Marine Heatwaves

Like heatwaves on land, marine heatwaves (persistent or continual above average ocean temperatures) can harm plants, animals and the environment.

Some waters around the coast of Tasmania are currently experiencing marine heatwave conditions, which started developing around September 2023. There are actions the community, industry and NRE Tas can take to reduce the impact of these events.​

​​Update on marine​​ heatwave status

​The anomaly remains concentrated in Bass Strait and off the south western side of the Tasman Peninsula. There appears to be cooler than usual waters along the south west and west coasts, and the same in offshore waters north east of the Furneaux Group and off the east coast.

According to the BOM forecast (the Sea Surface Temperature Anomaly Outlook), it is likely that the sea surface temperature anomaly will persist in some form in waters around Tasmania over the next few months—so potentially a warmer than usual winter. Go to Ocean Temperature Outlooks ( for the most up to date forecast.

According to the NASA JPL data as of 20 May:

  • NEW – Bass Pyramid, Deal Island and Wright Rock have been categorised as Moderate with the MHW duration in these locations now at 16 days.
  • NEW – Central North Coast, NW King Island and South West Island, have been categorised as Moderate with the MHW duration in these locations now at 13 days.
  • UPDATE – Wedge Island remains categorised as Strong with the MHW duration in this location now at 72 days.
  • UPDATE – Rocky Cape remains categorised as Strong with the MHW duration in this location now at 26 days.
  • UPDATE – Table Cape remains categorised as Moderate with the MHW duration in this location now at 35 days.
  • UPDATE – West Head remains categorised as Moderate with the MHW duration in this location now at 29 days.

All other areas remain categorised as Normal. This means the anomaly has not met the criteria for a MHW in these areas — i.e., ocean temperatures remain above the normal range for an extended period of five or more consecutive days.

The duration of areas where the MHW has moved to Normal conditions since the last update can be found in Table 1. 

​Abalone Block #
​Area Description
MHW start​
​MHW end
​Max Catrgory


NE King Island​



​12 days



​SW King Island



​6 days



​North D’Entrecasteaux



​11 days



​East of Bruny Island



​69 days






​12 days



​Maingon Bay



​57 days


​5 days
​7 days
​16 days
​St Helens
​8 days
​Eddystone Point
​6 days
​8 days
​5 days
​Ninth Island
​16 days
​Stony Head
​31 days
​Central North Coast
​30 days

Table 1: Areas around Tasmania where MHW conditions have now ended since the last update. Commercial abalone blocks are used as a proxy for areas. The NASA JPL data in this table is correct as of 21 May 2024. *Please note areas where the end date is within two days of the dataset date are subject to change, for if there is a period of two or less days where the anomaly has dipped below the threshold before it moves above it again then it is still considered to be the same event. If the anomaly drops below the threshold for more than two days, then that MHW event ends.

The map below shows the SST anomaly overlayed with the marine heatwave severity category (the coloured dots) at a one kilometre resolution (NASA JPL). The marine heatwave severity category dots on this map align with the commercial abalone fishing blocks.

Sea surface temperature anomaly and marine heatwave severity around Tasmania (21 May)

Sea surface temperature anomaly and marine heatwave severity around Tasmania (21 May)

​You can find a more detailed marine heatwave status update here:

 MHW status update - no. 23 (23 May 2024) 

Actions you can take

During marine heatwaves you should:

  • ​Be cautious when eating or using wild caught seafood - Harmful algal blooms (including paralytic shellfish toxins) and diseases are more common during marine heatwaves, which can increase your risk of getting sick from eating wild caught seafood. Visit the Department of Health's website for advice and current public health alerts.
  • Be vigilant about biosecurity - Diseases, like abalone viral gangleoneuritis (AVG) and vibrio, are more common during marine heatwave events. To prevent the spread of disease:
    • ​Wash down boats, fishing and dive gear when moving between areas. 
    • If you catch your own bait, source it from the same area where you fish.
  • Report signs of marine heatwaves - ​By reporting marine heatwave signs, you can help NRE Tas respond to and reduce heatwave impacts on the environment, industry and the community. See below for more detail.

Signs of a marine heatwave

​​During a marine heatwave, you may see:​

  • Fish and shellfish (including abalone, rock lobster and scallops) becoming sick or dying (e.g., sluggish or wasting animals, unusual piles of shells, discoloured or poor meat).
  • Changes to seagrass beds, kelp forests and other marine habitats.
  • Unusually large numbers of fish dying (and more rarely, birds, seals, dolphins, or whales). This may be due to increased biotoxins from harmful algae (known as an unusual mortality event).
  • Tropical or warmer water fish being seen in Tasmanian waters.​

Where to report signs of a marine heatwave

If you see signs of a marine heatwave, please report them. Your observations are crucial for helping us respond to and reduce the impact of marine heatwaves.

If you can, take photos of anything you see that may be an impact from a marine heatwave event to include in your report.

​Heatwave sign
​Where to report
Suspected disease emergency
(e.g. large numbers of dead or dying animals)
​Call the 24-hour Emergency Disease Hotline on 1800 675 888
For more information go to Animal Health Laboratory | NRE Tasmania
Sick, dying and dead marine mammals and seabirds​Call the Marine Wildlife Hotline on 0427 942 537. Time is critical during a rescue attempt, or for testing deceased animals to determine the cause.
For more information go to Marine Mammal Incident Response | NRE Tasmania
Mass fish kills
(take photos if you can)
​Call the EPA Incident Response Hotline on 1800 005 171, or email to
In order to minimise potential risk to yourself if you see a fish kill do not:
  • Touch the fish or water in the area.
  • Collect fish for bait or other purposes (such as garden fertilisers).
  • Consume any fish that have been caught in the area.
For more information go to Fish and Fish Kills | EPA Tasmania
​Small numbers of sick, dying and dead fish (including shellfish, crustaceans and other marine molluscs)​Call Biosecurity Tas (during office hours) on 03 6165 3777, or complete the online form to Report Signs of a Marine Heatwave.
Do not collect samples for testing unless directed to by Biosecurity Tasmania.
​Observed impacts on the threatened Maugean skate or handfish​Email to and provide as much detail as possible. The recovery teams for Maugean skate or handfish will be notified.
​Warm water species outside their normal range​Contact Redmap or make a report on the Redmap app (download from Google Play or the App Store).
​Other, non-urgent observations​Use the online form to Report Signs of a Marine Heatwave.
Do not use the online form to report marine mammals and seabirds.
Algal blooms may also be more common during marine heatwaves. Most blooms that are visible to the human eye are not dangerous and do not need to be reported. Blooms of Noctiluca (also known as a red tide) maybe highly visible, but are not regarded as harmful to humans and are only slightly toxic to fish. Large blooms are best avoided for recreational swimming because of possible skin irritation. For further information please visit Derwent Estuary Program - Red Tide Algal Blooms.

What is a marine heatwave?

A marine heatwave is when the ocean is unusually hot to a significant depth for a number of days, weeks, months or even years.

Marine heat waves can mean warmer waters for swimming and new species of fish in our waters, such as more yellowtail kingfish and tropical species like mahi mahi and marlin. They can also have harmful impacts on ocean-dependent industries like fishing and aquaculture, and recreational fishing.

The image below shows the Bureau of Meteorology’s sea surface temperature anomaly forecast maps for Victoria and Tasmania. The larger the anomaly, the warmer sea surface temperatures are than average for this time of year.

Bureau of Meteorology sea surface temperature outlook (27 April)

Bureau of Meteorology sea surface temperature outlook (27 April)

​Preparing for a marine heatwave

Fisheries and aquaculture are key industries for Tasmania, and recreational fishing plays a prominent role in lifestyle of nearly 1 in 4 Tasmanians. 

We’re working with research organisations and industry to develop a Tasmanian Marine Heatwave Response Plan. This includes actions government can take to boost fisheries resilience and promote recovery.  

We’re also researching the potential effects of a MHW on fish. For instance, this summer we will conduct a vibrio study, sampling three harvest areas (Moulting Bay, Great Swanport and Boomer Bay) weekly for four months to determine if environmental factors driving vibrio risk change during periods of a MHW event. This work is to determine where outbreaks occur and model risk profiles to predict where future outbreaks may occur. 

After the summer, we will assess the impacts, management approach and best practice for future MHWs.

More information

CSIRO Climate Change Adaptation Handbook

Marine Heatwave Information Sheet

Frequently asked questions

Are marine heatwaves part of climate change?

Marine heatwaves compound the damage being caused by long-term warming of the ocean. We already know that Australia’s marine ecosystems are expected to have some of the largest climate-driven changes in the Southern Hemisphere. 

We also know that over 100 Australian marine species have started migrating south towards cooler southern waters, including to Tasmania. These changes in distribution, abundance and species composition in our ecosystems mean that Australian fisheries are already being affected by climate change.  

One example of this is the long spined sea urchin migrating from its native habitat in NSW to the warming waters off the east coast of Tasmania, creating urchin barrens which affect kelp forests, and abalone and rock lobster habitats.

What causes marine heatwaves?

Like heatwaves over land, heatwaves in the ocean occur due to a range of factors, including ocean currents and the warming of the ocean surface from the atmosphere.

Climate drivers, like El Niño, are known to impact the frequency, intensity and duration of marine heatwaves. An El Niño has been declared by the Bureau of Meteorology and is underway.   

What research is being done on marine heatwaves?

There is a lot of research being done on marine heatwaves. For instance, the CSIRO are working on forecasting marine heatwaves and preparing for marine heatwaves.

Where can I learn more about marine heatwaves?

Learn more about marine heatwaves from the Bureau of Meteorology, the CSIRO and the Fisheries Research and Development Corporation.

CSIRO and the Bureau of Meteorology are sharing their knowledge through Fisheries Climate Briefings in conjunction with the Fisheries Research and Development Corporation.

View a global map of current oceans with the Marine Heatwave Tracker or the CSIRO/BOM Ocean Currents.

Can marine heatwaves cause disease in marine mammals and seabirds?

In other parts of the world, past marine heatwaves have seen unusual mortality events. Unusual mortality events have included a mass die-off of marine mammals or fish. If there is an unusual mortality event in Tasmania, there are a variety of channels to make a report. Reporting helps us investigate and take any further action (such as issuing a public health alert) and it may help us understand why an event occurred.


Level 3, 134 Macquarie St
GPO Box 44
Phone: (03) 6165 3233, 1300 720 647


Fishwatch Report illegal fishing

0427 655 557

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Contact us

Recreational Fishing

Level 3, 134 Macquarie St

Hobart TAS 7000

Phone: (03) 6165 3233, 1300 720 647


Commercial Fisheries

Level 3, 134 Macquarie St

GPO Box 44

Phone: (03) 6165 3000, 1300 368 550


Commercial Fisheries Licensing

Level 1, 134 Macquarie St

GPO Box 44

Phone: (03) 6165 3000, 1300 368 550