Matthew Birch Foster
Published: 2014
Total Pages: 38
Get eBook
From 2009 to 2012 a series of memos were written by Alaska Department of Fish and Game staff in Kodiak discussing reasons for the low runs of sockeye salmon to Karluk Lake that began in 2008 and persisted through 2011. Historical trends in escapement, run size, limnology, climate, and trends in fish size, age, and growth for Karluk Lake sockeye salmon were investigated. The authors emphasized the role that the small body size and low condition of outmigrating smolt in 2005 and especially 2006 likely played in determining marine survival and subsequent run strength. Major factors thought to cause the small size at smolt outmigration were decline of zooplankton biomass, decline in body size of the preferred sockeye salmon food source (Bosmina), decrease in Karluk Lake seasonal water temperatures, and overescapement. The suggested mechanism was that large escapements and favorable spawning conditions produced large numbers of fry for numerous years, which eventually overgrazed and reduced the number of zooplankton available to fry. Sockeye salmon fry then experienced slow growth and increased mortality, which led to poor condition (and fewer) smolts. Furthermore, it was predicted that Karluk would likely be depressed for a period of 3-5 years beginning in 2008. Data thus far remain consistent with the original hypothesis; however, the outlook appears to be one in which runs improve in 2012.