Between 2009 and 2017, the sea otter population in Elkhorn Slough on California’s Monterey Bay saw a twofold increase, which seems to have played a role in a significant reduction in the rate of bank erosion within the slough’s tidal creeks. Throughout this timeframe, erosion diminished as otters consumed crabs that burrowed into the creek banks, aiding in the stabilization of the edges. A study in 2024, spearheaded by Brent Hughes from Sonoma State University, made use of data available on GitHub to measure these shifts.
Prior to the revival of otters, whose population had been nearly driven to extinction, the banks of the creek experienced erosion at an average rate of 0.23 meters annually. Following the return of the otters and their active feeding, this rate decreased to 0.12 meters per year. A targeted study from the University of California, Santa Barbara demonstrated a 69% decline in creek bank erosion with a substantial otter population—although estimates from various analyses show slight variations.
The striped shore crab, which significantly influences erosion by consuming pickleweed roots that stabilize marsh soil, was predated upon by the otters. Studies, including controlled experiments within fenced areas, indicated that when otters could not access crabs, there was a marked decrease in plant matter and soil density—resulting in increased erosion. This outcome directly underscored the otters’ contribution to decreasing crab populations and consequently lessening root loss and soil destabilization.
By 2003, Elkhorn Slough had already experienced the loss of nearly half its salt marsh. Various historical pressures, such as enhanced tidal flow from levee constructions and escalating sea levels, exacerbated this loss. The reintroduction of otters provided some stabilization, but it fell short of fully reversing decades of degradation.
Historical aerial imagery dating back to the 1930s, extended to the current day by Hughes’s team, validates the relationship between otter populations and erosion rates. Fluctuations in the otter population corresponded with variations in erosion rates over the years, connecting the increase in otter numbers directly to the deceleration of creek widening.
Nevertheless, despite these ecological advantages offered by otters, broader environmental threats persist. Intensive agricultural practices, rising sea levels, and previous land-use transformations pose challenges to the marsh’s recovery. Hughes recognizes the otters’ role in mitigating these losses but warns against exaggerating their restorative influence. Future studies, such as initiatives focused on eelgrass restoration, aim to uncover how additional elements might contribute to further erosion reduction.
In conclusion, while otters play an essential ecological role in reducing some erosion, more comprehensive systemic solutions are necessary to tackle the fundamental environmental challenges confronting Elkhorn Slough’s marshes.