Did shortened nets reduce seal interactions?

12th March 2015

In March last year the newsletter reported on a project that aimed to reduce seal interactions with trawlers. The project was supported by AFMA through funding from the Australian Government and ExxonMobil Australia.

Reducing the chance of seal interactions is a logical step for the fishery which is actively working to improve its sustainability. Seals opportunistically feed on fish inside of trawl nets, and are occasionally caught in the net. Sometimes the seals are returned to the water unharmed, however some unfortunately drown.

Large trawl vessels are able to use grids that exclude seals from trawls; however, they are impractical and unsafe on the smaller vessels that are typical in the South East Trawl Fishery. Typical trawl nets are long, so that once a fish is in the net it cannot swim back out. South East fishermen hypothesised that seals would have a higher chance of swimming out of the trawl net if the net was as short as possible.

The “shortened cod-end” project aimed to compare the rate of seal interactions between a 27m “short” codend and a 39m “long” codend by alternating which net was used. Seal interactions are relatively rare so the project ran over a long time frame to ensure a large number of operations were completed; 683 shots (fishing operations) over 18 months. A vessel that regularly fishes off Tasmania’s west coast was selected because this is the area of the fishery with the highest seal interactions. The project was extended so it ran across the blue grenadier season, a time when seals are concentrated on Tasmanian’s west coast to establish if there were any factors in this part of the fishery that influenced the rate of seal interaction.

To ensure correct recording of the net type used and seal interactions, the skippers’ observations were verified by using colour coded nets and recording all shots on specialised video equipment that turned on and off automatically when setting and hauling the trawl net.
The project found that the short net had a seal interaction rate (proportion of shots with seal interactions) of 0.020 and the long net 0.018, however this small difference was not statistically significant. The project found no evidence to indicate that a short net catches less seals than a long one. Nonetheless the project was worthwhile and is an important step in the journey to reduce interactions.

SETFIA wishes to thank the Australian Government and ExxonMobil Australia for their financial support for the research project. Thanks also to the Phillip Island Nature Park who sat on the project’s steering committee. Finally thanks to the crew and owners of the fishing vessel the Western Alliance for alternating the two nets and agreeing to have video cameras installed for the life of the project.