. Bulletin. Science. 28 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Alamo River Fig. 1. Sampling sites at the Salton Sea. R—river mouth; N—nearshore; P—pelagic. Arrow in- dicates station where data were collected for assessing diel patterns in tilapia stomach acidity. brown, for well assimilated food. No identification of organisms from intestines was attempted because of the advanced stage of digestion. Stomach contents were grouped into sediment, plant material (macrophytes only), and Salton Sea biota. Sediment comprised sand, clay, and microbial or- ganisms (not identified) and was used as a s
. Bulletin. Science. 28 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. Alamo River Fig. 1. Sampling sites at the Salton Sea. R—river mouth; N—nearshore; P—pelagic. Arrow in- dicates station where data were collected for assessing diel patterns in tilapia stomach acidity. brown, for well assimilated food. No identification of organisms from intestines was attempted because of the advanced stage of digestion. Stomach contents were grouped into sediment, plant material (macrophytes only), and Salton Sea biota. Sediment comprised sand, clay, and microbial or- ganisms (not identified) and was used as a surrogate for determining foraging location within the water column. Macrophytes drift into the Salton Sea from land via the incoming tributaries. Marcophytes were considered because they are a potentially important tilapia food source, especially in the river mouth area. Salton Sea taxa were grouped further into benthos, zooplankton, and phytoplankton. Zooplankton were barnacles (planktonic stages of Balanus amphitrite), copepods (mostly Cyclopods spp), and rotifers (mostly Brachionus spp). Nematodes (mostly Spilophorella spp), ciliates, and pile worms (Neanthes succinea) were the benthic group. Phytoplankton consisted of dinoflagelates and diatoms. Groups of organ- isms other than the above were observed, but not analyzed due to low (< 1%) frequency of occurrence. Percentages based on numbers of organisms within taxa were defined for analyses within those groups for each stomach. Analyses of seasonal and spatial variation in feeding were done independently for all groups. Percentages within taxa were averaged over individual fish to show taxa relative abundances according to space and season. Percentages, therefore, did not nec- essarily add to 100%. As a hypothetical example, if one fish had 100% of diatoms and another an empty stomach, the stomach content proportion was 50% diatoms for both fish taken together. The same rationale applies to proportions within groups
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