Ghost fishing

Ghost fishing trammel net off Wales. Tangled gadoid
probably lured the shag into the net. © Blaise Bullimore/CCW

Fishing gear tends to be constructed from modern synthetic fibres that are non-biodegrable. This means that snagged or lost gear and torn fragments of net may continue to catch fish indefinitely. This is termed ghost fishing. Gear can be lost for a variety of reasons. For example, in northern Spain, set net fisherman exploiting anglerfish (Lophius piscatorius) on offshore grounds lost gear as a result of trawling activity in the area, whilst inshore fishermen targeting seabream (Sparidae) lost gear mainly as a result of bad weather.

A cycle of capture, decay and attraction tends to develop with lost gear. For nets, catches initially decline as the increasing weight of the catch causes the net to collapse. The decay of this catch attracts scavenging organisms such as crustaceans, many of which can be commercially important species. Once clear of fish remains and scavengers, the net may disentangle, return to an upright position and resume fishing. The longevity of this cycle can vary, depending on environmental conditions. For example, a net lost in shallow clear water will be rapidly fouled (i.e. algae and other organisms will grow on it), which increases the net's visibility and reduces its fishing capacity. Storms, swells and wave action will also abrade nets, breaking them up. For example, in the Irish Sea a net snagged between rocks continued to fish for over a year whilst a similar net off the north west of Spain was destroyed within a month due to the Atlantic swell.

  Wrasse caught in lost pot. Note damage
  due to escape attempts
  © Blaise Bullimore/CCW

Of greater concern are pots, creels and traps. These tend to be constructed with the more durable materials and have a rigid structure. Consequently, they can ghost fish for much longer periods than nets. Pots tend to be baited when they are set. If the pot is lost, in time the bait or lost catch will attract scavengers, some of which are commercially important species. These scavengers become entrapped and subsequently die, forming new bait for other scavengers. A creel made from indestructible material can therefore continue to fish indefinitely. As a result of this, escape panels and biodegradable materials are being introduced to reduce losses from ghost fishing in some areas.

The impact of ghost fishing depends upon the region and fishery. For example, in the USA it has been estimated that $250 million of marketable lobster is lost annually to ghost fishing whilst in the Bristol Bay crab fishery alone 31,600 pots were lost over a two year period. The scale of the problem was such that Canadian fisherman complained about it, resulting a grapnel survey was conducted on Georges Bank from which 8% of tows recovered lost gillnets (286 tows actually yielded a total 341 actively fishing ghost nets). Lost tangle nets have been found to catch anglerfish (Lophius budegassa and L.piscatorius) at similar rates to commercially set tangle nets. This was, however, dependant on the season. In contrast, in the Baltic Sea, capture rates of lost cod gill nets were found to be 80% less than commercially set nets within three months. They did, however, continue to fish for over two years with a tendency to catch smaller individuals than would be implied by their mesh size. In the Hawaiian lobster fishery, the spiny lobster (Panulirus marginatus) and the slipper lobster (Scyllarides squammosus) were able to exit traps easily and ghost fishing was, consequently, not considered to be a problem. In the Algarve (Portugal), ghost fishing of hake was thought to be 0.5% of the total annual catch and considered a minor problem in comparison to discarding.

Diver cleaning up lost angling sea gear © Blaise Bullimore/CCW

As well as the impact on commercial species, ghost fishing can affect other marine species, notably birds and marine mammals. For example, 99 seabirds were recovered from a 1.5km length of gill net found south of the Aleutian Islands whilst, off Newfoundland, it was estimated that over 100,000 marine birds and mammals were killed in a four year period by ghost fishing. In the north east Pacific, it was estimated that 15% of the mortality of young fur seals (Callorhinus ursinus) could be attributed to net debris, with the average seal expecting to encounter 3 to 25 pieces of net debris annually.

Ghost fishing

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