Using both satellite imagery and local environmental knowledge, researcher Jennifer Selgrath (@jennyselgrath) investigated how small-scale fishing has evolved over six decades on Danajon Bank, a double-barrier reef system in central Philippines.
With millions of small-scale fishers operating around the world, we need to understand the impact of these fisheries on coastal marine ecosystems. How well do marine habitats withstand and recover from overfishing and destructive fishing practices? What is the best way to track habitat destruction and recovery, and how can policy influence the fishing gears (e.g. trawl nets, traps, purse seines) that are used?
Jenny's research documents the long-term impact of small-scale fishing, as well as trade-offs between local knowledge and satellite imagery when it comes to mapping habitats and, ultimately, making policy recommendations.
(Banner photo: Project Seahorse)
The Philippines is in the coral triangle – the global center of marine biodiversity. It contains the third most extensive reef system in the world and is home to over 400 scleractinian coral species and several species of seahorses. In addition harboring rich ocean life, coral reefs in the Philippines provide food and livelihoods for many communities by supporting small-scale fisheries. Small-scale fisheries in coral reef ecosystems are characterized by the variety of fish and invertebrate species that they target and the many types of fishing gears that they use. Common fishing gears include spear fishing, various nets such as seines and gillnets, hand line fishing, and traps. Reef fisheries in the Philippines once provided abundant catches, but the reefs have become degraded and fishers now catch much less. In fact, coral reefs in the Philippines are considered to be some of the most threatened in the world due to damaging human activities, including fishing.
Changing Sustainability of Small-Scale Fisheries
For small-scale fisheries, the processes through which benign fishing becomes damaging is not well understood. Jenny interviewed hundreds of fishers to document how their fishing practices have changed over their lifetimes. She has found that small-scale fisheries have intensified over time with a growing use of gears that catch anything in their path and gears that directly damage corals and other beneficial coastal habitats, such as seagrass beds. Additionally Jenny considered if there was any evidence that changing fisheries governance influenced fishing practices. She found evidence for the ‘stickiness’ of unsustainable fishing policies; in some cases, practices adopted when governance promoted catching the maximum amount of fish over sustainability persisted decades after the policies had been revised.
Dynamic Spatial Patterns of Small-Scale Fisheries
The sustainability of small-scale fisheries could potentially be improved by identifying locations where direct impacts and habitat damage are concentrated. Using a participatory mapping approach, Jenny worked with fishers to map where people fish and how that has changed over half a century (1960 – 2010). She has found that during that time there has been a large areal expansion of fishing grounds and a dramatic increase in fishing pressure as many more people now fishing in each location. Locations that were popular early on remained the most popular fishing spots today. This shows that there has been long-term consistency in where the fisheries and their impacts are focused.
Mapping Underwater Habitats
Detailed habitat maps are critical for conservation planning, yet for many coastal habitats only coarse-resolution maps are available. As the logistic and technological constraints of habitat mapping become increasingly tractable, habitat map comparisons are warranted. Jenny compared the accuracy and conservation implications for two approaches for mapping shallow seafloor habitats: local environmental knowledge (LEK) obtained from interviews with fishers; and remote sensing analysis of very high spatial resolution satellite imagery (2.0 m pixel size). Her work helped to identify strengths and weakness of both mapping approaches for conservation planning. Because RS provided a more accurate estimate of habitat distributions, it would be better for conservation planning for species sensitive to fine-spatial scale seascape patterns (e.g. habitat edges), while LEK is more cost effective and appropriate for mapping coarse habitat patterns. Goals for maps used in conservation should be identified early in their development.
Spatial Resilience of Coral Reefs to Long-Term Fishing Impacts
Identifying coastal areas with a high capacity to absorb impacts from fishing without becoming degraded is one step towards effectively addressing threats to the ocean. This knowledge can be incorporated into plans for conservation actions, particularly those focusing on spatial management options such as reserves. Jenny is currently working to identify which parts of the Danajon Bank have been able to withstand high levels of fishing impacts without becoming degraded (i.e. changing from coral dominated to algae and rubble dominated). At the locations that have a high threshold to fishing impacts, she will identify the biophysical characteristics that contribute to the location’s resilience. These findings will be incorporated into conservation planning for the region, and can help managers, scientists, and stakeholders prioritize areas for protection.
Images from the field
Selgrath, J.C., S.E. Gergel and A.C.J. Vincent. (2017) Incorporating spatial dynamics greatly improves estimates of fishing pressure: Long-term participatory mapping of coral reef fisheries. ICES Journal of Marine Science. doi.org/10.1093/icesjms/fsx108
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