Assessment and ecological characterization of the blue crab (jaiba, Callinectes arcuatus) in the Gulf of Nicoya, Costa Rica

Farid A. Tabash

Background

The Gulf of Nicoya is an estuary on the Pacific side of Costa Rica. It is an important fishing area. Because of declining returns in the demersal fish and shrimp fishery, fishers are looking for alternative fish resources. Recently interest in the exploitation of the blue crab (Callinectes arcuatus) as an alternative resource has increased (see photos). In 1997 40 fishing permits were granted for blue crab in the Gulf of Nicoya. Because until now the crab population was unexploited, this is a good time to investigate the crab population and look at the effects of the emerging fishery.

Distribution and ecology

Work by DeVries et al. (1983) showed that the crabs are distributed in the inner Gulf of Nicoya and along the eastern side of the outer Gulf (see map). During the dry season (December to April), females migrate to the waters of higher salinity in the outer gulf to spawn. Larvae are probably carried back into the inner gulf by advective streams (Epifanio and Dittel 1982). Stomach content analysis shows that crabs are primarily carnivores with a preference for slow preys like molluscs and shrimps (Table 1).

Characteristics of crab traps

Some experiments were done to determine the catch characteristics of the crab traps used by the fishers. Traps are made of chicken wire, measure 60x43x28 cm and are baited with fish (jack, ray). Both the time needed for a trap to be saturated and the maximum number of crabs caught per trap are variable, ranging from 2 to 7 hours and from 4 to 28 crabs per trap, respectively (see Figure 1 with data from Cascante).

Figure 1. Saturation of crab traps in the Gulf of Nicoya, Costa Rica.

Reproduction and population dynamics

50% of C. arcuatus males and females are mature at a length (carapace width) of 82 mm and 67 mm, respectively. Some population dynamics parameters determined from samples collected between May 1996 and February 1997 are given in Table 2.

Further research

Crabs may play an important role in the ecosystem of the Gulf of Nicoya. If young crabs and shrimps are important in the diet of demersal fish (esp. sciaenids and snooks), then an increased exploitation of the crab population and the continuous exploitation of the shrimp may affect the productivity of the commercially important demersal fish (biological interaction). One point of interest is the sex ratio in the catches. In traps, the majority of crabs caught are males while in trawl hauls more females appeared (Dittel et al. 1985). Apparently males and females occupy different spaces in the gulf or display different migration patterns.

References

• Cascante, S. (in prep.) Determination of the optimal fishing effort in the fishery on the crab Callinectes arcuatus in the internal part of the Gulf of Nicoya. Tésis de Licenciatura, Universidad Nacional, Heredia.

• DeVries, M.C., C.E. Epifanio and A.I. Dittel (1983) Reproductive periodicity of the tropica crab Callinectes arcuatus Ordway in Central America. Estuarine, Coastal and Shelf Science 17, 709-716.

• Dittel, A.I., C.E. Epifanio and J.B. Chavarría (1985) Population biology of the portunid crab Callinectes arcuatus Ordway in the Gulf of Nicoya, Costa Rica, Central America. Estuarine, Coastal and Shelf Science 20, 593-602.

• Epifanio, C.E. and A.I. Dittel (1982) Comparison of dispersal of crab larvae in Delaware Bay, USA and the Gulf of Nicoya, Central America. p. 477-487 in: Estuarine Comparisons (ed. by V.S. Kennedy). Academic Press, New York.

• Saucedo, R.A. (1997) Hábitos alimentarios, morfometría y patrones de maduración de Callinectes arcuatus (Crustacea: decapoda) en el Golfo de Nicoya, Costa Rica. Tésis de Licenciatura, Universidad Nacional, Heredia. 68 p.

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