Estimates for the size at onset of maturity for New Zealand scampi (Metanephrops challengeri)

Abstract

The size at the onset of maturity (SOM) was estimated for New Zealand scampi, Metanephrops challengeri (Balss, 1914), from data collated over 30 yrs from commercial and research trawls within four fisheries management areas (FMAs). SOM for females was estimated using four methods: the size of smallest berried females, the size at which 50% of females bear eggs (L50eggs), the size at which 50% of females display mature gonads (L50gonads), and allometric changes in abdomen width in relation to carapace length (CL). Females appeared to mature over a wide range of sizes, with the size of smallest berried females within each FMA being markedly less than estimates from all other methods. Estimates of SOM from L50gonads (30–30.1 mm CL) were comparable to estimates of allometric changes in abdomen width (33.8 mm CL), but were smaller than estimates from L50eggs (39.8–48.8 mm CL), indicating that abdomen widening (morphological maturation) and early-stage gonad maturation (physiological maturation) occurs prior to the bearing of eggs. Estimates of SOM from L50eggs increased with higher relative latitudinal position of FMAs and corresponded with decreases in both water temperature and scampi density. The dependence of SOM on each of these interacting variables requires further investigation. SOM for male scampi was estimated through investigations of allometric changes in appendix masculina, occurring at 52.5 mm CL. Allometric growth was not observed in male chelae in relation to CL. The results indicate regional differences in maturation that may require greater consideration in managing harvesting of this important commercial species.