Observations on the Carapace Length-Width and Carapace Width-Weight Relationships of the Blue Swimming Crab, Portunus Pelagicus (Linnaeus, 1758) in Bahraini Waters PDF

Keywords

Crustacea, Decapoda, Brachyura, Portunidae, Biometric, Bahrain waters.

Abstract

Studies on the biometric relationships of the blue swimming crab Portunus pelagicus from Bahraini waters, have been undertaken in the present investigation in order to understand the growth pattern of this species in terms of carapace length-width (CL-CW) and carapace width-weight (CW-Wt.) relationships, in this part of the world. From the (759) male and (1,233) female crabs that were collected from the offshore study region from October to November 1999, data have indicated that slopes of (CL-CW) relationships are found to be similar in both genders. The average slopes for crabs in areas (A) and (B) had exhibited an isometric growth with (CW) being (1.7) times (CL). The slope recorded for area (C) proved to be significantly less than (1), indicating an allometric growth with (CW) getting relatively longer in bigger crabs. As for the (CW-Wt.) relationship, the total of (2,070) male and (3.005) female crabs, which were collected over a period of (14) months (i.e. March 1999. April 2000), showed that males are heavier than females at (2) cms (CW), becoming more so above (6) cms (CW). Male exponents varied significantly between study areas and from one month to another, unlike those for females which are found to be similar across the study areas and months, except for area (B), June 1999, where the exponent was at lowest at (2.71). The higher exponents of males throughout most of the study period indicate their better condition over females. Both genders were found to be heavier during the Summer months, i.e. May-September. However, male and female slopes for (CW-CL) and many exponents for (CW- Wt) exhibited small differences which prove statistically significant. This is attributed to the large number of observations that make small differences significant, yet the biological significance may be less obvious.