An Investigation of Factors Affecting the Decline of Delta Smelt (Hypomesus transpacificus) in the Sacramento-San Joaquin Estuary

WILLIAM J. MILLER, BRYAN F. J. MANLY, DENNIS D. MURPHY,
DAVID FULLERTON, and ROB ROY RAMEY

The delta smelt is a fish native to the Sacramento-San Joaquin Estuary and is protected under federal and California Endangered Species Acts. Record low abundances have occurred since 2004. The authors address three questions: What effects do environmental factors have on abundance? Do factors that may have indirect effects provide an explanation of abundance changes? How are these effects best accounted for?