Dear Editor, I seem to recall the learned Mr Tyler advancing very similar theories on fish abundance (or lack thereof) several years, or perhaps even over a decade ago.

I therefore have to admire his perseverance and total dedication to 'the search' for answers as to why fish appear to be so reluctant to bite on his hook.

I also recall attempting to provide him with an answer last time, around during my time as an employee of the Ministry of Marine Resources, but perhaps not publicly.

So by way of response to his letter, here goes again. In doing so, please allow me to elucidate some key points for your readers' consideration:

1. The tuna fisheries of the central and western Pacific are known as 'highly migratory', meaning they swim very large distances through the waters of multiple Pacific Island countries before ending up here in the Cook Islands. Oddly, they don't seem to recognise our borders, nor do they seem to want to stay here for any extended period of time.

2. It does however mean that these fish run a gauntlet of hooks and nets all the way from the Philippines and Indonesia, where the most prolific spawning grounds and largest abundances of tuna exist, all the way through to us over here in the central Pacific. They follow along the ocean currents, where most of the available forage accumulates, specifically the south equatorial currents, where the thermocline (the warm/cold water temperature break) is much shallower and more sharply defined, thus making them more 'catchable' by commercial operators at these latitudes.

3. The strength of these currents are heavily affected by the so called El Nino and La Nina events, which in turn strongly influence tropical tuna migratory patterns and the movements of tuna and associated species into the central Pacific.

3. Having just said that the largest abundances of tuna are concentrated in the western Pacific and along the equator, it is equally well established that the Cook Islands lies at the margins of this regional fishery, and consequently our 'footprint' in the fisheries (i.e. how much tuna is taken in our waters commercially) is comparatively smaller than our fellow Pacific Island countries across in the western Pacific - such as the Solomon Islands, Papua New Guinea, FSM, Marshall Islands, Nauru and Kiribati. These countries harvest fish commercially via longline, pole and line, and purse-seine methods to supply their canneries and processing centres for export to the EU and elsewhere. The fisheries in these countries also support very high artisanal (small-scale fishing fleets, and sport-fishing industries). My point here is that there is plenty of fish to support both small and large scale fisheries there with minimal interaction between the two.

4. Pelagic fish abundance in the Cook Islands is further complicated by a distinct 'separation' into northern and southern zones. The southern waters of the Cooks are even more strongly influenced by temperatures and currents than the north, and consequently the fishery exhibits very strong seasonal variability and even interannual variability - as ENSO, combined with the less well known impacts of long term climate change, make themselves felt. I would also point out that the low productivity of the southern zone is consistent with the waters of Niue and Tonga at the same latitudes, and is a reason why commercial catches in those countries have been virtually non-existent as well. 

5. This southern zone variability aspect is not new. There are published accounts of fish needing to be imported from NZ to Raro going as far back as the 1950's, and most local fishermen here in Raro will tell you that some years/months are very good, some years/months are not, irrespective of what the commercial guys up north are doing or not.

6. I could go into an entire thesis about the need to understand that tuna are thermoregulators, and move up and down the water column depending on the time of day and where their forage (food) is located, and that 'scratching the surface' might not always be the most successful strategy to catch a fish here, but I'll spare people the agony this time around.

All of this should hopefully lead your readers to the logical conclusion that catching fish in Raro has much less to do with what is happening commercially in the northern part of our zone, and much more to do with overall increases in fishing pressure across the region potentially creating some range contraction, but more importantly, the strong effects of climate, current and temperature on stock distribution and abundance. It is very convenient to blame the longliners and purse seiners for the lack of fish down here, but I've noticed we don't hear the same chorus of complaints quite so much during times when the fish are biting - but maybe I'll leave it to the psychologists among us to explain that one.

Ka kite,

Josh Mitchell, 

Former marine biologist and long-time interested observer of tuna fisheries in the Pacific and the Cook Islands.