356 
Fishery Bulletin 95(2), 1997 
TL = 6.01 + 5.56(2,0), 
where TL = estimated total length of the guitarfish; 
and 
2 D = second dorsal length (when 2D >3.5 cm 
and <20 cm). 
Reproductive maturity 
The smallest sexually mature female guitarfish was 
99 cm TL and was estimated to be seven years old, 
based on vertebral band counts. Developing ovaries 
were present in 26 specimens from 40 to 99 cm TL. 
These individuals showed no evidence of previous 
birthing or egg follicles: uteri were thin walled and 
shell glands were not distinguishable from surround- 
ing oviducts. Immature female guitarfish accounted 
for the majority of specimens taken (27 of 36). 
A well-developed shell gland (nidimental gland) 
was present in mature shovelnose. Females with full 
uteri contained a case as described by Cox (1963) for 
Rhinobatos. In four individuals with full uteri, no 
developing embryos were seen in any of the speci- 
mens. These specimens contained either four or five 
yolks within the right or left egg case and, with the 
exception of one specimen, had nine total yolks per 
mature female. These four fish were captured in Feb- 
ruary (one), April (one), and June (two). 
Male guitarfish reached maturity between 90 and 
100 cm TL. At maturity there was an abrupt increase 
in clasper length and claspers extended well beyond 
the pelvic fin (Fig. 9). Claspers of mature males were 
at least 13 cm in length, and clasper width at matu- 
rity was at least 1 cm. A well-developed spur was 
present on both claspers in mature males and was 
not present in immature males (Fig. 10). Immature 
male squaloid sharks also lack spines (Applegate, 
1967). Twelve of the 38 sampled were mature and 26 
were immature. 
Discussion 
Age and growth 
The shovelnose guitarfish is best described as a slow- 
growing species typified by linear growth after par- 
turition. Our total estimated age range (one to 11 
years) for R. productus was the same that Lessa 
(1982) found fori?, horkelii. Her specimens were also 
in the same size range as R. productus (20 to 120 
cm). Rossouw (1984) found ages 0 to 6 years in R. 
annulatus, and his largest specimen was 99.3 cm. 
Age estimates in this study were based on the as- 
sumption that one opaque and one translucent band 
• 
Mature 
• 
- 
o 
Immature 
n = 
38 
• 
- 
• 
• 
- 
^ ° o 
% o° 
o 
o© 
1 
<9 
1 1 
-I 1 1 
0 20 40 60 80 100 120 140 
Total length (cm) 
Figure 9 
Relation of clasper length with total length for males. 
Clasper length beyond 10 cm indicates a mature individual. 
