Technical, Logistical, and Economic Considerations for the Development and Implementation of a Scottish Salmon Counter Network: Scottish Marine and Freshwater Science Vol 7 No 2

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 agenci

6.0 Opportunities for Combining Technologies

Integrating Technologies to Improve Automated Counter Estimates

Existing counter technologies (resistivity, optical beam and hydroacoustics) can face challenges in relation to stock assessment and catchment management, especially in rivers with multiple tributaries that may contain distinct populations. Integrating other technologies with electronic counters may aid in the enumeration of fish populations.

One limitation associated with current counter technologies concerns the identification of target species. Of course it can be difficult to generate accurate species-specific abundances from counters when species have overlapping size distributions and migration periods. In Section 3.2.2, Species Identification Models, we developed a framework for estimating species-specific population sizes using video identification and fish lengths. In the absence of video footage, researchers can use electronic telemetry tags (passive integrated transponders [ PIT], acoustic, radio) to understand the relative proportion of multiple species and their migration timing over a counter.

In many rivers, high turbidity, local environmental characteristics (e.g., river width, bank shape), and specific differences in catchability or low fish densities may preclude the use of a single methodology (Martignac et al. 2014). In British Columbia, where the Fraser River is a vital pathway for many Pacific salmon species and populations, DIDSON hydroacoustic gear, drift gillnet test fishing and Genetic Stock Identification ( GSI) are used to generate in-season, population-specific estimates of the number of adult salmon returning to the Fraser River. This information is used in-season to guide fisheries openings and post-season to generate population-specific estimates of recruitment.

In many situations, the placement of a counter in a river may be determined by factors other than that which the study design identifies as optimal. A counter too far downstream in a watershed may not capture the spatial behaviour of the species or population of interest. Conversely, a site further upstream can fail to assess tributary and mainstem fish below. Pairing telemetry and counter technologies can aid in determining the distribution of fish in large watersheds with multiple tributaries. For example, counters are located in small side-channels of the Cheakamus River (British Columbia, Canada) to provide accurate estimates of abundance. PIT arrays are paired with the counters to determine the relative proportion of fish that pass over the counter (Fell et al. 2013). Fixed radio telemetry stations throughout the mainstem of the Cheakamus River confirm the distribution of fish in other reaches of the watershed. Data are used to determine reach-specific abundances and are combined to estimate abundance at a watershed scale.

Integrating Technologies to Provide Additional Biological Information

Linking counter technologies can provide researchers with the ability to overcome some of the individual limitations of each technology. In the Murray-Darling Basin in Australia, investigators combined the use of DIDSON, Vaki Riverwatcher and fish traps to assess the behaviour of fish migrating through a fish pass (Baumgartner et al. 2010). Researchers found that each unit provided complementary data on fish abundance and behaviour.

Currently, IFR collaborates with a research group at the University of British Columbia ( UBC) to study sockeye salmon fish passage at a diversion dam in southwestern British Columbia, Canada. Researchers in this watershed integrate telemetry and counter technologies to understand the factors that govern in-river survival of sockeye salmon (Casselman et al. 2014). Pairing telemetry stations with counters at strategic locations allows for cross-validation of technologies to determine if survival trends scale up from tagged individual animals to the population level. In addition, data on the migration timing and success of tagged fish can be linked to estimates of abundance through a counter to generate daily estimates of population level survival. Using this integrative approach, IFR and UBC have made ecologically relevant and accurate recommendations to dam managers on how to reduce the impacts of operations on salmon.

Biological and biochemical sampling can be combined with counter technologies to provide information on migration ecology and developmental processes. Collection of biological samples (e.g., scales, otoliths) from study subjects can provide fundamental information on the biology and ecology (e.g., one-sea-winter vs. multi-sea-winter) of the species being enumerated. Molecular analyses, chemical elements and isotopes or parasite identification are all natural marks that can provide insights into life history characteristics. In the River Moy, Ireland, the use of DIDSON and GSI allowed stock assessment of discrete sub-populations within a large river system (Brennan 2013).

Combining technologies with counters will advance fisheries research. Use of this integrative approach can lead to cost-effective solutions to challenging monitoring conditions and provide additional information relevant to the management of salmon populations (e.g., age and population structure, population dynamics). Moving forward, such approaches need to be developed, tested and applied to a wide range of sites and management objectives.


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