Capture fisheries

In short

Capture fisheries is the harvesting of fish and shellfish from wild stocks in seas, estuaries, rivers, reservoirs and lakes — as distinct from aquaculture, which rears stocked animals. It covers the craft, gear and methods of fishing, the biology of exploited stocks, stock assessment and the law that limits effort so that yield stays sustainable. India lands roughly 3.5–4 million tonnes of marine fish a year and has the world's second-largest total fish production (the CMFRI annual marine landings estimate and the DoF *Handbook on Fisheries Statistics* carry the current figures, which shift each year). The topic is examined in B.F.Sc papers on fishing gear and craft technology, fishing methods, and fish population dynamics, and in ICAR-JRF/SRF, ASRB-NET, and state fisheries officer recruitment tests. Employers who test it include ICAR institutes (CMFRI, CIFRI, CIFT, FSI), state fisheries departments, MPEDA, seafood exporters and fishing-vessel operators.

Explained

Scope, sectors and classification

• Capture (extractive) fishery - harvest of unowned wild stock; culture fishery - harvest of stocked, fed and managed stock. Capture is effort-limited, culture is input-limited.
• Marine capture fisheries in India: ~8,100 km coastline, 0.53 million km² continental shelf, and an Exclusive Economic Zone of about 2.02 million km² (including the island territories).
• Zonation of the Indian EEZ: territorial waters up to 12 nautical miles are under state/UT jurisdiction; 12–200 nm is under Union jurisdiction. Most artisanal and mechanised fishing happens within 12 nm; deep-sea fishing beyond it is poorly developed.
• Marine sub-sectors by craft and power:
  • Artisanal/traditional: non-motorised catamarans, dugout canoes, plank-built boats, *masula* boats; gear operated manually or from shore.
  • Motorised: traditional craft fitted with outboard motors (9.9–25 hp); operate ring seines, gill nets, hooks and line.
  • Mechanised: inboard-engine trawlers, purse seiners, gill-netters, liners; 10–25 m overall length.
  • Deep-sea/industrial: larger longliners, squid jiggers, tuna vessels; limited Indian fleet.
• Inland capture fisheries: rivers (Ganga, Brahmaputra, Indus and peninsular systems), estuaries, backwaters, lagoons (Chilika, Pulicat, Vembanad), floodplain wetlands (*beels*, *mauns*, *chaurs*), reservoirs and upland cold-water streams. CIFRI is the lead institute; reservoirs are increasingly "culture-based capture fisheries" (stocked, then captured) — a hybrid.
• Resource groups in Indian marine landings: pelagics (oil sardine, Indian mackerel, ribbonfish, anchovies, carangids), demersals (threadfin breams, sciaenids, perches, lizardfish, elasmobranchs), crustaceans (penaeid and non-penaeid shrimp, crabs, lobsters), molluscs (cephalopods, bivalves, gastropods). Oil sardine and mackerel together dominate the west coast and are strongly climate-driven.

Fishing craft and their features

• Non-powered craft: built of wood, bamboo or areca; catamaran (lashed logs, Coromandel coast), dugout canoe and plank-built canoe (Kerala, Karnataka), masula boat (sewn-plank surf boat, Andhra), teppa and shoe-dhoni. Hull materials now include FRP (fibre-reinforced plastic) for durability and lower maintenance.
• Mechanised craft by purpose: trawler (stern or side trawling, towing winch, otter boards), purse seiner (large deck space, power block, skiff), gill-netter (net hauler/drum), liner (line hauler), multi-day/multipurpose vessels with ice holds.
• Key naval-architecture terms examined: LOA (length overall), LBP (length between perpendiculars), beam, depth, draught, freeboard, sheer, camber, block coefficient (Cb), displacement, gross and net tonnage, metacentric height (GM) for stability, and reserve buoyancy.
• Positive GM gives a stable vessel; too large a GM gives a stiff, uncomfortable roll, too small gives a tender vessel at risk of capsize. Stability losses on fishing vessels usually come from free-surface effect in part-full tanks and fish holds, water on deck, and heavy gear high up.
• Deck machinery and electronics: trawl winch, net drum, power block, line hauler, echo sounder, GPS/chart plotter, VHF, fish finder, and NavIC/DAT (distress alert transmitter) devices subsidised in India for safety at sea.

Fishing gear: classification and operation

• FAO/ISSCFG classification groups gear into surrounding nets, seine nets, trawls, dredges, lift nets, falling gear, gill nets and entangling nets, traps, hooks and lines, grappling and wounding gear, harvesting machines, and miscellaneous.
• Trawl net (towed/dragged): a bag-shaped net towed over the bottom (bottom trawl) or in midwater (pelagic trawl). Parts: otter boards (doors), warps, bridles, headrope with floats, footrope with chain/bobbins, wings, square, belly, and codend. Otter trawls spread by doors; beam trawls by a rigid beam; pair trawls by two vessels; shrimp trawls are low-headline, often with twin or multi-rig configuration. India's shrimp trawl fishery is the largest source of bycatch and discards.
• Purse seine (surrounding): a long wall of netting encircles a pelagic shoal; the purse line through purse rings closes the bottom; catch is dried up and brailed or pumped. High catch per unit effort on sardine, mackerel, tuna. Ring seine, a smaller motorised version, transformed Kerala's small-pelagic fishery from the 1980s.
• Seine nets: shore/beach seine (*rampani*, *karamadi*, *yendi*) hauled from the beach; boat seine (*thangu valai*, *kollivala*) hauled from a craft. Both are non-selective and tend to catch juveniles.
• Gill net (passive, entangling): fish are gilled, wedged or entangled in a wall of netting. Set/bottom-set, drift, encircling and trammel (three-wall) types. Highly size-selective — selectivity follows a bell-shaped curve centred on a girth matching the mesh; economical in fuel, hence attractive at high diesel prices.
• Hooks and lines: handline, pole and line, troll line, longline (horizontal mainline with branch lines; bottom longline for perches and sharks, pelagic/drift longline for tuna and billfish), vertical line, jigging (squid). Low bycatch of non-target fish but a known source of turtle, shark and seabird capture if unmitigated.
• Traps and pots: bamboo and wire traps, lobster pots, crab traps, fixed engines such as stake nets (*khada*, bag nets) and Chinese dip nets of Kochi; filter nets (*behundi* jal) in estuaries.
• Lift nets and falling gear: cast net (*veesu valai*), dip net, boat-operated lift net, blanket net. Often used with light attraction and with FADs (fish aggregating devices) — anchored floating structures that concentrate pelagics.
• Gear materials: nylon (PA) multifilament and monofilament, polyethylene (PE), polypropylene (PP), polyester (PES); specified by R-tex/denier, twine diameter, number of meshes, hanging coefficient and mesh size. Mesh size is measured as stretched mesh (full mesh) or bar length; stretched mesh ≈ 2 × bar length.
• Destructive and prohibited methods: dynamiting, poisoning, pair trawling and bull trawling (banned by several states), light fishing in the EEZ (banned by the Union through circulars; state rules vary), use of nets below prescribed mesh size, LED light fishing and Shore-based "mini-trawl" operations. Students should note that state-level bans vary and are amended often.

Fish population dynamics and stock assessment

• A stock's biomass changes through recruitment + growth − natural mortality − fishing mortality. Total mortality Z = M + F; exploitation rate E = F/Z.
• Growth: von Bertalanffy model gives length at age; L∞ asymptotic length and K growth coefficient are estimated from length-frequency data (ELEFAN, FiSAT II software from FAO/ICLARM, widely used at CMFRI).
• Length–weight relationship W = aLᵇ; b ≈ 3 means isometric growth, b ≠ 3 allometric. Condition factor K = 100W/L³.
• Surplus production (holistic) models: Schaefer (logistic) and Fox (exponential) fit catch and effort to estimate MSY and the effort at MSY (*f*MSY). Data needed: a time series of catch and standardised effort.
• Analytical models: Beverton–Holt yield-per-recruit gives Y/R as a function of F and age at first capture (tc); used to recommend mesh size and minimum legal size. Thompson and Bell predicts yield and value at different F levels.
• Reference points: MSY (biological), MEY — maximum economic yield, at lower effort than MSY — and OSY (optimum sustainable yield, balancing biological, economic and social aims). Precautionary approach uses limit and target reference points (e.g. F0.1, B40%).
• CPUE (catch per unit effort) is the standard index of abundance — catch per hour trawling, per boat-day, per 100 hooks. It can be misleading (hyperstability) when fishers find shoals efficiently even as stock falls.
• Recruitment overfishing (spawning stock too small to replace itself) vs growth overfishing (fish caught too small, so yield per recruit is lost) vs economic overfishing (effort beyond MEY). Ecosystem overfishing shows as fishing down the food web (declining mean trophic level of landings).
• Stock assessment inputs in India: CMFRI's multi-stage random sampling of landing centres for marine catch estimation; FSI's resource surveys and potential-yield estimates; CIFRI for inland. The national marine fishery potential yield has been assessed at roughly 5 million tonnes in the EEZ (the last expert-committee estimate; treat as an estimate under revision).
• Bycatch and discards: non-target catch retained (bycatch) or thrown back (discards). Mitigation: TEDs (turtle excluder devices), BRDs (bycatch reduction devices), square-mesh windows, juvenile fish excluder-cum-shrimp sorting device (JFE-SSD) developed by ICAR-CIFT, circle hooks and tori lines on longliners.

Indian law, management and institutions

• Marine Fishing Regulation Acts (MFRAs): each maritime state/UT has its own, under the 1979 model Bill — these regulate zones reserved for traditional craft, mesh size, closed seasons, licensing and registration. Kerala, Tamil Nadu, Maharashtra, Gujarat, Andhra Pradesh, Odisha, West Bengal, Karnataka, Goa and the UTs each have separate rules, so specific limits differ by state.
• Uniform monsoon fishing ban on mechanised vessels: 61 days — roughly 1 June to 31 July on the west coast and 15 April to 14 June on the east coast (dates are notified annually and have been adjusted; verify the current year's notification).
• Maritime Zones of India (Regulation of Fishing by Foreign Vessels) Act, 1981 controls foreign fishing vessels; Letter of Permit schemes for chartered deep-sea vessels have been contentious and largely discontinued.
• Coast Guard Act, 1978 and Merchant Shipping Act, 1958 cover safety and enforcement at sea; fishing vessel registration under the Merchant Shipping Act and the online ReALCraft system of the DoF.
• Wildlife (Protection) Act, 1972 schedules protect sea turtles, dugong, whale shark, sea horses, giant clams, sawfishes and some corals — capture or trade is an offence; the Act was amended in 2022 and schedules renumbered.
• Environment Protection Act, 1986, CRZ Notification, 2019 and marine protected areas (Gulf of Mannar, Gulf of Kachchh, Sundarbans, Malvan) constrain fishing near sensitive habitats.
• Draft/enacted central frameworks: the Union has pursued a National Policy on Marine Fisheries, 2017, the National Fisheries Policy process, and an Indian Marine Fisheries Bill for the EEZ beyond territorial waters — legislative status has shifted repeatedly, so state it as "in process" rather than as settled law.
• International instruments India engages with: UNCLOS 1982 (EEZ regime), FAO Code of Conduct for Responsible Fisheries, 1995 (voluntary), FAO Port State Measures Agreement against IUU fishing, IOTC (Indian Ocean Tuna Commission) for tuna, CITES listings for sharks and rays, and the WTO Agreement on Fisheries Subsidies (adopted 2022, in force since September 2025).
• Measures used in management: input controls (licence limits, vessel and engine caps, closed seasons, closed areas, gear and mesh regulation) and output controls (minimum legal size (MLS) — states such as Kerala and Tamil Nadu have notified MLS for a set of species; quotas are rare in India). Co-management through fisher societies and *kadakkodi*-type traditional councils is promoted.
• Allied central interventions: PMMSY supports deep-sea vessel upgradation and resource surveys; artificial reefs and sea ranching are used for habitat and stock enhancement. (Scheme detail belongs to the schemes note.)

Key points

• Capture fishery - harvest of wild, unstocked stock; limited by fishing effort rather than feed input.
• Indian EEZ - about 2.02 million km²; states control 0–12 nm, the Union 12–200 nm.
• Trawl - active towed bag net, high catch, low selectivity, highest bycatch.
• Purse seine / ring seine - encircles pelagic shoals, closed by a purse line through rings.
• Gill net - passive, mesh-selective; selectivity curve is bell-shaped around a girth-matched size.
• Longline - mainline with baited branch lines for tuna, billfish, perches; selective but risks turtle and shark capture.
• Stretched mesh - full mesh size ≈ 2 × bar length; the legal quantity in most state rules.
• Z = M + F - total mortality is natural plus fishing mortality; E = F/Z is exploitation rate.
• von Bertalanffy - Lt = L∞[1 − e^{−K(t − t₀)}]; estimated by ELEFAN from length frequencies.
• Schaefer model - CPUE falls linearly with effort; MSY = rK/4 at fMSY = r/2q.
• MSY vs MEY vs OSY - biological maximum, profit maximum (lower effort), and socially optimum yield.
• Growth overfishing - catching fish too young, losing yield per recruit; fixed by larger mesh and MLS.
• Recruitment overfishing - spawning biomass cut below replacement level; the more dangerous failure.
• CPUE - abundance index; distorted by hyperstability, technology creep and shoal-finding skill.
• TED and BRD - excluder devices that let turtles and juveniles escape a shrimp trawl's codend.
• 61-day monsoon ban - closed season for mechanised vessels, west coast ~June–July, east coast ~April–June; notified yearly.
• MFRA - state-level Marine Fishing Regulation Act: zones, mesh, licence, closed season; differs by state.
• CMFRI, CIFRI, CIFT, FSI, DoF - marine assessment, inland fisheries, fishing technology, resource survey and policy respectively.

Formulas and examples

Example 1 — Von Bertalanffy growth of Indian mackerel. For *Rastrelliger kanagurta*, take L∞ = 25.5 cm, K = 1.2 year⁻¹, t₀ = 0. Length at 0.5 year: L = 25.5 [1 − e^{−1.2 × 0.5}] = 25.5 [1 − e^−0.6] = 25.5 (1 − 0.5488) = 25.5 × 0.4512 ≈ 11.5 cm. Length at 1 year: 25.5 [1 − e^−1.2] = 25.5 (1 − 0.3012) = 25.5 × 0.6988 ≈ 17.8 cm. Length at 2 years: 25.5 [1 − e^−2.4] = 25.5 (1 − 0.0907) = 25.5 × 0.9093 ≈ 23.2 cm. Growth is fast in year 1 and flattens afterwards — the classic reason small pelagics are harvested at age 0+ to 1.

Example 2 — Mortality, survival and exploitation rate. A sciaenid stock has Z = 2.1 year⁻¹ and M = 0.9 year⁻¹.

• F = Z − M = 2.1 − 0.9 = 1.2 year⁻¹.
• E = F/Z = 1.2/2.1 = 0.571.
• Survival S = e^−2.1 = 0.1225, so annual mortality A = 1 − 0.1225 = 87.7% of the stock dies in a year.
• Interpretation: E = 0.57 exceeds the rough optimum E ≈ 0.5, so the stock is over-exploited — fishing takes more than half of all deaths.

Example 3 — Schaefer model, MSY and MEY. Ten years of trawl data give the regression CPUE = 320 − 0.004 f, where CPUE is kg per boat-day and f is boat-days per year.

• a = 320, b = 0.004.
• fMSY = a/2b = 320 / 0.008 = 40,000 boat-days.
• MSY = a²/4b = 320² / (4 × 0.004) = 102,400 / 0.016 = 6,400,000 kg = 6,400 t per year.
• At current effort f = 55,000 boat-days: Y = 320 × 55,000 − 0.004 × 55,000² = 17,600,000 − 12,100,000 = 5,500,000 kg = 5,500 t — more effort, 900 t less yield. Classic biological overfishing.
• Economics: if price = ₹90/kg and cost = ₹9,000 per boat-day, revenue at MSY = 6,400,000 × 90 = ₹57.6 crore, cost = 40,000 × 9,000 = ₹36.0 crore, profit = ₹21.6 crore. At f = 55,000: revenue = ₹49.5 crore, cost = ₹49.5 crore, profit = ₹0 — this is the bionomic (open-access) equilibrium where rent is fully dissipated.
• MEY effort: profit = p(af − bf²) − cf, maximised at f = (pa − c)/(2pb) = (90 × 320 − 9,000)/(2 × 90 × 0.004) = (28,800 − 9,000)/0.72 = 27,500 boat-days, below fMSY — so MEY always occurs at lower effort than MSY.

Example 4 — Gill net mesh size from selection factor. A gill net for Indian mackerel has a selection factor SF = 3.5.

• To target fish of L50 = 20 cm: mesh = 20/3.5 = 5.7 cm stretched (bar length ≈ 2.9 cm).
• If a fisher uses 4.0 cm mesh instead: L50 = 3.5 × 4.0 = 14 cm — below the length at first maturity for mackerel (about 19–20 cm on the west coast), so the net harvests immature fish. This is the quantitative basis for minimum mesh-size rules.

Example 5 — Swept-area biomass estimate. A survey trawler tows at 3.0 knots for 1 hour with a 30 m headrope, X = 0.5, and lands 45 kg.

• 3.0 knots = 3.0 × 1.852 = 5.556 km/h, so D = 5.556 km.
• Swept area a = 5.556 × 0.030 × 0.5 = 0.0833 km².
• Density = 45 / 0.0833 = 540 kg/km².
• If the survey area A = 20,000 km² and catchability q = 0.5, biomass B = (540 × 20,000)/0.5 = 21,600,000 kg = 21,600 t. A rough MSY proxy of 0.5 M·B with M = 0.8 gives 0.5 × 0.8 × 21,600 ≈ 8,640 t per year.

Where it is used

• ICAR research institutes: CMFRI (marine landings estimation, stock assessment, MLS advisories), CIFRI (inland and reservoir fisheries), CIFT (gear design, TED/BRD, energy-efficient trawls), FSI (resource surveys aboard vessels such as *Matsya Nireekshani*/*Matsya Drushti* class).
• State fisheries departments: fisheries officer, inspector and extension roles — licensing, MFRA enforcement, monsoon-ban patrols, landing-centre data collection, ReALCraft registration.
• Seafood export industry: MPEDA registration, traceability, and catch certification for the EU market; buyers increasingly demand MSC certification or FIP participation, which rests on stock assessment and gear impact data.
• Fishing vessel operation and gear supply: skipper/mate roles (with DGS/state certificates of competency), net-making and gear-supply firms (Garware Technical Fibres and similar), FRP boatyards.
• Consultancy and NGOs: co-management projects, turtle-safe fishing programmes along Odisha's Gahirmatha coast, artificial-reef and sea-ranching projects under state and PMMSY funding.
• Academic and competitive routes: ICAR-JRF/SRF, ASRB-NET in Fish Biology/Fisheries Resource Management, UPSC/state civil-service optional papers, and MSc/PhD work in population dynamics and gear technology.

Interview questions

• Q: How does capture fishery differ from culture fishery? A: Capture harvests wild, unstocked populations and is managed by limiting effort, gear and season; culture rears stocked animals with feed and water management and is managed by inputs.
• Q: Why is bottom trawling the most criticised gear in India? A: It disturbs the seabed, has low size and species selectivity, lands large volumes of juveniles and low-value bycatch, and consumes the most fuel per kg of catch.
• Q: Why is a gill net more selective than a trawl? A: A gill net catches only fish whose maximum girth matches the mesh — smaller fish pass through and larger ones bounce off — whereas a trawl's codend retains everything above the mesh size.
• Q: What is the purpose of the 61-day monsoon fishing ban? A: It closes mechanised fishing during the main spawning and recruitment period of key species and the rough monsoon sea, reducing fishing mortality on spawners and improving safety; it is notified annually by the states.
• Q: What is the difference between growth overfishing and recruitment overfishing? A: Growth overfishing catches fish before they reach a size that maximises yield per recruit; recruitment overfishing cuts the spawning stock so low that it cannot replace itself — the second is far harder to reverse.
• Q: Why is MEY at a lower effort than MSY? A: Each additional unit of effort beyond MEY adds cost faster than it adds revenue, because CPUE falls as effort rises; profit therefore peaks before yield does.
• Q: Why can CPUE be a misleading abundance index? A: Technology improvements, GPS-aided shoal finding and schooling behaviour can keep CPUE high while the stock declines — the hyperstability problem — so effort must be standardised and surveys used alongside.
• Q: What is a TED and why is it mandatory in parts of India? A: A turtle excluder device is a grid in the trawl that deflects turtles out through an escape opening; Odisha and some other states require it in the shrimp fishery to protect olive ridley turtles nesting at Gahirmatha and Rushikulya.
• Q: What governs fishing in the 12–200 nm zone? A: The Union, since states' jurisdiction ends at 12 nm; foreign vessels are covered by the Maritime Zones of India (Regulation of Fishing by Foreign Vessels) Act, 1981, and a central framework for Indian vessels in the EEZ has been under legislative process.
• Q: How is mesh size specified and measured? A: Usually as stretched (full) mesh — the distance between opposite knots when the mesh is pulled taut, roughly twice the bar length — measured with a gauge under standard tension.
• Q: What does an exploitation rate of 0.7 tell you? A: That fishing accounts for 70% of total mortality, well above the rough optimum of about 0.5, indicating heavy over-exploitation and a case for cutting effort or raising the age at first capture.
• Q: Which two species dominate west-coast pelagic landings and why are they volatile? A: Indian oil sardine and Indian mackerel; both are short-lived, fast-growing and recruitment-driven, so landings swing sharply with monsoon upwelling and sea-surface temperature.

Common mistakes

• Treating culture-based fisheries in reservoirs as pure capture fisheries — they are stocked, so recruitment is managed, not natural.
• Confusing stretched mesh with bar length, which halves or doubles every mesh-size answer and every selectivity calculation.
• Writing Z = M − F or F = Z × M; total mortality is the sum Z = M + F, and E = F/Z.
• Treating MSY as a safe target: it is a knife-edge point estimated from noisy data, ignores economics and multispecies interactions, and MEY/precautionary reference points sit below it.
• Quoting a single national mesh size, closed season or minimum legal size — these are state-specific under each MFRA and are amended often; name the state or say the rule varies.
• Mixing units in swept-area and CPUE work — knots with km/h, metres with kilometres of headrope, kg with tonnes.
• Calling all non-target catch "discards": retained non-target catch is bycatch, only what is thrown back is a discard.
• Saying purse seines are selective because they target one species — they are species-selective but catch all sizes in the shoal, including juveniles.

Related topics

Fish processing and preservation · Fisheries economics and marketing · Fisheries schemes in India · Aquaculture and fish breeding · Fish biology and taxonomy · Oceanography and marine ecology