CROSS; BIOLOGY OV SCYLIORHINID SHARKS 



Table 4.— Stomach contents of 70 Parmaturus xaniurus (mean size = 438 

 mm TL, SD = 47, min = 341, max = 547). PO = percent occurrence, PN 

 = percent number, PW = percent weight, IRI = Index of relative importance. 



DISCUSSION 



Distribution and Abundance 



Apristurus hrunneus and Parmaturus xaniurus 

 were a common, though unwanted, part of the long- 

 line catch on the upper continental slope off south- 

 ern California. The abundance of both species was 

 underestimated by trawl. Among the 29 species 

 (12,074 individuals) caught on longlines, A. brunneus 

 ranked 7th in abundance and P. xaniurus ranked 

 10th. They ranked 29th and 34th, respectively, 

 among the 42 species (7,264 individuals) taken in 

 trawls (Cross 1987). The bias of small trawls against 

 large demersal fishes is well known (Day and Pearcy 

 1968; Haedrich et al. 1975). Most previous fish col- 

 lections on the slope off southern California were 

 taken with small trawls which explains why these 

 sharks are not considered common. 



Catches of A. hrunneus and P. xaniurus were 

 similar on bank sets, but A. hrunneus was more 

 abundant on mud sets. The two species occurred in- 

 dependently at the scale of one tub of longline gear 

 (about 650 m). Apristurus brunneus was equally 

 abundant on mud and bank sets, and seasonal dif- 

 ferences in distribution and catch were not appar- 

 ent. Parmaturus xaniurus was more abundant on 



bank sets than on mud sets, suggesting some habitat 

 selection. Catches of P. xaniurus were highest on 

 banks in the winter; the reason for this is not known. 



Juvenile A. brunneus and P. xaniurus were con- 

 spicuously absent from longline and trawl collections 

 on the slope. Catsharks are generally regarded as 

 demersal fishes (Compagno 1984), but A. brunneus 

 and P. xaniurus have been captured in the water 

 column. An undisclosed number of A. brunneus 

 larger than 260 mm (TL assumed) were collected 

 up to 172 m above the bottom in 373 m of water off 

 British Columbia, Canada (Jones and Geen 1977). 

 Sixty-nine P. xaniurus (99-320 mm) were collected 

 in 43 midwater trawls from 9 to 490 m above the 

 bottom in 527-582 m of water in the Santa Barbara 

 Basin, CA (Lee 1969). The livers of P. xaniurus con- 

 tain a high proportion of squalene, a low specific 

 gravity oil that aids in hydrostatic balance (Springer 

 1979). 



Juveniles and adolescents of both species were 

 taken in midwater trawls in the Santa Barbara 

 Basin (bottom depths between 490 and 576 m) 

 (UCSB3). Catsharks occurred in 31 (41%) of 75 mid- 



^UCSB. Collections taken by the University of California, Santa 

 Barbara, with an opening and closing net between 1965 and 1967 

 and deposited in the Los Angeles County Museum of Natural 

 History. 



699 



