Hydrographic observations in Elkhorn Slough and Moss Landing Harbor, California, October 1970 to November 1971. Annual report, Part 3, July 1972

In October 1970, Moss Landing Marine Laboratories began an observational program to determine/the seasonal changes in the water chemistry of Elkhorn Slough and Moss Landing Harbor. This data report contains the first year of data (October 1970 - November 1971). These data are of immediate interest in determining the flushing and mixing mechanisms of the slough and in establishing the effect that local domestic and industrial effluents have on the distribution of these chemical parameters. (Document contains 78 Pages)

The hydrography of Elkhorn Slough: a shallow California coastal Eebayment: Annual Report, Part 2, 1973

From October 1970 through February 1972, temperature, salinity, dissolved oxygen, secchi depth and five major nutrients were observed at approximately monthly intervals in Elkhorn Slough and Moss Landing Harbor. In addition, similar hourly observations were made during two tidal studies during the wet and dry seasons. From the salinity measurements during the summer, a salt balance for Elkhorn Slough is formulated and rnean eddy diffusion coefficients are determined. The diffusion nlodel applied to longitudinal phosphate distributions yielded a mean diffusive flux of 12 kg P04/day (140 pg-at/m^2/day) for the area above the mean tidal prism. Consistent differences, apparently due to differing regenerati on ra tes, were observed in the phosphate and nitrogen distributions. Bottom sediments are proposed as a possible source for phosphate and as a sink for fixed nitrogen. Dairy farms located along central Elkhorn Slough are apparently a source for reduced nitrogen. During summer, nitrogen was found to be the limiting nutrient for primary production in the upper slough. Tidal observations indicated fresh water of high nutrient concentration consistently entered the harbor from fresh water sources to the south. This source water had a probable phosphate concentration of 40 to 60 ug-at/l and seasonally varying P:N ratio of 1:16 and 1:5 during the winter and summer respectively. Net production and respiration rates are calculated from diurnal variations in dissolved oxygen levels observed in upper Elkhorn Slough. Changes in phosphate associated with the variations in oxygen was close to the accepted ratio of 1:276 by atoms. Document is 88 pages.

Ecologic and hydrographic studies of Elkhorn Slough, Moss Landing Harbor and near coastal waters, July 1974 to June 1976

In July 1974, we began a two-year baseline study of the Moss Landing Elkhorn Slough marine environment for Pacific Gas and Electric Company as mandated by the Coastal Commission. The original proposal included strong recommendations for more complete oceanographic studies and a third year of data collection. These further studies were not funded. This report is divided into three sections: oceanography, benthic invertebrate ecology and fish and zooplankton ecology. (PDF contains 480 pages)

A Baseline Study of the Moss Landing/Elkhorn Slough Environment

In July, 1974 we began a baseline study of the Moss Landing-Elkhorn Slough marine environment for PG&E as mandated by the Coastal Commission. This report constitutes results of the first year's program. It is divided into three sections, oceanography, benthic invertebrate ecology, and fish and zooplankton ecology. (PDF contains 226 pages)

A 30-Year History of Tide and Current Measurements in Elkhorn Slough, California

Elkhorn Slough was first exposed to direct tidal forcing from the waters of Monterey Bay with the construction of Moss Landing Harbor in 1946. Elkhorn Slough is located mid-way between Santa Cruz and Monterey close to the head of Monterey Submarine Canyon. It follows a 10 km circuitous path inland from its entrance at Moss Landing Harbor. Today, Elkhorn Slough is a habitat and sanctuary for a wide variety of marine mammals, fish, and seabirds. The Slough also serves as a sink and pathway for various nutrients and pollutants. These attributes are directly or indirectly affected by its circulation and physical properties. Currents, tides and physical properties of Elkhorn Slough have been observed on an irregular basis since 1970. Based on these observations, the physical characteristics of Elkhorn Slough are examined and summarized. Elkhorn Slough is an ebb-dominated estuary and, as a result, the rise and fall of the tides is asymmetric. The fact that lower low water always follows higher high water and the tidal asymmetry produces ebb currents that are stronger than flooding currents. The presence of extensive mud flats and Salicornia marsh contribute to tidal distortion. Tidal distortion also produces several shallow water constituents including the M3, M4, and M6 overtides and the 2MK3 and MK3 compound tides. Tidal elevations and currents are approximately in quadrature; thus, the tides in Elkhorn Slough have some of the characters of a standing wave system. The temperature and salinity of lower Elkhorn Slough waters reflect, to a large extent, the influence of Monterey Bay waters, whereas the temperature and salinity of the waters of the upper Slough (>5 km from the mouth) are more sensitive to local processes. During the summer, temperature and salinity are higher in the upper slough due to local heating and evaporation. Maximum tidal currents in Elkhorn Slough have increased from approximately 75 to 120 cm/s over the past 30 years. This increase in current speed is primarily due to the change in tidal prism which has increased from approximately 2.5 to 6.2 x 106 m3 between 1956 and 1993. The increase in tidal prism is the result of both 3 rapid man-made changes to the Slough, and the continuing process of tidal erosion. Because of the increase in the tidal prism, the currents in Elkhorn Slough exhibit positive feedback, a process with uncertain consequences. [PDF contains 55 pages]

Long-term Trends in Catch Composition from Elasmobranch Derbies in Elkhorn Slough, California

Long-term trends in the elasmobranch assemblage of Elkhorn Slough, Monterey Bay, California, were analyzed by documenting species composition and catch per unit effort (CPUE) from 55 sport fishing derbies that occurred during May, June, and July, from 1951 until 1995. The most abundant species (bat ray, Myliobatis californica; shovelnose guitarfish, Rhinobatos productus; and leopard shark, Triakis semifasciata) were also analyzed for size-weight relationships, trends in size class distribution, stage of maturity, and sex ratios. Changes in species composition over the course of the derbies included the near complete disappearance of shovelnose guitarfish by the 1970’s and a slight increase in the abundance of minor species (mainly smoothhounds, Mustelus spp., and thornback, Platyrhinoidis triseriata) starting in the mid 1960’s. The relative abundance of bat rays in the catch steadily increased over the years while the relative abundance of leopard sharks declined during the last two decades. However the average number of bat rays and leopard sharks caught per derby declined during the last two decades. Fishing effort appeared to increase over the course of the derbies. There were no dramatic shifts in the size class distribution data for bat rays, leopard sharks, or shovelnose guitarfish. The catch of bat rays and leopard sharks was consistently dominated by immature individuals, while the catch of shovelnose guitarfish was heavily dominated by adults. There was evidence of sexual segregation in either immature or mature fish in all the species. Female bat rays and shovelnose guitarfish were larger than their male counterparts and outnumbered males nearly 2:1. Female and male leopard sharks were more nearly equal in size and sex ratio. Changes in species composition are likely due to fishing pressure, shifts in the prevailing oceanographic conditions, and habitat alteration in Elkhorn Slough. The sex ratios, stage of maturity, and size class distributions provide further evidence for the theory that Elkhorn Slough functions as a nursery habitat for bat rays and leopard sha

Sea otter predation and the distribution of bivalve prey in the Elkhorn Slough National Estuarine Research Reserve

The California sea otter population is gradually expanding in size and geographic range and is consequently invading new feeding grounds, including bays and estuaries that are home to extensive populations of bivalve prey. One such area is the Elkhorn Slough, where otters have apparently established a spring and summer communal feeding and resting area. In anticipation of future otter foraging in the slough, an extensive baseline database on bivalve densities, size distributions, biomasses, and burrow depths has been established for three potential bivalve prey species, Saxidomus nuttalli, Tresus nutallii, and Zirphaea pilsbryi. In 1986, the Elkhorn Slough otters were foraging predominately at two areas immediately east and west of the Highway 1 bridge (Skipper's and the PG&E Outfall). Extensive subtidal populations of Saxidomus nuttalli and Tresus nuttallii occur in these areas. Shell records collected at these study areas indicated that sea otters were foraging selectively on Saxidomus over Tresus. The reason for this apparent preference was not clear. At the Skipper's study site, 51% of the shell record was composed of Saxidomus, yet this species accounted for only 16% of the in situ biomass, and only 39% of the available clams. Tresus represented 49% of the shell record at Skipper's, yet this species accounted for 84% of the in situ biomass and 61% of the available clams. There was no difference in mean burrow depth between the two species at this site so availability does not explain the disparity in consumption. At the PG&E Outfall, Saxidomus represents 66% of the in situ biomass and 81% of the available clams, while Tresus accounts for 34% of the in situ biomass and 19% of the available clams. Saxidomus accounts for 96% of the shell record at this site vs. 4% for Tresus, again indicating that the otters were preying on Saxidomus out of proportion to their density or biomass. High densities and biomasses of a third species, Zirphaea pilsbryi, occur in areas where sea otters were observed to be foraging, yet no cast-off Zirphaea shells were found. Although it is possible this species was not represented in the shell record because the otters were simply chewing up the shells, it is more likely this species is avoided by sea otters. There were relatively few sea otters in the Elkhorn Slough in 1986 compared to the previous two years. This, coupled with high bivalve densities, precluded any quantitative comparison of bivalve densities before and after the 1986 sea otter occupation. Qualitative observations made during the course of this study, and quantitative observations from previous studies indicate that, after 3 years, sea otters are not yet significantly affecting bivalve densities in the Elkhorn Slough.

Report of the marine work at Hopkins Marine Station, Pacific Grove, California during the six-week period from June 25 to August 5, 1938

The primary objective in doing this work was to become acquainted with as many forms as possible of the marine fauna of the intertidal zone and if possible to determine some of the environmental relationships which exist in as many different types of habitats as possible. Due to limited amount of time spent in this study no very intensive work could be done and only a general survey was made of the more conspicuous forms of life which were encountered. Most of the work consisted of collecting and observing animals in the tide pools during periods of low tides. The animals collected were then taken to the laboratory and observed and determined as to species. Notes were taken as to place, time, and situation under which the animals were found. As many different types of habitats as possible were visited which included rocky intertidal areas of Mussel Point, Point Pinos, Lighthouse Point, Pescadero Point and Carmel Point just east of Carmel Beach. Sandy beaches were visited at Monterey Beach, Carmel Beach and Asilomar Beach. A marine estuary habitat was visited at Elkhorn Slough. More than two hundred species were identified and observed during this six-week period. A rather hasty population study was made of the eelgrass, Phyllospadix, of the intertidal zone at Mussel Point and of an algae, Gigartina caniculata, which grows at the level just above the eelgrass.