260 



Abstract— Cowcod ISebastes levis) is 

 a large 1 100-cm-FL), long-lived (maxi- 

 mum observed age 55 yr) demersal 

 rockfish taken in multispecies com- 

 mercial and recreational fisheries off 

 southern and central California. It lives 

 at 20-500 m depth: adults (>44 cm TL) 

 inhabit rocky areas at 90-300 m and 

 juveniles inhabit fine sand and clay 

 at 40-100 m. Both sexes have simi- 

 lar growth and maturity. Both sexes 

 recruit to the fishery before reaching 

 full maturity. Based on age and growth 

 data, the natural mortality rate is 

 about M =0.055/yr, but the estimate 

 is uncertain. Biomass, recruitment, 

 and mortality during 1951-98 were 

 estimated in a delay-difference model 

 with catch data and abundance indices. 

 The same model gave less precise esti- 

 mates for 1916-50 based on catch data 

 and assumptions about virgin biomass 

 and recruitment such as used in stock 

 reduction analysis. Abundance indices, 

 based on rare event data, included a 

 habitat-area-weighted index of recre- 

 ational catch per unit of fishing effort 

 (CPUE index values were 0.003-0.07 

 fish per angler hour), a standardized 

 index of proportion of positive tows 

 in CalCOFI ichthyoplankton survey 

 data (binomial errors, 0-13% positive 

 tows/yr), and proportion of positive 

 tows for juveniles in bottom trawl sur- 

 veys (binomial errors, 0-30% positive 

 tows/yr). Cowcod are overfished in the 

 southern California Bight; biomass 

 during the 1998 season was about 7% 

 of the virgin level and recent catches 

 have been near 20 metric tons (t)/yr. 

 Projections based on recent recruitment 

 levels indicate that biomass will decline 

 at catch levels > 5 t/yr. Trend data indi- 

 cate that recruitment will be poor in 

 the near future. Recreational fishing 

 effort in deep water has increased and 

 has become more effective for catching 

 cowcod. Areas with relatively high catch 

 rates for cowcod are fewer and are far- 

 ther offshore. Cowcod die after capture 

 and cannot be released alive. Two areas 

 recently closed to bottom fishing will 



Biology and population dynamics of cowcod 

 (Sebastes levis) in the southern California Bight 



John L. Butler 



National Marine Fishenes Service 



Southwest Fishenes Science Center 



P. O Box 271 



La Jolla, California 92038 



E-mail address: John Butler(@noaa.gov 



Larry D. Jacobson 



National Manne Fishenes Service 

 Northeast Fishenes Science Center 

 166 Water Street 

 Woods Hole, Massachusetts 02543 



J. Thomas Barnes 



California Department of Fish and Game 

 Southwest Fishenes Science Center 

 P. O. Box 271 

 La Jolla, California 92038 



H. Geoffrey Moser 



National Manne Fishenes Service 

 Southwest Fisheries Science Center 

 P. O Box 271 

 La Jolla. California 92038 



Manuscript accepted 13 September 2002 



Manuscript received 31 December 2002 

 at NMFS Scientific Publications Office. 



Fish. Bull. 101:260-280 (2003). 



Cowcod (Sebastes levis) are a large (up 

 to 100 cm fork length, FL) laterally 

 compressed rockfish with large head 

 and large jaws that equip it for life as 

 an ambush predator in the deep conti- 

 nental shelf and upper slope waters off 

 the west coast of North America (Miller 

 and Lea, 1972; Eschmeyer et al., 1983). 

 Cowcod are found from central Oregon 

 to central Baja California and Guada- 

 lupe Island, Mexico (Eschmeyer et al., 

 1983). Like many rockfishes (genus 

 Sebastes), cowcod have been the object 

 of commercial and recreational fisheries 

 since at least the beginning of the 20'*^ 

 century (Lenarz, 1987). 



The southern California Bight (SCB, 

 Fig. 1) is located off southern California 

 between Point Conception in the north 

 and the Mexico-U.S. border in the 

 south. It is the center of the cowcod's 

 geographical distribution and they were 

 "abundant" there during the 1890s (Ei- 

 genmann and Beeson, 1894). They are 

 rare off Oregon and northern California 



and were taken in only 13 of 3245 tows 

 north of Cape Mendocino, California 

 (40°28'N. lat.), during National Marine 

 Fisheries Service ( NMFS ) triennial bot- 

 tom trawl surveys on the continental 

 shelf during 1976-98 (Wilkins' and see 

 "Discussion" section ). The NMFS survey 

 tends to avoid rocky ground, however, 

 where cowcod are most common. 



As with other rockfishes, fertiliza- 

 tion is internal and female cowcod 

 give birth to first-feeding stage plank- 

 tonic larvae (Moser, 1967; Boehlert 

 and Yoklavich, 1984). Gonadosomatic 

 indices of females are highest during 

 November-April when embryos are 

 maturing. Peak abundance of cowcod 

 larvae in California Cooperative Oce- 

 anic Fisheries Investigation (CalCOFI) 



' Wilkins, M. 1999. Personal commun. 

 Alaska Fisheries Science Center, National 

 Marine Fisheries Service, 7600 Sand Point 

 Wav, BIN C15700. Seattle, WA 98115- 

 0070. 



