Effects of fisheries on European marine biodiversity== |+|
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Image:food web competion. jpg|thumb|250px|right|Food-web competition: top predators (such as marine mammals) and fisheries may not directly compete (because they consume different species) but could indirectly affected by fisheries, because of limits on the primary productivity available to support the two groups. SOURCE: Reprinted from: Trites A.W., Christensen V. & Pauly D. (1997). Competition between fisheries and marine mammals for prey and primary production in the Pacific Ocean. ''Journal of Northwestern Atlantic Fishery Science'' 22: 173–187.]] |+|
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|−|Fishing is the most widespread human exploitative activity in the marine environment. Pauly and Christenen (1995) estimated that over 20 % of the [[primary production]] is required to sustain fisheries in many intensively fished coastal ecosystems.<ref name="Pauly1995">Pauly, D. & Christensen, V.(1995). Primary production required to sustain global fisheries. ''Nature'' 374: 255-257. </ref> |+|
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|−|Fishing has a number of direct effects on marine ecosystems because it is responsible for increasing mortality of target and [[by-catch]] species; an important physical impact on the habitat of benthic organisms is caused by [ http://en.wikipedia.org/wiki/Bottom_trawling bottom trawling]. The direct effects of fishing have indirect implications for other species as well. Fisheries remove prey that [ [piscivorous]] fishes, birds and mammals would otherwise consume, or may remove predators that would otherwise control prey populations. Reductions in the density of some species may affect competitive interactions and result in the proliferation of non-target species. The activities of fisheries also favor scavengers, they obtain more food by the discarded by-catch and because a range of species are killed, but not retained by towed gears.<ref name="Jennings1998">Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. ''Adv. Mar. Biol.'' 34: 201-352. </ref> |+|
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Successful use of video monitoring techniques in support of coastal management and engineering involves the quantification of relevant coastal state information from video data. Sophisticated, operational video analysis methods nowadays enable the quantification of:
- Shoreline evolution and beach width, to evaluate the potential for recreation or to assess the morphological impact of a storm event
- Erosional and accretional sediment volumes at the intertidal beach, for example to evaluate the morphological impact of coastal structures, to investigate seasonal fluctuations in beach dynamics and beach nourishments or to study the behaviour of morphological features such as sand spits and tidal flats near a harbour entrance
- Subtidal beach bathymetry, to evaluate coastal safety, to assess the behaviour and performance of shoreface nourishments or even to facilitate military operations
- Wave run-up, to evaluate the stability of coastal structures such as seawalls, harbour moles and revetments
- Coastal State Indicators with a high resolution in time through assimilation of model computations with Argus observations
In a research context, video monitoring techniques have been applied to quantify alongshore flow velocities, wave characteristics such as wave angle and period, the occurrence of algae bloom and the distribution and persistence of rip currents. Future applications may involve the monitoring of visitor density at the beach and the prediction of rip currents.
The continuous collection of long-term, high-resolution data sets carries the additional advantage of a posteriori data selection, for instance for the consistent assessment of storm damage to public and private property and the early recognition of important erosion trends.