101 
Age validation, growth, mortality, 
and demographic modeling 
of spotted gully shark ( Triakis megalopterus) 
from the southeast coast of South Africa 
Abstract— This study documents vali- 
dation of vertebral band-pair forma- 
tion in spotted gully shark ( Triakis 
megalopterus) with the use of fluoro- 
chrome injection and tagging of cap- 
tive and wild sharks over a 21-year 
period. Growth and mortality rates of 
T. megalopterus were also estimated 
and a demographic analysis of the 
species was conducted. Of the 23 QTC 
(oxytetracyeline) -marked vertebrae 
examined (12 from captive and 11 
from wild sharks), seven vertebrae 
(three from captive and four from 
wild sharks) exhibited chelation of 
the OTC and fluoresced under ultra- 
violet light. It was concluded that a 
single opaque and translucent band 
pair was deposited annually up to at 
least 25 years of age, the maximum 
age recorded. Reader precision was 
assessed by using an index of aver- 
age percent error calculated at 5%. 
No significant differences were found 
between male and female growth pat- 
terns (P>0.05), and von Bertalanffy 
growth model parameters for com- 
bined sexes were estimated to be 
1,^=1711.07 mm TL, £ = 0.11/yr and t 0 = 
-2.43 yr (n = 86). Natural mortal- 
ity was estimated at 0.17/yr. Age at 
maturity was estimated at 11 years 
for males and 15 years for females. 
Results of the demographic analysis 
showed that the population, in the 
absence of fishing mortality, was 
stable and not significantly different 
from zero and particularly sensitive 
to overfishing. At the current age 
at first capture and natural mortal- 
ity rate, the fishing mortality rate 
required to result in negative popu- 
lation growth was low at P>0.004/ 
yr. Elasticity analysis revealed that 
juvenile survival was the principal 
factor in explaining variability in 
population growth rate. 
Manuscript submitted 14 May 2010. 
Manuscript accepted 3 November 2010. 
Fish. Bull. 109:101-112 (2011). 
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. 
Anthony i. Booth (contact author ) 5 
Alan j. Foufis 1 
Malcolm J. Smale 2 
Email address for contact author: t.booth@ru.ac.za 
1 Department of Ichthyology and Fisheries Science 
Rhodes University 
P.O. Box 94 
Grahamstown, 6140, South Africa 
2 Port Elizabeth Museum 
P.O. Box 13147 
Humewood, 6013, South Africa 
and 
Department of Zoology 
Nelson Mandela Metropolitan University 
P.O. Box 77000 
Port Elizabeth, 6013, South Africa 
Spotted gully shark (Triakis mega- 
lopterus, Smith, 1839), is one of five 
Triakis species and is endemic to 
southern Africa (Compagno, 1988). 
Its distribution range extends from 
northern Namibia (although anec- 
dotal information indicates that it 
is caught as far north as Angola) 
southward around the coast to Coffee 
Bay in the Eastern Cape Province, 
South Africa (Compagno, 1988; Com- 
pagno et al., 2005). It is a shallow 
water (<50 m) (Compagno et ah, 
1989; Smale and Goosen, 1999), 
demersal species that is recreation- 
ally important to shore and ski-boat 
anglers. With the exception of some 
information pertaining to its repro- 
ductive and feeding biology (Smale 
and Goosen, 1999) there is little 
information available to guide its 
management. Given its narrow dis- 
tribution range and small popula- 
tion size, it could be vulnerable to 
overexploitation in a manner similar 
to its congener, T semifasciata, that 
has declined in abundance and is 
now carefully managed (Smith and 
Abramson, 1990; Cailliet, 1992). An 
equivalent analysis is required for 
T. megalopterus to assess its vulner- 
ability to fishing pressure. 
Demographic modeling has been 
conducted on many elasmobranch 
populations when there are insuf- 
ficient catch, effort, and abundance 
data available to conduct a full stock 
assessment ( Simpfendorfer, 1998; 
Romine et al., 2009). Demographic 
modeling is a popular approach be- 
cause it provides the best available 
description of the population being 
studied given several life history 
parameters. Demographic modeling 
therefore provides a compromise 
between simple life history tables 
and more detailed stock assess- 
ment models. Demographic models 
became popular in the 1990s and 
are now the most widely used popu- 
lation models used to assess shark 
populations (Simpfendorfer, 2005). 
A fundamental requirement for the 
application of age-structured demo- 
graphic models is that ages of sharks 
are available. 
Correctly determining the age of 
fish, particularly elasmobranchs, is 
crucial if (unbiased) time-based life 
history rates such as growth, ma- 
turity, and mortality are to be esti- 
mated. Although numerous fish age 
and growth studies have been under- 
taken, remarkably few have included 
