Tracing gun cartridges using MetOceanTrack

Cartridges released from the Waitara River potentially spread far.

Cartridges released from the Waitara River potentially spread far.

An unusual query from Taranaki Regional Council resulted in an interesting unravelling of the fate of plastic waste washing into the sea.
 
In August 2016, Dr Emily Roberts, Taranaki Regional Council’s Marine Ecologist, approached MetOcean Solutions to ask for help with some marine detective work. Emily is involved with Project Hotspot, a Taranaki based pilot project that is using citizen science to support the conservation of threatened and iconic species. As part of the project, Council worked with Oakura School and Highlands Intermediate to clean up Taranaki beaches. The children were puzzled to find dozens of plastic wads from shotgun cartridges washing up on beaches around Taranaki, including within the environmentally sensitive Tapuae Marine Reserve. They wanted help determining likely sources of the cartridges, and who better to answer this than New Plymouth’s resident oceanographers.

Emily discussed the case with Allen Stancliff, the Taranaki Fish & Game Council Field Officer. He suspected that the plastic wads came from the Manganui River (which flows into the Waitara River), where an annual club clay bird shoot event is held. The shoot has grown in popularity over the years, attracting about 200 shooters in recent years. As some of the traps are located on the riverbank, the plastic wads could easily have ended up in the river. Newer ammunition uses fibre wads, but up until 2014 the ammunition used had plastic wads. If Allen was right, thousands of plastic wads could have been washed down the Waitara River over the years. Allen also thought that some plastic wads may originate from gamebird hunters shooting ducks along streams and rivers throughout Taranaki. These hunters are required to use steel shot (rather than lead, which is toxic) and at present the only suitable wads are plastic, but he doubted that this was a significant source.

Some of the plastic wads found by Oakura School and Highlands Intermediate.

Some of the plastic wads found by Oakura School and Highlands Intermediate.

Emily asked MetOcean Solutions to help trace the likely source of the plastic wads.

“There’s a number of reasons why stuff washes ashore in certain places,” says Mariana Horigome, the oceanographer working on the project.  “The wind and currents are the drivers, but the coastal aspect and shoreline profile also has to be right for objects such as the plastic wads to beach and not get refloated on the next tide." 

Mariana met up with Emily who pinpointed the locations where the higher concentrations of cartridges were noticed, and with Allen who explained the potential sources. To investigate whether the Waitara River could be the source of the shotgun cartridges, Mariana ran the MetOceanTrack modelling tool, a marine particle tracing software developed by MetOcean Solutions. When the model was set to release particles from the Waitara River they spread widely to locations both north and south of New Plymouth, nicely replicating where the wads had been found.

Emily was also keen to determine the source of plastic parking tickets that had been found at the beach cleanup. A MetOceanTrack run showed that the location of the tickets recovered was consistent with them entering the water in New Plymouth City, thus making local beach-goers the likely culprits. The model runs indicated that over time both the cartridges and the parking tickets could potentially spread very far from the source, with some particles ending up north of Mokau.  

"It was great to get some help determining where the plastic came from," says Emily. "The modelling confirmed our suspicions and we can now take action to minimise the waste entering rivers and the marine environment."
 
Mariana enjoys being able to help the local community. “Software like MetOceanTrack has got wide applications, providing useful information for anyone wanting more information about where objects go once they have entered the ocean. In addition to tracing rubbish, MetOceanTrack can be used to trace the spread of invasive species, the fate of oil spills and even people lost at sea.”

For more information about the findings of project Hotspot, click here.