Bacheler et al : Variation in movement patterns of Sc/aenops ocellatus 
415 
The use of multiple tag types and age-dependent se- 
lectivity patterns in our study may have biased our 
analyses of movement patterns of fish by age. Most sub- 
adult red drum were tagged with internal anchor tags, 
which have been shown to have higher retention rates 
than dart tags that were primarily applied to adult red 
drum in our study (Bacheler et al., 2008a). Selectivity 
appears to be dome shaped and centered upon subadult 
red drum within the window limit for red drum catch 
(Bacheler et al., 2008a). Unequal retention rates of tags 
and age-dependent selectivity patterns likely did not 
bias movement rates or distances moved but may have 
biased our analysis of days at large. It is likely that 
adult red drum would have shown even greater differ- 
ences in days at large compared to subadult fish if a 
tag with greater retention had been used for adults and 
there would have been increased selectivity on adult red 
drum during fewer days at large. 
Determining whether estuarine or coastal species 
exhibit seasonally dependent movements is an impor- 
tant step in developing a broader perspective on the 
ecology of a particular species. The limited temporal 
scope and modest sample size of previous estuarine 
tagging studies have made it difficult to quantify sea- 
sonal variability in movement patterns of estuarine 
fish species like red drum. We documented a high rate 
of (primarily southward) movement by age-1 red drum 
during fall months, especially in northern regions of 
North Carolina (EPS and WPS); North Carolina hap- 
pens to be the most significant northern overwintering 
grounds for subadult red drum on the Atlantic coast 
(Ross et al., 1995). Atlantic silversides (Menidia me- 
nidia ) are known to migrate offshore in the northern 
but not the southern part of their range in the Atlantic 
(Conover and Murawski, 1982), presumably to avoid 
overwintering mortality due to acute cold stress in 
northerly latitudes (Munch et al., 2003). Adult bluefish 
(Pomatomus saltatrix) on the Atlantic coast appear to 
consist of three groups that exhibit different migratory 
behaviors; the group inhabiting the most northerly 
waters (i.e., New England) in summer months tends 
to exhibit the farthest southerly migration during fall 
(Shepherd et al., 2006). Likewise, southerly movements 
of age-1 red drum during fall months may be an avoid- 
ance response to acute cold stress (e.g., Gunter, 1941) 
that may be particularly hazardous in the northern 
part of the state. 
Despite the low sample size of conventionally tagged 
and recovered red drum in some age and region com- 
binations, regional variability was apparent. Regional 
variability in the movement of tagged estuarine fish 
is likely a result of the physiology of the species, geo- 
graphic barriers, and the specific fisheries operating 
in each region. In addition to the seasonal movements 
described above for age-1 red drum in northerly regions 
of the state, there appeared to be a coastward (easterly) 
migration for both age-1 and age-2 fish tagged in oligo- 
haline waters, whereas fish tagged in polyhaline waters 
primarily moved along the coast. Regionally variable 
movements may be due as much to the physiological 
0.8 
0.6 
0.4 
0.2 
0.0 
0.8 
0.6 
c 
o 
o 0.4 
Q- 
O 
□I 
0.2 
0.0 
0.8 
0.6 
0.4 
0.2 
0.0 
-8 -6 -4 -2 0 2 4 6 8 
Monthly change in salinity (psu) 
Figure 7 
Proportion of transmitter-tracked red drum ( Sciae - 
nops ocellatus) in Hancock Creek moving upstream 
(A), moving downstream (B), or emigrating (C) 
in relation to the change in salinity between two 
consecutive monthly relocation periods, 2005-2007. 
Salinity sampling took place midriver near the 
boat ramp, and monthly periods were included only 
if at least four tracked red drum were relocated 
in that period. Trend lines show a linear least- 
squares fit. 
requirements of red drum as to the geography of the 
North Carolina coast, which constrains the movements 
of red drum to specific directions (e.g., east-west in 
NPR, northeast-southwest in SNC). 
Because tag recoveries come from the fishery, conven- 
tional tagging analyses of movement can be biased by 
spatially heterogeneous fishing effort. The distribution 
of recoveries may therefore reflect the spatial distribu- 
tion of fishing more than the true extent of fish move- 
ment. Bolle et al. (2005) used electronic transmitters 
to show that conventional tagging provided a reliable 
interpretation of the movement patterns of European 
plaice ( Pleuronectes platessa) in most areas of the North 
Sea; the only areas that appeared to be undersampled 
