All water is not equal when it comes to fish habitat, and this is especially true in the varied salinity zones of the San Francisco Bay Estuary (the Estuary). For the protected species Delta and Longfin smelt, Delta Science Fellow Brittany Kammerer is uncovering the limits of just how much salt these fish can handle.
Smelt are thought to migrate and select their habitat based on water salinity, often preferring a low salinity zone, defined as ≤6 ppt. Little is known about how they adapt to the conditions in the Estuary, where freshwater flows are highly seasonal. These freshwater flows are also affected by California’s recent drought and high water diversion levels to provide water to industries, farms, homes and businesses throughout the state.
Recently, San Francisco Bay’s Estuary, the largest estuary on the west coast of the United States, has been rapidly changing. Several pelagic fishes of the Estuary have experienced a considerable decline since 2001; among these are the federally threatened Delta smelt and state threatened Longfin smelt, which have been subject to the changing habitat. Both species spawn in freshwater but transition into the dynamic estuary during the course of their life.
Kammerer, a postdoctoral researcher at UC Davis, has been conducting experiments to help predict the potential impacts of changing habitat location and conditions for smelt. She assessed the salinity tolerances and biomarkers (a.k.a. indicators) of salinity increases in smelt.
In her lab experiments at the UC Davis’ Fish Conservation and Culture Laboratory, Kammerer exposed Longfin and Delta Smelt larvae and juveniles to increases in water salinity. She found that both types of fish were able to survive salinity changes at these younger life stages.
Kammerer also tested how adult Delta Smelt adapted to salinity increases by identifying physiological biomarkers to salinity increases. After increases in salinity, adult Delta Smelt exhibited changes in chloride cells, the cells that secrete or absorb salt. Kammerer found that changes in chloride cells, body water content, and blood parameters could be used to monitor the fishes’ response to changing salinity conditions.
“I found that smelt of all life stages, and adult Delta Smelt in particular, are able to survive salinities of the low salinity zone very well, as well as higher salinities to about 10 ppt,” says Kammerer. “They also show classic physiological responses that support this and provide evidence of their acclimation to these salinities.”
To Kammerer, these results say the missing clue to smelt’s habitat preference in the Estuary may lie down another path. “It seems that smelt’s apparent habitat preference for salinities below 6 ppt is not due to their salinity tolerance, but some other factor in the estuary that may also be associated with this habitat,” she explains. “Delta smelt, at least, adapt quite well to a range of salinities, at least below 10 ppt.”
This is good news for an endangered fish trying to survive the challenges of drought and water diversions, but the Estuary is still changing.
“Since predicted increases in regional and global temperature may change the hydrology of the San Francisco Bay Estuary and Delta, it’s important that scientists address the influence of salinity as a habitat factor,” says Kammerer.
By knowing the timing and speed at which smelt can acclimate from fresh to salt water, and keeping an eye towards future changes, scientists and managers may be able to monitor and control Delta freshwater flows to maintain conditions that will keep smelt swimming for years to come.
Written by Caitlin Coomber and Deborah Seiler