Uniting historic perspectives, human behaviour, and habitat use to assess the future for overfished seahorses

This dissertation casts new light on reconciling fisheries and conservation. This reconciliation is particularly challenging for small-scale fisheries, because they are data-poor, but it is necessary to sustain biodiversity and food security. My research focuses on a typical small-scale fishery in the Central Philippines that catches seahorses.

I begin by providing an historic reconstruction of seahorse catch rates, the first of its kind despite a multi-decade, global trade for seahorses. I quantified fisher perceptions of the decline in trade to set historic baselines. Results showed that relying solely on recent decades of data could underestimate IUCN Red List extinction risk for historically exploited fish such as my study species, Hippocampus comes.

My research contributed robust approaches to incorporating fisher knowledge into quantitative assessments. I developed a novel approach to correct for inaccuracies in fishers’ memories of past events and showed, for the first time, that conservation assessments are sensitive to assumptions made when analyzing local knowledge. Comparisons I made between catch rate trends estimated by resource users and those obtained using standard approaches (catch landings or underwater surveys) suggest that fisher interviews or logbooks are a reasonable proxy for more costly ‘scientific’ methods. In contrast, interviews do not allow inferences about the absolute value of catch rates at scales relevant to management/conservation.

My findings raise questions about the assumed sustainability of small-scale fisheries and identified new strategies to protect them. I conducted a novel analysis of spatial fishing behaviour that illustrates the capacity of small-scale fisheries to exert considerable cumulative pressure on marine systems, despite their seemingly benign gears.

Finally, I conducted the first study on how depth refugia might help sustain coral-reef fish populations by combining fisheries modeling with IUCN Red List conservation assessments. Results emphasize the importance of locating some protected areas at depths inaccessible to small-scale fishers. Such tactics will contribute towards safeguarding biodiversity and food security in coral reef ecosystems. In summary, my thesis takes valuable steps towards finding solutions for marine biodiversity and fisheries crises; it uses pragmatic approaches to deduce key information that is highly relevant to the futures of coral-reef fish and small-scale fisheries.

O’donnell, K.P. (2011). Uniting historic perspectives, human behaviour, and habitat use to assess the future for overfished seahorses. Doctoral dissertation, University of British Columbia, Canada.