Theoretical size at the onset of maturity and its density-dependent variability as an option in crustacean fisheries management

Theoretical size at the onset of maturity (TSOM) for female Norway lobster was estimated by a new methodology based on the probability distributions of mature individuals built on physiological maturity measures. Onset of maturity using TSOM varied from 18.4- to 33.7-mm carapace length for the Irish functional management units (FUs). These estimates showed a significant negative linear relationship (R-2 = 0.60) with population density and a significant positive linear relationship with average size in females (R-2 = 0.84). The size class at which 50% of the females are sexually mature (L-50) was linked to the new TSOM metric by a significant positive linear relationship (R-2 = 0.40). This set of linear relationships ultimately allowed TSOM and L-50 to be estimated without a requirement for maturity stages to be distinguished. As well as contributing to the stock assessment and management of Nephrops (e.g. in data-limited FUs) and its potential for the calibration of more routinely used estimates, TSOM might be applied in new species and meta-analyses where size of maturity data are scarce. This new metric also better-defines the maturity process since, taken together, TSOM, L-50, and smallest berried female represent sequential maturity events: (i) onset of maturity, (ii) 50% mature (from gonad staging), and (iii) berried females.

Automated summary

A new methodology was utilized to estimate the Theoretical Size at Onset of Maturity (TSOM) for female Norway lobster, showing linear relationships with population density, average size in females, and the size class at which 50% of females are sexually mature (L-50). This new metric has the potential to contribute to stock assessment, management, and calibration in data-limited areas, as well as being applicable in new species and meta-analyses with sparse maturity data.