Evaluating the Efficacy of the Calcein Solution SE-Mark Batch Mark on Salmon Fry to Measure Trap Efficiency and Evaluate Estimator Assumptions

With many Pacific salmon and steelhead stocks in decline, monitoring of outmigrating juvenile salmonids by city, state, federal and tribal agencies is on the rise. Many of these stocks are listed as threatened and endangered under the Endangered Species Act. There are two methods used to evaluate freshwater production, census counts or mark-recapture experiments. Census counts are difficult if not impossible in most situations to conduct and consequently are rarely used. Whereas mark-recapture experiments with defined testable assumptions are widely used to estimate abundance. However, only one batch mark is available for sub-yearling outmigrant mark-recapture trap efficiency trials making it impossible to differentiate between mark groups and thus test estimator assumptions. Preliminary field trials using calcein as an alternate batch mark has shown some potential as a non-lethal and non-invasive method for marking large numbers of fish. Although the calcein mark was easily applied, a specialized reader with a small field of view was required to distinguish between marked and unmarked fish making it difficult and inefficient to use when processing large (>1000) catches. Building on what we learned in the initial trials we hope to eliminate the difficulties associated with mark recognition and recovery by testing whether a combination mark of Bismarck Brown dye and calcein is effective. Specifically (1) can a combination calcein and Bismarck Brown mark be used as a non-invasive easily recognizable batch-mark for partial capture trap mark-recapture efficiency trials in the field, (2) evaluate the quality of a combination calcein and Bismarck Brown mark versus conventional Bismarck brown marks, (3) test if differentially marked fish are captured at similar rates to one another, and (4) use both Bismarck brown and a combination calcein and Bismarck Brown mark as differential marks to test closed population mark recapture estimator assumptions.