A new study suggests that New Zealand's total fisheries catch since 1950 is 2.7 times higher than officially reported.
Between 1950 and 2013, 24.7 million tonnes of fish went unreported, compared with the 15.3 million that was officially reported to the UN Food and Agriculture Organisation, the international research led by the University of Auckland's Dr Glenn Simmons reports.
The researchers drew on stock reports, peer reviewed studies, unpublished reports and over 300 interviews with industry experts and personnel, to build an estimate of unreported catch.
The majority of unreported fish catch was commercial catch or fish discarded because they were the wrong size or species.
The research was published as a working paper as part of the Sea Around Us project by the Institute for the Oceans and Fisheries, University of British Columbia.
The Science Media Centre collected the following expert commentary on the report.
Owen Anderson, fisheries scientist, NIWA, comments:
"NIWA scientists have been estimating bycatch and discards of New Zealand offshore fish species for many years. These estimates are based on thorough and scientific analyses of catch and discard data collected by independent Government observers on board commercial vessels.
"Our analyses show that for 1991-2013, the overall discard rate from the observed part of the fishery (about 20-25 per cent of the total fishing effort) in offshore fisheries was 6.6 per cent. This is in stark contrast to the minimum 20 to 50 per cent reported in the Simmons report.
"An important difference between the studies is that the NIWA analyses are based on empirical data and, unlike the Simmons study, do not attempt to estimate the prevalence of discarding activity that may have been intentionally hidden from observers or make any assumptions about the influence of observer presence on discarding behaviour. We note that regulations allow for legal discarding of any QMS species when an observer is present.
"We also note that the Simmons report relies heavily on anecdotal evidence to apply multipliers to reported catches and discards. It is difficult to independently assess the appropriateness of these multipliers.
Prof Matthew Dunn, chairman in fisheries science, Victoria University Wellington, comments:
"I cannot comment too specifically as I have not yet seen the methodology and data underpinning this report. That said, I think everybody in the business knows that fish do get dumped and catches under-reported. I don't think there is any dispute that the reported catches that come through the Quota Management System are not as big as the real catches.
"The question of how big the unreported catch may be is difficult. It sounds as if much of the information in the new report comes from interviews with fishers. Having used interviews in the past, I know these kinds of data are particularly uncertain, and often biased. Where estimates come from Ministry reports, we should remember that the Ministry tends to target fisheries where they think there could be a problem, so these estimates are likely to be higher than the norm. I would expect there to be great uncertainty, and potential for bias, around the estimate of '2.7 times'.
"The report's findings don't detract from the fact that NZ does very well internationally for sustainable fisheries. Most of the main fisheries are doing well. Fish like hoki, ling, hake and southern blue whiting have been certified by the Marine Stewardship Council as meeting world's best standards for sustainability. Perversely, some of the ling stocks even seemed to get bigger after we started fishing them.
"If this report stands up scientifically, then we would have to modify some of our assessments of the size of our fish resources. Because catch estimates scale our stock estimates, the irony of that the '2.7 times' could mean there are more than twice as many of these fish in the sea as we think there is. This means sustainable catches, and catch quotas, could also be higher. If that was true I'd expect the industry to be saying "there's loads more fish out there, let us land it". Recently, the industry had the option of increasing the quota for hoki, but they actually declined. To me, this doesn't suggest that our catch and stock estimates are that wrong.
"This report does cover a wide time period. We know the under-reporting of catch in some deepsea fisheries was high back in the 80s, with the real catch being as much as half as much again, or even double, what was reported. But by the mid-90s that excess was largely gone. From the studies I am aware of, it true to say under-reporting was much more pronounced 20-30 years ago than it is now.
"These days fisheries are more heavily and easily observed. For example there are just half a dozen or so boats fishing orange roughy around New Zealand - there used be around 40 just on the Chatham Rise back in the 1980s. It is a very different fishery now.
"The hard thing about the QMS is the 'deemed value', where there is a penalty for catching more than your catch entitlement - it is very hard not to catch fish by accident sometimes, especially in inshore fisheries where many species are found on the same grounds. I don't know of an obvious alternative, but greater Ministry observer coverage would certainly help.
"The QMS is 30 years old and would certainly benefit from a review. Those associated with the industry are well aware of the shortfalls.
"The QMS and the deemed value system is not perfect, but it doesn't detract from the fact that a privatised fishery system, like our QMS, is still considered to be amongst the best, if not the best, way of managing fisheries resources.
"The focus should be on making sure our fisheries are sustainable now and into the future. As long as our industry is strong, and the resources are sustainable for them and for future generations, then we are doing a good job. In my opinion, we want our fisheries management and industry to be looking forward, not worrying about what happened 50 years ago. But if this kind of research helps to focus people on what needs to change, then that is a good thing. But litigating the past can seem a bit pointless if we know the current fisheries are sustainable, and our industry is performing well."
• This article originally appeared in Scimex, posted in Science Alert: Experts Respond, and has been republished in the Herald with their permission.