WETLANDS AND WATERSHEDS

The main channel of the slough extends in-land 7 km from the bay. Depth and width vary considerably with tidal height, but narrow and become shallower as one goes inland. Extensive mudflats fringe the main channel, and a network of tidal creeks meanders through the adjacent salt marshes.

Distribution and abundance of fishes from six sites (Figure 1) surveyed monthly in the mid-1970s to 1980 and repeated twice in the 1990s indicate that changes have occurred. In the 1970s fishes were more abundant in the main channel than in the tidal creeks. Both abundance and species diversity were highest near the slough mouth. The upper reaches of the main channel featured intermediate levels of diversity and abundance, and the tidal creeks had comparable diversity but the lowest mean abundance. Surveys in the 1990s documented abundances that were >70 percent lower than levels in the 1970s at the deep channel sites. Conversely, 1990s abundance was two to four times higher at most sites farther up the slough.

Overall species diversity appears to have decreased throughout the slough in the past twenty years. While the deep main channel stations once had higher numbers of species than the shallow upper slough stations, diversity is now similar and relatively low at all sites.

In the 1970s the fish assemblages differed considerably among stations, mainly by depth and distance from the ocean. Twenty years later, however, these geographical differences have disappeared. Fish assemblages in the lower main channel are mostly unchang-ed, but assemblages in the tidal creeks now resemble those of the lower slough. These changes in fish assemblages coincide with the continued erosion and scouring of the slough during the last twenty years, which has resulted in a geomorphology of the tidal creeks that is now more similar to the main channel.

As the main channel and tidal creeks of the slough continue to broaden and deepen, the species composition of fish predators and invertebrate prey apparently is being altered. From our interpretation of the studies on fishes of Elkhorn Slough from the 1970s to the present, it is obvious that changes in habitat significantly influence the distribution, abundance, and trophic patterns of the slough's fish assemblages.

For more information on the natural resources of Elkhorn Slough, visit this web site: www.elkhornslough.org.

--Mary M. Yoklavich
NOAA/NMFS Southwest Fisheries Science Center

--Gregor M. Cailliet
Moss Landing Marine Laboratories (MLML)

(The authors relied in part on the MLML M.S. theses of Dion Oxman and Dave Lindquist.)

Fecal Coliform Monitoring at Ocean Bathing Areas
Surfrider's Blue Water Task Force collects weekly data at up to twenty-four swimming and surfing sites along the Santa Cruz County coastline. The samples are tested for the presence of fecal coliform bacteria. The safe water contact level is 200 bacteria per 100 ml. In 216 samples taken, Surfrider recorded thirty samples (13 percent) that met or exceeded state standards for swimmable waters and thus reflected unsafe conditions.

Local Streams Meeting Water Quality Beneficial Uses
The Coastal Watershed Council monitors salmonid streams in Santa Cruz, San Mateo, and Monterey Counties. Data collected by the programs are compared to the water quality objectives for dissolved oxygen, pH, turbidity, conductivity, and temperature set by the RWQCB. Over the last three years, data from the stream monitoring programs have shown that, of the seven stream systems regularly monitored, the majority are meeting the water quality objectives for cold water fisheries. Incidences when water quality objectives were not met accounted for less than 2 percent of 1,071 sampling events. Failing parameters included temperature, pH, dissolved oxygen, and turbidity. Natural factors usually played a role in objectives not being met.

Urban Watch Program Identifies Detergents as Primary Urban Contaminant
The Urban Watch Monitoring Program monitors storm drain outfalls for common urban runoff pollutants including detergents, phenols, copper, chlorine, ammonia, oil sheen, and sewage. Over the program's last two years, detergent has been the primary pollutant

regularly identified in sampling events. In 1997, during 43 sampling events, detergents were present in 20 (46 percent) of the samples. In 1998, during 76 sampling events, detergents were present in 75 percent of the samples. The next most common contaminant was phenols, occurring in 6 percent of samples in 1997 and 11 percent of samples in 1998. Sewage was not recorded in any samples and oil sheen was present in 10 percent of samples in 1997 and 11 percent in 1998. Chlorine and ammonia did not occur in 1997 and occurred in 10 percent and 18 percent, respectively, of samples in 1998.

--Donna Meyers
Coastal Watershed Council

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