Spatial and temporal effects of lunar phase and sea surface temperature on spawning Barred Sand Bass (Paralabrax nebulifer) off Huntington Beach, CA

The Barred Sand Bass (Paralabrax nebulifer) is an aggregative spawning fish that forms large, transient spawning aggregations off the coast of Southern California. The species is a popular target among the sportfishing community, as the predictable nature of their spawning aggregations allows for high yield with minimal effort. This causes the species to be particularly susceptible to overharvest, as population declines may go undetected under the traditional catch-per-unit-effort (CPUE) assessment. Aggregative spawning fishes are spatially and temporally variable, making accurate stock assessments considerably more complex. A detailed understanding of their spatial and temporal spawning patterns is critical in the implementation of effective management protocol. It has been shown with other species that spawning variability can be linked to environmental cues that are ideal for offspring survival. The present study investigates the effects of lunar phase and sea surface temperature as potential environmental cues for spatial and temporal variations in Barred Sand Bass spawning activity. Split-beam SONAR technology was employed as a non-invasive means of recording positions of Barred Sand Bass across large spatial scales in low-visibility water off Huntington Beach, California. Data from 2010, 2012, 2014, and 2016 were compared. It was found that vertical activity was highest in 2010 and lowest in 2012 and 2014, and increased again in 2016. Decreasing vertical activity appeared to correspond with increasing sea surface temperature when El Niño conditions were present which, if vertical activity is spawning-related, may suggest a thermal maximum for eggs and larvae. Barred Sand Bass were also found to be the highest in the water column during third quarter moon events, which may be linked to variations in currents due to tidal patterns, and the resultant influence on larval transport to ideal juvenile areas. They were also detected over shallower areas during new moon periods, and occupied spaces over a wider range of depths during full moons. Information from this study can have important implications regarding seasonal or spatial management tactics that can be used to effectively manage the breeding stock of this economically valued species. Future population levels are reliant on the successful spawning of the present population, which is likely to be interrupted by fishing activities. Temporal management, such as prohibiting fishing activity during specified time frames, could eliminate much of this impact. Identifying environmental predictors could aid in decisions regarding ideal time frames to implement such regulations to minimize the impact on spawning activity.