Monthly Distribution and Catch Trends of Eulachon (Thaleichthys pacificus) in Chatham Sound, British Columbia, July 2018 to March 2019

Eulachon (Thaleichthys pacificus) is an anadromous species of smelt that spawns within rivers in British Columbia. Despite range wide population declines in recent decades there remain substantial knowledge gaps which limit the ability to develop focused conservation efforts. A monthly bottom trawl study was therefore conducted to address knowledge gaps relating to Eulachon biology, distribution, and the timing of migration into the Nass and Skeena rivers by observing Eulachon occurrence and biological condition in Chatham Sound. Eulachon catch per unit effort, size distributions, and sexual maturity observations varied over time, as did stomach contents and presence of teeth. Highest catches of Eulachon in Chatham Sound occurred in July and November. Catches were lowest in February and March, corresponding with the expected spawning periods in the Nass and Skeena rivers. The presence of Eulachon with developing gonads in Chatham Sound increased in frequency from July to November. In February and March, Eulachon had relatively smaller bodies with less-developed gonads, likely also corresponding to the spawning period and migration of mature individuals towards estuaries and rivers. Females that appeared to have spawned and returned to the marine environment were collected frequently in July and September, possibly providing some evidence of iteroparity, which has not been previously described for Eulachon. However, further histological analysis is required to confirm this finding, as resolving the potential for repeat spawning would provide useful information for future stock assessments and is a key knowledge gap for the species.