Where's the hitch? the distribution of hitch (Lavinia Exilicauda) in the Sacramento San Joaquin delta

Abstract

The degradation and loss of freshwater ecosystems worldwide has greatly impacted fish communities. In California’s highly altered Sacramento-San Joaquin Delta, flow modification, destruction of wetland habitat, and the establishment of invasive species have impacted the abundance of native fishes. The Sacramento Hitch (Lavinia exilicauda exilicauda) is an understudied native cyprinid fish that occupies only a fraction of its historic range in the Delta. Juvenile Hitch rear in vegetated nearshore areas before transitioning to a benthic environment as adults; however, the locations of crucial habitats within the Delta are not well defined. Identifying regions that support nursery and rearing functions is critical in understanding a species’ risk of extirpation. Multiple ongoing monitoring programs provide data showing the spatial distribution of Sacramento Hitch in near-shore areas. Using fork length as a proxy for maturity, catch data from 2018-2021 Delta Juvenile Monitoring Program’s littoral nearshore surveys, the Beach Seine Survey, and Boat Electrofishing Survey are analyzed to determine the distinct regions Hitch inhabit at different life stages. I expect fork lengths to increase from nursery areas in the small sloughs of the northwest Delta to more open water in the Central Delta. Hitch fork length distribution increased from suspected nursery areas in the upper Cache Slough Complex to the more tidally influenced Central and Western Delta, indicating a semi migratory pattern like that found in their relative the Clear Lake Hitch (Lavinia exilicauda chi). Fork length distributions in Cache Slough were skewed towards juveniles (<100 mm) while the Central Delta maintained clusters of fork lengths both >150 mm and >350 mm. The Cache Slough region provides shallow-water sloughs, side channels, and complex cover for juvenile Hitch to mature before moving to larger water in the Central Delta, migrating between the two. To target conservation efforts that best support Hitch survival in the Delta, environmental characteristics underpinning their choice in spawning and rearing grounds and cues leading to migration must be further explored.