Indices of Early Life History Diversity as a High Level Indicator of Salmon Performance

One of the goals of ecosystem restoration in the lower Columbia River and estuary is to increase the life history diversity of salmon stocks and thereby improve population resiliency and aid recovery.  Regional stakeholders use high-level indicators to assess progress toward program goals.  We searched the literature for a suitable high-level diversity indicator for early life history (fry to smolt stages), but none was not apparent.  Therefore, we developed a suite of ELHD indices using a binary, matrix-based approach where presence/absence data from beach seine catches are used to compute the proportion of incidences fish were present in the catch out of the total possible incidences.  For example, Chinook salmon over 4 size classes and 12 monthly sampling episodes would have 48 total possible incidences.  If we caught at least one Chinook salmon in 2 of 4 size classes during every one of the 12 months, the ELHD index would be 0.5.  The factors we investigated included size, timing of migration, habitat associations, and genetic stock groups.  We examined the ELHD indices with data from monthly sampling with beach seines in the LCRE in 2008, 2009, and 2010.  Index calculations indicated that compared with other salmon species, Chinook salmon had the highest length-month index values.  ELHD indices were higher for unmarked than marked Chinook salmon and higher for the Cottonwood Island site (rkm ~115) than the Sandy River delta site (rkm ~200).  We recommend development of a more integrative ELHD index than the simple presence/absence approach to incorporate information from and to allow expansion and constriction across space and time in the lower Columbia River and estuary depending on specific management applications of the ELHD as a high-level indicator of salmon performance.