I think this is saying there are at least 2 Harrison River sockeye stocks, one of which spends very little time in freshwater and is rated not at risk, and another with perhaps a different life history. Anyone out there have some more info on this other stock?
Good question, Dave. Maybe the abbreviation "U/S" means "upstream" (from the Lake) spawners?
From: Canadian Science Advisory Secretariat Pacific Region Science Response 2016/021:
Pre-Season Run Size for Fraser River Sockeye Salmon 2016 http://www.dfo-mpo.gc.ca/csas-sccs/Publications/ScR-RS/2016/2016_021-eng.html
Summer Run Stocks
In most years, the Summer Run stocks dominate total Fraser Sockeye returns. Six stocks in this timing group are forecast using the standard suite of forecast models: Chilko, Late Stuart, Quesnel, Stellako and the recently added Raft and Harrison (Table 1A).
Harrison (Harrison-River Type CU): Recently re-assigned from Late Run Group to the Summer group Harrison Sockeye have a unique life history and age structure compared to other Fraser Sockeye stocks. They migrate to the ocean shortly after gravel emergence (most Fraser Sockeye rear in lakes for one year after gravel emergence prior to their ocean migration). After two to three years in the ocean, Harrison Sockeye return as three or four year old fish (most Fraser Sockeye return as four and five year old fish). Proportions of three and four year old Harrison recruits vary considerably annually, with four year old proportions ranging from 10% to 90% of total recruits (Grant et al. 2010). Odd brood years, on average, produce a higher proportion of four year old recruits, and even years produce a similar proportion of three year old recruits (Grant et al. 2010). Though the difference in odd versus even year age proportions is accounted for in the Harrison forecast models (MacDonald & Grant 2012), the extreme variation in age-at-maturity for Harrison Sockeye increases the level of forecast uncertainty for this stock.
Late Run Stocks
The Late Run consists of five forecasted stocks (Cultus, Late Shuswap, Portage, Weaver, and Birkenhead) and one miscellaneous stock (miscellaneous non-Shuswap including Harrison stocks that migrate downstream to Harrison Lake as fry to rear in this lake) (Table 1A);
Miscellaneous Harrison/Lillooet Lakes (Harrison (downstream)-L) The 2012 brood year EFS for the miscellaneous Harrison/Lillooet Lake stocks is 1,400 (Table 1B, column C). Populations included in this group include those that rear in the Harrison-Lillooet Lake system, and are not included in the Harrison or Birkenhead forecasts (Big Silver, Cogburn, Crazy, Douglas, Green, Pemberton, Pool, Railroad/Sampson, Ryan, Sloquet and Tipella Creeks).
Weaver (Harrison (U/S)-L CU) The 2012 brood year escapement for Weaver (400 EFS) was the smallest escapement on record, falling well below the cycle average (1968-2012: 18,300 EFS) (Table 1B, column C). Spawning success in Weaver Channel (89%) was similar to average (90%); however, spawning success in Weaver Creek (61%) was well below average (87%). Early freshwater survival in the 2012 brood year (1,000 fry/EFS) was below average (1966-2012 average: 1,600 fry/EFS), and the resulting juvenile abundance (470,000 fry) was also below average (1966-2012 average: 31 million fry). The 2011 brood year escapement for Weaver (24,500 EFS) was larger than the cycle average (1967-2011: 18,300 EFS) (Table 1B, column D). Early freshwater survival in the 2011 brood year (1,600 fry/EFS) was identical to average (1966-2012 average: 1,600 fry/EFS), and juvenile abundance (39 million fry) was above average (1966-2012 average: 31 million fry).
Average (geometric) four year old survival (R/EFS) for Weaver Sockeye has been variable, with the largest peak of 41.8 R/EFS occurring in the late-1960 brood years (four year average at peak). This stock has not exhibited systematic survival trends through time (Grant et al. 2011; Peterman & Dorner 2012). Similar to other stocks, however, Weaver exhibited one of its lowest survivals on record (2.6 R/EFS) in the 2005 brood year (i.e. 2009 four year old return year) (Table 2, columns B to E; Figure 3). In the most recent generation (2007 to 2010 brood years), the average survival (15.0 R/EFS) has been above the long-term average (12.2 R/EFS). Amongst all Fraser Sockeye stocks, this stock exhibited exceptionally poor returns in 2015. Interestingly, this stock was not detected at the Mission smolt program or Strait of Georgia surveys in the 2013 outmigration year in expected proportions based on brood year escapements (DFO 2015b). The 2011 brood year fry assessments indicated average egg-to-fry survival, so one potential hypothesis is that lake rearing conditions were poor in this brood year, assuming there was no bias in the Mission or SOG sampling programs in 2013. These fish would have moved into Harrison Lake 1.5 years after the large Meager Creek landslide in 2010.