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Sei Whale (Balaenoptera borealis)

The sei whale is a baleen whale recorded in Australian Antarctic and Commonwealth waters, and infrequently off Tasmania, New South Wales, Queensland, the Great Australian Bight, the Northern Territory and Western Australia. It is an offshore, deep-water species, making offshore marine habitat relevant to works.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

South Australia, National Parks and Wildlife Act 1972: Vulnerable.

Western Australia, Biodiversity Conservation Act 2016: Endangered.

Commonwealth, EPBC Act 1999: Listed migratory. Listed migratory species are a matter of national environmental significance, so a significant impact needs referral.

Seasonal planning

In the Southern Hemisphere, breeding usually occurs from April to August, peaking in June.

Seasonal evidence: From published sources for this species.

Timing varies between sites and years.

  • Breeding season: In the Southern Hemisphere, breeding usually occurs from April to August, peaking in June.

Identification: Appearance

The sei whale has a dark blue-grey upper body, a pale underside, a tall steep dorsal fin towards the rear of its back and a prominent ridge on its snout. It has baleen plates rather than teeth.

The sei whale has a dark blue-grey upper body, a pale underside, a tall steep dorsal fin towards the rear of its back and a prominent ridge on its snout. It has baleen plates rather than teeth.

Identification: Confirming identity

Confirm the identity of any suspected record with a specialist and a photograph or voucher, as required by the relevant permit.

Distribution: Known range

Sei whales occur in Australian Antarctic Territory and Commonwealth waters, with infrequent records off Tasmania, New South Wales, Queensland, the Great Australian Bight, the Northern Territory and Western Australia. In summer they are found north of the Polar Front, sometimes as far north as Tasmania, and occasionally feed in the southernmost navigable Antarctic waters.

Sei whales occur in Australian Antarctic Territory and Commonwealth waters, with infrequent records off Tasmania, New South Wales, Queensland, the Great Australian Bight, the Northern Territory and Western Australia. In summer they are found north of the Polar Front, sometimes as far north as Tasmania, and occasionally feed in the southernmost navigable Antarctic waters.

Distribution: National mapping

The Commonwealth species distribution model (SNES) maps where the species or its habitat is known, likely or may occur. Use it with local records and site inspection.

Habitat: Habitat

Sei whales are primarily found in deep-water oceanic habitats and are rarely seen near the coast. They can be found at the surface or diving to a few hundred metres.

Sei whales are primarily found in deep-water oceanic habitats and are rarely seen near the coast. They can be found at the surface or diving to a few hundred metres.

Foraging habitat: Diet

Their food includes plankton such as copepods and krill, small schooling fish and squid. They feed by gulping and skimming.

Their food includes plankton such as copepods and krill, small schooling fish and squid. They feed by gulping and skimming.

Breeding habitat: Breeding

Winter breeding areas are unknown but are thought to be in deep tropical waters. A single calf is born after a pregnancy of about 11.5 months, and females are reported to breed every two to three years.

Winter breeding areas are unknown but are thought to be in deep tropical waters. A single calf is born after a pregnancy of about 11.5 months, and females are reported to breed every two to three years.

Sheltering habitat: Shelter

Not documented in the published sources used for this profile.

Not documented in the published sources used for this profile.

Threats: Threats

Human impacts identified for sei whales include chemical and noise pollution, ship strikes and entanglement in fishing gear.

Human impacts identified for sei whales include chemical and noise pollution, ship strikes and entanglement in fishing gear.

Threats: Works risk

Vessel activity may harm sei whales through ship strikes and noise pollution. Entanglement in fishing gear is also identified as a human impact.

Survey methodology: 1. Commonwealth guidance

Use methods consistent with the Commonwealth survey guidelines and engage a specialist with the right permits.

For EPBC Act referrals, survey effort and methods should be consistent with the ePBC Act publications, including the National Guidelines for the Survey of Cetaceans, Marine Turtles and the Dugong (2024), read with the Significant impact guidelines 1.1.

Survey methodology: 2. Limits

A non-detection is not proof of absence. Match survey timing to the species and season, and record effort.

Vegetation associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific vegetation association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Ecosystem associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific ecosystem association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Soil and substrate associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific soil association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Water and wetland associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific water association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Fauna records and mapped habitat: Not yet analysed

Record locations can be overlaid with mapping, but record frequency alone does not measure habitat preference. No species is excluded from desktop assessments by this analysis.

No quality-controlled record-to-map analysis has been completed for this species. The existing generalised distribution dots and indicative range polygons have not been treated as precise occurrence coordinates.

A defensible run needs dated, independently attributable records, coordinate uncertainty, duplicate and captive-record checks, layer versions and regional scope. Preference and absence require additional survey-effort and detection evidence.

Habitat limitations and contrary evidence: No supported exclusion recorded

Not recorded is not the same as cannot occur. Low suitability, resident habitat, breeding habitat and occasional movement are different conclusions.

This library has not established a vegetation, ecosystem or soil-type exclusion for this species. This does not mean all habitat is suitable; the evidence needed to justify an exclusion has not been assembled.

Habitat limitations and contrary evidence: Before using a negative association

  • Confirm the taxon, geographic region, life stage and habitat function covered by the evidence.
  • Check survey methods, season, repeated effort and detectability before interpreting non-detection.
  • Investigate credible contradictory records and microhabitats absent from broad mapping.
  • Do not convert a missing map class, low record count or failed data request into species absence.

Before disturbance: 1. Desktop and approvals

Confirm whether the project could affect the species before works begin.

Check national mapping, state records and recent surveys for the site. An action likely to have a significant impact on this nationally listed species needs EPBC Act referral, and state permits apply where it is state listed.

Before disturbance: 2. Plan to avoid

Plan in-water works, vessel movements and lighting to avoid known habitat and sensitive periods, and set observer and shutdown procedures before works start.

During disturbance: 1. Controls

Keep works inside the approved footprint and conditions.

Use spotters and exclusion zones for in-water works and vessels, and pause works if the species is seen within the zone.

During disturbance: 2. Stop and report

If the species is found unexpectedly, stop work at that spot and contact the project ecologist and the relevant agency.

After disturbance: 1. Records

Record outcomes.

Record sightings, habitat lost or retained and any injury or death, and report them under the approval conditions.

Rehabilitation: 1. Restore

Restore disturbed habitat where possible.

Remove temporary structures, restore natural flow and substrate, and monitor water quality until it returns to baseline.

Sources