Callihan et al.: Effect of demography on the spatial distribution of the Albemarle Sound-Roanoke River stock of Morone saxatilis 
137 
Table 2 
Diagnostics with Akaike’s information criterion (AIC) for candidate multinomial lo- 
gistic regression models that relate the recapture area (Albemarle Sound estuary, 
Pamlico Sound estuary. North Carolina ocean waters, or northern coastal waters 
from Virginia to Massachusetts) of tagged Striped Bass (Morone saxatilis) to fish 
length and total annual stock abundance for the years 1991-2008. Each model rep- 
resents a different combination of these explanatory variables. Note that A;=Akaike’s 
differences and tr^Akaike’s weights, where lower values of A; and higher values of 
W[ indicate greater relative empirical support for a model. 
Model 
AIC 
A; 
Wi 
Length + abundance 
1003.2 
0.0 
0.80 
Length only 
1007.0 
3.8 
0.12 
Length + abundance + length x abundance 
1007.8 
4.6 
0.08 
Abundance only 
1465.4 
462.2 
0.0 
Intercept only 
1496.1 
492.9 
0.0 
71 = 1040) occurred within the Albemarle Sound estu- 
ary (Fig. 5A). Yet, only 47% of returns of fish 600-799 
mm TL (?i= 102) and 2% of returns of fish >800 mm TL 
(ii=55) occurred in Albemarle Sound; most tag returns 
of these larger fish occurred in ocean waters (Fig. 5, 
B and C). Interestingly, the majority (78%) of tag re- 
turns of the largest fish in this study (800-1105 mm 
TL) occurred in distant coastal waters from New Jer- 
sey to Cape Cod, 780 to 1250 km from the release site 
(Fig. 50. 
Stock abundance also affected the areas in which 
Striped Bass were recaptured. The best model pre- 
dicted a slight increase ( ~ 5%) in recapture of small 
Striped Bass (<600 mm TL) in the Pamlico Sound re- 
gion as stock abundance increased from 1 to 2 million 
fish (Fig. 4B). This trend also was evident in empirical 
tag return data. Returns from the Pamlico Sound es- 
tuary, -6% of all returns, occurred only during years 
in which stock abundance exceeded 1.4 million fish. 
There were no returns from the Pamlico Sound estu- 
ary during years of lower abundance (1. 0-1.1 million 
fish) (Fig. 6). 
Discussion 
Continuous tagging over a 20-year period, a length 
of effort that is rare in most fisheries, allowed us to 
determine the strong effect of fish size and relative- 
ly smaller effect of stock abundance on a fish stock’s 
spatial distribution. Multiple stocks of Striped Bass 
co-occur along the East Coast of the United States 
during nonspawning periods. Therefore, by tagging 
fish on their natal spawning grounds (when stocks are 
separated), we were able to investigate stock-specific 
movements and spatial distribution — information that 
could otherwise not have been resolved with approach- 
es such as fisheries-independent surveys (e.g., trawl 
surveys). In this section, we provide further details 
on the effects of fish size and stock abundance on the 
spatial distribution of the AR stock of Striped Bass 
and on the implications for management of Striped 
Bass. 
Effects of fish size on recapture area 
The increase in tag returns of the AR stock from re- 
gions outside its natal estuary over the past 2 decades 
was largely due to expansion of the age and size struc- 
ture of the stock as it recovered. The majority of re- 
turns (67%) that occurred outside the Albemarle Sound 
estuary during the stock recovery period were from 
ocean waters. Model results and empirical data both 
showed the probability of Striped Bass being recap- 
tured in ocean waters increased dramatically with fish 
size beyond 600 mm TL, to the point where the larg- 
est individuals (>800 mm TL) were almost exclusively 
captured in ocean waters. Therefore, it is not surpris- 
ing that returns from ocean waters increased over the 
past 2 decades as more fish from this largest size class 
(which was the class most likely to emigrate to ocean 
habitats) became available for tagging and recapture 
as the age and size structure of the AR stock expanded. 
The strong size-dependent emigration pattern of 
Striped Bass revealed by this study helps explain 
the lack of recaptures in ocean waters by Hassler 
et al. 1 , who also focused on the AR stock. To collect 
fish for tagging, Hassler et al. 1 primarily used small- 
mesh (<150 mm stretched) gill nets that likely se- 
lected for smaller fish. Indeed, of the 2428 returns in 
their study, most (86%) were from fish 400-550 mm 
TL at tagging, and only 2 returns (<0.1%) were from 
fish >800 mm TL at tagging. Moreover, the vast ma- 
jority (88%) of tag returns in their study occurred 
within the first year at liberty. Therefore, given the 
small sizes of tagged fish and short-term nature of 
returns ( i . e . , small tagged fish did not have time to 
grow into larger size categories because of high har- 
