Research Document - 2010/089
Loggerhead Sea Turtles (Caretta caretta) in Atlantic Canada: Biology, Status, Recovery Potential, and Measures for Mitigation
By L.E. Harris, W.E. Gross, R.K. Smedbol, and L. Hussey-Bondt
Abstract
A recovery potential assessment (RPA) for the Canadian Atlantic population of loggerhead sea turtles (Caretta caretta) was undertaken for review in a February 2010 meeting. The assessment was conducted in anticipation of the Committee on the Status of Endangered Wildlife in Canada’s (COSEWIC) evaluation of the population’s status during their April 2010 meeting. In April, COSEWIC designated the loggerhead sea turtle in Atlantic Canada as Endangered. The RPA will inform the listing decision, socio-economic analyses, and consultations with the public. Should this species be legally listed as Endangered under the Species at Risk Act, the RPA will also inform the recovery strategy.
Loggerhead sea turtles in Atlantic Canadian waters are considered to be primarily oceanic juveniles, foraging where water depths are greater than 200m. Available data are limited to opportunistic sightings, fisheries bycatch, strandings and limited survey information. Absolute abundance or trends of the Canadian portion, or even the overall Northwest Atlantic loggerhead sea turtle population in the oceanic habitat, cannot be estimated. However, because females exhibit nesting site fidelity, trends in nests can be used as a proxy for trends in mature female abundance. There appears to have been a decline in the number of nests since 1998, notably in the largest breeding unit in the Atlantic (Peninsular Florida). Published population modeling studies suggest that the Northwest Atlantic loggerhead sea turtle population is likely to continue to decline given current estimates of population growth rates and the effects of human-induced mortality. However, these studies also indicate scope for recovery if total mortality is reduced. The reduction of mortality in Canadian waters alone may not be sufficient to achieve recovery, but it will be an important component. In addition to minimizing mortality of loggerhead sea turtles in Canadian waters, international cooperation to reduce threats to the population as a whole is likely required to achieve recovery.
The range of loggerhead sea turtles in Atlantic Canadian waters is from Georges Bank, along the edge of the Scotian Shelf and Grand Banks, to the limits of the Exclusive Economic Zone (EEZ) with occasional forays into waters on the shelf. There is no evidence of a reduction in their historical range. In Canadian waters, habitat appears to be defined geographically and temporally, in part, by sea surface temperature. They are encountered in waters greater than 15°C, especially between 20-25°C, which restricts them to thermally dynamic waters along the shelf break and offshore. The primary use of habitat in Canadian waters is thought to be for foraging. They do not have any known dwelling-place similar to a den or nest during any part of their life cycle in Canada; hence, the concept of “residence” does not apply.
Commercial fishing poses the most significant threat to loggerhead sea turtles in the Northwest Atlantic. The only documented source of human-induced harm or mortality in Canadian waters is fishery bycatch in the Canadian tuna and swordfish longline fishery. Ship-strikes, pollution in the form of entanglement in marine debris, offshore oil and gas production, climate change, and trophic change are potential human-induced threats. There are no documented cases of these threats causing harm or mortality in Atlantic Canadian waters, but this may be a reflection of the lack of information on loggerhead sea turtlesr than that none has occurred. Potential mitigation measures and alternatives to minimise the threat posed by the tuna and swordfish longline fishery have been identified (e.g., hook type and size, set time, bait type).
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