Late last year the State Water Contractors hosted a first-ever Longfin Smelt Science Symposium on in Sacramento. The meeting featured and was attended by all researchers with first-hand and on-the-water experiences with the species in a forum that addressed both its ecology and genetics. Information emerged that has direct and immediate application in the conservation of the fish.

The longfin smelt was listed as threatened by the State of California in 2009. The then Department of Fish and Game in its status review of the species, noted spare survey data and anecdotal records of the species across its coastal range from Alaska to just south of San Francisco Bay. The State relied particularly on longfin smelt records drawn from open-water fish surveys in San Francisco Estuary to support its decision to offer it protection. Those surveys showed dramatic declines in longfin numbers from peak levels in the 1970s and 1980s to its near absence in surveys since 2001. Clear at the time of the listing was that the habitats used by longfin smelt were not sampled in the generalized fish surveys. In fact, as mid-water trawls in the upper estuary were recording de minimis numbers of longfin smelt, the fish was appearing in large numbers in certain years in concurrent North Bay Aqueduct Plankton surveys. Over the past decade it has become increasingly clear that longfin smelt may not be imperiled as once thought.

The symposium presentations offered a breadth of current best available scientific information on longfin smelt, including –

  • Evidence from along the Pacific Coast indicates that populations from the Columbia River down to San Francisco Bay exchange genes, with fish from the southern populations passing genetic information northward, but apparently not vice versa. Those genetic ties call into question the assertion by the US Fish and Wildlife Service that longfin smelt in the San Francisco Estuary are a “distinct population segment” and warrant protection as a unique demographic entity.     
  • Survey returns that established that longfin smelt are not mostly restricted to the upper San Francisco Estuary and Sacramento-San Joaquin Delta but are frequent in and bay-ward of all the major tributaries into the bay. In wetter years longfin are abundant and spawning not only in the Suisun Marsh complex and along the Sacramento River above the confluence with the San Joaquin River, but in the wetlands and lower reaches of the Napa, Sonoma, and Petaluma rivers and adjacent San Pablo Bay in the north and Guadalupe River and Coyote Creek in the south bay. Records throughout the bay support the notion that longfin may reproduce in creeks and streams in every bay-side county.
  • Clarification that while a satisfying explanation for the decline of longfin smelt in “midwater” surveys is not at hand, emerging data show that those sampling schemes do not sample adequately the fish’s shallow, nearshore, and upstream habitats and miss the fish’s periods of crepuscular activity. While resource managers were wringing their hands over longfin smelt ostensibly disappearing from the estuary, it was apparently thriving just outside the midwater survey footprints., including areas outside of the Golden Gate. 
  • Longfin smelt are confirmed to now spawn in recently restored wetlands in the south bay fronting San Jose and neighboring cities, indicating targeted restoration efforts and management actions can contribute to increasing longfin numbers.    

This and other new information presented at the longfin smelt symposium has significant implication in management planning for the species. The state –https://www.wildlife.ca.gov/Conservation/Fishes/Longfin-Smelt — currently identifies a welter of environmental stressors acting on the fish: reduction in freshwater outflows; entrainment losses to water diversion; changes in food organisms; toxic substances; disease, competition, introduced species, and predation; and loss of genetic integrity. None of those factors has been demonstrated to be causing catastrophic losses of longfin smelt in the estuary.

Bay and Delta system expert Wim Kimmerer from the Romesburg Center in Tiburon, California, declared at the meeting that neither outflow through the Delta nor entrainment at the water export pumps in the south Delta appear to be factors limiting the population of longfin smelt in the San Francisco Estuary, indicating that conservation efforts should target other management options. Dr. Kimmerer’s declaration might serve to focus the attention of the state and federal resource agencies on the successful restoration of south bay marshlands and wetlands now contributing to the longfin population in San Francisco Bay.

Should conservation priorities continue to include actions targeting longfin smelt, lessons learned from restoration efforts in the south bay can be exported to other areas of the estuary, perhaps even those in the Delta, where longfin smelt and delta smelt might both benefit.

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Comments to: A new understanding of the status of longfin smelt and its conservation needs
  • February 24, 2021

    This waspretty beneficial material. Without a dobut I think this is well worth a bookmark, thanks

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