Tuesday, August 11, 2009

Tyee Steelhead Index To Aug.10th

Here is the Tyee Steelhead Index Cumulative graph up to Aug.10th.
We offer this with the long provisos copied below.

The Tyee Test Fishery has well known shortcomings ( we posted about this recently here:http://skeenafisheriesblog.blogspot.com/2009/07/tyee-test-fishery-uncertainty.html) highlighted by last years 38% overestimate of the sockeye run.
As such, please take any information presented in the Tyee Steelhead Index with this in mind.

Also, please keep in mind that on the longterm data sets from Tyee, the errors, both over and under, are NOT corrected. So, the numbers and graph line for 2008 are a percentage (exactly what % we dont know) over what they should be.

The Tyee Test Fishery is a sockeye salmon test fishery; it is only calibrated for sockeye (Babine River Weir counts), although the DFO use data from all salmon species for management, and MOE does for steelhead. As such, Tyee catches are not standardized and therefore, comparing data between years or even individual days or gillnet sets is not valid in the strictest scientific sense. That said, the Tyee Test Fishery has been operated in the same manner since 1956 and a conventional gillnet vessel makes a 60 minute set with 200 fathoms (1200 feet) of net on every slack tide that occurs during daylight from early June to late August/early September.

The Tyee Test Fishery has developed a propensity to overstimate the sockeye runs. Since 1995, it has overestimated the Skeena sockeye run by an average of 20%. In 2008, this overestimate was 38%. These overestimates apply directly to the steelhead Index according to DFO but to what extent or percentage they have not clarified.

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