for the gated barrier), and tracked from December 1995 through Sep 1997 to estimate escape rates. In addition, 18,000 triploid grass carp fitted with coded wire tags were stocked in December 1995 into the two confined areas. A low-voltage (3–4 V) electric barrier (Smith-Root, Inc.) was installed in December 1997 at one of the V-shaped funnel barriers, and an additional 84 grass carp were radio-tagged and tracked for 13 months. Based on verified locations outside the confined areas, an average of 9% of the grass carp escaped through the V-shaped, and 23% escaped through the gated barriers each year. However, based on missing fish, tag functioning rates determined from dead fish or expelled tags, and locations of fish before becoming missing, potentially up to 42% of the grass carp escaped from the V-shaped barriers and 35% escaped from the gated barriers each year. In addition, electrofishing surveys conducted in summer 1998 downstream of the tailrace in the Apalachicola River, Florida, indicated that 68% of the grass carp were escaped fish (coded wire tag present) that were stocked nearly 3 years earlier into the confined areas. After the V-shaped barrier was fitted with an electric barrier, no verified escapes occurred and with the exception of one fish, every radio-tagged grass carp was found within the confined area. Therefore, the maximum escape rate was only 1.3% per year, if this fish did indeed escape. Thus, the electric barrier and confinement structure have the potential to provide managers with a tool to confine grass carp in specific areas of large water bodies. Over many years, control of excessive aquatic macrophytes with this system is about 10% of the cost of herbicide treatments or mechanical harvesting.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0968:EOTBTF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We compared the effectiveness of a recreational shrimp trawl (used for Penaeus spp.) with that of trap nets for assessing populations of black crappie Pomoxis nigromaculatus. Lakes Griffin and Monroe were sampled with both gears simultaneously during Oct–December 1997. Coefficients of variation (CV = 100 × SD/mean) on mean catch per effort (CPE) values ranged from 105 to 161 for trap nets and from 62 to 96 for trawls. Both trawls and trap nets collected fish less than 150 mm total length (TL), but trawls sampled significantly more adult fish (>250 mm TL). Variable catches in trap nets would require more sampling effort than trawl sampling (up to 4 times as much) to obtain precise estimates of mean CPE. Trawl sampling was preferable to trap nets based on size of fish captured, precision of abundance estimates, cost of the gear, and required sampling effort to estimate mean CPE. However, trawl sampling may be impractical in water bodies with excessive submerged structures, debris, and submersed macrophytes. We are encouraged by the effectiveness of the trawl for assessing black crappie populations in lakes where it is possible to sample with a bottom trawl.

ISSN:0275-5947    

DOI:10.1577/1548-8675(1999)019<0977:COTNAO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor