During an 18-month study, we monitored (by beam trawl and tagging) a year-class of Dungeness crabs Cancer magister as crabs grew and as males recruited to the fishery at 154 mm in notch-to-notch carapace width (CW). We used an enhanced size-frequency analysis to estimate that males, inferred to be 2 years old in summer 1985 and mainly in the 104-mm (mean CW) instar, molted twice during an 18-month period to attain the 156-mm instar (SD = 13 mm). About 58% of males in the 156-mm instar had attained legally harvestable size. Similarly, females inferred to be 2 years old in summer 1985, and mainly in the 103-mm instar, molted to the 121-mm instar during summer and autumn 1985 and subsequently appeared to molt annually. Our size-frequency analyses were enhanced by (1) incorporating regression statistics for growth increments versus CWs, (2) simultaneously analyzing several size-frequency distributions obtained sequentially in time, and (3) accounting for the exploitation of legal-sized males. Our results for females indicated decreasing SDs of CWs for successive instars. This pattern follows from the negative relationship between the size of molt increment and CW, and it might be anticipated for other crab species with a similar growth function.
No takes yet. Share an insight, caveat, or question.
Smith et al. (1989) studied this question.