Demography, fishery yield and potential management strategies of painted spiny lobster (Panulirus versicolor) at Northwest Island, Great Barrier Reef, Australia Ashley J. Frisch A,C and Jean-Paul A. Hobbs B A ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Qld 4811, Australia. B The Oceans Institute and School of Plant Biology, The University of Western Australia, Crawley, WA 6009, Australia. C Corresponding author. Email: ashley.frisch@jcu.edu.au Abstract. Quantification of demographic parameters is important for understanding how populations interact with their environment and for developing sustainable harvest strategies. Our aims were to quantify demographic parameters and yield of painted spiny lobster (Panulirus versicolor) at Northwest Island, Great Barrier Reef and review fishery management regulations in view of the findings. Using catch-curve analysis and an intensive mark–recapture program, the local lobster population was found to be sparsely distributed (,1.3 ha 1 ), with low rates of natural mortality (0.25–0.28 year 1 ) and immigration (0.05 ha 1 year 1 ). Under current management regulations (no minimum size limit; MSL), yield-per-recruit peaked at 0.38 kg when fishing mortality was 0.4 year 1 . Implementation of a 100-mm (carapace length) MSL is recommended because it provides the best compromise between yield and stock size and has minimal impact on existing fishing practices. Revocation of the prohibition on possessing egg-bearing females is also recommended because it would reduce wastage of lobsters that are inadvertently killed by spear-fishers and because there appears to be little chance of localised recruitment overfishing. This study provides the first estimate of mortality rate for P. versicolor and highlights the importance of this parameter for understanding demographic processes and optimising management regulations. Additional keywords: coral reefs, fishery management, mortality, population dynamics, yield per recruit. Received 2 November 2011, accepted 16 January 2012, published online 30 April 2012 Introduction Spiny lobsters (Family Palinuridae) are a highly esteemed sea- food, not just in places where they are captured, but all over the world. Consequently, spiny lobsters are a high-value commod- ity and commercial, recreational and artisanal fisheries have developed wherever these animals are abundant (Pitcher 1993; Phillips 2006). Due to the increasing size and wealth of the human population, the future worldwide demand for spiny lobsters is expected to increase. However, most of the world’s spiny lobster fisheries are now considered to be either fully exploited or over exploited (Phillips and Melville-Smith 2006). The need for effective management of spiny lobster populations is therefore critical. Effective management of lobster populations requires knowledge about the fishery (e.g. catch per unit effort), biology of the target species (e.g. size at first maturity) and demography of the unit stock. One of the most important demographic parameters is mortality rate, because it is requisite for develop- ment of almost all fishery harvest models (Vetter 1988). Total mortality rate (Z ) is the sum of deaths caused by natural mortality (M ) and fishing mortality (F ). Surprisingly, Z, M and F are unknown for most species of spiny lobster, primarily because age determination is hindered by moulting (ecdysis). As such, mortality rates of spiny lobster populations are most often estimated by length-converted catch curve (LCCC) analy- sis (Morgan 1980; Pitcher 1993), which involves conversion of length frequencies to age frequencies using von Bertalanffy growth parameters (Pauly 1983). However, LCCC analysis is often unreliable because of errors associated with variable recruitment, size-specific gear selectivity and the poor empirical relationship between lobster length and age (King 1995). Another method for estimating mortality rate of spiny lobster populations is multiple mark–recapture. The Jolly–Seber mark– recapture model is particularly useful because it can simulta- neously estimate population size, mortality rate and recruitment (or immigration) rate and the model allows each of these parameters to vary with time (Krebs 1999). Once mortality rate and other demographic parameters have been adequately quantified, yield of lobster fisheries can be investigated via yield-per-recruit (YPR) analysis (Ebert and Ford 1986; Pitcher 1993). The YPR model examines the trade-off between capturing a larger number of young (or small) CSIRO PUBLISHING Marine and Freshwater Research, 2012, 63, 387–396 http://dx.doi.org/10.1071/MF11241 Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/mfr