Source: The Conversation (Au and NZ)
Rich Pillans/CSIRO Around the world, ocean warming is causing fish to move polewards in search of cooler water. But what if you’re a tiny prawn, barramundi or rare sawfish in a northern Australian gulf and your exit southwards is blocked by land?
To date, there’s been a global gap in understanding how shallow tropical gulfs and bays are responding to climate change. These marine environments are vital for nature, fisheries and coastal communities. However, their conditions are becoming more extreme and variable due to cumulative climate change.
Species are riding an environmental roller coaster, with the rapid changes hindering their recovery. Some of the world’s most populous countries – and unique species – are in the tropics. Lessons from remote northern Australia can prove insightful.
Our new research focuses on these unique Australian ecosystems and highlights their importance and complexity. It takes into account land barriers, the monsoonal climate, influence of cyclones and massive variability in sea levels.
Northern Australian seas are unique To help unravel the complex dynamics of these systems, our team drew on the CSIRO’s 50-year history of research in northern Australia, focused on the Gulf of Carpentaria, Joseph Bonaparte Gulf and Torres Strait.
Northern Australia has many seagrasses and mangroves, and is a stronghold for threatened species such as sawfish, dugongs, turtles and the snubfin dolphin. We analysed climate influences on popular fishing species, such barramundi, mud crabs and lobsters, as well as Australia’s largest and most valuable prawn fishery, the Northern Prawn Fishery.
And we discovered ocean temperature isn’t the only important indicator of climate change. Our research showed these marine systems are influenced by compounding climate events in complex ways, which can be simplified into four primary factors to explain how, why and when species are affected.
We found combinations of extreme temperatures, exposure to dehydration, cloudiness in the water (turbidity) and hydrologic disconnection – the restriction or changes to the natural movement of water – combined to bolster some populations while devastating others.
These patterns of change are largely influenced by El Niño or La Niña weather events. Species are riding more extreme climate rollercoasters, with steeper and larger changes in the marine environment hindering their recovery.
A good example is the brown tiger prawn.
The Goldilocks prawn The original impetus for our research was to understand why present-day brown tiger prawn populations in northern Australia had not bounced back to levels seen before the turn of the century, despite reduced fishing.
This region is the only place they exist. We called them the “Goldilocks” prawns because they like ocean conditions that are just right – not too hot or too cold. Furthermore, earlier research showed juvenile brown tiger prawns are very fussy about the kinds of seagrass they use for shelter and food.
Our research found strong evidence of a major step-change in physical conditions around 1998 or 1999. Specifically, there were more La Niñas over the past two decades, higher than average freshwater flows, including from the Roper River, and increased cyclone intensity.
Cyclones cause massive seagrass damage, while sediment from flooding rivers limits seagrass growth. This means reduced nursery habitat for the brown tiger prawn already under pressure from rising temperatures. Our modelling found a sustained decrease in brown tiger prawns connected to a shift in climate patterns.
By contrast, the more robust grooved tiger prawns were not similarly affected, and common and redleg banana prawns thrived in response to good river flows. In fact, Redleg banana prawns, sawfish and mangroves are at risk during El Niño periods, when dry weather and lowered sea levels disrupt the river-ocean connections they rely on.
Why this matters Climate change is playing out differently in northern Australia to the rest of the country. This new research will help us anticipate, prepare for and respond to compound climate events – when multiple weather or climate conditions interact with severe environmental consequences.
For example, fisheries could switch between tiger and banana prawns depending on environmental conditions. Conservation teams could benefit from knowing in advance how extreme climate events threaten species such as the endangered largetooth sawfish. Globally, better waterway management is needed, because taking too much water out of river systems threatens downstream ecosystems and marine livelihoods.
An extreme El Niño is forecast for later this year. Our work offers insights into its potential impacts across these marine environments and helps ecosystem and fisheries managers prepare. CSIRO researchers studied mangroves and collected seagrass samples in Australia’s Gulf of Carpentaria to help understand how compound climate events are influencing tropical ecosystems.
Rob Kenyon/CSIRO
Éva Plagányi works for CSIRO which receives funding from several sources, including the Fisheries Research and Development Corporation (FRDC) and the Australian Fisheries Management Authority (AFMA).
She is a scientific member of the Northern Prawn Fishery (NPF) Resource Assessment Group. Éva acknowledges NPF stakeholders as well as Torres Strait Traditional Owners who depend on these natural resources, and she acknowledges and pays respect to the Traditional Owners on whose country this research was conducted.
She is an editorial board member for Fisheries Research and an Associate Editor-in-Chief of Ecological Applications.
Laura Blamey works for CSIRO which receives funding from several sources, including the Fisheries Research and Development Corporation (FRDC) and the Australian Fisheries Management Authority (AFMA).
Laura is a scientific member of the Torres Strait Tropical Rock Lobster Resource Assessment Group and Working Group.
Laura acknowledges stakeholders from the Northern Prawn Fishery as well as Torres Strait Traditional Owners who depend on these natural resources, and she acknowledges and pays respect to the Traditional Owners on whose country this research was conducted.
Laura is an assistant editor at the Journal of Fish Biology.
Original source: https://analysis1.mil-osi.com/2026/06/11/climate-change-is-causing-fish-to-move-to-cooler-water-but-what-if-their-escape-route-is-blocked/