Timmons and Bray: Age, growth, and sexual maturity of Rhinobatos productus 
357 
are formed annually. One verification procedure, ex- 
amination of individuals held in captivity, provided 
support for the outer margin analysis; however, this 
analysis was based on only two specimens. The sec- 
ond verification procedure, outer margin analysis of 
field-caught specimens, indicated that band forma- 
tion was dependent on season; however, there was 
no correlation between width of the outer margin and 
month. Early band formations at the margin can be 
difficult to detect with whole centra. To avoid this 
difficulty we tried sectioning the centra; however, we 
were unable to obtain readable sectioned centra. Oth- 
ers, such as Tanaka ( 1990 ) and Gruber and Stout ( 1983 ) 
have had success in sectioning vertebrae to view band 
formations. Therefore, we do not consider our verifica- 
tion procedure to be complete. It is evident that guitar- 
fish have linear growth which might be somatic and 
not correlated with age of the guitarfish, as was sug- 
gested by Natanson et al. (1984) for Squatina cali- 
fornica. Further studies should be attempted to answer 
this question. Specifically, we suggest more tagging and 
injection studies to validate laboratory data. 
Reproductive maturity 
We encountered a problem collecting large ( >90 cm) 
females; it has been suggested by Baxter ( 1980) and 
Lane and Hill ( 1975) that individuals of this size are 
uncommon. Our largest female was 130 cm. In 
Almejas, Baja California Sur, Mexico, Villavicencio- 
Garayzar (1993) reported that his largest captured 
female R. productus was 137 cm. Females in the 
present study were mature at >99 cm TL, whereas 
Villavicencio-Garayzar (1993) suggested that matu- 
rity of R. productus was at >70 cm TL. The youngest 
free-living guitarfish obtained was 23 cm TL, and it 
appears that the estimate of 15 cm (Eschmeyer et 
al., 1983) for newborn pups might be low. Melouk 
(1949) reported 16-cm specimens of R. halavi that 
still had sizable yolk attachments in utero. It is pos- 
sible that Eschmeyer’s measurements of 15 cm were 
taken from expelled premature pups. Expulsion of 
embryos can occur from stressed females (Pratt and 
Casey, 1990). Another possibility is that mortality is 
high in postpartum pups and many do not survive. 
Perhaps the smallest specimens that we sampled were 
first-year survivors. Rossouw ( 1984 ) suggested that the 
average length of Rhinobatos annulatus at birth was 
23 cm TL and Dubois (1981) stated that embryos of 
R. productus at parturition were 23 cm. Villavicencio- 
Garayzar ( 1993) reported a free-swimming R. productus 
at 24 cm and suggested neonates are 20-24 cm. The 
first year class we collected (presumably represented 
as the smallest guitarfish we obtained) did not have 
any bands present beyond the birth mark. Many of the 
young guitarfish were captured by otter trawls in the 
Belmont Shores area in Long Beach, CA.; it appears 
that this is a nursery ground for guitarfish. 
Our estimates of nine offspring per female were 
also the mean number of offspring found by 
Villavicencio-Garayzar (1993) for Rhinobatos 
productus in Almejas, Baja California Sur, Mexico. 
He found thati?. productus females had a minimum 
of six pups and a maximum of 16. Additionally, 
Villavicencio-Garayzar (1995) found that Zapterix 
exasperata females contained a minimum of 4 and a 
maximum of 11 embryos (the most common numbers 
of embryos per individual were between 6 and 9). 
Males showed the same size at maturity as males 
sampled by Dubois (1981). His males were all ma- 
ture when TL exceeded 92 cm. No males in his study 
had clasper lengths in the range of 11 to 15 cm, indi- 
cating a definite size break in clasper length between 
immature and mature males. Our male guitarfish 
showed this same break between clasper lengths of 
11 and 13 cm, and all males in our study were ma- 
ture when TL exceeded 100 cm. Our smallest ma- 
ture male was 91 cm. Both of our studies indicated a 
lack of individuals with clasper lengths in the 10-13 
cm range, and Martin and Cailliet (1988) found a 
similar break in clasper lengths (between approxi- 
mately 22-37 cm) in Myliobatis californica. This in- 
dicated to us that sexual maturity occurred within a 
distinct size range (TL) for males. Visual examina- 
tions of the claspers confirmed maturity; they were 
well developed and occasionally contained semen. 
Villavicencio-Garayzar ( 1993) found male Rhinobatos 
productus with sperm in their vasa deferentia at 63, 
68, and 69 cm TL, but did not indicate a length at 
first maturity. For Zapterix exasperata , Villavicencio- 
Garayzar (1995) found males at 69 cm with semen. 
Information from this research will provide a start- 
ing point for persons who may be interested in regu- 
lating guitarfish catch in the future. The informa- 
tion on size at first maturity for both males and fe- 
males and the equation for estimating total length 
of guitarfish from tails sold to markets by fisherman 
will be useful management tools. Although the age 
estimates of the guitarfish are preliminary, total 
length (TL) at sexual maturity is most valuable. This 
information provides a starting point for evaluation 
of possible future size limitations for catches of gui- 
tarfish. We suggest further studies in order to attempt 
to age guitarfish over its entire population range. 
Acknowledgments 
We would like to thank the Orange County Depart- 
ment of Fish and Game and the Department of Biol- 
