In the open ocean, Pacific salmon use several navigation systems to return to the exact site of their origins, including sensitivity to polarized light, temperature and salinity gradients. The mineral and organic characteristics of a particular stream are monitored by salmon using a highly developed olfactory sense (smell discrimination has been measured in parts per trillion; Smith 1985). Specific homing to a natal spawning site is believed to be under genetic as well as environmental influences (Hara 1993). The classic study of Waddell Creek by Shapovalov and Taft in 1954 documented an average spawning run of 247 coho per year for the decade from 1930-1940. Current runs in this creek have declined to less than 10 fish per year (Hope 1993). Wild coho in the San Lorenzo River once numbered over 2,000 fish. San Lorenzo's run of wild salmon is probably gone, having been replaced by a small population of hatchery-raised fish (Schmidt 1994).
The recent petition to list coho salmon throughout its range in Washington, Oregon, Idaho, and California as endangered under the federal Endangered Species Act (National Marine Fisheries Service 1994), considered evolutionarily significant units (ESUs) of coho as listable "species" under the act (see Waples 1991 for definition of an ESU). In their review of population viability and genetic integrity, the NMFS considered wild coho populations from Punta Gorda south to the San Lorenzo River a separate ESU that was in danger of extinction. Genetic data indicated that most samples from this region differ substantially from coho north of Punta Gorda (Bartley et al. 1992; Nielsen 1994). The timing of spawning runs were very late (peaking in January), timed to coincide with single, brief flow events. The strong and consistent coastal upwelling in this region results in a relatively productive near shore marine environment, affecting the ocean migration distance within this ESU. Federal status review of coastal coho will be determined by the National Marine Fisheries Service some time during 1996-1997 (see Special Status Table).
Dams which block most rivers in California have contributed significantly to the decline in abundance and distribution of the various life histories of California chinook. Genetic data, however, indicates that reproductive isolation among the temporal spawning runs in the Sacramento River chinook remains intact, despite a significant drop the number of returning spawners (Nielsen et al. 1994c; Hedrick et al. 1994). The MBNMS plays a significant role in the life history of chinook along the California coast, providing near shore habitat and forage opportunities contributing to the growth and successful survival of this anadromous species.
Chinook remain the most economically important species of Pacific salmon in California because of the valuable sport and commercial fisheries they support. The recent declines in salmon abundance has been critical in California's chinook stocks. With historic runs at an all time low, one subspecies, the Sacramento River winter-run chinook, is currently listed at endangered under the U.S. Endangered Species Act. A status review by the NMFS is underway for all chinook temporal spawning runs (winter-run, spring-run, fall-run and late fall-run) that utilize the MBNMS waters.
The ability of the southern steelhead to exist and to sustain such unique genetic diversity, is probably contingent on special adaptations to the extreme environmental conditions found in this area (Nielsen et al. 1994a). Juvenile steelhead throughout California must deal with inhospitable warm water temperatures and dry stream reaches due to frequent drought conditions (Nielsen et al. 1994d). The periodic closure of the river mouth by sand bars in California coastal streams often prevents migration to and from the ocean environment (Goodwin et al. 1993), forcing steelhead to adopt extremely flexible life history schedules for smoltification and spawning.
A recent study of steelhead by the California Department of Fish and Game suggests that "the restoration of declining anadromous fish populations ....is intimately tied to the establishment of a new ethic for management of California's rivers and streams, an ethic that places a much higher priority on the continuance of essential physical, biological, and ecological processes" (McEwan and Jackson 1994). I would like to suggest that the near shore ocean conditions play an equally important role in the restoration and survival of these important anadromous species, and that the MBNMS is critical to the preservation of the unique genetic and phenotypic diversity they represent.
Next - Section III. Selected Anadromous Fishes Resources
Anadromous Fishes Table of Contents
