RPS ocean data opens door for sustainable management of whale remains offshore

While death is never a nice thing to talk about, it’s an important part of nature’s cycle.

In the ocean, a single whale carcass becomes a substantial source of nutrients for fish, birds, sharks and other marine species, who work together to break down the body and return its nutrients to the sea.

Most whales die offshore. But sometimes their bodies end up on the beach, and local authorities must work quickly to remove the carcass. Usually, this involves burying the remains on the beach, or moving them to a landfill or composting facility.

While these disposal strategies do work, they also pose challenges. Heavy machinery and disturbance of the beach environment is one problem, as are concerns about disease transmission, smell, the risk of groundwater contamination, and the attraction of (particularly non-native) scavengers.

Another option for disposal is towing whale remains to deeper waters offshore for a process of ‘assisted’ natural decomposition with the help of marine life, far away from shipping lanes, beach zones, and coastal communities. Offshore disposal is generally considered to be the most ethical and culturally sensitive way to deal with deceased whales. But to make this option viable, you need to be sure the remains won’t wash back ashore before they break down or create a navigational/safety hazard for vessels.

Is it even possible to predict a deceased whale’s drift with accuracy and avoid these risks? RPS' ocean science and technology team had the opportunity to test this in 2023 via a remotely monitored drift and predictive modelling exercise, in partnership with Griffith University and Sunshine Coast Council.

A drift study, backed by decades of ocean data science

On Sunday 16 July 2023, a 14 metre humpback whale carcass was first sighted off Noosa Heads on Queensland’s Sunshine Coast. When it was resighted the following day, a satellite tracing tag was attached to the floating remains. The device was set to transmit the carcass’ location at five-minute intervals.

With the remains drifting north-westward and likely to wash up on one of the region’s popular public beaches, the whale was intercepted and towed approximately 30 km offshore.

The next step was to forecast the drift of the deceased whale remains from the offshore relocation point using RPS’ own proprietary drift modelling application, Search and Rescue Model and Planning (SARMAP), to test how accurately we could predict the whale’s journey onwards.

Learn more about SARMAP

Whale remains a unique test for SARMAP

SARMAP was developed to model the movement of floating objects (such as a person in the water or a capsized boat) for maritime search and rescue purposes. Our system uses real time environmental variables like winds and currents, along with ‘drift behaviour’ characteristics that are unique to the specific object type.

From shipping containers to vessels and people overboard, more than 100 objects are available for predictive drift modelling in SARMAP. In fact, our system has been used by the Australian National Search and Rescue Council as the national standard for search and rescue (SAR) planning systems since 2011.

But with the drift behaviour of whale carcasses largely unknown, a key challenge was selecting objects in SARMAP that would offer the best comparison to how a whale carcass in an advanced state of decomposition would drift in terms of buoyancy, and windage (the air resistance of a moving object, or the force of the wind on a stationary object).

In order to gauge the different drift behaviour, we selected:

• A life raft equipped with a deep ballast system and canopy with a windage value of of 0.9%.
• A skiff in a swamped or capsized condition with a windage value of 1.7%.

The life raft was chosen because it closely mimics the reduced impact of wind on the exposed surfaces of a decomposing whale and the drag of a large fin.

Modelling proves whale drift is dynamic, but not unpredictable

After the remains were intercepted and relocated offshore, it was found to have drifted more than 171 km until the signal from the satellite tag was eventually lost. Once the corresponding positions of the tracked whale remains were available, it was found that the drift of the skiff matched most accurately, while the model-predicted life raft drift was too slow.

A key observation was the declining effect that the wind had on the carcass, and the corresponding increase in the impact of current as time went on. While it was not possible to visually review the condition of the remains in the field due to weather, it is believed this is likely due to the deteriorating condition of the carcass (advancing decomposition and ongoing scavenger predation) reducing its mass above the water and decreasing its windage factor.    

When you consider the highly variable environmental conditions and ongoing break down process that a whale carcass is subject to (and the unknown modelling variables that this introduces), the relative accuracy that we were able to achieve with SARMAP in predicting the journey of our Sunshine Coast whale’s remains was quite remarkable.

The study demonstrates the value that predictive drift modelling could provide authorities in understanding when whale remains become stranded on local beaches, and informing how they manage remains that reach active nearshore, or populated beach zones.

Science for sustainable management

Whales are incredible creatures, so a deceased one is never a nice sight to see. But even in death a whale has great value. Strategically placing a whale’s body offshore can enhance nutrient cycling and foster biodiversity. Their gradual decomposition sustains countless other marine creatures while supporting microbial communities and deep-sea organisms. Research suggests a ‘whale fall’ can enrich the marine floor for up to seven years.

It’s our hope that through predictive modelling, we can return more whales to the ocean and keep this beautiful cycle moving.

Learn more about our ocean technology and modelling services