Barred sand bass, Paralabrax nebulifer, are one of the most sought-after sport fishes in southern California. Since the 1960s, this species has ranked among the top ten sport fish caught by commercial passenger fishing vessels (CPFVs), or "party boats," in southern California, with annual catches averaging nearly one million fish over the last 20 years. For decades, CPFVs and private recreational boaters have targeted well-known spawning aggregation sites throughout southern California, including the Ventura Flats, Santa Monica Bay, Huntington Beach Flats, San Onofre, and San Diego. Approximately 71 percent of the annual barred sand bass catch is harvested by the CPFV fleet from June through August, during peak spawning season.
Records show that from 1961 to 2000 barred sand bass catches increased, followed by a dramatic decline in landings through 2008. These dramatic catch declines in recent years have caused concern among fisheries biologists and fishermen alike. A 2010-2011 fishery analysis on the basses (including barred sand bass) indicates that bass populations in the last decade have been negatively affected by cool oceanographic conditions and fishing. Answering scientific questions regarding barred sand bass spawning behavior, movements and spawning habitat requirements will be important for the management of this resource.
Barred sand bass catch location data was compiled by California Recreational Fisheries Survey samplers for private/rental boats from 2004-2008 in the southern California region. Samplers interview anglers at public launch facilities, ask questions about their fishing activities, examine their catch to determine the number and species of fish kept or discarded, weigh and measure the catch, and collect fishing location and depth information. The catch location data were mapped and analyzed and major "hotspot" catch locations (potential spawning grounds) were identified using a Geographic Information System. This analysis provides valuable information about where and when barred sand bass spawning aggregations may occur in southern California. In addition, areas fished around Huntington Beach were examined on a finer scale to examine any seasonal patterns of catch.
In the 1960s and 1990s, CDFW biologists tagged a total of 9,000 barred sand bass in southern California. The recapture information from these two time periods enabled us to document large-scale spawning-related movements of barred sand bass for the first time. Using this dataset we attempted to discover:
- How long individual barred sand bass remain at spawning grounds during spawning season
- How far fish migrate to spawn
- Whether fish show fidelity to certain spawning locations
In addition to large-scale spawning movements, we were also interested in the short-term, fine-scale spawning movements of barred sand bass. To address this, project staff worked with California State University, Long Beach professor Dr. Chris Lowe and his master's student, Megan McKinzie. Project staff assisted with field research that uses state-of-the-art technology to actively track adult barred sand bass at Huntington Flats during the spawning season. Fish were surgically fitted with acoustic transmitters and then followed by boat using an underwater hydrophone. Several transmitters contained depth sensors which emitted a signal that allowed the researcher to determine both the horizontal and vertical movements of the fish every two seconds.
The results from this research allowed us to characterize fine-scale horizontal and vertical movement patterns of tagged barred sand bass during the spawning and non-spawning seasons, and to quantify activity space size (area and volume), habitat use and preference, and patterns of activity throughout a 24-hour period. Movement patterns believed to be indicative of spawning and/or courtship were determined through the comparison of spawning and non-spawning season individuals.
(1) With the fish immersed in a saltwater anesthetic bath, the transmitter is inserted through a small incision in the lower abdominal cavity.
(2) Two to three sutures are used to close the incision.
(3) Prior to release, the fish is measured and fitted with an external dart tag for easy identification upon recapture.
CDFW photos by E. Jarvis
The timing and location of spawning aggregations are related to water temperature, lunar activity, and currents for some other aggregate spawners. However, depth and bottom habitat type are the only characteristics documented in historical descriptions for barred sand bass spawning aggregation sites. To understand whether barred sand bass spawning aggregation sites were unique, Fisheries Independent Assessment Project staff conducted field surveys in 2008 to determine the typical oceanographic (water temperature), seafloor habitat (type of substrate), and biological features (invertebrates living on and in the substrate) of areas where barred sand bass spawning aggregations occur and areas where they are absent.
Barred sand bass "resting" at spawning grounds. CDFW photo, circa 1961.
Findings to Date
During the summer months, five "hotspots" for barred sand bass catch were identified that are likely major spawning grounds for this species. The proportion of catch varied among these "hotspots" from 2004 to 2008 with Huntington Flats off Orange County and Imperial Beach ("I.B." Flats) on the U.S./Mexico border in San Diego County being the top catch locations. On a finer scale, natural reefs (Horseshoe Kelp and Palos Verdes Peninsula) and artificial structures (reefs, oil rigs, and breakwaters) were more important catch locations in the Huntington Beach Flats area outside of peak spawning season. This suggests that areas with higher relief or structure may serve as important habitat for barred sand bass before and after spawning activities.
Map of the Southern California Bight showing the number of barred sand bass kept and released by private/rental boats from 2004-2008 by 1x1 mile fishing block from June - August. The percentages represent the proportion of barred sand bass caught by county and standardized by area (1x1 mile fishing block).
Tag and Recapture Data
The CDFW received 972 barred sand bass tag returns from tagging efforts conducted in the 1960s and 1990s (an 11 percent recapture rate). Based on recapture frequencies, it appears that barred sand bass individuals remain on spawning grounds (e.g., Huntington Beach Flats) for at least one month during peak spawning season. Spawning residency at Huntington Flats was estimated by the frequency of returns over time; most same-year returns (82%, n = 141) were recaptured within a 35-day period, with secondary peaks in returns at 28 and 56 days at liberty.
Frequency of tag returns over time for fish tagged during peak spawning season (June through August)
at Huntington Flats and recaptured there within the same year.
Following spawning season, some fish remain, while others move away. The average migration distance from spawning locations was about 15 miles, although it appears that not all individuals at spawning grounds migrate to the same locations after spawning season. Overall, the farthest recapture distance was approximately 57 miles. Annual patterns in the timing and occurrence of recaptures strongly suggest barred sand bass visit the same spawning grounds year after year.
Recapture matrix of barred sand bass tagged during peak spawning season (Jun-Aug) and recaptured in subsequent peak spawning seasons.
Three distinct patterns of behavior were identified and believed to be representative of non-spawning season behavior, spawning season resting behavior, and spawning/courtship related behavior. Non-spawning season fish remained more closely associated with reef habitats than sand habitat, used smaller activity spaces, and remained more closely associated with the substratum than fish tracked during the spawning season.
Fish tracked during the spawning season used significantly more area and volume, and preferred sand over available reef habitats than fish tracked during non-spawning season. Spawning season fish typically utilized more of the available water column; individuals made dives toward the seafloor throughout the day and remained close to the seafloor at night. During the day, they remained primarily within or just below the thermocline (~ 16 °C), but continually made directed dives towards the seafloor lasting 15 to 30 seconds, a behavior believed to be analogous to vertical spawning rushes demonstrated by other serranids. Fish tracked during spawning season also demonstrated movement patterns similar to non-spawning season fish and was believed to be resting behavior.
Box and whisker plots of day versus night activity space-area during spawning and non-spawning seasons.
Box and whisker plots showing distance from bottom during day and night periods for both spawning and non-spawning fish.
3-D graphical representation of barred sand bass activity space usage during: (a) the non-spawning season, (b) presumed spawning/courting behavior and (c) resting periods.
Seafloor Habitat and Invertebrate Densities
Not surprisingly, our results indicated the Huntington Flats largely consists of a uniform, sandy substrate; however, our analysis of existing substrate maps also identified several previously unknown areas of hard substrate sparsely scattered over the study area. Exploratory scuba dives conducted by CDFW staff identified barred sand bass on these reefs (some natural, some artificial) during peak spawning season, but we never observed courtship or spawning behavior even though dives occurred during daylight hours when barred sand bass reportedly spawn. Although there is potential barred sand bass spawning over reefs, the reefs may actually serve as areas for reproductive staging, resting, refuge, and foraging during spawning season.
The distribution of observed CPFV activity on barred sand bass spawning aggregations did not appear related to the distribution and (or) relative abundances of larger bottom invertebrates and animals that dwell within bottom sediments/sand. Fishermen have long associated barred sand bass spawning aggregations with "clam beds"; however seafloor video footage taken during opportunistic events on the Flats did not reveal evidence of large clam beds in the area. Although we did not collect sand bass stomachs for stomach content analysis, as they become adults barred sand have been shown to shift their diet predominantly to fishes that live near the bottom and crabs. Therefore, although clams occurred frequently in our benthic survey of the Flats, barred sand bass probably form aggregations over sand flats for reasons other than the presence of clams or other soft bottom prey items.
Hard and soft substrate mapped within the Huntington Flats study area in southern California in 2008.
Data source: California Seafloor Mapping Project.
Some areas beyond state waters (3 nm) were not available.
Circled numbers reference small patches of hard substrate within the study area. AR=artificial reef.
Oceanographic Conditions at Huntington Flats
The development of a strong thermocline occurred during late July and early August and coincided with the highest, sustained catch of barred sand bass during peak spawning season. Thermocline temperatures measured within areas of presumed aggregation activity were significantly warmer than the average thermocline temperatures measured throughout the area during June, July, and August. In subsequent years, barred sand bass tracked during spawning season were associated with the thermocline during the daytime (see Fine-scale Movements above). Previous research on the optimal thermal habitat for barred sand bass egg and larval development suggests warmer thermocline temperatures may increase larval fitness.
Comparison of average thermocline temperatures on the Huntington Flats in June, July, and August, and during sampling events located within barred sand bass aggregation fishing activity, 2008. Error bars represent 95% confidence intervals, the asterisk denotes a statistical difference among means.
Daily catches of barred sand bass by the CPFV fleet were positively associated with fishing effort and tidal flux, and negatively associated with chlorophyll-a concentrations. These factors explained 72 percent of the variability in barred sand bass catch over the peak spawning season. Periods of high tidal flux occurred during both new and full moon phases; thus, the observed peaks in barred sand bass catch may represent a reproductive behavioral response to tidal amplitudes more so than moon phase. Sea surface currents were generally low during peak barred sand bass catches; however, Huntington Flats experienced large tidal fluxes of several feet.
The negative relationship between barred sand bass CPFV catches and chlorophyll-a concentrations is less clear. Chlorophyll-a concentrations are typically used as a proxy for phytoplankton abundance and tend to be inversely related to the ability of light to penetrate water in this area. A negative relationship with chlorophyll-a may reflect a preference of barred sand bass aggregations for increased water clarity, or it may reflect avoidance of forage fishes that eat plankton and zooplankton egg predators.