How we know how many dolphins are caught?
Four Hector's dolphins caught in a single gillnet
The impact of fishing on Hector’s and Maui’s dolphins is calculated using data obtained by official Ministry of Fisheries Observers who are present on a small proportion of commercial gill net boats. By combining this information with data on fishing effort (e.g., the number of times nets are set) it is possible to estimate the number of dolphins killed by all commercial gillnet boats in operation. The more comprehensive the observer coverage, the better the bycatch estimate (e.g. if all boast carried observers we would we would know exactly how many dolphins are killed).
Other data come from dolphins that are washed up on the beach, but this is only a small proportion of the total death toll.
Commercial Gillnets
Commercial gillnet can measure
up to 3 km.
Commercial gill netting on its own has been killing Hector’s and Maui’s dolphins faster than they can breed for three decades. Twenty three Hector’s dolphins drown each year in commercial gillnets off the east coast of the South Island alone. The sustainable limit for this area is about one dolphin a year.
Even if commercial gillnetting is considered in isolation, the odds are stacked against Hector’s dolphins. The likelihood that they won’t recover to even half their original numbers within five decades is a massive 80-92%. Yet without fishing, numbers could double to 15,000.
Even if commercial gillnetting is considered in isolation, the odds are stacked against Hector’s dolphins. The likelihood that they won’t recover to even half their original numbers within five decades is a massive 80-92%. Yet without fishing, numbers could double to 15,000.
Trawling
Judging by the limited data available for trawling, this fishing method may kill as many Hector’s dolphins as commercial gillnetting.
Recreational Gillnets
Recreational gillnets can be 60 m long.
Recreational gillnets pose another major threat. New Zealand is said to have the highest per capita ownership of boats in the world, and fishing, including with gillnets, is a national pastime. No one knows how many dolphins end up trapped in them because fishermen on unobserved commercial and private fishing boats tend not to report when dolphins get caught in their nets. Read more
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