California Sea Grant College Program

The majority of Northern California estuaries are small, flooded, river valleys that are largely unstudied due to their small sizes and remote locations. Yet these estuaries serve as important nursery areas for many marine fish species including rockfish, flatfish, smelt, and herring, and they are vital to anadromous species such as Chinook Salmon (Oncorhynchus tshawytscha) and Steelhead (O. mykiss). I sampled the summer and winter fish and invertebrate communities of the Big, Mad, and Ten Mile river estuaries. Fish were sampled via beach seine or fyke net and invertebrates were sampled via benthic cores, June 2014-June 2016. This research is part of a larger suite of studies establishing baseline conditions in Northern California Marine Protected Areas (MPAs). Big and Ten Mile river estuaries in Mendocino County were designated as MPAs in 2012. The Mad River Estuary in Humboldt County was selected as a non-MPA site to investigate its potential as a reference estuary. In the Mad River Estuary, additional sampling was conducted and a diet study was carried out on the feeding habits of two benthic fishes: Pacific Staghorn Sculpin (Leptocottus armatus) and English Sole (Parophrys vetulus). iii Fish abundance and diversity varied more by season (i.e. summer, winter) than by estuary, while invertebrate diversity varied more by estuary than by season. The Big River Estuary had the strongest ocean connection and the most marine fish and invertebrate species. The Mad River Estuary fish and invertebrate communities were most similar to the Ten Mile River Estuary, which had the least ocean connectivity and species diversity. Additional sampling in the Mad River Estuary showed that fish and invertebrate communities were diverse from spring through fall, and that invertebrate communities within an estuary differed more by upstream distance than by season. Staghorn Sculpin diet in the Mad River Estuary varied by location of capture, but not by season.