Hammerhead Sharks: decline of an ecologically unique marine animal Outline #1

This topic submitted by Katie Peticca ( peticckd@muohio.edu) at 11:18 AM on 5/2/09.

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Tropical Field Courses -Western Program-Miami University

In my paper, I am going to discuss the Hammerhead Shark. I will begin by giving a general background on the shark, providing a brief description of their characterization, movement, and reproduction. I will also mention the aspects, which make the Hammerhead so unique with a discussion of their characteristic ÒhammerheadÓ, its supposed evolution and purpose. I will however focus on the great decline of the Hammerhead shark in coastal waters due to human interaction (overfishing). I feel this topic is important to discuss to understand the damaging effects humans have on such ecologically important top predators such as the Hammerhead shark.

A. Hammerhead Shark
a. Characterization
i. 9 species of Hammerheads
b. Location
i. Worldwide- warmer waters along coastlines and continental shelves
c. Evolution
i. The Hammerhead sharks are thought to be related to the Carcharhinid sharks which evolved during the mid-tertiary period.
d. Reproduction
i. Once a year; Litter- 20 to 40 pups
ii. Mating courtship- violent (male bites female until she acquiesces allowing mating to occur)
e. Movement patterns
i. Aggregate in large numbers during day to avoid predation but disperse at night to find food
ii. form schools that contain up to 500 individuals, which is very unusual for sharks
f. Danger?
i. Of the 9 species, 3 are dangerous to humans- scalloped, great and smooth hammerheads
B. What makes the Hammerhead Shark Unique
a. ÒHammerheadÓ- Distinctive structure of headÑflattened and laterally extended into a ÒhammerÓ shape ÒcephalofoilÓ
i. Evolution of shape
1. Gradual or sudden mutation?
ii. Used for: sensory reception, maneuvering, prey manipulation
iii. Eyes and nostrils at tip of extensions
b. Electroreceptory sensory poresÑhammer shape provides more surface area
C. Endangered
a. Scalloped and great hammerhead sharks are endangered
b. Overfishing and demand for their fins- an expensive delicacy
c. Sharks -vulnerable because of their slow growth, late age of maturity, and low reproduction rates
d. In a study looking at the population decline of 20 species of sharks in the Mediterranean basin, Hammerheads showed the greatest decline
i. Declined between 96 and 99.9% relative to their former abundance
D. Implications
a. Lack of quantitative population assessments is impeding shark conservation in Mediterranean sea
b. This decline of sharks is causing major trophic cascades in the Caribbean and Mediterranean sea
c. Not only affecting sharks but other life in the sea
i. Sea is losing a wide range of intermediate and secondary predator species with the decline of the shark trophic cascade
E. Conservation
a. What can be done

References

Clarke TA (1971). The ecology of the scalloped hammerheadshark, Sphyrna lewini, in Hawaii.
Pac Sci 25, 33Ð144.
Ferretti, F, Myers, R, Serena, F, & Lotze, H (2008). Loss of Predatory Sharks from the
Mediterranean Sea. Conservation Biology, 22, 952-964.
Klimley, A (2006).Diel movements of scalloped hammerhead sharks, Sphyrna lewini Griffith and
Smith, to and from a seamount in the Gulf of California. Journal of Fish Biology. 33, 751-756.
Piercy, A, & Carlson, J (2007`). Age and growth of the scalloped hammerhead shark, Sphyrna
lewini, in the north-west Atlantic Ocean and Gulf of Mexico. Marine and Freshwater
Research. 58, 34-90.
Torres-Rojas, Y, Hernandex-Herrera, A, & Galvan-Magana, F (2006). Feeding habits of the
scalloped hammerhead shark, Sphyrna lewini, in Mazatlan waters, southern Gulf of
California, Mexico. CYBIUM. 30, 85-90.
Mello, W (2008).a. The electrosensorial pore system of the cephalofoil in the four most
common species of hammerhead shark (Elasmobranchii: Sphyrnidae) from the
Southwestern Atlantic.. Conservation Biology. 332, 404-412.
Holland, K, Wetherbee, B, Peterson, J, & Lowe, C (1993). Movements and Distribution of Hammerhead Shark Pups
on Their Natal Grounds . Copeia, 2, 495-502.

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