Fraser River Sockeye Fisheries and Fisheries Management - Cohen ...

eturned in 2010 instead, but that would be evidenced mainly by detecting changes in the agecomposition of various spawning stocks, if the estimates are reliable.In light of the above, it is recommended that the authors consider making adjustments to somesections and passages throughout the report, and then adjusting the executive summaryaccordingly.LGL Response: Information on the age composition of catches and adult returns isroutinely collected by the PSC. The reviewer’s hypothesis regarding a shift in the agecomposition (2009 four year olds delaying their return until 2010) has been assessed byPSC scientists. The age composition of the 2010 returns did not show a higher than normalportion of age 5 returns. Rather, the age-5/2 proportion was unusually low (Steve Latham,PSC Biologist, pers. comm.). Scale-based age estimates are highly reliable for Frasersockeye, especially for fishery samples from marine or lower river areas. Sockeye ages inmarine samples are often compared to those derived from an ADF&G laboratory in Alaskaand, except for some difficult ages (e.g., sockeye that don't rear in lakes), there is excellentagreement among independent estimates. Sampling was more comprehensive in 2010 thanin any other year (over 5,000 matched samples from marine areas and over 4,000 from inriverfisheries). A contractor has examined otoliths collected from spawning grounds in2010 and these independent age estimates confirm the low proportion of age-5/2 sockeyeprovided by our scale laboratory in-season. In addition to the information from these agesamples, it should be noted that over 70% of the 2010 return can be attributed to one lake,Shuswap, and the number of age-4 sockeye expected to return to Shuswap Lake in 2009(off-cycle year) was small. The stocks that should have carried the returns in 2009 wereChilko (record smolt output in 2007) and Quesnel (dominant cycle). Quesnel was a smallplayer in the 2010 return, especially considering 2010 is its sub-dominant cycle. Therewere no jacks observed for Quesnel in 2008, and the age composition of Quesnel in 2010comprises less than 5% age 5 sockeye. There is no evidence of good production of Quesnelsockeye from the 2005 brood year. For Chilko, the age composition in 2010 was over 97%age-4/2 (the vast majority) and age-5/3 sockeye. These age-4/2 and age-5/3 fish went to seain 2008 (Chilko Lake’s second highest smolt migration on record) and were not part of theforecast for the 2009 return. The preliminary estimate of the 2010 return rate of 2008Chilko smolts is average. In summary, available data support the conclusion that the mainreason for the large run of Fraser River sockeye in 2010 is the strong return of four-yearoldsockeye (particularly from Shuswap Lake). The data do not support the hypothesisthat the large 2010 run resulted from sockeye expected to return in 2009 returning at age-5in 2010 instead (Steve Latham, pers. comm.).M-25