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Long term and recent trends of fishes and invertebrates in Suisun Marsh

Center for Watershed Sciences John Muir Institute of the Environment


Suisun Marsh, at the geographic center of the San Francisco Estuary, is important habitat for alien and native fishes. The University of California, Davis, Suisun Marsh Fish Study has systematically monitored the marsh\textquoterights fish populations since 1980. The purpose of the study has been to determine the environmental factors affecting fish abundance and distribution, especially in relation to water management activities. Otter trawl catches of native fishes declined considerably from the study\textquoterights beginning until about 1995; since then, it has stabilized somewhat at relatively low levels. Although the trend was less severe, otter trawl catches of alien fishes also declined until the early 1990s. Since the study\textquoterights inception, otter trawl catch of alien fishes has been highly variable, primarily due to erratic recruitment and invasions of new species. Beach seine catch has gradually increased over the study\textquoterights history, which has been mainly the result of rising Mississippi silverside (Menidia audens) numbers. Both 2008 and 2009 were dry years, although Delta outflows remained higher and more variable later in 2009. In 2008, 286 otter trawls, 19 midwater trawls, and 76 beach seine hauls were conducted. Fish per otter trawl was the second lowest recorded in the study\textquoterights history, which was partially due to the negative effects of salinity and lack of flooding on reproduction. However, many fishes that declined in otter trawls [e.g., yellowfin goby (Acanthogobius flavimanus), shimofuri goby (Tridentiger bifasciatus), striped bass (Morone saxatilis)] became much more abundant in beach seines. Additionally, only 14 individual fish were captured in midwater trawls, catches of 4 plankton-feeding macroinvertebrates declined in otter trawls, and the abundance of mysids was very low. In 2009, 256 otter trawls and 75 beach seines were conducted. Relative to 2008, fish per otter trawl increased while beach seine catches declined, mainly due to the Table 2 Annual adult Eriocheir sinensis CPUE and estimated total salvage, 1996-2009. Bay Study CPUE is from October (year) to March (year+1), Suisun Marsh CPUE is from July to December, and Central Valley Project (CVP) and State Water Project (SWP) fish facilities salvage is from September to November. Year Bay Study CPUE Suisun Marsh CPUE CVP salvage SWP salvage ($\#$/tow) ($\#$/tow) est. total est. total 1996 0.02 0.00 50 1997 0.34 0.07 20,000 1998 2.51 0.89 750,000 1999 0.96 1.08 90,000 34,000 2000 0.93 0.02 2,500 4,700 2001 3.25 0.17 27,500 7,300 2002 1.07 0.04 2,400 1,200 2003 0.15 0.00 650 90 2004 0.12 0.00 750 370 2005 0.01 0.00 0 18 2006 0.00 0.00 12 0 2007 0.00 0.00 0 0 2008 0.00 0.00 0 0 2009 0.00 0.00 0 0 IEP Newsletter 27 fishes that most strongly contributed to the catches in 2008: striped bass and yellowfin and shimofuri gobies. This was partially due to favorable outflows spanning the recruitment period of these fishes into the marsh. Similar to the otter trawl catch of fish, catch trends of 3 of the 4 macroinvertebrates increased from 2008 to 2009, and large mysid catches co-occurred with high catches of small fishes. Consequently, catches of 2008 and 2009 appeared to be largely determined by the magnitude, variability, and timing of Delta outflows and the abundance of pelagic food supplies.

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