Abstract
The spotted box crab Calappa philargius (Calappidae) is an increasingly consumed species in China, mainly sourced from a claw-only fishery. Being a not well-characterized species in the literature, this study is warranted to inform sustainable management approaches. Here we report on the first in-depth overview on biology and fishery dynamics of C. philargius in the southern Taiwan Strait of China. Whole body crabs (N = 1,009) were collected monthly from January to December 2019 from trawlers, operating in the southern Taiwan Strait; sample collection was absent from May to July because of the national fishing moratorium regulation. Sex ratio, growth pattern, size at maturity and fecundity were estimated. The overall male: female ratio was 1: 1.47, significantly differing from the 1: 1 (p < 0.01); monthly sex ratio variations were also significant (p < 0.01), suggesting possible seasonal sexual segregation. We found the carapace widths (CW) of males were significantly larger than those of females (p < 0.01). Based on the occurrence and percentages of berried females, we identified twin spawning events in January–April and August–October with the overall peak occurring in February. Size at 50% female maturity was 11.47 cm CW. Female absolute fecundity was significantly related to CW via a power function relationship (N = 14, p < 0.01). The estimated average claw yield was 36.28 ± 3.07% of the whole body weight (N = 95), irrespective of sex and size (p > 0.5). Capture and trade data of C. philargius using trawl and trap fishing gears were documented to characterize claw-only fishery dynamics for future research and sustainable use.
Highlights
Claw-only crab fisheries have been developed since the 1970s and are commonly considered as renewable fisheries
For the rest of the sampling months there were no significant differences from an equal sex ratio (p > 0.05)
Males were mainly landed in size classes between 11.0 and 14.9 cm carapace widths (CW) (80.15%) and females between 9.0 and 13.9 cm CW (91.18%), determined by the size frequencies > 10% (Figure 4)
Summary
Claw-only crab fisheries have been developed since the 1970s and are commonly considered as renewable fisheries. After the collection of claws on board, the declawed live bodies are released This fishery mode includes the red crab Chaceon affinis (Geryonidae) in the Northeast Atlantic (Robinson, 2008), the brown crab Cancer pagurus (Cancridae) in Ireland (Fahy et al, 2004), Claw-Only Fishery in China the stone crabs Menippe spp. The estimated mortality rate for single-claw removal in M. mercenaria and C. borealis is reduced around 35–50% compared to two-claw removal in the fishery (Davis et al, 1978; Duermit et al, 2017; Goldstein and Carloni, 2021). Voluntary adherence to one-claw fishing regulations is not universal, and the seasonal closure to protect spawning stocks can be a better management measure (Duermit et al, 2017)
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