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Fishery Bulletin 99(3) 
criteria proposed by Beamish and Chilton (1977) and show 
that accurate ages for lingcod can be produced by using the 
fin-ray method combined with mean annular diameter mea- 
surements. 
Methods 
During 14-27 July 1982, a major tag and release program 
was conducted on the commercial fishing grounds. La 
Perouse Bank (48'45°N; 125'55°W), off southwest Vancou- 
ver Island. The primary focus of this tagging program was 
for validation of age determination. Methods and survey 
design are outlined in Cass et al. (1983). Prior to process- 
ing, all fish were anesthetized with tricaine methane sul- 
fonate (MS222). We measured their fork length (mm) and 
inserted an individually numbered Floy FD68 anchor tag 
into the connective tissue just below the anterior base of 
the first dorsal fin. 
We injected the tagged fish with a 25 mg/kg body-weight 
dosage of oxytetracycline into the interperitoneal cavity 
(McFarlane and Beamish, 1987). Of the injected fish, a 
random subsample was kept in 3000-L holding tanks for 
48 hours to assess short-term mortality due to the OTC 
injection, then released. We released a random subsample 
of tagged fish without OTC injections as a control group 
to assess long-term (6-month) mortality due to OTC injec- 
tion by comparing recapture rates for the control fish with 
those for the OTC-injected fish. 
Tagged lingcod were recovered by the commercial fish- 
ery off the southwest coast of Vancouver Island. Because 
the first annuli after the OTC mark would form during the 
winter of 1982-83, only tagged lingcod recovered after 1 
January 1983 were used in the validation of age determi- 
nation. Returned whole fish were measured for fork length 
(mm), and a portion of the second dorsal fin was removed 
for age determination according to Beamish and Chilton 
(1977). Sectioned fin rays were illuminated with ultravio- 
let light to fluoresce the OTC mark and with regular light 
to identify annuli. 
All recovered lingcod were aged in June and August of 
1987. In October 1987, a change in personnel led to an un- 
knowing change in the criteria for determining the first 
few annuli. Chilton and Beamish (1982) suggested that 
known average diameter of the first and second annuli 
could be used to estimate their location. The first and sec- 
ond annuli can be difficult to determine when resorption of 
the inner portion occurs or if the center becomes obscured 
by irregular-shaped deposits of opaque material. In addi- 
tion, the presence of checks can also make it difficult to 
identify the first two annuli. In all cases, an estimate of 
the position of the third annulus can be made by measur- 
ing the diameter of the first and second annuli from juve- 
nile fish or fish where these annuli are visible (Chilton and 
Beamish, 1982). By 1988, the primary reader was no lon- 
ger using the Chilton and Beamish (1982) criteria. The re- 
covered lingcod were re-aged after this change in criteria 
and second ages (using these criteria) were compared with 
original ages (not using these criteria) to assess bias. We 
compared age compositions of a subsample of the lingcod 
C 
i 
i 
i 
Figure 1 
Schematic representation of section of fin ray for measure- 
ments of first (A) and second (B) annular diameters. Mea- 
surements should be made along axes perpendicular to the 
axis (C) of the inner groove of the fin ray. 
with the two age estimates to illustrate the consequences 
of not using the Chilton and Beamish (1982) criteria. 
Juvenile lingcod (less than 48 cm) were captured in 
1987 in the recreational fishery in the Strait of Georgia. 
Fork lengths were measured (nearest mm) and dorsal fin 
rays were sampled during the creel survey program. These 
juveniles would not likely have resorbed fin-ray centers. 
The fin rays were sectioned (Beamish and Chilton, 1977), 
and illuminated with regular light. The diameter to the 
first and second annuli were measured with a micrometer 
eyepiece under 40x magnification to the nearest microm- 
eter (pm). Diameter measurements were made along an 
axis perpendicular to the inner groove of the fin ray (Fig. 
1 ). If an annuli appeared as a thick zone, the range from 
the beginning to the end of the zone was measured and the 
median used as the diameter measurement. 
Results 
A total of 7429 lingcod were tagged and released during 
July 1982. Of these, 6946 were injected with OTC and 
483 were not injected but were released as the control 
group for assessing long-term (6-month) mortality due 
to OTC injection. A total of 188 lingcod were held for 
48 hours after being tagged and injected with OTC. No 
mortality occurred prior to release. Within the first six 
months (i.e. by 31 December 1982) 1442 lingcod were 
recovered. During this period, the return rates of OTC and 
non-OTC-injected lingcod were similar (19.5% and 18.4%, 
respectively) indicating no long-term mortality from OTC 
injection. 
