Global finfish catches from capture fisheries peaked in the 1980s and have declined or remained stable since the early 1990s, yet global invertebrate catches have continued to climb [1]. Although some invertebrate fisheries have existed for centuries [2]–[4], many others have commenced or rapidly expanded over the past 2–3 decades [5], [6]. Today, shrimp has the largest share of the total value of internationally-traded fishery products (17% in 2006, including aquaculture), followed by salmon (11%), groundfish (10%), tuna (8%), and cephalopods (4%) [1]. In several ways, invertebrate fisheries represent a new frontier in marine fisheries: they provide an alternative source of animal protein for people, job opportunities in harvesting and processing, and substantial economic opportunities for communities due to their high value and expanding markets [1], [5], [6]. Yet, while finfish fisheries [7] and some more established invertebrate fisheries [8]–[11] have received increasing assessment, regulation, and rebuilding, many invertebrate fisheries do not get the same level of attention or care. They are typically not assessed, not monitored, and often unregulated [1], [2], [5], [6], [12], which threatens their sustainable development despite their increasing social, economic, and high ecological importance [6], [13].

The increase in invertebrate fisheries is in part a response to declining finfish catches that caused many fishermen to switch to new target species, often further down the food web [6], [14] although in many regions lower-trophic-level fisheries were added without declines in higher-trophic-level fisheries [15]. At the same time, the abundance and availability of many invertebrates may have increased due to release from formerly abundant finfish predators [16]. Once thought to be particularly resistant to over-exploitation [17], an increasing number of historical [3], [4] and recent invertebrate fisheries [2], [5], [12] tell a different story. Thus, in light of their increasing importance, we evaluated the current status, as well as the spatial and temporal trends of invertebrate fisheries around the world. Further, we aimed to assess their underlying drivers, and population and ecosystem consequences.

Unfortunately, stock assessments and research survey data that are available to evaluate many finfish populations [7] are often lacking for invertebrates [6], [12], [13]. Therefore, we used the Sea Around Us Project's catch database (Text S1) as the best available data source to analyze temporal and spatial trends in invertebrate fisheries on a global scale. It consists largely of a quality-checked version of the Food and Agriculture Organization's (FAO) catch database supplemented by regional and reconstructed datasets covering 302 invertebrate species or species groups (taxa) over 175 countries from 1950–2004 [18]. Wherever possible we have corroborated the observed patterns with recent taxa-specific global reviews (Text S1).

Since 1950, invertebrate fisheries have rapidly expanded on multiple scales, and today operate around the world (Fig. 1A). In 2000–2004, the highest concentrations of catch per unit area by Large Marine Ecosystem (LME) were in the Yellow Sea, East China Sea, and the Northeast U.S. Continental Shelf, followed by the Newfoundland-Labrador Shelf, South China Sea, and Patagonian Shelf. The bulk of the catch in these areas consisted of bivalves, shrimps, squids, and crabs (Table S1). Catches for all 4 of the larger invertebrate taxonomic groups (crustaceans, bivalves, cephalopods, and echinoderms) were heavily concentrated in the Yellow Sea and East China Sea (Fig. S1). In addition, catches for crustaceans were highly concentrated off the Newfoundland-Labrador Shelf, bivalves on the Northeast U.S. Continental Shelf, cephalopods off the Patagonian Shelf, and echinoderms off the Humboldt Current (Fig. S1). Since 1950, the total reported catch of invertebrates has steadily increased 6-fold from 2 to 12 million t (Fig. 1B). In comparison, the catch of invertebrates and finfish combined increased 5-fold over the same period, beginning to decline in the late 1980s [14], [19]. The increase in invertebrate catch is not driven by only a few countries, as the average catch per country has more than doubled (Fig. 1B). Also, in 2004 there were 1.5 times more countries fishing for twice as many invertebrate taxa compared to 1950 (Fig. 1C). This is in contrast to all finfish and invertebrate fisheries combined, where the number of countries reporting catch has been largely stable over the past 50 years (Fig. 1C). Although increasing trends in invertebrate fisheries may be partly explained by increasing precision in reporting (Fig. S2), there are clear underlying trends of expansion by catch, country, and taxa (Figs. 1B, 1C, 2). This is corroborated by studies on individual fisheries where assessments or effort data are available [20], [21].

The increase in invertebrate fisheries is driven not by a few major target species, but instead by increasing catch trends across all taxonomic groups (Fig. 2, Fig. S3). While catches have increased continuously since the 1950s for more traditionally fished crustaceans and bivalves, they rapidly increased in the 1980s and 1990s for often newly targeted cephalopods and echinoderms. Thus, already existing fisheries expanded and new fisheries were developed for species that had not been commercially fished before. Although overall catch trends for invertebrate fisheries paint a picture of continuing expansion (Fig. 1B), catches in several groups (e.g., octopus and echinoderms) have slowed or declined in recent years (Fig. 2B and 2D). The picture of universal increase changes even more drastically if we look at individual invertebrate fisheries by country. Here, some countries are still expanding their catches while others peaked long ago (Fig. S4, see also [5], [21]).

Based on individual catch trajectories, we assessed the current status and patterns of depletion of invertebrate fisheries. To do this, we modified a technique of Froese and Kesner-Reyes [22] to estimate the exploitation status of each invertebrate fishery from catch data (Fig. S5). Our modifications overcome previous weaknesses of this method by accounting for high variability in catch, spurious peak catch years, and fisheries that are still expanding (see Materials and Methods and Text S1). Our results suggest that half of the fisheries had peaked as of 2004 (Fig. 3A), with 18% fully exploited, 21% over-exploited or restrictively managed, and 13% collapsed or closed with little difference across functional groups (Fig. S6). This, combined with evidence of an increasing number of countries reporting catch and an increasing number of taxonomic groups targeted (Fig. 1C), indicates that the globally increasing invertebrate catches (Fig. 1B) are likely supplied by new taxa or new countries entering the fishery. In some invertebrate fisheries, such as many sea cucumber fisheries [21], decreasing catch trends have been directly related to population declines; however, we do not suggest that catch trends are generally good indicators of population status or have been driven solely by high exploitation pressure. Declines in catch can also have natural (e.g., recruitment failure due to climate) and other human-related (e.g., changing markets, restrictive management) drivers that can act in conjunction with each other [23].

Strong global markets may drive the expansion and serial depletion of some fisheries over space and time [3], [5], [24], particularly given the increasing availability of efficient fishing gear, rapid global transport, and the incentive to preferentially fish profitable marine resources [25]. If a fishery is declining in one region, fishing companies move into other regions, usually further away, to supply the demand of global buyers [5]. Some new invertebrate fisheries have a single strong market, as shown for sea urchins [5], where the global catch is related to the value of the Japanese Yen [26]. For other taxa, single driving markets are less obvious. For example, squid has 3 main importing nations (Japan, Italy, and Spain), while others have even more (Text S1). However, the vast majority of global sea cucumber catch is exported to Hong Kong (64% by volume between 1950–2004) or nearby Asian countries and the value of sea cucumbers has risen dramatically in recent decades [27]. To test whether spatial expansion has occurred, we used least-squares regression to compare the great-circle distance from Hong Kong with the year of peak sea cucumber catch for each country (Text S1) and found a significantly positive relationship (r = 0.62, p = 0.002, Fig. 3B). Given the generally poor stock status of sea cucumber fisheries [27], this may indicate a strong driving market where fisheries are sequentially exploited in relation to transportation distance. Such serial exploitation can have strong negative social and ecosystem consequences [5].

If markets and prices increase, new fisheries may develop more rapidly over time. To test this, we compared the time when invertebrate fisheries began or expanded with the time when they reached an initial peak in catch (see Materials and Methods and Text S1). We used an initial rather than overall peak in catch trajectories to treat new and old fisheries equally. Despite uncertainty within the results for individual taxa, we found a significant overall reduction in time to peak for newer fisheries (Fig. 3C). This corresponds to an approximate decrease of 6 years (3 years, 95% confidence interval) in time to peak when comparing the 1950s to the 1990s. We suggest this may be a result of better fishing technology combined with growing demand due to the increasing global human population, changes in diet preferences (e.g., the rise of sushi restaurants in Western countries), declines in finfish fisheries, as well as more and more smaller fisheries being exploited, facilitated by global transport. We note that a pattern of serial depletion and substitution of other species within each investigated taxonomic group could mask peaks in catch [21] causing us to underestimate the rapid development of fisheries. Where a peak in catch represents a peak in fishery productivity, it is unlikely that management and research can keep up with this rate of expansion to ensure sustainable development [5], [6].

The rapid expansion, and in some cases serial depletion, of global invertebrate fisheries may have strong ecosystem consequences due to the method of fishing and the functional roles invertebrates play in marine ecosystems. In 2000–2004, 53% of invertebrate catch by volume and 71% by taxa fished were caught by benthic trawling and dredging gear with these proportions remaining relatively stable since the 1950s (Fig. 4A, B). This is largely driven by benthic trawling for crustacean and cephalopod species and dredging for bivalves. In comparison, benthic trawling and dredging accounted for only 20% of global finfish catch (57% of taxa, 2000–2004 mean). Such gear has substantive negative impacts on most benthic habitats and communities by destroying three-dimensional structure, impacting spawning and nursery grounds, altering benthic community composition, and reducing future biomass, production, and species richness [28]–[30]. Moreover, together with mid-water trawls, benthic trawls and dredges can incur a substantial portion of incidental by-catch [31].

Beyond the predator-prey roles that most finfish play in marine ecosystems, invertebrates have more diverse functions and more often provide essential ecosystem services such as maintaining water quality [32], [33], regenerating nutrients [34], providing nursery and foraging habitat [35], and preventing algal overgrowth through grazing [36] (Fig. 4C). It has been shown that the massive historic removal of oysters, such as in Chesapeake Bay, was associated with increases in eutrophication and hypoxia [33]. We aggregated mean catch per year from 2000–2004 by functional groups to assess the potential removal impact (Fig. 4D, Table S4) (see Materials and Methods and Text S1). All invertebrate taxa form potentially important roles as prey for higher trophic levels while most cephalopods and crustaceans also perform predatory roles. Especially bivalve, but also krill and some sea cucumber fisheries, represent a substantial removal by volume (3 million t/year) of filter feeders. We estimate the removal of bivalves alone to equate to a loss of 11 million Olympic-sized swimming pools () in filtering capacity per day in 2000–2004 (Text S1). In addition, many bivalves form beds, banks, or reefs that structure the seafloor and provide important habitat [35]. Invertebrate fisheries further remove million t of detritivores and scavengers and million t of herbivores annually. Although recruitment and re-growth will compensate for some of these losses, the direct and indirect short- and long-term ecosystem effects of these removals are largely unknown.

Our results demonstrate that despite overall increasing catches, diversity, and country participation in global invertebrate fisheries, there is strong evidence that the underlying trends in many individual fisheries are less optimistic. Our new and more robust analysis of catch trends suggests that an increasing percentage of invertebrate fisheries may be over-exploited, collapsed, or closed. Some invertebrate fisheries, such as the rock lobster fishery in western Australia, have existed for a long time and are well-managed [9], yet even there factors beyond the management system, such as climate change, can present major challenges. However, the same is not true for many newer fisheries like those for sea urchins [5], [12] and sea cucumbers [27] for which new fisheries develop further away from their market(s) and at an increasingly rapid rate, likely driven by strong market forces. This means that global industries, markets, and free trade may enable the rapid expansion of new fisheries before scientists and managers can step in and make sensible decisions to secure the long-term, sustainable use of these resources [5]. On the one hand, we risk losing some of the last remaining viable and financially lucrative fisheries, bringing financial and social hardship to a large number of small communities dependent on these fisheries for income or food. At the same time, the population and ecosystem consequences of many invertebrate fisheries are largely unknown and unassessed [6], although there are notable exceptions [8]–[11]. Whereas there is increasing assessment, regulation, and rebuilding of finfish fisheries to achieve more sustainable harvesting [7], many invertebrate fisheries do not enjoy the same awareness or attention. Many of the described patterns are reminiscent of an earlier phase in finfish fisheries during which the rate of finding new fishing areas, new target species, and more efficient gears masked overall catch trends [14]. However, because of improved industrial fishing gear and global networks that allow rapid and accessible transport, we may be progressing through invertebrate fishery phases even faster.

In order to prevent further uncontrolled expansion and instead aim for a more sustainable development of invertebrate fisheries, we highlight the need for a global perspective in their management combined with local assessment, monitoring, and enforcement of fisheries regulations. A global perspective is essential to identify roving buyers, monitor foreign investments, and consider CITES (U.N. Convention on International Trade in Endangered Species) listing where appropriate [5]. Also, the displacement of fishing effort from highly- to less-regulated regions and illegal, unreported, and underreported (IUU) catches requires global regulations in invertebrates and finfish fisheries alike [7]. On a regional and local scale, stock assessments are infrequently or not performed for many invertebrate fisheries and often lack adequate knowledge on the species biology, population status, and response to exploitation [6]. Invertebrates are rarely monitored in research trawl surveys [7], and independent research surveys to assess population trends, by-catch, and habitat impacts of invertebrate fisheries are rarely done for many newer fisheries [5], [6], [12]. Based on such limited knowledge, the sustainable exploitation of invertebrates for fisheries may be difficult to achieve [13].

In contrast, after many decades of increasing exploitation and fish stock depletion, concerted management efforts in several regions around the world achieved the reverse: a reduction in overall exploitation rate and an increase in stock biomass in several finfish fisheries [7]. This was achieved by a combination of management tools adapted to local conditions as well as strong legislation and enforcement. Similar measures can be implemented in invertebrate fisheries to prevent current and future trajectories of depletion [10]. As an example, the addition of co-management and property rights in Chilean artisanal gastropod fisheries solved many overexploitation concerns, substantially increasing catch per unit effort and mean individual size [11]. Similarly, the New Zealand rock lobster fishery was on a path of declining abundance before a reduction in effort and season length substantially increased abundance, catch rates, and profitability [8]. Such successes provide a great opportunity to inform the management of other newer fisheries. It is our hope that increasing awareness of the ecological and economic importance of invertebrates may spur more rigorous scientific assessment, precautionary management, and sustainable exploitation to ensure long-term resilience of invertebrate populations, ocean ecosystems, and human well-being.