Trial of an industry implemented, spatially discrete ... et al Urchin Cull.pdf · Baulch, Vanessa...

Sean Tracey, Craig Mundy, Klaas Hartmann, Travis Baulch, Vanessa Lucieer, Martin Marzloff

Trial of an industry implemented, spatially discrete culling program for Centrostephanusrodgersii in Tasmania

Background/Objectives

Determine the effectiveness of divers physically destroying urchins in situ to allow the re-establishment of native flora and fauna

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Methods/Results Cull 1 Yr 2 Yr

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Results

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– The average cull rate was 7.0 (SE = 0.4) urchins per diver per minute, highest was 14 urchins per div/min

– The average time to complete a plot (1,500 m-2) was 4.8 hours, or, 5.2 m-2 /min.

Cull rate

Depth Air EAN35 EAN40DCIEM Tables

Suunto Dive

Computer

Nitrox Tables SuuntoDive

Computer

Nitrox Tables

Suunto Dive Computer

5m 720 Unlimited 720 Unlimited 720 Unlimited10m 150 165 300 Unlimited 720 Unlimited15m 75 65 150 156 300 20520m 35 35 75 66 75 8825m 20 22 35 41 50 MOD 56 MOD30m 15 15 25 MOD 29 MOD > MOD > MOD

Limitations: Dive time at depth

Working at depth – Air vs Nitrox

Determine dive profile strategies to enable safe harvest of urchins at depths greater than 15m

Example: Maximum dive times for repetitive divesDive 1 - 25 metres

Surface Interval 1 Hour Dive 2 - 25 metres

• Maximum dive times on AirDive 1 20 mins + Dive 2 11 mins = TOTAL TIME 31mins

• Maximum dive times on Nitrox EAN40Dive 1 50 mins + Dive 2 29 mins = TOTAL TIME 79mins

Air = approx. 31 x 7 = 217 urchinsNitrox = approx. 79 x 7 = 553 urchins

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Limitations: Repetitive dives

– Tasmanian Combined Dive Clubs Weekend (CCW)

– Coordinated via John Keane via the Tas Uni Dive Club (TUDC)

– Attracts ~9 Tasmanian clubs, ca. 150 divers

Recreational Culling – Dive Clubs

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Conclusions

Targeted culling by divers;– Is effective at reducing urchin abundance

– Does facilitate recovery of kelp beds

– Probably limited to small discrete reef patches at intermediate depths

– Could be applied to protect high value reef patches (biodiversity, fishery, eco-tourism, etc)

– Repetition? (every 5 to 7 years?)

N.B. Must determine which diving standard applies: Research, Fishing, Recreational, or Occupational?