TEGNER ET AL,: BIOLOGY AND MANAGEMENT OF RED ABALONES 



Here we report the results of five years of popu- 

 lation studies conducted concurrently with the tag- 

 ging studies. The objectives were to assess the rates 

 of settlement of young-of-the-year abalones and to 

 follow changes in size-frequency distributions and 

 densities of animals above and below the recrea- 

 tional and commercial fishery minimum size limits. 

 Predator densities and empty shells were used to 

 study predation patterns. 



We then use results of the joint study to evaluate 

 the appropriateness of the present size limit for red 

 abalones in southern California. Yield-per-recruit 

 analyses have been commonly used to evaluate size 

 limits and levels of fishing mortality for abalones 

 (e.g., Isibasi and Kojima 1979; Harrison 1983, 1986, 

 Sluczanowski 1984, 1986; Clavier and Richard 1985; 

 Breen 1986). Sluczanowski (1984, 1986), however, 

 showed that egg production from a cohort of females 

 could be reduced to a very small fraction of egg pro- 

 duction from an unfished cohort at size limits and 

 fishing rates that seemed reasonable in yield-per- 

 recruit analyses. He suggested that size limits and 

 fishing rates should be examined in the light of both 

 yield- and egg-per-recruit analyses. This approach 

 was used by Breen (1986) for northern abalones, 

 H. kamfschatkana, in British Columbia. Egg-per- 

 recruit analyses have also been used widely in 

 assessing size limits for the American lobster, 

 Homairus americamis, fishery (Saila and Flowers 

 1966; Campbell 1985; Ennis 1985). 



In this study, we use growth estimates and size- 

 frequency distributions to estimate the natural mor- 

 tality rate of red abalones, using the method of Four- 

 nier and Breen (1983). The mortality and growth 

 estimates are then employed in a yield-per-recruit 

 analysis, using the method of Beverton and Holt 

 (Ricker 1975); and with fecundity data in an egg- 

 per-recruit analysis described below. Results of the 

 egg- and yield-per-recruit analyses are examined 

 together, and implications for management of the 

 red abalone fishery are described. A similar anal- 

 ysis is carried out for pink abalones using data from 

 Tutschulte (1976) and Doi et al. (1977) to consider 

 the generality of the results. 



MATERIALS AND METHODS 



Field Studies 



Johnsons Lee is located on the south coast of 

 Santa Rosa Island Gat. 33°54'N, long. 120°06'W). 

 It is protected from the prevailing northwesterly 

 wind and swell typical of summer but is open to the 

 south and east. In part because of this protection. 



Johnsons Lee is frequented by both sport and com- 

 mercial fishermen. The Macrocystis pyrifera canopy 

 was generally about a kilometer wide by two or more 

 kilometers in length during this study. The substrate 

 consisted of rocky reefs separated by a network of 

 sand channels. The vertical relief was quite variable 

 but ledges, crevices, and rock piles provided exten- 

 sive abalone habitat. Macrocystis and several species 

 of foliose reds were the most abundant algae; other 

 common plants included Pterygophora californica, 

 Egregia menziesii, Laminariafarlowii, L. setchellii, 

 Desmarestia spp., Cystoseira, spp., articulated and 

 encrusting coralline algae, Codium fragile. Viva sp., 

 Phyllospadix sp., and Zostera marina. Drift algae 

 were abundant. 



The 300 X 1,200 m study site was located with its 

 long axis parallel to shore and divided in half by a 

 line perpendicular to shore; the goal was to divide 

 effort evenly between the two areas. The transect 

 protocol was adapted from a previous CDFG study 

 of red abalones at Point Estero (Ebert et al. in prep.) 

 so that the results would be directly comparable 

 Sampling strategy was based on the method of sim- 

 ple random sampling. Randomly selected transect 

 origins were located with the use of buoys marking 

 corners of the study areas and compass headings to 

 terrestrial topographic features. Ti"ansects were tied 

 to the skiff anchor and laid on a 60° compass course 

 paralleling the shoreline and depth contours. Tran- 

 sect depths varied from 7 to 16 m. Bat rays, Mylio- 

 batis californica, and California sheephead, Semi- 

 cossyphus pulcher, were counted as the line was laid 

 and horizontal visibility was estimated to calculate 

 the density of these predators. The 30 m transects 

 were divided into eight quadrats, each 7.5 x 2 m. 

 Habitat was graded as sand (<25% rock), rock/sand 

 (<75% rock), and rock (>75% rock). Transects that 

 fell on habitat which was greater than 50% sand 

 were not sampled; alternate locations had been pre- 

 selected. Benthic predators were counted, all aba- 

 lones visible without disrupting the substrate or the 

 use of an underwater light ("emergent" abalones) 

 were measured, and algae and sea urchins were 

 noted by species and graded as sparse, common, or 

 abundant in each quadrat. Two randomly selected 

 quadrats were destructively sampled. Red (Strongy- 

 locentrotus franciscanus) and purple (S. purpura- 

 tus) sea urchins and kelps were counted, all urchins 

 were moved to expose juvenile abalones under their 

 spine canopies, and all rocks turned to locate non- 

 emergent abalones. All abalone shells were collected 

 for measurement and description of shell damage 

 Transect sample sizes were limited by manpower in 

 1978 and winds in 1979. Td augment shell sample 



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