REF: 46

Shallow inlets and bays

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.

REF: 47

Reefs

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.

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

REF: 48

Estuaries

Reefs

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.

REF: 49

Estuaries

Reefs

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.

REF: 50

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).

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.