Salmonid Stocks Research Articles

Prioritizing Pacific Salmon Stocks for Conservation

Over 300 native stocks of Pacific salmon, steelhead, and coastal cutthroat trout (Oncorhynchus spp.) are at risk of extinction in the Pacific Northwest. With only limited resources available for conservation and recovery, prioritization of these stocks may become necessary if meaningful measures are to be implemented. We propose criteria by which prioritization may be guided. First, we rank stocks for risk of extinction, either by population viability analysis or by a set of surrogate measures. Then we rank stocks for biological consequences of extinction, using sets of questions designed to establish the genetic and evolutionary consequences and the ecological consequences if a stock were to become extinct. Together, these rankings allow stocks to be prioritized for a range of possible actions, with those stocks at highest risk and bearing the greatest biological consequences of extinction receiving attention first. Application of the prioritization process to 20 Pacific anadromous salmonid stocks worked as intended, although data limitations are considerable. The process is most likely to work successfully when applied to many stocks on which data exist, when several experts carry out the prioritization, and when the results are peer reviewed.

A simulation model of PCB dynamics in the Lake Ontario pelagic food web

Salmonid stocking and reduced phosphorous loading have led to major changes in the Lake Ontario ecosystem over the last 25 years and during the last 15–20 years PCB concentrations in age 4+ lake trout have dropped from ca. 9 to 3 mg kg −1. Here, I present a simulation model that examines PCB dynamics by coupling a dynamic prey supply to a multi-species functional response model of predation. At 1994 target levels of stocking, the model predicts that chinook salmon will increase, but alewife, lake trout and steelhead will decrease in biomass over the next 10 years. PCB concentrations of the sport fish are predicted to be 1.28, 1.77 and 3.06 mg kg −1 for steelhead, chinook salmon and lake trout, respectively. If alewife growth rates are not reduced farther, the model predicts that alewife could recover from a severe winter mortality. Decreases in the growth rates of sport fishes were accompanied by higher PCB concentrations and lake trout always had higher PCB concentrations for a given age class than chinook salmon and steelhead. Therefore if minimal sport fish PCB concentrations are a principal goal, managers should stock less lake trout, and stock more of the faster growing and less contaminated chinook salmon and steelhead.

Contrast of Constant and Bioenergetics‐Based Assimilation Efficiencies in Describing Ecosystems

Ecosystem models often follow the mass flow of matter (e.g., carbon, nutrients, trace metals, and contaminants) through food webs. Many ecosystem models (≈ 75% in a survey of recent literature) assume that carbon allocated to growth is a constant fraction of consumption. I use a simple predator‐prey model to demonstrate that the method of allocating consumed carbon to predator biomass (as a constant fraction or as a variable based on bioenergetics) can greatly affect the predicted dynamics of carbon and other matter. I then evaluate the potential disparity in the two carbon allocation methods by comparing predictions of constant and bioenergetics‐based assimilation versions of a Lake Ontario pelagic food web model under hypothetical management scenarios. Given current lake productivity and salmonid stocking, the version with constant assimilation efficiency predicted 22% more alewife (Alosa pseudoharengus) biomass than the bioenergetics‐based version at year 2005. When these models were calibrated to produce similar whole‐lake adult sport fish biomass, the constant assimilation model predicted 27% less alewife biomass at year 2005 than the bioenergetics‐based version. The two approaches predicted opposite directions of change in polychlorinated biphenyl (PCB) concentrations of stocked sport fish as their growth rates declined. Differences in the predicted PCB concentrations were as much as 450% when lake trout (Salvelinus namaycush) growth rates declined 60%. Assuming constant carbon assimilation may be acceptable for models of biomass when interest is only in one trophic level or where growth rates are static. However, constant assimilation efficiencies are inappropriate for models of trophic interactions (e.g., predictions of predation rates and prey sustainability), nutrient recycling, contaminants, trace metals, or changes in productivity.

Management Briefs: Short-Term Effects of Wildfire on Fishes and Aquatic Macroinvertebrates in the Southwestern United States

A brief (3-year) study on three headwater streams in the Tonto National Forest, Arizona, documented the immediate effects of wildfire on fishes and their food supply. Hydrologic events following a 1990 wildfire in Arizona effectively extirpated two populations of brook trout Salvelinus fontinalis and one population of rainbow trout Oncorhynchus mykiss. Aquatic macroinvertebrate densities in affected streams (1) declined to near zero within a month after the fire, (2) recovered to only 25–30% of prefire diversity in two of the streams 1 year later, and (3) continued to fluctuate postfire. Salmonid stocks reintroduced into two of the affected streams a year after the fire declined 75% within a year. The quality and quantity of hydrologic events interact after fires in southwestern landscapes and climatic regimes to markedly affect populations of fish and macroinvertebrates. Managers and researchers in the Southwest must be on the alert for field situations that provide an opportunity to cooperatively examine the long-term effects of both wild and prescribed fires on fishes and on their food supply and habitat.

A Survey of Healthy Native Stocks of Anadromous Salmonids in the Pacific Northwest and California

Abstract This report summarizes a survey of healthy native stocks of anadromous salmonids in the Pacific Northwest and California. We used a questionnaire approach combined with spatial analysis to describe the status and distribution of stocks considered to be in relatively good condition. These stocks now constitute a small fraction of the region's historic anadromous salmonid resource but are critical to maintaining current resource productivity. Several agencies have developed, or are in the process of developing, computerized databases that will help organize predominantly quantitative data on native stocks of anadromous salmonids. Our survey supplements those efforts by summarizing some of the knowledge of biologists familiar with the stocks and by making status assessments that at times go beyond conservative analyses of quantitative data. The survey identified 99 healthy native wild stocks of salmon and steelhead that biologists consider to be at least one-third as abundant as would be expected wi...

Growth and Survival of Rainbow Smelt, and Their Role as Prey for Stocked Salmonids in Lake Champlain

Abstract Estimates of mean length at age and survival of rainbow smelt Osmerus mordax captured at night during stepped-oblique midwater trawling in Lake Champlain in 1984–1985 were used to examine the condition of the population before a control program for sea lamprey Petromyzon marinus began. Stomach contents of lake trout Salvelinus namaycush, Atlantic salmon Salmo salar, and walleye Stizostedion vitreum were analyzed to assess the role of rainbow smelt as prey. Estimates of mean length at age did not differ among six sampling sites, suggesting there is only one population of rainbow smelt in the study area. Mean length-at-age estimates in 1984–1985 were similar to those observed in 1976 but substantially smaller than those observed in 1929 and 1950. Survival estimates of rainbow smelt in Lake Champlain were similar to those for rainbow smelt in the Great Lakes prior to salmonid stocking programs. Rainbow smelt was the dominant prey species identified in the diets of lake trout, Atlantic salmon, and wa...

How Will Decreased Alewife Growth Rates and Salmonid Stocking Affect Sport Fish PCB Concentrations in Lake Ontario?

Atmospheric deposition and resuspension from pelagic sediments are the two principal PCB sources to Great Lakes pelagic food webs today. The expansive nature of these sources makes their management...

The relationship between salmonid fish densities and critical ANC at exceeded and non-exceeded stream sites in Scotland

The critical load concept is now accepted throughout Europe as a means of estimating the sensitivity of key components of aquatic and terrestrial ecosystems to atmospheric inputs of sulphur (S) and nitrogen (N). Current UK freshwater maps, based on steady-state water chemistry, are derived using a critical acid neutralising capacity (ANCLIM) value of zero μeql−1, which is based on the probability of occurrence of salmonid fish in lakes. In practice most acidification damage to salmonid fish occurs in nursery streams at the emergence and first feeding stages. In general a clear relationship exists between salmon (Salmo salar L.) and trout (S. trutta L.) densities in Scottish streams and ANC values. However, differences between sites depend on which ANC value is used (eg maximum, minimum or mean). By contrast, when the exceedance of critical loads is compared with salmonid densities the relationship is less clear because many exceeded sites have good salmonid densities. Many of these latter sites are found in north-west Scotland where sea-salt inputs are high and ANC is usually greater than zero μeql−1, although diatom-based studies indicated slight acidification of these waters, with a point of change in diatom flora close to ANC=20 μeql−1. These false exceedances are probably due to preferential adsorption of acidic SO4 deposition which results in an overestimate of exceedance values. All sites with a mean ANC ≤ 0 are fishless but some sites with negative minimum ANC values had normal salmonid densities. Consequently a mean ANCLIM value of zero in the critical load equations for UK freshwaters appears to be too low to protect salmonid stocks. Values between 20–50 μeql−1 represent a more realistic range if prevention of long term damage to salmonid stocks is to be achieved.

Stress-induced impairment of predator evasion and non-predator mortality in Pacific salmon

This study examined whether rapid recovery from stress-induced impairment in predator evasion, observed in previous studies on coho salmon, Oncorhynchus kisutch (Walbaum), was a general characteristic of different stocks of the same species and different species of Pacific salmon. We monitored stress-induced non-predator mortality, predator evasion and Cortisol concentrations of smolts of coho and spring Chinook, O. tshawytscha (Walbaum), after administration of standardized single and multiple handling stresses. Marked differences in the response to handling stress among stocks of coho and spring chinook smolts were evident, with recovery from impaired predator evasion occurring within 24 h of a 30-s handling stress for coho smolts and 24 h of a 1-min handling stress for spring chinook smolts. Differences in stress-induced non-predator mortality among stocks were also observed. The results point to the importance of screening hatchery salmonid stocks to assess differing capabilities of dealing with stress.

The Enhancement of Salmonid Rivers in the Republic of Ireland1

AbstractThe paper describes (a) the methodologies which are used to carry out bioengineering baseline surveys of Irish salmonid rivers, and (b) the value of these exercises as a tool to identify the extent and degree of habitat degradation. The role of pilot instream physical enhancement schemes (in assessing the value of particular work schedules) is outlined, and the impact of excessive bankside vegetation on salmonid stocks is illustrated. Costs and benefits in relation to both a number of instream physical enhancement programmes and shrub‐pruning exercises are illustrated and compared with the gains which might be achieved from spending the same amount of money on stocking juvenile salmon. The rationale for undertaking such programmes in the Republic of Ireland is outlined.

Observer Variation in Counts of Meristic Traits Affects Fluctuating Asymmetry

Bilateral meristic characters can be used to assess trends in heterozygosity of fish stocks; however, variation in counts among observers or by the same observer might prevent identification of asymmetry in bilateral me ristics. We determined variability in meristic counts (pectoral fin rays, pelvic fin rays, upper gill rakers, lower gill rakers, and mandibular pores) of salmonids Onchorhyncus spp. made by independent observers and by the same observer on different occasions. The independent observers showed varying agreement for each meristic character, but the overall agreement was low. Low agreement was also found between counts by the single observer. We conclude that observer variation limits the usefulness of counts of meristic characters as a means of assessing trends in heterozygosity of salmonid stocks.

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon (Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon (Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.

Application of semi-quantitative electrofishing to juvenile salmonid stock surveys

Application of semi-quantitative electrofishing to juvenile salmonid stock surveys

Application of semi‐quantitative electrofishing to juvenile salmonid stock surveys

A semi‐quantitative electrofishing technique is described, which has applications for assessing distribution and densities of 0+ salmonids in streams. Linear regressions of logarithmically‐transformed data satisfactorily described the relationship between numbers of 0+ Atlantic salmon (Salmo salar L.) and 0+ brown trout (Salmo trutta L.) captured in a standard 5 min fishing and quantitative population estimates obtained using a commonly used method. Applications of the semi‐quantitative technique to management are discussed and a categorization system proposed.

Overview of the interactions and environmental impacts of hatchery practices on natural and artificial stocks of salmonids

Artificial propagation of Pacific salmon has been carried out for over a century. Salmonid stocks used in hatcheries were made homogeneous to be more easily manipulated. The stocks that form the basis for most coastal net and troll fisheries are currently of hatchery origin, and a 3–5% escapement of hatchery stock is considered adequate for reproduction. During the period 1960–1980, although numbers and average sizes of coho released from Columbia River hatcheries increased, returning adults declined between 1970 and 1980. Massive efforts were made to improve the efficiency of production in salmon hatcheries. Adult biomass potential decreased where there was a proportional increase in precociousness, resulting in a decrease in older mature individuals. Fisheries based upon enhancement have consistently fostered the over-fishing of naturally reproduced stock. For reasons never satisfactorily explained, salmonids have been released for decades in upstream areas without a basic understanding of instream ecological requirements of the salmonids, a knowledge of what resources these released salmonids are being superimposed upon, or a concern for the ecological devastation caused by these practices. A policy based on artificial propagation served as an accomplice in reducing wild salmonid stock genetic diversity among wild salmonid stocks and average size and age of returning adults. Fishery policy-makers were provided a convenient excuse for the worst possible resource use practices, and used hatcheries to affect wild salmonid stocks profoundly.

Initial observations on the effects of varying levels of deciduous bankside vegetation on salmonid stocks in Irish waters

Abstract. The effects of varying levels of deciduous bankside vegetation on salmonid stocks in Irish rivers were investigated. In summertime, when marginal vegetation limited the extent of incident light reaching the river bed, a marked decline in both juvenile salmon, Salmo salar L., and juvenile and adult trout, Salmo trutta L., numbers were observed relative to stocks in adjacent areas with a less dense canopy. This appears to be a countrywide phenomenon in all available salmonid habitats. In the case of both juvenile salmon and all trout numbers a correlation is evident between the extent of shade, as measured in terms of the reduction in aquatic vegetation, and fish numbers, which fall as shade levels increase. Data also suggest that the length of tunnelled channel, upstream of tunnelled sites electrofished, seems to influence the standing crop of juvenile salmon with numbers of these fish falling with increasing tunnel length. This relationship is not evident in relation to trout numbers.

Ulcerative dermal necrosis (UDN) in wild salmonids

Ulcerative dermal necrosis is predominantly a condition of the head skin of salmonid fish native to the waters of the British Isles. It has, however, occureed in the Baltic, noerthwest France and possibly elsewhere. It has never been reported in farmed fish. It was firsty reported in teh 19th century. It probably occured prior to 1868 but the main epizoolit was first in 1877 when it was referred to as Salmon Disease. The disease largely disappeared until the mid 1960s when it first occurred in southwest Ireland and then gradually spread to almost all rivers of the British Isles and subbsequently to neighbouring areas. It had disappeared again by the mid 1970s. Salmon and grlse ( Salmo salar0 and sea trout ( Salmo trutta) are susceptible and there is evidence that some brown trout may also show clinical signs. The disease is characetristically found in adult wild fish as tey congregate at sea prior to entering fresh water adn during their upstream river migration. The lesion is a progressive cytolytic necrosis of epidermal Malpighian cells, of the pemphigoid type which is restricted to spefic sites ion the head. On entry to fersh water, these rapidly ulcerate and may become infected with a number of opportunitist pathogensm, principal of which is the oomycete Saprolegnia diclina. Once this occurs the lesion extended by fungal activity, death being due either to secondary bacterial infection of the ulcer or, more often, circulatory failure resulting from the osmotic haemodilution induiced by the large area of ulceration. The condition is primarily found in the colder months of the year and usually persists at high for 3 or 4 years in a river system after which it gradually disappears. Attempts to isolate a specific viral or bacterial agent from the lesions, or from other organs, have failed and the evidence that is an infectious disease is very limited. Investigation into other more complex possible aetiologies have been equally unsuccesfully. The charcetristics early lesion, the pemphigoid bulla has, however, also been induced y photosensitisation and this may represent a further possibility for its investigation. Currently the disease is in a period of remission and no outbreaks have been reported for some years. It may be no coincidence that the inccidence of epizzotics has appeared always to coincide with very high wild salmonid stock levels.

Lake Michigan Salmonid Stocking Costs in Wisconsin

The costs of stocking salmonids in the Wisconsin waters of Lake Michigan are estimated for 1985. Estimation procedures and costs per stocked and captured fish are presented. Fingerlings of a species were found in most cases to cost more per captured fish than yearlings. However chinook salmon fingerlings were least expensive at an average cost of only $0.35 per captured fish. Most expensive were brook yearlings and fingerlings at $12.67 and $10.14, respectively. While a full policy evaluation awaits additional research on speciesspecific benefits, three tentative conclusions can be drawn for the Wisconsin fishery. First, the role of brook trout in the fishery should be reviewed. Second, despite difficulties with lake trout rehabilitation, the role of lake trout in the sport fishery is encouraging and may justify continued stocking. Finally, increased stocking of the popular chinook salmon may be justified if the recent problems of low capture-per-release rates can be solved.

Ecological and Genetic Effects of Salmonid Introductions in North America

Stocking of non-native Salmoninae into North American waters began around 1870. Brown trout (Salmo trutta) from Europe established populations across North America and is the only successful inter-continental introduction. Introductions of native salmonids within North America but outside their native ranges have been common. Ecological effects of salmonid introductions. include competition, predation on native salmonids and other fishes, environmental modification through digging of redds in stream bottom substrates during spawning, and introduction of parasites and disease to native fish. Direct genetic effects from stocked salmonids are caused by interbreeding with native species. Indirect genetic effects may result through selective forces and/or a reduction of effective population size, genetic drift, and inbreeding. Management actions used to remove non-native salmonid populations include chemical reclamation and construction of barriers to movement. Salmonid stocking as a management practice is appropriate for species or population rehabilitation. Continued stocking of non-native salmonids should cease where viable native salmonid populations exist. New introductions of Eurasian species should not be made because effects are unpredictable. Aquaculture and the creation of transgenic fish pose special threats to North American salmonids. The era of widespread, intentional introductions of salmonids by man justifiably is drawing to a close.