Use of the SAFE Index to Evaluate the Status of a Summer Aggregation of Atlantic Sturgeon in Minas Basin, Canada, and the Implication of the Index for the USA Endangered Species Designation of Atlantic and Shortnose Sturgeons

Abstract

Sturgeon species worldwide have undergone population declines due to habitat alteration and overexploitation and many are listed by the International Union for Conservation of Nature (IUCN) and national agencies. Atlantic and shortnose sturgeon on the east coast of North America are listed as “endangered” or “threatened” over most of their ranges. It has been proposed, however, that IUCN risk categories are ambiguous and do not consider the threat status of a species in relation to a minimum viable population level. Here, we examine the Species Ability to Forestall Extinction (SAFE) Index, which is a heuristic measure of a species relative distance from extinction, and other available information on Atlantic and shortnose sturgeon with regard to the risk status of the two species. To move beyond a ‘tipping point’ designation of threatened, the SAFE Index requires a species abundance of 5000 adults (SAFE Index = 0.0). DNA and mark-recapture data for Atlantic sturgeon in Minas Basin, Canada indicates a USA/Canada mixed stock of ∼10,000 fish aggregate there in summer. The SAFE Index for this population is 0.28 indicating abundance is within the “vulnerable” threshold range for the Index although it includes but a small portion of the Atlantic sturgeon in the western Atlantic. Estimates for the east coast of North America suggest the Atlantic sturgeon population could consist of ∼177,000 sub adults and adults for a SAFE Index of 1.55. Additionally, the present spawning range of Atlantic sturgeon in North America is ∼99% of the historically known range and the number of stocks is near the historic level (33+) which means the species does not meet IUCN criteria for listing. Similarly, shortnose sturgeon has an Atlantic coast population of ∼96,800 adults (SAFE Index of 1.29) and a species range and number of stocks (26+) that has not changed substantially from the historical situation. Since the abundance of Atlantic and shortnose sturgeon are well above the SAFE threshold for “threatened” and they lack other accepted criteria for endangered or threatened designation, we conclude that the risk status of both species should be reconsidered.

Keywords:

• population sizes
• risk status
• SAFE index
• sturgeons

ACKNOWLEDGMENTS

We thank A. Redden and J. Broome of the Acadia Centre for Estuarine Research for deployment of the Acadia line of acoustic receivers in Minas Passage. We thank the Ocean Tracking Network (OTN) of Dalhousie University for their deployment of a Minas Passage line of receivers. We are grateful to T. Lewis, W. Linkletter, R. Wilcox and D. Porter for allowing us to sample in their fishing weirs. We thank Captain G. Travis and C. Travis for allowing us to sample their trawler catches. We thank S. Wehrell, A. Spares, G. Nau, M. McLean, W. Roberts, T. Gregoire, L. Boudreau, M. Gregoire, J. Breadsall, S. Munroe, D. Quinn, M. Baker, and J. Whidden for sturgeon tagging field work in all weather and at all times of the day and night. G. Wippelhauser provided us with unpublished data on the number of individually, acoustic tagged sturgeon in Maine. We thank P. Rago for insight on coastal population analysis; C. Chambers for discussion, sushi, and review; and K. Sulak for providing an excellent critical review full of ideas, suggestions, and further reading.

Additional information

Funding

Funding for students was provided by A. Redden through Nova Scotia Power and the Fundy Ocean Research Center for Energy and for T. Avery by the Department of Fisheries and Oceans Canada. M. Stokesbury's and M. Dadswell's students were funded by the Natural Sciences and Engineering Research Council (NSERC) through OTN Canada, and the Acadia University Faculty Research Fund. M. Stokesbury was supported by the Canada Research Chairs Program. M. Balazik was supported by postdoctoral funding through the Virginia Commonwealth University.