Publication type: Thesis (Doctor of Philosophy in Zoology)
Publisher: The University of British Columbia
Author: Jennifer C. Selgrath
Fishing provides an essential source of protein for half a billion people, but many fisheries damage ocean ecosystems including coral reefs. I demonstrated that small-scale fisheries in the Philippines shifted from benign to damaging through several mechanisms and had long-term effects on corals. Fishing effort increased 2.5-fold overall, and over 20-fold in some locations. Increases in total fishing effort were driven by a growing number of fishers, rather than by changes in individual fishers’ behaviour. I documented a growing diversity and spatial overlap of fishing gears, with a growing amount of fishing effort dependent upon destructive, non-selective, and illegal fishing gears. Living corals were less prevalent in places that had experienced heavy fishing during the past 30 years, particularly where coral reefs were close to large villages. In contrast, corals were more likely to be present in deeper locations and in areas that were protected from fishing.
Growing human populations place multiple pressures on social-ecological systems, including coastal oceans. However, the effects of long-term and/or overlapping stressors remain poorly understood, particularly over large spatial scales. My dissertation evaluated how pressures from fishing and co-occurring stressors correspond to current ecological conditions in the Danajon Bank, a coral reef ecosystem in the central Philippines. I used long-term local ecological knowledge (LEK) to map fishing practices (1950-2010) and high spatial resolution satellite imagery to map coastal habitats. This innovative suite of methods enabled me to examine patterns over broader spatial scales and longer time periods than those usually assessed. I met five primary objectives: (1) quantify the spatio-temporal dynamics of fishing effort and gear use; (2) examine the influence of fisheries governance; (3) map the spatial distribution of benthic (seafloor) habitats; (4) model the spatial distribution of living corals in relation to co-occurring stressors and biophysical conditions; and (5) explore the conservation implications of these relationships.
While individuals’ fishing practices were fairly consistent over time, this small-scale fishery has changed dramatically. First, total fishing effort (days per year fished by all fishers) accelerated between 1960 and 2010 because of rapid growth in the number of fishers. Aggregate fishing effort increased almost 2.5-fold and spatially-explicit fishing effort increased over 20-fold. Second, the areal extent of fishing grounds expanded greatly. Third, use of fishing gears changed over time. Diversity of fishing gears increased, as did fishing effort with destructive, active, and non-selective gears. Considering the timing of these changes, I found a lasting influence of fishing policies, and small improvements in the sustainability of fishing gears following implementation of co-management. Finally, I found that the probability that an area supported living corals was affected by fishing through both long- & short-term mechanisms, and I documented strong coral-landscape relationships. My research demonstrates that to strengthen ocean conservation, it will be essential to reduce the frequency and intensity of stressors, remove some areas from exploitation, foster resilience traits of ecosystems, gather data to better understand systems, and strengthen the institutions that can support these endeavors.