Threats to Cetaceans - Bycatch

The term bycatch refers to the unintended mortality of non-target species during fishing practices. It is a worldwide issue and can affect a wide range of species including marine mammals, sea birds, turtles, sharks and also non-target fish species.

Every year it is estimated that 300,000 cetaceans per year die from being caught up in fishing gear. 10,000 per year are thought to be killed in EU waters. For some species the scale of the problem is so great it can affect the structure and function at the population, community and ecosystem levels. It is thought that up to 5% of the common dolphin population is being caught per year in the regional of the English Channel. The International Whaling Commission has stated that a continual kill rate of only 1% of a cetacean population whould be cause for concern and investigation should take place as a matter of priority (IWC 1995). Therefore this is a very real threat to the population as a whole.  In the Celtic sea, up to 6,000 porpoise have been taken per year over recent years, about 6% of the population.

In March, Goverment figures show there was a 66% increase in the number of common dolphins stranded on the beaches of Cornwall. 94% of those post-mortemed were found to have died as a result of bycatch.

Many of the animals found dead or stranded are found to have injuries such as broken beaks, bruising, cuts, torn flippers and flukes, indicating that the animals have been under a lot of pain.  This is also therefore a concern from an animal welfare point of view as the animals are suffering a prolonged and painful death.

The main types of fishing that can result in bycatch are the following:

•   Gillnets
  
  

  Gillnets are a very passive form of fishing. The net is a sheet of netting suspended vertically in the water column. Bottom set gillnets are buoyed along the top and weighted and the bottom. Harbour porpoises are particularly vulnerable to these as they often feed at the sea bed. Tangle nets are gillnets which are not buoyed, they catch fish through entanglement and are often used for crustaceans. Tangle nets are used locally in Scotland . For more information on this, click here. Since the introduction of nylon monofilament fibres, nets have become far more durable and effective. Gillnets are very unselective in what they catch and because of their durability carry on fishing if they are lost (ghost fishing).
  
  

• Drift nets
  
  

  Drift nets are the same as gillnets but are left to drift near the sea surface, sometimes attached to a boat at one end. Nets can be up to 21km in length. Long driftnets are now banned in EU waters apart form the Baltic sea , although illegal drift netting does occur. Small scale netting for mackerel and herring occurs in inshore waters.
  
  

• Pelagic or mid water trawling
  
  

  This involves the use of a bag net with a very wide open mouth, tapering down to a narrow end, the cod end. Nets can be towed by a single vessel or by a pair – pair trawling. The target species are trawlers are often prey for cetaceans and so they are often found together. Pair trawler has the highest numbers of bycatch as they can operate with much large nets.
  
  

 

For more information on bycatch please visit the following sites:

'The Net Effect' report by Greenpeace

European Cetacean Bycatch Campaign