Feasibility of Escapement monitoring of the Lillooet River Coho Salmon CU via Digital Imaging

Inconsistent, and sometimes absent, annual funding and a lack of resources to develop a Coho centric assessment program have resulted in DFO being unable to generate an estimate of Coho salmon escapement to the Lower Fraser River Management Unit (LFR MU) from observed data. The absence of reliable escapement estimates for Coho in the LFR MU and its three component Conservation Units (Lillooet, Boundary Bay and Lower Fraser) represents a critical information gap for Southern Boundary Coho salmon Management. Despite more than a decade of stream specific Coho escapement estimates within the Lillooet CU, DFO does not have an acceptable way of using these estimates to generate a CU specific aggregate escapement estimate to the Lillooet CU.

Coho returning to the Lillooet CU must transit through the Lower Lillooet River, thus providing the unique potential for a census-style assessment for much of the CU. Funding from the PSC in 2018 enabled LGL Limited and the Lil’wat Nation to identify a site near Rogers Creek (a Lillooet River tributary) where digital imaging technology, specifically an Adaptive Resolution Imaging System (ARIS) 1200, could be installed to assess escapement of Coho salmon to the Lillooet CU. Herein we propose to operate an ARIS 1200 at Rogers Creek for a period of up to 5 weeks to test the feasibility of the site and the technology to assess the abundance of passing Coho, while estimating escapement to the Lillooet CU. If successful over the five-week period, in future years this project could operate over the entire Coho migration window and would negate the need to determine in-filling factors while providing a consistent and repeatable escapement estimation method. This project will improve management of Southern Boundary Coho salmon, and better enable the implementation of both the Wild Salmon Policy and the Pacific Salmon Treaty through improved stock assessment. Results from this project could be leveraged to estimate aggregate Coho salmon escapement to the LFR MU in future years.