2007 Status Review of Atlantic sturgeon - National Marine Fisheries ...

from subadults (possible strays from other systems). The SRTs most reliable genetic data is
restricted to 12 subpopulations.
To further investigate significant relationships among Atlantic sturgeon subpopulations, the SRT
used genetic distances and bootstrap values, and assignment test values to help determine
subpopulation groupings. As described earlier, assignment or classification tests resulted in 94%
accuracy for identifying sturgeon to their DPS with a range of 88 – 96% when using data
collected only from YOY and adults (Table 6). Genetic trees produced from only YOY and
adult samples were similar among mtDNA and nDNA, and bootstrap values for these trees were
relatively high (at least for nDNA) (Figure 16 and 17). Based on the similarities seen between
mtDNA and nDNA genetic trees, high bootstrap values and classification rates, the SRT
identified five population groupings that were considered to be markedly different: 1) Gulf of
Maine 2) New York Bight, 3) Chesapeake Bay, 4) Carolina, and 5) South Atlantic (Figure 15).
Significant Gap in the Range of the Taxon
Determining whether a gap in the range of taxon would be significant if a DPS went extinct is
somewhat difficult to ascertain with an anadromous fish such as the Atlantic sturgeon. Atlantic
sturgeon are known to migrate great distances between their natal rivers and overwintering areas.
Therefore, estuarine and marine populations are comprised of mixed stocks. Despite this
extensive mixing of migratory sub-adults and adults, adults are known to return to their natal
river to spawn. Therefore, the loss of a DPS would mean the loss of riverine spawning
subpopulations, while marine and estuarine habitat may still be occupied by migratory sturgeon
from other DPSs. Because gene flow is low among subpopulations, Atlantic sturgeon from other
DPSs are not expected to re-colonize systems except perhaps over a long time frame (e.g.,
greater than 100 years) (Secor and Waldman 1999). Thus, the loss of one or more DPSs is
expected to result in a significant gap in the range of the species given that the DPSs as
designated are relatively large. The SRT contends that the loss of one or more of these DPSs
could negatively impact the species as a whole.
Significance Conclusion
The SRT concluded that it is reasonable to conclude that five population groupings of Atlantic
sturgeon within the United States should be considered significant under the DPS policy
guidelines. The five groupings are: 1) Gulf of Maine, 2) New York Bight, 3) Chesapeake Bay,
4) Carolina, and 5) South Atlantic. These conclusions are based on the information presented
above, which note that Atlantic sturgeon are 1) found in five unique ecological settings, 2)
genetic analyses suggest that subpopulations can be easily grouped into five populations with
high certainty (94%) and these groupings correlate well with the five unique ecological settings,
and 3) due to low gene flow among populations, the loss of one or more these five populations
could negatively impact the species as a whole.
Though the SRT is recommending that five DPSs be designated for Atlantic sturgeon, the team
also recommends that individual river subpopulations should be considered distinct
management/recovery units within the DPS for any future recovery planning, as subpopulations
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