Studies and analyses conducted from 2009-15 have demonstrated the spatially-stratified hydroacoustic counts can be combined with species composition data from the fishwheels and Whonnock test fisheries to produce scientifically defensible estimates of the number of sockeye and pink salmon that pass the Mission hydroacoustic site in odd-number years (Robichaud et al. 2010; English et al. 2016). In 2013 and 2015, fish length data derived from images acquired by imaging sonar DIDSON was used in mixture-model discrimination analysis to derive species composition estimates for the near-shore strata monitored by the DIDSON systems at the Mission hydroacoustic site (Grant et al. 2014). Substantial differences have been observed between the DIDSON length-based species composition estimates for near-shore strata and those derived from fishwheel samples (English et al. 2016). Both methods have their strengths and weaknesses. For the fishwheel, species should be identified accurately, but sockeye and pink salmon may not be equally vulnerable to the gear. For the imaging sonar systems, both species should be equally vulnerable to being observed in the image, but the measurement of lengths from the DIDSON images is less precise than manual measurements and the length distributions of sockeye and pink salmon are highly overlapped. To date, the PSC1 estimates of sockeye proportions derived from DIDSON length-based approach have tended to be higher than those derived from the fishwheel samples. Being a next generation of DIDSON, the adoptive resolution imaging sonar (ARIS) can provide a much higher down-range resolution than DIDSON for fish images. Through this project, we will assess the reliability of the ARIS length-based species composition estimates and further explore the potential causes of the discrepancies between ARIS and fishwheel based species proportions.

Our goal is to address the Fraser River Panel Priority #2, the examination of mechanisms affecting early survival of Fraser River Sockeye Salmon, as early marine life is expected to set recruitment dynamic patterns of Pacific salmon. In this two-year project, we propose to examine the factors influencing the size of Fraser Sockeye during their first year at sea, a hypothesized critical time in determining their survival, given that fish must be large enough to avoid predators and have sufficient reserves to survive their first winter (Beamish and Mahnken 2001). Currently, there is no consensus on the importance of size-selective mortality and compensatory growth as mechanisms regulating the mortality and abundance of Fraser River Sockeye Salmon.

We propose retrospective and comparative analyses of growth characteristics derived from the scales of two Fraser River stocks demonstrating contrasting patterns of freshwater and marine residence and, importantly, opposite trends in adult returns. Over the last decade Harrison (sea type) has had a high number of adult returns contrary to Chilko (lake type) Sockeye Salmon returns, which have been low. These stocks differ in their life-history in that Harrison fry outmigrate to sea ~ 2 months after Chilko smolts (Beamish et al. 2016).

Our goals are to: (a) evaluate the extent of size-selective mortality, (b) determine the factors influencing juvenile length at the end of their first year at sea, and (c) determine the factors influencing the number of returning adults.