Artisanal fish fences pose broad and unexpected threats to the tropical coastal seascape

Gear restrictions are an important management tool in small-scale tropical fisheries, improving sustainability and building resilience to climate change. Yet to identify the management challenges and complete footprint of individual gears, a broader systems approach is required that integrates ecological, economic and social sciences. Here we apply this approach to artisanal fish fences, intensively used across three oceans, to identify a previously underrecognized gear requiring urgent management attention. A longitudinal case study shows increased effort matched with large declines in catch success and corresponding reef fish abundance. We find fish fences to disrupt vital ecological connectivity, exploit > 500 species with high juvenile removal, and directly damage seagrass ecosystems with cascading impacts on connected coral reefs and mangroves. As semi-permanent structures in otherwise open-access fisheries, they create social conflict by assuming unofficial and unregulated property rights, while their unique high-investment-low-effort nature removes traditional economic and social barriers to overfishing

Quantifying the development of small-scale fisheries on coral reefs, and their impact on habitats

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.Science, Faculty ofZoology, Department ofGraduat

How Much is Enough? Improving Participatory Mapping Using Area Rarefaction Curves

Participatory mapping is a valuable approach for documenting the influence of human activities on species, ecosystems, and ecosystem services, as well as the variability of human activities over space and time. This method is particularly valuable in data-poor systems; however, there has never been a systematic approach for identifying the total number of respondents necessary to map the entire spatial extent of a particular human activity. Here, we develop a new technique for identifying sufficient respondent sample sizes for participatory mapping by adapting species rarefaction curves. With a case study from a heavily fished marine ecosystem in the central Philippines, we analyze participatory maps depicting locations of individuals’ fishing grounds across six decades. Within a specified area, we assessed how different sample sizes (i.e. small vs. large numbers of respondents) would influence the estimated extent of fishing for a specified area. The estimated extent of fishing demonstrated asymptotic behavior as after interviewing a sufficiently large number of individuals, additional respondents did not increase the estimated extent. We determined that 120 fishers were necessary to capture 90% of the maximum spatial extent of fishing within our study area from 1990 to 2010, equivalent to 1.1% of male fishers in the region. However, a higher number of elder fishers need to be interviewed to accurately map fishing extent in 1960 to 1980. Participatory maps can provide context for current ecosystem conditions and can support guidelines for management and conservation. Their utility is strengthened by better consideration of the impacts of respondent sample sizes and how this can vary over time for historical assessments.Forestry, Faculty ofNon UBCForest and Conservation Sciences, Department ofReviewedFacult

Mapping for coral reef conservation: Comparing the value of participatory and remote sensing approaches

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. Here we compare two mapping approaches: local environmental knowledge (LEK) obtained from interviews; and remote sensing analysis (RS) of high spatial resolution satellite imagery (2.0 m pixel) using object-based image analysis. For a coral reef ecosystem, we compare the accuracy of these two approaches for mapping shallow seafloor habitats and contrast their characterization of habitat area and seascape connectivity. We also explore several implications for conservation planning. When evaluated using independent ground verification data, LEK-derived maps achieved a lower overall accuracy than RS-derived maps (LEK: 66%; RS: 76%). A comparison of mapped habitats found low overall agreement between LEK and RS maps. The RS map identified 5.4 times more habitat edges (the border between adjacent habitat classes) and 3.7-6.4 times greater seascape connectivity. Since the spatial arrangement of habitats affects many species (e.g., movement, predation risk), such discrepancies in landscape metrics are important to consider in conservation planning. Our results help 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), whereas 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

Shifting gears: Diversification, intensification, and effort increases in small-scale fisheries (1950-2010)

<div><p>Locally sustainable resource extraction activities, at times, transform into ecologically detrimental enterprises. Understanding such transitions is a primary challenge for conservation and management of many ecosystems. In marine systems, over-exploitation of small-scale fisheries creates problems such as reduced biodiversity and lower catches. However, long-term documentation of how governance and associated changes in fishing gears may have contributed to such declines is often lacking. Using fisher interviews, we characterized fishing gear dynamics over 60 years (1950–2010) in a coral reef ecosystem in the Philippines subject to changing fishing regulations. In aggregate fishers greatly diversified their use of fishing gears. However, most individual fishers used one or two gears at a time (mean number of fishing gears < 2 in all years). Individual fishing effort (days per year) was fairly steady over the study period, but cumulative fishing effort by all fishers increased 240%. In particular, we document large increases in total effort by fishers using nets and diving. Other fishing gears experienced less pronounced changes in total effort over time. Fishing intensified through escalating use of non-selective, active, and destructive fishing gears. We also found that policies promoting higher production over sustainability influenced the use of fishing gears, with changes in gear use persisting decades after those same policies were stopped. Our quantitative evidence shows dynamic changes in fishing gear use over time and indicates that gears used in contemporary small-scale fisheries impact oceans more than those used in earlier decades.</p></div

A brief overview of four eras of Philippines fisheries governance.

<p>A brief overview of four eras of Philippines fisheries governance.</p

Map of the study area and 23 sampled villages in the Danajon Bank, Philippines, a biodiversity hotspot within the Coral Triangle.

<p>Symbols indicate the location of villages in the ecosystem.</p

Changes in fishing gears during four eras of fisheries governance (1950–2010) (n = 391 respondents).

<p>(a) Mean number of small-scale fishing gears used by individual fishers. (b) Richness of small-scale fishing gears (i.e. total number of gears used by all fishers). (c) Simpson’s Index of Diversity of small-scale fishing gears used by all fishers. Fishing gears were classified as 93 specific gears and six randomly selected years were sampled during each Governance Era. Letters denote significant differences in gear use between Governance Eras at p < 0.05 as indicated by a Kruskal-Wallis Multiple Comparison post-hoc test. This change was largely due to the growing number of fishers.</p