An unsustainable fishery on the Great Barrier Reef

This rather interesting looking chap is a holothurian – or as it’s more commonly known, a sea cucumber.  There are some 1,250 species of holothurians, most of which scavenge on whatever they find on the sea floor.  This rather unfussy diet has severed this group well- you can find holothurians across all oceans, from the deep sea through to shallow coastal waters. And if you type ‘sea cucumber’ into Google, it will give you this nutritional information…. Amount per 100 grams Calories 56 Total Fat 0.4 g Total Carbohydrate 0 g Protein 13 g Vitamin A 6% Calcium 3% Iron 3% of your daily value.

Sea cucumber fisheries and aquaculture have long formed part of a subsistence diet for island and coastal communities.  They have also become a luxury food item in one country in particular….China. Statistic from the Food and Agriculture Organization (FAO) indicate that between 2000 and 2009, Africa, Asia, and Oceania exported some 100,000 tonnes of dried sea cucumbers – most of which ended up in China.  Overfishing is rife, with an estimated 70% of tropical sea cucumber fisheries classified as fully exploited, over-exploited or depleted^^.  Most of these fisheries come from nations which lack the financial means to manage their fisheries as well as they could be.  Most, but not all – such as the fishery in Australia.  And not just anywhere in Australia – in the Great Barrier Reef Marine Park.  This might sound a little odd, but the Great Barrier Reef Marine Park is a multiple-use park.  Many different activities occur on the reef, but they are carefully managed.

Or at least they should be…right?

This assumption is exactly what Hampus Eriksson of the Stockholm University in Sweden, and Maria Byrne of the The University of Sydney in Australia decided to test in relation to the sea cucumber fishery (Queensland East Coast beche-de-mer fishery).  Let’s make no mistake - the fishery on the reef is managed.  The modern-day fishery has been around since the 1980’s, but it wasn’t until 1995 that it became what is known as a limited entry fishery, with just 18 licences held by 3 operators.  Various changes in management practices have taken place over the years, with reductions in the total allowable catch, recording of processed weight, and the introduction of a rotational zoning scheme, which opens and closes different areas on a 3 year cycle to try to prevent over-exploitation in one area after another (known as serial depletion).

What seems to have been missing over the years is action to prevent serial depletion of different sea cucumber species themselves.  Between 1991 and 1999, the fishery favoured the black teatfish (Holothuria whitmaei) before switching in the late 1990's to white teatfish (Holothuria fuscogilva).  From 1999, surf redfish (Actinopyga mauritiana), elephant trunkfish (Holothuria fuscopunctata), lollyfish (Thelenota anax), leopard fish (Bohadschia argus), and the now endangered prickly redfish (Thelenota ananas) were all added to the list of targeted species.  So why the switch?  Well it turns out that the black teatfish catches had been undergoing marked declines since the mid-1990s when catches peaked at some 350 tonnes.  1999 saw a catch of just 100 tonnes – representing just 29% of the historically highest catch – and this is despite increases in fishing effort.  The managers subsequently closed the fishery, and it has not opened since.  Like the prickly redfish, the global population of the black teatfish has been listed on the IUCN red list as ‘endangered’

Now because the fishery diversified into many different species doesn’t mean that this serial depletion of species stopped.  From 2005 onwards, most of those replacement species were missing from catches with only the prickly redfish and the white teatfish from the list above continuing to be caught to this day.  Incidentally, the global population of white teatfish is now considered vulnerable by the IUCN.  However, there are a couple of other species we haven’t talked about yet – those that fall in the blackfish and the curryfish group.  Blackfish (primarily the burying blackfish - Actinopyga spinea) has been targeted since the early 2000’s, and now makes up a substantial part of the catch.  Curryfish (mainly Stichopus herrmanni) was also targeted, but catches didn’t really take off until the mid-2000.  Just to put the catch levels of these guys into perspective, in the 2009-2010 season, burying blackfish made up 70% of the total catch of the fishery, and 60% in the 2010-2011 season.  Curryfish catches have increased rapidly over the years.  Between 2007 and 2011, curryfish increased on average 200% each year.  In the 2009-2010 season these critters made up 9% of the total catch, increasing to 18% in 2010-2011.

Looks pretty bad doesn’t it.  Well the researcher’s findings don’t quite stop there.  They note that despite the diversification of species over the years, no baseline data was collected for any of these species to figure out if they could be fished, and if so how many could be taken.  They also note that even on the Great Barrier Reef, the ecological role of these apparently tasty critters play is not well understood.  Whilst data is recorded on the fishery, this is kept secret – not for public viewing, and abundance and ecological surveys are carried out by the fishery itself and not independent scientists.

The paper published in the journal Fish and Fisheries is sitting behind a paywall, so you will need to have journal access (or pay) to access the paper.  If you fancy it, the paper can be found here

A little while ago, Catlin Seaview Survey made a short (1 ½ minute) video on sea cucumbers

Image: Holothurians are found all over the world.  This particular holothurian, which goes by the common name of 'donkey dong sea cucumber' (Holothuria mexicana) was found in San Salvador Island, Bahamas.   Credit James St. John/Flickr (CC BY 2.0)

^^ The UN FAO definitions of fishery status are as follows: - Fully exploited:  The fishery is operating at or close to an optimal yield level, with no expected room for further expansion;

- Over-exploited:  The fishery is being exploited at above a level which is believed to be sustainable in the long term, with no potential room for further  expansion and a higher risk of stock depletion/collapse;

- Depleted:  Catches are well below historical levels, irrespective of the amount of fishing effort exerted