Africa: Whales, Dolphins and Porpoises Suffer Dramatic Declines From Bycatch in Fishing Nets

by Oct 24, 2011Marine & Coastal

Bonn — For 86 per cent of all toothed whale species, entanglement in gillnets, traps, weirs, purse seines, longlines and trawls is resulting in an unsustainably high death toll.

This is among the findings of a report published today by the Convention on the Conservation of Migratory Species of Wild Animals under the UN Environment Programme.

The report is an encyclopaedia on the 72 species of toothed whales compiled by Professor Boris Culik of Kiel University in Germany and represents the most recent scientific findings on the distribution, migration, behavior and threats to this suborder of the cetaceans, which includes sperm whales, beaked whales, porpoises and dolphins which have teeth rather than the baleen of other whales.

Most marine species are heavily affected by ongoing and unsustainable mortalities through fishery interactions. Even if whales are not targeted directly by the fisheries, over-fishing of their predominant prey species was identified as a threat to 13 species (or 18%) in 2011 as opposed to 11 (or 15%) in 2001. Lack of food and forced dietary shifts due to overfishing pose additional threats to these 13 species.

Although hunting on a commercial scale has largely come to an end, many toothed whales still suffer losses from ongoing local hunting, deliberate killings or live-captures. A total of 50 species (or 69%) is now affected by such operations, as opposed to 47 (or 66%) in 2001.

Compared to the Review of Small Cetaceans first published online by CMS in 2001, the new report shows that the conservation status of the toothed whales has dramatically worsened over the past 10 years. Seas and oceans are increasingly affected by human activities, with impacts on an increasing number of species around the world.

“Toothed whales face major threats from bycatch, ship strikes, ocean noise and climate change. These threats need international regulation. The CMS Scientific Council has proposed a resolution on gillnet fisheries for adoption next month, calling for immediate action by the international community to improve fishing practices towards reducing the unnecessary death of so many marine mammals.

Data collection and new scientific findings can facilitate the development and implementation of action plans under the Convention on Migratory Species to reduce the threats to many whale species,” said UNEP/CMS Executive Secretary Elizabeth Mrema.

“The conservation status of toothed whales has worsened dramatically since 2001. Bycatch in fishing gear is the predominant threat to all toothed whale species. After the Baiji River Dolphin, more species will become extinct unless urgent action is taken to mitigate this threat,” said the author of the report, Professor Boris Culik.

CMS works with fisheries’ organizations to identify emerging techniques and best practices to mitigate bycatch.

Gear modifications towards using more selective types of nets or hooks, as well as acoustic repellents deterring marine mammals from fishing nets, are already being deployed. In addition, the establishment of seasonal protected areas also reduces incidental capture in fisheries.

Many human activities result in discharge of wastes and subsequent pollution of the environment. Massive accumulation of biologically active pollutants is dangerous to the whales’ health. Ingestion of plastic debris or the effects of pollution by an ever-increasing cocktail of chemicals have been reported for 48 species.

The ingestion of plastic debris and subsequent obstruction of the digestive tract might lead to starvation. This includes persistent and heavy metals, such as mercury and butyltins, the latter used in anti-fouling paint for ships, as well as persistent chemicals such as PCB’s, DDT and others. While they posed a threat to 40 species (56%) in 2001, now they affect 48 (66%) of all species.

Whales rely on sound to communicate underwater, to navigate and to find and capture prey. Man-made noise caused by seismic explorations, marine construction projects as well as military sonar now poses an increasing threat to 24 (33%) species of these marine mammals compared to two species identified in 2001.

Ship strikes also have a serious impact on 14 species while habitat degradation due to construction of dams and withdrawal of water from rivers and lakes threatens 18 species. China’s Baiji River Dolphin, which used to live in the Yangtze River is now probably extinct as no living specimens have been documented in the wild since 2002.

With only 150 individuals remaining in the wild, the Vaquita, one of the smallest toothed whale species living in the northern Gulf of California, is facing the same destiny as the Baiji. The latest survey in its habitat estimated the population size being in the range of 177 to 1,073 animals in 1997.

A recent statistic in 2009 based on inferred fisheries by-catch mortalities assumes that only 71 to 430 animals survive today. In 2008, the International Whaling Commission estimated that the species may become extinct by 2013.

The two following species have been classified as endangered by the IUCN Cetacean Specialist Group in 2008:

With its current population size ranging from 48-252, a sub-species of the Hector’s dolphin of New Zealand is actually threatened with extinction and Critically Endangered, according to the IUCN Red List.

A sub-species of the South Asian river dolphin, living in the Indus and its tributaries in Pakistan and India has a remaining population ranging between 100 and 1,000.

UNEP/CMS has reacted to this increasing level of threats to toothed whales. 37 species of toothed whales are listed in the Appendices to the Convention, and four targeted regional agreements gave been concluded for their protection.

At the upcoming 10th Meeting of the Conference of the Parties, a Global Programme of Work for Cetaceans will be considered for adoption. It will further strengthen the role of UNEP/CMS in supporting countries efforts to protect these animals with strong science and sound policy advice.

The report was supported and co-funded by CMS, ACCOBAMS, ASCOBANS, Greenpeace, IFAW, Loro Parque Fundación, Artescienza and IUCN.