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     Some Yukon River fishers see a change, some don’t.
Some studies show a change, some don’t.

   About fifteen years ago and prior, it was common for Rampart, Tanana and Rapids fishwheel fishermen who fished the whole season to catch one or more 50 pound Chinook salmon each year, and a 30-35 pound fish was not considered that large back then. Of note is the fact that prior to that time, our local fish buyer would only buy 14 lb king and larger as a matter of policy. Then it went to 12 lb and 10 and now, except for grayling size king we often sell any size. Currently the same fishermen, fishing the same gear as then, have been getting about an 11.6 lb average the past 4 years. Out of 4007 Chinook weighed by the student data collection project at Rapids in these 4 years, the below 49.5 lb fish (see picture) is the largest with the next largest being only 36.5 lbs. So far after 1064 samplings in 2008 only 5 are over 30 lbs (largest - 36 lbs) Sampling done further upriver at Eagle in 2006 show even lower averages, of less than 10 lbs. This is getting close to the average weight for chum salmon not king.   

The below data was randomly taken at Rampart Rapids from established king fish wheel sites
for the complete season, each year listed

      Some current expressed reasons for the possible size and age decrease include years of selective and/or over fishing, the tendency for Ichthyophonus infection to progress to it’s disease state much faster in larger Chinook (below graph), changes in the marine environment, global warming, Bering Sea pollack fleet bycatch of king and the recent increased use of large mesh nets due to the significant reduction of fish camps and fishwheel use drainage wide.

       
   As of the 2007 State Board of Fisheries meeting where all proposals dealing with large mesh net selectivity issues failed, the State and majority of Yukon fishers expressed that a problem with declining size of king salmon did not exist. The Yukon River Drainage Fisheries Association, made up of fishers from the coastal districts to the Canadian Border (at that time) had twice come one vote short of complete consensus that a problem did not exist also. For the past decade net mesh reduction proposals have gone before the Board of Fish as a means of better managing king runs. These were put there by a small number of upper river fishers who believed that selective large mesh net overfishing was being allowed year after year in the Yukon.
   Since 2007 the USFWS has put their support behind some similar proposals that are now going before the Federal Subsistence Board and a few more fishers are voicing their concern about smaller king. A significant number of Yukon biologists and managers are privately expressing that the damage has already been done and many generations will be needed to undo what is essentially a genetic shift in age class of Yukon king salmon. Below is a catch of king from the first pulse in 2008 - these size king are making up a significant part of fishwheel catches in the upper river as of late.

     The problem with determining whether a size and/or age shift has happened is there are few projects that were run long enough, consistent enough or with the confidence that would allow an opinion on the subject. An example of what we end up with then is, comparisons between the recent 5 years of size data collected by Rapids Research (solid data) and fishers anecdotal info (say so data) from the past which is overall not solid science. The Chinook weirs being run are expensive and few (especially on the Canadian stocks) but do provide solid unbiased data. Some of the data we have on Chinook escapement is from carcass surveys. While suitable for some purposes these are incapable of the accuracy necessary to say anything at all about size or age composition (see AFS abstract next). These surveys and other questionable data are currently being used to suggest the size of king and amount of females making it to the spawning grounds in the Yukon are healthy and fine.
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Fisheries Society Online Journals
DOI: 10.1577/1548-8659(2002)131<1194:SDROCS>2.0.CO;2
Transactions of the American Fisheries Society 2002;131:1194–1202

Size-Dependent Recovery of Chinook Salmon in Carcass Surveys
by Shijie Zhou

Oregon Department of Fish and Wildlife, Post Office Box 59, 2501 Southwest First Avenue Portland, Oregon 97207, USA

      Abstract.—Accurate estimation of the age and sex composition of Pacific salmon Oncorhynchus spp. is essential for understanding their population dynamics. Unfortunately, the data collected from spawning ground surveys are generally biased by the probability of recovery. Using 11 years of mark–recapture data for fall Chinook salmon O. tshawytscha in the Salmon River, Oregon, I developed logistic models to examine the influences of stream flow and the sex and size of the fish on the probability of carcass recovery from spawning grounds. The results indicated no significant differences in recovery rates for males and females. The probability of recovery generally increased as fish size increased and as stream flow decreased. However, the relationships were nonlinear; the probability leveled off for very large fish and increased slightly at very high stream flow. Directly computed age and sex compositions from survey samples underestimated the ages of small fish and males while overestimating those of large fish and females. For example, in 2000, age-2 jacks were underestimated by 75% while age-6 fish were overestimated by 21%, and male Chinook salmon were underestimated by 8% while females were overestimated by 12%.

Received: February 9, 2002; Accepted: May 23, 2002

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Declining Size of Chinook Salmon Issue Reports

 2006 Chinook Weights, YRDFA Funded Data Collection Project at Rapids,
Discussion and Comparisons back to 2004, Stan Zuray

 What We Know About Changing Size of Fish:
YR Panel Joint Technical Committee (JTC) Whitepaper, 2006

 Size-Selective Fishing and Its Implications for Salmon 
Presented by Jeff Hard, Conservation Biology Division, Northwest Fisheries Science Center

 Tanana Conservation Outreach 2004-2005, Student Data Collection Project Report (graphs and tables related to Chinook length, sex and weight taken on the Yukon River)

 Alaska Fisheries Technical Report Number 87, 'Chinook Salmon Age, Sex, and Length Analysis from Selected Escapement Projects on the Yukon River 2005

 Presentation - Chinook Salmon Age, Sex, and Length Analysis from Selected Escapement Projects on the Yukon River by Karen Hyer and Cliff Schleusner, Office of Subsistence Management, USFWS

 Changing Size of Chinook - Article by Chris Talbot Associated Press Writer, The Associated Press, Fairbanks, Alaska Jan 6, 2006