Callihan et al.: Effect of demography on the spatial distribution of the Albemarle Sound-Roanoke River stock of Morone saxatilis 
141 
fishery (ASMFC 4 ). However, this study revealed that 
some members of the AR stock, those fish surviving to 
sizes >800 mm TL, are indeed migratory and, there- 
fore, unequivocally contribute to (i.e., are harvested by) 
the mixed stock fishery of the Atlantic coast. Because 
management benchmarks for the mixed stock fishery, 
such as the threshold fishing mortality (Fmsy= 0-41; 
ASMFC 4 ), currently are based on data from Chesa- 
peake, Hudson, and Delaware stocks that are poten- 
tially more productive than the AR stock, it is possible 
that the mixed stock fishery could affect the AR stock 
disproportionately. Accordingly, future research should 
establish the productivity of the AR stock of Striped 
Bass in relation to other stocks. If the AR stock is found 
to be less productive, then future work also should de- 
termine the implementation costs of more stringent 
fishing regulations in the mixed stock fishery, namely 
the amount and value of harvest that would be lost 
from more productive stocks (Chaput, 2004; Crozier et 
al., 2004; Hilborn et al., 2004). 
Results from this study also have implications 
for the assessment and management of Striped Bass 
within North Carolina. Currently, landings of Striped 
Bass outside the Albemarle Sound estuary (region 1; 
Fig. 2B) are not included in the AR stock assessment 
(NCDMF and NCWRC 2 ). Stock status is based on the 
estimate of fishing mortality (F , t h res hold = 0-27) for fully 
recruited Striped Bass of age 4-6 and 400-600 mm TL, 
a size group for which fish were found in this study 
to increase their movement to adjacent estuarine sys- 
tems outside the stock boundary as they increased in 
abundance. Therefore, by not including fish that move 
to and are harvested in adjacent systems, the AR stock 
assessment underestimates fishing mortality. Accord- 
ingly, future research should examine the sensitivity of 
fishing mortality estimates from the AR stock assess- 
ment to additional landings of age-4-6 Striped Bass of 
AR origin outside the Albemarle Sound estuary. 
Caveats 
It is important to note that the analyses in this study 
indicate the probability of recapture location; move- 
ments are inferred from these data. Fishermen behav- 
ior (e.g., spatiotemporal differences in fishing effort 
or size targeting because of regulations and economic 
value) can affect and potentially bias tag returns and 
inferences about movement patterns (Hilborn, 1990; 
Gillanders et al., 2001). The size-dependent migration 
pattern that we observed could be due to differences in 
selectivity between ocean and estuarine fisheries; that 
is, small tagged fish could have migrated to the ocean 
but not been caught in the fishery. However, fisheries- 
4 ASMFC (Atlantic States Marine Fisheries Commission). 
2003. Amendment 6 to the Interstate Fishery Management 
Plan for Atlantic Striped Bass. Fishery Management Re- 
port No. 41 of the Atlantic States Marine Fisheries Commis- 
sion, 63 p. [Available from http://www.asmfc.org/uploads/ 
file/sbAmendment6.pdf.] 
independent data indicate that it is predominantly 
the large Striped Bass of the AR stock that migrate to 
ocean waters. In a mobile telemetry study, Haeseker et 
al. (1996) searched the Albemarle Sound during sum- 
mer (May-August) for the presence of 26 telemetered 
Striped Bass (all but 1 fish <600 mm TL) that partici- 
pated in the April Roanoke River spawning run. They 
relocated 25 (96%) of these fish in the Albemarle Sound 
at least 1 month after spawning, providing evidence 
that smaller Striped Bass mostly remain in the estuary 
after spawning. Furthermore, in an ongoing telemetry 
study, 163 Striped Bass ranging in length from 445 to 
1146 mm TL (mean=580 mm TL) were telemetered in 
the Roanoke River during spring, beginning in 2011, by 
Harris and Hightower. 5 Most large fish in their study 
(15 of thel8 individuals >900 mm TL at tagging) have 
been detected by coastal receiver arrays in Massachu- 
setts, New York, New Jersey, Delaware, and Virginia, 
but no smaller individuals have been detected in these 
northern ocean waters (Harris and Hightower 5 ). Hence, 
results from these fisheries-independent telemetry 
studies corroborate the strong size-dependent emigra- 
tion pattern of the AR stock of Striped Bass that we 
inferred from tag recaptures in our study. 
A limitation of our study was that nearly all tag 
returns (99%) from larger fish (>600 mm TL) occurred 
during years of higher stock abundance (>1.5 million 
fish). Therefore, it is possible that the observed ocean 
emigration of larger fish was due in part to the higher 
abundance of similar size conspecifics (i.e., density- 
dependent mechanisms). However, ocean emigration 
of the AR stock of Striped Bass appears to be a size- 
dependent phenomenon related to bioenergetics as de- 
scribed and is probably largely independent of ambi- 
ent population density or abundance. Two lines of evi- 
dence support this notion. First, data on large Striped 
Bass (>600 mm TL) across the more restricted range 
of annual values of stock abundance (1. 5-2.0 million 
fish) indicate that density had little effect (an increase 
<3%) on the probability of large fish being recaptured 
in ocean waters. Second, just as we found in our study, 
Dorazio et al. (1994) found a strong size-dependent em- 
igration pattern for the Chesapeake Bay stock: most 
fish >800 mm TL were recovered in northern ocean wa- 
ters from New Jersey to Maine. Their study occurred 
in 1988-91, years when the Chesapeake Bay stock was 
at relatively low abundance levels and still rebuilding, 
demonstrating that substantial ocean emigration of 
large fish, albeit from a different stock, still occurs at 
low densities. 
5 Harris, J. E., and J. E. Hightower. 2013. Unpubl. data. 
North Carolina Cooperative Fish and Wildlife Research Unit, 
U. S. Geological Survey, and Department of Applied Ecology, 
North Carolina State Univ., Raleigh, NC 27695. 
