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The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts - page 3 / 12





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Figure 1. The distribution of Lophelia corals in Norwegian waters. The black circles represents records from the literature or verified records of Lophelia. Grey circles represent non-verified information from fishermen. Four regions R1–R4 are defined and used for estimates of areas (see Table 3). Framed areas to the left and right show ROV-inspected localities: (1) Aktivneset, (2) Korallneset, (3) Sørmannsneset, (4) Maurdjupet and (5) Iverryggen.

the area was visually inspected with the ROV-cameras. The side scan sonar was used to document trawl tracks. Dead coral fragments lying on the slopes of reefs are commonly seen as they are part of the natural pro- cess of decay in coral reefs (Wilson, 1979; Mortensen, 2000). Therefore, in order to distinguish natural de- cay from impacts by human activities, such as bottom trawling, we looked for broken living colonies tilted, turned upside down and/or in unexpected/awkward positions on levelled sea bottom. The remains of fish- ing gear such as gillnets, anchors, and trawl nets among corals added to the evidence while furrows or scars in the sea bottom are unmistakable evidence of trawling activity (see e.g. Lindeboom & de Groot, 1998).

Size estimation of coral areas

Estimation of the size of coral areas was done on charts with a scale of 1:500 000. Single point records were assumed to represent a normal sized reef of about 200 m in diameter (Mortensen et al., 1995). Area in- dicated by lines or stretches between two co-ordinates were calculated using two alternative widths: 200 and 500 m, which represent an estimation of the extent of the bottom surface affected by a trawl. The choice of the widths are based on the following assumptions: the trawls used in these areas are around 100 m between the trawl doors and have 30–40 m wide gear (Dag M. Furevik, unpublished information). In a frequently trawled area, however, the surface area affected will

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