Overfishing: A brief overview

By Michael Roach

Overfishing has been called the “most serious threat to our oceans” [1]. In a 2023 opinion survey of over 1,500 marine researchers, the issue came out on top as posing the greatest threat both to marine environments and to human society [2]. Without a doubt, overfishing is a major concern to conservationists, local communities, and the fishing industry alike. But what is overfishing? How does it differ from “overfished”? And what is the state of the world’s fisheries today?

In the context of fisheries, the fish populations that are targeted by them are referred to as “stocks” [3]. Any given stock has what’s called a “maximum sustainable yield” (MSY), which is the largest possible yield or harvest that can be taken from the population over time without compromising its ability to replenish itself [4]. The concepts of “overfishing” and “overfished” both relate to MSY. “Overfishing” refers to the practice of harvesting from a stock at a greater rate than that which would produce its MSY — in other words, catching faster than the population can replenish itself. “Overfished”, on the other hand, refers to a state in which a stock’s population size has become too low, putting its MSY at risk [4].

This is an important distinction to make because it is possible for a stock to be overfished but not actively subject to overfishing or, conversely, to be subject to overfishing but not yet overfished. For example, a stock may be overfished (its population is too small) but is in the process of rebuilding, or it may be subject to overfishing (its population is shrinking) but not yet at the point of being overfished. It’s even possible for a stock to be “overfished” as a result of other stressors, such as disease (which naturally can cause a population to decline) [4]. For this reason, simply describing a stock as “overfished”, while not ideal, is painting an incomplete picture. Knowing whether a stock is actively subject to overfishing is arguably more important since, if left unchecked, overfishing indicates a shrinking population, caused directly by human activity.

Humans have long exploited marine ecosystems, particularly in the form of overfishing [5]. Fishing reached industrial scale in the early 19th century, and through the middle part of the 20th century, advances in technology and techniques led to a rapid growth in fisheries and their catches [6]. The subsequent collapses of the Norwegian spring spawning herring in the late 1960s [7], the Peruvian anchoveta in 1972 [6], and the Atlantic cod in 1992 [8] underscore the dire threat overfishing can pose. Today, global marine fisheries catches have been on the decline since peaking in 1996 [9].

In fisheries research, catch rates have been used as a sort of proxy for the health of a fish stock, but this approach has been criticized as misleading, because other factors can influence catch rates besides just stock status [10], [11], [12]. It is perhaps for this reason that there are such diverging views on the health of fisheries among researchers [10]. Indeed, the status of the world’s marine fisheries, and the role that overfishing may play, is a complicated issue fraught with controversy [11], [13]. This overview will not by any means put the debate to rest, but it will attempt to provide clarity based on a general review of the literature.

In short, the situation is varied. Studies that are global in scope suggest that the median fishery is both overfished and subject to continued overfishing [14] and that fishery biomass is declining [15]. However, there are differences from this general picture based on place and management approach. In so-called “developed” countries, with typically stronger management of fisheries and reliable stock assessments, stocks are on the whole showing favorable progress toward rebuilding and sustainability [11], [16]. On the other hand, in so-called “developing” countries, with often weaker management and a general lack of stock assessment, the situation is more concerning, with a general decline in the biomass of both large and small fisheries [11], [16].

Analysis by the United Nations Food and Agriculture Organization indicates that the percentage of overfished assessed stocks around the world has been increasing almost continuously since 1974, from 10 percent back then to 37.7 percent in 2021 [17]. As described above, an overfished stock is not necessarily a result of overfishing, but this is no doubt a trend that warrants attention. What’s more, studies show that a considerably greater percentage of fisheries, both assessed and unassessed, are in need of rebuilding, even if they are not quite overfished — 63 percent and 64 percent, respectively [11], [18]. These findings underscore the continued importance of improving management and data collection to avoid overfishing and help these fisheries rebuild.

In conclusion, the status of the world’s marine fisheries, and the role overfishing plays, is a complex issue. Historically, overfishing has been instrumental in the collapse of several key fisheries, and it certainly remains a very real threat today. There is perhaps cause for guarded optimism when it comes to the status of assessed and intensively managed stocks, but the precarious state of unassessed and weakly managed stocks creates a global situation that is on the whole concerning. Considering the economic significance of these unassessed stocks for high- and low-income countries alike [11], [19], it would seem wise to take the issue of overfishing very seriously.

[1] Environmental Defense Fund. Overfishing: The most serious threat to our oceans. https://www.edf.org/sustainable-fishing/overfishing-most-serious-threat-our-oceans (2023).

[2] Kvamsdal, S. et al. Expert opinions on threats and impacts in the marine environment. Marine Policy 147 (2023).

[3] Marine Stewardship Council. Definition of fish stock. https://www.msc.org/en-us/about-the-msc/definitions/fish-stock [no date].

[4] NOAA Fisheries, Status of Stocks 2023. https://www.fisheries.noaa.gov/national/sustainable-fisheries/status-stocks-2023 (2025).

[5] Jackson, J. B. C. et al. Historical overfishing and the recent collapse of coastal ecosystems. Science 293, 629–637 (2001).

[6] Pauly, D. et al. Towards sustainability in world fisheries. Nature 418, 689–695 (2002).

[7] Hannesson, R. Stock crash and recovery: The Norwegian spring spawning herring. Economic Analysis and Policy 74, 45–58 (2022).

[8] Hayes, P. et al. 500 years of the once largest fishery in the world: A comprehensive catch reconstruction for the Newfoundland cod fishery (1508–2023). Fisheries Research 285 (2025).

[9] Pauly, D. & Zeller, D. Catch reconstructions reveal that global marine fisheries are higher than reported and declining. Nature Communications 7 (2016).

[10] Branch, T. A. et al. Contrasting global trends in marine fishery status obtained from catches and from stock assessments. Conservation Biology 25, 777–786 (2011).

[11] Costello, C. et al. Status and solutions for the world’s unassessed fisheries. Science 338, 517–520 (2012).

[12] Ricard, D. et al. Examining the knowledge base and status of commercially exploited marine species with the RAM Legacy Stock Assessment Database. Fish and Fisheries 13, 380–398 (2012).

[13] Branch, T. A. Citation patterns of a controversial and high-impact paper: Worm et al. (2006) “Impacts of biodiversity loss on ocean ecosystem services”. PLoS One 8 (2012).

[14] Costello, C. et al. Global fishery prospects under contrasting management regimes. PNAS 113, 5125–5129 (2016).

[15] Palomares, M.L.D. et al. Fishery biomass trends of exploited fish populations in marine ecoregions, climatic zones and ocean basics. Estuarine, Coastal and Shelf Science 243 (2020).

[16] Hilborn, R. et al. Effective fisheries management instrumental in improving fish stock status. PNAS 117, 2218–2224 (2020).

[17] FAO, The State of World Fisheries and Aquaculture 2024 – Blue Transformation in action. (2025).

[18] Worm, B. et al. Rebuilding global fisheries. Science 325, 578–585 (2009).

[19] Watson, R. A. et al. Global seafood trade flows and developing economies: Insights from linking trade and production. Marine Policy 82, 41–49 (2017).