Toxic Rotting Fish Nearly Killed Three Crewmembers on Australian Longliner
Marine investigators in New Zealand are yet again highlighting the dangers that fishing vessel crews continue to face from toxic gas associated with rotting catch, following a near-fatal incident aboard an Australian-registered vessel in February last year.
The warning comes after the Transport Accident Investigation Commission (TAIC) released its report on an incident aboard the Antarctic Discovery, in which a routine maintenance job quickly spiraled into a life-threatening emergency. Four workers were exposed to hydrogen sulfide (H2S), a colorless, flammable and highly toxic gas that is a byproduct of decaying fish. All four were hospitalized, and all recovered.
Purchased by Australian Longline in 2015, the Antarctic Discovery is a 55.3-meter longline fishing vessel that regularly operates in the Southern Ocean, fishing for Patagonian and Antarctic toothfish. Investigators established that in early January 2025, the vessel had completed a Southern Ocean voyage and was returning to Nelson, New Zealand, to discharge its catch and undergo maintenance.
On January 3, the crew discovered that the overboard discharge valve for the offal pump was blocked or seized, preventing them from pumping offal directly overboard. A temporary fix was made before the vessel sailed to the Port of Lyttelton for dry dock maintenance, with various repair and maintenance tasks beginning on February 10.
On February 21 at about 0900, two apprentice fitters descended a ladder into the vessel's confined bow thruster machinery space to reinstall pipework for the anchor chain lockers. The pipe components were tucked behind a tank holding a mixture of decaying fish offal and seawater, immediately adjacent to the control panel and start/stop buttons for the offal pump.
While performing the task, one of the fitters may have accidentally pressed the pump's unlabeled start button. About 30 minutes later, the fitters noticed water raining down on them from the open end of a hose at the top of the access ladder. The flow quickly increased and began to take on a foul odor. They decided to vacate the space, climbing the ladder against the flow of water to exit into the forecastle and then out onto the open deck, where they made their way to the bridge to inform the vessel's second engineer.
Toxic gas was by then building up below. Concerned, the vessel superintendent went below to investigate and was briefly overcome by the gas while attempting to enter the forecastle, but managed to retreat. The chief engineer and second engineer entered the forecastle through another entrance to investigate the source of the liquid, and both collapsed. The second engineer regained enough consciousness to crawl to safety, while the chief engineer was rescued by crewmembers using breathing apparatus.
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The incident aboard the Antarctic Discovery was not the first time fishing vessel crews had been exposed to the gas. Over the past three decades, there have been several documented cases involving fishing vessels in which H2S was considered a cause of, or a contributing factor in, 23 deaths and 37 injuries.
Following the release of the report, TAIC issued recommendations that include a direction to Australian Longline to obtain appropriate approval for proposed modifications to all safety-critical systems before carrying out any work. Lyttelton Port Company was also directed to put measures in place to enhance dry dock safety.
