Carcass Addition Does Not Enhance Juvenile Salmonid Biomass, Growth, or Retention in Six Northwestern California Streams

Abstract

Fisheries managers commonly consider the addition of salmon carcasses when seeking to enhance salmonid populations. However, the range of environmental conditions under which the technique is effective remains poorly defined. We addressed this issue by measuring the effects of wintertime addition of salmon carcasses on the biomass, growth, and retention of juvenile salmonids in an experiment that included two study reaches within each of six northwestern California streams. In the first 2 years of the study, half of the streams received carcasses in both study reaches; in the subsequent 2 years, we added carcasses only to the downstream reach in all six streams. For juvenile salmonid biomass, growth, and retention, the change in carcass distribution did not affect general patterns in the relationship of the upstream and downstream reaches within streams. Artificial addition of salmon carcasses during winter in streams similar to those we studied appears unlikely to benefit juvenile salmonids in the short-term; management alternatives focused on increasing escapement should probably take priority.