About the TAD

Conventional pingers (Dukane, Fumunda, Aquatec, SaveWave, Airmar) were initially thought to alert porpoises to nets, but are now known from several studies to be aversive devices, that drive porpoises away. The fact that they do not make porpoises aware of the net is shown by the animals' movements and by the reduced echo-location detected in the vicinity of the pinger when it is active.

In the only study to-date of porpoise bycatch and echo-location activity, the highest bycatch on any trip was associated with low levels of porpoise echolocation. The commonest fish species present was mackerel, which has no swim bladder and is relatively hard to detect with sonar. So perhaps porpoises are sometimes silent, listening to the fish swimming as they chase them.

In the same fishery study, porpoises were often echo-locating close to nets without any getting caught. So is it mostly silent porpoises that get caught?

In order to test true alerting, a simple stimulus has been tested. The sound is a 4-click train at 130 kHz lasting 0.4 seconds, produced every 4 seconds at 130 dB re 1 µPa. The response is that the number of porpoise detections next to the device increased by 2.5 times to 18 times in several different locations, including one with very active feeding. No habituation was seen. So this is a truly alerting device (TAD), unlike pingers which drive porpoises away, producing a profound fall in detections of porpoises at the pinger.

If a TAD reduced bycatch by a useful amount it would have substantial advantages:

the power consumption of a TAD is less than 5% of a pinger, so the TAD requires no battery changes.
it could be date stamped at manufacture making it easy to monitor.
its smaller battery makes it a lighter device, easier to use on nets.
it creates no habitat exclusion, so porpoises are not adversely affected.
it produces much less noise pollution than a pinger.

Despite these possible advantages, we still do not know whether bycatch will be reduced by TADs. The development work required to produce TADs suitable for commercial fishery trials has been completed. No copyright or patent protection is involved. If you know of any potential funding opportunity for testing this in a commercial fishery please contact us.

References

Tregenza and Northridge (1998). High bycatch with low click detection rates. High rates of non-lethal encounters with nets. Poster. European Cetacean Society conference.

Tregenza and Fisher (2004), TAD effect. Poster. European Cetacean Society conference.

Cox et al, Goodson, Culik et al, Carlstrom et al. Pinger effect.

Cox, T. M., A. J. Read, A. Solow and N. J. C. Tregenza (2001). Will harbour porpoises (Phocoena phocoena) habituate to pingers? Journal of Cetacean Research and Management3(1): 81-86.

Joergensen, P. B., J. Tougaard, J. Teilmann, N. I. Bech, L. A. Kyhn and T. Dabelsteen (2005). Habituation and habitat exclusion of harbour porpoises in a simulated gillnet fishery with pingers. Poster. Society for Marine Mammology Biennial Conference, 16.San Diego.