Santa Barbara–San Luis Borderland is an important area for undefined aggregations of one shark, one ray, and one chimaera species.

The West Coast Groundfish Bottom Trawl Survey (WCGBTS) is conducted annually between May –July and August–October along the USA west coast between the USA-Canada border and the USA-Mexico border, at depths ranging from 55 to 1,280 m (Keller et al. 2017). The survey area is subdivided into ~12,000 equal-area grid cells, from which 188 cells are randomly selected each year within depth and latitudinal strata to ensure representative spatial sampling. All sharks and rays captured are sorted to species level (or the lowest possible taxonomic resolution) and weighed, and subsamples of selected species are measured. The trawl net used in the survey has a headrope measuring 25.9 m and a footrope measuring 31.7 m. Trawling is conducted during daylight hours at a target speed of 2.2 ± 0.5 knots, with a standard tow duration of 15 minutes (approximately 0.55 km) (Keller et al. 2017). Between 2011–2025, 8,338 tows were conducted in the entire survey area, of which 928 were within this area (11.1%) (NOAA NWFSC FRAM 2026).

Brown Catsharks were captured in 2,875 tows in the entire survey area (34.3% of total tows) at depths between 61–1,271 m. Within this area, this species was captured in 353 tows (38% of tows in this area) at depths between 102–757 m. The average CPUE for Brown Catshark outside this area was 749.6 ind/km², while in this area it was 1,090.6 ind/km². The average number of individuals in a single tow that had Brown Catshark captures outside this area was 14.5, while in this area it was 20.2 while for the same average area (0.02 km²) (NOAA NWFSC FRAM 2026). Of the 353 tows with Brown Catshark in this area, 138 (39.1%) were considered to capture aggregations as 112 tows captured 10–50 individuals, 15 captured 51–99 individuals, and 11 captured 100–739 individuals. Additionally, egg cases were recorded from five tows within this area (n = 752 egg cases) in 2012, 2014, 2015, and 2016, and 32 outside this area (n = 119 egg cases). Deepwater sharks, skates, and chimaeras are known to aggregate with temporal changes related to sex and life-stage segregations (Finucci et al. 2018). Based on specimens collected during survey cruises conducted between June 2001 and October 2004 from northern Washington to San Diego, California, depth segregation was documented in Brown Catsharks (NOAA NWFSC FRAM 2026). Additional fishery-independent bottom trawl and longline surveys targeting commercial groundfish species were conducted monthly between June 2002 and March 2004 from Davenport to Monterey, California by the Federal Ecology Division of the NOAA Fisheries Service Southwest Fisheries Science Center (SWFSC). Subadult Brown Catsharks were found significantly deeper (691 ± 8 m) than adults (580 ± 17 m), which in turn were deeper than pregnant females (440 ± 24 m; P < 0.001) (Flammang et al. 2011). Of the 352 tows with Brown Catshark in this area, 55.2% (n = 195) were between 450–600 m depth and 31.7% (n = 112) between 300–450 m depth, suggesting a higher proportion of mature individuals based on the depth layers.

Longnose Skates were captured in 5,138 tows in the entire survey area (61.6% of total tows) at depths between 2–1,184 m. This species was captured in 681 tows within this area (73.4% of tows in this area) at depths between 64–748 m. The average CPUE of Longnose Skate outside this area was 571.1 ind/km², while in this area it was 893.5 ind/km². The average number of individuals in a single tow that had Longnose Skate captures in this area was 15.2 (maximum = 172), while outside this area it was 9.7 (maximum = 130) for the same average area (0.02 km²) (NOAA NWFSC FRAM 2026). Of the 681 tows with Longnose Skate in this area, 270 captured 10–50 individuals, 32 captured 51–97 individuals, and 7 captured 108–172 individuals. Skates are often spatially aggregated and may be segregated by size and sex, with their distribution influenced by bottom habitat and depth, and occurring either in association with or independently of other skate species (Bizzarro et al. 2014).

Whitespotted Chimaeras were captured in 4,429 tows in the entire survey area (53.1% of total tows) between 2–959 m depth, with 477 in this area (51.4% of tows in this area) between 64.3–594.4 m depth. Based on Kernel Utilization Distribution (KUD) weighted by CPUE (number of individuals per square kilometre; ind/km²), this area is one of the only five areas with KUD >75% along the USA West Coast. Of the 100 highest CPUE along the coast (ranging 9,808.8–252,718.3 ind/km²), 25 are within this area (ranging 9,953.6–76,242.9 ind/km²). The average CPUE for the remaining 476 tows with Whitespotted Chimaera in this area was 1,254.3 ind/km². Outside this area, the average CPUE of the remaining 3,877 tows with Whitespotted Chimaera captures (also not considering the 75 highest values) is 843.7/km². The average maximum number of individuals in a single tow that had Whitespotted Chimaera captures in this area was 38.4, while outside this area it was 24.1 for the same average area (0.02 km²) (NOAA NWFSC FRAM 2026).

Data comprised the number of individuals and total kilograms per species in each tow, and the Precaudal Length (PCL) of Whitespotted Chimaeras was calculated based on the length-weight relationship (King & McPhie 2013). The average size of individuals in tows outside this area ranged 6–106 cm PCL, while in this area it ranged 910–54 cm PCL. Size-at-maturity for the species is 30 cm PCL for males and 39 cm PCL for females (King & McPhie 2013). Of the 477 tows with Whitespotted Chimaera in this area, 334 had the average size of individuals >30.2 cm PCL (70%) and 418 had the average size of individuals <39.3 cm PCL (87.6%) suggesting that aggregations were mainly composed of juveniles and subadults. Whitespotted Chimaeras are known to form large aggregations that can be size-specific (Barnett et al. 2009).  Sharks, rays, and chimaeras can aggregate in high density areas resulting in large catches in specific areas within the broader seascape (e.g., Bizzarro et al. 2014). Elevated CPUE relative to surrounding areas can be used as an indicator of aggregations of deepwater species (Orlov & Volvenko 2022). Specifically for chimaeras, high densities of individuals have been shown to be indicative of aggregations (Finucci et al. 2018).

Further information is required to understand the nature and function of these aggregations.