Population Biology of the Swimming Crab Portunus Sanguinolentus in the Waters off Northern Taiwan

Abstract

The growth, mortality, and reproduction of Portunus sanguinolentus were studied using size-frequency data obtained from crabs collected in pots in the waters off northern Taiwan from October 2000 to March 2001, and October 2001 to January 2002. The Bhattacharya's method and seasonal von Bertalanffy growth curve were used to estimate growth parameters. The growth curve for males was |${\rm L}_{{\rm t}} = 204.75 \times \{1 -e^{-[0.87{\rm t} + 0.4(0.87/2\pi)\sin2\pi(t)]}\}$| and the curve for females was |${\rm L}_{{\rm t}} = 194.25 \times \{1 -e^{-[0.97{\rm t} + 0.4(0.97/2\pi)\sin2\pi (t)]}\}$|⁠. A size-converted catch curve was used to estimate the instantaneous total mortality rate (Z), and Pauly's empirical equation was used to estimate the instantaneous natural mortality rate (M). For males, |${\rm Z} = 3.16/{\rm year}$| and |${\rm M} = 1.65/{\rm year}$|⁠. For females, |${\rm Z} = 3.37/{\rm year}$| and |${\rm M} = 1.8/{\rm year}$|⁠. The instantaneous fishing mortality rate (F) was 1.51/year and 1.57/year, and the exploitation rate (E) was 0.48 and 0.47 for males and females, respectively. The exponential relationships were presented for relationships of fecundity in number and weight of egg mass in terms of carapace width and body weight. Those relationships were statistically significant |$(P \lt 0.01)$|⁠, indicating that the fecundity increased with the size from |$4.05 \times 10^5$| to |$2.44 \times 10^6$| eggs.