Even when fisheries are managed successfully, the price of fish may rise, making eating fish more cost prohibitive for ordinary people. There are two types of aquaculture: fed aquaculture, which involves providing feed, as in the case of yellowtail, and non-fed aquaculture, which involves growing organisms without providing feed, as in the case of scallops. Fed aquaculture is an industry that adds value to marine products, and eating sardines directly by humans provides a greater source of protein than when used as feed for other fish. This is true whether the feed is fish meal or agricultural produce. However, it would make more sense to use bycatch for aquaculture feed, rather than simply discarding it.

As technology advances to select and catch only target fish, it will no longer be possible to eat lesser value fish at low prices. Even so, low trophic fish species such as sardines are available in large quantities. In 1970, when global fishing catches totaled about 100 million tons, the catch of a single species, Peruvian anchovy, in Peru alone was 12 million tons. There are fish species that we can use if we are less particular about catching high-level predators. Fish may cost more than meat, but if we face food scarcity in future, or if we learn that fishing is better for the environment and climate than livestock farming, eating more fish will make sense.

While populations of high-grade fish may decrease in future, further rises in fish prices will mean that fishing could become a growth industry. That path is different from mass catches of mesopredators. These are not necessarily binary opposites, however the future of the fishing industry will change significantly depending on which aim we pursue.

In the past, environmental organizations tended to criticize the fishing industry as a whole. Since around the 1990s, there have been movements to encourage sustainable fishing. Following the roll out of forestry certification by the Forest Stewardship Council (FSC) and similar bodies, eco-label certification(*2) for marine products, such as MEL Certification, a Japanese certification scheme developed by the Marine Eco-Label Japan Council (MEL), is also becoming more widespread. Since getting certified involves financial expense, the scheme mainly targets high value fish in the context of captured fisheries.

*2　Marine Eco-Label Certification: a framework for certifying wild-catch and aquaculture fishing carried out in a way that is considerate to the environments of marine resources and ecosystems.

The Convention on Biological Diversity has previously focused on unspoiled nature with the aim to reduce human impact. When Japan chaired the conference of the parties in 2010, a resolution on the satoyama issue, which emphasizes the value of human-influenced nature, was approved, however the idea did not yet reach the mainstream. Then, over a decade later in 2022, "living in harmony with nature" was raised as a topic of the Kunming-Montreal Global Biodiversity Framework. Wild-catch fisheries should also be reconsidered in future. Fed aquaculture is also becoming more environmentally friendly, however the status of food production industries is different to that of value-added industries. Non-fed aquaculture will surely keep advancing even further.

Ecological Footprint (FP) indicators, which show the impact of human life on natural resources and the environment in terms of the earth's area, are useful in comprehensively understanding these environmental impacts. Carbon footprint, nitrogen footprint, water footprint, and more have also been proposed as indicators of environmental impacts, such as the greenhouse effect, soil and seawater pollution from fertilizers, and the over-extraction of groundwater. A footprint can be calculated from the balance of production to consumption and disposal using input-output tables. Through this, we can understand which impacts are worsening due to our patterns of consumption, and in which countries. Some aspects of the assessment are still unrefined, however improvements are underway. Overall, the question is how we can make our diets more environmentally friendly, and how the fishing industry should operate to support this.

This is true for other environmental issues, too, but it is important to take care when assumptions on resource assessment are unproven, particularly in the case of the fishing industry. I will give two of the most obvious examples here. Atlantic bluefin tuna was considered overfished in around 2010, with stocks facing depletion within five years. A proposal to ban imports and exports was rejected at the CITES-CoP in March 2010. Stocks later recovered, with catch quotas expanded in stages. Had a ban been put in place at that time, the fishing industry would not be where it is today. Just four years later, stocks of parent fish were assessed as having returned to the highest levels in history.

In respect of stock assessment, both are hard to believe. Catch size is a known factor, however natural mortality rates are unknown. Assuming an inappropriate value yields strange results.

Much of environmental science is not empirical science that is verified before being reported more widely. Some aspects do not even have any mechanism for follow-up verification. Although the most plausible assumptions at the current point in time are used, these assumptions are not necessarily correct. It would be dangerous and reckless to take such science as absolute.

Stock assessment of chub mackerel is also doubtful. While the species was considered overfished constantly since 2010, stock has steadily increased; these days it is close to the high levels seen in the 1970s. That assessment has recently been slightly retroactively revised. However, stock is still assessed as being lower than the MSY level. Like sardines, chub mackerel also repeatedly undergoes natural fluctuations over several decades at a time, with periods of low and high influx. Since the model used averages out these values, the assessment is as shown below.

Marine resources are also extremely affected by how good the environment is from year to year. In good years, stock increases regardless of how much is caught, while in bad years, stock decreases even if fishing embargoes are put in place. Even if academics calculate using the average natural increase, fishermen will not trust the results. The fishermen are right to do so. That does not mean, however, that resource management is unnecessary. Such wild fluctuation is the same as is seen in gambling and investing. Risk management is necessary. Fisheries science still has much to learn from others on this point.