In a three-part series, retired lawyer Reuben Tylor argues commercial fishing in the Northern Cook Islands can impact on our catches of yellowfin tuna in the South.

Late last year I wrote three articles about the state of our fishing resources. At that time local fishermen were struggling to catch any fish let alone yellowfin tuna. Fish prices had soared to the point where most families could not afford to buy fish. Rarotonga was importing fish from New Zealand and Tahiti to supply the local restaurants. I looked at the possible reasons for what appeared to be the collapse of our resource, in particular yellowfin tuna, which was the main target species for artisan and sports fishermen. I suspected purse seining and over fishing in the Northern group were the main culprits. My concern was that foreign fishing boats had damaged our resident stock of yellowfin tuna.

My articles met with angry denial from Josh Mitchell, who worked as a senior advisor for (Ministry of) Marine at the time the purse seiners and current fleet of longline boats were being licenced. Amongst other arguments, he insisted that the tuna resource in the Northern group was distinct from and different to the tuna resource in the Southern group, and that the absence of tuna in the South could not be related to commercial fishing in the North. He also repeated Marine Resources position that the La Nina weather event was responsible for the absence of fish in the south. Finally Josh said we have always had periods when tuna were scarce, and that there was no evidence for the existence of a resident tuna stock.

At that time La Nina was coming to an end and El Nino was starting up, so I decided to wait until El Nino was in full swing before responding.

In the intervening months I have also researched these issues. I have asked Marine several questions and their answers have been helpful. I have also accessed information from the website for marine resources in Tahiti. 

So are there separate stocks of yellowfin tuna for Northern and Southern groups?

To find out I asked Marine if they had any “scientific evidence that shows commercial fishing in the Northern group … has no impact on tuna stocks or catches in the Southern group”. I also asked for “scientific evidence that shows migratory tuna entering the Southern group fishery … do not originate from migrating tuna entering the Northern group…”

Marine replied that a tagging programme between 2009 and 2011 did not show any consistent pattern of migration for yellow fin. However, there was evidence from an analysis of catches in 2019 that albacore being caught in the North were likely a different stock to those being caught in the South. (That information isn’t terribly relevant to me because albacore are caught by longline and are not part of the usual artisanal catch). However, for yellowfin tuna, which is the major part of the artisanal catch, the same analysis showed that it was likely the North and South stocks of yellowfin tuna were the same.

The consequence of Marine getting this wrong earlier are serious. Commercial fishing in the North CAN impact on our catches of yellowfin tuna in the South.

What about La Nina? Is it perhaps responsible for the periodical shortage of yellow fin tuna?

Happily, as La Nina retreated and El Nino advanced, there has been a dramatic increase in the yellowfin catch, both in size and numbers. So it appears La Nina was at least partly to blame for the shortage of tuna during the last few years.

I say La Nina was “partly to blame” because I believe it is not the only factor at play here. If the schools of tuna migrating eastwards from the Western Pacific don’t reach the Cook Islands during La Nina, then we can expect our immediate neighbour to the east, French Polynesia, to also suffer. Yet Tahiti has not experienced the same scarcity of fish. In fact, Marine resources in Tahiti report a record longline catch of 7528 tonne in 2022. To make things more complicated their website states that: “The La Nina climatic phenomena since 2021 and which continued into early 2022 also benefitted tuna catches”. And I am sure we all remember our fishermen having excellent catches of yellowfin tuna during Covid, in the middle of La Nina.

A possible explanation for Tahiti not suffering from a shortage of fish during La Nina is that there is a properly managed resident stock of tuna in French Polynesian waters, which does not rely totally on an annual top up from migratory tuna. Perhaps this is evidence for resident stocks of yellowfin tuna?

There may be further evidence for resident stocks of tuna in the longline catch figures for Cook Islands waters. I will look at these in my next article.

Going back to the impact of La Nina, when La Nina began, a senior official from WWF (World Wildlife Fund) advised fisheries managers to adjust commercial catches to safeguard fish stocks during La Nina. Marine did not do this, presumably because the advice at that time was that the North and South stocks of fish were separate. The weather experts say this El Nino cycle is only going to last until late 24, when La Nina is expected to swing back again for another 3-5 years. Are we then going to have another 3-5 years with no fish?

Which leaves us with the Spanish purse seiners and the longline fleet. Were they also to blame? Did they also contribute to a collapse of our yellow fin tuna resource? I want to look at their catch figures next week to see if there is any evidence of this. I also want to look again at Vaine Wichman’s report, “Fishing For Answers”, published in 2011. That report called for a balance between commercial and artisanal fishing. It is more important now we know the North and South stocks of yellow fin tuna are not separate from each other.