Stave River Water Use Plan - BC Hydro

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Stave River Water Use Plan Monitoring Terms of Reference June 13, 2005 arose through constraints linked to Stave River fish benefits. The uncertainty in the fish biomass - productivity relationship lead to the following management questions: a) Is the relationship between fish production and littoral production such that the expected increase in littoral productivity as a result of the Combo 6 operating strategy leads to a measurable increase in fish biomass? b) By what extent does littoral productivity have to change in order to elicit a fish biomass response? The management questions above assume that pelagic production does not change with the implementation of Combo 6 operations and therefore does not contribute to increases in fish biomass. As indicated in the pelagic monitor, there is uncertainty as to whether this is the case. Evaluation of the management question should also include tests with indicators of pelagic productivity. This is reflected in the statement of impact hypotheses, as well as in the description of methods. 1.3 Summary of Impact Hypotheses There are two null hypothesis that are being tested with this monitor: H01: Overall fish biomass in Stave reservoir does not change over time following implementation of Combo 6 WUP operations. If the Combo 6 operation does indeed increase littoral productivity in Stave Lake reservoir as expected by the CC, the corresponding fish biomass response will be gradual if it exists and may take several years to fully manifest. This is in response to the time it takes for this increased littoral productivity to work its way through the various trophic levels of the food web, as well as through all the different age classes of all fish species. If the increase in littoral productivity is persistent every year, and fish mortality remains the same, a new plateau in annual fish biomass will be reached. H02: Between-year differences in species and cohort-specific fish biomass estimates are not correlated to indicators of littoral and pelagic primary productivity following the implementation of Combo 6 WUP operations. Test of this hypothesis will assess the likelihood that a direct link exists between fish biomass and indicators of pelagic and littoral productivity. This is a key assumption adopted by the CC to evaluate the reservoir benefits of various operating strategies of during the WUP process. The species and cohorts of interest will be those that are detectable by the hydro acoustic equipment during the initial survey period. Choice of productivity indicators will depend on the outcome of the pelagic and littoral monitors. Given the inter annual variability in Stave Lake reservoir hydrology, it is unlikely the degree of reservoir stability will be the same each year, and therefore neither would the extent of littoral and pelagic production. These inter-annual differences in BC Hydro Page 42
Stave River Water Use Plan Monitoring Terms of Reference June 13, 2005 productivity could have a direct consequence on the year’s abundance and/or size data of specific cohorts. Where as H01 examines the integrated effects of operations on fish biomass over time, H02 examines the direct impact of operations on the year’s fish cohorts, particularly during the summer growing season. Together, they provide the information necessary to address the management questions in the preceding section. It is important to note that fish biomass (kg·m -2 ) is not a measure of fish production. Rather it is an instantaneous measure of net fish production (kg·m -2 ·yr -1 ), which is defined as the gross production of new fish matter minus the losses due to respiration, excretion, secretion, death and predation (includes fishing and entrainment losses). In addition, the response of the biomass measure will likely be gradual over time as the impact of increased productivity works its way through the food web and through the full multi-year life cycle of different fish species. 1.4 Key Water Use Decisions Affected The importance attached to the issue of reservoir stabilisation by the CC was in part driven by the belief that it would result in increased fish production, and hence overall fish biomass, because of the increased littoral zone productivity it would bring. If the linkage between reservoir stabilisation and fish biomass is indeed confirmed, it would lead to a greater emphasis by the CC on trying to achieve a more stable reservoir operation, though the extent to which that would occur would be limited due to the high costs associated with it. Conversely, if the linkage were would to be weak, emphasis on reservoir stabilisation goals would lessen, and therefore may lead to a relaxation of fishbased reservoir constraints. The high cost of reservoir stabilisation would likely spawn innovative, alternative solutions to the issue. Examples may include the use of artificial reefs to increase the surface area that attached algae and other plants can bond to within the ELZ, or the introduction of slow release fertiliser in increase its production potential. Results of the monitor would help in defining the magnitude and scope of such initiatives. 2.0 Monitoring Program Proposal 2.1 Objective and Scope The objective of this monitor is to collect the data necessary to test the impact hypotheses outlined in Section 1.3 and hence, address the management questions presented in Section 1.2. The following aspects define the scope of the study: a) The study area will consist only of Stave Lake Reservoir b) Biomass estimates are to be collected annually at a standardised time of year. c) The monitor is to continue to until the next WUP review period (10 years). BC Hydro Page 43
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Stave River Water Use Plan - BC Hydro

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