Excessive or indiscriminat take by ocean based enterprises represents only a small percentage of the overall numbers of fish delivered to the sea. It must be concluded that these fish are dying in the estuary or during their sojourn in the ocean. Certainly there is less food in the estuary due to development, human endeavor and natural river alteration. Carrying capacities in these environments are further diminished by the large numbers of smolts returned to the river in bulk by barge. There have always been changing ocean conditions, predation levels and fluctuating food supplies, but the fish have always survived.
Logic leads to the dams themselves.
Statistics confirm the progressive decline of fish runs with the construction of each subsequent dam, indicating that although the fish are able to survive the out migration past the dams, there is something about that journey that leaves them unable to survive long enough to complete their cycle. Their condition when they enter the coastal zone leaves them unable to compete. Physical and physiological stress damage, nitrogen saturated, and slack water, limited natural imprinting and hatchery genetics all combine to create a devastating effect on anadromous fish. Only a dramatic change in their migration routes will improve their condition and substantially increase their chances for survival. Relatively small, but very expensive improvements such as surface collectors, flip lips and moving screens have helped, but they have not been enough to overcome the cumulative effects of eight dams.