Salmon Carcass Movements in Forest Streams

Abstract

AbstractThe movements of salmon carcasses over time were studied in two forest streams in the context of a large‐scale salmon carcass supplementation program. The objectives were to assess both the level of treatment after stream flows had displaced carcasses and to evaluate whether the magnitude of carcass movements outside of a given reach could be predicted. The movements of hand‐placed, radio‐tagged salmon carcasses were studied and compared with those of flagged carcasses dropped by helicopter. Repeated surveys showed that, in both streams, radio‐tagged carcasses moved, on average, only a short distance, even after high‐flow events, the maximum observed movement being 1.14 km after 77 d. In‐channel wood and slow‐water habitats contributed most to the retention of carcasses. The amount of wood that was incorporated into jams of medium and high complexity (including accumulated pieces of small wood) was the best predictor of the proportion of carcasses that would be retained within a given length of stream, whereas the amount of pool habitat contributed to a lesser degree. A particular high‐complexity debris jam, however, confounded the use of hand‐placed carcasses to predict the distribution of movements of helicopter‐dropped carcasses by retaining almost all carcasses that encountered it. As in other studies, our results demonstrate the importance of wood in retaining salmon carcasses and show that complexity in the form of branches and accumulated small wood makes wood jams effective carcass collectors.