Abstract
Processes affecting the estimation of the size at onset of maturity (SOM) using ovigerous setae were investigated in southern rock lobsters Jasus edwardsii. Comparison of estimates of SOM based on ovigerous setae in samples collected during summer months (December-March) with those based on the presence of external eggs from winter months (June-August) indicated that ovigerous setae provide an accurate classification of maturity. Females with partially developed setation on pleopods are frequently observed in research catch-sampling projects and their maturity status was unclear. Our results show that these females with partially developed setae are most appropriately classed as immature, based on comparison between estimates of SOM determined by presence of external eggs or setae. The seasonal timing of field sampling affected estimates of SOM based on ovigerous setae, though tag-recapture data indicated that this was not associated with a loss of setae during a second annual moult. Estimates of SOM for populations of Jasus edwardsii around Tasmania can be based on maturity classification using ovigerous setae but care should be taken to ensure that seasonal timing of sampling is consistent.
Highlights
The size at onset of maturity (SOM) of female lobsters is an important parameter for lobster fisheries worldwide as it influences management through size limits and targets for egg production
This paper examines several of these assumptions in the use of pleopod setation for classifying the maturity status of southern rock lobsters Jasus edwardsii around Tasmania, Australia
Estimates of SOM based on presence and absence of ovigerous setae on pleopods in summer provided similar estimates of SOM as determined by the presence or absence of eggs in winter for most sites (Fig. 2)
Summary
The size at onset of maturity (SOM) of female lobsters is an important parameter for lobster fisheries worldwide as it influences management through size limits and targets for egg production. Size at onset of maturity in lobsters is usually quantified by a logistic curve that spans the transition from small immature animals to large mature animals. In this process of modelling maturity, observations are taken from the DOES PLEOPOD SETATION INDICATE JASUS MATURITY? The classification of female lobsters as mature can be made on the basis of several characters, including ovarian development, the presence of external eggs, endopodite processes of pleopods bearing ovigerous setae, sperm within seminal receptacles or spermatophore (tar spot), and the morphometry of the abdomen, legs or pleopod exopodite This measure of maturity is related to the need for setae for egg attachment after extrusion, so there is an expectation that females without setose endopodites would be unable to successfully brood eggs
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