The science of sustainable seafood, explained

Status of Global Fisheries Trends and the Role of Catch Reconstructions: Implications for Current Stock Levels

A paper by Pauly and Zeller published in January 2017, highlights and discusses four criticisms of the most recent release of the biannual State of the World Fisheries and Aquaculture report (SOFIA) published by FAO in June 2016. Specifically, Pauly and Zeller argued that “poor and incomplete statistics from virtually all fishing countries… are to blame for the incorrect global trends derived from data submitted annually to and reported by FAO.” Further, they criticized FAO for, “ignoring the catch reconstruction process that has been ongoing for the last decade” and failing to include these reconstructions in the SOFIA report. Finally, Pauly and Zeller questioned the interpretation and significance of FAO’s aquaculture production statistics.

Shortly after, in March 2017, Ye et al. released a response to Pauly and Zeller’s comments refuting their criticisms, claiming “that their critique is based on fundamental misunderstandings caused by mixing up statistical metrics and using simple normative explanations to interpret highly complex datasets.”

The four main criticisms presented by Pauly and Zeller are outlined and defined below, and include Ye et al.’s responses to these claims.

Criticism 1: Is the catch of world marine fisheries really stable?

Pauly and Zeller claim that the ‘stability’ of wild capture fisheries catches stressed in SOFIA is a myth, and “that global catches have actually been declining since peak global catches in the mid-1990s” (see Figure 1 in Pauly and Zeller 2017). Specifically, “poor and incomplete statistics from virtually all fishing countries…are to blame for the incorrect global trends derived from data submitted annually to and reported by FAO.”

Ye et al. responded by highlighting that “in the FAO’s database, capture fisheries production covers only landed catches converted to their live weight equivalents. Pauly and Zeller “catch reconstruction,” by contrast, includes estimates of discards and IUU catches.” In other words, “Pauly and Zeller compare total fish removals with FAO landings data,” and given the difference between these two, “it should be easy to see that figures for the two are not comparable and, given the uncertainty in the latter, that it would not be sensible to argue about differences in their trends.” Further, “as reported catches in Pauly and Zeller are almost the same as FAO’s records (see Figure 2 in Ye et al. 2017), the declining trend of reconstructed catches is mainly caused by the trends in discards and IUU estimates (“unreported” catch). Given the huge uncertainty involved such estimates it would seem imprudent to read too much into the trend of the signal. Moreover, even if such declines were real, a reduction in discards and IUU catches should be a reflection of improvements in fisheries management, which may also be responsible for the relative stability in landings in recent decades.”

Criticism 2: What will future catches be?

Pauly and Zeller argue that the increase in the percentage of overfished stocks in recent years, as reflected in SOFIA 2016, supports the decreasing trend seen in their reconstructed catches. They suggest that this is in contradiction with the stability in capture fisheries production reported in SOFIA. They cite Worm et al. 2006 in support of this interpretation, who warned of the risks to the status of fisheries resources by mid-century if current overexploitation trends continue. Additionally, Worm et al. has been roundly criticized.

In response, Ye et al. claim that there is no contradiction between SOFIA’s statements on global stability in landings and the increasing rate of overfished stocks. “First, it is well known that landings do not necessarily reflect abundance and stock status. Interpreting catch trends without considering management regulations and effort changes requires caution. Second, percentages of overfished stocks calculated by FAO and presented in the SOFIA report are based on the number of stocks, i.e. large and small stocks bearing the same weight in the calculation. Therefore, for example, when smaller stocks are overfished and large stocks recover or move from under-fished to fully fished, total landings increase, generating opposite trends.” Further, “overfishing top predators could reduce natural predation, increase fishable biomass of prey species at lower trophic levels, and consequently total landings. This has indeed been recently demonstrated by Szuwalski et al., consistent with the fishing down the food web theory.”

Criticism 3: Why keep pretending that catch reconstructions do not exist?

Thirdly, Pauly and Zeller claim that FAO has been “ignoring the catch reconstruction process that has been ongoing for the last decade.” Specifically, incompleteness in data reported by FAO includes “heavily focusing on industrial fisheries and under-representing or even omitting artisanal, subsistence and recreational fisheries” as well as lack of reporting on discard and illegal catch data.

Ye et al. again stress the importance of differentiating between landings and total removals, stating that “it is important to differentiate original data (FAO data) from secondary data (reconstructed catches) consisting of estimates based on the original. Blending them does not necessarily add value to the original dataset, and may cause confusion and raise the risk of significant misinterpretation.”

Further, “FAO has always been aware that its global capture database does not include all fish removals, as it is not its objective.” Rather than “pretending that catch reconstructions do not exist”, “the recent FAO Committee on Fisheries (COFI) in July 2016, a meeting attended by delegates from 126 countries and 212 observing organizations, and which coincided with the release of the 2016 SOFIA report, included a side event on catch statistics, with participation of Pauly and Zeller’s team. Various catch reconstruction methods were presented, and member countries and NGOs discussed the opportunities and challenges they face in their data collection. No country has to date revised its statistics as a result of the catch reconstruction exercise.”

Ye et al. also highlight the difference between interpolation and extrapolation in response to Pauly and Zeller’s claim that “the same method of interpolation FAO uses to estimate catches for a given single year when data is missing can easily be applied to estimate IUU catches and discards.” “Considering the scarcity and methodologically diverse estimates of IUU fishing and discards, especially in many developing countries, such estimates may be obtainable not by interpolation, nor extrapolation, but rather by means of some magical method able to produce a large amount of estimates out of a very small original database.”

In this context, Ye et al. find it “remarkable that Pauly and Zeller have been able to estimate IUU and discard volumes for every country in the world, and for every year from 1950 to 2010, based on a six-step approach. Combining their estimates with FAO’s capture database as the main baseline, they quantified total fish removals from all ecosystems. A huge uncertainty is involved in such reconstruction, as recognized by the authors. It is not FAO’s role to validate academic publications that partially use FAO’s data, but it is worth noting that the methodology used in catch reconstructions has already attracted criticisms in the scientific literature.”

While FAO recognizes the potential value of catch reconstructions, they claim that “it would be beneficial to keep original and secondary statistics separated, to avoid confusion in their interpretation…and to recognize their methodological differences and complexities.”

Criticism 4: What’s up with aquaculture?

Lastly, Pauly and Zeller raise concerns about “the notion that the growing aquaculture industry may replace capture fisheries for global food security purposes.” Specifically, they claim that “combining aquaculture statistics and capture fisheries statistics implies serious double counting will occur unless clear data adjustments are done…because a sizable fraction of aquaculture relies on fishmeal and fish oil or other fish products for feed in their operation,” and suggest excluding “fish used as food for other (farmed) fish…when summing up the fish produced globally and available for human consumption.”

Ye et al. responded by stating that “SOFIA 2016 did explicitly carry out such statistical adjustments. Table 1 in SOFIA 2016 clearly separates the utilization of fisheries and aquaculture production from what is used for human consumption and nonfood uses. Moreover, Figure 29 presents per capita fish consumption, excluding fish used to produce fishmeal and fish oil or used as direct feeding for aquaculture, livestock, as well as other production destined to non-food purposes.”

In light of these concerns raised by Pauly and Zeller, FAO realizes the need “to communicate more efficiently so that the thoroughness and care behind its data collection and curation efforts is understood, valued and appropriately recognized.”

Concluding Remarks

CFoodUW would note that the major difference between FAO data and the Pauly and Zeller catch reconstructions is unreported landings, both discarding and IUU. FAO reports landings, while Pauly and Zeller have attempted to estimate unreported landings for each country of the world. The reliability of this has been questioned by scientists from a number of countries and often relies on little, if any, actual data.

In a recent paper, Reg Watson, who formerly worked with Pauly and Zeller and is now a Professor at University of Tasmania, reported his own catch reconstruction that does not show the same decline shown in Pauly and Zeller’s catch reconstructions. Professor Watson harmonized more than 867 million fisheries landings records between 1950 and 2014 into a global dataset, which resulted in a mapped dataset of catch rates (tonnes per square km of ocean) for each spatial cell based on taxonomic and fisheries logistic considerations (year, fishing nation and fished taxa). These data were associated with fishing gear, then IUU and discard catch rates were estimated. According to an interview of Professor Watson reported in an IMAS news update, “the total tonnage of fish taken per annum has been static for almost 30 years, but overall, it’s risen from 27.6 million tonnes in 1950 to 120.2 million tonnes in 2014.” Further, “the annual take could yet increase if we took a bigger proportion of global fish stocks, but currently it’s peaked around 120 million tonnes, including 17 million tonnes taken illegally and 15 million tonnes discarded.”

Finally, Pauly and Zeller argue that their estimated declining trend in catches indicates that stock status is worse than FAO estimates. On the contrary, as Rudd and Branch have shown, if unreported catches are declining, assessments would tend to be too pessimistic, and the real status of stocks would be better than estimated. The objective of their study was “to quantify the direct impact of different scenarios of misreported catch on stock assessment results and proceeding management recommendations.” Their results show that given the assumptions made in catch reconstructions based on limited data on unreported catches, and thus the high level of uncertainty, “catch reconstructions and monitoring would need to be conducted stock by stock, which is time-consuming and expensive.” Further, under-reported catch itself does not lead to overfishing unless reporting rates deteriorate over time, suggesting a key area of focus for catch reconstruction efforts, resource management strategies and data collection.” Results of this study demonstrate that “monitoring programs and catch reconstructions should be geared towards understanding the trend in catch reporting over time when data collection and research capacities are limited in management strategy development.”

Share this story:


Subscribe to our newsletter:

Read more:

Leave a Reply

Ray Hilborn's every-so-often newsletter

The best way to keep up with our stories.