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The harvesting of the puerulus of rock, or spiny, lobsters for seed for aquaculture is a large industry throughout the Indo-Pacific region, and an increasing number of puerulus collectors are deployed. Little is known about the 'crowding effect' of the collectors and how catch might be influenced by their placement relative to each other owing to a lack of aggregate statistics for puerulus collectors in this region. The rock lobsters puerulus is also collected for fisheries research, as an index of puerulus catches on collectors can provide an indicator of recruitment strength. Both as a management tool and for commercial purposes, the collectors should act independently, not reducing or influencing catch rates on adjacent or other collectors in the area. We explored the independence of collectors of the puerulus of the southern rock lobster (Jasus edwardsii (Hutton, 1875)) using a long-term-data series from four sites on the east coast of Tasmania, Australia. Arrays of collectors were in grid and cross-shaped configurations, with individual collectors spaced three metres apart. Patterns in catches were examined using generalised least squares (GLS) modelling to determine if collectors filter pueruli as they swim shoreward, testing directional, neighbour, edge, and radial effects. The results revealed that there were no significant differences in puerulus settlement among collectors at this scale of spacing, meaning that arrays with collectors even as close as 3 m apart did not interfere with each other. This finding also suggests that collectors at this spacing only capture a small proportion of the available pueruli, allowing a significant number to pass through collector grids, with no significant reduction in catch of collectors further inshore. Such a result implies that it cannot be assumed that recruitment to a natural reef will be reduced by harvesting of pueruli with this type of collector and configuration. [ABSTRACT FROM AUTHOR]

Context: In Tasmania, Australia, the government's response to range-extending, barren-forming longspined sea urchin (Centrostephanus rodgersii) includes rebuilding of southern rock lobster (Jasus edwardsii) stocks to increase predation. But lobster preference for native species and continued barren expansion challenges the control efficacy. Aims: To determine the impact of lobster predation on C. rodgersii in different habitats. Methods: Multi-method dietary analysis consisting of stomach contents, faecal DNA and stable isotopes was performed on 64 lobsters from four habitats varying in barren extent and density of urchins and lobsters. Key results: C. rodgersii contributed to lobster diet in all barren habitats and was found in lobsters of every size class. Stable isotope and DNA analyses showed that C. rodgersii was more common in lobster diet than were targeted native species at incipient barren sites. Surprisingly, in extensive barrens C. rodgersii is less prominent in lobster diet. Conclusions: Combined with site-specific urchin population data, our findings indicated that lobster predation may be less effective at sites where most C. rodgersii individuals have reached a size refuge than at sites dominated by small urchins. Implications: Lobster predation may provide a useful control for smaller C. rodgersii , but top–down predatory control may be constrained at sites dominated by urchins that exceed the size suitable for lobster predation. Using a diverse set of methods, we investigated lobster diet in Tasmania to see whether lobsters prey on, and, consequently, contribute to the control of a destructive, range-extending sea urchin. We found that lobsters do consume the urchins, but to a lesser extent in the habitat where suitably sized urchins are scarce. These findings highlight the complexity of using native predators for pest control. [ABSTRACT FROM AUTHOR]

Trophic discrimination or fractionation factors (TDFs), such as ∆15N and ∆13C, are used in stable isotope mixing models to account for differences between source tissues (diet/prey) and consumer tissues (predator). We aimed firstly to obtain TDF values for a spiny lobster, the southern rock lobster Jasus edwardsii (Hutton, 1875), to better understand lobster diet in the wild and secondly to investigate variability in isotope signature within tissues of individuals and across a temporal scale to test if non-lethal sampling can be used in an ecological context. We conducted an 18-mo captive feeding trial with juvenile lobsters using three diet treatments and analysed dorsal and leg muscle, along with dorsal and leg exoskeleton for δ 13C and δ 15N values. Average TDFs for the three diet treatments were 3.86 ± 0.98‰ (∆13C) and 5.06 ± 0.65‰ (∆15N) for leg muscle, and 4.45 ± 1.04‰ (∆13C) and 4.36 ± 0.6‰ (∆15N) for dorsal muscle. When tested against wild lobsters and prey, these TDFs outperformed multi-taxa TDFs found in the literature. Isotope values from lobster leg muscle were not identical to associated dorsal muscle but the two were highly correlated, indicating that non-lethal sampling is acceptable. Values for exoskeleton isotope were significantly different from muscle, likely due to the exoskeleton not being in a constant state of growth and replacement, unlike the muscle tissue, which constantly incorporates new material. We conclude that our experimentally derived TDFs are suitable for mixing model analysis for J. edwardsii and when tested on a wild sample of lobsters they outperformed other TDFs reported in the literature. We show that non-lethal sampling using leg muscle is an appropriate sampling method, since this tissue is highly correlated to the commonly used dorsal muscle. This option for non-lethal sampling enhances the potential to widely sample wild populations or sample during industrial processing without the need to sacrifice whole animals. [ABSTRACT FROM AUTHOR]

To advance economic and sustainability objectives in a lobster fishery, four broadly different management policies were evaluated: minimum and maximum size limits, constant catch quotas, and quota set yearly in proportion to the previous year's catch per unit effort (CPUE). The performance of each policy was evaluated based on its discounted economic yield, together with egg production, catch, and catch stability. Maximum size limits performed poorly for all indicators. Raising the minimum size increased economic yield by improving yield-per-recruit. Output controls, both constant and dynamic, uniformly outperformed size limits, leading to substantially higher economic yield and egg production. A dynamic harvest control rule, setting quota in proportion to the previous year's catch rate, achieved the highest economic yield, catch, and egg production over 20 years. The optimal (30%) exploitation rate under this policy produced a 182% improvement in economic yield compared with a baseline strategy of only minimum size, but led to a mean year-to-year change in quota of 11.5% in response to yearly variable recruitment. This quota-setting management regime is straightforward to implement, using only catch rate as input. When absolute exploitation rate estimates are not available, this quota-setting harvest control rule can be constructed using only a target level of effort. Pour favoriser l'atteinte d'objectifs economiques et de durabilite dans une peche au homard, quatre politiques de gestion generalement distinctes ont ete evaluees, a savoir les limites de taille minimum et maximum, des quotas de prises constants et l'etablissement annuel des quotas en fonction des les captures par unite d'effort (CPUE) de l'annee precedente. La performance de chacune de ces politiques a ete evaluee sur la base de son rendement economique actualise, combine a la production d'oeufs, aux prises et a la stabilite des prises. La performance de limites de taille maximum est faible pour tous les indicateurs. En ameliorant le rendement par recrue, l'augmentation de la taille minimum s'est traduite par une augmentation du rendement economique. La restriction, dynamique ou constante, des prises a uniformement donne de meilleurs resultats que les limites de taille, produisant un rendement economique et une production d'oeufs sensiblement plus importants. Une restriction dynamique des prises, soit l'etablissement de quotas en proportion du taux de prise de l'annee precedente, a donne le rendement economique, les prises et la production d'oeufs les plus eleves sur 20 ans. Le taux d'exploitation optimal (30 %) en vertu de cette politique a produit une amelioration de 182 % du rendement economique par rapport a une strategie de reference basee sur la seule taille minimum, mais a mene a une variation interannuelle moyenne des quotas de 11,5 % en reponse aux variations interannuelles du recrutement. Ce regime de gestion base sur l'etablissement de quotas est simple a appliquer, ne necessitant que le taux de prise comme intrant. Quand des estimations des taux d'exploitation absolus ne sont pas disponibles, cette regle de controle des prises basee sur l'etablissement de quotas peut etre elaboree a la lumiere d'un niveau cible d'effort. [Traduit par la Redaction], Introduction Evaluating broadly different policies for managing a fishery can help determine which management regimes are more likely to achieve stated objectives, with resource sustainability the most common. However, the [...]