Seals can become entangled in broken nets and other debris.
Some species are particularly sensitive to disturbance. Now the rarest mammal in Europe, the Mediterranean monk seal numbers just 650 because its breeding sites have been turned into tourist beaches and hotel complexes - and because it is seen as a compet itor to commercial fisheries. Subsistence sealing by isolated communities had little effect on seals, but commercial hunting from the 18th century onwards slaughtered vast herds and brought some species to the verge of extinction.