The Tlell River salmon counting weir provides one of the very few reliable wild coho salmon escapement counts on the north coast of BC and for Haida Gwaii. The Tlell River adult coho spawner count is the primary indicator and absolute index of abundance for Graham Island Lowland coho. Haida Gwaii resides within the Department of Fisheries and Oceans (DFO) statistical areas 1 and 2 for which 227 separate coho spawning populations have been identified and aggregated into 3 conservation units. Graham Island Lowland coho are located on the northern portion of Haida Gwaii in closer proximity to the main commercial and recreational fishing areas. It consists of more than 27 coho streams that due to access, dark tannic waters, undercut banks, and vegetation are impossible to enumerate by any means other than the Tlell River adult weir.
The coho and pink salmon enumeration data contributes to a long time-series of salmon spawner abundance maintained by DFO for stock assessment and conservation purposes, including discussions at the Pacific Salmon Treaty negotiations and dialogue between commercial and recreational fishing sectors. This data also contributes to local resource management by the Haida Nation and information for BC Parks and the Haida Nation who co-manage the Tlall Conservancy and Heritage Site.