Study reveals horrific scale of Indonesian bomb fishing

AI acoustic monitoring has revealed the scale of bomb fishing, also known as blast fishing, in one of the world’s most biodiverse marine regions, according to a new study.

Researchers monitoring the Spermonde Archipelago off the southwest coast of Sulawesi, Indonesia, detected 3,567 bomb fishing incidents from nearly 3,700 hours of underwater recordings collected between May 2023 and September 2024.

Bomb fishing, or blast fishing, uses improvised explosives to stun or kill fish, which can then be easily caught as they float to the surface.

Although illegal, the practice has been documented in at least 34 countries and is particularly associated with tropical coral reefs.

Repeated blasting can destroy shallow coral reefs, reducing the entire structure to rubble – something many scuba divers will have seen at dive sites in Indonesia without realising its significance.

The team, led by Ben Williams of the Zoological Society of London (ZSL), used low-cost HydroMoth acoustic microphones together with a machine-learning system called BombDetect to detect explosions in the recordings.

The system was able to detect blasts from around 17km away, and recorded an average of 23.14 incidents per day – in other words, nearly one bomb blast every hour.

The researchers estimated around 8,446 blast fishing incidents occurred during a single year, with up to 17 hectares of reef damaged by the practice.

‘The sound of bomb fishing is so loud that if you’re on a dive it can shake you out of your skin,’ said Williams. ‘You feel it more than you hear it, but if you put your head up on the surface, you likely won’t even see the boat responsible because the sound of bomb fishing travels such a huge distance underwater.’

Bomb fishing occurred throughout the study period and showed clear daily and weekly patterns. Most (around 75 per cent) of the incidents were during the day, peaking between 9 am and 10 am.

Without the new technology, Williams said it has been difficult to establish how widespread the practice actually is.

‘We know bomb fishing has been an issue in this archipelago and many others around the world,’ he said, ‘but the challenge has been, we don’t really know to what extent it goes on.

‘It could be a few bombs get dropped a month; it could be hundreds. This is the first time we’ve got real tangible counts of this.’

Dr Tim Lamont of Lancaster University, who was part of the research team and a co-author of the study, described the findings as ‘horrifying’.

‘It’s horrifying to discover that bomb fishing is still so prevalent in places like this – it causes so much destruction in globally important biodiversity hotspots,’ he said. ‘But the technology developed in making this discovery is also an encouraging proof of concept.’

The BombDetect algorithm reduced the amount of audio that needed to be reviewed by a human by more than 50 times.

The researchers say that the software, coupled with the HydroMoth recorders which cost less than $150 each, could be adapted to identify bomb fishing hotspots and support targeted patrols and intervention.

‘Now it’s possible to automatically detect bombs with low-cost equipment, it opens the door for strides forward in monitoring and enforcement,’ said Lamont. ‘This technology could really help in the fight to end bomb fishing around the world.’

Williams said enforcement at sea alone was unlikely to be sufficient, as although it’s easy to hear the blasts, it’s difficult to target precisely where the bomb was dropped, and by whom.

‘It’s like whack-a-mole targeting the bomb fishers,’ he said. ‘The best approaches should tackle the illegal supply chain that gets the materials needed to make explosives to bomb fishers or sellers of these.’

The Spermonde Archipelago has lost 76.26 per cent of its live coral cover over the past 30 years, according to research cited in the paper.

Bomb fishing has been identified as the primary driver of that decline, although Williams cautioned that the new results were ‘not the smoking gun’ but provided ‘strong evidence that bomb fishing is the primary cause of reef loss in this area’.

The study, ‘Widespread Bomb Fishing in Indo-Pacific Archipelago Revealed Through Machine Learning Accelerated Passive Acoustic Monitoring’, by Ben Williams et al, is published under an open-access licence in Remote Sensing in Ecology and Conservation.

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