Abundance and Run Timing of Adult Fall Chum Salmon in the Teedriinjik River, Yukon Flats National Wildlife Refuge, Alaska, 2024 (Alaska Fisheries Data Series Number 2025-2)

Abstract: In 2024, Adaptive Resolution Imaging Sonar (ARIS) was used to assess the abundance of adult fall Chum Salmon Oncorhynchus keta in the Teedriinjik River, a tributary of the Yukon River in Alaska. In 2024, sonar was deployed on August 5. Daily operations began on August 6 and continued through September 26. Thirty-minute subsample ARIS sonar recordings from each hour were counted and expanded to estimate hourly passage. During 2024, a total of 1,222.58 hours of acoustic data were analyzed, resulting in 25,601 upriver swimming fish enumerated. After adjusting for missed time, the total fall Chum Salmon passage estimate for 2024 was 51,433 fish (95% confidence interval = 51,304 to 51,562). This 2024 fall Chum Salmon passage estimate is 27.6% of the historical (1995–2024) average of 181,829. The estimate is below the current lower limit of the sustainable escapement goal (SEG) for the Teedriinjik River (SEG range 85,000–234,000). The upriver swimming fall Chum Salmon passage estimate was 439 fish on the first day of counting and 1,817 fish on the last day of counting. The first-quarter point of the run occurred on September 6, the midpoint on September 13, and the third-quarter point on September 20, indicating near-average run timing. Most upriver swimming fish were observed in the nearshore half of the ensonified zones on both banks, and few were observed near the outer range limits of the ensonified zones, suggesting that most fish were within the detection range of the ARIS. These passage estimates are conservative because they only include fish that passed during the dates of sonar operation and within the ensonified portions of the river.