Mystery prawn: Aussie invaders?

Mystery prawn.  Written by John Eichelsheim

I recently caught a reasonable-sized gurnard on a soft-plastic bait from beneath working birds in 12m of water close to Rangitoto Island in the Hauraki Gulf. That’s no big deal, but the large prawn the gurnard spat out as I swung it aboard the boat is.

The prawn measured about 90mm stretched out, which would classify it as small if you were buying it from the fish market, but here’s the interesting bit: to my knowledge we don’t have prawns as big as this in New Zealand, or indeed any prawns that fit this description.

The creature looked just like the prawns you can buy fresh or frozen at most supermarkets and fresh fish outlets.

One explanation is that I happened to catch the gurnard just after it had snaffled another angler’s bait. Prawns are becoming popular as bait, especially with fishers of Asian descent.

However, this prawn appeared very fresh – it hadn’t been inside the gurnard for long, if it had even made it to the fish’s stomach at all. Anyway, since there were no other boats or anglers within half a mile when I caught the fish, and we hadn’t seen any boats near this area in several hours, I think it highly unlikely that the prawn was another angler’s bait.

Not knowing the identity of this mystery creature, I took some photos and got on with my fishing. Unfortunately, someone the tossed the prawn over the side without thinking during the clean up at the end of the fishing session. Without a specimen, making a positive species identification is almost impossible.

Nevertheless, I made contact with Dr Clive Roberts at Te Papa, sending him my photos. He put me onto Dr Rick Webber, Curator of Crustacea at the same institution and Rick came back to me immediately, confirming that my catch was indeed unusual.

With his permission, I have reproduced his reply below.

Dear John,

You obviously have a good eye for it, so thanks for spotting this prawn.

Yes, your find is unusual. I'm pretty certain that the prawn is a prawn of the family Penaeidae. The Penaeidae include many of the commercial prawns of Australia and Asia, which we only otherwise enjoy as imports.

Of the several genera in the Penaeidae, this looks from the shape of its rostrum (pointy prong at the front) likely to be a species of Metapenaeus which is commercially important, or Parapenaeus which is much rarer and not often caught even in Australia where there are three species.

I believe penaeid prawns are occasionally seen in the warm north and was told by a fisherman several years ago that he had caught a few Australian ones between Three Kings (Islands) and Reinga. But the only positive record I have is from Norfolk Island, which is far too far north and too shallow to suggest it is in our waters. Speculating here, if shallow water penaeids like this turn up in New Zealand, they don't appear to set up home. Perhaps their larvae are occasionally brought to NZ in currents and they grow to be prawns but the current circulation (and water temperature) of NZ probably doesn't suit their life cycle, so they fail to complete their life cycle (breed successfully).

Your photos are good, thanks (I get some pretty bad ones to identify at times), but as you will appreciate, they still don't show me the details for further, certain identification. I would very much like to identify that prawn in the flesh if at all possible.

You may well have made a (small) meal of it but, on the off chance you've kept it frozen or preserved, could you possibly keep it for me and/or send it to me at Te Papa? I would place it in our collections to be kept long-term.

Sorry Rick! Members take note: if you catch an unusual or interesting, crustacean (shrimp, prawn, crab or crayfish), keep it and contact the good folk at The Museum of New Zealand, Te Papa Tongarewa. Photograph it and place the specimen on ice immediately, then follow the instructions at the bottom of this article for preserving and posting crustaceans to Te Papa.

In the week or two since catching this prawn I have heard reports of others and seen posts on this website reporting strange ‘shrimps’ or ‘prawns’ in the gut contents of snapper and kahawai from the inner Hauraki Gulf – even reports of anglers snagging them on jigs and softbaits.

Well-known angler and author Sam Mossman found one in good condition inside the stomach of a snapper he caught on Sunday March 20, which he has forwarded to Dr Webber, so hopefully a positive identification will be forthcoming soon.

What is certain is that this new prawn species must be well established in our waters, so it is entirely possible Fishing.net members may come across further examples while fishing in the Hauraki Gulf, or perhaps elsewhere around New Zealand this autumn.

If you do, Dr Webber would like to hear from you, at least until he has been able to positively identify the species.

In an email from a few days ago, Rick Webber shed more light on my mystery, but perhaps not-so-unusual, prawn:

Dear John,

Since telling you I thought the prawn you sent me a photo of, that fell out of a gurnards mouth might be a Parapenaeus or Metapenaeus I have sent one of your photos to a colleague in Sydney. He has told me before that he has heard of the 'inshore greasyback' prawn of eastern Australia being caught a few times around Auckland, so I sent him the photo to check. Like me, he says he can't be completely sure without seeing the animal itself but he has a lot more experience with these prawns than I do and says it's very likely to be the inshore greasyback (Metapenaeus bennettae).

So there you are, it has been found a few times before and looks as though it might actually have established itself in Hauraki Gulf. What little information I have on this prawn says it lives from southern Queensland to northeastern Victoria, 32-37 degrees south (nowhere else) in 14 m or shallower water in bays and estuaries and right into the lower reaches of rivers. That sounds like it may be quite well pre-adapted to Auckland's harbours and estuaries and has been accidentally introduced in something like ships' ballast water.

It's an important fishery in southern Queensland and NSW so you might like to see if you can gather more yourself. If you do, please send specimens to me for the collection so that we can name this thing properly.

Best wishes,

Rick Webber

Curator of Crustacea

So, if any members come across a prawn like this, or indeed any unusual or unidentified catch, be sure to send it to Te Papa.

Dr Webber suggests the following procedure for preserving crustaceans. (Finfish are better frozen, as per the instructions on the ‘Somehing Fishy’ pages in every issue of New Zealand Fishing News.)

Preserving a crustacean

• Plonk it into 100% methylated spirits for 10 days plus (make sure it's covered) to fix it.

• Take it out, wash it off and seal it in plastic bags (any leakage or smell might put the postie off).

• Post to me (Dr Rick Webber) fast-post at the address below.

Rick Webber
Curator of Crustacea
Museum of New Zealand Te Papa Tongarewa
PO Box 467 Wellington New Zealand
Resource Centre 169 Tory Street
Ph. 64 (4) 381 7316; rickw@tepapa.govt.nz