NOTE Wallin et al.: Retention of coded wire and internal anchor tags in juvenile Centropomus undecimalis 
877 
Table 2 
Internal anchor tag retention rates and fish survival rates at 14 and 30 d after tagging for each treatment (t-bar-tagged fish, 
disk-tagged fish, and control fish) and fish sizes at the time of tagging. Starting no. = number of fish at the beginning of the 
experiment. Survival rates are from the start of the experiment until 14 or 30 d after tagging. Standard length at the time of 
tagging is given as the mean with standard deviation in parentheses. 
Trial 
Treatment 
Starting 
no. 
Standard 
length (mm) 
Tag retention rates (%) 
Survival rates (%) 
14-day 
30-day 
14-day 
30-day 
1 
T-bar-tagged 
78 
139(13.1) 
100 
100 
93.6 
93.6 
Disk-tagged 
78 
138 (13.0) 
100 
100 
91.0 
75.6 
Control 
78 
137 (13.7) 
— 
— 
97.4 
82.1 
2 
T-bar-tagged 
61 
135 (11.3) 
100 
100 
100 
100 
Disk-tagged 
61 
136(10.4) 
100 
98.4 
100 
100 
Control 
61 
134(10.7) 
— 
— 
100 
100 
Overall 
T-bar-tagged 

136 (12.5) 
100 
100 
96.8 
96.8 
Disk-tagged 
— 
137 (11.9) 
100 
99.2 
95.5 
87.8 
Control 
— 
137 (12.6) 
— 
— 
98.7 
91.1 
that most CWT loss in juvenile fish occurs within two 
to four weeks after tagging, the time period correspond- 
ing with the time required for the tagging puncture 
wound to heal (Dunning et al., 1990). Although there 
was no significant change in retention rates after 30 
days, tag retention rates in the smallest fish (mean 
SL 62 mm) continued to decline between 30 and 60 
days (Fig. 2), providing further evidence of the impor- 
tance of fish size for tag retention. 
Thirty-day retention rates of both types of inter- 
nal anchor-external streamer tags were very high 
(>99%), indicating that these tag types are effective 
tools for marking >110 mm common snook. However, 
other studies have suggested that retention of disk- 
and T-anchor tags may decrease over months or years 
and should therefore be evaluated for longer periods 
of time (Collins et al., 1994). Although the incisions 
required to apply disk tags are larger than incisions 
required for T-anchor tags, there was no difference 
in survival or growth rates of fish with either tag 
type. Both tag types caused similar incidences of ir- 
ritation at the tag insertion site. Similar irritation 
has been noted in other fish species and can eventu- 
ally result in tag loss (Mattson et al., 1990; Collins 
et al., 1994). After 30 days, disk anchors were more 
frequently encapsulated and attached to the inside 
of the body wall than were T-anchors. Both tag types 
were equally likely to be incorrectly inserted in the 
swim bladder or gastrointestinal tract when the in- 
cision was made with a scalpel; overall, incorrect in- 
sertions were noted in 10-20% of the fish examined. 
We recommend using scalpels to insert the T-anchor 
tags; when a tag applicator needle was used, inci- 
dences of incorrect insertion increased to 60%, prob- 
ably because of difficulty in controlling puncture 
depth. 
In conclusion, because CWT retention rates were 
significantly improved for fish >70 mm SL, we rec- 
ommend tagging snook at this size whenever pos- 
sible. We also recommend that CWT retention in 
snook be evaluated for 30 days after tagging so that 
accurate estimates of tag-loss rates can be calculated. 
For snook >110 mm SL, both the T-anchor and disk 
internal anchor-external streamer tags were effec- 
tive marking techniques. For all types of tags and 
all sizes of fish in our study, tagging did not signifi- 
cantly affect snook survival or growth. 
Acknowledgments 
We thank Greg Vermeer for advice in fish health and 
review of a draft manuscript. We also thank Buck 
Dennis and the staff of FDEP’s Stock Enhancement 
Research Facility and the Fisheries- Independent Moni- 
toring Program for their technical assistance. Harry 
Grier, Lynn French, Judy Leiby, and Jim Quinn also 
provided helpful comments on the manuscript. This 
project was funded in part by the Department of the 
Interior, U.S. Fish and Wildlife Service Federal Aid for 
Sportfish Restoration (Project F-43) and by funds from 
Florida Saltwater Fishing License sales. 
Literature cited 
Bruger, G. E. , and K. D. Haddad. 
1986. Management of tarpon, bonefish, and snook in 
