Species recovery and recolonization of past habitats: lessons for science and conservation from sea otters in estuaries

Brent B Hughes; Kerstin Wasson; M Tim Tinker; Susan L Williams; Lilian P Carswell; Katharyn E Boyer; Michael W Beck; Ron Eby; Robert Scoles; Michelle Staedler; Sarah Espinosa; Margot Hessing-Lewis; Erin U Foster; Kathryn M Beheshti; Tracy M Grimes; Benjamin H Becker; Lisa Needles; Joseph A Tomoleoni; Jane Rudebusch; Ellen Hines; Brian R Silliman

doi:10.7717/peerj.8100

Species recovery and recolonization of past habitats: lessons for science and conservation from sea otters in estuaries

PeerJ. 2019 Dec 10:7:e8100. doi: 10.7717/peerj.8100. eCollection 2019.

Authors

Brent B Hughes^{1

2}, Kerstin Wasson^{3

4}, M Tim Tinker^{4

5}, Susan L Williams⁶, Lilian P Carswell⁷, Katharyn E Boyer⁸, Michael W Beck⁹, Ron Eby³, Robert Scoles³, Michelle Staedler¹⁰, Sarah Espinosa⁴, Margot Hessing-Lewis¹¹, Erin U Foster^{11

12}, Kathryn M Beheshti⁴, Tracy M Grimes¹³, Benjamin H Becker¹⁴, Lisa Needles¹⁵, Joseph A Tomoleoni⁵, Jane Rudebusch¹⁶, Ellen Hines¹⁶, Brian R Silliman²

Affiliations

¹ Department of Biology, Sonoma State University, Rohnert Park, CA, USA.
² Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, NC, USA.
³ Elkhorn Slough National Estuarine Research Reserve, Watsonville, CA, USA.
⁴ Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA.
⁵ U. S. Geological Survey, Western Ecological Research Center, Santa Cruz, CA, USA.
⁶ Department of Evolution and Ecology, Bodega Marine Laboratory, University of California, Davis, Bodega Bay, CA, USA.
⁷ Ventura Fish and Wildlife Office, United States Fish and Wildlife Service, Ventura, CA, USA.
⁸ Estuary & Ocean Science Center, Department of Biology, San Francisco State University, Tiburon, CA, USA.
⁹ Institute of Marine Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA.
¹⁰ Monterey Bay Aquarium, Monterey, CA, USA.
¹¹ Hakai Institute, Heriot Bay, BC, Canada.
¹² Applied Conservation Science Lab, University of Victoria, Victoria, BC, USA.
¹³ Department of Biology, San Diego State University, San Diego, CA, USA.
¹⁴ Point Reyes National Seashore, United States National Park Service, Point Reyes Station, CA, USA.
¹⁵ Center for Coastal Marine Sciences, Department of Biological Sciences, California Polytechnic State University-San Luis Obispo, San Luis Obispo, CA, USA.
¹⁶ Estuary & Ocean Science Center, Department of Geography and Environment, San Francisco State University, Tiburon, CA, USA.

Abstract

Recovering species are often limited to much smaller areas than they historically occupied. Conservation planning for the recovering species is often based on this limited range, which may simply be an artifact of where the surviving population persisted. Southern sea otters (Enhydra lutris nereis) were hunted nearly to extinction but recovered from a small remnant population on a remote stretch of the California outer coast, where most of their recovery has occurred. However, studies of recently-recolonized estuaries have revealed that estuaries can provide southern sea otters with high quality habitats featuring shallow waters, high production and ample food, limited predators, and protected haul-out opportunities. Moreover, sea otters can have strong effects on estuarine ecosystems, fostering seagrass resilience through their consumption of invertebrate prey. Using a combination of literature reviews, population modeling, and prey surveys we explored the former estuarine habitats outside the current southern sea otter range to determine if these estuarine habitats can support healthy sea otter populations. We found the majority of studies and conservation efforts have focused on populations in exposed, rocky coastal habitats. Yet historical evidence indicates that sea otters were also formerly ubiquitous in estuaries. Our habitat-specific population growth model for California's largest estuary-San Francisco Bay-determined that it alone can support about 6,600 sea otters, more than double the 2018 California population. Prey surveys in estuaries currently with (Elkhorn Slough and Morro Bay) and without (San Francisco Bay and Drakes Estero) sea otters indicated that the availability of prey, especially crabs, is sufficient to support healthy sea otter populations. Combining historical evidence with our results, we show that conservation practitioners could consider former estuarine habitats as targets for sea otter and ecosystem restoration. This study reveals the importance of understanding how recovering species interact with all the ecosystems they historically occupied, both for improved conservation of the recovering species and for successful restoration of ecosystem functions and processes.

Keywords: Endangered Species Act; Estuary; Fisheries; Food web; Marine Mammal Protection Act; Recovery; Restoration; Top predator.

Grants and funding

Brent B. Hughes was funded through the David H. Smith Research Conservation Fellowship and Cedar Tree Foundation and the Rebecca and Steve Sooy Fellowship in Marine Mammals. Kerstin Wasson was supported by a grant from NOAA’s Office for Coastal Management to the Elkhorn Slough National Estuarine Research Reserve. Margot Hessing-Lewis and Erin Foster were supported by the Hakai Institute and Erin Foster was supported by an NSERC Vanier. Susan L. Williams was supported by the University of California’s Agricultural Experimental Station. Michelle Staedler was supported by the Monterey Bay Aquarium. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.