Fishing is the most widespread destructive anthropogenic activity on coral reefs (Jennings and Polunin, 1996). Over-fishing will cause a decrease in the abundance, biomass and the mean size of the fish (Russ and Alcala, 1989; Jennings et al., 1995). However it is the techniques used to fish that are the most destructive to the coral. Severe damage is caused by entanglement in fishing lines (Yoshikawa and Asoh, 2004), blast fishing (Figure 3), where explosives are deployed in the water in order to kill the fish (Öhman et al., 1993), and cyanide fishing (Halim, 2002). These lead to localised damage on the reefs and may lead to a phase shift (Jennings and Polunin, 1996).
The extensive removal of certain species of fish can lead to a shift in species composition (Jennings and Polunin, 1996). For example in Kenya the removal of large predatory fish resulted in the increase of herbivorous species such as burrowing sea urchins, which erodes the reef in order to burrow. This increases the rate of reef erosion and lowers coral cover in heavily fished areas (McClanahan and Muthiga, 1987). The mass mortality of urchins in the Caribbean, led to a substantial increase in algal cover (Hughes, 1994). In Fiji the removal of the predatory fish lead to a dramatic increase in reef-eating starfish which resulted in a loss of coral (Dulvy et al., 2004). The removal of herbivorous fish also has an effect, their removal releases the algae from grazer pressure allowing it to outcompete the coral resulting in a more algae dominated reef (Roberts, 1995).