Research Shows Northern Crays in BIG Trouble

Talk to any OLD diver (that is any who were diving in the 1960’s) and you will hear stories of crayfish feelers bristling out of every crevice at Tiritiri Island, 7-pound crays at Ponui Island, plenty of crays around Waiheke Island, and giant 20-pound plus packhorse crawling around in the kelp at the Cavalli Islands. What has happened to them? If the Quota Management System is so good at sustaining our fisheries, why aren’t there still lots of big crays out there?

Large crayfish used to be common on our shallow reefs.  What has happened to them?  The short answer is we have both exported and eaten them!

Large crayfish used to be common on our shallow reefs. What has happened to them? The short answer is we have both exported and eaten them!

These days most divers are pleased if they can catch a couple of crays around 2 or 3 pounds in weight. The phenomenon of our understanding of what is “normal”, changing over time, is called a “sliding baseline”. Each generation of divers thinks what they are seeing is “normal”, and are unaware that what was “normal” 30 years ago is far different from what you see now. Each generation has a new starting point and does not become alarmed until they see a serious decline within their lifetime.

Well, we now have a “reality check”. We have some Marine Reserves which have been established for long enough to show what crayfish populations would have been like about 50 years ago. And the results are a bit of a shock.

I have been studying crayfish at Mimiwhangata and Tawharanui in a long-term monitoring programme which began in the mid 1970’s. Mimiwhangata and Tawharanui are Marine Parks on the northeast coast, which have been in existence since the early 1980’s. At Mimiwhangata, commercial fishing ceased in 1994, but recreational fishing has continued. At Tawharanui, all fishing ceased in 1983, and the area has been totally protected since that time, like a Marine Reserve but set up under special fishing regulations instead. In 2011 Tawharanui was changed to a Marine Reserve, which was really just an administrative change and the fishes wouldn’t have noticed a thing.

My studies covered several years with normal fishery regulations before any special protection was established in these areas, and continued to follow changes after protection occurred, that is data from “before and after” protection. In addition my sampling included comparison between the protected areas and the normal fishing areas outside the marine parks.

A full analysis of results was published in 2006 in the scientific journal Biological Conservation (Shears et.al., 2006 Long-term trends in lobster populations in a partially protected vs. no-take Marine Park, Biological Conservation 132:222-231). All rather technical and necessary, but the guts of the results are presented in the following graph.

Decadal trends in red crayfish numbers at Mimiwhangata and Tawharanui Marine Parks.  Tawharanui open fishing area [front, in blue], Mimiwhangata partial protection [middle, red], and Tawharanui no-take area [back, pale yellow].  From 1970’s to 2010’s.  Only in the no-take area have crayfish numbers recovered from the hammering all crays had in the 1960’s and 70’s.

Decadal trends in red crayfish numbers at Mimiwhangata and Tawharanui Marine Parks. Tawharanui open fishing area [front, in blue], Mimiwhangata partial protection [middle, red], and Tawharanui no-take area [back, pale yellow]. From 1970’s to 2010’s. Only in the no-take area have crayfish numbers recovered from the hammering all crays had in the 1960’s and 70’s.

To summarise the data, I have presented the information in three histograms. The front one in blue shows results for Tawharanui outside the protected area, where normal fishery regulations have always applied. The middle one in red shows results for Mimiwhangata partially protected marine park, and the back one in pale yellow shows what happened in the totally protected area at Tawharanui.

The horizontal axis is time, presented for simplicity as data lumped into decadal intervals. The vertical axis is the mean number of legal-sized red crays on permanent fixed transects on the rocky reefs, each transect being 50×10 metres or 500 square metres. There are nine sites at Mimiwhangata, five in the open fishing area at Tawharanui, and five in the totally protected Tawharanui Marine Park (now Marine Reserve).

The trends are pretty obvious. In the unprotected areas at Tawharanui, legal-sized red crays quickly dropped away to nothing! At Mimiwhangata, although numbers were the highest of the three areas in the 1970’s, over time they have dropped away to very small numbers despite the lack of commercial fishing since 1994. In contrast, in the no-take zone at Tawharanui crayfish numbers have increased dramatically with very high numbers in the current decade. Not only are there high numbers, but there are many large crays too, with 10-pounders not uncommon! The results represent 1000 kilogrammes of legal-sized red crays per hectare of reef in the protected area, whereas outside the protected area on the transects there are none!

To bring this to a level anyone can understand, I did a simple 20-minute count and size estimate of crays inside and outside the western boundary of Tawharanui Marine Park in January 2006. The map shows where I counted, the two sites being only one kilometre apart, on the same reef type and in a depth of eight metres. Anyone can do this. Just anchor your boat and search around on the bottom for 20 minutes.

Map of Tawharanui Marine Park.  Red diamonds indicate locations of 20-minute counts of crayfish outside and inside the protected area.  Results in accompanying graph.

Map of Tawharanui Marine Park. Red diamonds indicate locations of 20-minute counts of crayfish outside and inside the protected area. Results in accompanying graph.

The graph shows the results. The front graph is from the open-fishing area, and the back graph from the no-take zone. The vertical axis represents numbers seen, and the horizontal axis is size of crays, shown as sublegals or undersize crays, and “legal” sizes in terms of pounds weight (I can estimate cray sizes in pounds, but have difficulty with kilos!).

20-minute counts of red crayfish at Tawharanui.  Outside the no-take zone [front, blue] and inside the no-take zone [back, red].  Crayfish sizes on horizontal axis.  Graph shows a few undersized crays in the open fishing area, but good numbers of small and large crays in the no-take zone.

20-minute counts of red crayfish at Tawharanui. Outside the no-take zone [front, blue] and inside the no-take zone [back, red]. Crayfish sizes on horizontal axis. Graph shows a few undersized crays in the open fishing area, but good numbers of small and large crays in the no-take zone.

The difference is again very obvious. There are far more crays in the no-take zone, and a good size range up to three at 6 to 7 pounds. There were NO legal-sized crays seen in the open fishing area.

Notably there were far fewer sublegal crays in the unprotected area which raises an interesting point. If people don’t take sublegal crays, why are there far more in the protected area than outside? The answer lies in crayfish behaviour. Crayfish are gregarious, meaning they like to be together in groups. And little crayfish like to be where there are already lots of other crayfish including big ones.

Female cray [left] and male cray [right] caught on the end of Whangaparaoa Peninsula in 1980.  Female crays have a 10-day window in which to find a suitable large male to mate with.  If unsuccessful the eggs degenerate in the ovaries and make the crayfish partly sterile.  Large males are now hard to find.  This has serious implications for the crayfish population and fisheries management.

Female cray [left] and male cray [right] caught on the end of Whangaparaoa Peninsula in 1980. Female crays have a 10-day window in which to find a suitable large male to mate with. If unsuccessful the eggs degenerate in the ovaries and make the crayfish partly sterile. Large males are now hard to find. This has serious implications for the crayfish population and fisheries management.

Research by Dr Alison MacDiarmid has brought to light some very interesting facts about crayfish breeding. Not only do large crayfish produce far greater numbers of eggs than small ones, but apparently when a female cray is ready to mate, it seeks large males to breed with because the fertilisation success is much greater than if she breeds with a small male. She has only a 10-day time window, however, in which to find a mate, after which time if not successful the eggs are resorbed into the ovaries which causes partial sterilisation! Because of overfishing, there are now very few large males in the general population, so the chances of a female cray finding a suitable mate are greatly reduced. In no-take marine reserves and parks, however, there is the full size and age range of crays including big males, so only in these areas is breeding success assured.

A dozen large crays around 3-4 pounds on an open rock wall at 15 metres depth, Tawharanui Marine Park no-take zone.  The crays are so numerous and unafraid that often they just sit around in the open.

A dozen large crays around 3-4 pounds on an open rock wall at 15 metres depth, Tawharanui Marine Park no-take zone. The crays are so numerous and unafraid that often they just sit around in the open.

A lonely sublegal crayfish is about all you see at Mimiwhangata Marine Park these days.  Although commercial crayfishing ceased in 1994, the recreational take is still too high to allow a recovery, and crayfish have continued to decline to a very low level.

A lonely sublegal crayfish is about all you see at Mimiwhangata Marine Park these days. Although commercial crayfishing ceased in 1994, the recreational take is still too high to allow a recovery, and crayfish have continued to decline to a very low level.

All this should be ringing serious alarm bells for the crayfishing industry and fisheries managers. If I was a commercial crayfisherman, I would be screaming out for more marine reserves! I would be demanding at least 10 kilometres of coastline protected in every 100 kilometres. The current way the fishery is managed has led to very serious depletion of crayfish stocks. We may be approaching a point where the few marine reserves we have may be starting to prop up the crayfish stocks outside the reserves.

Past management has led to grossly depleted numbers, wrecking of the natural size and age structure of the population, disruption of natural behaviour and social organisation, erosion of natural levels of breeding success, and probably loss of genetic diversity. Not to mention difficulty for fishermen catching their quota. In CRA 1&2 (Northland and Auckland east coasts) catch per unit effort is down to 0.47kg and 0.43kg per pot haul. That is on average each time a fisherman hauls a pot he gets one just-legal cray! That would hardly cover his fuel costs.

It is time for a complete overhaul of philosophy of management of our crayfish populations. If you are concerned write to the Minister of Fisheries, Parliament Buildings, Freepost, Wellington, and express your views.

Lets get real and make some Marine Reserves.

Marine Reserves – more crayfish – good idea!

Roger Grace
2 April 2007, revised 8 April 2007, major revision 20 July 2014

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: