264 



Fishery Bulletin 101(2) 



Eres'). Total landings estimates for 1980-81 from PacFIN 

 were imprecise because of inadequate port sampling, so we 

 used the ratio estimates of cowcod landings for 1980-81 in 

 further analysis. 



Recreational landings 



We developed a time series of annual recreational cowcod 

 catch from three sources including MRFSS surveys 

 (PSMFC3) for 1980-89 and 1993-97, California CPFV 

 logbooks for 1964—98 (Hill and Barnes^) and Los Angeles 

 Times newspaper reports for 1959-97 (Butler et al., 1999). 

 The Los Angeles Times reports daily CPFV catches in Cali- 

 fornia by species (including cowcod since 1959 and rockfish 

 since 1939) and port. Small cowcod (<2 kg) in catches may 

 not be identified to species and were likely counted as 

 "rockfish" in logbooks and Los Angeles Times reports. 



From 1964 through 1979, we estimated recreational 

 catch of cowcod by expanding annual catch from CPFV log- 

 books and annual catch in Los Angeles Times reports. Ex- 

 pansions used ratio estimators based on MRFSS estimates 

 of total recreational cowcod catch during years ( 1980-89 

 and 1993-97) when the MRFSS survey was conducted in 

 California. Expanded estimates based on CPFV logbook 

 and Los Angeles Times records were similar Therefore, 

 expanded CPFV and Los Angeles Times estimates were 

 averaged to obtain a single time series of recreational 

 cowcod catch estimates for 1965-97. For 1951-64, recre- 

 ational cowcod catches were estimated by using the ratio 

 of cowcod and total rockfish catch from CPFV logbooks dur- 

 ing 1965-97, and CPFV logbook estimates of total rockfish 

 catch in earlier years. 



Age, growth, and reproductive biology 



We used otoliths to estimate age and growth for 129 

 cowcod sampled from the recreational fishery during 

 April 1975-June 1981 and 131 cowcod sampled from the 

 commercial fishery during February 1982-January 1986. 

 Four juveniles sampled from bycatch in the spot prawn 

 pot fishery during 1996 were used as well. Otoliths were 

 sectioned and read independently by three readers (four 

 readers for some specimens). Individual age estimates 

 for each fish were averaged and rounded to the nearest 

 integer to obtain a single age estimate for each specimen. 

 Von Bertalanffy growth curves were fitted to size-at-age 

 data for male and female cowcod. The hypothesis of sexual 

 dimorphism in growth was evaluated with a likelihood 

 ratio test (Kimura, 1980). 



Maturity at age was estimated by converting maturity- 

 at-length estimates in Love et al. ( 1990) to maturity at age 



based on a von Bertalanffy curve. Body weights (in grams) 

 were calculated from fork lengths by using W=0.0101 L^'^^, 

 where L was fork length in cm (Love et al., 1990). The re- 

 lationship between body size and fecundity for 27 female 

 cowcod (46-80 cm FL) was £=0.170 L^^^, where E was 

 fecundity in millions of eggs (Love et al., 1990). 



Natural mortality 



Four methods based on age data (i.e. catch curves, Heincke, 

 1913; Robson and Chapman, 1961; Ricker, 1975; and 

 Hoenig, 1983) were used to estimate average total annual 

 mortality rates (Z) for cowcod during 1975-86. The purpose 

 in estimating Z from age composition data was primarily to 

 find bounds for estimates of the annual natural mortality 

 rate (M) in cowcod. In addition, we used Jensen's ( 1997) 

 method based on von Bertalanffy growth parameters to 

 estimate M. Age data for cowcod used in our study were 

 for an exploited stock; so total mortality estimates included 

 natural mortality (M) and fishing mortality (F). 



Biological reference points 



We calculated biological reference points (Thompson and 

 Bell, 1934; Clark, 1991) for cowcod based on yield-per- 

 recruit (Fjv/a.y ^'^'^ ^o i' ^^^^ spawning biomass-per-recruit 

 (F^,,,, ). Managers use F^g„^ as a proxy for Fj,;,„„,,„/j and F^gy 

 (the fishing mortality rate for maximum sustained 3aeld) 

 in managing rockfish (PFMC, 1982). Fishery selectivity 

 assumptions in reference point calculations were based 

 on catch curve results and fishery length composition data 

 (Butler et al., 1999). Female body mass was used to mea- 

 sure reproductive output in reference point calculations. 



CalCOFI ichthyoplankton data 



We used CalCOFI ichthyoplankton survey data to construct 

 an index of larval presence-absence for cowcod (Mangel 

 and Smith, 1990; Smith, 1990). The CalCOFI index gives 

 the probability of a positive tow (i.e. catching one or more 

 cowcod larvae) under standard conditions. CalCOFI ich- 

 thyoplankton data are used routinely to track spawning 

 biomass of pelagic fish (Jacobson et al., 1994; Deriso et 

 al., 1996; Hill et al.'') but are seldom used for rockfish 

 because of difficulties in identifying the species of rockfish 

 larvae and lack of overlap between the area surveyed and 

 distribution of many groundfish stocks. However, cowcod 

 are one of several rockfish species readily identifiable as 

 larvae (MacGregor, 1986; Moser, 1996; Jacobson et al.'"). 



' Eras, J. 1999. Personal commun. California Department of 

 Fish and Game, 4665 Lampson Ave., Suite C, Los Alamitos, CA 

 90720. 



» Hill, K. T., and J. T. Barnes. 1998. Historical catch data from 

 California's commercial pas.sengor fishinp vessel fleet: status and 

 comparisons of two sources. Calif. Dept. Fish and Ciame, Marine 

 Region Tech. Rep. 60, 44 p. lAvailable from California Depart- 

 ment of Fish and Game, Marine Region Mhrary, 4(i65 Lampson 

 Ave., Suite C, Los Alamitos, CA 90720 I 



3 Hill, K. T, M. Yaremko, and L. D. Jacobson. 1999. Status of 

 the Pacific mackerel resource and fishery in 1998. Calif Dep. 

 Fish Game, Marine Region Admin. Rep. 99-3. 57 p. (Available 

 from: California Department of Fish and Game. Marine 

 Region Library, 4665 Lampson Ave.. Suite C, Los Alamitos, CA 

 90720.1 

 '" Jacob.son, L.D., S. Ralston, and AD. MacCall. 1996. Histor- 

 ical larval abundance indices for bocaccio rockfish (Si'bastes 

 pauciapinis) from CalCOFI data. Southwest F'isheries Sci- 

 ence Center. Admin. Report LJ-96-06, .'«) p. (Available from: 

 Southwest Fisheries Science Center, P.O. Box 271, La Jolla, CA 

 920:!H.| 



