2016: Post Season Analysis Outlook and Forecast for Yukon Chinook Salmon Timing

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The outlook anticipated the first significant pulse (15% point of the migration) on the delta at around June 9, and the observed 15% point was in fact June 9, which is earlier than average. The outlook called for the half-way point (50%) to be a little early to average, occurring about June 19, and the observed 50% point was in fact June 19 a little earlier than average. The weather and ocean conditions in the northern Bering Sea were warmer than average in spring of 2016. The April mean air temperature at Nome (1.3 C) was the second warmest since 1907. The average sea surface temperatures (-0.6 C) adjacent to the delta were close to average, and the average spring (March 20 – May 31) sea ice concentrations (41.6%) in waters between the delta and St. Lawrence Island (Shpanberg Strait) were lower than average. For more information contact phil.mundy@noaa.gov.

A partnership to predict run timing

Researchers from NOAA Fisheries and the Alaska Department of Fish and Game, with the support of the Alaska Ocean Observing System, have identified a combination of spring conditions that is closely related to the timing of Chinook salmon on the Yukon delta.  Using percent spring ice cover between St. Lawrence Island and the Yukon delta, April air temperatures in Nome, and marine surface temperatures just offshore of the delta in May.

Why is it so important to get the run timing right?

Known for navigating the longest annual freshwater migration route of any salmon to reach their spawning grounds, Chinook salmon can start arriving on the Yukon River delta at almost any point in June. Over the past 50 years the first pulse of Chinook has occurred sometime between June 6 and June 26. Traditional knowledge on the Yukon holds that spring weather conditions, including ice, temperatures and wind determine when in June the fish enter the river, but each spring brings a different combination of conditions, so pinning down a schedule for the arrival of the first pulse can be tricky. Twenty days can be a long time to wait to find out when the fish are actually coming and if there are enough of them to harvest.

Management of the Chinook salmon fishery is closely linked to expected time of arrival in harvest areas. When the migration begins earlier than expected, it’s reasonable for fishery managers to conclude that the run is stronger than it actually is, possibly resulting in over-harvesting near the river’s mouth and loss of harvest opportunities upriver. Likewise, in years when the first pulse of fish comes late, it is reasonable for fishery managers to conclude that the run is very weak, perhaps so weak that fishing needs to be slowed or stopped altogether.

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