Sea turtles and survivability in demersal trawl fisheries: Do comatose olive ridley sea turtles survive post-release?

Sara M Maxwell,Jacob Nzegoue,Carmen Karen Kouerey Oliwina,Matthew J Witt,Micheline Schummer Gnandji,Pierre Didier Agamboue,Guy-Philippe Sounguet,Jean Churley Manfoumbi,Emmanuel Chartrain,Gaspard Abitsi,Jean Noel Bibang Bi Nguema,Felicien Mavoungou Makanga,Georges Mba Asseko,Marie Pierre Aboro,François Boussamba,Brice Didier Koumba Mabert,Angela Formia

doi:10.1186/s40317-018-0155-1

Abstract

Incidental capture of air-breathing species in fishing gear is a major source of mortality for many threatened populations. Even when individuals are discarded alive, they may not survive due to direct injury, or due to more cryptic internal physiological injury such as decompression sickness. Post-release mortality, however, can be difficult to determine. In this pilot study, we deployed survivorship pop-up archival tags (sPAT) (n = 3) for an air-breathing species, the olive ridley sea turtle (Lepidochelys olivacea), one of the first studies to do so. We found that at least two of the three turtles survived after being captured in demersal fish trawl nets and being resuscitated from a comatose state following standard UN Food and Agriculture Organization guidelines. One turtle died; however, the absence of a change in light level but continued diving activity suggested that the turtle was likely predated. Whether capture contributed to the turtle’s susceptibility to predation post-release is unknown, and average tow duration during this fishing trip was similar in duration to that of a turtle that survived (1.5 h). The two surviving turtles displayed normal horizontal and vertical movements based on previous tagging studies. This study suggests that resuscitation techniques may be effective; however, additional study is necessary to increase sample sizes, and to determine the severity of decompression sickness across different levels of activity and in other fishing gears. This will result in better population mortality estimates, as well as highlight techniques to increase post-release survivorship.

Highlights

IntroductionThe incidental capture of non-target species in fishing gear, is a major human threat to marine species worldwide [1]
Fisheries bycatch, or the incidental capture of non-target species in fishing gear, is a major human threat to marine species worldwide [1]
They can potentially be resuscitated from this state, and several protocols exist for resuscitation (e.g., [5, 15, 16]), of which one of the most common is elevation of the rear end of the turtle to allow the lungs to drain

Summary

Introduction

The incidental capture of non-target species in fishing gear, is a major human threat to marine species worldwide [1]. While sea turtles have behavioral and physiological adaptations to reduce the potential of decompression sickness in their normal diving activity [7, 8], there is evidence that capture in fishing operations results in increased metabolic and locomotor activity, and exertional myopathy [9]. As a result of these physiological impacts, many turtles are brought onboard fishing vessels in a comatose state, where they are unresponsive but still alive. They can potentially be resuscitated from this state, and several protocols exist for resuscitation (e.g., [5, 15, 16]), of which one of the most common is elevation of the rear end of the turtle to allow the lungs to drain. Resuscitation may occur for up to 24 h, or until the turtle appears vagile and alert (reanimated) at which point it is released from the vessel

Methods

Results

Conclusion