A Comparative Study on the Allometric Characteristics of Blue Swimmer Crab (Portunus pelagicus) Populations from Tayabas Bay and Manila Bay

Abstract

To estimate differences in the allometries of two populations of Portunus pelagicus, specimens were sampled within a three-month period from Tayabas Bay in San Juan, Batangas and from Manila Bay in Paranaque, Metro Manila. The body weight (BW), carapace height (CH), cheliped height (ChH), cheliped propodus length (ChP) and cheliped dactyl length (ChD) of each crab were employed as dependent variables, and carapace width (CW) as the independent variable, in linear regression analyses to test for variations in relative growth. Overall, the relationship between BW and CW among the crabs showed high levels of allometry. Males were found to have faster ChP growth than females, revealing a sexual dimorphism for this particular trait. The increase of the studied body dimensions becomes greater among adults than among the juveniles. Water quality testing revealed that when compared to the Tayabas Bay site, Manila Bay waters were relatively hypoxic, a stress condition, along with overharvesting and parasitism, to which lower relative growth of crabs from this site may be attributed.