Predicting Grunion Migration Patterns and Spawning Areas in Response to Changes in California's Oceans

The California grunion (Leuresthes tenuis) is a species of fish endemic to the California coastline that plays an important role in the marine food chain as a consumer of zooplankton and a food source for larger marine creatures. Grunion spawning events, commonly referred to as "grunion runs," occur when the tide is highest during nights surrounding a new or full moon, allowing the fish to "run" up the beach to deposit and fertilize their eggs before returning to sea. These runs happen most frequently during the summer months along beaches in Los Angeles, Orange, and San Diego counties. However, spawning events documented over the last three decades in the San Francisco Bay suggest a pattern of northern migration caused by changes in ocean conditions and increased human beach activity. In collaboration with the Grunion Greeters Project and the California Department of Fish and Wildlife, the team evaluated oceanic environmental and ecological factors that affect grunion spawning patterns. Earth observation data products, including NASA Multi-scale Ultra-high Resolution Sea Surface Temperature (MUR SST) and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) chlorophyll-a (chl-a), were used to create time series of the California coastline and nearby Pacific Ocean from 2003 to 2018. Upwelling, sea surface current, air temperature, and harmful algal bloom (HAB) data were also considered to derive correlations between the above parameters and grunion spawning events. Analyzing how a changing ocean affects the California grunion will allow for more accurate predictive modeling of spawning behavior and will provide the knowledge base needed to protect this unique species.