CROSS: BIOLOGY OF SCYLIORHINID SHARKS 



washed in water, sorted, and identified to tlie lowest 

 taxon practicable; pieces of bait were ignored. 



Size at sexual maturity was estimated for males 

 by change in relative size of the claspers and testes, 

 and for females by change in relative size of the 

 ovaries and presence of egg cases in the oviducts 

 (Pratt 1979). Polynomial regressions were fit to the 

 data for males (SAS 1982). The reproductive season 

 was determined by enlarged testes in the males and 

 the presence of full-sized eggs in the ovaries of the 

 females. The gonadosomatic index (GSI) was cal- 

 culated for the sexes of both species from 



GSI = (gonad weight/body weight) x 100. 



Analyses of stomach data were summarized by the 

 index of relative importance (IRI) modified from 

 Pinkas et al. (1971): 



IRI = PO{PN + PW) 



where PO is percent occurrence, PN is percent 

 numbers, and PW is percent weight calculated for 

 each prey category. The length of intact prey was 

 measured. 



Catch/effort data (where a unit of effort was one 

 tub of line) were transformed to logjo and analyzed 

 for habitat, season, and depth differences by analysis 

 of covariance (ANCOVA) for unbalanced designs 

 (SAS 1982) with habitat and season as the main ef- 

 fects and depth as the covariate. Catch per tub for 

 each positive set was determined by averaging the 

 catches of the constituent tubs. 



Fish size data were analyzed for habitat, season, 

 and depth differences by ANCOVA for unbalanced 

 designs. The data were not transformed because size 

 was approximately normally distributed. 



Geometric mean weight-length regressions were 

 calculated from the logarithmic transformation of 



W = aL^ 



where W is weight in grams, L is total length in 

 millimeters, and a and b are fitted constants (Ricker 

 1973). The regression coefficients (b) were compared 

 by the method of Clarke (1980). 



The sediments of the upper continenal slope off 

 Newport Beach are predominantly green silty clays. 

 Sand content is fairly constant down slope (mean 

 = 12% by dry weight); areas around the offshore 

 banks and the shoulders of the submarine canyons 

 are sandier (25-50% by dry weight). Organic con- 

 tent increases from 5 to 7% (as total volatile solids) 



at 290 m to 11-14% at 625 m (SCCWRP 19832). 

 Between 600 and 700 m, the slope gives way to the 

 low-oxygen San Pedro Basin to the northwest and 

 to the deeper San Diego Trough to the southeast 

 (Fig. i). 



Longline fishermen recognize two habitats on the 

 slope: hard substrate banks and soft, relatively 

 featureless (on a fathometer) mud bottom. Surface 

 sediments on the banks are a mixture of coarse sand, 

 shell hash, and occasional rocks. As used herein, 

 banks include submerged mountains, shoulders of 

 submarine canyons, and isolated mounds as small 

 as a few hundred meters across and 20-30 m high. 

 The mud bottom is green silty clay and is the pre- 

 dominant habitat on the slope. 



Oceanographic measurements in the water column 

 off Newport Beach showed weak and decreasing 

 gradients with increasing depth. The mean annual 

 temperature was 8.3°C (SD = 0.3, N = 64, min = 

 7.5, max = 9.1) at 300 m and 6.5°C (SD = 0.2, N 

 = 25, min = 6.0, max = 6.9) at 500 m. Mean an- 

 nual dissolved oxygen was 1.21 ppm (SD = 0.26, A'' 

 = 54, min = 0.76, max = 1.94) at 300 m and 0.48 

 ppm (SD = 0.10, N = 20, min = 0.31, max = 0.72) 

 at 500 m. Some of the variation at 300 m was the 

 result of seasonal changes related to upwelling. In 

 the spring, temperature and dissolved oxygen 

 decreased, and salinity and density increased 

 (SCCWRP fn. 2). 



RESULTS 



Distribution and Abundance 



The occurrence of scyliorhinid sharks in trawl 

 catches was markedly different from longline 

 catches. Catsharks were caught in 3 (6%) of the 48 

 otter trawls. The six individuals collected accounted 

 for <0.1% of all fish caught in trawls. Catsharks 

 were caught on 62 (87%) of the 71 longline sets (212 

 tubs of gear examined). The 698 individuals collected 

 accounted for 5.8% of the fish caught (2.8% of catch 

 weight) on longlines. 



Apristurus brunneus were caught on 50 (70%) 

 sets; 475 individuals were collected. Parmaturus 

 xaniurus were caught on 53 (75%) sets; 223 in- 

 dividuals were collected. The two species occurred 

 independently on the tubs of longline gear (x^ = 

 0.39, P > 0.05). They were equally abundant on bank 



^SCCWRP. 1983. A survey of the slope off Orange County, 

 California. Report to Countj' Sanitation Districts of Orange Coun- 

 ty. Long Beach: Southern California Coastal Water Research 

 Project, 208 p. 



693 



