| This thesis explores some fundamental questions about seamount ecology and fisheries. Initially, I characterized the seamount distribution on the Azores Exclusive Economic Zone using two bathymetry datasets. The algorithm developed was able to map and describe 63 large and 332 small seamount-like features in the EEZ of the Azores. The distribution suggests that large proportion of seamounts occur in chains along the Mid Atlantic Ridge, however, few isolated seamounts are also present in the Azores. In clarifying how seamounts affect primary productivity, I show that primary production enhancement is not sufficient to support often-observed large aggregations of fish. My work supports an alternative hypothesis, that a horizontal flux of prey is the key factor in sustaining rich communities living on seamounts. Additionally, the importance of seamounts to some large pelagic fish, marine mammals and seabirds is also demonstrated. In the case of skipjack and bigeye tuna, common dolphin and Cory's shearwater, these species were significantly more abundant in the vicinity of some seamount summits. I found that seamounts may act as feeding stations for some of these visitors. The methodology developed, however, failed to demonstrate seamounts' association for bottlenose dolphins, spotted dolphin, sperm whale, terns, yellow-legged gull, and loggerhead sea turtles. Fisheries exploitation is a major threat to seamount ecosystems, but I am not presently able to quantify the amount of catches taken from seamounts around the world. Instead, I demonstrate that global landings of demersal marine fishes have shifted to deeper water species over the last 50 years, an indirect indication that seamounts have also increased in importance. Moreover, I show that 'deep-water', 'seamount' and 'seamount-aggregating' fish stocks may be at serious risk of depletion, since their life histories render them highly vulnerable to overfishing with little resilience to overexploitation. Finally, ecosystem modelling analyses indicate that sustainable seamount fisheries with tolerable ecosystem impacts can be found only by maximizing an 'ecological' objective function. This suggests that industrial fisheries are not viable on seamounts. However, regulated small-scale artisanal fishing fleets could be sustained by seamount ecosystems. |
