Summaries of reviewed publications – references 46 – 50.

Details are limited to information relevant to the UK marine habitats and species listed in the Habitats Directive and the Birds Directive.

[pr] indicates that the paper is from a peer reviewed journal or report


Natura 2000 Habitats & Species

Fishing Technique




REF: 46

Shallow inlets and bays


Beam trawling

Effects of 4m and 12m beam trawls investigated.

Habitat effects - sole plate of 4m trawl exerted a force of about 2N/cm2 at commercial trawling speeds. Trawl marks on coarse sand visible up to 52hrs after fishing.

Species and community effects - Range of mortalities of discarded, non-target species due to capture and handling. High mortalities for undersized fish discarded, 50% or less for most crabs and molluscs and very little mortality (<10%) for starfish. Overall decrease of 0-85% from initial numbers for different mollusc species (solid-shelled or very small species such as Chamelea gallina, Corbula gibba, Dosinia lupinus and Apporhais pespelicani not affected. More vulnerable species such as Abra alba, Mactra corallina, Ensis ensus, Arctica islandica and Turritella communities had mortalities between 12-85%), 4-80% for crustaceans Corystes cassivelaunus and Ebalia spp. approx. 30%, Eupagurus bernardus showed size dependent mortality 15% for large animals and 74% for small animals; Callinassa spp. lived too deeply to be disturbed by beam trawling, 0-60% for annelids and 0-45% for echinoderms A. rubens, A. irregularis, A. filiformis and O. texturata little affected and E. cordatum too deeply buried to be harmed. Considering the high mortality of certain species and the fishing intensity, it can be expected that commercial beam trawling affects the structure and composition of the benthic community in the North Sea. Benthic animals damaged, dislodged or discarded by beam trawls may contribute significantly to the diet of scavengers whose populations may thus become enhanced.

Investigations into scavengers showed that dab, gurnard, dogfish and whiting increased intake of prey after fishing. Dab fed largely on bivalves Arctica, Acanthocardium, Donax and Spisula and crustaceans Upogebia and Callianassa the latter of which are not normally accessible to them. Gurnards and whiting fed on dislodged amphipods and whiting fed on the damaged burrowing heart urchin Spatangus purpurreus. Fish rapidly migrated into trawled areas to feed on animals damaged or disturbed by fishing.

North Sea

De Groot S.J. & Lindeboom H.J. (eds) (1994). Environmental impact of bottom gears on benthic fauna in relation to natural resources management and protection of the North Sea. Netherlands Institute for Sea Research. NIOZ-Rapport 1994-11, RIVO-DLO report CO26/94.

REF: 47



Lobster creels

Report of otter mortalities in lobster creels off S. Uist. Most were drowned foraging in depth of 2-5m of water. Greatest depth was 15m, 65% of known status were adult females 15% were juveniles, 10% sub-adult females and 10% adult males. The low number of males perhaps because fewer adult males in the favoured breeding area. Also because of their size the males may not be able to enter the parlour of the creel. Fish such as saithe, small cod and congers swim into the creels and are trapped and it is likely that the otters are attracted to this rather than the lobster bait.

The incorporation of a parlour in these pots has greatly increased its ability for holding lobsters as well as otters. Does not appear to be as much a threat from crab creels as they are usually set on sandy bottom in deeper water further offshore rather than the favoured otter foraging areas.

Report of catches off coast of South Uist

Twelves J. (1983). Otter Lutra lutra mortality in lobster creels. Journal of Zoology, London. 201: 585-588.


REF: 48




Eel fyke nets


Accidental drowning of otters has occurred in crustacean and fish traps such as lobster pots, crab pots, and eel fyke nets in both freshwater and marine situations. Review of reports shows that this has taken place in parlour creels, single-compartment box creels, single compartment 'inkwell’ creels and fyke nets. Work to prevent otter damage to fyke cod-ends suggests that in some cases they attack the nets from the outside and if severing the mesh proves impossible, move to the fyke entrance or directly to the entrance. Uncertain whether otters are attracted to crustacean traps by the bait or the catch -seems that both can occur. In the latter case this is because they tend to contain particularly favoured prey such as eels, crayfish and crabs. Estimates of times otters can submerge are for more than 3-4 mins, normal dive time is far shorter and they run out of time and drown. Sex and status of otters drowned in lobster creels off S. Uist mostly females. Adult males may be less active in the favoured breeding areas and may be unable to enter the parlour of the most widely-used creel. No data to support the view that those otters which drown are young and inexperienced. Some evidence to suggest that they escape more readily from single-compartment creels than double-chamber creels. Family parties are known to have drowned on five occasions. Juvenile casualties have involved animals towards the size where independence is reached, at about 10 months.

Suggestions to alleviate the problem of drowning otters discussed in the paper. These are intermittent operation, size of net, depth, floating cod-ends, opaque covers for traps, excluders over fyke entrances; and ledges in box traps exposed to the air. Satisfactory, preventative measures for a given trap might vary, dependent upon local fishing conditions and the state of the regional otter population.

Report of catches off Devon coast, off the east coast of South Uist, Orkney, Skye, Shetland and west Sutherland

Jefferies D.J., Green J. & Green R. (1984). Commercial fish and crustacean traps: a serious cause of otter Lutra lutra (L.) mortality in Britain and Europe. Vincent Wildlife Trust, London. 31pp.

REF: 49




Eel fyke nets


A major cause of mortality to otters has been accidental capture and drowning in fish and crustacean traps. Four types of guards for eel fyke nets were constructed and tested - square guard, ring guard, front net guard, grid guard. Effects on catches of eels (total weight, number and catch of saleable eels) were recorded. Techniques other than guards discussed but it was considered that the only safe and continually working otter protection device was a physical barrier at some point near the mouth of the fyke. The Steering Committee set up to look at the problem suggested authorities should consider and adopt most suitable designs for their situation and then consider ways of implementing and ensuring use.

Otters investigate eel fyke nets because of the artificially concentrated prey in the cod end. They are unable to bite their way through modern multifilament nylon netting therefore the only way to get the prey is through the fyke entrance and down through the funnels. The time they can submerge is not sufficient in many cases for an otter to negotiate its way back to the entrance so it drowns. Between 1975-1984, 89 otters are known to have been caught in underwater traps (50, 33 and 6 in eel fyke nets, crustacean and fish nets). In the Solway verified data considered by an observer to be only 20-50% of the real total. Fish traps can be effective at reducing otter populations when set for a long period in a single locality.

Report of catches in the Solway

Vincent Wildlife Trust (1988). The effects of otter guards on the fishing efficiency of eel fyke nets. Vincent Wildlife Trust, London 47pp.

REF: 50


Monofilament net (discarded)

European otters have been caught and drowned in active gear such as wade nets off Pembroke, fyke nets in freshwater and estuaries and parlour creels set for lobsters. Chance encounters with cast-off fragments of "plastic" netting was not considered a cause of fatality. Otters may be attracted to explore such debris but their dexterity was thought to prevent fatalities. This now appears not to always be the case and could be an increasing problem for coastal otters.

The paper describes condition of a dead otter found on the beach near Scarista on the Isle of Harris. It was emaciated and the cause of death strands of monofilament nylon which had become embedded into the flesh around the neck. It was a small section of fishing net (square aperture approximately 50mm).

It seems likely that the otter was entangled at an early age (3-5 months) and as it grew the nylon became enclosed in tissues of the neck. Unknown how many are lost in this way and whether it is large enough to be a conservation problem and one of animal welfare. Needs monitoring. This case shows that even a small section of discarded net can be lethal therefore the solution is difficult.

Isle of Harris

Jefferies D.J., Johnson A., Green R. & Hanson H.M. (1988). Entanglement with monofilament nylon fishing net: a hazard to otters. Journal of the Otter Trust. 1988. p11-15.


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