Is there a net benefit from offshore structures?

摘要

Understanding the utilisation of seafloor heterogeneity by different fish species is an essential prerequisite for the implementation of effective spatial management of marine ecosystems. The North Sea has long been a vital ground for the exploitation of natural resources, supporting one of the world’s most active fisheries as well as oil and gas exploration which has resulted in the construction of over 500 offshore platforms across the region. These facilities represent the major manmade structures installed on the seabed, adding substantial components of seafloor heterogeneity to the normally flat, featureless or soft sedimentary surroundings. While there is a growing body of evidence demonstrating that a variety of fishes aggregate around these subsea features, it still remains unclear whether the fish individuals merely concentrate around the structures from surrounding areas or whether such effects can have beneficial effects for fisheries by facilitating net increase in fish stock sizes. The research presented here investigates the relationship between fish and the physical presence of artificial structures in order to elucidate the potential role of offshore oil and gas platforms in the ecology of fish populations in the North Sea. To capture representative fish specimens closely associated with offshore platforms, seasonal fish sampling has been carried out since September 2010 at the BP Miller platform, a large steel jacketed facility in the Central North Sea. Although fishing from an operational platform is normally banned in the North Sea due to safety concerns, the Miller platform provides a unique opportunity for researcher to examine the possible effects of obsolete platforms on fish populations because it ceased production in 2007 and has since been used as a search and rescue helicopter base with minimum manning. Results show that commercially important fish such as cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and saithe (Pollachius virens) were the most characteristic species observed around Miller platform. However, there were marked changes in species composition and their relative abundances between seasons as well as years, suggesting highly dynamic nature of interactions between fish movements and the physical presence of the platform. Based on these results together with a range of studies from the relevant literature, implications for the ecological impacts of decommissioning on North Sea fish populations will be discussed.