Caulerpa now in BOI

[K4309 350]

15 hours ago, Psyche said:

Thats game over? At this point suction dredging seems pathetic unless its a very tiny outbreak, cleaning ground tackle and raising awareness is probably the best action to take.

In my view there are two separate issues here.

The anchoring ban is futile. With 50 Ha of it banning fishing and anchoring is a nonsense. Mind you, it's a nonsense if there are only small patches of it as well. Anyway, lets not go over old ground.

If there is 50Ha of it, there is an arguement that suction dredging is very much worth doing. Two premise explain this:

1) Suction dredging needs scale to make it both effective and cost effective. If there is loads of it, you can just hover it up all day.

2) We are told the issue with caulerpa is smothering everything and kill off the existing benthic habitat. If you do wide spread suction dredging, you are giving relief to the existing benthic habitat. Basically you pull the caulerpa off everything so it doesn't die / can rejuvenate. Sure, it may grow back, but this is so new we don't know how fast. With the change from La nina to El nino, we are likely to get reduced sea temps, and definately shouldn't get the non stop N'Easters and associated ocean currents and wave action. This is a reasonable possibility that growing conditions will change so it doesn't favour caulerpa and it either dies off or doesn't spread much more. Doing wide spread suction dredging at the same time would help nature along.

This is a similar approach they are doing with kauri die back. Try and stop everything dieing and wait for something to change. Either natural weather systems or tech / research to create a silver bullet (cough).

That, and in my view the cost of all the talky talk, beuacrates and cultural consultation is so much, you could just pay for a suction dredge to rotate through all the hotspots and mitigate the impact for a similar cost to all the mucking around they are doing now. More so if you add in the social and cultural costs of banning fishing and boating...

 

[Psyche 709]

50 hectares is huge, and who's to say that its only 50? I get your point about dredging but I'm unconvinced that it could keep up with the spread. Just trying to think this through, you'll need teams of divers controlling the suction end carefully inspecting the terrain for any fragments left behind. If it can suck up the pest then it can suck up everything else, so if it was 50 hectares of flat paddocks, thats massive but 50 on broken ground is quite another. Still it could be done but we would need hundreds of divers and operators, multiple machines working many areas whenever the weather permits

[Black Panther 1,674]

At what depth?

[Cheap Transport 72]

10 hours ago, Psyche said:

50 hectares is huge, and who's to say that its only 50? I get your point about dredging but I'm unconvinced that it could keep up with the spread. Just trying to think this through, you'll need teams of divers controlling the suction end carefully inspecting the terrain for any fragments left behind. If it can suck up the pest then it can suck up everything else, so if it was 50 hectares of flat paddocks, thats massive but 50 on broken ground is quite another. Still it could be done but we would need hundreds of divers and operators, multiple machines working many areas whenever the weather permits

Agree 100%, if the suction can remove something rooted into the sand, it'll remove all shell fish, other plant life and anything in amongst it etc.

[LBD 160]

I did a good few years suction gold dredging and also work in heavy mining where we pump slurry for kilometers.

I cannot understand how this would work?... solids make up 5% to 10% of the slurry. They cannot return all that water to land surely? There must be some separation on the floating dredge with the water returning to the ocean, in which case how will the live spores/seeds/cuttings not make it back into the ocean to start again?

50 Hectares is a lot of land...50 x 10,000m2 x say 0.25m into the sea bed = 125,000 cubic meters of sand/mud... that is a lot. and if the intention is to pump it all to shore including all the water, then you are looking at sucking up and pumping about 1.5M tons of slurry to a holding/settling/sterilizing location on shore... that in itself will be a huge engineering undertaking.

The scale just seem too large.

[Psyche 709]

Try mowing 50 hectares, in low low!

[LBD 160]

1 hour ago, Psyche said:

Try mowing 50 hectares, in low low low low low low low low low low low low gear!

I know how long it takes to suck up sand and silt... On a good day I could move  to 12 cubic meters  if it was not packed too hard. If this stuff has an intertwined root system the the going will be slow. 

[K4309 350]

8 hours ago, LBD said:

I did a good few years suction gold dredging and also work in heavy mining where we pump slurry for kilometers.

I cannot understand how this would work?... solids make up 5% to 10% of the slurry. They cannot return all that water to land surely? There must be some separation on the floating dredge with the water returning to the ocean, in which case how will the live spores/seeds/cuttings not make it back into the ocean to start again?

50 Hectares is a lot of land...50 x 10,000m2 x say 0.25m into the sea bed = 125,000 cubic meters of sand/mud... that is a lot. and if the intention is to pump it all to shore including all the water, then you are looking at sucking up and pumping about 1.5M tons of slurry to a holding/settling/sterilizing location on shore... that in itself will be a huge engineering undertaking.

The scale just seem too large.

You would need a separator / clarifier tank on the dredge, with a direct water return to the area you are dredging. The technical challenge would be the size and effectiveness of a separator. 

You'd need to give up on this whole concept of avoiding any fragments going back in. The whole objective would be to reduce total biomass. Given that tide and waves are moving this around anyway, the whole concept that boat anchors are spreading it is a nonsense. Related to this is the re-growth rate of fragments. I think there has been a load of PR and scaremongering saying 1 fragment can grow into 2 rugby fields in two weeks (or what ever the stats were). For that to happen you need ideal growing conditions. I'd posit that was put about to get more funding from MPI, and to scare us a whole lot to get better compliance with their twaddlebollocks rules.

That is the whole premise of dredging, to reduce total biomass on the basis that growing conditions are not ideal. This give nature a chance of getting ontop of it naturally. The main premise about growing conditions are:

1) Natural growing conditions. We have changed from La Nina to El Nino. Water temps should be substantially different this summer, along with the incidence of blowey N'Easters and swell, which break up and spread the caulerpa. We should have a lot more SW and calm periods. Additionally, it is reported that caulerpa doesn't like direct sunlight. With all the rain, and blowey NE last summer, viz was constantly shithouse. With El Nino we should have good viz. If you are into spear fishing you will know exactly what I'm on about. The good viz lets the light down far deeper, and is of higher intensity shallower.

2) Knocking the biomass back with dredging. Changing weather cycles buy itself might just be enough to slow the caulerpa. With an aggressive suction dredge process knocking the biomass on the head, it might just be enough to get rid of it. All based on natural cycles in weather and climate making adverse growing conditions for it. The only issue is the window of opportunity is right now, right on the change in weather cycles. All we need is a large and cumbersome bureaucracy to move quickly...

[Steve Pope 253]

Trying to beat nature! good luck with that!

[LBD 160]

Guess the stuff when free from the soil it would have an SG about 1 and would remain in suspension, you could gravity separate out the higher density sand stones shells etc, then run all the rest over a filter belt say with a 2mm aperture .... that should work.

[harrytom 671]

Talking to NIWA divers downtown who were carrying out some sort of study.the are more concerned with fan worm removal and will heading north shortly.BOI to do more eradication.Asked about dredging the calpulas weed and verdict was waste of time.But yes more likely we have moved it from barrier to others places unknowingly as not report to til 2 yrs ago.

[harrytom 671]

slipped under the radar, wonder what the results will show?

https://www.waihekegulfnews.co.nz/divers-suck-up-more-than-10-tonnes-of-caulerpa-at-aotea/

[SHK 12]

Good that they're finally doing something about it instead of just backing anchoring for the third season in a row. 

[Psyche 709]

I spoke to a mussel farmer, he's seen this kind of pest a few times, it has a burst then settles down- hes not too worried

[harrytom 671]

Where are we up to with weed invasions?? seems to of gone very quiet,obviously hasnt gone away by its self or has bio security realised its no great risk?

[harrytom 671]

TV 1 at 7.30 tonight has a segnent on its removal I believe. Close the gate but horse has bolted.

[eruptn 98]

2 hours ago, harrytom said:

TV 1 at 7.30 tonight has a segnent on its removal I believe. Close the gate but horse has bolted.

There was a bit more to it than that…becoming a complex story. For me I learnt more about the issues…

[ex Elly 219]

Is this the biggest-ever threat to NZ’s marine life? | Sunday Investigates

 

[Sail Rock 30]

5 hours ago, ex Elly said:

Is this the biggest-ever threat to NZ’s marine life? | Sunday Investigates

 

Watched it and it is enough to make you weep 😢 

[harrytom 671]

Govt dont seem over concerned as $$ need to spent. Minister of AG didnt have a answer or overly concerned.Could be billions lost,fish/seafood/tourism and even having ships banned at overseas ports.

So what they allocated $5 mil,spend $100 mil and get it gone.