page_title: Ecology of the San Francisco Estuary
section_title: Fish
hierarchical_section_title: Ecology of the San Francisco Estuary / Consumers / Fish
caption_attribution_description: English: A depiction of a shad fish, as taken from the author's published portfolio of prints in 1902. This print was published on p.&#160;130 of the First Annual Report of the Commissioners of Fisheries, Game, and Forests of the State of New York (1896).[1]
context_page_description: The San Francisco Estuary together with the Sacramento–San Joaquin River Delta represents a highly altered ecosystem. The region has been heavily re-engineered to accommodate the needs of water delivery, shipping, agriculture, and most recently, suburban development. These needs have wrought direct changes in the movement of water and the nature of the landscape, and indirect changes from the introduction of non-native species. New species have altered the architecture of the food web as surely as levees have altered the landscape of islands and channels that form the complex system known as the Delta.
  Reconstructing a historic food web for the LSZ is difficult for a number of reasons. First, there is no clear record of the species that historically have occupied the estuary. Second, the San Francisco Estuary and Delta have been in geologic and hydrologic transition for most of their 10,000 year history, and so describing the "natural" condition of the estuary is much like "hitting a moving target". Climate change, hydrologic engineering, shifting water needs, and newly introduced species will continue to alter the food web configuration of the estuary.
context_section_description: Because fish are a taxonomically and morphologically diverse group, species vary in their trophic ecologies. In general, fish can be divided into four broad feeding categories: filter feeders, planktivores, piscivores and benthic feeders.
  Filter feeders strain the water column indiscriminately for small prey, typically phyto- and zooplankton. This category of fishes includes threadfin shad (Dorosoma petenense), American shad (Alosa sapidissima), inland silversides (Menidia beryllina), and anchovies (Engraulis mordax). Some evidence suggests that some of these species are food-limited due to the depressed levels of plankton after the introduction of the Amur River clam. Anchovies have left the LSZ in favor of more productive regions of the estuary in the San Pablo and Central Bays.
  Planktivores selectively prey upon individual zooplankton, such as copepods, mysids and gammarids. This group includes most fish larvae, delta smelt (Hypomesus transpacificus) and longfin smelt (Spirinchus thaleichthys), tule perch (Hysterocarpus traski), and salmon smolts. The delta smelt is of particular interest due to its endangered status. It may be food-limited, but the evidence is somewhat contradictory. Other factors, such as entrainment of eggs and larvae in the export pumping of fresh water from the Delta may also explain the decline.
  The main piscivore of the LSZ is the striped bass (Morone saxatilis), which was introduced in the 1890s and preys heavily upon native fishes. Striped bass are an important sport fishery in the San Francisco Estuary, and as such, represent a minor withdrawal of biomass from the estuary.
  Benthic, or bottom-dwelling, fishes include white sturgeon (Acipenser transmontanus), white catfish (Ameiurus catus), and starry flounder (Platichthys stellatus). Because of their habitat orientation, they feed primarily on epibenthic organisms such as amphipods, bay shrimp, and bivalves. These fish are known to feed at least occasionally on the Amur River clam, which would represent one of the few channels for energy flow from that species, except for detrital production.
  The sole commercial fishery in the LSZ is for bait shrimp. There are a variety of sports fisheries that represent a minor flow of carbon, but significant flows of capital to local economies around the estuary. Most of the recreational fisheries surround striped bass, sturgeon, and introduced fresh water basses in the freshwater Delta. This paucity of fisheries makes the San Francisco Estuary unique. Nearly all estuaries worldwide support at least remnants of significant fisheries. The San Francisco Estuary at one time supported major fisheries for salmon, anchovies, and Dungeness crabs until the 1950s. The demise of these fisheries was probably due more to habitat loss than overharvesting.
caption: Pregnant American shads compete for food with the Amur River clam.
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