Demersal fish

Harvey estimated the mean annual biomass of demersal fish in the English Channel at 1.0-1.25 g dry wt^m-2 (Table 7.1). With a calorific value of 5 kcal^g-1 dry wt the energy content of this biomass is 6 kcal •m-2 approximately. Harvey put the annual yield at 30-50 per cent of stock (say 40 per cent) so annual production can be calculated as 6 X 0.4 = 2.4 kcal^m-2^yr-1. If the GCE is 0.1, this level of production requires an energy intake of 24 kcal^m-2^yr-1.

Demersal fish feed partly on benthic and partly on pelagic prey. We have calculated above that from the annual production of 17 kcal • m-2 •yr-1 of pelagic predators 1.5 kcal. m-2. yr-1 is removed by pelagic fisheries, and we have assumed that 3.4 kcal^m-2^yr-1 is lost by natural death, i.e. not eaten by other predators. This leaves approximately 12 kcal^m-2^yr-1 available as food for demersal fish. If this is all consumed by demersal fish, there is a balance of 24 - 12 = 12 kcal^m-2^yr-1 to be made up by devouring benthic fauna. As a fraction of the annual production of benthic herbivores this is 12 X 100/37.5, or about 30 per cent. Comparing this with Thorson's estimate quoted earlier (see page 241) that demersal fish take only 1-2 per cent of available fish food, with the rest consumed by invertebrate predators, it is clear that some assumptions are considerably astray. More information is necessary.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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