The biggest threat to Hector’s dolphins is gillnetting. This fishing practice is legal in New Zealand and the dolphins become entangled in these nets and drown (remember that dolphins need to come to the surface to breath air). Gillnet entanglement causes about 60% of the mortality where cause is known (DOC and Mfish, 2007) and a lot of these kills are do to amateur (not just commercial) gillnetting (Dawson and Slooten, 2005). Other threats include: trawling; marine pollution; vessel traffic; habitat modification and disease (Sone and Yoshinaga, 2000).
What are gillnets?
You may have heard of drift nets or set nets, which are types of gillnets banned in many countries due to their impact on marine mammals, sea birds and other non-target species. Gill nets comprise a long net set vertically, normally in a straight line and usually left unattended for a period of time. Most fish become caught in the net when they move partially through it and then become caught behind their gill covers when they struggle to free themselves. Larger fish become entangled when fins, spines etc are caught and dolphins become caught when their noses, fins, or tail become caught. They then struggle to make it to the surface to breath and end up drowning https://edpharmacie.fr/generique-viagra/. Maui’s dolphins are particularly susceptible because of their small size and coastal ranges.
In New Zealand, gillnetting is still legal, with some restrictions imposed as part of an overall Threat Management Plan (TMP). Many consider that the regulations do not go far enough to provide adequate protection and the TMP is up for review this year (2014) for South Island Hector’s dolphins.
The New Zealand Ministry for Fisheries has established some good practice guidelines for set gill netting:
This site shows the recorded Maui dolphin human impacts by threat type: