Growth rates of juvenile southern rock lobster (Jasus edwardsii) estimated through a diver-based tag]recapture program

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1 CSIRO PUBLISHING Marine and Freshwater Research Growth rates of juvenile southern rock lobster (Jasus edwardsii) estimated through a diver-based tag]recapture program Adrian Linnane A,D, David Hobday B, Stewart Frusher C and Caleb Gardner C A South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, SA 5022, Australia. B Fisheries Research Branch, Department of Primary Industries, PO Box 114, Queenscliff, Vic. 3225, Australia. C University of Tasmania, Institute of Marine and Antarctic Studies, Private Bag 49, Hobart, Tas. 7001, Australia. D Corresponding author. Adrian.Linnane@sa.gov.au Abstract. Despite being one of the most economically important fisheries in south-eastern Australia, growth rates of juvenile southern rock lobster (Jasus edwardsii) have not previously been quantified in the wild. This study utilised a diver-based tag recapture program to estimate growth rates of individuals between mm carapace length (CL) in temperate reef sites across south-eastern Australia. Of the 7064 lobsters tagged and released, 978 (14%) were recaptured with recapture rates of 23, 5 and 7% in the States of Tasmania, South Australia and Victoria respectively. Although individual growth increments were similar between the sexes, differences in annual growth rates were evident at 50 mm CL, with males growing,1.4 times faster than females. Increased levels of growth in males resulted from a higher moult frequency, which was found to significantly reduce in females as they reached sexual maturity at,70 80 mm CL. No significant difference was found in growth rates of males or females between the States when all sites within each State were combined. The growth estimates from this work contribute to the understanding of juvenile lobster population dynamics and will improve current fishery models by confirming relationships between early juvenile, pre-recruit abundance and entry to the fishable biomass. Received 3 June 2011, accepted 8 October 2011, published online 28 November 2011 Introduction Given the economic importance of lobster fisheries, growth rates of several species have been highly profiled worldwide. Research to date on palinurid lobsters has largely focussed on late-juvenile and adult life history stages whereas estimates for post settlement to late juveniles are less numerous. This primarily relates to the behavioural characteristics of these species combined with size-selectivity effects from commercial fishing gear on which many recapture studies depend. Early juvenile (,35 mm carapace length; CL) palinuridae are asocial and dwell solitarily in vegetation or isolated holes with reef habitat (Butler and Herrnkind 1991; Edmunds 1995). At around mm CL, juveniles undergo ontogenetic changes in sociality that alters their aggregation patterns and use of shelters (Ratchford and Eggleston 1998; Butler et al. 1999). Driven by chemical cues released by conspecifics (Ratchford and Eggleston 1998), juveniles start to congregate in crevice shelters. However, even as larger crevice-dwelling juveniles, movement away from shelters appears limited (,25 m), only increasing as individuals reach the pre-recruit and adult stages (MacDiarmid et al. 1991). As a result, juvenile Journal compilation Ó CSIRO 2011 lobsters are less likely to come into contact with commercial pots during routine fishing operations. In addition to behavioural characteristics, commercial fishing gear is now designed to minimise catches of undersized lobsters, with escape gaps compulsory in many fisheries worldwide. Mandatory mesh sizes are also enforced with the aim of releasing juvenile lobsters before hauling. Consequently, the combination of behavioural traits and commercial pot design mean that smaller-sized juveniles are rarely seen in fisheries where pots as used as a method of capture. In Australia, the palinurid southern rock lobster (Jasus edwardsii) supports important commercial and recreational fisheries across the south-eastern States of South Australia, Victoria and Tasmania with a combined catch of,3000 tonnes annually (Linnane et al. 2010). Fishing methods have generally remained unchanged over time, consisting of baited pots that are set individually overnight and hauled at first light. Previous tagging studies in the fisheries (Punt and Kennedy 1997; McGarvey et al. 1999) have relied on commercial pots as a method of capture and, as a result, provided growth estimates for pre-recruit and adult individuals only.

2 B Marine and Freshwater Research A. Linnane et al. Table 1. Summary of the key habitat features within each study site Site (State) Location (Latitude, longitude) Reef type Algal assemblages Depth (m) Gerloffs (South Australia) Livingstons (South Australia) Port Campbell (Victoria) Glenvar Bay (Tasmania) Pigeon Holes (Tasmania) Pt Leuseur (Tasmania) S, E Medium-high profile, limestone with some deep ledges Cystophora/Sargassum, and Caulerpa S, E Low profile, limestone platforms, Cystophora/Sargassum, Caulerpa 2 5 shallow ledges and Posidonia/Amphibolis S, E Medium-high profile, limestone, Cystophora and Caulerpa 2 7 deep ledges and complex boulder reef S, E Flat-lying, arenite/lutite boulders topped Ecklonia radiata and red algae 5 9 with rubble S, E Medium profile, arenite/lutite Ecklonia radiata and red algae S, E Medium profile, dolerite reef with vertical cracks and larger boulders Ecklonia radiata and Phyllospora comosa 4 10 Table 2. Numbers of tagged, recaptured and recapture rates within each of the study sites State Site Number tagged and released Number recaptured % Recaptured South Australia Livingstons Gerloffs Total Victoria Port Campbell Tasmania Point Leuseur Glenvar Bay Pigeon Holes Relocated to Pigeon Holes Total Total (all States) Recent research in south-eastern Australia has highlighted the need for growth rate estimates across all life history stages. For example, the Tasmanian rock lobster fishery is regarded as being ideally placed to be an early warning signal for Australian fisheries generally (Pecl et al. 2009). Being at the interface of the East Australian Current and southern ocean waters, it is experiencing climate warming faster than any other region in the southern hemisphere. Warming waters have already altered species distributions and impacted ecosystems within the region (Ling et al. 2009). Given the relationship between water temperature and growth rates in many crustacean species, this has the potential to further impact on lobster population dynamics through changes in survival or recruitment processes. In South Australia, recent estimates suggest that growth rates in adult lobsters are declining, which may be also linked to climate changes processes in the region (Linnane et al. 2010). The aim of our study was to investigate the growth rates of juvenile lobsters from 40 to 80 mm CL on temperate reef habitat and relied on tag and release by divers rather than potting or trapping techniques normally used for pre-recruit and adult growth studies. Materials and methods Study location and habitat Six study sites were chosen: two in South Australia, one in Victoria and three in Tasmania. The habitats generally consisted of limestone ledges with associated algal assemblages (Table 1). Juvenile tagging and recapture Between June and October 2002, 7064 juvenile lobsters were caught across the three States (Table 2). Lobsters were captured by SCUBA divers using snares, wires (by permit in Victoria) or gloved hand, or a combination of these, then transferred to a mesh catch bag where they were held until the completion of the dive or until sufficient numbers had been collected. Lobsters were then returned to a boat, where they were individually tagged using numeric Hallprint mini T-bar tags (Hindmarsh Valley, SA). All tags were inserted ventrally, using a Dennison tag-fast III tag applicator (Elizabeth West, SA), into the anterior oblique muscle between the first and second abdominal sterna. Data recorded upon initial tagging and subsequent recapture included location (GPS coordinates), sex, CL, depth, sexual maturity based on setal development and damage, including loss of legs or antennae and scars caused by tag shedding. A plastic cable tie, placed around the base of an antenna on each lobster, aided identification and meant that unnecessary handling of lobsters tagged the previous day could be avoided. During the entire process, lobsters were kept cool and out of direct sunlight to reduce stress. Once measurements were completed, lobsters were released onto the reef site. Sites across all States were resurveyed by SCUBA from March 2003 to October of Growth estimation To investigate the moult increment and frequency of moulting, recaptures were separated into three size classes based on the

3 Growth rates of juvenile lobster Jasus edwardsii Marine and Freshwater Research C Table 3. Estimates of the von Bertalanffy growth parameters for each site (Minimum time at liberty 0.6 years) Site (State) Sex n Distribution model K s.d. (%) l N (mm) Gerloffs Bay (South Australia) Female 7 Gamma Male 13 Gamma Livingstons Bay (South Australia) Female 26 Gamma Male 35 Gamma Pigeon Holes (Tasmania) Female 104 Weibull Male 69 Weibull Glenvar Bay (Tasmania) Female 29 Weibull Male 24 Gamma Point Leuseur (Tasmania) Female 26 Weibull Male 23 Weibull Port Campbell (Victoria) Female 15 Gamma Male 5 A A Unable to estimate growth parameters. initial size when tagged. The smallest size represented lobsters that were,50 mm CL. The medium size range included lobsters from mm CL and the largest size range contained lobsters that were mm CL. Moult increments were determined by identifying principal modes in the frequency distributions of increments for recaptured juveniles that were at large for less than 6 months. The frequency of moulting was similarly investigated by looking at recaptures at liberty for up to 1 year. Due to the small recapture sample sizes at some sites, only Pigeon Holes and Livingstons could be analysed for all size groupings and time periods. Average annual growth rates were determined using several stochastic versions of the von Bertalanffy Fabens growth model (Troynikov et al. 1998). Inputs to the analyses were CL at release and recapture and time at liberty. These models were used for calculating growth transition matrices for a rock lobster stock assessment population dynamic model (Punt et al. 2006). The deterministic von Bertalanffy Fabens growth parameters l N and k were estimated for each sex at each site (Table 3). As the stochastic growth models are in the form of probability density functions, the likelihood-ratio test was used for comparison of growth between different sites. Originally, the von Bertalanffy Fabens growth model was developed for populations with continuous growth, when a small time at liberty will produce a small length increment. However, the discontinuous growth of rock lobsters means that for very short times at liberty, the increment in size can be zero or significant, depending on whether the lobster has moulted whilst at liberty. In this situation, the stochastic von Bertalanffy Fabens growth model can only use data that have time-atliberty of more than,6 months to allow sufficient time for moulting to occur, providing a balance between data loss and the ability to fit the data. As a result, records retained for analysis were restricted to those where time at large was 7 months to exclude records where no moulting had occurred. Annual mean growth rates were calculated for three reference lengths of 50, 60 and 70 mm CL. Results Recapture rates Of the 7064 lobsters tagged and released, 978 (14%) were recaptured with recapture rates of 23, 5 and 7% in Tasmania, South Australia and Victoria respectively (Table 2). In Tasmania, the highest recapture rate of 40% was at Point Leuseur, with Glenvar Bay and Pigeon Holes having recapture rates of 20 23%. The higher recapture rate at Point Leuseur was related to the comparatively low amount of cryptic habitat enabling greater access by divers and the isolation of the reef by surrounding sand, which restricted movement of tagged lobsters away from the study area. South Australian recaptures were much lower than in Tasmania, with only 1.5% recaptured at Gerloffs and 7% at the Livingstons site. These lower recapture rates again reflect the more cryptic nature of the habitat in South Australia and the fact that the sites were not significantly isolated from other reef structures thereby reducing their ability to retain lobsters. In Victoria, the recapture rate was 7% which was similar to that in South Australia, again reflecting the cryptic nature of the habitat and increased difficulty to capture and then recover tagged lobsters in a complex reef system. Moult frequency The following interpretation is subjective and serves only to provide an indication of moult frequency. At Pigeon Holes, the highest proportion of males,50 mm CL at initial tagging and recaptured up to 1 year after release had grown mm CL (Fig. 1a). This likely represents two full moults as there was a smaller peak at 4 5 mm. Other males of the same initial size had grown 15 and mm CL, representing a further two moults. Males,50 mm CL at tagging were, therefore, probably moulting four times per year. Similarly, females released at,50 mm CL showed peaks in growth increment of 4, 8 12, and 20 mm CL indicating at least four moults per year (Fig. 1b). In the mid size range, males that were mm CL at tagging had grown 5 7 mm CL (Fig. 1a). This likely represents

4 D Marine and Freshwater Research A. Linnane et al. (a) 70 Pigeon Hole males (b) Pigeon Hole females <50 mm mm mm <50 mm mm mm Proportion Increment (mm) Increment (mm) (c) 70 Livingstons males (d ) Livingstons females <50 mm mm mm <50 mm mm mm Proportion Increment (mm) Increment (mm) Fig. 1. Percentage frequency of growth increments of male and female lobsters for size ranges of,50, and mm CL at Pigeon Holes ((a) males, (b) females) and Livingstons ((c) males, (d ) females). All growth increments occurred within 12 months of tagging. two to three full moults as there were smaller peaks at and 17 mm also. Similarly, females released at mm CL, showed peaks in growth increment at 5, 11, 14 and 16 mm CL (Fig. 1b). In the largest size range, males initially tagged at mm CL showed a broad spread of increments indicating a high moulting frequency (Fig. 1a). In contrast, female frequency was highest in the 3 5 mm CL increment only (Fig. 1b), indicating only one moult per year. At Livingstons, the highest proportion of males,50 mm CL at initial tagging and recaptured up to one year after release had grown 8, 10, and 17 mm CL (Fig. 1c). Assuming the initial peak at 8 mm CL represents two moults, this suggests that this size range is probably moulting four to five times per year. Females showed peak increment frequencies at 4, 6 and 9 mm CL or three moults per year (Fig. 1d). In the mid size range, males that were mm CL at tagging had grown 4, 7, 9, and 16 mm CL (Fig. 1c), suggesting four to five moults per year. Females appeared to be moulting at least three to four times per year with peak increments at 3, 6, 9 and mm CL (Fig. 1d). In the largest size range, males initially tagged at mm CL had grown 4 6, 8, 12 and 16 mm CL suggesting around four moults per year (Fig. 1c). In contrast, female increment frequencies peaked at 3 and 6 mm CL (Fig. 1d) suggesting just two moults per year. Overall, the results suggest that up to 50 mm CL, there is no difference in moult frequency between the sexes. However, at sizes.50 mm CL males are moulting,1.4 times more often than females, suggesting that as females reach sexual maturity, moult frequency is reduced. Likelihood estimates of von Bertalanffy growth rate (k) and maximum length parameter (l N ) for each site are provided in Table 3. Annual growth increments South Australia At 50, 60 and 70 mm CL, males at Livingstons (Fig. 2a) were growing between 5 and 7 mm year 1 faster than females (Fig. 2b). At Gerloffs (Fig. 2c), males were growing at a rate of mm year 1. As only seven females were recaptured, an estimation of mean growth was not possible. Likelihood ratio comparison of within-state sites showed no significant

5 Growth rates of juvenile lobster Jasus edwardsii Marine and Freshwater Research E (a) Male Livingstons (b) Female Livingstons (c) Male Gerloffs (e) Male Pigeon Holes (g) Male Point Leuseur (d ) (f ) (h) Female Port Campbell 13.9 Female Pigeon Holes Female Point Leuseur Growth at 50 mm Growth at 60 mm Growth at 70 mm Mean growth at 50 mm Mean growth at 60 mm Mean growth at 70 mm Fig. 2. Estimates of growth using the stochastic model at Livingstons ((a) males, (b) females), Gerloffs ((c) males only), Port Campbell ((d ) females only), Pigeon Holes ((e) males, ( f ) females) and Point Leuseur ((g) males, (h) females). Time at liberty was.0.6 years. difference (P. 0.05) in male growth between the two South Australian localities. Victoria A stable estimate of growth was only possible for females in Port Campbell (Fig. 2d) because of the low number of male recaptures. Females were growing at an average of 13.9, 11.5 and 9.1 mm year 1 at 50, 60 and 70 mm CL respectively. Tasmania Growth at Pigeon Holes was similar to that at the other Tasmanian sites, with male growth (2e),7 mm year 1 higher

6 F Marine and Freshwater Research A. Linnane et al. (a) Mean growth (mm year 1 ) (b) Mean growth (mm year 1 ) Males Livingstons Pigeon Holes Glenvar Bay Point Leuseur Growth at 50 mm CL Growth at 60 mm CL Growth at 70 mm CL Females Livingstons Pigeon Holes Glenvar Bay Point Leuseur Growth at 50 mm CL Growth at 60 mm CL Growth at 70 mm CL Fig. 3. Estimates of (a) male and (b) female growth per year using the stochastic model for all sites with sufficient recaptures. than females (Fig. 2f ) for each size group estimated. At Point Leuseur, the difference was,5 mm year 1 between males (Fig. 2g) and females (Fig. 2h). No significant differences in growth were found between sites for either sex. Comparison across sites Overall, the highest male growth rate was at the Tasmanian Point Leuseur site (Fig. 3). Comparisons of growth between sites in the different States showed only one significant difference; females at Point Leuseur in Tasmania grew significantly faster than at Livingstons in South Australia (Table 4). No significant difference was found in growth rates of males or females between the States when all sites within each State were combined. Discussion Sex-specific growth This is the first study to provide growth estimates from wildcaught lobster juveniles (,80 mm CL) in south-eastern Australia. An unexpected finding was the difference in sexspecific growth at such a small size. Growth rate of females has been shown to decrease after reaching sexual maturity (Annala and Bycroft 1988; McGarvey et al. 1999). However, our findings indicate that growth is already differentiated between the sexes well before females show external signs of sexual Table 4. Comparison of growth between sites in Tasmania, Victoria and South Australia using the stochastic model for minimum time at liberty of 0.6 years ns, not significant Site comparison Sex n Chi-square P-value Livingstons (SA) Males 35 0 ns Glenvar Bay (Tas) 24 Livingstons (SA) Males ns Pigeon Holes (Tas) 69 Livingstons (SA) Females ns Pigeon Holes (Tas) 104 Livingstons (SA) Males ns Point Leuseur (Tas) 23 Livingstons (SA) Females P, 5 Point Leuseur (Tas) 26 Port Campbell (Vic) Females ns Livingstons (SA) 26 Port Campbell (Vic) Females ns Pigeon Holes (Tas) 104 Port Campbell (Vic) Females ns Point Leuseur (Tas) 26 maturity. No difference in growth was found between the sexes up to 40 mm CL, but at 50 mm CL, males were growing 1.4 times faster than females. This difference resulted from males moulting more frequently than females. On reaching mm CL, female moult frequency decreased from,3 4 moults each year to a single annual moult. The L 50 values at which females reach sexual maturity in southeastern Australia range from 74 to 92 mm CL (Gardner et al. 2006; Linnane et al. 2008), suggesting that growth declines in females at the onset of reproduction. In comparison, males continued to undertake between 3 4 moults annually over all the range of size classes sampled. This faster growth of males than females, at a size well below that at which females divert energy to gonad development, is especially surprising given that production of sperm by males occurs at,70 mm CL and below the size at onset of maturity of females (Turner et al. 2002). Clearly, some changes in female physiology must be occurring between 40 and 50 mm CL. This size range corresponds to the size when juvenile J. edwardsii form social aggregations (Edmunds 1995), but whether this could impact more on females than males remains unclear. Hooker et al. (1997) found significantly higher growth in two year old males that corresponded to mm CL in size class. However, it is important to note that female maturity is generally measured by external characteristics only. As there may be some time lag in assessing maturity, somatic growth could be slowed by internal development of reproductive organs one or more moults before external features indicating maturity are apparent. Spatial variation in growth Point Leuseur (Tasmania) had the highest growth rate across the study sites in the three States which is consistent with trends in adult growth among the study sites. Within Tasmania, the adult growth rate at Point Leuseur is intermediate between the slowgrowth areas of the fishery in the south-west and the higher

7 Growth rates of juvenile lobster Jasus edwardsii Marine and Freshwater Research G growth areas in the north (Punt and Kennedy 1997). The South Australian sites were situated in the slowest growth-rate area for that State (McGarvey et al. 1999) whereas the Victorian site was in a slow-intermediate growth area (Punt et al. 2006). Despite these variations in growth, no significant difference was found in growth rates of males or females between the States when all sites within each State were combined. Factors impacting lobster growth Growth rates of juvenile lobsters in the wild are impacted by a range of factors that affect moulting frequency. In Panulirus species, water temperature is a key element, with growth rates of tropical species such as P. ornatus and P. argus much faster than those of temperate species such as P. cygnus (Phillips et al. 1992). In aquaculture conditions, the role of temperature in controlling lobster growth has also been highlighted for both Panulirus and Jasus species where moulting frequency is typically higher in warmer water (Crear et al. 2000; Hazell et al. 2001; Dubber et al. 2004; Johnston et al. 2008). Both the South Australian and Victorian sites in the current study are influenced by annual cold-water upwelling events (Lewis 1981) which may impact on growth. In South Australia, recent studies have suggested that growth rates of adult lobsters are decreasing, which may be linked to exceptionally strong upwelling events in the region (Linnane et al. 2010). The association between key prey items and habitat type appears to be another primary factor controlling growth rates in lobsters. In J. lalandii, growth rates were highest in mussel bed sites (Newman and Pollock 1974). Mayfield et al. (2000) also associated growth rates with the availability of preferred prey in the benthos. Similar relationships between key macrofaunal assemblages and growth have been identified for P. cygnus (Edgar 1990) and Homarus americanus (Gendron et al. 2001). In aquaculture, the role of diet and growth has been intensely studied for a range of species, with growth highly dependent on feed type and feeding regimes (e.g. Crear et al. 2000; Dubber et al. 2004; Smith et al. 2005). Diets of adult lobsters in southern Australian waters appear dominated by the spiny urchin Heliocidaris erythrogramma, as well as crab and prosobranch species (Hoare 2008) but given the difficulties associated with juvenile dietary analyses, the effects of food type or availability on growth estimates in the current study remain largely unknown. Effects of tagging and physiological stress Overall, the diver-based recapture rates of 14% were comparable with those from large-scale fishery-dependent studies where recapture rates were,15% (Gardner et al. 2003; Linnane et al. 2005). However, the potential impacts of tagrelated injuries, as well as the timing of tagging, are known to bias growth estimates and require consideration. Working on J. lalandii, Dubula et al. (2005) used similar T-bar anchor tags to the ones used in our experiments and found that loss of appendages and restricted feeding reduced growth. In addition, tagged premoult lobsters grew significantly less than untagged controls while lobsters tagged during intermoult grew significantly more than those treated during premoult. Working on the same species, Brouwer et al. (2006) also identified significantly lower growth and increased levels of mortality associated with injured lobsters compared with uninjured controls. Other potentially negative effects that may be associated with diver-based tag recapture programs include adverse on behaviour of juveniles post handling (Vermeer 1987; Haupt et al. 2006). Specifically, physiological stress associated with exposure to air may diminish lobsters response time and ability to escape, making them more vulnerable to predation on subsequent release. However, such behaviours were not seen during the current study, with most juveniles observed to immediately locate and enter a crevice or ledge shelter upon reaching the seabed after release. Model performance Although the stochastic model provided a useful description of growth, some recaptures could not be used because of short times at liberty (between 0.3 and 0.5 years). This is due to the model assumption of constant growth, which is not applicable to crustaceans where, for short times at liberty, length increments can vary considerably, depending on the timing of the recapture within the moult cycle. Estimates of growth at length decreased as the time at liberty was reduced in the analysis, so a consistent minimum time at liberty was required if growth estimates were to be compared between sites. Unfortunately, the need to set a minimum time at liberty causes considerable data loss but is unavoidable when using this type of model and suggests that there may be value in the use of stepped growth models. The deterministic growth model developed by Francis (1998) was also used but did not perform as consistently as the stochastic method, particularly with small sample sizes at short times at liberty. We suggest the growth estimates from this work will contribute to the current length-structured models currently used in the fishery (Punt and Kennedy 1997; Hobday and Punt 2001) and will improve the ability to link datasets on puerulus settlement, pre-recruit abundance and entry to the fishable biomass. Conclusions The results of this study demonstrate that a diver-based tag recapture program is appropriate for estimating growth rates of wild crustacean populations. In particular, it can provide growth estimates for smaller size classes not normally sampled by conventional fishing gear such as pots or traps. It is important, however, to consider the timing of tagging in relation to the moult stage, as well as the potentially adverse effects of excessive handling on behaviour and subsequent survival. Nonetheless, this sampling technique has the potential to improve the overall understanding of crustacean population dynamics and, in particular, can contribute to current fishery models by confirming relationships between different life history stages. Acknowledgements Funding for this research was provided through the Fisheries Research and Development Corporation of Australia (Project Number 2001/070). We acknowledge Dave Reilly, Alan Jones, Peter Hawthorne and Sam Ibbott for dive support during the study. Finally, we thank the three anonymous referees whose comments greatly improved the quality of this manuscript.

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