Steelhead deaths in Pescadero are still a mystery

Every year, juvenile steelhead die in Pescadero Marsh before they are able to make it out to sea. Last year, 300 died. This year, there is no accurate count.  Steelhead are a threatened species that comes to the creek to spawn every year. According to the County Times, it’s unclear whether the fish are dying from natural or human causes, but disease has been ruled out.

Every spring, adult steelhead swim upstream to spawn. As water levels decrease, a 40-foot sandbar forms on the beach, dividing stream from ocean and creating a brackish estuary rich in plankton for their newborn trout to feed. The first storms of winter break the sandbar open, delivering the young fish to the ocean and beginning the process anew.

The problem, explained Joanne Kerbavaz, a resource ecologist with State Parks, is that a portion of the young fish suffocate before they reach the ocean.

There are a number of theories as to why, one of which has to do with the movement of water in the marsh. The water contains saltwater on the bottom and freshwater on top. When the sandbar breaks and the marsh flows out to sea, the water gets mixed together and the fish lose their oxygen. Another hypothesis is that naturally occurring hydrogen sulfides are stirred up off the bottom of the lagoon, killing the fish.

There is some concern that the die-off may be the result of changes made over the last 20 years. California State Parks has been working for twenty years to restore the creeks. They have removed numerous farmers’ levees built to prevent flooding. In 1991, Caltrans built a bridge over the watershed.