REF: 51

Estuaries

Reef

Fyke nets

Further reports of otter deaths in fyke nets and creels. These include 2 males in fyke nets in the upper Ythan estuary after nets in the river for only 3 days, indicating the speed at which an eel fyke net will operate as an otter trap in a catchment with normally high otter density. Also reports the release of an otter from a fyke net providing an example of otter surviving capture when in shallow water if struggles bring the cod-end to the surface.

Deaths in creels reported from a lobster creel in Scapa Flow, crab creel off Isle of Arran and prawn creel off Skye.

Data confirm the potential of eel fyke to attract and kill otters living at very low density. Also appears to be considerable attraction when silver eels begin their seasonal migration - August/September on East Coast, October/November in Severn. This must be one of the last opportunities for otters to feed on eels in quantity before capture becomes too difficult until spring. Overall monthly distribution of all drownings in fykes, creels and fish traps shows a marked concentration in autumn and winter. Partly explained by seasonality of fishing but also when main food may be reduced for seasonal reasons.

Four otter guard test results shows only a significant difference with the square guard but only approximately 17% reduction. This guard is used by the Danes as mandatory on fyke nets. They have been mandatory in some UK regions since the 1980's.

Jefferies D.J. (1989). Further records of fyke net and creel deaths in British otters Lutra lutra with a discussion on the use of guards. Journal of the Otter Trust. 1989 p13-19.

REF: 52

Sandbanks

Review of data on penetration of depth of ticklers and chain arrays of beam trawls.

REF: 53

Estuaries

Reefs

Shallow marine inlets and bays

Sandbanks

90m long gill net (100mm diameter mesh) and trammel net (100mm with 600mm diameter outer mesh) set by commercial fisherman and cut at one end to simulate net loss. Survey of catches by direct observation, still and video photography for the following 9 months.

Species and community effects - Both nets caught large numbers of elasmobranchs which took about 3 weeks to decompose. Gadoids were eaten within 72hrs therefore not possible to tell how many were caught throughout the observation period and estimates were considered by authors to be conservative. Initially both nets caught more fishes than crustaceans but by 20 days crustacean catch was greater than fishes and was greatest 43 days after initial deployment. Catch per 24hr period declined with time and for fish was nearly zero at 70 days for gill net and 22 days for trammel net. Catch per 24hr for crustaceans remained higher than for fish for both nets throughout the study. Reduction of catch rate probably linked to reduction in net size and degree of entanglement. Overall catch over the 134 day experiment was 261 animals in the gill net and 292 in the trammel net.

Maja squinado and Scyliorhinus canicula were the 2 species most commonly caught in both nets. Other species caught were lobster, brown crab, swimming crab, Nurse hound and Smooth hound. All the crustaceans caught known to scavenge carrion. Other scavengers also aggregated to feed on the animals in the nets included A. rubens, M. glacialis, O. fragilis (in large swarms) and E. esculentus. Three shags were also caught. When nets retrieved (3 months after last survey) 2 spider crabs, previously marked were still alive after more than 102 days in the net. Towards the end of the experiment the free end of the nets began to roll up reducing the total length of net.

Kaiser M.J., Bullimore B., Newman P., Lock K. & Gilbert S. (1996). Catches in 'ghost fishing’ set nets. Marine Ecology Progress Series. 145: 11-16.

REF: 54

Experimental work in situ and in laboratory to evaluate the importance of the upwelling of sediment during dredging and, in particular, the amount of sediment particles, nutrients and oxygen consuming substances released during dredging as these factors can effect macrophyte and phytoplankton growth as well as affecting fish and bivalves.

Habitat effects - Preliminary results suggest a minimum flux of 2km², corresponding to about 0.9cm penetration of the gear. The release of particles, nutrients and oxygen-consuming substances seems to have little effect on the overall environmental conditions in the fjord. Where 10-15 boats dredge for several days, authors note that this will alter the local concentrations of nutrients and suspended matter directly, but the effect would probably only be visible or significant, during the dredging operations. Total annual release of suspended particles shown to be relatively unimportant compared with total annual wind-induced resuspension and release of nutrients compared to load from land.

REF: 55

Garthe S, Camphuysen K.C.J. & Furness R.W. (1996). Amounts of discards by commercial fisheries and their significance as food for seabirds in the North sea. Marine Ecology Progress Series. 136:1-11.