Mortality in megafaunal benthic populations caused by trawl fisheries on the Dutch continental shelf in the North Sea in 1994

Published source details Bergman M. & Van Santbrink J.W. (2000) Mortality in megafaunal benthic populations caused by trawl fisheries on the Dutch continental shelf in the North Sea in 1994. ICES Journal of Marine Science, 57, 1321-1331.
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This study is summarised as evidence for the following.

	Action	Category
	Reduce the number or modify the arrangement of tickler chains/chain mats on trawl nets Action Link
	Use a smaller beam trawl Action Link
	Use an otter trawl instead of a beam trawl Action Link

Reduce the number or modify the arrangement of tickler chains/chain mats on trawl nets

A replicated, paired, controlled study in 1992–1995 in one area of sandy seabed in the south-eastern North Sea, Netherlands and Germany (Bergman & Van Santbrink 2000) found that using a beam trawl with a chain mat caused lower mortality of benthic invertebrates in the trawl tracks (not caught by the nets) compared to using a beam trawl with tickler chains. Mortality using a chain mat varied between 4 and 15% depending on species and was lower than when using tickler chains (1–30%). In spring-summer 1992–1995 parallel strips (2,000 x 60 m, 300 m apart, number unspecified) were fished with 4-m beam trawls with either a chain mat or tickler chains. Prior to trawling, ‘mega’-invertebrates >10 mm) and ‘macro’-invertebrates (between 1 and 10 mm) were counted from samples taken from each strip using a dredge and a sediment grab. After 24–48 h following trawling, all strips were sampled again using the same methods. Mortality (from trawling) of invertebrates present in the trawl tracks was calculated using the difference between the before and after-trawling abundances (assuming all animals killed by trawling had been eaten by predators).

(Summarised by: Anaëlle Lemasson & Laura Pettit)
Use a smaller beam trawl

A replicated, paired, controlled study in 1992-1995 in four areas of silty or sandy seabed in the south-eastern North Sea, Netherlands and Germany (Bergman & Van Santbrink 2000) found that using a smaller beam trawl caused similar mortality of invertebrates in the trawl tracks compared to using a larger beam trawl. Mortality using a 4-m beam trawl varied between 2 to 80% depending on species, similar to a 12-m beam trawl (1–82% mortality). Mortality did not differ across sediment type (sandy or silty). In spring-summer 1992–1995, parallel strips (2,000 x 60 m, 300 m apart, number unspecified) in one sandy location and three silty locations were fished with either a 12-m (commercially used) or 4-m beam trawl (both with tickler chains). Prior to trawling, mega-invertebrates (>1 cm) and macro-invertebrates (>1 mm) were counted from samples taken from each strip using a dredge and a sediment grab. After 24–48 h following trawling, all strips were sampled again using the same methods. Mortality (from trawling) of invertebrates present in the trawl tracks was calculated using the difference between the before and after-trawling abundances (assuming all animals killed by trawling had been eaten by predators).

(Summarised by: Anaëlle Lemasson & Laura Pettit)
Use an otter trawl instead of a beam trawl

A replicated, paired, controlled study in 1992–1995 in four areas of sandy or silty seabed in the south-eastern North Sea, Netherlands and Germany (Bergman & Van Santbrink 2000) found that the effects of otter trawls compared to beam trawls on invertebrate mortality varied with the sediment type. Otter trawls caused similar mortality of invertebrates in the trawl tracks compared to beam trawls in sandy areas (otter: 0–41%: beam: 1–53%) but lower mortality in silty areas (otter: 1–65%: beam: 2–82%). In spring-summer 1992–1995 parallel strips (2,000 x 60 m, 300 m apart, number unspecified) in one sandy location and three silty locations were fished with either a commercially used beam trawl with tickler chains or an otter trawl. Prior to trawling, mega-invertebrates (>1 cm) and macro-invertebrates (> 1 mm) were counted from samples taken in each strip using a dredge and a sediment grab. After 24–48 h following trawling, all strips were sampled again using the same methods. Mortality (from trawling) of invertebrates present in the trawl tracks was calculated using the difference between the before and after-trawling abundances (assuming all animals killed by trawling had been eaten by predators).

(Summarised by: Anaëlle Lemasson)