Do “Catch Reconstructions” really Implicate Overfishing? / by Francisco Blaha

As expected there was some answers and rebuttals of the Pauly and Zeller paper I referred in my last post. Not surprisingly some of it comes from Ray Hilborn, as those two are sitting in opposite sides of life (I posted about his views before). Here are some of the responses:

Juan is deconstructing catch

Juan is deconstructing catch

Ray Hilborn, Professor in the School of Aquatic and Fishery Sciences at the University of Washington

This paper tells us nothing fundamentally new about world catch, and absolutely nothing new about the status of fish stocks. It has long been recognized that by-catch, illegal catch and artisanal catch were underrepresented in the FAO catch database, and that by-catch has declined dramatically.

What the authors claim, and the numerous media have taken up, is the cry that their results show that world fish stocks are in worse shape than we thought. This is absolutely wrong. We know that fish stocks are stable in some places, increasing in others and declining in yet others.

Most of the major fish stocks of the world, constituting 40% of the total catch are scientifically assessed using a mixture of data sources including data on the trends in abundance of the fish stocks, size and age data of the fish caught and other information as available. This paper really adds nothing to our understanding of these major fish stocks.

Another group of stocks, constituting about 20% of global catch, are assessed using expert knowledge by the FAO. These experts use their personal knowledge of these fish stocks to provide an assessment of their status. Estimating the historical unreported catch for these stocks adds nothing to our understanding of these stocks.

For many of the most important stocks that are not assessed by scientific organizations or by expert opinion, we often know a lot about their status. For example; abundance of fish throughout almost all of South and Southeast Asia has declined significantly. This is based on the catch per unit of fishing effort and the size of the individuals being caught. Estimating the amount of other unreported catches does not change our perspective on the status of these stocks.

In the remaining fisheries where we know little about their status, does the fact that catches have declined at a faster rate than reported in the FAO catch data tell us that global fisheries are in worse shape than we thought? The answer is not really. We would have to believe that the catch is a good index of the abundance.

Looking at Figure 1 of the Pauly and Zeller paper we see that a number of major fishing regions have not seen declines in catch in the last 10 years. These areas include the Mediterranean and Black Sea, the Eastern Central Atlantic, the Eastern Indian Ocean, the Northwest Pacific and the Western Indian Ocean. Does this mean that the stocks in these areas are in good shape, while areas that have seen significant declines in catch like the Northeast Atlantic, and the Northeast Pacific are in worse shape?

We know from scientific assessments that stocks in the Mediterranean and Eastern Central Atlantic are often heavily overfished – yet catches have not declined. We know that stocks in the Northeast Pacific are abundant, stable and not overfished, and in the Northeast Atlantic are increasing in abundance. Yet their catch has declined.

Total catch, and declines in catch, are not a good index of the trends in fish stock abundance.

Pauly and Zeller have attempted to estimate the extent of unreported catch for all the fish stocks of the world. For any individual stock in the U.S. the hardest part of doing the stock assessment is often estimating the total catch. Historical discards are often unreported, species were often lumped in the historical catch data, recreational catch was poorly estimated, and illegal catch totally unreported. Scientists can spend months trying to reconstruct these data for an individual stock and it is recognized that these estimates may not be reliable. Pauly and Zeller’s attempt to do this for thousands of global stocks with a consultant spending perhaps a few months to cover every fishery in an individual country just cannot be very reliable.

We need to move beyond trying to understand the historical fish catches, and instead concentrate on understanding the status of fish stocks at present. If all the effort that had been spent in trying to estimate historical catches by Pauly and Zeller had instead been devoted to analysis of what we know about the status of a sample of fish stocks in different places, we would know much more about the status of world fisheries.

David Agnew, Director of Standards, Marine Stewardship Council

The analysis of such a massive amount of data is a monumental task, and I suspect that the broad conclusions are correct. However, as is usual with these sorts of analyses, when one gets to a level of detail where the actual assumptions can be examined, in an area in which one is knowledgeable, it is difficult to follow all the arguments.  The Antarctic catches “reconstruction” apparently is based on one Fisheries Centre report (2015 Volume 23 Number 1) and a paper on fishing down ecosystems (Polar Record; Ainley and Pauly 2014). The only “reconstruction” appears to be the addition of IUU and discard data, all of which are scrupulously reported by CCAMLR anyway, so they are not unknown. But there is an apparent 100,000 t “unreported” catch in the reconstruction in Figure 3, Atlantic, Antarctic (48). This cannot include the Falklands (part of the Fisheries Centre paper) and it is of a size that could only be an alleged misreporting of krill catch in 2009. This is perhaps an oblique reference to concerns that CCAMLR has had in the past about conversion factors applied to krill products, or perhaps unseen (net-impact) mortality, but neither of these elements have been substantiated, nor referenced in the supporting documentation that I have seen (although I could not access the polar record paper).

The paper does not go into much detail on these reasons for the observed declines in catches and discards, except to attribute it to both reductions in fishing mortality attendant on management action to reduce mortality and generate sustainability, and some reference to declines in areas that are not managed. It is noteworthy that the peak of the industrial catches – in the late 1990s/early 2000s – coincidentally aligns with the start of the recovery of many well managed stocks. This point of recovery has been documented previously (Costello et al 2012; Rosenberg et al 2006; Gutierrez et al 2012) and particularly relates to the recovery of large numbers of stocks in the north Pacific, the north Atlantic and around Australia and New Zealand, and mostly to stocks that are assessed by analytical models. For stocks that need to begin recovery plans to achieve sustainability, this most often entails an overall reduction in fishing effort, which would be reflected in the reductions in catches seen here. So, one could attribute some of the decline in industrial catch in these regions to a correct management response to rebuild stocks to a sustainable status, although I have not directly analyzed the evidence for this. This is therefore a positive outcome worth reporting.

The above-reported inflection point is also coincident with the launch of the MSC’s sustainability standard. These standards have now been used to assess almost 300 fisheries, and have generated environmental improvements in most of them (MSC 2015). Stock sustainability is part of the requirements of the standard, and previous analyses (Gutierrez et al 2012, Agnew et al 2012) have shown that certified fisheries have improved their stock status and achieved sustainability at a higher rate than uncertified fisheries. The MSC program does not claim responsibility for the turn-around in global stocks, but along with other actions – such as those taken by global bodies such as FAO, by national administrations, and by industry and non-Governmental Organisations – it can claim to have provided a significant incentive for fisheries to become, and then remain, certified.

Original source for these two here

I also got a mail from my friend Bob Gillett, an extremely experienced fisheries consultant (his publishing record goes back to 1978), I have his knowledge (and friendship) in the highest regards. He says:

I have run into these "catch reconstructions" for almost every country in my present work of re-writing the ADB Benefish book.  I have come to the conclusion that the concept of having graduate students estimate fisheries production in countries they have never visited by remote control- just does not work.