Introduction
In Australia, the eastern rock lobster (Sagmariasus verreauxi) inhabits rocky reef and sand/mud substrates in depths ranging from 1 to 200 m from southern Queensland to the South Australian border, including Tasmania (Figure 1) (Montgomery and Liggins, Reference Montgomery and Liggins2013). Highest abundances are found along the New South Wales coastline where the species supports both commercial and recreational fisheries. The commercial fishery is managed using a range of controls including a total allowable commercial catch (TACC). The fishing season extends from 1 August to 31 July, with the TACC for the 2021/2022 season set at 180 t (Liggins et al., Reference Liggins, Miller and Ballinger2021).
Figure 1. Map showing the location of eastern rock lobster specimens caught in South Australia during the 2020/2021 fishing seasons at Rivoli Bay, the Neptune Islands, and Point Drummond. Shaded area (inset) shows the normal range distribution of the species.
The spawning stock of eastern rock lobster is spatially distinct being limited to the north coast of New South Wales (Montgomery and Craig, Reference Montgomery and Craig2005). Spawning occurs from September to January (Booth, Reference Booth1984) with phyllosoma undergoing 17 stages of larval development over a 9–12-month period (Kittaka, Reference Kittaka1994) before settling as puerulus into inshore reef habitat along the entire New South Wales coastline. Notably, the eastern rock lobster is also found in New Zealand, and while earlier research indicated minimal larval connectivity (Brasher et al., Reference Brasher, Ovenden, Booth and White1992; Ovenden et al., Reference Ovenden, Brasher and White1992), more recent studies suggest genetic homogeneity across the Tasman Sea encompassing both Australian and New Zealand populations (Woodings et al., Reference Woodings, Murphy, Doyle, Hall, Robinson, Liggins, Green, Cooke, Bell and Strugnell2018).
Within South Australia, lobster fishing occurs exclusively for southern rock lobster (Jasus edwardsii). The fishery is divided into two zones for reporting and management purposes, the northern and southern zones (Figure 1), which at the start of the 2021/2022 seasons had TACCs of 1246 t and 296 t, respectively (Linnane et al., Reference Linnane, McGarvey, Feenstra and Graske2021a, Reference Linnane, McGarvey, Feenstra and Hawthorne2021b). Most of the catch is taken from October to May with a minimum legal size of 98.5 mm carapace length (CL) in the southern zone and 105 mm CL in the northern zone. As with the eastern rock lobster, commercial fishing can only be undertaken by using baited traps. The southern rock lobster fishery is South Australia's most valuable fishery resource with a gross value of production in the 2020/2021 season of AUS$83 million (BDO EconSearch, 2022a, 2022b).
Reports of eastern rock lobster being landed in South Australian waters are extremely rare, being primarily limited to a few individuals caught in the southern zone, off Port MacDonnell at the southernmost end of the distribution range within the southern zone fishery (Figure 1). However, over the past three fishing seasons, reports of eastern rock lobster being caught in South Australia have increased. Notably, some reports have been from regions west of Port MacDonnell from areas where S. verreauxi have not previously been observed. This study reports on three verified westerly specimens caught during the 2021/2022 South Australian southern rock lobster fishing season. This includes the first ever reporting of eastern rock lobster in the northern zone of South Australia's southern rock lobster fishery.
Materials and methods
At-sea catch sampling
The three eastern rock lobster specimens were recorded as part of a southern rock lobster at-sea catch sampling programme that has been undertaken in South Australia since 1991 in collaboration between commercial fishers and scientists from the South Australian Research and Development Institute (SARDI). The aim of the programme is to provide temporal and spatial stock assessment data relating to the catch of legal and undersized lobsters as well as information on bycatch species.
Participating fishers record the contents from up to three traps daily which is supplemented by SARDI scientific observers who undertake routine onboard sampling trips and record information from all traps. Data recorded from each trap include (i) number of legal and undersized lobsters; (ii) lobster sex as determined by position of the gonopores (at the base of the third pereiopods in females and fifth pereiopods in males); (iii) lobster size; (iv) reproductive condition of females, e.g. ovigerous or sexually immature; (v) identification and number of all bycatch species; and (vi) latitude, longitude, and depth of each trap sampled.
Fishing is undertaken using steel-framed traps which are generally baited with either Australian salmon (Arripis truttaceus), blue mackerel (Scomber australasicus), barracouta (Thyrsites atun), or carp (Cyprinus carpio). Traps are set overnight and hauled at first light. On capture, photographs of each S. verreauxi specimen were taken onboard the commercial fishing vessel and sent to SARDI in Adelaide, South Australia for visual identification.
Results and discussion
One S. verreauxi was captured at Rivoli Bay in the southern zone fishery while two were recorded in the northern zone fishery at North Neptune Island and Point Drummond (Figure 1). All three specimens were male, ranged in size from 122 to 160 mm CL, and were caught in depths ranging from 4 to 22 m (Table 1 and Figure 2). Specimens caught at Neptune Island and Point Drummond represent the first verified observations of S. verreauxi in the northern zone fishery of South Australia and are the most westerly records ever documented in terms of overall distribution for this species.
Figure 2. Specimens of eastern rock lobster Sagmariasus verreauxi caught at Neptune Islands (A) and Point Drummond (B) in South Australia. Specimen of Jasus edwardsii (C) is included for comparison with S. verreauxi caught at Rigoni Bay (D).
Table 1. Details of three Sagmariasus verreauxi specimens caught during the 2020/2021 South Australian rock lobster fishing season (CL, carapace length)
Range expansion and changes in distribution due to climate change are well documented for numerous oceanic species globally (Poloczanska et al., Reference Poloczanska, Brown, Sydeman, Kiessling, Schoeman, Moore, Brander, Bruno, Buckley, Burrows, Duarte, Halpern, Holding, Kappel, O'Connor, Pandolfi, Parmesan, Schwing, Thompson and Richardson2013; Pecl et al., Reference Pecl, Araújo, Bell, Blanchard, Bonebrake, Chen, Clark, Colwell, Danielsen, Evengård, Falconi, Ferrier, Frusher, Garcia, Griffis, Hobday, Janion-Scheepers, Jarzyna, Jennings, Lenoir, Linnetved, Martin, McCormack, McDonald, Mitchell, Mustonen, Pandolfi, Pettorelli, Popova, Robinson, Scheffers, Shaw, Sorte, Strugnell, Sunday, Tuanmu, Vergés, Villanueva, Wernberg, Wapstra and Williams2017; Pinsky et al., Reference Pinsky, Fenichel, Fogarty, Levin, McCay, St Martin, Selden and Young2021). Within Australia, the south-east region is considered a climate change hotspot where southward latitudinal shifts in species distribution have been documented for a variety of reef-dwelling organisms (Pecl et al., Reference Pecl, Frusher, Gardner, Haward, Hobday, Jennings, Nursey-Bray, Punt, Revill and van Putten2009; Last et al., Reference Last, White, Gledhill, Hobday, Brown and Edgar2011; Gervais et al., Reference Gervais, Champion and Pecl2021). These shifts are strongly influenced by known changes to the eastern Australia current (EAC), which has increased in terms of strength, duration, and frequency of southward incursion (Ridgway, Reference Ridgway2007) resulting in the transportation of larvae from northern regions southward into Tasmania (Ling et al., Reference Ling, Johnson, Frusher and King2008; Johnson et al., Reference Johnson, Banks, Barrett, Cazassus, Dunstan, Edgar, Frusher, Gardner, Haddon and Helidoniotis2011).
One such species is S. verreauxi which is now identified as being resident in Tasmanian waters (Pecl et al., Reference Pecl, Frusher, Gardner, Haward, Hobday, Jennings, Nursey-Bray, Punt, Revill and van Putten2009; Robinson et al., Reference Robinson, Gledhill, Moltschaniwskyj, Hobday, Frusher, Barrett, Stuart-Smith and Pecl2015). Within New South Wales, the species has a natural north-to-south recruitment pattern (Montgomery and Craig, Reference Montgomery and Craig2005), which facilitates the natural movement of larvae from the region into Tasmania as the EAC extends further south. While the process for the range extension of S. verreauxi southward is relatively understood, less is known about its expansion westward.
The connectivity of ocean currents from Australia's western and eastern coastlines with the southern shelf has potential implications for influencing species distributions (Griffin et al., Reference Griffin, Wilkin, Chubb, Pearce and Caputi2001; Coleman et al., Reference Coleman, Feng, Roughan, Cetina-Heredia and Connell2013). The predominant current along the south coast of Australia is the Leeuwin current which flows south along the west coast of Australia and extends eastwards into the Great Australian Bight principally during the Austral autumn and winter (Griffiths and Pearce, Reference Griffiths and Pearce1985; Church et al., Reference Church, Cresswell, Godfrey, Neshyba, Mooers, Smith and Barber1989). In the east, the Flinders current (FC) (Figure 1) transports subsurface water westwards along the southern shelf of Australia (Middleton and Cirano, Reference Middleton and Cirano2002). The FC has the potential to transport larvae from the south and west coasts of Tasmania westward into South Australia (Griffin et al., Reference Griffin, Wilkin, Chubb, Pearce and Caputi2001; Middleton and Bye, Reference Middleton and Bye2007). In addition, a north-westward flowing nearshore coastal current (CC) associated with south-easterly winds prevalent during the Austral summer is also expected to connect Bass Strait and western Victorian coastal waters with the southern zone and the south coast of Kangaroo Island (Rochford, Reference Rochford1957; Middleton and Bye, Reference Middleton and Bye2007). Both the FC and CC are linked with the occurrence of summertime upwelling events along the southern shelf of Australia (Kämpf et al., Reference Kämpf, Doubell, Griffin, Matthews and Ward2004; Middleton and Bye, Reference Middleton and Bye2007) and provide a possible mechanism for eastern rock lobster larval transport between Victoria and South Australia. Connectivity between Tasmania and South Australia has been confirmed through stable isotope analyses (Richardson et al., Reference Richardson, Middleton, Kyser, James and Opdyke2019), particularly during upwelling seasons, providing further evidence for a possible larval transport mechanism between the two regions.
The occurrence of eastern rock lobster in South Australia suggests a change in environmental factors allowing settled larvae to survive through to adulthood. The normal temperature range of S. verreauxi in New South Wales is approximately 14.5–21.5 °C while that of southern rock lobster in south-eastern Australia tends to be cooler at approximately 9–21 °C (Holthuis, Reference Holthuis1991). However, while investigating temporal changes in size at sexual maturity in J. edwardsii, McLeay et al. (Reference McLeay, Doubell and Linnane2019) highlighted high rates of increase in sea-surface temperature within South Australia since 1991. This suggests that local environmental conditions within South Australia are now favourable to eastern rock lobster settlement, survival, and maturity, to adult stages.
Finally, the local ecological impacts of S. verreauxi expansion into South Australia remain largely unknown. Early research, however, indicates that J. edwardsii may be more dominant than S. verreauxi in direct food competition and that this dominance is sustained under a wide temperature range (Twiname et al., Reference Twiname, Fitzgibbon, Hobday, Carter, Oellermann and Pecl2022). Given the importance of the southern rock lobster fishery to South Australia, further research is warranted on the competitive interactions of S. verreauxi with J. edwardsii, as well as the broader ecological consequences of eastern rock lobster range expansion.
Analyses of oceanographic information available through the Integrated Marine Observing System (IMOS) series of National Reference Stations (http://imos.org.au/), which are deployed to monitor ocean climate in Australian coastal ocean waters, coupled with cross jurisdictional fishery monitoring data, may assist in predicting range shifts of marine species such as eastern rock lobster and any ecological impacts under the influence of climate change.
Acknowledgements
We thank South Australian commercial rock lobster fishers Richard Leech, Les Polkinghorne, and Ros Brown who reported the eastern rock lobster specimens. We acknowledge SARDI rock lobster fishery observers Douglas Graske, Andrew Hogg, and Peter Hawthorne.
Author's contribution
A. L. and L. M. recognised the importance of these observations and wrote the first draft of the manuscript; A. L. and L. M. morphologically verified the identity of Sagmariasus verreauxi specimens; M. D. provided oceanographic expertise; all authors contributed to the refinement of the final manuscript.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Competing interests
None.
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