The impact of size truncation on reproductive success in the southern king crab (Lithodes santolla)

Sex-biased fishing mortality caused by male-only fishing may result in sperm limitation and recruitment overfishing. These effects can be observed by studying the size at functional reproduction (SFR) of lithodid females. We studied changes in the ratio of males to females, size truncation, and changes in SFR in the southern king crab (SKC) in two areas experiencing different fishing pressures in southern Chile. SFR was estimated with the Richards Function, a generalized 4-parameter logistic model. The shrinking of SFR of females may occur due to the proportional shrinking of reproductive and non-reproductive females and/or because the shape of the ogive changes, setting the inflection point back to smaller sizes. In the region with low fishing pressure the functional reproductive ogive was symmetric (gamma = 1, and the asymptote was similar to 1, indicating a balance in male availability. In the region with high fishing pressure gamma was 82 % lower and the asymptote was 23 % lower, an indicator of sperm limitation. The symmetric shape of the logistic curve, which is widely assumed when fitting maturity ogives, is not the most appropriate assumption in SKC and possibly in other males-only crab fisheries. More general shapes of the ogive should be estimated and studied.

Automated summary

Sex-biased fishing mortality and male-only fishing can lead to sperm limitation and recruitment overfishing. By studying the size at functional reproduction (SFR) of lithodid females, we observed changes in male-to-female ratio, size truncation, and SFR in southern king crab populations in two areas with different fishing pressures. The shape of the reproductive ogive changed in response to fishing pressure, indicating sperm limitation in the heavily fished region. The assumption of a symmetric logistic curve may not be appropriate for fitting maturity ogives in male-only crab fisheries, and more general shapes of the ogive should be considered and studied.