Invasion versus Isolation: Trade-Offs in Managing Native Salmonids with Barriers to Upstream Movement

Abstract: Conservation biologists often face the trade‐off that increasing connectivity in fragmented landscapes to reduce extinction risk of native species can foster invasion by non‐native species that enter via the corridors created, which can then increase extinction risk. This dilemma is acute for stream fishes, especially native salmonids, because their populations are frequently relegated to fragments of headwater habitat threatened by invasion from downstream by 3 cosmopolitan non‐native salmonids. Managers often block these upstream invasions with movement barriers, but isolation of native salmonids in small headwater streams can increase the threat of local extinction. We propose a conceptual framework to address this worldwide problem that focuses on 4 main questions. First, are populations of conservation value present (considering evolutionary legacies, ecological functions, and socioeconomic benefits as distinct values)? Second, are populations vulnerable to invasion and displacement by non‐native salmonids? Third, would these populations be threatened with local extinction if isolated with barriers? And, fourth, how should management be prioritized among multiple populations? We also developed a conceptual model of the joint trade‐off of invasion and isolation threats that considers the opportunities for managers to make strategic decisions. We illustrated use of this framework in an analysis of the invasion‐isolation trade‐off for native cutthroat trout (Oncorhynchus clarkii) in 2 contrasting basins in western North America where invasion and isolation are either present and strong or farther away and apparently weak. These cases demonstrate that decisions to install or remove barriers to conserve native salmonids are often complex and depend on conservation values, environmental context (which influences the threat of invasion and isolation), and additional socioeconomic factors. Explicit analysis with tools such as those we propose can help managers make sound decisions in such complex circumstances.     

Learning to recognize novel predators under weakly acidic conditions: the effects of reduced pH on acquired predator recognition by juvenile rainbow trout

Summary. Recent studies have demonstrated that under weakly acidic conditions (pH 6.0), many prey fishes, including juvenile rainbow trout (Onchorhynchus mykiss), do not exhibit overt antipredator responses to conspecific chemical alarm cues. In laboratory trials, we investigated the potential effects of reduced pH on the ability of hatchery reared, predator naïve juvenile rainbow trout to acquire the recognition of a novel predator (yellow perch, Perca flavenscens). Initially, we exposed trout to the odour of a predatory yellow perch, buffered to pH 6.0 (weakly acidic) or pH 7.0 (neutral) paired with conspecific skin extracts (also buffered to pH 6.0 or 7.0) or a distilled water control. Juvenile trout exhibited significant increase in antipredator behaviour when exposed to neutral skin extract (pH 7.0). When retested 48 hours later to perch odour alone (pH 7.0), only trout initially conditioned with neutral skin extracts (pairs with either neutral or acidic perch odour) exhibited a learned recognition of perch odour as a predator risk. Those initially exposed to weakly acidic skin extract or the distilled water control did not show a learned response to predator odour. These results demonstrate that the ability to acquire the recognition of novel predators is impaired under weakly acidic conditions, as would occur in natural waterways affected by acidic precipitation.     

Nonrandom, Size- and Timing-Biased Breeding in a Hatchery Population of Steelhead Trout

Abstract:  Hatcheries have been built and operated to buffer salmon and trout populations from overfishing and to compensate for habitat lost or degraded by human activities. These facilities are now so prevalent that in some cases hatchery-produced salmon outnumber salmon produced in the wild. By default, this makes them an important component in the current ecology and evolution of salmonids. Hatcheries differ from natural environments in many ways, and among the most fundamental is the necessity that humans select fish for breeding instead of allowing natural processes of mate choice and competition. We examined the mating system for steelhead trout ( Oncorhynchus mykiss ) at Forks Creek Hatchery in southwest Washington and investigated factors affecting selection of individual steelhead for spawning by the hatchery staff. Despite efforts by the staff to not spawn selectively, data on steelhead spawned over 7 years revealed selection for large adult body size and early reproductive timing and a tendency for size-assortative mating (i.e., large with large). Selection on size was related to selection on reproductive timing because early returning fish tended to be larger than those returning later. To improve the fitness of both hatchery fish destined to spawn in the wild and hatchery fish designated to be spawned in the hatchery, a better understanding of factors associated with the range of reproductive success and mate-choice mechanisms in the wild is vital. This knowledge may then be applied to artificial propagation programs designed for conservation or enhancement.     

THE LETHAL AND SUB LETHAL EFFECTS OF A ZIRCONIUM PROCESS EFFLUENT ON JUVENILE SALMONIDS1

ABSTRACT: An effluent (ZPE), with high concentrations of ammonia was compared with solutions of ammonium chloride in both lethal and sublethal tests. The ZPE was more toxic than were solutions of ammonium chloride in acute toxicity tests, although ammonia was shown to be the major toxicant. The secondary toxicants present in the effluent were not identified. Growth was used as a sublethal test parameter and ZPE was again more toxic than ammonium chloride solutions at the same ammonia concentration. Concentrations of ammonia less than 3 mg/liter in ammonium chloride solutions actually stimulated the growth of juvenile chinook salmon. Concentrations of ZPE in the river at extreme low river flow could have sublethal effects on juvenile salmonids below the outfall.     

LONG-TERM CHANGES IN STREAMFLOW FOLLOWING LOGGING IN WESTERN OREGON AND ASSOCIATED FISHERIES IMPLICATIONS1

ABSTRACT: The long-term effect of logging on low summer streamflow was investigated with a data set of 36 years. Hydrologic records were analyzed for the period 1953 and 1988 from Watershed (WS) 1 (clear-cut logged and burned), WS 2 (unlogged control), and WS 3 (25 percent patch-cut logged and burned) in the H. J. Andrews Experimental Forest, western Cascade Range, Oregon. These records spanned 9–10 years before logging, and 21–25 years after logging and burning. Streamfiows in August were the lowest of any month, and were unaffected by occasional heavy rain that occurred at the beginning of summer. August streamfiows increased in WS 1 compared to WS 2 by 159 percent following logging in WS 1, but this increase lasted for only eight years following the start of logging in 1962. Water yield in August for 1970–1988 observed from WS 1 was 25 percent less than predicted from the control (WS 2, ANOVA, p=0.032). Water yield in August increased by 59 percent after 25 percent of the area of WS 3 was patch-cut logged and burned in 1963. In contrast to WS 1, however, water yields from WS 3 in August were consistently greater than predicted for 16 years following the start of logging, through to 1978. For the 10 years, 1979–1988, water yield observed in August from WS 3 was not different than predicted from the control (WS 2, ANOVA, p-0.175). The contrasting responses of WS 1 and 3 to logging are thought to be the result of differences in riparian vegetation caused by different geomorphic conditions. A relatively wide valley floor in WS 1 allowed the development of hardwoods in the riparian zone following logging, but the narrow valley of WS 3 and limited sediment deposits prevented establishment of riparian hardwoods. Low streamflows during summer have implications for salmonid survival. Reduced streamflow reduces the amount of rearing habitat, thus increasing competition. Combined with high water temperatures, reduced streamflow can lead directly to salmonid mortality by driving salmonids from riffles and glides, and trapping them in drying pools. Low streamflow also increases oxygen depletion caused by leaves from riparian red alders.     

Testing Bioassessment Metrics: Macroinvertebrate, Sculpin, and Salmonid Responses to Stream Habitat, Sediment, and Metals

The purpose of this article is to report on the testing of responses of multimetric macroinvertebrate and habitat indices to common disturbances to streams: stream habitat alteration, excessive sediment, and elevated metals concentrations. Seven macroinvertebrate community metrics were combined into a macroinvertebrate biotic index (MBI), and 11 channel morphology, riparian, and substrate features were combined into a habitat index. Indices were evaluated by comparing the habitat results to fish population surveys and comparing the macroinvertebrate results to habitat ratings, percent fine sediments measured by Wolman pebble counts, and copper concentrations. Macroinvertebrate scores decreased with increasing percentages of fine sediments measured either across the bankfull or instream channel widths. Macroinvertebrate scores decreased with increasing copper. One metric, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa, was more responsive to both copper and sediment than was the multimetric MBI. Habitat scores corresponded well with the age class structure of salmonids, but not with that of benthic sculpins. Both salmonid and sculpin age classes declined with increasing percentages of fine sediments. The decline was graded with the sculpin age classes, whether fine sediments were measured across the instream or bankfull channel, whereas salmonids consistently responded only to the instream fine sediments.     

INTERACTION BETWEEN RIPARIAN VEGETATION,WATER TEMPERATURE,AND SALMONID HABITAT IN THE TUCANNON RIVER1

ABSTRACT: This analysis relates physical-process, ecological, and economic models to: (1) analyze the instream water temperatures with respect to existing and proposed riparian vegetation under natural conditions; (2) use these water temperatures to determine salmon and steel-head fish populations that were based upon actual field count and known temperature preference data; and (3) determine the economic worth based upon the estimated carrying capacity of the river, the estimated number of return spawners, and the economic value of commercially caught and sport-caught salmon and steelhead. The economic evaluations are in accordance with procedures outlined by the U.S. Water Resources Council (1983).     

Use of sibling relationship reconstruction to complement traditional monitoring in fisheries management and conservation of brown trout

Declining trends in the abundance of many fish urgently call for more efficient and informative monitoring methods that would provide necessary demographic data for the evaluation of existing conservation, restoration, and management actions. We investigated how genetic sibship reconstruction from young‐of‐the‐year brown trout (Salmo trutta L.) juveniles provides valuable, complementary demographic information that allowed us to disentangle the effects of habitat quality and number of breeders on juvenile density. We studied restored (n = 15) and control (n = 15) spawning and nursery habitats in 16 brown trout rivers and streams over 2 consecutive years to evaluate the effectiveness of habitat restoration activities. Similar juvenile densities both in restored and control spawning and nursery grounds were observed. Similarly, no differences in the effective number of breeders, N_b(SA), were detected between habitats, indicating that brown trout readily used recently restored spawning grounds. Only a weak relationship between the N_b(SA) and juvenile density was observed, suggesting that multiple factors affect juvenile abundance. In some areas, very low estimates of N_b(SA) were found at sites with high juvenile density, indicating that a small number of breeders can produce a high number of progeny in favorable conditions. In other sites, high N_b(SA) estimates were associated with low juvenile density, suggesting low habitat quality or lack of suitable spawning substrate in relation to available breeders. Based on these results, we recommend the incorporation of genetic sibship reconstruction to ongoing and future fish evaluation and monitoring programs to gain novel insights into local demographic and evolutionary processes relevant for fisheries management, habitat restoration, and conservation.     

ANADROMOUS SALMONID RECOVERY IN THE UMATILLA RWER BASIN,OREGON: A CASE STUDY1

ABSTRACT: The Umatilla River Basin Fisheries Restoration Plan was initiated in the early 1980s to mitigate salmonid losses caused by hydroelectric development and habitat degradation. The objectives are to enhance the abundance of endemic steelhead and reintroduce extirpated chinook and coho salmon. The project prompted collaborative effort among federal, state, and tribal agencies, and local water users. It has incorporated habitat restoration, flow enhancement, fish passage improvements, and population supplementation through artificial production. Water exchanges have successfully increased minimum flows during spring and fall migration. While flows remain depressed compared to historic conditions, there is potential for improved habitat, passage, and homing. The mean adult‐to‐adult return rate of hatchery‐reared steelhead exceeded replacement and that of the naturally‐spawning population. Although the smolt‐to‐adult survival rates of hatchery‐reared fish fluctuate, salmonid escapement has increased in recent years, permitting steelhead and spring chinook harvest. Enumeration of potential spawners and observed redds reveals an increase in natural production of all supplemented species. Comparison of hatchery‐reared and naturally‐spawning steelhead populations revealed differences in life history characteristics (in age composition and sex ratios) though run timing and genetic stock compositions of the two components of the populations have not differed. Sustained monitoring is needed to determine benefits of integrating habitat restoration and artificial production in restoring salmonid populations.