Fish stocks off icy Heard Island bounced back when illegal fishing stopped and sustainable fishing continued
- Written by The Conversation
In the middle of the Southern Indian Ocean lies a vast underwater volcanic ridge known as the Kerguelen Plateau. At its centre sits Australia’s most remote territory: Heard Island and McDonald Islands. These icy outposts about 4,100km southwest of Perth are home to Australia’s only active volcanoes.
These isolated islands are a biodiversity hotspot. Seals and penguins abound on rocky beaches. Underwater, seabed fish species have evolved antifreeze-like compounds in their blood to cope with near-freezing temperatures.
Isolation doesn’t mean protection. The discovery of many dead elephant seal pups on Heard Island suggests highly pathogenic avian influenza may have arrived. For years, the rich fisheries around these islands were targeted by illegal fishers hunting for the sought-after Patagonian toothfish.
There is good news. Our new research has found increasing numbers of fish species and wider distributions around Heard and McDonald Islands. While it’s difficult to pinpoint the exact drivers of these increases, we believe it’s a combination of factors: the removal of illegal fishing, changes in fishing practices to reduce bycatch, a long-established marine reserve, and possibly climate-driven increases in ocean productivity.
Fish communities rebounding
The undulating terrain and nutrient-rich waters washing up from 4,000m deep onto the Kergeluen Plateau have helped make this area a hotspot for fish species.
Before Australia established an exclusion zone around the islands, the region was heavily targeted by international trawlers likely causing significant damage to many forms of life on the seafloor.
In the 1990s, illegal fishers using longlines targeted these waters for the high-value toothfish and large catches of species such as marbled rockcod. By the early 2000s, illegal, unreported and unregulated fishing was stamped out due to joint surveillance efforts by Australian and French authorities. France controls the Kergeluen Islands 450km away. The waters are now monitored by satellite.
Historically, authorised fishers also relied on trawling to catch toothfish. In 2003, the fishing industry began shifting to longline methods for catching toothfish which has likely benefited seafloor habitats, bycatch species and fish communities. Today, trawling efforts in the region are much reduced outside a small fishery for mackerel icefish.
The toothfish is sought after by top restaurants around the world and the area has a well-managed and lucrative toothfish and mackerel icefish fishery considered sustainable. Only 2,120 tonnes can be taken a year under catch limits set by the Australian Fisheries Management Authority.
A no-take marine reserve was declared over some of the waters around Heard and McDonald Islands in 2002 and expanded in 2014. This is also likely to have contributed to the increase in fish communities. In January 2025, the Australian government significantly expanded the size of the reserve, including no-take, habitat protection and national park zones. This should further boost protection.
The region’s remoteness, harsh conditions and ocean depth make it very difficult to study how fishing and climate change affect fish communities.
The data we used in our research comes from a long-term monitoring program conducted by fishers and managed by the Australian government. Every year since the late 1990s, a fishing vessel undertakes a number of short trawls at different depths. The presence and abundance of different species is recorded.
We used contemporary statistical approaches to model the entire dataset, examining how all seabed fish species respond to factors such as water temperature, depth, climate and marine reserve status.
Our analysis of data from 2003–16 found that despite a warming ocean, bottom-dwelling fish numbers have broadly increased. This includes species more likely to be caught as bycatch in fishing nets, such as Eaton’s skate, grey rockcod and deep-water grenadier species. Strikingly, the number of species in a single sample more than doubled over a 13 year-time period.
What’s next?
This area is a climate change hotspot. Major ocean currents such as the Polar Front are changing and water temperatures are rising. These changes are boosting production of phytoplankton, the microscopic floating plants that underpin food webs. We don’t know yet if this is another reason fish distributions are changing, and we don’t know what rising water temperatures will mean for polar-adapted fish species.
This year, the Australian research vessel RSV Nuyina will visit the Heard and McDonald Islands twice for research such as surveying marine ecosystems to inform fisheries management. For researchers, the next step will be to build broader collaboration with French researchers, fishers and fishery managers to better track changes to ecosystems across the entire Kerguelen Plateau.
We can’t definitively say these species have fully recovered, as we don’t know the distribution and abundance of these species before human pressure began. But overall, our research is good news. It suggests fish species under pressure can recover strongly and that management methods are working.
