Effects of sea-level rise and storm enhanced flooding on Pacific harbor seal habitat: a comparison of haul-out changes at the Russian and Eel River Estuaries in California, USA

Patterns and changes in the distribution of coastal marine mammals can serve as indicators of environmental change which fill critical information gaps in coastal and marine environments. Coastal habitats are particularly vulnerable to the effects of near-term sea-level rise. In California, Pacific harbor seals (Phoca vitulina richardii) are a natural indicator species of coastal change due to their reliance on terrestrial habitats, abundance, distribution, and site fidelity. Pacific harbor seals are marine top predators that are easily observed while hauled out at terrestrial habitats which are essential for resting, pupping, and molting. While increasing inundation from recent sea-level rise and storm driven flooding has changed the California coastline, little is known about the effect of future sea-level rise and increased storm frequency and strength on harbor seal haul-out availability and quality in California. We modeled harbor seal habitat at two sand bar-built estuaries under a series of likely sea-level rise and storm scenarios. The primary findings of these scenarios reveal that, over time, habitat at both estuaries decreased with increasing sea-level, and storm enhanced water levels contributed significantly to habitat flooding. These changes reflect pressures on coastal habitats that impact human and natural systems.