42 
Fishery Bulletin 119(1) 
Age determination for the spiny dogfish and its closely 
related congeneric species, the Pacific spiny dogfish (S. suck- 
leyi) has been studied extensively. Note that, until 2010, 
S. suckleyi was considered the same species as S. acanthias 
(Ebert et al., 2010; Verissimo et al., 2010), and many studies 
did not distinguish between the 2 species. For the purposes 
of this paper, however, spiny dogfish refers only to S. acan- 
thias. Both species have been aged since at least the 1930s, 
through the use of a variety of methods (Kaganovskaia, 
1933; Holden and Meadows, 1962; Jensen, 1965; Ketchen, 
1975; Jones and Geen'; Nammack et al., 1985; McFarlane 
and Beamish, 1987; Saunders and McFarlane, 1993; 
Campana et al., 2006, 2009; McFarlane and King, 2009; 
Tribuzio et al., 2010; Bubley et al., 2012; Tribuzio et al., 
2017). The use of dorsal-fin spines has long been considered 
the standard for age determination of spiny dogfish because 
early researchers were unable to elucidate band pairs in 
vertebrae (Kaganovskaia, 1933; Tribuzio et al., 2016). The 
use of fin spines, meanwhile, has the issue of wear that 
obscures or eliminates growth bands and requires the use of 
correction factors that may or may not be suitable (Ketchen, 
1975; Taylor et al., 2013). 
Over time, improvements in the ability to enhance band 
pairs led to attempts at age determination with vertebrae 
because the use of these structures did not require correc- 
tion factors. This development has allowed comparisons 
between band-pair counts of dorsal-fin spines and ver- 
tebral centra (Bubley et al., 2012; Tribuzio et al., 2017). 
Bubley et al. (2012) concluded that use of vertebral counts 
resulted in more reliable and accurate age estimates that 
produced biologically appropriate growth parameters for 
spiny dogfish than the variable ages from the use of dorsal- 
fin spines that requires correction factors to account for 
lost annuli from wear. On the other hand, Tribuzio et al. 
(2017) found vertebral counts underestimated counts of 
unworn dorsal-fin spines of Pacific spiny dogfish over 10 
years old. 
Compounding the decision of what structure to use 
to age spiny dogfish are various age validation studies. 
In a reevaluation of data from early studies (McFarlane 
and Beamish, 1987) that used oxytetracycline (OTC) on 
dorsal-fins spines of Pacific spiny dogfish at liberty for 
up to 20 years, the band pairs on the dorsal-fin spines 
were considered annual. However, in 3 individuals at 
liberty for 20-21 years, 7-18 band pairs were missing 
(McFarlane and King, 2009). Campana et al. (2006) vali- 
dated ages of spiny dogfish from the region of the western 
North Atlantic Ocean in Canada, using bomb radiocarbon 
techniques, and determined that band-pair formation 
in dorsal-fin spines was annual up to at least 25 years. 
Neither Bubley et al. (2012) nor Tribuzio et al. (2017) val- 
idated band-pair deposition in vertebral centra, but in 
both studies marginal increment analysis was used and 
results indicate annual periodicity in band-pair formation 
' Jones, B. C., and G. H. Geen. 1977. Age and growth of spiny 
dogfish (Squalus acanthias) in the Strait of Georgia, British 
Columbia. Fish. Mar. Serv., Tech. Rep. 699, 16 p. [Available from 
website.] 
in vertebral centra. Given the importance of age esti- 
mates in stock assessment, it is vital to validate the age 
determination methods. 
Appropriate stock assessment and management rely 
on accurate age determinations for spiny dogfish because 
these ages facilitate calculation of growth, mortality, age 
at maturity, and longevity estimates. In view of the his- 
tory of the spiny dogfish fishery, and the need for accu- 
rate biological information for management, an intensive 
cooperative research program was initiated by NOAA to 
obtain detailed life history data. This paper reports on one 
portion of this program, specifically, the use of vertebrae 
and dorsal-fin spines to determine age and growth. The 
primary goal of this study was to attempt to validate the 
periodicity in formation of band pairs in vertebral centra 
of spiny dogfish by using individuals injected with OTC. 
Of secondary importance for this work was confirming val- 
idation of annual band-pair deposition in dorsal-fin spines 
of this species. 
Materials and methods 
Tagging and sample collection 
Sampling cruises were conducted by 3 vessels in the Gulf 
of Maine, on Georges Bank, and off southern New England 
5 times: in February 2011, in July 2011, in November and 
December 2011, in July and August 2012, and in Novem- 
ber and December 2012. Spiny dogfish were collected 
during 20-min tows of otter trawls. During sampling in 
2011, the first 5 spiny dogfish out of every 25 brought 
on board were selected for injection with OTC; however, 
in 2012, only the first 5 individuals from each tow were 
selected for injection with OTC. Straight-line fork length 
(FL), total length (TL), and stretch total length (STL) to 
the nearest millimeter, weight to the nearest 0.05 kg, and 
sex were recorded. Oxytetracycline was injected intramus- 
cularly into each spiny dogfish at a dosage of 25 mg of OTC 
per kilogram of body weight (Holden and Vince, 1973). A 
rototag (Dalton ID Ltd.?, Henley-on-Thames, UK) was 
then attached to the first dorsal fin before release (Kohler 
and Turner, 2001). 
Recaptured sharks were returned whole to the Nar- 
ragansett Laboratory of the NOAA Northeast Fisheries 
Science Center. All specimens were frozen prior to exam- 
ination. Spiny dogfish were measured (FL, TL, and STL) 
and weighed. Whole vertebral columns and the second 
dorsal-fin spine were extracted for age validation. 
Validation of ages from vertebrae and dorsal-fin spines 
For consistency, vertebrae 19-23, which are among the 
largest vertebrae, were removed from each specimen 
of spiny dogfish. Only vertebrae from individuals with 
2 Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
