Aquaculture Thematic Methods

Aquaculture thematic methods connect to economy-wide measurement through TG-2.5 Structure and Function of the Ocean Economy, pollution accounting through TG-2.7 Pollution and Other Flows to Environment, and social dependencies through TG-2.3 Social and Livelihood Dependencies on Ocean Ecosystems. Wild-capture methods are in TG-6.7 Fisheries Accounting: Integrating Stock Assessment.

This Circular requires familiarity with:

• TG-4.3 Administrative Data Sources — aquaculture licensing, site consent and production returns are the primary source for the site-level accounts in Section 3.2.
• TG-0.1 General Introduction to Ocean Accounts — for environmental-economic accounting principles, asset boundaries, and production concepts.
• TG-3.9 Aquaculture Accounts — for foundational physical asset account methods, including the cultivated versus non-cultivated biological resource distinction.

Aquaculture activities are classified according to:

• ISIC Division 03: Specifically Group 032 (Aquaculture) with classes 0321 (Marine aquaculture) and 0322 (Freshwater aquaculture)
• SEEA CF land use and water area categories: Land used for aquaculture (1.3), including hatcheries (1.3.1) and managed grow-out sites (1.3.2), plus water area categories for inland and coastal waters

Offshore aquaculture in EEZ waters has no discrete numeric sub-category in SEEA CF 2012 Annex I. Where offshore EEZ aquaculture is present, compilers should use the closest applicable coastal water area category and document the extension in supplementary tables, following the national extension guidance in TG-0.1.

Marine cage aquaculture involves net-pen structures moored in coastal or offshore waters, typically for finfish such as salmon, sea bass, and cobia.

BSU assignment for offshore aquaculture: For fixed installations, the BSU should be determined by the centroid of the lease area polygon. For floating installations, by the lease area boundary. Where a lease area straddles two or more BSU boundaries, allocate production to the BSU containing the majority of the stocking area. See TG-0.1 and TG-1.2 Marine Spatial Planning for BSU framework specifications.

3.1.2 Coastal Pond Systems

Pond-based aquaculture uses constructed enclosures on land or in intertidal areas, commonly for shrimp, tilapia, and milkfish.

3.1.3 Integrated Multi-Trophic Aquaculture

Integrated multi-trophic aquaculture (IMTA) co-cultures species at different trophic levels, where waste from fed species (e.g., finfish) provides nutrients for extractive species (e.g., seaweed, shellfish). Accounting considerations:

• Nutrient cycling: Internal recycling reduces net environmental loading. Accounts should distinguish gross and net nutrient flows. Whether net loading is negative depends on site-specific mass balance data and should be verified empirically before recording negative residual flows. Where negative residual flows are recorded, apply the separate recording treatment in TG-3.4.
• Multiple outputs: Production accounts record outputs from each component species with appropriate allocation of shared inputs, following standard SNA treatment of joint production

3.1.4 Production Boundary: Aquaculture versus Sea Ranching

Output released to open water without retained ownership should be classified as natural stock and excluded from cultivated asset accounts. A notation should be made in escape and release records (Section 3.2.4) indicating species, quantities, and intended enhancement purpose. This classification is consistent with SEEA AFF paras. 3.179—3.181 and FAO Technical Guidelines for Responsible Fisheries No. 5, Supplement 4 (2010).

Table 3.1: Aquaculture species groups and key accounting considerations

3.2.1 Carrying Capacity Assessment

Carrying capacity represents the maximum production intensity that can be sustained without unacceptable environmental degradation. Four dimensions are assessed:

Physical, production, and ecological dimensions can be expressed in measurable physical units and recorded as supplementary physical data in the asset account. Social carrying capacity reflects stakeholder preferences and is not a standard SEEA account variable. Record it as a supplementary social indicator consistent with TG-2.3.

The asset account for aquaculture sites should record carrying capacity estimates as context for stock and production data. The ecological dimension connects to condition accounting in TG-2.3, and residual flows should be recorded consistently with TG-3.4.

3.2.2 Production Cycle Accounting

Aquaculture production cycles vary by species and system, from several months (shrimp) to multiple years (salmon). The physical flow account should record:

1. Reference period: Calculate historical average and standard deviation using a minimum of five accounting years of site-level mortality data. For sites with fewer than five years of records, use the full period of operation.
2. Reference population: Use site-specific records where sufficient data are available. Where site-level records are insufficient (fewer than three years), apply a national species-and-system-type average.
3. New sites: Apply the national species-and-system-type average threshold until a site-specific record is established. Where no national average is available, apply a documented expert judgement threshold and note this in account metadata.

For a production series with mean μ and standard deviation σ, the threshold is μ + 2σ (example: mean mortality 4.4%, σ = 0.49 pp, threshold = 5.38%, so observed mortality of 7.2% would be classified as catastrophic). Document the threshold derivation method following TG-0.7 Quality Assurance.

Escapes from aquaculture facilities require reclassification from cultivated to natural stocks. The SEEA AFF acknowledges this complexity:

“Challenges may arise when recording reclassifications of cultivated and natural fish stocks, for example when wild fish are introduced as breeding stock or when cultured seeds are released into the wild; escapes by fish from aquaculture facilities in river and marine environments can also occur.”

Escapes should be recorded as reductions in cultivated stock with corresponding entries in wild population accounts where these are maintained. For consistency with TG-3.1 Asset Accounts and TG-6.7 Fisheries Accounting, the record of each escape event should include species, estimated numbers and biomass, and whether the species is native to the receiving environment. Where escaped species are not subject to commercial fisheries, the wild stock account entry may be recorded as a supplementary table.

Table 3.3: Aquaculture environmental interaction matrix

Fed aquaculture systems release nutrients through uneaten feed, faeces, and metabolic excretion. Nutrient loading accounts should record:

Boundary with TG-6.13. Catchment-derived nutrient loads reaching coastal waters are accounted for in TG-6.13 Freshwater-Marine Interaction Accounting Section 3.2. The two accounts partition on the point of discharge, not on the industry: a marine cage or other system discharging directly to coastal or marine waters is recorded here, and a land-based pond or hatchery discharging to a river or to sewer is a catchment source recorded under TG-6.13 and excluded from this account. Compilers running both accounts should record which convention each site falls under, so that a site converting from pond to cage production moves between accounts once rather than appearing in both.

Table 3.4: Nutrient mass balance components for aquaculture

The SEEA AFF provides guidance on nutrient budgets: “The basis for measuring nutrient budgets is tracking the nitrogen and phosphorous [sic] cycles… Through consistent measurement of each part of those cycles, an overall indication of change can be obtained along with measures of surpluses or deficits of nitrogen and phosphorus” (para. 4.79).

Aquaculture nutrient discharges should be recorded as emissions to water using the residual flow methods in TG-3.4 Flows from Economy to Environment.

Aquaculture development can modify marine and coastal habitats through four pathways:

Conversions of natural habitats (e.g., mangrove forest, seagrass beds) to aquaculture use should be recorded as land use change, consistent with SEEA EA extent accounting principles. Benthic condition beneath cage sites provides an indicator for the ecological carrying capacity dimension (Section 3.2.1).

Escaped farmed fish may interbreed with wild populations, potentially affecting genetic diversity and local adaptation. Whilst quantitative genetic accounting methods remain under development, the following information supports qualitative assessment of genetic interaction risks.

Minimum genetic impact recording standard: For each accounting period where escape events are recorded, compile the following supplementary table and cross-reference it from condition accounts. Cross-reference also from TG-3.1 Asset Accounts where condition account linkages are maintained.

Table 3.5: Supplementary genetic impact recording template

3.4 Feed and Resource Use

3.4.1 Fishmeal and Fish Oil Dependency

Marine ingredients in aquafeed create linkages between aquaculture production and wild fish stocks. The SEEA AFF notes:

“Fish products… in granule or pellet form… provide nutrition in a stable and concentrated form… Many of the intensively farmed fish are carnivorous, including, among others, Atlantic salmon, trout, sea bass and turbot. In line with the emergence of modern aquaculture in the 1970s, fish meal and fish oil have become major components of feed for those species.”

Table 3.6: Feed component recording for aquaculture accounts

Feed ingredient sourcing should be linked to wild fish stock accounts in TG-3.9 and TG-6.7 to enable assessment of net contribution to fish supply.

3.4.2 Fish-In Fish-Out Ratios

The Fish-In Fish-Out (FIFO) ratio measures the quantity of wild fish required (as feed ingredients) to produce one unit of farmed fish:

$\text{FIFO}=\frac{(\text{Fishmeal quantity}\times {\text{FCR}}_{\text{meal}})+(\text{Fish oil quantity}\times {\text{FCR}}_{\text{oil}})}{\text{Farmed fish output (tonnes)}}$FIFO=Farmed fish output (tonnes)(Fishmeal quantity×FCRmeal​)+(Fish oil quantity×FCRoil​)​

where FCR_meal and FCR_oil are the species-specific wild-fish inclusion factors (kg wild fish per kg of meal or oil) derived from FAO reduction fishery yield ratios. Where fishmeal and fish oil are co-products of the same reduction fishery batch, allocate total wild-fish input between the two products based on their respective mass yield ratios to avoid double-counting.

• Service life exceeding 12 months: Record as GFCF and depreciate over the asset’s service life. Applies to purpose-built treatment systems, permanent barriers, and net structures with expected operational life of more than one accounting year.
• Service life of 12 months or less: Record as intermediate consumption in the period of acquisition or replacement. Applies to biosecurity nets replaced on a cycle of 12 months or less.
• Rolling replacement: Where nets or other biosecurity components are replaced on a rolling basis, record the full replacement cost in each period as intermediate consumption, regardless of the component’s individual service life.

Step 1: Data assembly and validation

Assemble aquaculture production data from fisheries agencies, site registration records from licensing authorities, and environmental monitoring data from regulatory programmes. Validate internal consistency between production records and site capacity data. Document data quality issues following TG-0.7 Quality Assurance.

Step 2: Site-level asset account compilation

For each aquaculture site or site cluster, compile a physical asset account (Table 3.2 format) recording opening stock, stocking (seed inputs), natural growth, harvest, mortality, escapes, and closing stock. Aggregate site-level accounts to species groups and production system types. Verify: Closing stock = Opening stock + Stocking + Natural growth - Harvest - Mortality - Escapes.

Stocking is a positive addition of cultivated biomass to the site, consistent with the SEEA AFF treatment of additions to cultivated biological resources; it is an entry in the physical asset account, not a revaluation. Where a cohort is stocked once at the start of a multi-year production cycle, the stocking term is zero in subsequent years of that cycle but should still be shown explicitly so that the identity is transparent.

Step 3: Environmental flow recording

Apply nutrient mass balance calculations (Table 3.4) to estimate nitrogen and phosphorus discharges from fed aquaculture systems. Record residual flows following TG-3.4. For coastal pond systems, record measured effluent volumes and nutrient concentrations where monitoring data are available.

Step 4: Feed dependency analysis

Compile feed use data by species and system type. Decompose feed into fishmeal, fish oil, vegetable protein, and other ingredients (Table 3.6). Calculate FIFO ratios using the mass-ratio allocation method (Section 3.4.2). Link fishmeal and fish oil use to wild fish stock accounts in TG-6.7.

Step 5: Integration with economy-wide accounts

Account inputs: Site-level asset accounts (Section 3.2), carrying capacity estimates (Section 3.2.1), nutrient loading data (Section 3.3.1), habitat modification records (Section 3.3.2).

Analytical outputs: Production potential by coastal zone, environmental loading relative to assimilative capacity, cumulative impact assessment, spatial optimisation of site allocation.

Connection to other circulars: Carrying capacity links to TG-2.3. GVA and employment projections link to TG-2.5.

3.7.2 Environmental Footprint Monitoring

Account inputs: Nutrient mass balance (Table 3.4), treatment chemical use (Table 3.8), escape records (Section 3.2.4), benthic condition indicators (Section 3.3.2).

Analytical outputs: Trends in nutrient loading intensity, chemical use per unit production, escape frequency, and benthic impact indices against regulatory limits.

Connection to other circulars: Nutrient discharges aggregate into TG-2.7 Pollution and Other Flows to Environment. Habitat impacts connect to TG-2.8 Climate Change Indicators.

3.7.3 Feed Conversion Efficiency Tracking

Account inputs: Feed composition (Table 3.6), FIFO ratios (Section 3.4.2), feed conversion ratios, wild fish stock status from TG-6.7.

Analytical outputs: Trends in FIFO ratios, share of feed from by-products versus reduction fisheries, actual versus best-practice FCR, net contribution to fish supply.

Connection to other circulars: Wild fish use in feed links to TG-6.7. Protein supply links to TG-2.3.

This worked example illustrates compilation of a site-level aquaculture account for a hypothetical marine cage salmon farm. The example demonstrates the physical asset account, production flow recording, nutrient loading calculation, and feed use accounting described in Section 3.

The example site comprises a marine cage salmon farm with 12 net-pen cages located in a coastal embayment. The farm operates on a 24-month production cycle, stocking smolts in Year 1 and harvesting market-size fish in Year 2. The site is classified under ISIC 0321 (Marine aquaculture) and occupies a lease area recorded under the applicable SEEA CF coastal water area category (see Section 2.2).

4.2 Physical Asset Account

• Feed input: 4,320 tonnes of feed at 6.5% N content = 281 tonnes N
• Nitrogen retained in biomass gain: 1,800 tonnes of growth at 2.8% N content = 50 tonnes N (retention is measured on growth, not harvest, because 2,000 tonnes of the harvest were stock carried from Year 1)
• Mortality and escapes: 200 tonnes, already within the biomass gain (3,600 harvest + 200 mortality and escapes - 2,000 stock drawdown = 1,800), so not deducted again
• Net N discharge to environment: 281 - 50 = 231 tonnes N

Wild fish equivalent in feed, using the mass-ratio allocation FIFO method (Section 3.4.2): fishmeal and fish oil are co-products of the same reduction fishery batch and must be treated as a single joint input. Combined fishmeal and fish oil: 648 + 432 = 1,080 tonnes. Using a combined mass yield of 22.5% (fishmeal) + 5.0% (fish oil) = 27.5% from live weight, following Tacon and Metian (2008):

• Total wild fish attributed to this feed: 1,080 ÷ 0.275 = 3,927 tonnes
• FIFO ratio: 3,927 / 3,600 = 1.09

This FIFO value reflects the standard mass-ratio allocation method following Tacon and Metian (2008) and Jackson (2009).

A FIFO ratio of approximately 1.0 indicates wild-fish input is roughly equivalent to farmed output by weight.

Feed conversion ratio (FCR): 4,320 tonnes feed / 1,800 tonnes biomass gain = 2.4. FCR is computed on biomass gain, not harvest, because most of the harvested fish were grown in Year 1. The illustrative value is above the typical range for salmon cage culture (1.1—1.3); in a real compilation it would prompt a check of the feed and growth records (Step 1).

4.5 Integration with Supply-Use Framework

Table 4.3: Integration with ocean economy supply-use table (ISIC 0321 — Marine aquaculture)

• Production data: Generally available from industry reporting and FAO aquaculture statistics, and typically the most complete data category. Verify consistency between national statistical agency records and industry association reports.
• Feed data: Often commercially sensitive, and may require survey-based collection or estimation using species-specific feed conversion ratios. Document the estimation methodology and associated uncertainty where direct data are unavailable.
• Environmental data: Variable availability depending on monitoring requirements. Some jurisdictions mandate site-level environmental monitoring, whilst others rely on ambient water quality monitoring that may not capture site-specific impacts.
• Disease data: May be subject to confidentiality restrictions. Aggregate mortality rates and treatment chemical use statistics may be available where case-level data are restricted.

Minimum data requirements are production quantities by species and system type, and site location data. Additional data categories enable progressively more complete accounts as described in the phased implementation approach below.

The phases below define the widening content of an aquaculture account. They sit inside the general readiness and sequencing pathway at TG-0.8 Implementation Readiness Assessment Sections 3.1 and 3.2, which is not restated here.

Minimum viable account: A TG-6.8 aquaculture thematic account is considered complete at Phase 2 (environmental interaction accounting). Phase 1 alone represents a partial account consistent with TG-3.9. It does not constitute a complete TG-6.8 compilation. Compilers completing only Phase 1 should label their output “TG-3.9 consistent” and include a note on planned progress toward Phase 2. Document account completeness following TG-0.7 Quality Assurance completeness and comparability rating conventions.

1. Phase 1 — Production and asset accounting: Compile physical quantities of production, stock, and harvest by species and system type, drawing on existing aquaculture production statistics.
2. Phase 2 — Environmental interaction accounting: Add nutrient loading estimates using mass balance calculations, habitat modification recording, and escape quantification. Phase 2 represents the minimum complete TG-6.8 account.
3. Phase 3 — Feed dependency and disease accounting: Incorporate detailed feed composition, FIFO calculations, disease loss recording, and treatment chemical use.
4. Phase 4 — Full integration with ocean accounts: Link aquaculture thematic accounts with TG-3.1 Asset Accounts, TG-3.4 Flows from Economy to Environment, and ecosystem condition accounts.