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 Questions1. 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)

Insi

de C

lasp

er L

engt

h (m

m)

JuvenileAdultsTransitional

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)

Freq

uenc

y

Females n = 63Males 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)

Shar

k W

eigh

t (k

g)

Anacapa IslandCarpinteriaSanta 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. ReferencesEbert, 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.