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April-June 2006
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Marine Salmon Interactions Program

Migrant Salmonid Counts at Auke Creek Weir

Activities through June 2006 at Auke Creek weir concluded 112 consecutive days of weir operations and fish counting, sampling, and marking. The weir was installed 1 March and operated in the downstream mode until 22 June, then converted to count upstream migrants. This was the 27th consecutive year of total downstream counts of all migrant salmonids at Auke Creek. A total of 65,894 pink salmon fry were counted at the weir in 2006, nearly 50,000 fewer than the 1973-2005 average. Most fry, 63,474, migrated in April, and the migration declined rapidly during the last week of that month. Only 595 fry were captured in May. The May component of the historic run is no longer present. The midpoint of downstream migration was 14 April, 6 days earlier than average. The earliest midpoint of migration was 1 April 1998 and the latest was 7 May 1982; the average is April 20. There is a trend of earlier migration timing of pink salmon fry over the last three decades.

The count of sockeye salmon smolts, 25,515, was nearly 8,000 fish greater than the 1980-2005 average, and the fourth highest total count on record for Auke Creek. The midpoint of migration was 26 May, close to the average of 23 May at Auke Creek. Only the 1981 migration was earlier, with a midpoint of 11 May. Yearling smolts accounted for 22% of the migration, and averaged 4.3 g and 83 mm, and 2-year-old smolts were 14 g and 117 mm, both above-average sizes for sockeye salmon smolts at Auke Creek. The total biomass of sockeye salmon smolts leaving Auke Lake this year was the highest on record.

A total of 4,532 coho salmon smolts migrated downstream at Auke Creek this year. This was the fifth lowest count on record. The 1980-2005 average is 6,048. Auke Lake coho smolt production is in a decreasing trend that spans more than two decades. The midpoint of the 2006 emigration was 24 May, the latest in 15 years, but within the range observed in other years. The average migration midpoint is 19 May. Scales collected throughout the coho migration showed that yearling smolts accounted for 62% of the migration, and averaged 11.3 g and 105 mm, and 2-year-old smolts were 19.3 g and 124 mm. These fish were slightly larger than average sizes for these age groups of coho salmon leaving Auke Lake. Most smolts, 4,506, were tagged with coded-wire micro tags and released.

This is a NMFS and ADF&G cooperative project to determine marine survival and fishery contribution of Auke Lake coho. The Auke Creek Dolly Varden and cutthroat trout populations are in a decade-long downward trend. The Dolly Varden count this year, 4,975, was about 1,000 fish less than average; the 1980-2005 average at Auke Creek is 6,115. The midpoint of migration was 13 May, about a week later than average and one of the earliest on record, but within the range observed in other years. A total of 208 cutthroat trout were counted 2006, about 40 fewer than average. The midpoint of the migration was 25 May, 10 days later than average, and the third latest on record. The average midpoint is 15 May. There was a 26-day difference between midpoints of cutthroat trout migration dates from 2005 to 2006, the largest difference observed between consecutive years at Auke Creek.

By Jerry Taylor
 

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