Supplementary comments from newspaper interviews about Japanese eels

Supplementary comments on the interview in the Mainichi Shimbun (reported on October 29, 2025 "Are Japanese eel populations increasing? Two conflicting papers, third-party assessment") Japanese blog of 8 Nov. 2025

• Kaifu et al. (2025)'s criticisms of Tanaka (2014, 2025) are based on three main points:

1. The CPUE data for glass eels includes both under-reporting and over-reporting.
2. The data includes a mixture of information on eel fishing and bycatch, meaning that effort is not limited to eels.
3. The catch, including releases, cannot be said to reflect the resource abundance.　However, Tanaka (2025) conducted a sensitivity analysis that took into account unreported data (Figure 6b).

• On the other hand, Tanaka (2025, p. 8, left column, below Figure 7) criticized Kaifu & Yokouchi (2019) for failing to ensure representativeness of the resource status due to the lack of a sampling plan and the small scale of the survey.
• These criticisms are valid for both (and also for Kaifu et al. 2025). This is unavoidable, as the assessment is based on incomplete information.
• Regarding the criticism of Tanaka (2025), the question is whether the stock assessment would qualitatively change if these factors were corrected. If the unreported rate has remained constant both in the past and now, the absolute stock abundance would actually be higher (Tanaka Figure 6b). If the unreported rate was much higher in the past, it is unlikely that the stock has recovered (although it is questionable whether it continues to decline sharply). (2) If dependence on eel fishing has been lower in recent years, using total effort as the denominator of CPUE would actually underestimate the stock recovery rate. If dependence has been higher in recent years, the opposite would be true. (3) If the glass eel catch rate is lower now, an analysis including releases would not necessarily underestimate the true rate of decline. If it is higher now, the opposite would be true.
• I don't mind Kaifu et al. using unpublished data, but to maintain anonymity, the catch amount data are not shown. Unfortunately, we are unable to confirm their regression model (though Kaifu can replicate Tanaka 2025 to some extent). It's likely that the reviewers also pointed this out. Furthermore, Kaifu et al. (2025, Table 3) treat each fishing ground as an independent population and provide point estimates of the decline rate for each fishing ground. However, the Japanese eel stock is actually a single entity, and parent and offspring likely do not migrate upstream to the same location. A single overall decline rate should be estimated as an interval estimate. Including Chiba, where the population increased 4.5-fold (this could be adjusted, for example, by limiting the overall population to the October-December period), would result in a value with a reasonable range. To begin with, CPUE is not suitable for quantitatively assessing the true decline rate of stock abundance (R. Myers's infamous 90% decline in tuna species was later criticized, and it's now said to be at most 30-50%). However, Kaifu's analysis is also valuable. The fact that it can only be published anonymously is "abnormal." He persisted in his analysis. 
• The results for glass eels are consistent in both cases, suggesting a flat population (or no significant increase or decrease, as stated in the abstract of Kaifu et al. 2025). However, Kaifu et al. 2025 includes the results for glass eels, excluding as many unreported cases as possible, in Figure 4 and Table 4. Table 4 does not specify the estimates and SEs, but the likely growth rates are -0.021 and +0.101 (per year?). Simply applying SE (whether this is appropriate or not is unclear, but the paper lacks the data necessary for further analysis) would suggest a 0.17 increase and a 0.09 decrease (unclear increase or decrease). This is probably the most reliable conclusion. If this is the case, we cannot deny the possibility of continued decline (a decrease of more than 80% over 24 years [or, at the same rate, a decrease of more than 60% over 14 years] is likely less than 5%), but there is also a possibility of recovery. 
• This alone may not be sufficient evidence for listing species under CITES. There is no doubt that the decline has been significant compared to half a century ago. However, it is unclear whether the decline has continued since 2010. If the proposal had been made at the same time as the European eel, there would have been little opposition to listing it on CITES Appendix II, but it would be better to wait a little longer to see the results of subsequent conservation efforts. It's unclear why it's being proposed now.
• The international treaty could be throwing cold water on the issue without waiting for the results of Asian countries' efforts since around 2015, but perhaps that's their raison d'être. Like the IWC, CITES is a "fossilized" treaty based on a dichotomy.
• The Red List is determined based on past decline rates, so it likely met the numerical standards of the IUCN (criteria A) and the Japan Ministry of the Environment at the time (criteria E). The Red List is not based on extinction risk itself, so even with a CR rating, fishing is still possible, as with bluefin tuna, and some species are recovering through exploitation. I have been criticizing the Red List criteria for about 30 years (Matsuda et al. 1997), saying they are strange, but the IUCN criteria (ver. 3.1) has been clearly stated that "species that meet the numerical criteria will be included even if they are known to have a low risk of extinction".

Resolutions from the World Heritage Committee regarding Steller Sea Lions in Shiretoko

In 2024, we revised the Basic Management Policy for the Steller Sea Lion (see below), which included the Shiretoko World Heritage Site within the management area. We gained a general understanding of this from the World Heritage Committee (see 47 COM 7B.7). We are very grateful for this. It was important for us to gain an understanding of the concerns of both the local fishers, who suffer damage to their industry due to sea lions, and the World Heritage Committee, who are concerned with the Outstanding Universal Values of Shiretoko. We will continue to strengthen the scientific evidence in order to promote the coexistence of fisheries and sea lions, while striving for both conservation and human activities.

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