San Francisco Estuary and Watershed Science

For many imperiled species, comparisons between wild and cultured populations are invaluable for informing conservation measures, though opportunities to do so may be rare. In this study, we asked whether spawning between and among wild and cultured Delta Smelt varies in terms of behavior or resulting egg fertilization success. We conducted two laboratory experiments in which we allowed wild females to spawn with wild males (wild × wild) and cultured females to spawn with wild males (cultured × wild). Due to small sample sizes, we qualitatively compared our results to published studies of all cultured Delta Smelt (cultured × cultured). Across all three groups, Delta Smelt exhibited spawns that were similar in sequence and manner, varied widely in diel timing, and occurred predominantly between a single female and one or two males. Egg fertilization success was higher in wild × wild trials than in cultured × wild ones, but both fell within the wide range observed among cultured × cultured fish. Thus, spawning was generally similar between cultured and wild Delta Smelt, whether they were in same- or mixed-origin groups. These findings provide rare insight into the spawning behavior of wild Delta Smelt and inform ongoing conservation efforts.