This study examined the population characteristics of horn sharks (Heterodontus francisci) along the coast of Carpinteria and the Northern Channel Islands in California. A total of 109 horn sharks were collected and measured from these areas between May and August 2004. The results showed a female-biased sex ratio of 1.4:1 across all sites. No significant differences were found in size or weight between sharks at island versus mainland sites. For male sharks, clasper length was found to increase rapidly with total length, indicating sexual maturity is reached at approximately 625 mm in total length.

1. POPULATION ASSESSMENT OF THE HORN SHARK, HETERODONTUS
FRANCISCI, ON ROCKY REEFS IN CARPINTERIA AND THE NORTHERN
CHANNEL ISLANDS, CALIFORNIA.
Hoobler, S. M. Marine Science Institute, University of California Santa Barbara.
4. Results
Figure 1. Total length–frequency distributions
of female and male H. francisci used in study.
Figure 2. Length–weight relationship of H.
francisci across all study sites. N = 109
Figure 3. Relationship between total length
(mm) and inside clasper length (mm) for
males across all stages of maturation. N = 45
1. Introduction
The horn shark, Heterodontus francisci, is a small near-
shore rocky reef shark that ranges from central California
to the Gulf of California. Santa Barbara county and the
Northern Channel Islands are at the northern extension of
their known range. The horn shark is nocturnal and
actively feeds at night on invertebrates and small fishes.
Although there is no commercial value for this shark, they
are often taken as by-catch in trawls and occasionally by
recreational fishermen. In recent years, they have been
maintained in public aquariums and are sold commercially
to private aquarium collectors.
Very little information has been collected regarding the age
and growth of horn sharks. Additionally, studies to date
have made general inferences as to horn shark size at
sexual maturity. Here I present the results to date a study
that is designed to gain information on life history
characteristics of this local population including: age,
growth, size of sexual maturity, and population structure at
Carpinteria, Anacapa Island, and Santa Cruz Island,
California.
2. Research Questions
1. What is the sexual distributions of H. francisci found at
Carpinteria, Anacapa Island, and Santa Cruz Island?
2. Is there a difference in size structure of sharks found at
island sites or mainland sites?
3. At what size does a male horn shark sexually mature in
relationship to total length and clasper length?
3. Methods
• 109 Horn sharks were collected by
SCUBA divers off the coast of Carpinteria,
Anacapa Island, and Santa Cruz Island
between May and August 2004.
• Data collected on all sharks consisted of
sex determination, length, weight, GPS
location, and presence of ectoparasites.
• Male sharks had their claspers measured
and were checked for the presence of
calcified claspers, rhipidion, and if their
siphon sac inflated.
• All sharks were tagged and released in the
area of capture.
Horn Shark Total Length vs. Inside
Clasper Length
y= 2.5788e0.0052x
R2
= 0.9284
15
65
115
165
325 425 525 625 725 825
Total Length (mm)
InsideClasperLength
(mm)
Juvenile
Adults
Transitional
Length Frequency Histogram of Male
and Female Horn Sharks
0
5
10
15
20
300 350 400 450 500 550 600 650 700 750
Length (mm)
Frequency
Females n= 63
Males n= 45
Length vs. Weight
y = 0.0572e0.0057x
R2
= 0.9343
0.00
1.00
2.00
3.00
4.00
5.00
6.00
200 400 600 800 1000
Shark Total Length (mm)
SharkWeight(kg)
Anacapa Island
Carpinteria
Santa Cruz Island
5. Conclusions
• The pooled ratio of females to males indicates a bias
towards females (1.4:1) across all sites (Fig. 1).
• Sharks found at mainland and island sites (Fig. 2) are
significantly similar in length and weight (P < 0.001).
• There is a significant relationship between clasper
growth and total length of sharks (P < 0.0001).
Claspers of male horn sharks rapidly increase in length
as they approach maturation at approximately 625 mm
TL (Fig. 3). Claspers were fully calcified, rhipidions
were calcified and opened, and siphon sacs inflated
between 675 and 780 mm TL.
6. References
Ebert, D A 2003. Sharks, Rays, and Chimaeras of
California. pp.81-86. Berkeley and Los Angeles, CA:
University of California Press.
Sergio et al. 2001. Reproductive biology of the Caribbean
sharpnose shark, Rhizoprionodon porosus, from
northern Brazil. Mar. Freshwater Res. 52: 745 – 752.
Strong, W R, Jr. Behavioral ecology of horn sharks,
Heterodontus francisci, at Santa Catalina Island,
California, with emphasis on patterns of space utilization.
MS. California State University, Long Beach, 1989. 265
pp. Advisor: Nelson, D.R.
7. Acknowledgements
This study was funded by a grant from PADI Project
Aware. Thanks are extended to Dr. Jenn Caselle for her
constructive comments and support. Additionally, thanks
are extended to the UCSB PISCO Subtidal team for
helping with shark collections.