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

enefited from improved technologies and research in recent years (Xie et al. 2005, 2007,2008).Prior to 2004, the Mission estimates were derived using fixed and mobile single beamhydroacoustic systems. A fixed side-scan system was deployed on the south bank whilethe mobile downward-looking system was operated from a vessel during cross channeltransects. Split-beam hydroacoustic systems were tested in 2002 and 2003 and have beenthe primary method for producing the official Mission estimates since the beginning ofthe 2004 sockeye season. 2006 was the first year that an independent side-scan splitbeamsystem was fully operational on the north shore (i.e., “right bank”) for the entiresockeye escapement period and a DIDSON system was tested at the Mission site.DIDSON hydroacoustic systems have been tested at a variety of locations and proven tobe a superior system for enumerating migrating salmon at Mission and Qualark duringperiods of peak abundance.Qualark Hydroacoustic SystemThe Qualark Creek hydroacoustic monitoring site is located on the Fraser mainstem 15km north of Hope, B.C. and 95 km upstream from Mission hydroacoustic site. Themedian travel time for adult sockeye migrating between Mission and Qualark is 2.9 daysfor Summer-run stocks and 3.5 days for Late-run stocks (Robichaud et al., in prep.). TheQualark site was initially developed using split-beam systems between 1993 and 1998.The site was not operated for 10 years due to funding constraints and the high personnelcosts associated with operating the split-beam technology. In 2008, DIDSON sonarsystems were tested at the site and proved to be a reliable method and that was easier touse and less costly to operate than the split-beam system (Enzenhofer et al. 2010).DIDSON systems were deployed on both banks of the Fraser River at Qualark in 2009and 2010 and provided daily estimates of the numbers of salmon passing the site thatwere used in-season for comparison with the Mission estimates. Species composition atthe Qualark site is determined using 30 m gillnet drifted from 150 m upstream of the siteto 700 m downstream, six times each day. In 2009, the test fishery mesh sizes andmethodology were modified based on advice from the PSC to ensure that the sample wasrepresentative of the salmon passing the Qualark site at the time of sampling. The meshsizes used included 4, 4 ¾, 5 ¼, 5 ¾, 6 ¾ and 8 inch (stretched mesh). Further details onthe Qualark hydroacoustic system and test fishing methods can be found in Enzenhofer etal. (2010).91