Background
New Zealand's marine environment is exceptionally rich and biodiverse. The described marine biodiversity accounts for approximately 80% of New Zealand's total biodiversity, with 44% of this being endemic to the country.[1] The marine area is vast, covering 15 times the size of New Zealand's terrestrial area, and the Exclusive Economic Zone (EEZ) is the fifth largest in the world (Figure 1). Despite its expansive marine territory, the number of marine activities in New Zealand remains lower compared to countries in Asia and Europe (Scott, 2016). Nevertheless, New Zealanders have a profound connection to the ocean, which is integral to their identity and culture. A variety of marine activities occur in New Zealand waters, ranging from recreational and customary fishing to commercial endeavours such as fishing, aquaculture, and oil and gas. The types and intensity of these activities continue to grow.
Figure 1: The New Zealand (NZ) EEZ (blue continuous line) is one of the largest in the world. The red dotted line represents the NZ Continental Shelf (CS) and the yellow line is the NZ coastal marine area. Everything else outside the EEZ and CS is international waters.
With increasing pressures on the marine environment, it is crucial to assess potential new activities thoroughly before their implementation to ensure the protection of marine biodiversity and ecosystems.

Environmental Impact Assessments (EIA) are a critical tool for evaluating the potential consequences and significant effects of proposed projects or developments on the environment. The United Nations defines EIA as “a formal, systematic process to analyse and address the environmental effects of policies, plans and programmes and other strategic initiatives. This process applies primarily to development-related initiatives that are known or likely to have significant environmental effects, notably those initiated individually in sectors, such as transport and energy, or collectively through spatial or land use change”(Abaza et al., 2004).
In simpler terms, EIA is a tool used to identify impacts, assess risks, and evaluate the costs and benefits of development projects, thereby avoiding adverse and costly environmental changes (NZAIA, 2024). Established in the United States in 1969, EIA has since been adopted worldwide (Glasson et al., 1999). However, its interpretation and application varies depending on local legislation and policies. For example, some jurisdictions adopt a broader definition of "environment", encompassing social and cultural dimensions, while others take a more restrictive approach, emphasizing biophysical aspects. These variations influence the scope and limitations of EIAs, shaping their effectiveness in addressing environmental challenges (Abaza et al., 2004).

Environmental Impact Assessment in the marine environment of New Zealand
Environmental Impact Assessments (EIAs) were introduced in New Zealand during the mid-1970s to 1980s, initially applied to large-scale government resource development projects and private enterprises requiring consents  (Matunga, 2018).  However, their use in the marine environment only began in 1991, with the enactment of the Resource Management Act 1991 (RMA), as part of the consenting process.

New Zealand’s marine management framework involves multiple legislative instruments, with the RMA serving as the primary statute governing activities and regulating environmental effects from the high tide mark to 12 nautical miles, the extent of the country’s territorial sea. Beyond this lies the EEZ, spanning from 12 to 200 nautical miles, managed under the Exclusive Economic Zone and Continental Shelf (Environmental Effects) Act 2012 (EEZ Act). Waters beyond 200 nautical miles constitute the high seas, which are regulated under international law and fall outside New Zealand’s jurisdiction. The EEZ Act governs activities within 96% of New Zealand’s maritime zone, highlighting its critical role in marine management.

The RMA does not explicitly mandate EIAs for resource consent applications. Instead, Section 88 requires an "assessment of the activity's effects on the environment," as outlined in Schedule 4[2],  a process commonly known as the "Assessment of Environmental Effects" (AEE). While the AEE is not explicitly termed an EIA, it serves a similar purpose[3]. Its scope is generally broader, reflecting the RMA’s inclusive definitions of "environment" and "effects," which extend beyond biophysical components to encompass social, cultural, and economic dimensions.

Conversely, the EEZ Act explicitly incorporates the term "Impact Assessment" (IA) within its provisions. The scope and detail required for an IA under the EEZ Act align with its narrower definition of "environment." Unlike the RMA, which includes human communities and built structures, the EEZ Act focuses on ecosystems, their constituent parts, natural resources within the EEZ and continental shelf, and the waters beyond these zones.[4] Additionally, existing interests are also a major focus of the EEZ Act, however, these interests are not considered part of the environment, and they are distinct factors to be considered in the legislation (refer to section 59 of the EEZ Act). This narrower scope reflects the lower intensity of human activity in the EEZ compared to territorial waters (Brake & Peart, 2015).

Section 39 of the EEZ Act establishes the baseline requirements for assessing environmental effects of activities within the EEZ. This provision underscores the Act's commitment to balancing environmental integrity with sustainable development. By adopting an ecosystem-based management approach, the EEZ Act addresses the unique challenges of New Zealand’s offshore marine environments while ensuring that development aligns with environmental sustainability (Brake & Peart, 2015).

An overview of the EEZ Act
The EEZ Act establishes a legislative framework for managing the environmental effects of activities within the EEZ and the continental shelf (CS). Under this framework, the Ministry for the Environment is empowered to develop regulations addressing technical matters, with decision-making processes centralised at the national level. The EEZ Act aims to protect the EEZ and CS marine environment from pollution by regulating the environmental effects of marine activities including discharge and dumping.  The responsible regulator of the EEZ Act is the Environmental Protection Authority (EPA).

The primary purposes of the EEZ Act are found in section 10 of the EEZ Act as follows:

  1. Promote the sustainable management [5] of natural resources in the EEZ and Continental Shelf
  2. Regulate activities that may cause environmental harm, such as discharges and dumping of harmful substances
  3. Ensure compliance with international obligations and the Treaty of Waitangi.

Within the EEZ and the CS, the EEZ Act defines three broad activities that it regulates (Table 1), and therefore, the EPA is responsible for regulating. Note that these definitions may be also classified at discretion of the Minister of the Environment (Ellis et al., 2017).
The Role of Impact Assessment in the EEZ Consenting process
Under the EEZ Act, any activity classified as discretionary requires a marine consent before it can proceed (Section 38). The Act defines three types of consents: marine consent, marine discharge consent, and marine dumping consent (EPA, 2018). While each type of consent serves a distinct regulatory purpose, the general application process follows a similar structure.

Applicants must submit a prescribed form detailing the proposed activity, along with an IA in accordance with Section 39 and any additional requirements specified in regulations. The application is lodged with the EPA, which assesses whether it is complete, meaning it meets all requirements under Section 38, as well as relevant sections and regulations (EPA, 2025b). Once deemed complete, the application proceeds to the next stages, including a detailed evaluation of the proposal and its IA, ultimately leading to a final decision by the decision-makers.

Any discretionary activity cannot be carried out a without a marine consent because it will trigger one or more activities that are restricted.

Section 20 outlines restrictions on activities other than discharge and dumping within New Zealand’s EEZ and CS. It is a critical component of the marine consenting process as it defines a broad set of activities that require consent, including but not limited to seabed disturbance, removal of living material from the seabed, installation of submarine cables, and the long-term placement, mooring, or anchoring of structures. For example, a developer planning to install an offshore structure will likely need consent for multiple Section 20 activities, such as seabed disturbance during installation and the long-term presence of the structure itself.
Specific restrictions on the discharge of harmful substances, such as oils and ecotoxic substances, from structures and submarine pipelines are outlined in Sections 20B and 20C, while restrictions on the dumping of waste or other materials are covered in Section 20G. Like Section 20, these sections define restricted activities that require consent before they can proceed. Additionally, Sections 20E and 20F prohibit specific dumping activities, including the disposal of toxic or radioactive waste.

When submitting a marine consent application, an applicant typically seeks approval for multiple activities regulated under Sections 20, 20A, 20B, or 20G. These activities form the basis for assessing potential environmental impacts and help guide the focus of the IA.

The Impact Assessment an important tool to support the decision-making process and shaping the consent conditions
As discussed earlier, any marine consent application under the EEZ Act must include an IA prepared in accordance with Section 39 and relevant regulations. Section 39 outlines the specific information requirements, including the criteria and level of detail necessary for an IA. Compliance with these requirements is critical, as the EPA evaluates applications against Section 39 criteria to determine their completeness (EPA, 2025b).  

Section 39 requires the EPA to assess whether an IA provides sufficient detail proportional to the scale and significance of the proposed activity’s effects on the environment and existing interests. The IA must enable both the EPA and affected parties to fully understand the activity and its potential impacts. If the information provided is inadequate, the EPA may either return the application as incomplete or request further details to address gaps (Section 42 of the EEZ Act). Additional information or expert advice may also be sought later in the process to clarify uncertainties (Sections 54 and 56). At this stage, the IA becomes a crucial tool for identifying the potential environmental effects of the proposed activity and informing the decision-making process.

To reach a final decision, decision-makers must consider the environmental effects of the activity, including cumulative impacts and broader effects beyond the immediate application area. The EEZ Act explicitly requires decision-makers to account for the protection of rare and vulnerable ecosystems, the habitats of threatened species, biological diversity, and the integrity of marine ecosystems and processes (EPA, 2025a). If uncertainties remain regarding the potential effects of an activity, the EPA may issue further information requests and commission expert reviews to provide additional technical input.[6]

Under section 100 of the EEZ Act, the EPA is required to prepare a Key-Issues Report (KIR) for marine consent applications determined by a Board of Inquiry. For applications decided by an EPA-appointed decision-maker, a KIR may be prepared upon request; however, it is not a statutory requirement. If necessary, decision-makers may also request a Conditions Report [7], which evaluates whether the proposed consent conditions are adequate or require modification to effectively mitigate environmental risks. Technical experts, such as marine ecologists and industry specialists, may be consulted to assess the application, identify deficiencies, suggest improvements, and recommend conditions to ensure environmental protection. KIR [8] and related expert reviews inform further information requests sent to the applicant, addressing areas of the IA that require clarification or additional supporting data.

Throughout this process, decision-makers must adhere to the principle of Best Available Information, a core tenet of the EEZ Act [9]. This principle requires that decisions be based on the most reliable information accessible within reasonable time, cost, and effort constraints. Where information gaps exist, decision-makers must actively seek further data from the applicant, expert advisors, or independent technical assessments. This ensures that decisions are well-informed, scientifically robust, and account for any uncertainty or inadequacy in the available information.

Once a decision has been made, it is common for decision-makers to impose conditions to avoid, remedy, or mitigate the environmental effects of the activity (EPA, 2025b). These conditions may include requirements for monitoring, reporting, and implementing specific environmental protection measures before, during, and after the activity.

A well-prepared IA, developed with the appropriate level of detail as required by the EEZ Act, can streamline the consenting process. A comprehensive IA not only enhances the efficiency of the application process, reducing the time and costs associated with obtaining consent, but also ensures a more transparent, well-informed decision-making process that aligns with the Act’s environmental protection objectives.

Case study: The Great South Basin project
OMV New Zealand Limited (OMV), which has operated in New Zealand since 1999, was granted Petroleum Exploration Permit (PEP) 50119 under the Crown Minerals Act 1991 (CMA 1991) on 7 July 2007. This permit allowed OMV to explore for oil and gas reserves in the Great South Basin (GSB)(EPA, 2019a), located in the EEZ off the Canterbury region of the South Island, NZ (Figure 2). The GSB covers approximately 100,000 km², with water depths ranging from 100 to 1,500 metres. It is a complex intracontinental rift system formed during the mid-Cretaceous period, containing several distinct sub-basins with up to 8.6 km of sedimentary fill. Exploration in the GSB dates back to the early 1970s, when Hunt International Petroleum Company conducted a large-scale regional seismic acquisition programme (Karaket et al., 2021; Sahoo et al., 2014).
Figure 2: Location of the AOI in the GSB (map adapted from EPA, 2019: Decision on Marine Consent and Marine Discharge Consent Applications. OMV GSB Limited. EEZ200009)
Under the terms of PEP 50119, OMV was required to drill an exploration well, Tāwhaki‐1, by 10 July 2021 or surrender a minimum of 7,349 km² of the permit area, or the entire permit. If OMV proceeded with the drilling, it was then obligated to drill two additional exploration wells: one by 10 April 2022 and the second by 10 July 2022. To undertake these drilling activities, OMV was required to obtain several consents from the EPA, as mandated under the EEZ Act (EPA, 2019a).

On 9 August 2019, OMV lodged an application with the EPA seeking both a marine consent and a marine discharge consent to carry out activities restricted under the EEZ Act as part of its multi-well Exploration and Appraisal Drilling (EAD) programme (EPA, 2019a). As required by the EEZ Act, an IA was submitted alongside the application to assess the potential environmental effects of the proposed activities[10].

The Role of the IA in the Decision-Making Process
During its assessment of the application, the EPA identified information gaps that needed to be addressed before an informed decision could be made. The IA played a crucial role in this process, as it included a comprehensive survey of the GSB’s marine environment, which had previously been poorly described in the scientific literature. The documents supporting OMV’s IA represented the most detailed assessment of the region’s ecological characteristics at that time.
The 2019 Benthic Baseline / Tāwhaki‐1 Pre‐drill Survey (refer to Beaumont et al., 2019), conducted as part of the IA, provided evidence of a diverse benthic epifauna across three broad habitat structures, including several sensitive environments as defined by Schedule 6 of the EEZ and Continental Shelf (Environmental Effects – Permitted Activities) Regulations 2013. The survey also identified at-risk and threatened species within the project area. Three key sensitive environments were recorded:

  1. A brachiopod bed at a seamount.
  2. Branching stony coral thickets at multiple seamount sites.
  3. Xenophyophore beds across eleven sites.

Additionally, the survey documented the presence of taxa protected under Schedule 7A of the Wildlife Act 1953, including:

  • Black corals (Antipatharia).
  • Gorgonian corals (Gorgonacea).
  • Stony corals (Scleractinia).
  • Hydrocorals (Stylasteridae).

Given these findings, the decision-makers required further information to ensure an adequately informed decision. This additional information was sourced from two main avenues:

  1. Reports commissioned and expert advice sought under Section 56 of the EEZ Act.
  2. Further information requested from OMV under Section 54(1) of the EEZ Act.

These inputs were essential in assessing the application and establishing appropriate conditions for the proposed activities.

Expert Reviews and Information Gaps
External experts largely concurred with OMV’s assessment of environmental risk but identified several information deficiencies, particularly regarding the IA’s risk rankings for benthic environments and sensitive habitats [11].

Given the identification of sensitive environments, the decision-makers commissioned a detailed expert review of OMV’s proposed mitigation measures. The review concluded that while the mitigation, management, and monitoring measures outlined in the IA were generally appropriate, several caveats required further attention. These concerns were recorded in the EPA Conditions Report (refer to EPA, 2019a), which advised that pre-drill surveys and mitigation measures should be explicitly encoded in consent conditions. The report further recommended that an Environmental Management Plan (EMP) be established to outline pre- and post-drill monitoring requirements, ensuring that the EPA could review consent conditions under Section 76 of the EEZ Act if necessary.

To provide flexibility for incorporating new monitoring approaches or technologies, the report advised that the EMP should be certified by the EPA before any activities (other than drilling at Tāwhaki-1 commenced). The recommended conditions also included requirements for pre-drill surveys, notifications, and reporting at each well site.

The Final Decision
After considering all available information, the decision-makers reviewed the mitigation framework and reassessed the proposed consent conditions to ensure the integrity of marine benthic species, ecosystems, and processes (including protected species) in the EEZ. This resulted in the adoption of a conservative approach, particularly regarding activity thresholds and environmental monitoring requirements.
OMV accepted these conditions, recognising the presence of sensitive environments and agreed to adopt a precautionary approach. For example, where a sensitive environment was identified, its proximity to the well site was modelled using a deposition model to determine whether it fell within the newly established conservative threshold zone.

Following a comprehensive and iterative decision-making process, the decision-makers, relying on the best available information and fulfilling their obligations under the EEZ Act, granted the consents on 16 December 2019 (EPA, 2019b). The final consents included a range of conditions designed to avoid, remedy, or mitigate the environmental effects of the proposed activities, as required under Section 59(2)(j) of the EEZ Act.

In making their decision and setting the consent conditions, the decision-makers carefully considered:

  • The extent to which conditions could mitigate adverse environmental effects.
  • The environmental effects outlined in the IA.
  • The findings of expert reports and reviews.
  • The conditions proposed by OMV and their adequacy in addressing identified risks.
  • The recommendations contained in the EPA Conditions Report.

The decision-making process also incorporated inputs from the EPA’s Māori Advisory Committee, Ngā Kaihautū Tikanga Taiao (NKTT), and invited further comments from OMV regarding proposed conditions. This ensured that the final decision was based on a robust, science-based assessment that adhered to the principles of the EEZ Act, particularly the requirement under Section 61 to use the best available information without unreasonable cost, effort, or delay.

Conclusion
The GSB case study highlights the critical role of the IA in the EEZ consenting process. The comprehensive environmental assessments conducted as part of the IA provided the foundation for identifying sensitive environments, refining risk assessments, and shaping consent conditions. The iterative process of information gathering, through expert reviews, further information requests, and stakeholder engagement, ensured that the decision-makers had sufficient information to make an informed decision. This case underscores the importance of a well-prepared IA in supporting a transparent, scientifically rigorous decision-making process that aligns with the EEZ Act’s environmental protection objectives.


Footnotes
[1] Ministry for the Environment, Environment New Zealand 2007 (Ministry for the Environment, Wellington 2007) (hereinafter, Environment New Zealand 2007) at p. 316
[2] Section 88(2)(b) of the RMA 1991
[3] Note that evaluation reports and reports to local authorities under sections 32 and 42A of the RMA, respectively, also serve a similar purpose to an IA under the EEZ Act.
[4] Section 4 of the EEZ Act 2012, Definitions: Environment.
[5] Sustainable Management has been defined in the EEZ Act 2012 in section 10(2)
[6] Section 56 and 54 of the EEZ Act 2012.
[7] Note that Conditions Reports are compulsory for notified applications.
[8] Under clause 1 of Schedule 4 of the EEZ Act the EPA must prepare or commission a KIR relating to the activity and the application.
[9] Section 61 of the EEZ Act 2012.
[10] Refer to Section 39 of the EEZ Act 2012.
[11] Other deficiencies pertaining to the assessment of effects related to the risk ranking used in the IA included:
a) Effects on mammals and seabirds from the presence of the MODU; b) Lack of seismic assessment; c) Lack of detail regarding cumulative impacts; and d) Subjectivity regarding the magnitude of effect.


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