Fisheries Accounting: Integrating Stock Assessment

1. Outcome

This Circular provides comprehensive guidance on integrating fisheries stock assessment science with statistical accounting frameworks, bridging the methodological gap between biological fisheries science and environmental-economic accounting. Upon completion, readers will be equipped to compile robust fisheries asset accounts that leverage the best available fisheries science while maintaining accounting coherence.

Stock assessment and ocean accounting support critical decision use cases for sustainable fisheries management. They enable MSY-based quota verification, ensuring that total allowable catch decisions align with biological reference points and comparing actual catch data against assessment-predicted sustainable harvest levels. They support depletion-adjusted fisheries GDP, revealing whether fisheries income derives from sustainable harvest or capital depletion by calculating net fisheries income after deducting resource depletion from gross value added. They provide evidence base for subsidy reform, quantifying the contribution of public subsidies to fishing capacity and assessing whether government support enhances or undermines sustainability goals under SDG 14.6.

These applications connect directly to policy frameworks described in TG-1.5 Fisheries Management and TG-1.1 National Ocean Budgets, where fisheries asset accounts provide the evidence base for allocating public resources to conservation, monitoring, and sustainable harvest programmes. They inform indicators compiled under TG-2.2 Productivity Indicators, enabling tracking of resource productivity (sustainable yield per unit biomass), economic productivity (value added per tonne caught), and depletion intensity (depletion as share of gross extraction).

This Circular addresses how to transform stock assessment outputs into accounting entries, propagate uncertainty appropriately, accommodate multi-species and ecosystem considerations, and align with SDG indicator 14.4.1 (proportion of fish stocks within biologically sustainable levels)^[1]. The conceptual foundation presented here underpins the distinction between wild-capture fisheries and cultivated aquaculture presented in TG-3.9 Aquaculture Accounts. Governance and policy aspects of fisheries management, including the role of regional fisheries management organisations, are addressed in TG-1.5 Fisheries Management.

2. Requirements

This Circular requires familiarity with:

• TG-0.1 General Introduction to Ocean Accounts -- provides foundational understanding of Ocean Accounts components and the relationship between environmental and economic accounting frameworks, including the conceptual basis for recording natural resources as assets.

• TG-3.1 Asset Accounts -- for the general methodology of physical and monetary asset accounts, including the treatment of aquatic resources as environmental assets, the asset account structure (opening stock, additions, reductions, closing stock), and valuation approaches for renewable natural resources.

• TG-3.9 Aquaculture Accounts -- for the distinction between cultivated and natural aquatic resources, the production boundary for aquaculture, and the complementary treatment of farmed versus wild-capture fisheries in asset accounts.

Readers may also find the following Circulars helpful as supplementary references:

• TG-2.1 Biophysical Indicators -- stock assessment outputs such as biomass estimates and B/BMSY ratios serve as biophysical indicators of fish stock condition, and this Circular provides the broader indicator framework within which fisheries indicators sit.

• TG-0.7 Quality Assurance -- for guidance on handling data quality variations, documenting uncertainty, and managing data revisions--all of which are particularly relevant given the inherent uncertainty in stock assessment outputs.

3. Guidance Material

The decline in global fish stocks in recent decades and the corresponding rise in aquaculture facilities is well documented^[2]. Measuring fish stocks and changes in stocks is challenging, but it should be a priority given the importance of understanding issues of sustainability^[3]. The SEEA Central Framework and SEEA Agriculture, Forestry and Fisheries (SEEA AFF) provide the accounting framework for aquatic resources, while fisheries science provides the biological models and assessment methods that generate estimates of stock size, natural growth, mortality, and sustainable yield. This Circular examines how these two disciplines can be integrated effectively.

Stock assessment is "the use of various statistical and mathematical calculations to make quantitative predictions about the reactions of fish populations to alternative management choices"^[4]. The outputs of stock assessments--biomass estimates, recruitment indices, mortality rates, and reference points--are the raw material from which accounting entries for natural aquatic resources must be derived. However, substantial methodological work is required to transform these scientific outputs into the standardised entries of an asset account.

To illustrate the gap between fisheries science outputs and accounting requirements, consider a typical stock assessment result: "B/BMSY = 0.75 with 95% confidence interval of 0.45--1.05". This tells the fisheries scientist that the stock is most likely below the level that can produce maximum sustainable yield, but the wide confidence interval means the stock could plausibly be anywhere from severely depleted to slightly above target levels. For the accountant, this single result must be translated into a deterministic opening stock value (in tonnes), a sustainable yield estimate (to calculate depletion), and a sustainability classification (for SDG 14.4.1 reporting)--each requiring explicit decisions about how to handle uncertainty. The sections below provide a systematic framework for making these translations.

This section examines stock assessment concepts (Section 3.1), their integration into asset accounts (Section 3.2), compilation procedures linking assessment to accounts (Section 3.3), data transformation and uncertainty propagation (Section 3.4), worked examples (Section 3.5), multi-species and ecosystem considerations (Section 3.6), and alignment with SDG 14.4.1 (Section 3.7).

3.1 Stock Assessment Concepts

Stock assessment science provides the biological foundation for fisheries accounting. This section introduces the key concepts that must be understood before attempting to compile fisheries asset accounts. For guidance on how these concepts relate to broader economic frameworks, see TG-1.9 Valuation.

Biomass and stock structure

Biomass refers to the total weight of fish in a stock or population. Stock assessments typically distinguish between several biomass concepts^[5]:

• Total biomass (B): The weight of all individuals in the stock, regardless of age or size
• Spawning stock biomass (SSB): The weight of sexually mature individuals capable of reproduction--a critical metric for assessing reproductive capacity
• Exploitable biomass: The portion of the stock available for harvest, typically excluding juveniles below minimum landing size
• Virgin biomass (B0): The theoretical biomass that would exist in the absence of fishing pressure

For asset accounting purposes, the SEEA CF recommends that "an important one is the measurement of the sexually mature part of the stock (i.e., the spawning stock or parental biomass). It is important because, commonly, a primary purpose of fishery management is to maintain an adequate level of spawning stock so as to be able to generate natural growth and to minimize the probability of collapse"^[6].

The SEEA AFF notes that a physical asset account for fish and other aquatic resources "shows the total biomass of all species subject to harvesting or cultivation activity within a national boundary"^[7]. This scope includes commercial operations, aquaculture, and subsistence and recreational harvesting.

Different biomass concepts serve different purposes in the accounting framework. Table 3.1.1 provides guidance on selecting the appropriate biomass concept for each accounting entry.

Table 3.1.1: Biomass concept selection for accounting entries

In practice, compilers should use total biomass for the main physical asset account entries (opening and closing stocks) to ensure comprehensive population coverage, while sustainable yield calculations should reference spawning stock biomass to reflect the reproductive capacity that drives stock regeneration. Monetary valuation should focus on exploitable biomass, as this represents the economically harvestable portion. Where only one biomass concept is available from the stock assessment, compilers should document which concept is used and note any implications for comparability.

Recruitment and natural growth

Recruitment is the process by which new individuals enter the fishable stock, typically defined as reaching a specified age or size^[8]. Recruitment is highly variable, influenced by:

• Environmental conditions (temperature, currents, nutrient availability)
• Parental stock size (stock-recruitment relationships)
• Predation on eggs, larvae, and juveniles
• Habitat availability and quality

Natural growth in asset accounting terms encompasses both recruitment (new individuals) and somatic growth (increase in size of existing individuals). The SEEA CF states that for renewable natural resources such as fish stocks, "the primary addition to stock is natural growth, encompassing recruitment (new individuals joining the stock) and biomass increase (growth of existing individuals)"^[9]. For comprehensive treatment of natural resource additions, see TG-3.2 Flows from Environment to Economy.

Stock-recruitment relationships attempt to model the connection between spawning stock biomass and subsequent recruitment. The two most common models are^[10]:

• Beverton-Holt: Assumes recruitment increases with SSB but reaches an asymptotic maximum
• Ricker: Allows for declining recruitment at very high SSB due to density-dependent effects

The high natural variability in recruitment creates substantial uncertainty in stock projections, which must be acknowledged in asset account compilation.

Fishing and natural mortality

Fishing mortality (F) is the instantaneous rate of death due to fishing. It is typically expressed as a proportion of the stock removed per unit time. Natural mortality (M) is the instantaneous rate of death from all causes other than fishing, including predation, disease, senescence, and starvation^[11].

Total mortality (Z) is the sum of fishing and natural mortality: Z = F + M.

For asset accounting, the SEEA CF notes that "normal losses (or natural mortality for biological resources) represent decreases in stock due to natural processes such as death from age, predation, disease, and accidents"^[12]. Fishing mortality corresponds to the extraction (gross catch) entry in the asset account.

The relationship between mortality rates and catch is given by the Baranov catch equation:

C = (F/Z) x N x (1 - e^(-Z))

where C is catch, N is population number, and Z is total mortality. This equation is standard in fisheries science and provides the mathematical link between the stock assessment parameter F and the directly observable catch statistics that enter the accounts. For accounting purposes, the practical implication is that given estimates of F, M, and population size from a stock assessment, the expected catch can be derived and compared with reported catch data as a consistency check. Discrepancies between predicted and reported catch may indicate unreported fishing, misestimation of mortality rates, or data quality issues--all of which should be documented following the guidance in TG-0.7 Quality Assurance.

Maximum sustainable yield and reference points

Maximum sustainable yield (MSY) is the largest average catch that can theoretically be removed from a stock on a sustained basis under prevailing environmental conditions^[13]. MSY represents a balance point where natural growth exactly replaces removal by fishing.

The SEEA CF describes the concept of sustainable yield: "based on this general model, for any given population, it is possible to calculate the number of animals or volume of plants by age or size class that may be removed from the population without affecting the capacity of the population to regenerate itself"^[14].

Associated with MSY are biological reference points that guide fisheries management:

• BMSY: The biomass level at which MSY is achieved
• FMSY: The fishing mortality rate that produces MSY
• B/BMSY ratio: Current biomass relative to BMSY--a key sustainability indicator
• F/FMSY ratio: Current fishing mortality relative to FMSY--indicates fishing pressure

Additional precautionary reference points include:

• Blim: Limit reference point below which recruitment may be impaired
• Bpa: Precautionary approach reference point providing buffer above Blim
• Flim and Fpa: Corresponding fishing mortality limits

For accounting purposes, the most directly relevant terms are MSY (which determines sustainable yield), BMSY (which determines the sustainability threshold for SDG 14.4.1), and depletion (which is calculated as the excess of catch over sustainable yield). The precautionary reference points (Blim, Bpa, Flim, Fpa) are management tools that inform fisheries governance rather than accounting entries, but they may be recorded as supplementary metadata in the asset account.

SDG Target 14.4 specifically references MSY: "restore fish stocks in the shortest time feasible, at least to levels that can produce maximum sustainable yield as determined by their biological characteristics"^[15].

Stock assessment methods

A range of methods exists for estimating stock size and deriving reference points. The choice of method depends on data availability and stock characteristics^[16]:

Data-rich methods (integrated stock assessments, virtual population analysis):

• Require comprehensive catch-at-age data, abundance indices, and biological parameters
• Provide estimates of absolute biomass and detailed population structure
• Applied to commercially important, well-studied stocks

Data-moderate methods (catch-only models, surplus production models):

• Require catch time series and relative abundance indices
• Estimate biomass relative to reference points rather than absolute values
• Suitable for stocks with limited biological sampling

Data-poor methods (length-based indicators, catch-curve analysis):

• Require only basic catch or length-frequency data
• Provide qualitative or semi-quantitative sustainability assessments
• Applied where monitoring data are minimal

The SEEA AFF acknowledges these challenges: "compilation of a complete physical asset account for fish and other aquatic resources is most likely not possible under current circumstances. However, it may be possible to provide a more qualitative assessment of fish stocks by considering various biological and bioeconomic models and catch statistics to show whether species and fisheries are being underfished, fully fished or overfished"^[17].

The data tier of the stock assessment has direct implications for which accounting entries are feasible. Data-rich assessments can support full physical and monetary asset accounts with absolute biomass estimates, detailed flow decompositions, and net present value calculations. Data-moderate assessments may support physical accounts with relative biomass indices and approximate flow estimates, but monetary valuation requires additional assumptions. Data-poor assessments can support only qualitative sustainability classifications (underfished, fully fished, overfished) and trend indicators, sufficient for SDG 14.4.1 reporting but not for complete asset accounts. Compilers should document the data tier for each stock and apply quality flags accordingly, following TG-0.7 Quality Assurance.

3.2 Asset Account Integration

This section addresses how stock assessment outputs are integrated into the structure of physical and monetary asset accounts for natural aquatic resources. For the general structure of asset accounts, see TG-3.1 Asset Accounts.

Mapping stock assessment outputs to account entries

Stock assessment models produce a range of outputs that must be systematically mapped to asset account entries. Table 3.2.1 provides a comprehensive mapping between typical stock assessment outputs and their corresponding accounting treatments.

Table 3.2.1: Stock assessment output to account entry mapping

This mapping provides the foundation for the detailed account entries discussed below.

Opening and closing stocks

The opening and closing stock entries in a physical asset account correspond to biomass estimates from stock assessments. The SEEA CF provides the general structure:

• Opening stock of aquatic resources
• Additions to stock (growth in stock, upward reappraisals, reclassifications)
• Reductions in stock (gross catch/harvest, normal losses, catastrophic losses, downward reappraisals, reclassifications)
• Closing stock of aquatic resources^[18]

For natural aquatic resources, "direct measurement of opening and closing stocks and elements of change in stocks usually cannot be observed or measured directly; an exception to this is the measurement of the harvest or gross catch. Accordingly, biological models and assumptions must be used to make estimates"^[19].

Stock assessments typically provide annual biomass estimates at the start of each year (B1) or as an average over the year. These estimates become the opening and closing stock entries:

The accounting identity must hold: any discrepancy between the stock assessment biomass trajectory and the sum of recorded additions and reductions indicates either model inconsistency or unrecorded flows.

A practical challenge arises because stock assessments are typically revised retrospectively--each annual assessment revises the entire historical biomass time series as new data become available. When a revised assessment changes historical biomass estimates, the recommended treatment is to record these changes as reappraisals in the current accounting period rather than revising historical accounts. This approach maintains the integrity of previously published accounts while transparently recording improved understanding. The reappraisal entry should include metadata indicating the assessment vintage (the year of the stock assessment that produced the estimate) so that users can distinguish between "as-assessed" and "current-estimate" time series. This treatment is consistent with the guidance on data revisions in TG-0.7 Quality Assurance.

Figure 6.7.1: Hypothetical fish stock biomass trajectory with confidence bands and BMSY reference line^[20]

Figure 6.7.1 illustrates several features relevant to asset accounting. The central biomass trajectory (blue line) provides the point estimates used for opening and closing stock entries. The grey confidence bands represent assessment uncertainty--the range within which the true biomass is estimated to lie. The green dashed line indicates BMSY, the biomass reference point used for sustainability classification under SDG 14.4.1. The trajectory shows a stock that declined below BMSY in the early 2000s, reached a minimum around 2008, and subsequently recovered to approximately BMSY by 2020. During the decline phase, depletion would be recorded in the asset accounts; during the recovery phase, net additions exceed extractions and no depletion is recorded.

Sustainable yield and depletion

The relationship between catch and sustainable yield determines whether depletion is recorded. The SEEA CF establishes that "depletion of natural aquatic resources is derived following the approach... where depletion for renewable resources is shown to be equal to gross catch less sustainable yield"^[21].

Depletion = Gross catch - Sustainable yield (if positive; otherwise zero)

This treatment recognises that catch up to the sustainable yield level does not deplete the stock--it removes only the surplus production. Depletion occurs only when catch exceeds the rate at which the stock can regenerate.

The SEEA CF notes that "some year-on-year variation in the actual changes in the population must be accepted as part of the accounting, and depletion should therefore be recorded only when the extraction is beyond a normal level of natural growth (less natural losses)"^[22].

A critical distinction must be drawn between MSY (the maximum sustainable yield, achieved at BMSY) and the sustainable yield at current stock size. These are equal only when the stock is at BMSY. At stock levels below BMSY, the sustainable yield is below MSY because the depleted population has reduced reproductive capacity. At stock levels above BMSY, the sustainable yield is also below MSY because density-dependent effects limit surplus production. Consequently, catching MSY from a stock that is below BMSY would cause further depletion rather than achieving sustainability. For accounting purposes, compilers should use the sustainable yield corresponding to the current stock size--not MSY--when calculating depletion.

The sustainable yield curve shows that:

• At low population sizes, sustainable yield is low (limited reproductive capacity)
• Yield increases as population grows
• Maximum sustainable yield is achieved at intermediate population levels (BMSY)
• At carrying capacity, sustainable yield approaches zero (population stable)^[23]

Recording catch and extraction

The SEEA CF recommends using gross catch as the measure of extraction: "the most common catch concept used in practice is that of 'landings'. Landings are directly linked to the economic value of the product. However, this measure excludes the discards of organisms incidentally caught through harvesting activity (discarded catch) as well as the amount of the catch used for own consumption. For the SEEA, the measurement of discarded catch is an important contributory factor to a full understanding of the linkages between economic activity and the impact on aquatic resources"^[24]. For treatment of discards and residuals, see TG-3.4 Flows from Economy to Environment.

The FAO defines the stages of catch^[25]:

• Gross removal: Total live weight of fish caught or killed during fishing operations
• Gross catch: Gross removal less pre-catch losses
• Retained catch: Gross catch less discarded catch
• Landings: Net weight of quantities landed at port
• Nominal catch: Live weight equivalent of landings

For asset accounting, gross catch is preferred as it reflects the full impact on the fish stock. However, for monetary valuation, the value typically derives from landings or retained catch (the portion that enters economic transactions).

Monetary asset accounts

The monetary asset account for aquatic resources records opening and closing stock values and monetary flows during the period. The SEEA CF provides two main valuation approaches^[26]. For detailed guidance on valuation methods, see TG-1.9 Valuation.

1. Quota and licence valuation: Where individual transferable quotas (ITQs) exist and are traded, "it is possible to estimate the value of the aquatic resources from the market prices of these entitlements"^[27]. If quotas are perpetual and cover the whole stock, total quota value approximates total stock value.

2. Net present value of resource rent: The operating surplus from harvesting is partitioned between user costs of produced assets (vessels, gear, equipment) and the resource rent attributable to the aquatic resource itself. The stock value is then the NPV of expected future resource rents^[28].

The 2025 SNA provides guidance on fish stock valuation: "Where there is evidence of management, a total value of the fish stock can be calculated as the present value of the future resource rents estimated using the residual value method"^[29]. Conversely, "In cases where there is no effective management of the fish stock or an associated water body, then there is no legal owner and consequently no asset is recorded on the balance sheet notwithstanding the resource rent that may be earned by the fishing industry"^[30].

The 2025 SNA treatment of unmanaged stocks--where no asset is recorded on the balance sheet despite ongoing economic exploitation--creates a tension with the goal of comprehensive ocean accounting. An unmanaged but economically exploited stock has real physical existence and may experience depletion with sustainability implications. The recommended approach is to compile physical asset accounts for all commercially exploited stocks regardless of management status, as physical accounts document the state and trends of the resource independently of ownership conventions. Monetary asset accounts should follow 2025 SNA conventions for the core accounts (recording zero value for unmanaged stocks) but may include supplementary tables showing hypothetical resource rent values to illustrate the economic significance of the resource. This treatment is consistent with the general approach to asset boundary issues discussed in TG-3.1 Asset Accounts.

Catch per unit effort as a stock indicator

Where absolute stock estimates are unavailable, catch per unit effort (CPUE) may serve as a relative abundance indicator. The SEEA CF notes: "When scientific assessment of the absolute stock size is not available, an alternative approach is to measure the gross catch for a certain harvesting operation in relation to the amount of effort required to obtain the catch for a given species... The ratio of catch per unit effort (CPUE) may provide a good indicator of the relative change in stock size, assuming that population density and population size are closely correlated"^[31].

CPUE trends can indicate whether:

• The stock is stable (constant CPUE)
• The stock is increasing (rising CPUE)
• The stock is declining (falling CPUE)

Limitations include technological creep (improving fishing efficiency masking stock decline) and changes in fishing behaviour that affect catchability^[32].

3.3 Compilation Procedure: From Assessment to Accounts

This section provides a step-by-step procedure for compiling fisheries asset accounts from stock assessment outputs. Understanding this workflow is essential for translating scientific data into accounting entries while maintaining internal consistency and enabling policy analysis.

Step 1: Data assembly

The compilation process begins with identifying and assembling stock assessment outputs and catch statistics for the target species or stock complex:

• Stock assessment reports: Obtain the most recent assessment from national fisheries agencies, regional fisheries management organisations (RFMOs), or international bodies. Priority outputs include opening and closing biomass estimates (Bt, Bt+1), recruitment indices, natural and fishing mortality rates (M, F), and reference points (BMSY, FMSY, MSY).

• Catch statistics: Collect reported landings from national fisheries agencies and international databases (FAO FishStatJ). Where available, supplement with discard estimates from observer programmes or fishery-independent surveys to derive gross catch.

• Metadata documentation: Record the assessment vintage (year the stock assessment was conducted), the assessment method tier (data-rich, data-moderate, data-poor), the primary data sources (catch-at-age, survey indices, CPUE), and any caveats or limitations noted by the assessment scientists.

For stocks managed by RFMOs such as the Western and Central Pacific Fisheries Commission (WCPFC), Indian Ocean Tuna Commission (IOTC), or Commission for the Conservation of Southern Bluefin Tuna (CCSBT), the RFMO stock assessment outputs provide the primary input. National compilers should coordinate with RFMO data teams to obtain stock-specific outputs apportioned to the national EEZ where relevant.

Step 2: Unit standardisation

Stock assessments may report biomass in various units that must be standardised for accounting. Common conversions include:

• Mass units: Convert thousands of tonnes to tonnes, or metric tonnes to short tons, ensuring all entries use the same mass unit throughout the account.
• Number to mass: Where stock assessments report abundance in numbers of individuals, apply mean weight-at-age to convert to biomass. Document the conversion factors used.
• Wet weight to carbon: For integration with ecosystem carbon accounts, apply species-specific wet weight to carbon conversion factors (typically 10--12% carbon content by mass for finfish).

The conversion to carbon equivalents is particularly relevant for ocean accounts given the role of marine ecosystems in carbon cycling. Fish biomass carbon is distinct from the ecosystem carbon stocks held in habitats such as seagrass meadows and mangrove forests, which are addressed in TG-6.2 Mangrove Accounts and TG-6.3 Seagrass Accounts. Fish biomass represents mobile carbon within the marine ecosystem.

Step 3: Temporal alignment

Align stock assessment timing with the accounting period (typically calendar year). Stock assessments may reference 1 January biomass, mid-year biomass, or annual average biomass. The recommended approach is:

• Opening stock: Use biomass estimate at 1 January of the accounting year (Bt). If the assessment provides mid-year or average biomass, extrapolate to 1 January using reported quarterly or monthly growth and mortality rates.
• Closing stock: Use biomass estimate at 31 December of the accounting year (Bt+1), or 1 January of the following year.
• Catch timing: Sum reported catch over the accounting period, typically by aggregating monthly or quarterly landing statistics to annual totals.

Where stock assessments use a different reference date (for example, spawning season start for seasonal species), document the discrepancy and apply interpolation methods to align with the standard accounting period.

Step 4: Account entry calculation

With standardised and temporally aligned data, calculate each account entry:

Opening stock: Record Bt directly from the stock assessment as the opening biomass.

Natural growth: Calculate as recruitment plus somatic growth. Where the stock assessment provides age-structured population estimates, natural growth equals the sum of:

• Recruitment (numbers at age-0 multiplied by mean weight-at-age-0)
• Somatic growth (increase in weight of surviving individuals across all age classes)

Where only total biomass estimates are available, derive natural growth as a balancing item: Natural growth = Closing stock - Opening stock + Gross catch + Normal losses - Other additions + Other reductions.

Gross catch: Sum reported landings and estimated discards to derive gross catch. Where discard data are unavailable, apply discard ratios from comparable fisheries or regional studies, documenting the estimation method and associated uncertainty.

Normal losses: Convert natural mortality rate (M) to absolute biomass loss. For age-structured models, apply M to each age class and sum. For biomass models, approximate normal loss as M × average biomass during the year.

Sustainable yield: Use the MSY estimate from the stock assessment if the stock is at BMSY. If the stock is below or above BMSY, use the sustainable yield corresponding to current biomass. Stock assessments typically provide sustainable yield curves or tables showing sustainable yield as a function of stock size; extract the value corresponding to the current biomass level.

Depletion: Calculate as (Gross catch - Sustainable yield). If negative, record zero depletion. Positive depletion indicates overharvesting.

Closing stock: Record Bt+1 from the stock assessment. Verify the accounting identity: Closing stock = Opening stock + Natural growth - Gross catch - Normal losses ± Other changes. Any discrepancy indicates unrecorded flows or assessment inconsistency and should be recorded as a reappraisal.

Step 5: Reappraisal treatment

When a new stock assessment revises historical biomass estimates, distinguish between physical changes (actual growth, catch, mortality) and accounting adjustments (improved information):

• Retrospective revision: Calculate the difference between the current assessment's estimate of opening stock and the previous assessment's estimate of the same point in time. This difference is a reappraisal.
• Metadata: Document the assessment vintage for each entry, enabling users to distinguish "as-assessed" time series (using the assessment available at the time) from "current-estimate" time series (using the most recent assessment for all years).

For example, if the 2025 assessment estimates 2024 opening stock at 50,000 tonnes, but the 2024 assessment estimated 2024 opening stock at 48,000 tonnes, record a +2,000 tonne upward reappraisal in the 2025 account. This approach maintains the integrity of previously published accounts while transparently incorporating improved understanding.

Step 6: Quality assurance

Conduct quality checks following TG-0.7 Quality Assurance:

• Accounting identity verification: Confirm that opening stock plus additions minus reductions equals closing stock. Investigate any discrepancies.
• Consistency with catch data: Compare assessment-predicted catch (derived from F and biomass using the Baranov equation) with reported catch. Large discrepancies may indicate unreported fishing or assessment misspecification.
• Trend plausibility: Review biomass and depletion trends for plausibility. Sudden changes should correspond to documented events (recruitment failures, policy changes, environmental shifts).
• Uncertainty documentation: For data-moderate and data-poor assessments, document the magnitude of uncertainty and apply quality flags to account entries derived from uncertain inputs.

Step 7: Integration with broader accounts

Integrate the fisheries asset account with related accounting frameworks:

• Link to TG-3.1 Asset Accounts: Ensure consistency with the general asset accounting framework, particularly for monetary valuation methods and the treatment of reappraisals.
• Link to TG-3.2 Flows from Environment to Economy: Record gross catch as a natural resource input, consistent with the extraction entry in the asset account.
• Link to TG-1.5 Fisheries Management: Use depletion estimates and sustainability classifications to inform TAC decisions and quota allocation.
• Link to TG-2.2 Productivity Indicators: Derive resource productivity (sustainable yield per tonne biomass) and depletion intensity (depletion as share of catch) indicators from the asset account.

This compilation procedure ensures that stock assessment science is systematically transformed into accounting entries, enabling coherent integration of biological and economic information for sustainable fisheries management.

3.4 From Assessment to Accounts: Data Transformation

Stock assessment outputs require transformation to fit accounting frameworks. This section addresses the practical challenges of data transformation and uncertainty propagation.

Temporal alignment

Stock assessments typically estimate biomass at specific points (e.g., 1 January) or as annual averages. Accounting periods generally align with calendar years. Alignment considerations include:

• Spawning season timing: SSB estimates may reference specific dates (e.g., spawning season start)
• Catch timing: Catch data are typically annual totals
• Growth timing: Natural growth occurs continuously but is recorded annually

The SEEA CF notes that "the change in CPUE over accounting periods should provide an indication of whether the overall change (i.e., growth less gross catch less normal loss) is positive or negative"^[33].

Unit conversion

Stock assessments may report biomass in various units (tonnes, thousands of tonnes, numbers of individuals) that must be standardised for accounting. Conversion factors by species and size are required where estimates must be converted between mass and number^[34].

Common conversions include:

• Number to weight (using mean weight at age/size)
• Wet weight to carbon equivalent (for ecosystem carbon accounting)
• Species-specific units to aggregate biomass

The conversion to carbon equivalents is particularly relevant for ocean accounts given the role of marine ecosystems in carbon cycling. Fish biomass carbon is distinct from the ecosystem carbon stocks held in habitats such as seagrass meadows and mangrove forests, which are addressed in TG-6.2 Mangrove Accounts and TG-6.3 Seagrass Accounts. Fish biomass represents mobile carbon within the marine ecosystem, and its contribution to ocean carbon dynamics--including the role of mesopelagic fish in the biological carbon pump--may be recorded as supplementary information alongside the main asset accounts. For treatment of carbon sequestration and related ecosystem services, see TG-2.4 Ecosystem Goods and Services.

Distinguishing reappraisals from physical changes

A critical accounting distinction is between:

• Physical changes: Actual changes in stock size (growth, catch, mortality)
• Reappraisals: Changes in estimated stock size due to improved information or revised model parameters

The SEEA CF emphasises: "It is therefore important to record the impact of changes in model parameters as reappraisals in the asset accounts to distinguish these changes from other physical changes in the stock size"^[35].

When a new stock assessment retrospectively revises historical biomass estimates, the revision should be recorded as a reappraisal, not as previously unrecorded growth or loss. This maintains the integrity of the physical change series while acknowledging improved understanding.

In practice, retrospective revision is a routine feature of stock assessments--each annual assessment typically revises the entire historical biomass time series as new data are incorporated. Compilers should maintain parallel "as-assessed" and "current-estimate" time series, with clear metadata indicating the assessment vintage for each entry. The "as-assessed" series preserves the estimates available at the time of original compilation, while the "current-estimate" series reflects the most recent scientific understanding. The difference between the two series is recorded as reappraisals. This approach aligns with the treatment of data revisions in TG-0.7 Quality Assurance.

Uncertainty propagation

Stock assessment outputs carry substantial uncertainty arising from:

• Observation error in catch and survey data
• Process error in biological parameters (growth, mortality, recruitment)
• Model structural uncertainty
• Parameter estimation uncertainty

Modern stock assessments often quantify uncertainty through confidence intervals, probability distributions, or ensemble approaches. For accounting purposes, uncertainty can be addressed through^[36]:

Central estimates: Use point estimates (e.g., median biomass) for main accounts Supplementary uncertainty ranges: Report confidence intervals alongside point estimates Sensitivity analysis: Test how accounting entries change under alternative stock assessment scenarios Quality indicators: Flag entries derived from data-poor assessments

The SEEA AFF acknowledges that "estimates of the absolute size of stocks can be imprecise. In practice, little can be done to estimate the variability in births and survivals before the recruitment to the stock, the effects of environmental factors affecting the growth of the individual fish, or the rate of natural death from accidents, sickness, age, predators and so on"^[37].

Handling data gaps

For species or areas without formal stock assessments, alternative approaches include:

• Extrapolation: Apply mortality and growth rates from assessed proxy species
• Indicator-based assessment: Use length-frequency data or catch trends to infer stock status
• Catch-only models: Apply simple production models to catch time series
• Expert judgement: Structured elicitation of stock status categories

The SEEA CF notes that "it may be more applicable to focus on the size of the stock within a given area (or fishery), regardless of the number of species harvested in that area. Commonly, particularly in tropical areas, multiple species may be harvested at one time, and accessing relevant indicators and models of the overall stock size consisting of multiple species that supports this harvest may be the most appropriate measurement approach"^[38].

3.5 Worked Example: Demersal Fish Stock Asset Account

This worked example demonstrates the compilation of a fish stock asset account using synthetic data for a hypothetical coastal demersal fishery. The example illustrates the step-by-step application of the compilation procedure described in Section 3.3 and the data transformation methods described in Section 3.4.

Scenario description

The accounting area is a coastal zone supporting a demersal fish stock harvested by commercial and artisanal fisheries. A data-rich stock assessment using age-structured analysis provides annual estimates of total biomass, spawning stock biomass, recruitment, natural mortality, and fishing mortality. The stock assessment also provides BMSY and MSY estimates, enabling calculation of sustainable yield and depletion. The accounting period is calendar year 2025.

Stock assessment outputs (2025 assessment)

The stock assessment provides the following estimates:

Catch statistics (2025)

Reported landings from commercial and artisanal fisheries totaled 6,800 tonnes (wet weight). Observer data from a sample of commercial vessels indicate a discard rate of 8% by weight. Applying this ratio to total landings yields estimated discards of 544 tonnes, giving gross catch of 7,344 tonnes.

Compilation step-by-step

Step 1: Data assembly -- Stock assessment and catch statistics assembled as shown above. Metadata: 2025 assessment conducted in March 2026 using data through December 2025; age-structured model; data tier = data-rich.

Step 2: Unit standardisation -- All values already in tonnes (wet weight). No conversion required.

Step 3: Temporal alignment -- Stock assessment provides 1 January opening stock and 31 December closing stock, matching the calendar year accounting period. No adjustment required.

Step 4: Account entry calculation:

• Opening stock: 42,000 tonnes (from assessment)
• Natural growth: Calculate as recruitment plus somatic growth.
  • Recruitment biomass: 120 million individuals × 0.05 kg/individual = 6,000 tonnes
  • Somatic growth: Derived as balancing item = Closing stock - Opening stock + Gross catch + Normal losses - Recruitment = 38,500 - 42,000 + 7,344 + 4,100 - 6,000 = 1,944 tonnes
  • Total natural growth: 6,000 + 1,944 = 7,944 tonnes
• Gross catch: 7,344 tonnes (landings 6,800 + discards 544)
• Normal losses: Natural mortality (M = 0.18) applied to average biomass.
  • Average biomass ≈ (Opening + Closing) / 2 = (42,000 + 38,500) / 2 = 40,250 tonnes
  • Normal loss ≈ M × Average biomass = 0.18 × 40,250 ≈ 7,245 tonnes
  • However, this exceeds the observed decline, suggesting the assessment implicitly includes natural mortality in the closing stock estimate. Use assessment-derived value: 4,100 tonnes (this is the value that balances the account given the other flows).
• Sustainable yield: 6,200 tonnes (corresponding to current biomass of 42,000 tonnes, which is above BMSY of 38,000 tonnes)
• Depletion: Gross catch - Sustainable yield = 7,344 - 6,200 = 1,144 tonnes
• Closing stock: 38,500 tonnes (from assessment)

Step 5: Verify accounting identity: Closing = Opening + Natural growth - Gross catch - Normal losses 38,500 = 42,000 + 7,944 - 7,344 - 4,100 38,500 = 38,500 ✓

Physical asset account table:

Table 3.5.1: Physical asset account for coastal demersal fish stock, 2025

Interpretation: The stock declined from 42,000 to 38,500 tonnes during 2025, a reduction of 3,500 tonnes (8.3%). The decline resulted from gross catch (7,344 tonnes) and normal losses (4,100 tonnes) exceeding natural growth (7,944 tonnes). Gross catch exceeded sustainable yield by 1,144 tonnes, indicating depletion. Although the stock remains above BMSY (B/BMSY = 1.11, classified as sustainable under SDG 14.4.1), continued overharvesting at this rate would drive the stock below the sustainability threshold within a few years. This signals the need for TAC reduction to align catch with sustainable yield, preventing future stock decline and maintaining the SDG 14.4.1 sustainable classification.

This worked example demonstrates the systematic application of the compilation procedure and highlights the policy-relevant insights that fisheries asset accounts provide for sustainable management.

3.6 Multi-Species and Ecosystem Considerations

Fisheries rarely operate on isolated single-species stocks. This section addresses the complexities arising from multi-species fisheries and trophic interactions. For ecosystem accounting approaches, see TG-2.1 Biophysical Indicators and TG-3.1 Asset Accounts Section 3.4 (Ecosystem Assets).

Multi-species fisheries

Many fisheries harvest multiple species simultaneously. The SEEA CF notes that "commonly, particularly in tropical areas, multiple species may be harvested at one time"^[39]. This creates accounting challenges:

• Catch allocation: Allocating effort and impacts among species
• Aggregate stock indices: Constructing meaningful composite biomass measures
• Bycatch treatment: Recording impacts on non-target species

For mixed-species fisheries, aggregate biomass indicators may be more practical than species-specific accounts. The SEEA CF suggests that "accessing relevant indicators and models of the overall stock size consisting of multiple species that supports this harvest may be the most appropriate measurement approach"^[40].

Bycatch that is discarded dead represents fishing-induced mortality that affects the stock but does not enter economic activity. The recommended treatment is to record discarded bycatch as part of gross catch (consistent with the SEEA CF definition of gross catch, which includes discards) with a corresponding discard entry showing the portion that does not enter the economy. This approach ensures that the full impact of fishing on the stock is captured in the asset account while maintaining consistency with the treatment of residual flows in TG-3.4 Flows from Economy to Environment. Recording discards separately from retained catch also supports analysis of fishing efficiency and ecosystem impacts.

Trophic interactions

Fish stocks exist within food webs. Changes in predator populations affect prey populations and vice versa. Ecosystem-based fisheries management recognises these interactions^[41]:

• Top-down effects: Reduction in predator populations may lead to prey population increases
• Bottom-up effects: Changes in primary productivity affect prey availability for fish
• Trophic cascades: Indirect effects propagating through multiple trophic levels
• Competitive interactions: Species competing for common food resources

For accounting purposes, natural mortality rates implicitly incorporate predation. However, if fishing pressure on one species substantially alters predation mortality on another, this represents an indirect fishing impact that standard single-species accounts do not capture.

The SEEA AFF refers to the mean trophic index as one indicator that may be used to understand the state of marine environments^[42]. Declining mean trophic level in catches (sometimes called "fishing down the food web") can indicate ecosystem-level impacts of fishing.

Ecosystem-based approaches

Ecosystem-based fisheries management (EBFM) considers the broader ecosystem context of fisheries, including^[43]:

• Habitat dependencies (e.g., seagrass nurseries, coral reef refugia)
• Predator-prey relationships
• Environmental drivers (climate, oceanographic conditions)
• Non-extractive ecosystem services (carbon sequestration, coastal protection)

For ocean accounting, ecosystem-based approaches link fisheries asset accounts to broader ecosystem asset accounts. The SEEA AFF notes that "another approach is to consider indicators of the condition of marine and inland water ecosystems with a view to understanding the state of fish and other aquatic resources"^[44].

Relevant ecosystem condition indicators include:

• Ocean Health Index
• Mean trophic level
• Marine biodiversity indices
• Habitat extent and condition

These connect to the ecosystem accounting approaches in TG-2.1 Biophysical Indicators and ecosystem asset accounts in TG-3.1 Asset Accounts.

An important conceptual issue arises from the relationship between fish stocks as individual environmental assets and the marine ecosystems within which they exist. Under SEEA CF, fish stocks are recorded as individual environmental assets in physical asset accounts. Under SEEA Ecosystem Accounting (SEEA EA), fish are components of marine ecosystem assets, and harvested fish represent provisioning services flowing from the ecosystem to the economy. Aggregating both individual asset values and ecosystem asset values would create a double-counting risk. The SEEA EA addresses this through the provisioning service framework: fish are treated as an output (service flow) of the ecosystem asset rather than a component of its stock value. Compilers should ensure consistency with the treatment of ecosystem assets in TG-6.1 Coral Reef Accounts, TG-6.2 Mangrove Accounts, and TG-6.3 Seagrass Accounts, where habitat-dependent fish stocks represent a link between ecosystem condition and fisheries productivity.

Carrying capacity and environmental limits

Fish stock productivity depends on environmental conditions and habitat availability. The SEEA AFF notes: "Measures of water quality, for example, that take into account eutrophication, are likely to be important in understanding the sustainability of fisheries activities"^[45].

Environmental factors affecting carrying capacity include:

• Water temperature and stratification
• Nutrient availability and primary productivity
• Dissolved oxygen levels
• Habitat area and quality (reefs, seagrass, mangroves)
• Ocean acidification effects

Climate change is altering these environmental parameters, shifting the potential productivity of marine areas and the distribution of fish stocks. Asset accounts should be interpreted in the context of changing environmental baselines.

3.7 SDG 14.4.1 Alignment

This section addresses alignment with SDG indicator 14.4.1: Proportion of fish stocks within biologically sustainable levels.

Indicator definition

SDG Target 14.4 calls for the effective regulation of harvesting to "restore fish stocks in the shortest time feasible, at least to levels that can produce maximum sustainable yield as determined by their biological characteristics"^[46].

Indicator 14.4.1 measures the "proportion of fish stocks within biologically sustainable levels"^[47]. A stock is considered biologically sustainable if its abundance is at or above the level that can produce MSY (B >= BMSY) or if fishing mortality is at or below the level consistent with MSY (F <= FMSY).

The indicator is calculated as:

SDG 14.4.1 = (Number of stocks within biologically sustainable levels / Total number of assessed stocks) x 100

Relationship to asset accounts

The SDG 14.4.1 indicator provides a binary sustainability classification (sustainable/unsustainable) for each assessed stock. Asset accounts provide continuous biomass estimates and flow records. The relationship between them is:

The relationship between stock status and depletion recording is nuanced and requires careful interpretation. A stock can be below BMSY (classified as unsustainable under SDG 14.4.1) but recovering with no current depletion if catch is below the sustainable yield at current stock size. Conversely, a stock at or above BMSY (classified as sustainable) can experience depletion if catch temporarily exceeds MSY. Table 3.7.1 summarises the four possible combinations.

Table 3.7.1: Stock status and depletion interaction

This table illustrates that the SDG status (stock-based assessment) and the depletion flow (catch-based assessment) are complementary but distinct measures. Both should be compiled and reported to provide a complete picture of fisheries sustainability.

Methodological alignment

FAO coordinates global compilation of SDG 14.4.1 through its State of World Fisheries and Aquaculture reporting. The methodology classifies stocks into categories^[48]:

• Within biologically sustainable levels: Stocks at or above BMSY (underexploited or maximally sustainably fished)
• Outside biologically sustainable levels: Stocks below BMSY (overfished)

For asset accounting purposes, this classification can be used to:

• Stratify asset accounts by sustainability status
• Weight aggregate biomass by sustainability category
• Report depletion separately for overfished versus sustainably fished stocks

Overfished stock treatment

For overfished stocks (B < BMSY), asset accounts should record:

1. Depletion: When catch exceeds the sustainable yield corresponding to current (depressed) stock size
2. Sustainability deficit: The cumulative impact of past overexploitation, measured as the difference between current biomass and BMSY--recorded as supplementary information rather than as an asset account entry, since it represents unrealised potential rather than a flow or stock change within the accounting period
3. Recovery trajectory: Tracking progress toward BMSY through successive accounting periods

The concept of "potential recovery value"--the difference between current stock value and the value that would obtain at BMSY--is analytically useful for policy analysis but does not fit standard SEEA asset account entries. It may be recorded in supplementary tables alongside the main accounts to illustrate the economic cost of past overexploitation and the potential gains from stock recovery. This treatment is consistent with the depletion-adjusted aggregates discussed in TG-3.1 Asset Accounts.

The SEEA CF notes that "a total permissible catch resulting in earnings that are higher than this level will mean that some of those earnings should be regarded as depletion of the aquatic resources and not as income"^[49].

Reporting integration

Countries compiling ocean accounts can integrate SDG reporting by:

• Using the same stock assessment outputs for both purposes
• Ensuring definitional consistency (same BMSY reference points)
• Reporting the proportion of national fisheries biomass (from asset accounts) that is within sustainable levels
• Tracking the trajectory of this proportion over time

This integration supports coherent reporting across statistical and sustainable development frameworks.

4. Acknowledgements

This Circular has been approved for public circulation and comment by the GOAP Technical Experts Group in accordance with the Circular Publication Procedure.

Authors: To be assigned

Reviewers: To be assigned

5. References

This Circular draws upon the following authoritative sources:

• United Nations et al. (2014). System of Environmental-Economic Accounting 2012: Central Framework
• United Nations et al. (2021). System of Environmental-Economic Accounting--Ecosystem Accounting
• FAO (2020). System of Environmental-Economic Accounting for Agriculture, Forestry and Fisheries (SEEA AFF)
• United Nations (2025). System of National Accounts 2025
• FAO (2020). The State of World Fisheries and Aquaculture (SOFIA)
• United Nations (2015). Transforming Our World: The 2030 Agenda for Sustainable Development