The first fish tracking arrays were deployed in the Salish Sea over a decade ago. These arrays have yielded a rich data set which have provided the first direct estimates of early marine-survival and migratory behavior for acoustic-tagged juvenile sockeye, Chinook, Coho and steelhead \u3e130 mm in fork length (FL). In spring of 2015, as part of the Salish Sea Marine Survival Project, the Pacific Salmon Foundation, the Ocean Tracking Network and Kintama Research deployed additional arrays in the Discovery Islands and Johnstone Strait (north of the Strait of Georgia) to provide higher resolution survival data. These new arrays use receivers that can detect VEMCO acoustic tags that transmit at 69 kHz, as well as new, smaller tags that transmit at 180 kHz. These new tags can be implanted into smaller salmon smolts (\u3e100 mm FL), but the disadvantage is reduced detection range and battery life. When designing the array, we considered the tradeoffs between detection efficiency, survival estimation, array design, and costs, and then tested the performance of the smaller tag by double-tagging 50 steelhead smolts with both tag types. We used high powered 69 kHz V9 tags to estimate presence because these tags have had excellent detection efficiency in past studies. The smaller 180 kHz V4 tag programming emulated the programming typically used to track small salmon smolts through the SOG. To estimate the detection efficiency of the smaller tag, we compared the number of 180 kHz ID codes to the number of 69 kHz ID codes detected on each array. The resulting detection efficiency of the V4 tag on the Discovery Islands sub-array was 74% (SE=0.10). Thus for the many salmon populations that migrate north through the Salish Sea (e.g. many Fraser River populations), it is now possible to estimate early-marine survival over a wider range of smolts sizes
