Fecundity of Cancer johngarthi carvacho 1989 (Decapoda: Brachyura: Cancridae) from Southern Baja California's western coast, Mexico.

ABSTRACT Fifty-two ovigerous females of Cancer johngarthi were caught from the Baja California Peninsula's western coast, Mexico. Carapace length, carapace width and total weight of each specimen were registered. Fecundity estimates were obtained from the wet weight of eggs in each organism. Mean fecundity was 765,227 eggs, corresponding to a mean carapace width of 117 mm, and the mean relative fecundity was 4,305 eggs per gram of female body weight. Fecundity data (F) were fitted in relation to carapace width (CW) to the power model F = [0.84CW.sup.287], [R.sup.2] = 0.52. C. johngarthi has a high population renewal capacity compared with other larger species like Maiopsis panamensis, which produces between 351,000 and 1,162,668 eggs, and Stenocionops ovata, which produces between 35,187 and 180,057 eggs; in both species, the relative fecundity is lower than 1,000 eggs per gram of female body weight.

KEY WORDS: Cancer johngarthi, fecundity, Baja California Peninsula

INTRODUCTION

Cancer johngarthi is a crab belonging to the Cancridae family, distributed from Guadalupe island, Mexico (29[degrees]N, 118[degrees]W) to Panama bay (7[degrees]N) (Carvacho 1989). This species is commercially important because of the flavor and texture of chelae meat, mainly from males. In the Southern Baja California's western coast, as well as in the Gulf of California, this species lives in soft substrates, at depths in excess of 90 m, and aggregated in populations, which may sustain a fishery (Fiol-Ortiz & Cervantes-Diaz 1996, Sanchez-Ortiz et al. 1997, Carvacho 1989, Leija et al. 1992, Ramirez-Rodriguez et al. 2003). Based on these results, the Mexican government recently offered two commercial fishing permits for C. johngarthi using traps.

This implies the need to conduct detailed studies on the crab's biology and dynamics aimed at generating useful information for the design of fishery-management measures. For the previously mentioned, the main objective of this work is to produce fecundity estimates for C. johngarthi, of particular interest because of its relationship with the population renewal capacity of this species in the study area (Garcia-Montes et al. 1987).

MATERIALS AND METHODS

In January 2003, C. johngarthi specimens were caught from the Southern Baja California Peninsula's western zone (24045' to 25[degrees]10'N; 112[degrees]31' to 112[degrees]44'W and 23[degrees]34' to 23[degrees]52' N; 111[degrees]04' to 111[degrees]04' W, Fig. 1). The capture was conducted using a 25-m long fishing ship with a net capacity of 130 t, adapted to operate conical traps measuring 150 cm x 75 cm x 65 cm, with a plastic-coated steel frame and baited with sardine at a depth between 73 and 300 m (Ramirez-Rodriguez et al. 2003).

[FIGURE 1 OMITTED]

Fecundity was determined from the wet weight of eggs in each ovigerous mass. The number of eggs in three subsamples of 0.02 g each was counted using a stereomicroscope. Individual fecundity data were obtained by extrapolating the number of eggs in each in the three subsamples to the total weight of the egg mass in each female, and then the mean per female fecundity and the standard deviation were calculated. For each specimen, fecundity data were adjusted in relation to carapace width (CW). CW was defined by the greatest straight-line distance (excluding lateral spines) across the carapace and chelae width and carapace length (CL) was defined by the line midway between the eyes to the midpoint of the posterior margin of the carapace. Also, the relative fecundity was calculated for each female as the number of eggs per gram of female body weight.

RESULTS

Of the three thousand eight hundred and thirty-six organisms sampled, 3,362 were males (87.6%) and 473 females (12.4%), of which 52 were ovigerous. The sex rate for the total sample was 1M:0.14F and significantly deviates from the 1:1 rate. Male size ranged from 98 mm to 176 mm in c W, with a mean of 146 mm [+ or -] 11 mm, whereas females measured 87-153 mm in CW, with a mean of 122 mm [+ or -] 9 mm.

The 52 ovigerous females had a CW ranging between 98 and 131 mm, with a mean of 117 mm [+ or -] 8.4 mm; CL lied between 51 and 81 mm with a mean of 74 mm [+ or -] 6.9 mm. Fecundity varied between 381,441 and 1517,668 eggs, with a mean of 765,227 eggs [+ or -] 233,415 eggs, whereas the relative fecundity ranged between 1,033 and 8,510 eggs/g with a mean of 4,305 eggs/g [+ or -] 1,402 eggs/g of female body weight.

A power equation was fitted to fecundity data, with CW as the independent variable [r.sup.2] = 0.52 [alpha] = 0.05, Fig. 2). The fit was poor in relation to CL ([r.sup.2] = 0.31), whereas it failed to display a defined relationship with respect to chelae length and body weight. Relative fecundity also failed to show a clear relationship with CW ([r.sup.2] = 0.003, Fig. 3).

[FIGURES 2-3 OMITTED]

DISCUSSION

According to the results of this work, C. johngarthi is a species with a high population renewal capacity, compared with other species of larger deep crabs like Maiopsis panamensis, which produces between 351,501 and 1162,668 eggs, and Stenocionops ovata, which produces between 35,187 and 170,057 eggs; both species have a relative fecundity lower than 1,000 eggs per gram of female body weight (Villalejo-Fuerte et al. 1998, 1999).

In crustaceans, fecundity estimates derived from incubating eggs carried by females in their abdomen yield lower numbers compared with the estimates based on the number of intragonadal oocytes, because resorption of intraovarian oocytes during the maturation process occurs frequently. Additionally, many eggs fail when adhered to the pleopods at the time of spawning (Farmer 1974). Another factor that accounts for extraovarian fecundity estimates being lower than intraovarian ones is egg predation during incubation (Abello & Sarda 1982); however, fecundity estimates obtained from incubating-egg data yield more precise information to determine the renewal capacity of a population.

The ovigerous masses analyzed were evenly colored, ranging from orange to dark brown, which suggests that the spawning period takes place rapidly with embryonic development occurring synchronously, so that no difference is evident, at least to the naked eye. Histological evidence suggest that C. johngarthi can produce more than one batch of eggs in a breeding cycle, as is the case of the deep-living Majids Maiopsis panamensis and Stenocionops ovata (Villalejo-Fuerte et al. 1998, 1999). This would account for the low determination coefficient of the potential fit to fecundity data, because the number of eggs produced in successive partial spawning events decreases, resulting in a less adequate relationship with the organism's morphometric variables, however there is no evidence in the fecundity-length data.

According to Leija et al. (1992), the reproduction process for C. johngarthi takes place in October and recruitment during March and September; however, in this work ovigerous females were caught in January, so that the spawning, fertilization and incubation of eggs is likely to occur during the fall and winter, with recruitment taking place in the spring. To prove the earlier discussed, it is required to conduct sampling across a whole annual cycle, recording the frequency of ovigerous females to confirm this information.

ACKNOWLEDGMENTS

The authors thank Direccion General de Estudios de Postgrado e Investigacion del Instituto Politecnico Nacional (IPN) for funding this work, and acknowledge the fellowships of Comision de Operacion y Fomento de Actividades Academicas del IPN and Estimulo al Desempeno de la Investigacion to M. Villalejo-Fuerte and Mauricio Ramirez and the projects SIP-IPN 20061006 and CONACYT SAGARPA 200366.

LITERATURE CITED

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Sanchez-Ortiz, C., I. Cristobal-Huerta, J. L. Cervantes & J. Fiol. 1997. Crustaceos decapodos de aguas profundas de La Bahia de La Paz, B.C.S. In: R. J. Urban & M. R. Ramirez, editors. La Bahia de La Paz, investigacion y conservacion. UABCS-CICIMAR-SCRIPPS. pp. 129-137.

Villalejo-Fuerte, M., M. Arellano-Martinez & B. P. Ceballos-Vazquez. 1998. Fecundity of the panamic spidercrab Maiopsis panamensis Faxon, 1893 (Brachyura: Majidae) in the Gulf of California, Mexico. J. Shellfish Res. 17:299-301.

Villalejo-Fuerte, M., B. P. Ceballos-Vazquez, M. Arellano-Martinez & F. Garcia-Dominguez. 1999. Fecundity of the velvet spidercrab Stenocionops ovata (Bell, 1835) (Brachyura: Majidae) in the Gulf of California, Mexico. J. Shellfish Res. 18:181-183.

MARCIAL VILLALEJO-FUERTE, (1) * MAURICIO RAMIREZ-RODRIGUEZ, (1) EDUARDO F. BALART (2) AND CARMEN RODRIGUEZ-JARAMILLO (2)

(1) Centro Interdisciplinario de Ciencias Marinas-Instituto Politecnico Nacional, A.P. 592, La Paz, B.C.S., Mexico; (2) Centro de Investigaciones Biologicas del noroeste, A.P. 128, La Paz, B.C.S., Mexico

* Corresponding author. E-mail: [e-mail]