Skipper Meggs Amidships

Mangrove Jack have always intrigued me.

It seems that every time I head up north and I look around at the mangrove lined river systems my thoughts always turn to this particular species. 

The Mangrove Jack or Lutjanus Argentimaculatus (I know - it sounds like a Serbian olympic discus thrower) is common throughout Northern Australia, East Africa, Samoa and Japan but has even been known to turn up (lost?) in Sydney Harbour.

They can grow up to 1.2m in length, weigh in at 16kg and can live a very full life to 40 years of age.

The Queensland Department of Primary Industry conducted a comprehensive study of Mangrove Jack in 2003 which turned up some interesting findings - one of which I believe to be quite sad.

Lets start at the beginning though.

The name “Mangrove Jack” conjures up a misleading picture of this great fighting fish as adults actually live and spawn offshore on coral reefs in depths up to around 100m.

Research indicates that after spawning the juvenile fish make their way to estauries and coastal streams during the wet season and some may even head to freshwater up to over 100km inland.

However, the highest numbers of Mangrove Jack reside in the estuary mouth area.

Tagged fish are generally resident in a particular spot with 73% caught within 1km of release point but don’t be fooled because one has been known to travel over 330km! Research shows that they can move intra and inter rivers, along the coast or offshore.

No Juvenile Justice for Mangrove Jack

Now here’s the sad part - all estaury, river based and freshwater Mangrove Jack are juveniles or more correctly sub-adult. They do not actually reach maturity until they head offshore to the coral reefs. Generally this occurs between the ages of 3-11 years when they are 23-40cm in length.

The Queensland study found 50% of female Mangrove Jack (Jill?) matured at just over 50cm and males at around 46cm.

So?

Well the issue is that the legal size of Mangrove Jack in Queensland happens to be 35cm with no limit on keepers (except for the Gulf of Carpentaria where there is a bag limit of 5).  

So why not spare a thought for the kids next time you catch a Mangrove Jack anywhere else but on an offshore reef?

In the meantime, I intend to write to the Queensland Department of Primary Industry and ask what needs to be done to change the regulations regarding the minimum size requirements of fish in this predicament.

 As always, I will keep you posted with their reply.

Sea you later,

Skipper Meggs

This entry was posted on Friday, March 7th, 2008 at 12:57 am and is filed under Fish Life Cycle Posts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.