Longspined Sea Urchin (2020)
Date Published: June 2021
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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.
Stock Status Overview
Catch, effort, CPUE trends, fishery-independent survey estimates of biomass.
Over the last several decades the Longspined Sea Urchin, Centrostephanus rodgersii, 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 [Johnson et al. 2005, Ridgway 2007, Ling 2008].
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.
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 [Creswell et al. 2019]. In 2019, 560 t were caught [Creswell et al. 2019]. This fishery is now the third largest in Tasmania per wet tonnage harvested. Despite the catch increase there is no evidence of widespread decrease in biomass as catch rates have remained stable except in the most heavily fished area of Sloop Reef in the northeast.
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 [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 6–24 m depth region (where the dive fishery operates) estimated Longspined Sea Urchin biomass at 2 523 t. This depth band covered 80 per cent of the urchin biomass. A resurvey was conducted in 2016–17 and biomass was estimated at 4 434 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 153 tonnes. Catch in each of the three years since the last survey has exceeded this amount [Cresswell et. al. 2019].
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 not decreased over the total area fished from 2009 to 2019 but has a downward trend in the most heavily fished area. 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 (2018–19) annual catch increased fivefold from the first 10 years of the fishery since 2009. Despite this large increase, catch is spatially concentrated, with 80 to 90 per cent of catch coming from a small area of the east coast, around the St Helens region. While stock for the entire east coast of Tasmania is likely to be sustainable despite the increases in total catch, there is evidence of a decrease in catch rates in the most heavily fished areas over time. This suggests that for the more heavily fished areas at the current level of fishing we would expect to see a further decrease in catch rates and localised depletion. However despite signs of localised depletion when assessed across the Tasmanian stock the above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, Longspined Sea Urchin in Tasmania is classified as a sustainable stock.
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
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New South Wales – Indigenous 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 fishing licence under the provisions of the Commonwealth’s Native Title Act 1993.
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