Age, growth, and mortality of California halibut, Paralichthys californicus, along southern and central California

California halibut, Paralich­ thys californicus, collected by a 400­ mesh eastern trawl in southern (Mex­ ican border to Point Conception) and central (Point Conception to Tomales Bay) California were aged by using whole and sectioned otoliths (sagittae) to determine age, growth, and mor­ tality. Males represented 69% of the sample from southern California and 53% of the sample from central Califor­ nia. A higher proportion of California halibut were older in southern Califor­ nia than in central California. Although California halibut can live as long as 30 years, the oldest fish found in our study was 13 years old. For southern Califor­ nia, the von Bertalanffy growth func­ tion (VBGF) was Lt=925.3(1–e –0.08(t+2.2)) for males and Lt=1367.7(1–e –0.08(t+1.2)) for females. For central California, the VBGF was Lt=956.7(1–e) for males and Lt=1477.1(1–e –0.10(t+0.2)) for females. The VBGF showed that at the same age, females on average were larger than males in both southern and central California. The VGBF also showed that both male and female hal­ ibut in central areas on average were larger than halibut from southern Cal­ ifornia. Instantaneous mortality rates of halibut in southern California were estimated at 0.91 for males and 0.68 for females. Mortality estimates for cen­ tral California could not be calculated because of small sample sizes. Manuscript accepted 9 March 2001. Fish. Bull. 99:588–600 (2001). Age, growth, and mortality of California halibut, Paralichthys californicus, along southern and central California Leslie S. MacNair Michael L. Domeier Calvin S. Y. Chun California Department of Fish and Game 4665 Lampson Avenue, Suite C Los Alamitos, California 90720 E-mail address (for C. S. Y. Chun, contact author): cchun@dfg.ca. gov California halibut, Paralichthys califorand Point Conception, and central Cali­ nicus, is an important flatfish species fornia as the area between Point Con­ for sport and commercial fisheries in ception and Tomales Bay. Bottom trawl nearshore waters off central and southsurveys were conducted off central Cal­ ern California (Frey, 1971). The gear ifornia from 8 July through 3 August most commonly used commercially to 1993 and off southern California from harvest California halibut are otter 14 February through 18 March 1994. trawls, gill nets, and trammel nets, California halibut were caught with a whereas hook-and-line or spear are 400-mesh eastern trawl (15 m wide × used mostly in the recreational fishery 1.5 m high; 9.8 cm mesh body, 8.5 cm (Kramer and Sunada, 1992). mesh codend). For both areas, sampling Information on age, growth, and moreffort was stratified by depth: 0–20 tality of California halibut are imporfathoms (fm), 21–40 fm, and 41–60 fm. tant to the management of both the Fifty stations within each depth stra­ sport and commercial halibut fisheries. tum were randomly selected for samPrevious studies have addressed these pling by trawling parallel to isobaths issues to a limited extent. Pattison and at each station. The sample sizes were McAllister (1990) studied techniques to not proportional to the estimated area age halibut and determined length-atof the strata (Table 1). age of halibut along the California coast, An additional ten California halibut but most of the fish were taken south were collected with the same 400-mesh of Point Conception and they did not do eastern trawl gear in southern Cali­ separate analyses for southern and cenfornia from July 1994 to June 1995. tral California. Sunada et al. (1990) anThese were included in the age and alyzed age, size, and sex composition of growth determinations. However, they commercial landings in southern Calwere not used for mortality estimates ifornia. Haaker (1975) studied the bibecause they were collected at a differ­ ology of California halibut in Anaheim ent time period from the other halibut Bay, including age and growth, but the collected off southern California. fish he used were generally less than Each halibut was measured to the three years of age, immature, and innearest millimeter for total length (TL) cluded fish only to 510 mm total length. and standard length (SL). Gonads were In contrast to other studies, our study examined visually to determine the sex provides information on age and growth of the fish. Sagittal otoliths were re­ for central and southern California sepmoved and stored dry in vials for age arately. Mortality for southern Califordetermination. Pattison and McAllis­ nia was also calculated. ter (1990) determined that when com­ pared with other fish structures, oto­ liths provided the most reliable ages for Methods California halibut. They found that in an otolith, an opaque band was formed Southern California was defined as the during spring and summer (from April area between the U.S.-Mexico border to October) and a translucent band was MacNair et al.: Age, growth, and mortality of Paralichthys californicus 589 Table 1 Number of trawls and number of California halibut used in age and growth analyses by depth strata and region. Asterisk (*) indicates that these fish were not used in the mortality estimates because they were caught at a later date. Southern California Central California Stratum Depth (fm) No. of trawls No. of halibut used Area (nmi2) No. of trawls No. of halibut used Area (nmi2) 1 0–20 913 +3* 575 47 254 587 2 21–40 165 +2* 495 39 22 905 3 41–60 13 +1* 425 40