Report of the workshop on marine turtle longline post-interaction mortality

The National Marine Fisheries Service (NMFS), Office of Protected Resources (OPR), was charged with conducting a review of the NMFS post-hooking mortality criteria, established in February 2001, and determining whether, and if so, how, those criteria should be modified. As part of this review, OPR convened a Workshop on Marine Turtle Longline Post-Interaction Mortality (Workshop) in Bethesda, Maryland on 15-16 January 2004. Seventeen experts in the areas of sea turtle biology, sea turtle anatomy/physiology, sea turtle veterinary medicine, sea turtle satellite telemetry, and longline gear deployment participated in the workshop. Consideration of the workshop discussion, along with a comprehensive review of all of the information available on the issue, led OPR to establish revised post-hooking interaction mortality criteria. Despite the refinement of the criteria, knowledge of the effects of sea turtle interactions with longline gear remains limited and is unlikely to be elucidated further in ways that will be particularly relevant to sea turtle recovery. What is certain is that reducing sea turtle interactions with longline gear is necessary for the long-term survival and recovery of these highly migratory species. A summary of the key changes to the 2001 criteria follows.

Categories: The February 2001 injury categories have been expanded to better describe the specific nature of the interaction. The February 2001 criteria described two categories for mouth hooking: (1) hook does not penetrate internal mouth structure, and (2) mouth hooked (penetrates) or ingested hook. The revised criteria (Appendix 1) divide internal hooking events into three categories that reflect the severity of the injury and account for the probable improvement in survivorship resulting from removal of gear, where appropriate, for each injury. The new criteria also separates external hooking from mouth hooking, eliminates the 'no injury' category, and adds a new category for comatose/resuscitated turtles.

Probable Improvement in Survivorship When Gear is Removed: The new criteria recognize that in most cases removal of all or some of the gear (except deeply ingested hooks) may improve the probability of survival. The categories for gear removal are: (1) released with hook and with line that is greater than or equal to half the length of the carapace; (2) released with hook and with line that is less than or equal to half the length of the carapace; and (3) released with all gear removed. Turtles that have all or most of the gear removed, depending on the nature of the interaction, are expected to have, on average, a higher probability of survival.

Species Difference: Species differences between hard-shelled turtles and leatherbacks likely play a role in post-interaction survivorship. The new criteria takes this into consideration and assigns slightly higher rates of post-interaction mortality for leatherback turtles.