Elkhorn Slough

Elkhorn Slough flows nearly seven and a half miles inland through productive farm fields of Brussels sprouts and strawberries, thickets of yellow field mustard, red-stem filaree and lavender lupine. The slough is a meandering belt of tide flats, tidal creeks and marshes, all teeming with aquatic plant life. The uplands flanking the slough harbor coastal dunes, grasslands, oak woodlands and rare maritime chaparral with populations of four federally endangered plant species: Yadon's rein orchid, Santa Cruz tarplant, Monterey spineflower and sand gilia.

Elkhorn Slough is the second-largest remaining salt marsh in California, supporting an abundance of invertebrates that provide food for more than 100 species of fish and nearly 300 species of birds. The estuary's ever-changing environment is a nursery to some species, a lifetime home to others and a water purifier for the coast. On any day, you might spot sea otters hunting the rich waters or, satiated, lounging on their backs.

At high tide, sharks swarm in the slough's shallow waters where they feed, breed and give birth to their young. Five threatened or endangered species are found at Elkhorn Slough: the California brown pelican, California least tern, Santa Cruz long-toed salamander, southern sea otter and American peregrine falcon. Elkhorn Slough is one of the premier birdwatching sites in the western United States.

For more information visit the Elkhorn Slough Foundation website.

Olympia oysters once formed dense beds across California estuaries, but overharvesting and increased sedimentation have left the species functionally extinct in California. Today, only 1% of their historical population remains.

TNC is hard at work to recover native oyster beds, and we’re developing new approaches to address the unique challenges of restoration along California’s coast. Among many efforts, we are collaborating with Moss Landing Marine Labs, Elkhorn Slough Research Reserve and Amah Mutsun Land Trust to test methods to scale oyster restoration and make the processes more efficient. In addition to trying out different substrates, or surfaces, for young oysters to settle on in the tidal mudflats, we are trialing a technique called remote setting.

Remote setting is used to commercially grow and restore oyster species throughout the world. This process involves transferring oyster larvae from the hatchery (a facility where oysters can be raised for restoration and conservation in a controlled setting) to an offsite location just before the oysters choose a permanent material to settle on, in this case, recycled shell. In this trial, the larvae are held in a protected and aerated system at Elkhorn Slough, reducing the time they spend in limited, expensive hatchery settings. Once they settle onto a shell, these oysters will join the population in the slough, where we will continue to monitor their growth and success.

This remote setting experiment—the first for Olympia oysters in California—is currently running with 1.2 million oyster larvae. If this project succeeds and the oysters are able to settle and survive in the wild, we can use this model to significantly scale our restoration work for Olympia oysters across California.

A History of Protection

In 1971, to protect Elkhorn Slough from major development, The Nature Conservancy purchased the first wetlands there for conservation. Public and private partners continued to acquire wetland and upland areas leading to the designation of the Elkhorn Slough National Estuarine Research Reserve in 1979.

In September 2012, The Nature Conservancy transferred ownership of the majority of its Elkhorn Slough land holdings (750 acres) to the Elkhorn Slough Foundation for continued management. This was the largest single transfer of conservation lands in the history of Elkhorn Slough and cemented the Elkhorn Slough Foundation as a significant conservation leader and land trust in the central Bay Area.

Prior to this transfer, TNC owned more than 850 acres in the Elkhorn Slough watershed. The Elkhorn Slough Foundation provided on-site management of those lands along with their ownership of 2,800 acres. The Elkhorn Slough Reserve, managed by the California Department of Fish and Game in cooperation with the National Oceanic and Atmospheric Administration, protects 1,740 acres, and another 728 acres are conserved as the State Moss Landing Wildlife Area.

Other conservation lands are managed by the Department of Parks and Recreation, the Moss Landing Harbor District and the Monterey County Parks Department. These combined efforts have conserved more than 6,000 acres of key properties in the Elkhorn watershed.