Fishery
A fishery encompasses the systematic harvesting or cultivation of fish, shellfish, and other aquatic organisms from marine, freshwater, or brackish environments, primarily for human consumption, economic gain, or sustenance.[1] These activities include both capture fisheries, which involve extracting wild populations, and aquaculture, the controlled farming of aquatic species, with the latter increasingly dominating production growth due to stagnant wild catches.[2] In 2022, global fisheries and aquaculture output totaled 223.2 million tonnes, representing a critical protein source that accounts for about 17 percent of animal protein consumed worldwide and supporting food security for billions, especially in regions with limited terrestrial protein alternatives.[2][3] Fisheries employ nearly 60 million people directly, predominantly in small-scale operations in developing nations, generating substantial economic value through trade exceeding $150 billion annually.[2] However, persistent overexploitation has led to the unsustainable fishing of 35.5 percent of assessed marine stocks, driven by excess harvesting capacity and inadequate management, resulting in biomass declines, biodiversity loss, and ecosystem disruptions that undermine long-term yields.[4] Despite advancements in stock assessments and regulatory efforts, the causal chain of unchecked extraction continues to challenge the sector's viability, with aquaculture's expansion offering partial mitigation but introducing issues like disease outbreaks and habitat alteration.[4]
Definitions and Terminology
Core Concepts and Distinctions
A fishery denotes the aggregate of fishing operations directed at a specific aquatic resource, such as a particular species or group of species, or the locale in which these operations are conducted.[5] This encompasses both the biological targets—typically fish, crustaceans, mollusks, or other aquatic organisms—and the human activities of capture or cultivation aimed at their harvest for food, economic value, or other uses.[6] Fisheries are distinguished from mere fishing by their systemic nature, involving ongoing exploitation patterns that necessitate management to balance harvest with resource renewal.[7] Fundamental distinctions arise between capture fisheries and aquaculture. Capture fisheries rely on harvesting wild aquatic populations from natural habitats like oceans, rivers, lakes, or coastal zones, where fish stocks reproduce independently without direct human intervention in their lifecycle.[8] In contrast, aquaculture involves the intentional breeding, rearing, and harvesting of aquatic organisms under controlled conditions, such as in ponds, raceways, cages, or recirculating systems, allowing for enhanced productivity through feed, genetics, and environmental manipulation.[9] These differ in risk profiles: capture fisheries face variability from environmental factors and stock fluctuations, while aquaculture contends with disease outbreaks, feed costs, and site-specific pollution but offers greater predictability in output.[10] Globally, capture fisheries provided 90.2 million tonnes of production in 2020, compared to 87.5 million tonnes from aquaculture, highlighting their complementary roles in supply.[6] Core to fisheries science are concepts like fish stock, maximum sustainable yield (MSY), and overfishing. A fish stock constitutes a discrete, self-sustaining population of a species or group, delineated by geographical, genetic, or behavioral traits, serving as the unit for assessment and management.[11] MSY is the largest average annual catch theoretically achievable from a stock over time without depleting its reproductive capacity, calculated via models incorporating growth, reproduction, and mortality rates under prevailing conditions.[12] Overfishing transpires when harvest rates surpass the MSY threshold, impairing the stock's ability to replenish and often reducing biomass below levels supporting long-term yields; for instance, U.S. data from 2020 identified 77 stocks as overfished, necessitating rebuilding plans.[13] [14] These terms underpin management strategies focused on controlling fishing effort to avert collapse, as evidenced by historical depletions like the North Atlantic cod fishery in the 1990s.[15]Historical Overview
Ancient and Pre-Industrial Fisheries
Archaeological evidence indicates that human fishing originated in the Paleolithic period, with the earliest confirmed deep-sea practices dating to approximately 42,000 years ago in East Timor, where over 38,000 fish bones from species inhabiting waters 70-120 meters deep were found alongside shell fishhooks in a cave site.[16] Earlier signs of marine resource use appear around 125,000 years ago along the Red Sea coast, evidenced by stone and obsidian tools with fish residues, while inland and coastal fishing by Homo sapiens is documented in South Africa circa 70,000 years before present through bone middens and tool marks.[17][18] These early methods relied on rudimentary tools like sharpened bones, stones, and woven plant fibers for hooks, gorges, and traps, targeting freshwater and nearshore species to supplement hunter-gatherer diets amid variable terrestrial resources. In ancient Egypt, fishing centered on the Nile River and its Delta, forming a dietary staple from at least 20,000 years ago as evidenced by fishing camp remains like those at Wadi Kubbaniya, where ground stone tools processed catfish and tilapia.[19] Predynastic settlements (circa 4000-3100 BCE) yield copper and bone hooks, lines, and sinkers, while tomb depictions and artifacts show techniques including cast nets slung between boats, hand-held scoop nets, spears, harpoons, and basket traps for species like mullet and perch.[20][21] Preservation methods such as salting, drying, and smoking—documented by Herodotus in the 5th century BCE—enabled trade and storage, with large-scale netting capturing schools during floods, though overexploitation risks emerged in densely populated areas.[21] Mesopotamian fisheries, sustained by the Tigris, Euphrates, and Persian Gulf marshes, employed skin-covered rafts and coracle boats for hook-and-line angling, cast nets, and weirs from the Sumerian period (circa 4500-1900 BCE), as illustrated in cuneiform texts and seals depicting carp and barbel catches stored in ponds for later consumption.[22][23] These practices supported urban economies in cities like Uruk, where fish provided protein amid arable limitations, with traps and spears targeting migratory species; continuity into later periods is seen in Assyrian reliefs showing net hauls, though salinization and irrigation diverted focus to agriculture.[24] Greek and Roman fisheries expanded offshore capabilities, with Aegean and Mediterranean operations using longlines, drift nets, purse seines, and amphora-preserved products like garum sauce from the Archaic period (circa 800-480 BCE), motivating Black Sea colonization for tuna and anchovy stocks as early as the 7th century BCE.[25][26] Roman innovations included stake nets in lagoons and oyster beds, contributing substantially to provincial economies—evidenced by legal texts regulating markets and wrecks yielding fishing gear—while elite consumption of fresh seafood via coastal villas underscored class disparities, with small-scale fishers dominating capture via oared vessels under 10 meters.[27][28] Pre-industrial fisheries, spanning medieval Europe to the 18th century, remained labor-intensive and localized, relying on sail- and oar-powered boats with handlines, fyke nets, and tidal weirs; in northern Europe, Norwegian stockfish drying—exported commercially from around 1100 CE—sustained Hanseatic trade, processing cod via air-drying on wooden racks for preservation without salt.[29] Asian methods paralleled this, with bamboo traps and stake nets in rivers like the Yangtze, though records emphasize subsistence over scale until European colonial expansion.[30] Economic integration grew via guilds regulating access, yet yields were constrained by weather and gear limits, averaging 1-5 tons per vessel annually in coastal fleets, fostering community dependence on seasonal migrations without mechanized hauling.[31][32]Industrial Era and Expansion
The industrial era in fisheries began in the mid-19th century, driven by the adoption of steam power, which supplanted traditional sail-dependent vessels and enabled operations over greater distances and in harsher conditions. The inaugural steam trawler, Enterprize, was constructed in 1854 at Granton, Scotland, by J. & M.W. Ruthven, representing an early mechanized shift in beam trawling practices.[33] This innovation allowed for more consistent hauls of bottom-dwelling species, initially targeting grounds inaccessible to smaller sailing smacks. By the 1880s, steam trawlers proliferated across British fishing ports, with Grimsby and Hull leading the transition; for instance, Hull fully replaced its sailing fleet with steam vessels by 1900, while Scarborough operated over 20 steam screw trawlers by 1883.[34][35] In parallel, trawling techniques spread to other regions, including the Pacific Coast of the United States, where two-boat paranzella nets were introduced in San Francisco Bay in 1876.[36] These advancements facilitated a surge in catch volumes, as steam engines permitted towing larger nets at higher speeds, often yielding several tons per trip compared to the limited hauls of sail-powered craft.[37] The expansion extended beyond Europe and North America, with steam technology influencing Scandinavian fisheries through imitation of British models, enhancing fleet capabilities for distant-water operations.[38] In New England, the industrial revolution integrated into groundfishing around 1900, coinciding with steam-powered trawlers that targeted species like cod and haddock more intensively.[37] This period saw global commercial production rise modestly from low baselines, though mechanization's full impact on yields manifested later; empirical records indicate inshore whitefish stocks in parts of the North Sea declined by the mid-1850s, predating widespread steam adoption but exacerbated by subsequent effort intensification.[39] Technological synergies, including improved net designs and early icing for preservation, supported market growth by reducing spoilage and enabling transport to urban centers amid 19th-century population booms.[40] However, the unchecked scaling of fleets—without contemporaneous stock assessments—initiated patterns of localized depletion, as evidenced by stable catch rates masking shifts to new grounds and underreporting of early overexploitation signals.[34][41] By the early 20th century, these dynamics set the stage for regulatory responses, though industrial momentum prioritized output over sustainability.[42]Post-1945 Globalization and Aquaculture Rise
Following the end of World War II, global capture fisheries experienced accelerated expansion driven by technological innovations and heightened demand for affordable protein amid postwar economic recovery. Vessels increasingly equipped with echo-sounders and radar improved fish detection, while the development of larger stern trawlers and factory ships enabled extended operations and onboard processing, boosting efficiency and range.[43] This period marked the rise of distant-water fishing fleets, particularly from Japan, which rapidly rebuilt its industry to secure domestic food supplies, and the Soviet Union, whose state-sponsored armadas targeted high-seas stocks in the North Atlantic and Pacific.[44] By the 1950s and 1960s, nations including South Korea, Taiwan, and Spain extended operations thousands of kilometers from home ports, contributing to a trebling of world marine and inland capture production from 18 million tonnes in 1950 to around 54 million tonnes by 1970, with average annual growth of 6 percent.[45] Globalization intensified through international trade and access agreements, but also precipitated widespread stock depletion as unregulated high-seas fishing exceeded biological productivity in key areas like the North Atlantic and Peru's anchovovy grounds.[46] In response, the 1982 United Nations Convention on the Law of the Sea facilitated coastal states' establishment of 200-nautical-mile Exclusive Economic Zones (EEZs) starting in the 1970s, enclosing approximately 99 percent of commercially viable fish stocks and curtailing foreign fleets' unrestricted access.[47] This shift prompted distant-water nations to negotiate bilateral fishing agreements or redirect efforts to remaining international waters and developing coastal states' zones, sustaining global output but often at the expense of local sustainability. Capture production peaked near 90 million tonnes in the late 1980s and has since plateaued, reflecting limits imposed by overexploitation and environmental factors rather than lack of effort.[45] Parallel to these dynamics, aquaculture production transitioned from marginal contributions—less than 1 million tonnes annually in the early 1950s—to the dominant growth vector in global seafood supply, motivated by stagnating wild catches and rising consumption in populous regions. Initial advancements occurred in Asia, with carp farming in China expanding under state policies from the 1960s, followed by diversification into shrimp, salmon, and tilapia via improved hatchery techniques and feed formulations.[48] By 2022, aquaculture yielded 130.9 million tonnes, surpassing capture fisheries for the first time and accounting for over 50 percent of global aquatic animal production, with China producing more than 60 percent of the total.[2] This expansion alleviated pressure on wild stocks but introduced challenges including disease outbreaks, reliance on wild-sourced feed, and localized pollution, underscoring the need for integrated management to align farmed output with ecological carrying capacities.[49]Classification of Fisheries
By Environment and Scale
Fisheries are classified by environment into marine, which occur in oceanic and coastal waters, and inland, which encompass freshwater bodies such as rivers, lakes, and reservoirs, as well as brackish estuarine zones.[50][51] Marine fisheries dominate global capture production, accounting for approximately 81 million tonnes out of 92.3 million tonnes total in 2022, driven by the vast productivity of pelagic and demersal stocks in open oceans.[2] Inland capture fisheries, by contrast, yielded 11.3 million tonnes in the same year, often supporting localized subsistence and contributing disproportionately to regional food security despite lower volumes, due to factors like accessibility and lower processing needs.[2] Overall aquatic production, including aquaculture, shows marine environments providing 115 million tonnes or 62 percent of the global total in recent assessments, reflecting the scale of ocean-based harvesting but also highlighting inland aquaculture's growth in controlled freshwater systems.[52] Independently, fisheries are categorized by scale into small-scale (also termed artisanal or subsistence) and large-scale (industrial or commercial) operations, distinguished primarily by vessel size, gear complexity, labor intensity, and market orientation.[53][50] Small-scale fisheries involve household-based or community-level efforts using rudimentary equipment like handlines, traps, or small boats under 12 meters, typically targeting nearshore or inland resources for local consumption or modest trade, and they comprise at least 40 percent of global catches, equating to 37.3 million tonnes annually while supporting the animal protein needs of 2.3 billion people.[54] These operations often exhibit higher efficiency in resource use and lower bycatch rates per unit caught compared to industrial methods, though they face vulnerabilities from climate variability and habitat degradation.[55] Large-scale fisheries, employing factory trawlers, purse seiners, and longline vessels exceeding 24 meters, focus on high-volume extraction for international markets, utilizing advanced sonar, refrigeration, and processing onboard to target migratory species like tuna and cod across exclusive economic zones and high seas.[53][56] This segment drives export revenues but contributes to overexploitation pressures, with production estimates filling the remainder of global catches after small-scale shares.[54] The interplay of environment and scale yields hybrid categories, such as small-scale marine fisheries in coastal artisanal fleets of Southeast Asia or industrial inland operations via large reservoir trawling in Africa, influencing management challenges like enforcement in vast marine areas versus localized inland governance.[50] Data from FAO assessments underscore that while marine industrial fisheries lead in tonnage, small-scale inland efforts provide critical nutritional resilience in developing regions, with combined scales informing sustainability metrics like maximum sustainable yield.[2][54]Capture Fisheries vs. Aquaculture
Capture fisheries refer to the harvesting of wild aquatic organisms from natural environments, including marine, brackish, and inland waters, without direct human intervention in their rearing.[57] This method relies on the inherent productivity of ecosystems, where fish stocks are exploited through methods like netting, line fishing, and trapping. In contrast, aquaculture involves the farming of aquatic species—such as fish, crustaceans, molluscs, and aquatic plants—under controlled conditions in ponds, raceways, cages, or tanks, often with supplemental feeding and management to enhance growth. This distinction underscores a fundamental difference: capture fisheries extract from self-sustaining populations, while aquaculture actively produces biomass akin to terrestrial agriculture. Global production trends highlight aquaculture's rapid expansion. In 2022, capture fisheries yielded 91.0 million tonnes of aquatic animals (live weight equivalent), stable after decades of stagnation since the late 1980s due to limited wild stock productivity.[57] Aquaculture, however, produced 94.4 million tonnes of aquatic animals that year, marking the first time it exceeded capture output and comprising 51% of total aquatic animal production.[2] By 2023, overall fisheries and aquaculture production reached nearly 228 million tonnes, with aquaculture driving growth amid flat or declining capture volumes in many regions.[58] Asia dominates both, but aquaculture's share has risen from 26% in 2000 to over 50% recently, fueled by demand and technological advances like recirculating systems. Sustainability challenges differ markedly. Capture fisheries face biophysical limits from stock dynamics, with 35.4% of assessed marine stocks classified as overfished in 2017—the latest comprehensive FAO estimate—leading to reduced yields and ecosystem disruptions like "fishing down the food web" toward less valuable species. Overexploitation, illegal fishing, and climate impacts exacerbate declines, though well-managed stocks (e.g., via quotas) can sustain yields. Aquaculture offers scalability independent of wild stocks but introduces risks such as disease outbreaks requiring antibiotics, nutrient pollution from feed and waste causing eutrophication, and genetic pollution from escaped farmed fish interbreeding with wild populations.[59] Feed dependency—often on wild-caught forage fish—creates a "feed conversion" inefficiency, where 2-5 kg of lower-trophic fish may yield 1 kg of carnivorous farmed species like salmon.[60] Peer-reviewed analyses indicate aquaculture's environmental footprint varies: intensive systems can have lower land use than livestock but higher local water quality impacts compared to sustainable capture methods.[61]| Aspect | Capture Fisheries | Aquaculture |
|---|---|---|
| Production (2022, mt aquatic animals) | 91.0[57] | 94.4[2] |
| Primary Constraint | Natural stock replenishment rates | Disease, feed availability, site pollution[59] |
| Environmental Risks | Bycatch, habitat damage (e.g., trawling), overfishing | Escapes, eutrophication, antibiotic resistance[60] |
| Growth Potential | Limited; stable since 1990s | High; projected to supply 60%+ by 2030[62] |
Harvesting Methods and Technologies
Gear Types and Practices
Fishing gear in capture fisheries encompasses a range of devices designed to harvest aquatic organisms, classified primarily by their mode of operation into active and passive categories. Active gears, such as trawls and seines, pursue and encircle fish, while passive gears, including gillnets and traps, rely on fish encountering the device. The Food and Agriculture Organization (FAO) recognizes 14 main gear categories, encompassing traps, lines, nets, and grappling devices, with selection depending on target species, habitat, and vessel capabilities.[65][66] Trawling employs large, cone-shaped nets towed by one or more vessels to sweep volumes of water or the seabed. Bottom trawls, fitted with ground gear like rollers or doors to maintain contact with the ocean floor, target demersal species such as cod and flatfish, often in depths up to 1,000 meters, though they can disturb benthic habitats. Midwater or pelagic trawls operate in the water column for schooling fish like herring, minimizing seabed impact. Globally, trawls account for a significant portion of marine catch, with beam trawls using rigid frames for precision in shallow waters.[67][68][69] Purse seining involves deploying a deep net around a detected school of fish, typically using sonar or spotter planes, then closing the bottom like a drawstring to trap the aggregation. This method dominates catches of small pelagics such as sardines, anchovies, and tunas, representing the highest volume gear in marine fisheries, with vessels often using power blocks to haul the net efficiently.[66][67] Gillnets and entangling nets drift or are set stationary to ensnare fish by gilling, wedging, or tangling their bodies or fins, effective for species like salmon and groundfish in both freshwater and marine environments. These passive nets vary in mesh size for selectivity but pose risks of bycatch and ghost fishing from lost gear.[70][67] Longlining deploys horizontal lines, either surface or bottom-set, baited with thousands of hooks spaced at intervals, targeting high-value species like tuna, swordfish, and halibut. Bottom longlines sink to the seabed via weights, while pelagic versions float near the surface; practices include soaking periods of hours to days, with buoys for retrieval.[68][67] Traps and pots, rigid enclosures baited to attract crustaceans or finfish, allow entry but hinder escape, commonly used for lobsters, crabs, and octopus in coastal waters. Deployment involves dropping weighted pots to the bottom, marked by surface buoys, with retrieval after set times to minimize predation losses.[65][67] Dredging scrapes the seabed with heavy frames or rakes to collect bivalves like scallops and oysters, typically in shallow coastal areas by smaller vessels, though deeper operations exist. This method physically dislodges organisms, often requiring sorting post-haul.[67][69] Hook-and-line methods, including handlines, rods, and poles, offer high selectivity by targeting individual fish with baited hooks, practiced from small boats or shores for species like tuna via pole-and-line techniques that avoid bycatch through live bait dispersion.[71][72]Vessels, Processing, and Innovations
Commercial fishing vessels encompass a diverse array of designs optimized for gear deployment, endurance at sea, and catch handling, ranging from small artisanal boats to large industrial factory ships. The global fishing fleet numbered approximately 4.6 million registered vessels in 2020, of which 3.0 million were powered, enabling operations from coastal waters to distant oceanic grounds.[73] Small vessels under 12 meters in length constitute over 85 percent of the total by count, primarily supporting nearshore and inland fisheries, whereas vessels exceeding 24 meters, though only about 2 percent of the fleet, generate roughly 35 percent of marine capture production due to their capacity for extended voyages and larger gear.[73] Common types include trawlers, which deploy otter boards or beam setups to drag nets along the seabed or midwater; purse seiners that encircle schools of pelagic species like tuna with vertical nets; and longliners that set arrays of baited hooks over vast distances.[74] [75] Fish processing begins immediately after capture to minimize spoilage from enzymatic and bacterial activity, with methods varying by vessel scale and target species. On smaller boats, primary handling involves icing or slurry chilling to maintain temperatures near 0°C, often at ratios of 1:1 fish to ice by weight, preserving freshness for shore delivery.[76] Larger vessels employ onboard facilities for gutting, filleting, heading, and skinning, followed by blast freezing to -18°C or below, or canning and smoking in factory trawlers and processor ships that can handle thousands of tons annually without port returns.[77] [78] Automated lines on modern processors integrate sorting by size and species via optical sensors, reducing labor while ensuring hygiene standards that extend shelf life to months.[79] Shore-based plants receive unprocessed catch from day boats, applying similar techniques but with greater capacity for value-added products like minced fillets or dried products.[80] Innovations in vessels and processing emphasize efficiency, safety, and reduced environmental impact, driven by regulatory pressures and technological advances. Electronic monitoring systems, including GPS, sonar, and acoustic sensors, enable precise navigation and fish detection, with echo sounders mapping school densities to optimize gear deployment and minimize fuel use, which accounts for up to 60 percent of operating costs in some fleets.[81] [82] Automated processing technologies, such as robotic filleting and AI-driven species identification via cameras like CSIRO's WANDA system, enhance yield accuracy to 95 percent while curbing bycatch through real-time selectivity adjustments.[83] Vessel designs incorporate hybrid electric propulsion and dynamic positioning thrusters, cutting emissions by 20-30 percent compared to diesel-only systems, alongside data analytics platforms that predict stock movements from satellite and VMS data for sustainable harvesting.[84] These developments, while increasing initial costs, have demonstrably lowered operational waste and improved compliance with quotas in monitored fisheries.[85]Biological and Ecological Principles
Fish Stock Dynamics and Productivity
Fish stock dynamics refer to the processes governing the size, structure, and abundance of fish populations over time, primarily driven by recruitment, growth, somatic maintenance, natural mortality, and fishing mortality. Recruitment represents the influx of new individuals into the exploitable population, often modeled as a function of spawning stock biomass, with density-dependent effects limiting growth at high densities. Growth rates vary by species, influenced by environmental factors such as temperature and food availability, while natural mortality encompasses predation, disease, and senescence, typically estimated via age-structured data. Fishing mortality, the human-induced component, interacts with these processes, potentially shifting equilibrium biomass levels.[86][87] Stock assessments employ analytical models to quantify these dynamics, categorizing them into data-limited (e.g., surplus production models like Schaefer, which aggregate age classes and estimate intrinsic growth rate r and carrying capacity K) and data-rich approaches (e.g., age-structured models like VPA or integrated assessments incorporating catch-at-age, survey indices, and biological parameters). These models simulate population trajectories under varying exploitation rates, revealing that excessive fishing often reduces spawning biomass below levels producing maximum recruitment, leading to depensation where per-capita productivity declines nonlinearly at low abundances. Empirical validation from species like Atlantic cod demonstrates how ignoring spatial heterogeneity or environmental covariates can bias projections, underscoring the need for spatially explicit metapopulation frameworks.[88][89][90] Productivity in fish stocks is quantified as the potential biomass production available for harvest, with the maximum sustainable yield (MSY) defined as the largest long-term average catch extractable without depleting the population, occurring theoretically at half the unexploited biomass for logistic growth models (MSY = rK/4). Actual productivity varies by life history traits—r-selected species like anchovies exhibit high r but low K, enabling rapid recovery but vulnerability to serial overfishing, whereas K-selected species like tuna sustain lower yields but larger biomasses. Global assessments indicate that productivity has been eroded by overexploitation, with approximately 35.5 percent of monitored marine stocks overfished or depleted as of 2024, though fishing pressure has declined 30 percent and biomass risen 15 percent in assessed stocks since prior baselines, reflecting partial recovery in managed systems.[91][4][4] Sustained productivity requires maintaining stocks above MSY biomass levels (B_MSY), as harvesting below this threshold accelerates depletion due to reduced recruitment elasticity, a principle evident in collapsed stocks like Peruvian anchoveta in the 1970s, where El Niño exacerbated overfished states. Management targets often aim for F_MSY (fishing mortality at MSY), but uncertainty in parameters like natural mortality (M, typically 0.1-0.8 year⁻¹) necessitates precautionary buffers. Recent FAO data from 2,570 assessed stocks show 64.5 percent fished within sustainable limits, yet regional disparities persist, with overfishing prevalent in underexplored areas due to illegal, unreported, and unregulated (IUU) catch inflating apparent productivity short-term while undermining long-term yields.[92][4]Ecosystem Roles and Limits
Fish species occupy diverse trophic positions within aquatic ecosystems, functioning as primary consumers, mid-level predators, or apex predators that regulate prey populations and maintain community structure through top-down control. Forage fish, such as anchovies and sardines, form the base of many marine food webs, supporting higher trophic levels including larger predatory fish, seabirds, and marine mammals, with global models indicating they transfer substantial biomass to predators and contribute to ecosystem productivity. In freshwater systems, fish diversity correlates positively with biomass production, enhancing overall ecosystem function via complementary resource use and reduced competitive exclusion.[93] Fish also play critical roles in biogeochemical cycling, assimilating and redistributing nutrients like nitrogen, phosphorus, and carbon across habitats. Through excretion, fecal pellets, and post-mortem sinking of carcasses, fish facilitate vertical nutrient transport in marine environments, fueling primary production and contributing to the biological carbon pump; mesopelagic fish alone may sequester carbon equivalent to 0.1–1.9 Pg C globally via these mechanisms. Industrial fisheries disrupt this cycling by extracting biomass—removing approximately 431 million tonnes of carbon and 110 million tonnes of nitrogen from 1960 to 2018—potentially reducing sequestration efficiency and altering elemental budgets in exploited ecosystems.[94][95][96] Ecological limits to fisheries arise from finite ecosystem productivity, constrained by primary production, nutrient availability, and trophic efficiencies, beyond which extraction leads to stock declines and reduced resilience. Overfishing often results in "fishing down the food web," where sequential depletion of high-trophic-level species shifts exploitation to lower levels, decreasing mean trophic levels in catches by 0.1–0.5 units per decade in many regions since the mid-20th century. This trophic downgrading diminishes ecosystem stability, as evidenced in large marine ecosystems where predator removal cascades to alter prey dynamics and biodiversity.[97][98] Such shifts exacerbate vulnerability to perturbations like climate variability, with overexploited systems showing impaired recovery and heightened extinction risks for component species. Ecosystem-based management recognizes these limits by incorporating habitat impacts, bycatch, and multi-species interactions, rather than single-stock maximum sustainable yields, to preserve functional diversity and long-term productivity. Empirical data from U.S. large marine ecosystems indicate widespread overfishing when viewed holistically, underscoring the need to cap harvests below levels that erode foundational ecological processes.[99][100]Economic Role
Production Statistics and Trade
Global production of aquatic animals, seaweed, and other fishery products reached 223.2 million tonnes in 2022, marking a record high and a 4.4 percent increase from 2020.[2] Aquaculture contributed 130.9 million tonnes (58.7 percent of the total), surpassing capture fisheries at 92.3 million tonnes (41.3 percent) for the first time in history when considering aquatic animals specifically, where farmed production hit 94.4 million tonnes against 79.7 million tonnes from wild capture.[2] [101] This shift reflects stagnant wild capture yields over decades, constrained by biological limits and overexploitation in many stocks, contrasted with aquaculture's expansion driven by technological advances and demand in Asia.[2] China dominated production with a 36 percent global share in 2022, followed by India (8 percent), Indonesia (7 percent), Viet Nam (5 percent), and Peru (3 percent); the top ten producers accounted for over half of output.[2] These nations leverage diverse environments, from China's intensive pond systems for carp and tilapia to Indonesia's marine capture and seaweed farming, though data reliability varies due to underreporting in some developing economies.[2] International trade in fishery products was valued at approximately USD 195 billion in 2022, equivalent to about 1 percent of global merchandise trade but supporting food security for 3.3 billion people through nutrient-rich imports.[2] Traded volume hovered around 60 million tonnes live weight equivalent, with processed forms like frozen fillets commanding higher values; top exporters included China (USD 22.4 billion), Norway, Viet Nam, Ecuador, and Chile, while major importers were the United States, China, Japan, Spain, and France.[2] [102] Trade flows often counterbalance domestic shortfalls, with developing countries exporting low-value species to fund imports of high-value ones, though 2023 saw a 3.9 percent value decline amid inflation and supply disruptions.[103]| Major Exporters (2022 Value, USD Billion) | Major Importers (2022 Value, USD Billion) |
|---|---|
| China: 22.4[102] | United States: ~20 (est.)[2] |
| Norway: ~15 (salmon focus)[2] | China: ~15[2] |
| Viet Nam: ~10 (shrimp, pangasius)[2] | Japan: ~10[2] |