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The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts - page 2 / 12

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trawl in earlier inaccessible areas due to the rough- ness of the bottom, e.g., by presence of coral reefs. The fishery on the continental break targeted Green- land halibut (Reinhardtius hippoglossoides (Walbaum, 1792), redfish (mostly Sebastes marinus (L., 1758)) and saithe (Pollachius virens L., 1758)). By the end of the 1990s, the practice increasingly involved double- trawls, which sweep larger areas per unit time (per- sonal communication with O.A. Misund, Institute of Marine Research).

It was in the early 1990s that long-line and gillnet fishermen contacted the Institute of Marine Research (IMR) to express their concerns about the effects of trawling on coral reefs. They claimed that corals had disappeared from trawling grounds, and that their catches in these areas were lowered. Their worries also concerned the potential function of the reefs as nursery areas for fish.

Currently, there has been an increased interest and concern around the effects of fisheries on benthic in- vertebrates and bottom communities (e.g., Jennings & Kaiser, 1998; Lindeboom & deGroot, 1998; Wat- ling & Norse, 1998; Hall, 1999). Tropical coral reefs represent high diversity communities endangered by a range of human activities (Reaka-Kudla, 1997). The Lophelia reefs represent a highly complex habitat on the continental shelf, slope and seamount environ- ments with a highly diverse associated fauna (Fosså & Mortensen, 1998; Rogers, 1999). The ecological effects of degraded or completely destroyed reefs may thus be substantial.

Since there were no estimates of the total area oc- cupied by deep-water coral reefs in Norway, it was thus not possible to estimate the extent of the dam- age caused by fisheries. Therefore, the purpose of the present study was two-fold. Firstly, to gather informa- tion on the occurrence of Lophelia pertusa as given by fishermen and the literature in order to provide estim- ates of the extent of corals in Norwegian waters. And secondly, to inspect selected sites in order to confirm the damage reported by the fishermen so as to provide documentation of impacts of bottom trawling on the reefs.

Methods

Published and non-published information

Dons (1944) compiled the oldest published records of Lophelia in Norwegian waters. Since he plotted

the findings on maps of different scales, we read the geographical co-ordinates as accurately as possible. Additional published material derives from Strømgren

  • (1971)

    , Fernandez Pulpeiro et al. (1998), Freiwald

  • (1998)

    and Mortensen et al. (2001). These authors

note the sites on maps as well and, occasionally, as geographical co-ordinates. Information from annual reports of lost gillnets in areas with heavy net fisher- ies, including coral reefs, performed by the Norwe- gian Directorate of Fisheries (NDF) retrievals (Anon, 1991–99), was also used. NDF record the presence of corals as stretches between geographical co-ordinates. The Norwegian State Oil Company (Statoil) has re- gistered accurate positions for 70 reefs in the Hal- tenbanken area using a Remotely Operated Vehicle (ROV) (Hovland et al., 1997; Mortensen et al., 2001). Lastly, the records of coral sites encountered during trawl surveys carried out by IMR, which are reported as co-ordinates in station lists.

Information from fishermen

We provided the fishermen with bathymetrical charts to plot the occurrence and status of coral reefs. If necessary, details were discussed on the telephone. Fishermen records were gathered during 1997 and 1998. Their observations are based on what the fish- ermen usually call ‘glass coral’ (Lophelia) caught in trawls, nets or on long-lines. Observations of prom- inent gorgonians, also called ‘red forest’ or ‘bushes’ were excluded. We declined the use of questionnaires since our experience is that very few answer and we used our network of known fishermen along the coast instead.

ROV-inspections

Five locations were visited to verify the information provided by the fishermen. In 1999 we used the Uni- versity of Bergen’s ROV ‘Aglantha’ with video camera operated on board RV ‘Johan Hjort’ (IMR). In 1998 we used the ROV ‘Solo’ (equipped with side scan sonar) on board SV ‘Seaway Surveyor’ and 1999 a Triton-ROV on board SV ‘Geograf’. These two vessels, which are equipped with multibeam echo- sounders were used to check information from fish- ermen on damages to coral reefs. With these two vessels we could work differently than with the sim- pler ‘Aglantha’-system. We chose first an arbitrary section in a reported area. We then used data from the multibeam echosounder to produce a topograph- ical map with a vertical resolution of 0.5 m. Finally,

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