Tuesday, July 21, 2009

Tyee Steelhead Update

Here is a couple of new graphs showing the Tyee Steelhead Cumulative Steelhead Index to July 20, 2009 with an 'All Years' as well as the 2000's Decade average for comparison.
The second graph adds the 1998 'Best Year' and the 1958 'Worst Year' for comparison.

Also, the standard provisos with regard to interpeting Tyee data copied below.

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 36%. These overestimates apply directly to the steelhead Index according to DFO but to what extent or percentage they have not clarified.

Original data sets copyright/courtesy of DFO North Coast and Ministry of Environment, Smithers

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