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Over recent decades, the Longspined Sea Urchin has extended its range southwards to VIC and TAS, reflecting the increasing influence of the south-flowing Eastern Australian Current in those latitudes. At high densities, Longspined Sea Urchins can damage kelp habitats through overgrazing, leading some jurisdictions to pursue urchin removal programs. Longspined Sea Urchin stock structure is uncertain and management arrangements differ across jurisdictions, so this assessment is presented at the jurisdictional level. Longspined Sea Urchin are classified as sustainable in NSW, TAS and VIC.

Within its historic endemic distribution along the central east coast of Australia, the Longspined Sea Urchin, Centrostephanus rodgersii, inhabits coastal reefs in habitats consisting of a mosaic of foliose and turfing algae, typically in relatively shallow water (less than approximately15 m depth). In these areas, Lonspined Sea Urchin grazing can create and maintain habitats devoid of foliose algae and dominated by crustose coraline algae-covered rock, commonly termed ‘barrens’ [Underwood et al. 1991]. Within this historic range and over the 30 years to 2020, Glasby and Gibson [2020] estimated that there had been relatively small changes in the aerial extent of barrens, with some sites showing very little change or a reduction in extent. Densities of Longspined Sea Urchins are typically lower in nearshore mosaic habitats than in barrens [Blount 2004; Ling et al. 2009], likely a reponse to food supply [Ling and Johnson 2009]. In contrast, age structures appear similar between habitats, with evidence indicating no difference in the longevity of Longspined Sea Urchins between fringing and barrens habitats [Blount et al. 2024]. 

Over the last several decades the Longspined Sea Urchin has undergone a range extension to Victoria and Tasmania from NSW due to extensions in the warm East Australia Current brought about by climate change and modulated by larval thermal tolerance limits [Johnson et al. 2005; Ridgway 2007; Ling 2008; Byrne et al. 2022]. This southerly movement is likely to continue, accompanied by density reductions in northern parts of the range [Davis et al. 2023].

The strength of connectivity between regions and the species' capacity for self-recruitment at the extremes of its distribution remain poorly understood and are currently under investigation as part of an FRDC project 'Larval dispersal for Southern Rock Lobster and Longspined Sea Urchin to support management decisions.

Understanding Longspined Sea Urchin population structure has been of particular importance as high urchin densities can damage kelp forests through overgrazing [Ling et al. 2009; Johnson et al. 2011; Marzloff et al. 2016], and this has resulted in notable habitat changes in areas of range extension. Due to this impact and the range-extending nature of this species, management measures are being actively pursued to decrease the population density in some jurisdictions.

 Due to limited knowledge regarding stock structure and different jurisdictional management objectives this species is assessed here at the jurisdictional level—New South Wales, Tasmania and Victoria.

Tasmania

The first official report of Longspined Sea Urchin presence in Tasmania came from the state's north-east coast in 1978 [Edgar and Barrett 1997], with surveys and studies suggesting initial establishment of this species occurred further north in the Kent group (Bass Strait) during the mid-1960s [Johnson et al. 2005]. Since then, populations have expanded in Tasmania, being most abundant in the north but occurring with increasing abundance between Eddystone Point in the north and Recherche Bay in the south [Johnson et al. 2005]. Longspined Sea Urchin has been harvested commercially in Tasmania since 2009. The annual catch remained below 100 t until 2018, when it increased to 185 t [Cresswell et al. 2019]. In 2019, 560 t were caught [Cresswell et al. 2019]. This fishery is now the third largest in Tasmania per wet tonnage harvested, with approximately 500 t harvested in the last two seasons [Cresswell et al. 2023]. Despite the catch increase there is no evidence of widespread decrease in biomass as catch rates have remained stable in all regions.

Catch rates would not necessarily decline as biomass falls because divers can shift to new areas. A recent survey of commercial divers has suggested that in some areas divers have been forced into deeper waters by using Nitrox to sustain high catch rates, adding significantly to the cost of a dive trip [Cresswell et al. 2019]. Fisheries-independent surveys indicate that biomass increased between 2001 and 2017 on the east coast of Tasmania, during which period only small fishing catches were taken. The survey showed a general trend of highest biomass/densities in the northeast to the lowest in the southeast [Johnson et al. 2005; Ling and Keane 2018]. Given that this species is not endemic to Tasmania and has a negative impact on the ecosystem here, a depleting status for the fishery may be desired.

In 2001–02, a fishery-independent survey in the 6–26 m depth region (where the dive fishery operates) estimated Longspined Sea Urchin biomass at 4,147 t. This depth band covered 80 per cent of the urchin biomass. A resurvey was conducted in 2016–17 and biomass was estimated at 5,856 t. Some small-scale removals from harvesting occurred through this period. Over the period between the two surveys, and accounting for removals by fishing, the average annual biomass increase was 139 t. A third survey took place in 2020–21 estimating the biomass at 6,435 t, an increase of 435 t per year since 2016-17. Catch since and including the 2018–19 season has exceeded this amount except in 2019-20, averaging 478 t per year [Cresswell et. al. 2023].

Biomass in the Longspined Sea Urchin fishery is assessed by two methods: extrapolation from counts obtained from fishery-independent transect surveys; and trends in catch per unit effort (CPUE) by commercial divers. Biomass assessed by fishery-independent transect data has increased over the last two decades. State-wide CPUE has remained stable from 2008–09 to 2021–22. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

Fishing mortality in the Longspined Sea Urchin fishery is assessed using catch (t) as a proxy. In the most recent season (2021–22) annual catch increased fivefold to 494 t from the first 10 years of the fishery since 2009. Despite catch being spatially concentrated (greater than 90%) to the St Helens region for up to the 2016–17 season, catch has now spread down the coast with around 30% of catch coming from both the St Helens and Wineglass Bay regions, and less than 10% for the other regions. The stock status for the entire east coast of Tasmania is likely to be sustainable despite the increases in total catch in recent years, with the current level of fishing mortality unlikely to cause the stock to become recruitment impaired. An increase in dive depth over time is the only indication that this species may be becoming harder to find in shallower depths.  

On the basis of the evidence provided above, Longspined Sea Urchin in Tasmania is classified as a sustainable stock.

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Distribution of reported commercial catch of Longspined Sea Urchin.

New South Wales – Indigenous (Management Methods). https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

Victoria – Indigenous (Management Methods). A person who identifies as Aboriginal or Torres Strait Islander is exempt from the need to obtain a Victorian recreational fishing licence, provided they comply with all other rules that apply to recreational fishers, including rules on equipment, catch limits, size limits and restricted areas. Traditional (non-commercial) fishing activities that are carried out by members of a traditional owner group entity under an agreement pursuant to Victoria’s Traditional Owner Settlement Act 2010 are also exempt from the need to hold a recreational fishing licence, subject to any conditions outlined in the agreement. Native title holders are also exempt from the need to obtain a recreational fishinglicence under the provisions of the Commonwealth’s Native Title Act 1993.

Tasmania - Living Marine Resources Management Act 1995. https://www.legislation.tas.gov.au/view/html/inforce/current/act-1995-025

Commercial catch of Longspined Sea Urchin - note confidential catch not shown.

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