Although strategies to meet most management objectives are relatively clearcut in single-species catchable trout programs, strategies become much more complex when two or more species are involved. A difficult problem that must be faced in evaluating catchable trout fisheries management strategies is defining management objectives. One approach to testing alternative management strategies in complex resource systems, such as catchable trout fisheries, is systems simulation. A computer-implemented catchable trout fishery simulator (CATS) was developed to evaluate fishery response under various management strategies in a multi-species stocking program. The user of CATS can select alternative management strategies and functions which generate predictions of fishing pressure on a particular fishery. To evaluate the effect of each system component, CATS was exercised over a wide range of potential system component alterations. Predominant stocking of brook trout appreciably increased average catch per angler hour and percentage return to creel. Altering the stocking ratio to favor brown trout substantially increased the number of angler hours. Stocking predominantly rainbow trout reduced the effects caused by stocking predominantly brook or brown trout. Estimates of expected angling pressure ru1d catchability coefficients of each species stocked are of primary importance because of their considerable effect on other system components. A user must have a sound objective before deciding where, when, which species, and how many fish to plant. The primary utility of CATS is to enable the user to evaluate management strategies prior to implementation. / Master of Science

M.S.

Ergasilus sieboldi has been reported from a number of trout fisheries in England and Wales. The population dynamics of this parasitic copepod in Rutland Water, a large reservoir in Central England was studied from 2003 to 2005. A combination of angler and net caught fish were examined to record numbers of adult females and egg production throughout each year. The parasite overwintered in large numbers on trout and commenced egg production in April which then continued until October/November. The prevalence of infection and the abundance of the parasite were very high in overwintered rainbow trout but these parameters then decreased in March as large numbers of uninfected fish were stocked into the reservoir. The parasite population then increased until October. Infection levels in 2004 and 2005 were significantly lower than in 2003. Infections of cage-held rainbow trout showed that E.sieboldi could become ovigerous within two weeks of attachment to trout in July and August. New infections occurred from June until November. Several species of coarse fish examined were also shown to be infected by the parasite. Cage trials showed that triploid rainbow trout were infected by significantly higher numbers of the parasite than diploid rainbow, brown trout or “blue” rainbow trout. Observations of infected fish in experimental tanks showed that overwintering parasites were stimulated to commence oviposition by increasing water temperatures. Photoperiod had no noticeable effect on the parasite. Egg viability and rate of development was studied using tank held infected fish and in vitro incubation techniques. Viability of eggs in sacs detached from the adult parasite was greater than those remaining attached. The rate of egg development was modelled and was shown to be predicted by temperature. Development of eggs was estimated to commence at 3.6ºC. Eggs developed more rapidly at higher temperatures and at peak production, inter-clutch interval was between 0 and 0.5 days. Egg production models estimated that an overwintered parasite could produce up to 19 clutches of eggs between April and October under normal temperature regimes measured at the reservoir. Ovarian development during the winter was confirmed using classifications of ovary size and shape based on parameters measured using image analysis techniques. The life span of E.sieboldi was estimated at 10-12 months. Nauplii culturing techniques were compared, and nauplii to stage V were successfully developed. Nauplii hatched from the eggs of adult parasites occurring in the spring were larger and conditioned to develop at lower temperatures than those hatched later in the year. Nauplii were fed on 4 different types of algae held in monocultures but development occurred only in algal polycultures. A comparison was made of nauplii feeding preferences and development with algae recorded in Rutland Water in 2003 and 2005 but no correlations were found. Fish stock assessment was carried out using models of angler catch, effort and stocking figures from the fishery. Parasite numbers on the overwintered fish were estimated at 12 million parasites in April 2003, 8.3 million in April 2004 and 1.2 million in April 2005. Stock assessments suggested a reduction in number of overwintering trout and effects of stocking policy to be at least partially responsible for the decline in the parasite population. The results of this study formed a management strategy for the operation of the trout fishery.

Stocking trout to create successful sport fisheries is an irresistible lure to fisheries managers and sport anglers alike, but the implicit assumptions behind this simple process have seldom been questioned or assessed. Using common fisheries monitoring techniques, combined with social surveys, at nine Alberta lakes, I quantified three main assumptions behind put-and-take stocking. Surprisingly, 1) stocking high densities of Rainbow Trout created very low-density populations; 2) these populations supported mediocre fisheries; 3) these mediocre fisheries, if above a threshold catch rate, attracted very large numbers of satisfied anglers. Based on these findings, the stocking density and the direct cost of stocking were reduced by 80% at three experimental lakes. No major decreases in fishing quality, angler participation, or angler satisfaction were observed. I suggest refinements in the stocking process focus on determining how to provide adequate numbers of trout to create a basic level of satisfaction with the fishing experience.

Thesis (MA)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

No description available.

Approximately 24 alien fish species, equivalent to 9 percent of all South African freshwater fish species, were introduced and established into South African waters during the 19th and 20th Centuries (Skelton, 2001). Of the 24 species introduced, the Rainbow trout and the Brown trout have over time become South Africa's most widely spread and used freshwater fish species (Bainbridge, Alletson, Davies, Lax and Mills, 2005). The National Environmental Management: Biodiversity Act, no.10 of 2004 has, however, cast considerable doubt on the future of trout as a food source and a recreational fishing resource in South Africa. More specifically, Section 64 of the Act has the following aims: “(a) to prevent the unauthorized introduction and spread of alien species and invasive species to ecosystems and habitats where they do not naturally occur; (b) to manage and control alien species and invasive species to prevent or minimize harm to the environment and to biodiversity in particular; and (c) to eradicate alien species and invasive species from ecosystems and habitats where they may harm such ecosystems or habitats.” The uncertainty surrounding the future of trout in South Africa is mainly underpinned by aim (c) of Section 64 of the Act. Regarding the eradication of trout and in keeping with aim (c) of Section 64 of the Act, three remarks can be made. First, there exists a paucity of published studies which offer validated proof of the impacts which may be ascribed entirely to the introduction of alien trout in South Africa, since no pre-stocking assessments were conducted (Bainbridge et al., 2005). Second, the elimination of trout is feasible in a few limited closed ecosystems, such as small dams, but is highly impractical and untenable from an environmental and cost perspective where open and established river systems are concerned (Bainbridge et al., x 2005). More specifically, there are no efficient or adequate eradication measures which may be used in wide-ranging open ecosystems, which selectively target alien fish species. Moreover, most, if not all, measures have the potential to cause considerable adverse impacts on indigenous aquafaunal species. Finally, the elimination of trout could undermine the tourism appeal of many upper catchment areas in South Africa. The trout fishing industry is well established and is a source of local and foreign income, as well as a job creator in the South African economy (Bainbridge et al., 2005; Hlatswako, 2000; Rogerson, 2002). In particular, the industry provides a two-tier service: first, in food production at the subsistence as well as commercial levels, and second, as an angling resource. Recreational angling, including fly-fishing for trout, is one of the fastest growing tourism attractions in South Africa. Furthermore, the trout fishing industry is sustained and underpinned by a considerable infrastructure consisting of tackle manufacturers and retailers, tourist operators, professional guides, hotels, lodges and B&Bs. The economic case for the trout fishing industry in South Africa has, however, not been convincingly made. The economic benefit provided by trout and trout fly-fishing is priced directly in the market place by expenditures made by fly-fishers, and indirectly in property values, which provide access to fly-fishing opportunities. The benefit of trout and trout fly-fishing can also be valued through non-market valuation techniques. Non-market valuation is used to calculate values for items that are not traded in markets, such as environmental services. There are several non-market valuation methods available to the researcher, namely those based on revealed preference and those based on stated preference. The former includes the hedonic pricing method and the travel cost method, while the latter includes the contingent valuation method and the choice modelling method. Of the available non-market valuation techniques, the travel cost method is the most suitable method for determining the value of trout and the trout fishing industry because travel cost is often the main expenditure incurred. xi The aim of this study is threefold: first, to value the economic contribution of trout and trout fly-fishing to the Rhodes region, North Eastern Cape; second, to determine the willingness-to-pay for a project that entails the rehabilitation and maintenance of trout streams and rivers in and around Rhodes village so as to increase their trout carrying capacity by 10 percent; third, to determine the willingness-to-pay for a project aimed at eradicating trout from streams and rivers in and around Rhodes village so as to prevent trout from harming the indigenous yellowfish habitat. The first aim was achieved by applying the travel cost method, whereas the second and third aims were achieved by applying the contingent valuation method. The study aimed to provide policy makers with information regarding the value of trout fishing in the Rhodes region, so as to create an awareness of the economic trade-offs associated with alien fish eradication. Through the application of the travel cost method, the consumer surplus per trout fly-fishermen was estimated to be R19 677.69, while the total consumer surplus was estimated to be R13 774 384.40. The median willingness-to-pay for a project to rehabilitate trout habitat was estimated to be R248.95, while the total willingness-to-pay amounted to R199 462.20. The median willingness-to-pay for a project to eradicate alien trout from the Rhodes region rivers and streams was estimated to be R41.18, while the total willingness-to-pay amounted to R28 829.36. This study concludes that trout and trout fly-fishing make a valuable economic contribution to the Rhodes region. The extent of the economic benefit provided by trout and trout fly-fishing services in the Rhodes region should be carefully considered in any stream management project.

The gravel environment of 30 brown trout (Salmo trutta) redds and adjacent nonredd sites in two western North Carolina streams were studied during the incubation period in 1979-1980 and 1980-1981. Intragravel water temperature, dissolved oxygen concentration, and percent oxygen saturation were highly correlated with surface water measurements, indicating that intragravel water is of surface origin. Permeability ranged from 250 to 149,350 cm/hr and averaged 6,150 cm/hr. Apparent velocity varied from 0 to 1,000 cm/hr and averaged 30 cm/hr. Permeability in redds was significantly greater than at nonredd sites. No significant differences in apparent velocity were found between redd and nonredd sites. No consistent differences in permeability or apparent velocity were found between streams or over time. Permeability and apparent velocity decreased significantly with depth. Freeze cores were collected from redd and nonredd sites and divided into three 10-cm layers for analysis. Geometric mean diameter, sorting coefficient, fredle index, percent fines <2.00 mm, and percent porosity were highly variable and averaged 11.8 mm, 2.8, 4.2, 17.0 percent, and 19.0 percent, respectively. No significant differences were found among factors tested. Correlations between these gravel indices and permeability and apparent velocity were low. The gravel and intragravel environments appeared to be adequate for larval survival. Measurements did not reveal any clear trends during the incubation period. Brown trout did not by choice or redd construction appear to select or create (by redd construction) a subsurface environment different from the surrounding stream bed. / M.S.

Species of Argulus are macro-, ecto-parasites known to infect a wide variety of fish, but in the UK mainly cause problems in rainbow (Oncorhynchus mykiss) and brown trout (Salmo trutta). Argulus foliaceus is estimated to have caused problems in over 25% of stillwater trout fisheries in the UK. While A. foliaceus does not usually cause high levels of mortality, the parasite affects fish welfare, and also makes fish harder to catch due to morbidity and reduced appetite. This can cause severe economic problems for the fishery, resulting in reduced angler attendance due to poor capture rates and the reduced aesthetic appearance of fish; in the worst-case scenario this can result in the closure of the fishery. Current methods of control include chemical treatment with chemotherapeutant emamectin benzoate (Slice), physical intervention with egg-laying boards which are removed periodically and cleaned in order to reduce the number of parasites hatching into the environment, and the complete draining and liming of the lake to remove all free-living and egg stages of the parasite. While these treatments have all been shown to reduce parasite numbers, none are known to have resulted in permament eradication of the parasite. There is evidence to suggest that A. foliaceus will eventually develop resistance to Slice - the only currently available chemical treatment against the infection - and egg-laying boards and the draining and liming of the lake are both time- and labour-intensive. Previous studies have shown that slow fish turnover is a risk factor with respect to A. foliaceus infections, and with a wide variety of stocking practices occurring in the UK one of the first aims of this project was to determine their impact on the host-parasite dynamics. Mathematical models provide a cost-effective way of examining the impact of such practices, and after a literature review (chapter one), in chapter two a three-compartment mathematical model was adapted for use in the A. foliaceus-trout system. Four generalised stocking methods were then incorporated and analysed, and a minimum threshold host density was found to be necessary to sustain the parasite. Including a function which reduced the capture rate as the parasite burden increased allowed the parasite to survive at a lower host density, as susceptible fish were removed from the water at a slower rate, and attached parasites also remained in the water for longer. This resulted in hysteresis in the model, as the invasion threshold for the parasite remained the same, but once established the parasite became harder to eradicate, requiring significant reductions in the host density. In chapter three the model was further developed in order to improve its biological real- ism. Several features were added and these included: natural host mortalities, a separate compartment for the parasite egg population, and parasite survival after the natural or parasite-induced mortality of its host. In chapter four seasonality was added by incorporating temperature-dependent egg-laying rates and an over-wintering period during which the parasite was unable to reproduce. The model was then fit to the available data, and estimates for the rate of parasite-induced host mortalities and the parasite’s rate of attachment to a host were found. In chapter five we returned to stocking methods, this time looking at the frequency and timing of stocking events and the impact of imposing a rod limit (whereby anglers are only permitted to capture four fish per visit); it was concluded that while current guidelines suggest that very frequent trickle stocking is recommended when dealing with Argulus spp. infections, monthly stocking does not appear to worsen the infection, and if the fish capture rate is high then less-frequent stocking may also be permissable - particularly if stocking occurs towards the end of the year when the parasite is no longer active. This practice may, however, be detrimental to the fishery due to low fish densities in the summer months. In chapter six treatment with Slice was included in the model, and it was demonstrated that with constant treatment, and in the absence of reservoir hosts and a withdrawal period from the drug prior to stocking treated fish into the fishery, the parasite was eradicated. Under current veterinary cascade guidelines, however, trout are required to undergo a withdrawal period of 500 degree days prior to being made available for human consumption. When this was included in the model the drug still decreased parasite abundance, but did not eradicate it - this is in agreement with results reported by communications with fishery managers currently treating fish with Slice. A reduction in the withdrawal period of 25% was shown to further decrease parasite abundance, but still did not result in parasite extinction. As constant treatment with Slice is not advisable due to the potential for resistance build-up, we then sought to find time at which to apply a single treatment of Slice, and found that this was in August when the temperature was highest and the parasite was reproducing and attaching to hosts quickly. Egg-laying boards were also incorporated into the model and similarly to findings by Fenton et al. [11] the success of this treatment was mostly dependent on the proportion of eggs being laid on the boards (as opposed to natural substrates). In contrast with the A. coregoni system, however, the boards would have to be cleaned and replaced more frequently that once per year, as several cohorts of A. foliaceus emerge during a single year.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2007. / Small farm dams (< 20 ha) in the Western Cape Province provide adequate water conditions for intensive cage production of rainbow trout (Oncorhynchus mykiss). A major environmental concern of cage aquaculture, however, is the high inputs of nutrients via commercial diets and the subsequent eutrophication of the water source. Eutrophication can result in the degradation of the general water quality (increasing pH levels, oxygen depletion, increased hydrogen sulphide and free ammonia) and shifts in the phytoplankton structure (increased biomass, single species dominance). Deterioration of water quality will affect the success of the fish farming enterprise as well as the performance of irrigation equipment by increasing the risk of clogging and corrosion. Water quality, phytoplankton and zooplankton compositions were monitored at four sites from June 2005 to November 2006 to determine the effects of cage culture on the farm dam environment, its associated biota as well as irrigation water quality. The distribution of nutrients, nitrogen and phosphorus, was mainly influenced by the stratification and mixing regime of the water bodies. Nutrient concentrations increased during the winter mixing period while in the summer months, they seem to settle to the lower part of the water column. Nutrient concentrations of production sites and reference sites were comparable except for the ammonia levels that were significantly higher at the production sites. Phytoplankton corresponded with nutrient availability resulting in high biomass during winter. In terms of biomass, phytoplankton was approximately two times more abundant in production sites compared to reference sites. Assemblage dominance by cyanophytes (Anabaena circinalis, Microcystis spp.) was found more often in production sites, while reference sites were dominated by dinophytes (Ceratium hirundinella, Peridinium spp.). Zooplankton biomass concurred with high phytoplankton biomass in winter. Zooplankton assemblages in production sites sustained much higher biomass. Effects of cage culture on irrigation water quality are evident from increased algal biomass and shifts in species composition. These results indicated that at its present production level, cage culture had impacts on the farm dam environment and irrigation water quality. The most significant evidence was given by increased plankton biomass and single species dominance in production sites. However, these findings can not solely be ascribed to the introduction of aquaculture as various other factors may also contribute to the water quality of these ecosystems.