Modeling habitat and bycatch risk for dugongs in Sabah, Malaysia

Abstract

Bycatch of marine megafauna in fishing gear is a problem with global implications. Bycatch rates can be difficult to quantify, especially in countries where there are limited data on the abundance and distribution of coastal marine mammals, the distribution and intensity of fishing effort, and coincident interactions, and limited bycatch mitigation strategies. The dugong Dugong dugon is an IUCN-listed Vulnerable species found from the eastern coast of Africa to the western Pacific. As foragers of seagrass, they are highly susceptible to bycatch in small-scale fisheries. To address the knowledge gaps surrounding marine mammal bycatch, we used existing survey and fishing effort data to spatially characterize the risk of bycatch for this species. Using Sabah, Malaysia, as a case study, we employed presence-only modeling techniques to identify habitat associations of dugongs using a maximum entropy distribution model (MaxEnt) based on published sightings data and several geophysical parameters: coastal distance, depth, insolation, and topographic openness. Model outputs showed distance from the coast as the highest-contributing variable to the probability of dugong presence. Results were combined with previously published fishing effort maps of this area to develop a predictive bycatch risk surface. Our analyses identified several areas of high risk where dugong surveys were conducted, but also identified high-risk areas in previously unsurveyed locations. Such methods can be used to direct field activities and data collection efforts and provide a robust template for how existing sightings and fishing effort data can be used to facilitate conservation action in data-limited regions.

Seagrass Habitat Suitability Map at Merambong Shoal, Johor: A Preliminary Study Using Multibeam Echosounder and Maxent Modelling

“…Each of the replicates used a randomly selected seagrass presence-only data. The seagrass presence-only data were separated into training data and test data (75% and 25% of the data, respectively) (Briscoe et al, 2014;Wang et al, 2017). A set of seagrass occurrence data that contained five (5) drop locations within the surveyed area was used.…”

Embracing Complexity and Complexity-Awareness in Marine Megafauna Conservation and Research

“…Spatially-explicit risk assessments have been used to support conservation of habitats in coastal Belize (Arkema et al, 2014;Verutes et al, 2017), marine and terrestrial fauna in Washington state, USA (Samhouri and Levin, 2012;Duggan et al, 2017), freshwater lenses (aquifer) in The Bahamas (Holding and Allen, 2014), and dugongs (Dugong dugon) in Sabah, Malaysia (Briscoe et al, 2014). In Belize, the InVEST habitat risk assessment model (naturalcapitalproject.org) is a spatial risk assessment tool that was applied as part of a coastal zoning process where risk to habitats was used to alter inputs to ecological production functions in mechanistic complex, process-based models of spiny lobster catch and revenue, tourism visitation and expenditures, and natural protection provided by coastal habitats during storms (Arkema et al, 2015;Guannel et al, 2016).…”

Addressing fisheries bycatch in a changing world

“…These and other advances in quantifying spatial patterns have enabled the identification of "bycatch hotspots, " i.e., areas of persistent bycatch events for one or multiple species of conservation concern to focus mitigation efforts (Lewison et al, 2009;Yeh et al, 2013). Characterization of bycatch spatial patterns and hotspots in conjunction with research on animal movement patterns has identified relationships between sea surface temperatures, chlorophyll, geostrophic currents, and other ocean, fishery or gear characteristics and bycatch (James et al, 2005;Polovina et al, 2006;Sims et al, 2008;Zydelis et al, 2011;Briscoe et al, 2014). For example, by identifying oceanographic conditions and habitat features associated with loggerhead and leatherback turtles off Hawaii, the NOAA-led program Turtlewatch creates weekly maps depicting ocean areas where bycatch of both species is more likely (Howell et al, 2008(Howell et al, , 2015.…”