For example, the input of chemical substances can lead to reduced available energy of a species due to the energy exerted in combating the chemical. The effects can also be hierarchically dependent. One human activity can cause many different pressures, and each of these pressures can affect organisms in various ways. 2012).īeside the assessment of incidental by-catch, hunting must also be taken into account (See Chapter 4.6 Species removal by fishing and hunting) because the total anthropogenic mortality has to be related to the population in order to assess its impact.Ī HELCOM core indicator to assess the number of drowned mammals and waterbirds caught in fishing gear is undergoing further development (HELCOM 2018au). Incidental by-catches also occur in other types of fishing gear, such as longlines and traps (ICES 2013b).Ī rough estimate indicated that between 100,000 and 200,000 waterbirds drown annually in the North and Baltic Seas, of which the great majority drowns in the Baltic Sea (Žydelis et al.

Diving waterbirds are especially vulnerable to being entangled in gill nets and other types of nets. Drowning in fishing gear can be a strong pressure on populations of divers, grebes, cormorants, alcids, mergansers and ducks, especially in wintering areas with high densities of waterbirds.

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