Bottom Trawling

 

Figure 6: Two images showing the effects of bottom trawling gear in contact with sea floor leaving dead or damaged coral matter (Images by Les Walting).

Figure 5: Two images showing the effects of bottom trawling gear in contact with sea floor leaving dead or damaged coral matter (Images by Les Walting).

In the 1990s, sophisticated equipment was used to explore the deep marine ecosystems of the ocean. These activities began to show severe damage and habitat losses in the marine environment. Commercial bottom trawling being one of these major threats became a concern for scientists, and those of the fishing industries. Actions took place such as open access policies and subsidy-driven over-capitalization in order to help marine ecosystems such as CWCs. Bottom fishing activities has caused directional and unidirectional damage to marine organisms including CWCs. The dragging of fishing gear (bottom trawls and dredges) along the ocean bottom and any sort of contact of gear with the sea floor has caused a major threat to CWCs. Figure 5 shows the damage caused to the sea floor by bottom trawling activities.

On average, bottom trawlers sweep about 33 km2 of seabed (Hall-Spencer et al, 2002). By analysing the deep sea that has been affected (figure 5), there is clear evidence that bottom trawling disrupts CWC communities. Parts of the trawl such as the doors and ground line rollers also flatten corals. Corals are also ripped and broken from the contact with the base of the trawl net. These effects cause CWC communities to reduce in structure of coral grounds. It has been shown that species diversity and survival has a positive correlation with the structural complexity of corals. Therefore bottom trawling has caused a decrease in coral productivity and species richness. Long lived species have been stated to have low growth and reproduction rates (Pauly et al, 1998). This further affects trophic levels of marine ecosystems that are related. These long lived species become short lived (Freiwalk et al, 2004).

The video below will give a better look at what occurs during bottom trawling and its impacts to the sea floor habitats including CWCs.

Leave a Reply