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The present work deals with the temporal and bathymetrical variations of the epifaunal community associated with two species of pearl oysters (Pinctada mazatlanica and Pteria sterna) during a seed collecting season from June to November 1989 . A total of 63 items (species, genera and/or families) were recorded ; their variations in presence and abundance were followed during three periods (June-July, August-September and October-November) . The collectors were examined for different immersion times (2, 4, 6 and 8 weeks) for each period . Community structure was compared through the Brillouin Index, the Morisita Index and the Importance Value .We define the chronology of spatfall for both species of pearl oysters and their bathymetrical distribution . Relationships between these species and the epifaunal community present into the collectors were analysed, searching for possible noxious effects on the survival of juvenile pearl oysters, and identifying index species related with their spatfall . A strategy for starting massive seed collection of both species is established, particularly for P. mazatlanica .

The relationship between the shell dimensions of pearl oysters. Pinctada nmzallaiiica (Hanley 1856) and Pteria sterna (Gould lHSl), was studied to determine the possible change of form of Ihc shell during growth. The intention was to delermine the number, size and location of nuclei that could be implanted in oysters used for Mabe pearl production. Using the database of our Pearl Culture Research Programme developed in Bahia de La Paz. Mexico, we obtained measurements of 500 shells of P. mazatlaniai and 500 shells of P. sterna, representing i years of continuous growth under extensive culture conditions. The heightlength, height-thickness and the height-weight relationships of both species were analysed, as was the height-wing length relationship for /'. sterna. There was isometric growth up to tOOmm shell height, and negative-allometric growth after 120-12 5 mm for P. mazatlanica. The heightthickness relationship followed a linear model. whereas the height-weight relationship was exponential. No clear allometric pattern was found in P. sterna and all relationships litted the power equation.

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Spatfall of pearl oyster, Pteria sterna (Gould), was analysed at two sites, stations Gaviota and Merito, at Bahía de La Paz, South Baja California, Mexico, during an annual cycle in 1991‐1992. and from surface to 15 m depth. Sampling was carried out monthly using experimental collectors which remained immersed for 60‐65 days. Four different substrates were tested for spat settlement preference: a native bush called ‘chivato’, dry palm leaves, and red and yellow plastic onion bags: temporal variations, and horizontal and vertical spatfall distribution patterns were evaluated between and within stations. Spat settlement showed significant differences depending on the structure and texture of the substrate type. Chivato bush was in general the best spat collector, but was difficult to handle for large‐scale operations; plastic onion bags were more suitable and spat yield was adequate; palm leaves were poor spat collectors. There was no evidence for colour preference of spat settlement between red and yellow onion bags. Pteria sterna spat were present throughout almost all of the study period. Main spatfall was detected in winter‐spring, coinciding with low temperatures; most spat then occurred from surface to 4‐5 m depth. Few spat were present in summer and most then occurred below 7‐9 m depth. The distribution patterns of spat within substrate replicates were apparently influenced by the abundance of spatfall. Aggregated spatial patterns were evident in shallow water during months of maximum spatfall but not when spat was less abundant. These events did not occur in the same substrate type, and differences were also detected between stations. Trends were related to oceanographic conditions prevailing at each site. Two patterns of spatfall abundance and vertical distribution were evident, one for winter‐spring, and the other for summer. Samples at station Gaviota were grouped by spatfall abundance and spat vertical distribution patterns, while the latter defined better the grouping of samples at station Merito. Geographical variations of spatfall characteristics for Pteria sterna itself, and in comparison with Pinctada mazatlanka (Hanley) in the Gulf of California, are discussed.

Abstract.-Pearl farms with pearl oysters, abalones, freshwater pearl mussels, and some snails and bivalves having attractive shell, stand out for their general feasibility and commercial value of products. To achieve acceptable profitability, technique-operational validation and assimilation are required in real conditions into multivariate scenarios where the plans sometimes present radical differences even at spot-scale. Pearl culture appears as added value that depends on the input of viable juveniles and efficient management of production cycles. In this work the art of pearl culture is presented as a skill to be acquired from practice and training, which is accessible to any producer that accomplished continuity in the farming procedures. The historical development of pearl culture, from the ancient Buddha Pearls to pearls in vitro, has happened in linear events through improvements of manual and mechanical means. The wide diffusion of pearl farms relies on episodes of environmental history throughout special coincidences in the regions. The review of these transformation processes, based on study and interpretation of evidences and evaluation of potentials in the 21 st century, projects about mollusk farming for shells, nacre or pearls, are analyzed under objective arguments in terms of advantages, disadvantages and prospects to access on one of the most sensitive luxury markets, for its characteristics of natural wealth, dependence on regional and global dynamics and intrinsic difficulties to start and maintain a high-risk technological project, with unpredictable results.Key words: Pearl-bearing mollusks, pearl farms, feasibility analysis, regional development, business plans, commodities marketResumen.-Las granjas productoras de nácar y perlas con ostras perleras, abulones, náyades, y algunos caracoles y bivalvos de concha atractiva, destacan por su factibilidad general y el valor comercial de los productos. Para alcanzar rentabilidad aceptable se requiere un proceso de validación técnica-operativa y asimilación en condiciones reales, que aplica en escenarios multivariados donde la planeación presenta diferencias radicales incluso a escala puntual. La perlicultura aparece como un valor agregado que depende del suministro de juveniles viables y manejo eficiente de los ciclos de producción. En este trabajo se presenta al arte de inducir perlas como una habilidad práctica con entrenamiento accesible para cualquier productor que logre continuidad en los procesos de cría. El desarrollo histórico de la perlicultura, desde las milenarias Perlas de Buda a las perlas in vitro, se ha dado en eventos lineales a través del perfeccionamiento manual y de medios mecánicos. La gran difusión de las granjas perleras se apoya en episodios de historia ambiental a través de particulares coincidencias en las regiones. El examen de estos procesos de transformación, estudio e interpretación de evidencias, y evaluación de los potenciales en el siglo XXI, son analizados bajo argumentos objetivos en términos de ventajas, desventa...

The Calafia mother‐of‐pearl oyster, Pinctada mazatlanica (Hanley), and the Rainbow nacre shell, Pteria sterna (Gould), represent an important resource for México because of their potential in pearl production. The present work deals with the effect of different sequences of nursery culture‐late culture on growth and survival of P. mazatlanica, from September 1993 to October 1994. The collected spat presented two main size groups: small (mean shell height of 7 mm), and large (13 mm). They were arranged into four experimental batches for each size group at a constant stocking density of 40–45 juvenile pearl oysters per Nestier cage. Three batches remained in nursery culture for 2, 4 and 6 months respectively, after which they were transferred to late culture in rail cages. A control group remained in nursery culture for 12 months. Growth was evaluated monthly and compared through anova and HSD Tukey tests. In addition to the shell height, width, depth (mm) and weight (g), data of shell volume (height × width × depth, in mm3) was also introduced to estimate and compare growth among the experimental groups. Mortality was estimated by counting the dead specimens every month and obtaining the percentage from a 100% initial survival at the start of the experiment. The juveniles showed different responses to the change from nursery culture to late culture; the level of each response varied significantly among the experimental groups at the end of the study. It seemed that a 6‐month period for nursery culture was propitious for P. mazatlanica.