Science Advisory Report  2012/041

Assessment of Leatherback Turtle (Dermochelys coriacea) Fishery and Non-fishery Interactions in Atlantic Canadian Waters

Summary

• In support of a five-year review of the Recovery Strategy and development of an Action Plan for the leatherback turtle in Atlantic Canada, interactions with fisheries and non-fishery activities occurring in Atlantic Canadian waters during 2006 – 2010 were examined.
• Information available to determine encounter and mortality rates for fishery and non-fishery related threats to leatherback turtles in Atlantic Canadian waters was summarized.  
• This assessment identified some fisheries interactions that were not identified previously in the Recovery Strategy (e.g., whelk pot). In addition, the geographic analysis of known fisheries interactions has expanded to include the Gulf of St. Lawrence. 
• A rough estimate of the mortality rate for large pelagic longline interactions (21-49%) and other fixed gear fisheries (20-70%) has been suggested based on the available information and expert opinion. Further work would be required to determine other fishery-specific mortality rates.
• Data and methods needed to determine current annual mortalities for each fishery require additional work before credible estimates of total leatherback mortality in Atlantic Canadian waters can be provided. However, information provided in this report is expected to contribute towards refinement of an approach to quantify and rank threats to leatherbacks in Atlantic Canadian waters, as well as an approach to estimate total annual mortality.    
• The risk of interaction with leatherback turtles and resulting mortality is influenced by management measures, fishing practices, and variation in both spatial and temporal distribution of fishing effort and turtle distributions, such that the relative ranking of threats can change over short time scales.     
• Analyses of co-occurrence of fisheries and leatherbacks, as well as information available from sightings networks, are tools to potentially identify and evaluate the threat of fisheries for which observer coverage is limited, as well as to identify fisheries for which mitigation measures should be developed or refined.
• The ability to detect and evaluate fishery and non-fishery interactions remains low. Co-occurrence of vessel traffic with leatherback distribution in Atlantic Canadian waters indicates that the threat of vessel collisions with leatherbacks may be larger than the documented interactions would suggest. Seismic noise and marine debris (plastics) remain potential but undocumented threats to leatherback turtles in Atlantic Canadian waters.
• Cumulative impact and impact trends need to be interpreted in the context of concurrent changes in total Atlantic leatherback population size.

This Science Advisory Report is from the March 1-2, 2012, Leatherback Sea Turtle Part 2: Assessment of Fisheries and Non-Fisheries Related Interactions in Atlantic Canadian Waters.  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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