Untangling the origin of ghost gear within the Maldivian archipelago and its impact on olive ridley (Lepidochelys olivacea) populations

Abstract

There is little documentation available on the impact of abandoned, lost or discarded fishing nets ('ghost nets') on turtle populations. Here, we utilise data collected over a 5 year period to assess (1) if a particular net type or characteristic was identifiable as entangling more turtles and (2) if particular fishing practices (i.e. types of nets) could be managed to reduce turtle entanglement in the Maldivian archipelago. A total of 131 turtles were entangled in the 752 reported ghost nets, and olive ridley turtles Lepidochelys olivacea appeared to be the most vulnerable (making up 97% of entangled turtles). However, we estimate that the 752 nets in this study, reported over a 51 month period, could have entangled between 3400 and 12 200 turtles across the Indian Ocean prior to being detected in the Maldives. Mesh size, seasonality (i.e. north east monsoon), and the presence of floats were all identified as variables significantly affecting the likelihood of turtle entanglement. The probability of entanglement increased as the mesh size increased but decreased when floats were present. Additionally, turtles were more likely to be entangled during the north east monsoon when currents flow from east to west. Cluster analysis indicated that there were at least 11 broadly assigned net types found floating in the study area, and these were dominated by trawl and gill nets. Our analyses highlight the need for a detailed database of existing gear types coupled with gear marking to improve traceability of ghost nets in the Indian Ocean.

Sublethal Injuries and Physical Abnormalities in Maldives Manta Rays, Mobula alfredi and Mobula birostris

“…obs. ), and ghost drift nets are also a problem (e.g., Stelfox et al, 2019Stelfox et al, , 2020, overall, the impacts of destructive net fishing practices are greatly reduced in the region because of these protective measures. However, the potential for net entanglement to result in the death of an individual may mean that its prevalence is underreported here.…”

The Olive Ridley Project (ORP): A successful example of how to engage researchers, conservation practitioners and civil society

“…Engaging in such practices means that there is a marked increase in the volume of data gathered compared with if researchers were left to generate this themselves. This in turn results in a parallel increase of model estimates, and more accurate predictions/projections related to the question being asked (see, for example, Stelfox et al, 2019).…”

Threats and Vulnerabilities for the Globally Distributed Olive Ridley (Lepidochelys olivacea) Sea Turtle: A Historical and Current Status Evaluation

“…Foraging area locations can overlap with trawl fishery areas, increasing the possibility of turtles becoming entangled in longlines, shrimp nets, and bomb fishing, among other things [ 50 , 88 ]. The Maldives islands have reported 131 entangled sea turtles during a period of 5 years in trawl or gill nets, and olive ridley turtles appeared to be the most vulnerable accounting for 97% of the incidents [ 19 ]. Unfortunately, the accumulation of plastics debris from fishing nets at crucial nesting sites puts both adult females and hatchlings turtles at risk of becoming entangled in it, preventing them from reaching the sea [ 95 ].…”

“…Despite the fact that olive ridley nesting beaches are protected by many nations, eggs are still taken, and nesting females are slain for their flesh and skin. In addition, and although many commercial fishing fleets now use TEDs in their nets, fishing nets also take a heavy toll, snagging and drowning these turtles on a regular basis [ 19 , 162 ]. Therefore, olive ridley worldwide populations will continue to decline unless poaching laws are better enforced and the universal use of turtle excluder devices is implemented in trawl nets fishing vessels, mainly in the most important feeding and breeding sites of this species [ 163 ].…”

“…This flexibility might allow them to cope with unpredictable changes in dynamic ecosystems, and could help explain why olive ridleys are the most abundant of all sea turtles [ 5 , 18 ]. However, because of their slow intrinsic growth rate and anthropogenic pressures, olive ridley turtles are vulnerable, and many populations have decreased Coastal development and commercial fishing activities continue to degrade, change, and destroy natural conditions at nesting and feeding grounds, endangering the long-term existence of many olive ridley rookeries worldwide [ 4 , 19 ]. Along the seaside, olive ridleys face a number of dangers.…”