Fine Scale Horizontal and Vertical Movement Patterns of Barred Sand Bass, Paralabrax nebulifer, On a Known Spawning Ground

Barred sand bass, Paralabrax nebulifer, have been and continue to be, one of the most sought after gamefish in southern California waters.  The majority of landings occur when individuals move away from nearshore reef habitats to their offshore summer spawning grounds.  Active acoustic telemetry was used to quantify fine-scale horizontal and vertical movement patterns of barred sand bass within one known spawning aggregation location, the Huntington Beach Flats, California.  Fish were internally fitted with either Vemco V13 pingers or V13P depth sensor transmitters.  Individuals were actively tracked over multiple nonconsecutive 24 hr periods; transmitter battery life ranged from 14 d to 4 mo depending on transmitter type.  Several individuals left the spawning site for several weeks and were relocated 0.5-3.0 km from last known detection.  Data suggests both transient and resident individuals use the Huntington Flats spawning ground, with some fish potentially transiting between their home range site and spawning habitat or utilizing more than one spawning area throughout the summer breeding season.  Sand bass used soft, sand habitats in 15-30 m of water; several individuals showed strong associations with natural and artificial reef habitats located randomly throughout the spawning grounds, and displayed distinct diel patterns of activity.  Daily activity spaces averaged 0.21 km² (range 0.002-1.89 km²), using significantly larger areas during the day than at night.  Individual behaviors varied significantly from day to day which may be indicative of spawning periodicity or frequency.  Fish displaying presumed spawning behaviors preferred sand to available reef habitat and used significantly larger activity spaces (mean = 0.31 km², range 0.005-1.89 km²) than non-spawning fish (mean = 0.011 km², range 0.002-0.036 km²).  These animals remained approximately 3.6 ± 4.3 m (± SD) off the seafloor at night and moved up into the mid-water column (8.3 ± 6.0 m off substratum) during the day remaining primarily within or just below the thermocline (~ 16 °C).  During the day, they continually made directed dives towards the seafloor lasting 15-30 sec; a behavior believed to be analogous to vertical spawning rushes demonstrated by other serranids.  Non-spawning individuals were associated with reef structures and remained an average 2.5 ± 2.3 m off the seafloor throughout both day and night periods. Understanding how barred sand bass utilize their spawning grounds and their unique spawning behaviors may lead to more effective management strategies for this species and protect the long-term sustainability of the fishery.