Tribuzio et al.: Age and growth of Squalus acanthias in the Gulf of Alaska 
131 
Table 6 
Summary of von Bertalanffy parameters (model 1) for growth models for female spiny dogfish ( Squalus acanthias ) from the 
North Pacific and North Atlantic oceans and the North and Black seas. Parameters are asymptotic length (L„) size at birth 
(L 0 ), growth coefficient (k), and the theoretic age-at-size length zero (t 0 ). Here, L 0 was solved for from the published parameter 
estimates for the purposes of comparison. 
Location 
k 
t Q 
L 0 
Reference 
Alaska, Gulf of Alaska 
121.4 
0.034 
-12.1 
40.9 
This study 
Alaska, Prince William Sound 
110.4 
0.038 
-11.6 
39.4 
Vega (2006) 
British Columbia, Hecate Strait 
125.1 
0.031 
-10.6 
35.0 
Ketchen ( 1975) 
British Columbia, Strait of Georgia 
129.1 
0.034 
-7.3 
28.4 
Ketchen ( 1975) 
British Columbia, Strait of Georgia 
114.9 
0.044 
-3.6 
16.8 
Saunders and McFarlane (1993) 
British Columbia, offshore 
128.5 
0.036 
-6.9 
28.3 
Jones and Geen (1977) 
U.S., inshore (WA north) 
113.5 
0.04 
-5.2 
21.3 
Vega (2006) 
U.S., inshore (WA south) 
100.4 
0.036 
-8.4 
26.2 
Vega (2006) 
U.S., offshore (WA) 
123.6 
0.027 
-6.9 
21.0 
Vega (2006) 
U.S., offshore (WA) 
152.9 
0.036 
-6.7 
32.8 
Ketchen (1975) 
U.S., offshore (OR) 
101.9 
0.027 
-12.7 
29.6 
Vega (2006) 
U.S., offshore (OR and CA combined) 
90.9 
0.031 
-13.0 
30.2 
Vega (2006) 
U.S., offshore (CA north) 
158.9 
0.009 
-25.3 
32.4 
Vega (2006) 
U.S., offshore (CA south) 
123.6 
0.027 
-6.9 
21.0 
Vega (2006) 
Northwest Atlantic (U.S.) 
100.5 
0.106 
-2.9 
26.6 
Nammack et al. (1985) 
Northeast Atlantic (Ireland) 
98.8 
0.090 
-1.6 
13.3 
Fahy (1989) 
Northeast Atlantic (Ireland) 
112.0 
0.150 
-3.4 
44.7 
Henderson et al. (2002) 
Northwest Atlantic 
104.5 
0.095 
-3.7 
31.0 
Soldat 2 
North Sea 
137.1 
0.054 
-4.7 
30.7 
Sosinski 1978 (as cited in Avsar, 2001) 
North Sea 
101.4 
0.110 
-3.6 
33.2 
Holden and Meadows (1962) 
Black Sea 
145.0 
0.170 
-0.7 
16.3 
Avsar (2001) 
1 Soldat, V. T. 2002. Spiny dogfish ( Squalus acanthias L.) of the northwest Atlantic Ocean (NWA). NAFO Sci. Counc. Res Doc 02/84, 33 p. 
fish from offshore Washington State waters (Fig. 7) but 
greater than those caught in inshore Washington State 
waters (Puget Sound) and British Columbia (Ketchen, 
1975; Jones and Geen, 1977; Saunders and McFarlane, 
1993; Vega, 2006). The age and growth studies from 
British Columbia were conducted on spiny dogfish col- 
lected in inshore waters (Strait of Georgia and Hecate 
Strait); therefore the possibility cannot be ruled out 
that spiny dogfish from the British Columbia offshore 
region would have growth estimates similar to those 
of Washington offshore and GOA spiny dogfish. The 
vB growth model parameter estimates (L x and k ) for 
northern California spiny dogfish (defined as spiny dog- 
fish between Point Conception to the Oregon border; 
Vega, 2006) were radically different from our results 
for the GOA, but the fits for California may have been 
adversely affected by small sample size. 
The wide variability in length-at-age contributes to 
the lack of statistically significant differences among 
growth models and worn-band estimation models. This 
variability may be attributable to one or more of the 
following factors: measurement error in either length 
or age readings, sampling bias, true underlying vari- 
ability in growth at age, and misidentification of worn 
and unworn spines. We considered the potential role of 
each of these factors. 
Measurement error in the length measurements alone 
is insufficient to explain the relatively large variabil- 
ity in the size-at-age data. Aging errors may take two 
forms: imprecision and bias. We found no bias among 
the three readers tested, but imprecision of the band 
counts among readers could contribute to variability 
in the size-at-age data, especially for older ages. We 
used the median band count (from the three readers) 
to account for reduced precision because this measure 
of central tendency is less sensitive to outliers than the 
mean for small sample sizes (Dudewicz and Mishra, 
1988). A more thorough analysis of the precision of age 
estimates for spiny dogfish in the Pacific Ocean revealed 
the overall coefficient of variation for aging estimates 
among four laboratories to be 19% (Rice et al., 2009). 
Systematic bias was found for two of the laboratories 
(one biased high, the other biased low) in relation to 
the other two, but relative bias did not always result 
in statistically different parameters estimated from vB 
growth curves (Rice et al., 2009). 
Age validation is crucial for growth studies to assure 
that physical structures used for aging are correctly in- 
terpreted. For instance, a systematic aging error could 
result if the periodicity of band formation is not an- 
nual. Annual periodicity of band deposition on second 
dorsal spines was validated for spiny dogfish in British 
