Maritime Transport and Ports

1. Outcome

This Circular provides thematic methodology for compiling ocean accounts relating to maritime transport and port activities. Maritime transport carries more than 80 per cent of global merchandise trade by volume.^[1] The compilation of maritime transport accounts supports port investment planning, shipping decarbonisation tracking, and trade facilitation assessment.

Upon completion, users will be able to:

• Identify and classify maritime transport and port activities according to ISIC Revision 4 Division 50 (Water Transport) and Class 5222 (Service Activities Incidental to Water Transportation), applying the ocean economy thematic and extended account framework described in TG-3.3 Economic Activity Relevant to the Ocean^[2]
• Compile physical and monetary accounts for shipping emissions, including greenhouse gases and air pollutants, following the SEEA Central Framework air emissions accounting approach detailed in TG-3.4 Flows from Economy to Environment^[3]
• Measure the economic contribution of maritime transport through value added, employment, and trade flows using SNA 2025 production account methods, integrating these measures with the ocean economy structural indicators in TG-2.5 Structure and Function of the Ocean Economy^[4]
• Account for port infrastructure--including land use, dredging, and capital formation--within the asset accounting framework established in TG-3.1 Asset Accounts and extended in TG-6.11 Coastal Infrastructure Accounting^[5]
• Record environmental interactions including ballast water, hull biofouling, anchoring impacts, and underwater noise as residual flows and ecosystem condition impacts, linking to the emissions methodology in TG-2.8 Climate Indicators^[6]

This Circular connects maritime transport accounts to broader ocean economy measurement (TG-2.5), climate policy (TG-2.8), infrastructure investment (TG-6.11), and labour accounts (TG-3.5 Social Accounts; see Section 3.4.2 for the operational employment-to-social-accounts linkage).

2. Requirements

This Circular builds upon the following prerequisites:

• TG-0.1 General Introduction to Ocean Accounts—foundational framework for GOAP Technical Guidance, including core concepts, terminology, and accounting principles.

• TG-3.3 Economic Activity Relevant to the Ocean—general approach to compiling accounts for ocean-related economic activity, including industry classifications, supply and use tables, and the ocean economy thematic and extended account framework. The maritime transport accounts compiled under this Circular are a sector-specific application of the methods in TG-3.3.

Related Circulars (optional but recommended):

• TG-2.5 Structure and Function of the Ocean Economy—indicator derivation methodology for transport GVA shares, employment intensity, and export contribution.
• TG-2.8 Climate Indicators—GHG emission indicators and integration into climate monitoring frameworks.
• TG-3.1 Asset Accounts—produced asset accounting framework underlying valuation of port infrastructure and vessel capital stock.
• TG-3.4 Flows from Economy to Environment—detailed emissions accounting methodology, including classification of residual flows underpinning the shipping emissions accounts in Section 3.3.
• TG-4.1 Remote Sensing—port area spatial delineation using satellite imagery and GIS, supporting land use mapping in Section 3.2.1.
• TG-6.9 Offshore Energy—accounting treatment of offshore support vessels and maritime logistics of offshore energy installations.
• TG-6.11 Coastal Infrastructure Accounting—broader infrastructure accounting framework within which port capital formation is situated.

3. Guidance Material

3.1 Maritime Transport Activities

3.1.1 Industry Classification Framework

Maritime transport activities are classified according to ISIC Revision 4.^[7]

Division 50—Water Transport

This division encompasses the transport of passengers or freight over water, whether scheduled or not, distinguishing between sea-going vessels and inland waterway vessels based on vessel type.^[8]

These codes have been verified against the official ISIC Rev.4 publication.^[9] Compilers should also note the correspondence with the Central Product Classification (CPC) Ver.2.1 for product-level analysis of transport services, which aligns with the supply and use table approach described in TG-3.3 Economic Activity Relevant to the Ocean.

Inland waterway transport (ISIC 502). For inland navigation emissions, compilers should refer to the IPCC 2006 Guidelines, Volume 2, Chapter 3, which provides default emission factors for water-borne navigation including inland vessels.^[10] Vessels operating in both inland and coastal environments should be classified by predominant area of operation; compilers should document the classification rule in metadata and apply it consistently across the time series.

Supporting Activities (Division 52)

The "Coverage" column distinguishes ISIC classes that are mandatory components of maritime transport accounts (ISIC 5222 and the maritime-attributable share of ISIC 5224) from those that are supplementary. ISIC 5224 (Cargo Handling) covers both maritime and non-maritime cargo handling; compilers should apply a maritime ratio to apportion the maritime share, as illustrated in the worked example in Section 3.7 using an illustrative 0.70 ratio.^[11]

(Note: ISIC Division 30—ship building [3011] and pleasure boats [3012]—is excluded from TG-6.10 scope; record under general industry accounts.)

3.1.2 Vessel Categories

For accounting purposes, the commercial fleet may be disaggregated by vessel type. Table 3.1.1 below summarises the principal categories^[12].

This disaggregation is important for emissions accounting because emission factors vary significantly by vessel type, size, and engine configuration. The vessel classification should be used consistently across physical activity accounts, economic accounts, and emissions accounts. The Fourth IMO GHG Study (2020) provides comprehensive emission factor data by vessel type and operating mode that can serve as a starting point where country-specific factors are not available.^[13]

3.1.3 Trade Flow Measurement

Maritime trade flows are measured through:

• Volume (physical): Tonnes loaded and unloaded at ports
• Value (monetary): Value of goods transported (CIF/FOB basis)^[14]
• Activity (operational): Vessel movements, port calls, cargo handling operations

Data sources include port authority records, customs declarations, automatic identification system (AIS) tracking, and shipping company reports. Satellite AIS covers most commercial vessels over 300 gross tonnes in major shipping lanes, though coverage in remote ocean areas, smaller vessel classes, and terrestrial AIS-predominant regions remains incomplete.^[15] Compilers should cross-check AIS-derived activity data against vessel registry sources such as UNCTAD's Review of Maritime Transport and document coverage limitations in metadata.

3.2 Port Infrastructure

3.2.1 Port Areas and Land Use

Port infrastructure accounting requires spatial delineation of port areas. Table 3.2.1 below summarises the main land-use components of a port^[16].

Port areas should be mapped using consistent spatial references (see TG-4.1 Remote Sensing) and linked to the SEEA land cover and land use classifications.^[17] The port boundary should encompass the full operational area including anchorages, fairways, and approach channels.

3.2.2 Dredging and Land Reclamation

Dredging activities modify the seabed to maintain or create navigational channels and berthing areas. The distinction between capital and maintenance dredging determines SNA treatment:^[18]

Compilers should apply this rule to dredging expenditure records from port authorities and contractor invoices, documenting the criterion used where invoices do not clearly distinguish the two. For the fuller treatment of capital versus maintenance distinctions for coastal works, cross-reference TG-6.11 Coastal Infrastructure Accounting Section 3.2.4.

Physical measures:

• Volume of sediment removed (cubic metres)
• Disposal location (ocean dumping, beneficial reuse, confined disposal)
• Channel depth and width specifications

Dredge spoil as a material flow. Dredged sediment should be recorded as a material flow in the SEEA Central Framework physical flow accounts. SEEA CF paragraph 3.267 treats dredging material flows under physical flow accounting, with contaminated spoil recorded as a residual flow within waste accounts and unpolluted spoil excluded from the waste-flow boundary.^[19] Compilers should record dredge spoil volumes by disposal pathway and sediment quality classification.

Environmental considerations:

• Sediment quality (contaminant levels)
• Impacts on benthic habitats
• Turbidity and sedimentation effects

Land reclamation for port expansion should be recorded as a transformation of marine extent to land (cross-reference TG-3.1 Assets).^[20] Port expansion through reclamation may also trigger requirements under coastal infrastructure accounting (see TG-6.11 Coastal Infrastructure Accounting).

3.2.3 Port Capital Formation

Gross fixed capital formation in ports includes investment in:^[21]

• Breakwaters and seawalls
• Quay structures and berths
• Container handling equipment (cranes, straddle carriers)
• Warehouses and storage facilities
• Navigational aids and vessel traffic systems
• Environmental protection infrastructure (oil spill response, waste reception)

Capital formation should be recorded following SNA 2025 principles, distinguishing new construction and major improvements (gross fixed capital formation) from routine maintenance (intermediate consumption). Depreciation schedules vary by asset type--quay structures may have useful lives of 50 years or more, while handling equipment typically depreciates over 15--25 years. The perpetual inventory method (PIM) is the standard approach for compiling port capital stock.^[22]

3.2.4 Vessel Capital Stock

Vessels are produced assets that should appear in national balance sheets as transport equipment under SNA 2025 asset classification AN1131.^[23] Vessel capital stock is required for: (i) calculating consumption of fixed capital used to derive net value added in Table 3.7.1; and (ii) supporting complete asset accounting for the maritime transport industry.

Data sources for vessel capital stock:

• National vessel registries and maritime administration records (acquisition costs, vessel age, type)
• Lloyd's Register / IHS Markit (now LSEG/Clarksons) maritime fleet databases (vessel characteristics, valuation benchmarks)
• Customs records on vessel imports and exports
• Shipping company financial statements (book values, depreciation schedules)

PIM application. Compilers should apply the perpetual inventory method to vessel acquisition costs using vessel-type-specific service lives and depreciation profiles (container vessels typically 20--30 years; bulk carriers and tankers 25--30 years; passenger ferries 30--40 years). For the general PIM framework, see TG-3.1 Asset Accounts. The depreciation entry for ISIC 501 in Table 3.7.1 represents vessel depreciation derived through this PIM approach.

3.3 Emissions Accounting

3.3.1 Greenhouse Gas Emissions

Following the SEEA Central Framework, air emissions accounts record the generation of emissions by resident economic units by type of substance.^[24]

GHG emissions from shipping include:

GWP100 values are taken from IPCC AR6 WGI Chapter 7 Supplementary Material Table 7.SM.7.^[25] Compilers should align the GWP cycle (AR5 vs. AR6) used in maritime transport accounts with the cycle adopted in their country's national GHG inventory under UNFCCC reporting. AR5 GWP100 values may be retained for historical comparability in time series where the national inventory has not yet transitioned.

Estimation methodology:

Shipping emissions are typically estimated using activity-based methods:^[26]

$$E = \sum_{v} \sum_{m} (A_{v,m} \times EF_{v,m})$$

Where:

• E = Total emissions
• A = Activity (fuel consumption or distance travelled)
• EF = Emission factor
• v = Vessel type
• m = Operating mode (cruising, manoeuvring, at berth)

Data sources:

• Ship fuel consumption records
• AIS-derived activity data
• Port call statistics
• National fuel sales data with maritime allocation

The Fourth IMO GHG Study (2020) provides emission factor data by vessel type and operating mode; compilers may also draw on the IPCC 2006 Guidelines, Volume 2, Chapter 3.^[27]

Table 3.3.1: Shipping emission calculation methods

Ballast water discharge is not an air emission or a SEEA residual air flow; it is a biological pressure with ecosystem condition implications. The accounting treatment for ballast water is set out in Section 3.5.1.

Residence principle application:

Following the SEEA CF residence principle, emissions should be attributed to the country where the operating enterprise is resident, not the flag state of the vessel.^[28] In practice, emissions from a vessel flagged in one country but operated by an enterprise resident in another should be attributed to the country of the operator.

Reconciliation with IPCC national inventories. The SEEA-based residence attribution will differ from IPCC national inventory treatment, which excludes international marine bunker fuels from national totals and reports them as a memo item.^[29] Compilers should prepare a bridging table in metadata distinguishing SEEA-attributed shipping emissions from IPCC memo-item international marine bunker fuel quantities. For broader reconciliation between thematic emissions accounts and national climate reporting, see TG-2.8 Climate Indicators.

Flag-of-convenience and complex vessel ownership. Compilers should apply the following decision tree for residence attribution:

Practical sources include the IMO Global Integrated Shipping Information System (GISIS) and Lloyd's Register / IHS Markit (LSEG/Clarksons) maritime databases. Open or international registries account for the majority of global gross tonnage, so most compiling countries will encounter Case 2 or Case 3 in practice.

3.3.2 Air Pollutants

Beyond GHGs, maritime transport releases air pollutants with local and regional health impacts:^[30]

IMO MARPOL Annex VI regulates these emissions and has established Emission Control Areas. The 2020 global sulphur cap of 0.50 per cent m/m has had a material effect on fuel composition and emissions profiles that should be reflected in time series accounts.^[31]

For linkage to health impacts, see TG-2.7 Pollution and Other Flows. For integration of shipping GHG emissions into national climate indicator frameworks, see TG-2.8 Climate Indicators.

3.3.3 Underwater Noise

Shipping is a major source of chronic underwater noise pollution, particularly at low frequencies (10--1000 Hz) that overlap with marine mammal communication bands.^[32]

Noise emissions can be characterised by:

• Source level (dB re 1 microPa at 1 m)
• Frequency spectrum
• Temporal patterns (continuous vs. intermittent)

Accounting for underwater noise requires:

• Vessel traffic density data (AIS)
• Source level models by vessel type and speed
• Propagation modelling for spatial distribution
• Overlay with sensitive habitats and species distributions

Underwater noise accounting is an emerging area where data availability and standardised methods remain under development. The IMO Guidelines for the Reduction of Underwater Noise from Commercial Shipping (MEPC.1/Circ.833) provide a voluntary framework, while regional initiatives such as JOMOPANS are developing monitoring methodologies.^[33] Compilers should record noise indicators where feasible and note limitations in metadata. For linkage to ecosystem condition assessment, see TG-2.1 Biophysical Indicators.

3.4 Economic Measurement

3.4.1 Value Added

Maritime transport value added is calculated according to SNA 2025 principles:^[34]

Gross Value Added (GVA) = Output—Intermediate Consumption

For maritime transport industries (ISIC 50, 5222):

• Output = Freight revenue + passenger revenue + charter income + ancillary services
• Intermediate consumption = Fuel, port fees, insurance, maintenance, provisions

Net Value Added = GVA—Depreciation

Illustrative calculation structure:

For countries with significant transshipment activities, care should be taken to correctly attribute output to resident enterprises, consistent with the balance of payments treatment of freight transport described in BPM6.

3.4.2 Employment

Employment in maritime transport includes:^[35]

Seafarers:

• Officers and ratings on commercial vessels
• Measured by nationality (flag state vs. residence state considerations)

Shore-based employment:

• Port workers (stevedores, crane operators)
• Port authority and maritime agency staff
• Ship agents, freight forwarders
• Ship repair and maintenance workers

Employment data should distinguish:

• Number of persons employed
• Full-time equivalents (FTEs)
• Hours worked
• Compensation of employees

Residence-basis measurement and seafarer reconciliation. Employment should be measured on a residence basis consistent with SNA 2025 Chapter 19, adjusting flag-state data from MLC 2006 sources to reflect the number of seafarers resident in the compiling country regardless of vessel flag.^[36] The BIMCO/ICS Seafarer Workforce Report (2021 edition) provides national seafarer supply estimates by country of residence that may be used as a reference benchmark.^[37] Compilers should document the reconciliation approach in metadata and reflect the adjustment in the employment row of the worked example (see the note attached to Table 3.7.2).

Linkage to social accounts. For integration of maritime transport employment data with social accounts, including labour income distribution, working conditions, occupational safety, and gender disaggregation, see TG-3.5 Social Accounts.

3.4.3 Supply Chain Linkages

Maritime transport has extensive backward and forward linkages:^[38]

Backward linkages (inputs):

• Shipbuilding and repair (ISIC 3011)
• Fuel suppliers
• Port services
• Classification societies
• Marine insurance

Forward linkages (outputs):

• Wholesale and retail trade
• Manufacturing (imported inputs)
• Agriculture (commodity exports)
• Tourism (cruise industry)

These linkages can be quantified using supply and use tables and input-output analysis (see TG-3.3 Economic Activity Relevant to the Ocean).^[39]

3.5 Environmental Interactions

Table 3.5.1 summarises the main environmental interactions of maritime transport and their corresponding SEEA account entries.

Table 3.5.1: Maritime transport environmental interactions and SEEA flow types

3.5.1 Ballast Water

Ships take on ballast water for stability, potentially transporting organisms across biogeographic boundaries.^[40] Ballast water discharge is treated as a biological pressure indicator rather than a SEEA residual air or water flow. Compilers should record ballast water indicators alongside ecosystem condition variables and link them to invasive species monitoring programmes.

Accounting elements:

• Volume of ballast water discharged (by port, by vessel origin)
• Species detection monitoring
• Compliance with Ballast Water Management Convention
• Expenditure on ballast water treatment systems (recorded as environmental protection expenditure)

Cross-reference: See TG-2.1 Biophysical Indicators.

3.5.2 Hull Biofouling

Hull biofouling is a pathway for invasive species introduction.^[41]

Accounting elements:

• Antifouling system application and maintenance
• Hull cleaning activities and waste disposal
• Biofouling inspections at ports
• Linkage to invasive species monitoring

3.5.3 Anchoring Impacts

Anchoring causes physical damage to seabed habitats, particularly seagrass meadows and coral reefs.^[42]

Accounting elements:

• Anchorage locations and frequency of use
• Duration of anchor events
• Overlap with sensitive habitat areas
• Mooring buoy installation as mitigation

Cross-reference: See TG-6.1 Coral Reef and TG-6.3 Seagrass.

3.5.4 Oil and Chemical Spills

Despite improved safety, shipping remains a source of marine pollution from accidental and operational discharges.^[43]

Accounting elements:

• Spill volume and substance type
• Location and environmental sensitivity
• Response costs
• Natural resource damage assessments
• Linkage to SEEA pollution flow accounts (TG-3.4 Flows from Economy to Environment)

Operational discharges (bilge water, cargo residues) remain a persistent source of chronic pollution that should be captured in flow accounts alongside acute events.

3.6 Compilation Procedure: Maritime Transport Supply-Use Table

Compiling maritime transport accounts follows a systematic procedure for extracting maritime transport sub-matrices from national supply and use tables, adapted from SNA 2025 Chapter 15 and the ocean economy thematic account compilation approach in TG-3.3 Economic Activity Relevant to the Ocean Section 3.4.^[44]

Step-by-step compilation

Step 1: Identify maritime transport industries by ISIC code. Using Table 3.1.1, identify all ISIC classes constituting maritime transport: Division 50, Class 5222, Class 5224 (port portion), and related industries. For each class, determine whether it is wholly maritime-related (ocean ratio = 1.0) or partially maritime-related (ocean ratio < 1.0).

Step 2: Extract maritime transport sub-matrices from national SUTs. From the balanced national supply and use tables, extract columns corresponding to maritime transport industries to create a maritime transport supply table and use table.

Excluding non-resident enterprise output. For countries that are major port hubs or transshipment centres, maritime transport columns may include services provided by non-resident enterprises. The residence principle requires excluding non-resident maritime output before deriving GVA. Practical data sources include balance of payments supplementary data on transportation services and port authority records of vessel nationality and operator residence. Cross-reference BPM6 paragraphs 10.73--10.88 on transportation services.^[45]

Step 3: Determine the maritime share for mixed industries. For partially maritime-related industries, estimate the share of output attributable to maritime activity. For Class 5224 (Cargo Handling), the 0.70 ratio used in Section 3.7 is illustrative; compilers must derive their own country-specific ratio from primary data. At least one of the following methods must be documented in metadata: (a) Revenue-based split—share of cargo handling revenue attributable to seaport establishments from structural business surveys or port authority financial accounts; (b) Physical-unit split—seaport cargo handling tonnes as a share of total cargo handling tonnes from port authority and customs statistics. Where neither method is feasible, apply a sensitivity analysis around the assumed ratio and report the range of resulting GVA estimates in metadata.

Step 4: Calculate Maritime Transport Direct GVA. For each maritime industry, multiply the industry's gross value added from the Use Table by its maritime ratio:

$$\text{Maritime Transport Direct GVA} = \sum_i (\text{GVA}_i \times \text{Maritime ratio}_i)$$

Step 5: Compile employment accounts. Using labour input rows from the Use Table, calculate maritime transport employment by applying the same maritime ratios to employment data by industry.

Step 6: Derive trade flow indicators. From the Exports column in the Use Table, sum across maritime transport service products to calculate maritime transport service exports. From customs data, compile merchandise trade volumes and values passing through ports.

Step 7: Integrate emissions accounts. Using the emissions calculation methods in Section 3.3, compile air emissions by maritime transport industries from national air emissions accounts, ensuring consistency with GVA and activity data in the maritime transport SUTs.

Data sources

Key data sources for maritime transport account compilation:^[46]

• National supply and use tables (primary source for GVA and output)
• Port authority statistical reports (cargo volumes, vessel calls, employment)
• Maritime administration records (vessel registries, seafarer certification)
• Structural business surveys (port and shipping company financial data)
• Customs declarations (trade values and volumes)
• AIS tracking data (vessel activity, voyage data)
• Fuel sales records (maritime fuel consumption for emissions)
• Balance of payments transport services supplementary data (for resident/non-resident enterprise attribution)

3.7 Worked Example: Synthetic Port/Shipping Account

This section presents a worked example for a synthetic medium-income coastal state ("Country B") with a total GDP of approximately USD 80 billion, total employment of 15 million persons, and two major ports handling combined cargo volumes of 45 million tonnes per year. The example illustrates the mixed-industry apportionment for ISIC 5224 using an illustrative maritime ratio of 0.70.

Table 3.7.1: Country B Maritime Transport Account—Production Account

All monetary values in millions of USD at current prices. The ISIC 5224 column shows the maritime-attributable share after applying the 0.70 maritime ratio (total ISIC 5224 output of 350 x 0.70 = 245). The depreciation entry for ISIC 501 (USD 120 million) reflects vessel capital consumption derived through the perpetual inventory method described in Section 3.2.4.

Table 3.7.2: Country B Maritime Transport Employment

Sea transport employment is measured on a residence basis as set out in Section 3.4.2. For Country B, seafarer employment from MLC flag-state data has been adjusted to a residence basis using the BIMCO/ICS Seafarer Workforce Report (2021) national supply estimates.

Table 3.7.3: Country B Maritime Transport Emissions

Panel A: Greenhouse gases (tonnes CO2e, AR6 GWP100)

Note (biogenic CH4): The CH4 row applies the AR6 GWP100 of 29.8 for fossil-sourced methane. As biofuel blends and bio-LNG become material under IMO's 2023 GHG Strategy fuel-mix scenarios, biogenic CH4 should be reported separately at GWP100 = 27.0 (AR6 non-fossil value). Compilers should document the fuel-type split and apply the corresponding GWP factor for each CH4 emission stream once biofuel uptake is material.

Panel B: Air pollutants (tonnes; illustrative, derived from the same fuel-consumption activity data using EMEP/EEA emission factors)

The figures in Panel B are derived from the same fuel-consumption activity data used for Panel A, applying air pollutant emission factors from the EMEP/EEA Air Pollutant Emission Inventory Guidebook (2019), Chapter 1.A.3.d. Emission factors applied at the IMO 2020 global 0.50% sulphur cap (non-ECA). Compilers applying this method to pre-2020 data or ECA-regulated routes should substitute factors consistent with the applicable sulphur limit. For linkage to health impact assessment, see TG-2.7 Pollution and Other Flows.

Table 3.7.4: Country B Port Infrastructure Capital Stock (PIM approach)

All monetary values in millions of USD at current replacement cost. The net capital stock of USD 1,270 million represents approximately 4.2 times the annual GVA from port services (USD 300 million). Vessel capital stock for ISIC 501 (not shown—see Section 3.2.4) is compiled separately under SNA asset class AN1131 using vessel-type-specific PIM parameters.

The maritime transport sector contributes 1.3 per cent of Country B's GDP (USD 1,055 million / USD 80 billion) while employing 0.30 per cent of the workforce (45,600 / 15 million). The GHG emission intensity of 1,287 kg CO2e per USD 1,000 of GVA provides a baseline for tracking decarbonisation progress under IMO targets.

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 confirmed]

Reviewers: [To be confirmed]

Contributing frameworks and sources:

This Circular draws upon:

• SEEA Central Framework (UN et al., 2012)
• ISIC Revision 4 (UN, 2008)
• SNA 2025 (UN et al., 2025)
• MARPOL Convention (IMO)
• Ballast Water Management Convention (IMO)
• Fourth IMO GHG Study (IMO, 2020)
• UNCTAD Review of Maritime Transport
• IPCC Guidelines for National Greenhouse Gas Inventories
• IPCC AR6 WGI Chapter 7 Supplementary Material (GWP100 values)
• BIMCO/ICS Seafarer Workforce Report (2021)
• EMEP/EEA Air Pollutant Emission Inventory Guidebook (2019)
• OECD Measuring Capital: OECD Manual (2009)

5. References