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The size at the onset of sexual maturity for female rock lobsters, Jasus edwardsii, was defined as the size or size class at which 50% of the rock lobsters in a sample were mature, and was estimated at 27 localities around New Zealand. Animals were regarded as mature if they were bearing external eggs attached to the pleopods or if there were well developed setae on the endopodites of the pleopods. Samples from the same location in different years showed little variation in the size at the onset of maturity. There was, however, considerable variation between localities, ranging from 72 mm carapace length near Gisborne to 121 mm carapace length in eastern Foveaux Strait. Size at the onset of maturity showed an inverse relationship with water temperature. The relationship between the size at the onset of maturity, age, growth rate, and water temperature is discussed.

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Two general types of yield model, stock production and dynamic pool (yield-per-recruit), were used to analyse available data for the New Zealand rock lobster, Jasus edwardsii (Hutton). An exponential stock production model was applied to commercial catch and effort data from 1945 to 1975 for the North and South Islands combined. The results suggest a maximum sustainable yield of 4227 t with an estimated optimal level of fishing effort of 784 vessels, about 60% of the 1975 number. Empirical and von Bertalanffy growth equations were derived from limited tag-recapture data from the Gisborne area. Both equations indicate that males grow faster than females. The empirical growth equation, based on moult increment and frequency as functions of size, is considered the more realistic. Two yield-per-recruit models provided different results, especially at low levels of natural and fishing mortality. One model (Beverton-Holt) incorporated the von Bertalanffy growth equation and the other (empirical model) an empirical growth equation; the latter model is considered more realistic. The empirical model suggests that a reduction in fishing mortality below the estimated present values will not result in a substantial increase in yield-per-recruit. No strong evidence for changing the minimum size at first capture emerged from the results of the empirical model. A need is evident for more data, spanning a greater size range, to provide better estimates of growth and natural mortality, because the yield-per-recruit models were found to be sensitive to both. INTRODUCTIONThe reck lobster, Jasus edwardsii (Hutton), is of great economic significance, and is now the single most valuable renewable resource taken by the New Zealand fishing industry. The fishery began to expand rapidly with the development of export markets in the latf 1940s. The latest statistics show that about 1979 t, [valued at approximately N.Z. $23 667 000 were exported in 1977 (Anon. 1978), compared with 1799 t ^valued at N.Z. $4 619 000 in 1966. Thus, it seems prudent to develop management plans as quickly as possible to ensure sustained high productivity cf this resource and to avoid the results of over-fishing.Some information on the geographic distribution, breeding biology, and development of this species is availab , e (Kensler 1967, Sorensen 1969. Street 1970Street , 1973a has provided important information on growth, moulting, movements, reproductior, and predation, and estimates of exploitation rates from field observations and marking studies. Kenslet (1968) examined the size-fecundity relationship ofj a limited number of females.Streejt (1973a, b) described some of the management measures being used and their probable significance, but management regulations should be reexamined in the light of recent information. Since 1974 a tagging programme has been carried out by personnel of the Fisheries Research Division using the western rock lobster tag (Chittleborough 1974), which is retained through ecdysis. In addition, catch sampling, analysis of fishi...

Samples of berried female Jasus edwardsii (Hutton) were taken from rock lobster pots fished by commercial fishermen from eight areas around New Zealand, and the number of eggs counted using an electronic egg counter. The size of females ranged from 74 to 157 mm carapace length (CL) and fecundity from 37 499 to 407 032 eggs per female. The fecundity-size relationship was described by a power function of the form fecundity (f ) = a CL b . There were no significant differences between most samples, which resulted in a considerable degree of overlap in the fecundity-size relationship between areas. The maximum fecundity observed in this study is considerably less than the maximum observed in two previous studies of J. edwardsii. Egg loss at Kaikoura between the early and middle stages of the egg-bearing period was 20%. The fecundity of J. edwardsii is generally less than the fecundity of three other closely related Jasus species (J. lalandii, J. novaehollandiae, and J. frontalis) at similar sizes.