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

Determining if a population is discrete requires either one of the following conditions:
1. It is markedly separated from other populations of the same taxon as a consequence
of physical, physiological, ecological, or behavioral factors. Quantitative measures of
genetic or morphological discontinuity may provide evidence of this separation.
2. It is delimited by international governmental boundaries within which differences in
control of exploitation, management of habitat, conservation status, or regulatory
mechanisms exist that are significant in light of Section 4(a)(1)(D) of the Act.
If a population is deemed discrete, then the population segment is evaluated on terms of
significance which may include, but is not limited to, the following:
1. Persistence of the discrete population segment in an ecological setting unusual or
unique for the taxon.
2. Evidence that loss of the discrete population segment would result in a significant gap
in the range of the taxon.
3. Evidence that the DPS represents the only surviving natural occurrence of a taxon
that may be more abundant elsewhere as an introduced population outside its historic
range.
4. Evidence that the discrete population segment differs markedly from other
populations of the species in its genetic characteristics.
If a population segment is deemed discrete and significant then it is a distinct population
segment. The DPS should be evaluated for endangered and threatened status based on the Act’s
definitions of those terms and a review of the factors enumerated in Section 4(a)(1). 19
2.2. DPS Determination
The SRT concluded that Atlantic sturgeon should be divided into five distinct population
segments (Figure 15). The five DPSs were named: 1) Gulf of Maine, 2) New York Bight 3)
Chesapeake Bay, 4) Carolina, and 5) South Atlantic. The Saint Lawrence and Saint John rivers
were not evaluated as a DPS because of a combination of the following factors:
• Both mtDNA and nDNA studies have been performed on the Saint Lawrence and Saint
John River populations (King et al. 2001, Waldman et al. 2002, Supplemental data from
Ike Wirgin and Tim King 2006). Mitochondrial DNA analysis has shown that little
divergence has occurred in northern populations of Atlantic sturgeon as populations
ranging from the Kennebec River, ME to the Saint Lawrence River, Canada are
predominately homogenous (1 genotype). However, nDNA microsatellite analysis has
found these same rivers to be genetically diverse (T. King supplemental data 2006). The
19 ESA Section 4(a)(1) states that a species is “threatened” or “endangered” if any one or more of following factors
causes it to be, or likely to become, in danger of extinction throughout all or a significant portion of its range: (A)
the present or threatened destruction, modification, or curtailment of habitat or range; (B) overutilization for
commercial, recreational or educational purposes; (C) disease or predation; (D) the inadequacy of existing
regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence.
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