Acoustic monitoring of the juvenile pink salmon food supply and predators in Prince William Sound, Alaska

Previous research has indicated that juvenile pink salmon survival in Prince William Sound is positively correlated with the abundance of the large-bodied copepods of the genus Neocalanus. Neocalanus serves both as a valuable food supply for the juveniles and as a prey-sheltering mechanism. In spring 2000, the Prince William Sound Science Center initiated annual monitoring of the spring abundance and distribution of both macrozooplankton and fish predator populations. The monitoring includes multiple frequency acoustic systems and zooplankton net tows. The program has now completed five years of measurements, and there have been four associated adult pink salmon returns. Pink salmon returns were found to be positively correlated with average plankton net catches of both large copepods and euphausids in the nursery year. Some data gaps prevented correlation between acoustic scattering and pink salmon returns, but both 420 kHz and 120 kHz backscatter were positively correlated with the plankton net catches of large copepods. The acoustic data also allowed detailed examination of the spatial trends of the plankton distribution. Patchiness was relatively low, which may explain why the net catches seemed to provide a reasonable measure of overall abundance. Some changes in the monitoring procedures may be necessitated by the indication that euphausid abundance may also be an important factor in pink salmon survival.