Atlantic salmon ( Salmo salar) have significant ecological, cultural and economic importance in Scotland. In recent years, salmon have become the target of large conservation actions due to growing concerns about their population status and the potential impacts of human activities on their productivity. Accurate estimates of population sizes are needed to: (1) adequately assess the current and future status of salmon populations, and (2) comply with various legislative and policy requirements, such as the EU Water Framework Directive (Directive 2000/60/EC) and the Habitats Directive (Directive 92/43/EEC). Spawner abundance estimates are also important when assessing conservation limits ( CLs), which represent the abundance of adult spawners required to fully populate a river with juveniles ( ICES 2013). In Scotland, electronic fish counter technology has been the cornerstone to accurately assess salmon population sizes. Marine Scotland Science ( MSS) seeks to expand the current distribution of counters to include new sites throughout Scotland. An expanded network will provide valuable information for salmon fisheries management, sustainable marine planning, the development of renewable energy, and the growth of aquaculture. Design, implementation and operation of a counter network, however, require significant knowledge and experience with counter technology and the associated economic costs. This report aims to fill a significant knowledge gap with regards to the technical, logistical and economic considerations for the development and implementation of a Scottish salmon counter network in MSS.
Accurate population estimates are critical for effective management and conservation. Dependable abundance estimates over time will allow the assessment of population trends and how they may respond to environmental change or anthropogenic stressors (Connors et al. 2014). Few rivers in Scotland have accurate, catch-independent estimates of adult spawners and juvenile recruitment; this represents a major challenge to Scotland's ability to assess salmon populations with confidence.
Although there are a number of existing electronic counters in Scotland (Eatherley et al. 2005), additional counting sites are required to determine conservation limits at the national scale. Eatherly et al. (2005) assessed 29 counter sites, and discovered that only 12 of the counter sites produced reliable data. This study demonstrated the relatively low coverage of reliable adult spawner counts that currently exist in Scotland. Building from these existing sites, the development of a large-scale network of counting sites could provide improved data for estimating spawner abundance, establishing CLs and determining compliance with CLs over time. Given this context, the development of a national counter network has been identified as an important goal for MSS.
The cost and effectiveness of counter site locations are important considerations that can determine the success of a counter network. Additional factors such as the selection of the counter technology, watershed, channel and population characteristics, and budgetary and management objectives can influence the cost and effectiveness of developing a counter site. No single counter technology will suit all sites and many counter technologies may be feasible in a single site; the trade-off between cost and effectiveness of a range of counter scenarios must be evaluated.
This report provides an extensive review of electronic counter technologies and their potential for implementation in Scotland's rivers. We consider all major types of proven counter technologies and software implemented by companies and government agencies worldwide. The overall objective of this report was to inform the future development of a fish counter network for Scotland. Specific objectives of this report were to:
- Assess the technical benefits and limitations, and economic costs of deploying different counter technologies in different environmental settings, including a consideration of engineering requirements.
- Assess the opportunities for automating signal processing and quality control associated with different counter technologies, considering existing processes and protocols where these can be identified.
- Determine the costs of maintaining and validating the various counter options in the range of environmental contexts explored, including the costs of data processing and validation.
- Combine data collated from Objectives 1-3 to produce an economic and technical optimization model to inform the choice of counter options in particular environments.
Following this section, Chapter 2 - Technical Considerations and Costs, provides an overview and discussion of the benefits and limitations of different counter technologies and their associated structures. We review each major counter technology in detail, providing associated cost estimates, and summaries of key structures commonly associated with electronic counters. Chapter 3 - Software: Automating Counts and Quality Control, provides a thorough review of new and existing software used to automate counts and evaluate data quality. We also provide an evaluation of Echoview, a third party software tailored for hydroacoustic counters, and review its cost and effectiveness for semi-automating counts. We also present a new R package, FishCounter, developed for Logie resistivity counter data that provides data management and quality control features such as error removal and creating a master dataset from individual download files. We also describe a model created to predict species using body length data collected from Vaki optical beam counters. In Chapter 4 - Operational Costs and Validation, we discuss general counter operations and associated costs for technology. Major topics include maintenance, field-based operations, data collection and validation, and producing population estimates with acceptable levels of uncertainty. Chapter 5 - Counter Decision and Cost Model: Integrating technological and economic considerations to determine choice of counter technology and structure, provides a synthesis of previous sections into a concise model, which is the major deliverable of this project. MSS can use this model as a tool to evaluate different counter scenarios to best fit the objective and budget for a proposed counter site. Chapter 6 - Opportunities for Combining Technology, discusses future opportunities for integrating electronic counters with other technologies to improve estimates of population size and other biological data such as migration timing and marine survival estimates for fish populations. Finally, Chapter 7 - Spatial Considerations for a Counter Network, outlines methods for integrating spatial considerations, including the proximity of existing counter sites and covariation in abundance among populations when developing an electronic counter network.
Connors, B.M., Cooper, A.B., Peterman, R.M., and Dulvy, N.K. 2014. The false classification of extinction risk in noisy environments. P Roy Soc B-Biol Sci 281: 20132935-20132935. doi: 10.1098/rspb.2013.2935.
Eatherley, D., Thorley, J.L., Stephen, AB, Simpson, I., MacLean, J.C., and Youngson, A. 2005. Trends in Atlantic salmon: the role of automatic fish counter data in their recording. In Scottish Natural Heritage Commissioned Report No. ROAME No. FNB.
ICES. 2013. Report of the Working Group on North Atlantic Salmon ( WGNAS), 3-12 April 2013, Copenhagen, Denmark.
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