Operational Plan for the Restoration of Diadromous Fishes to the ...

4. American Shad
Management Stock Structure
A peer review of the ASMFS stock assessment for shad (Limburg et al. 2007)
confirmed the use of individual river stocks as the management unit and also
suggested the use of assessment approaches using regional models that reflect life
history differences in the stocks (southern, Mid-Atlantic and North Atlantic). The
State of Maine currently manages shad stocks based on the river of origin. No
specific information is known about the stock structure, size, or spawning locations
of shad in the Penobscot River or tributaries except that a remnant population exists.
Anecdotal information suggest that the remnant population is small because of the
low frequency and number of shad documented in the Veazie Project fishway, the
low frequency collected during past surveys, and the estimated starting populations
in other river systems.
Meristic/Morphology or Genetic Investigations
Earlier work on American shad included the analysis of otoliths (Williams 1985) and
meristic and morphometric characteristic (Melvin 1984) to assign shad from a mixedstock
summer fishery to one of three broad regions (Canadian Atlantic, mid-US
Atlantic, and south-US Atlantic). Later work by Melvin et al. (1992) examined
morphology and meristic characteristics for American shad from fourteen rivers
between Florida and Quebec. They were able to discern a south to north separation
within four broad regions (Florida to Cape Lookout; Cape Lookout to Cape Cod; Bay
of Fundy; and Gulf of Saint Lawrence). The separation between adjacent regions
was less apparent than between regions more geographically distant. They were
able to correctly classify individuals from a mixed-stock to each region with a 79 and
89 percent correct classification.
Genetic investigations to discriminate populations of American shad based on
morphology, protein electrophoresis, and analysis of mitochondrial DNA (mtDNA)
and nuclear DNA microsatellite variation have found shad populations to be only
weakly to moderately differentiated and subject to substantial amounts of gene flow
(Nolan et al. 2003).
Four studies that used restriction endonuclease (RE) analysis of mitochondrial DNA
(mtDNA) found that differences among 23 east coast shad populations occurred
primarily as variations in the frequencies of common and shared mtDNA haplotypes
(Bentzen et al. 1989; Nolan et al. 1991; Epifanio et al. 1995), and haplotype
frequencies generally were temporally stable (Brown et al. 1996). Because no
single or group of haplotypes completely discriminated river stocks or regional
complexes, only 28 percent of individual fish could be correctly reallocated to their
river of origin (Epifanio et al. 1995). Surprisingly, a major life history variation
(semelparity in populations south of Chesapeake Bay and iteroparity to the north)
was not revealed by the mtDNA analysis. In a study of three anadromous fish
PRFP Page 122