119 
Age and growth of spiny dogfish 
{Squalus accmthias ) in the GuSff of Alaska: 
analysis of alternative growth models 
Cindy A. Tribuzio (contact author ) 1 
Gordon H. Kruse 1 
Jeffrey T. Fujioka 2 
Email address for contact author: cindy.tribuzio@noaa.gov 
1 School of Fisheries and Ocean Sciences, Juneau Center 
University of Alaska Fairbanks 
17101 Pt. Lena Loop Road 
Juneau, Alaska 99801 
Present address for contact author: National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
Auke Bay Laboratories 
17109 Pt. Lena Loop Road 
Juneau, Alaska 99801 
2 National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
Auke Bay Laboratories 
17109 Pt. Lena Loop Road 
Juneau, Alaska 99801 
Abstract — Ten growth models were 
fitted to age and growth data for spiny 
dogfish ( Squalus acanthias ) in the 
Gulf of Alaska. Previous studies of 
spiny dogfish growth have all fitted 
the t 0 formulation of the von Berta- 
lanffy model without examination 
of alternative models. Among the 
alternatives, we present a new two- 
phase von Bertalanffy growth model 
formulation with a logistically scaled 
k parameter and which estimates L 0 . 
A total of 1602 dogfish were aged 
from opportunistic collections with 
longline, rod and reel, set net, and 
trawling gear in the eastern and cen- 
tral Gulf of Alaska between 2004 and 
2007. Ages were estimated from the 
median band count of three indepen- 
dent readings of the second dorsal 
spine plus the estimated number of 
worn bands for worn spines. Owing to 
a lack of small dogfish in the samples, 
lengths at age of small individuals 
were back-calculated from a subsam- 
ple of 153 dogfish with unworn spines. 
The von Bertalanffy, two-parameter 
von Bertalanffy, two-phase von Ber- 
talanffy, Gompertz, two-parameter 
Gompertz, and logistic models were 
fitted to length-at-age data for each 
sex separately, both with and without 
back-calculated lengths at age. The 
two-phase von Bertalanffy growth 
model produced the statistically best 
fit for both sexes of Gulf of Alaska 
spiny dogfish, resulting in L 00 = 87.2 
and 102.5 cm and £ = 0.106 and 0.058 
for males and females, respectively. 
Manuscript submitted 17 February 2009. 
Manuscript accepted 3 November 2009. 
Fish. Bull. 108:119-135 (2010). 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
The spiny dogfish (Squalus acanthias ) 
is a small long-lived shark common 
among temperate coastal areas in 
the Atlantic and Pacific oceans (Com- 
pagno, 1984). This species has been 
the target of commercial fisheries over 
much of its range, in some cases for 
over a century (Ketchen, 1986). In 
some areas, severe declines in popu- 
lation abundance and stock structure 
have occurred (e.g., Rago et al., 1998). 
Many elasmobranchs, including spiny 
dogfish, are “equilibrium strategists” 
that are highly susceptible to over- 
fishing because of their slow growth 
rates, low fecundity, and late matu- 
ration (King and McFarlane, 2003), 
all of which are directly related to 
recruitment and parental stock sizes 
(Holden, 1974; 1977). Off the west 
coast of North America, spiny dogfish 
were depleted by intense fisheries in 
the 1940s, owing to the quantity and 
quality of vitamin A in their livers 
(Ketchen, 1986); the fishery demand 
decreased by 1950 with the develop- 
ment of synthetic vitamin A (Ketchen 
et al., 1983). Since the 1970s, spiny 
dogfish have continued to be targeted 
by commercial fisheries in British 
Columbia and the state of Washing- 
ton for human consumption. 
Although not targeted, spiny dog- 
fish is a common bycatch species in 
many fisheries in both state and fed- 
eral waters off the coast of Alaska. 
In the Gulf of Alaska (GOA) spiny 
dogfish are taken in Pacific salmon 
(Oncorhynchus spp.) gillnet fisher- 
ies, sablefish ( Anoplopoma fimbria) 
fisheries, Pacific halibut (Hippoglos- 
sus stenolepis) longline fisheries, and 
groundfish trawl fisheries (Boldt, 
2003). Although an estimated aver- 
age of 482.1 metric tons (t) of spiny 
dogfish was taken annually from 
1997 to 2007 in observed fisheries 
(Tribuzio et al., 2008), the bycatch 
in state waters is unknown and the 
bycatch rates in federally managed 
fisheries are likely underestimated 
because of unobserved fisheries (e.g., 
the halibut individual fishing quota, 
IFQ). Nearly all of this unintended 
bycatch was and still is discarded at 
sea. Even though estimated catch is 
<1% of estimated spiny dogfish bio- 
mass (Courtney et al., 2006), the po- 
tential development of a commercial 
fishery demands further investigation 
