Sagip Sarihay Series features critically endangered species in the Philippines, with weekly posts of alternating plant and animal species, and with the primary aims of awareness and call to action. This series is a project of the SciTech and the VA sections of UST-CSJ. (Note: Weekly order of posting does not reflect actual order of intensity of endangerment. Database reference for selection of species is the IUCN Red List.)

SAGIP SARIHAY #8

Species: Sphyrna lewini (“Scalloped Hammerhead”)

Words by Michelle Charina Gomez
Artwork by Iona Sofia Ramos

A visual representation of Scalloped Hammerhead.

Description

Sphyrna lewini is a coastal-pelagic species of shark from the family Sphyrnidae, with its distribution being in tropical and warm temperate seas (Quintanilla et al., 2014). S. lewini exhibits the characteristic hammer-shaped head shared by the members of the said family. This distinguishable head shape is caused by the lateral expansion of its head, with the location of the eyes and nostrils being at the edges (Muriana et al., 2017). S. lewini is an apex predator, playing a significant role in the top-down control of other marine organisms. Its efficient prey capture behavior is influenced by its ability to move fast and its high maneuverability, with the latter being due to S. lewini having a large head width accompanied by a small cross-sectional area for its trunk (Kaijura & Holland, 2002; Wells et al., 2018).

Locality

S. lewini has a global distribution (Hadi et al., 2020). In the Philippines, S. lewini can be found on Cabilao Island, Bohol, Philippines (Green, 2002).

Threats

The primary threat for S. lewini is overexploitation due to their high economic value and popularity in the shark fin trade, with the population decline influenced by their slow growth rate and a long period required for gestation (Hadi et al., 2020). Their sexual maturity also occurs much later, with sexual maturity occuring after 10 years for males and 15 years for females; this overweighs the high fecundity exhibited by the species, as they can produce 12 to 30 pups per year (Quintanilla et al., 2014). However, regardless of their age, their risk of mortality is still relatively high (Anna et al., 2020). Moreover, due to the schooling behavior exhibited by the species, numerous individuals may be captured at once (Wells et al., 2018).

Threats

Upon the evaluation of its extinction risk, the populations of S. lewini in the Pacific and Atlantic Ocean were declared to be the first protected shark species in accordance with the U.S. Endangered Species Act (Wells et al., 2018). Moreover, since S. lewini utilizes nursery areas, the identification and conservation of these nursery areas may aid in mitigating the population decline of this species (Quintanilla et al., 2014). In Indonesia, regulations have been implemented by the government in order to monitor the export of S. lewini products, with such regulation implemented in order to prevent the uncontrolled production of scalloped hammerhead products (Anna et al., 2020).

References

Anna, Z., Hindayani, P., Suryana, A., Ihsan, Y., & Salsabila, A. (2020). Sustainability Study of Scalloped Hammerhead Shark (Sphyrna lewini) in Indramayu Waters. Sustainability, 12. doi:10.3390/su122410459

Green, S. (2002, January 18). Marine Ecotourism & Community Participation: Case Studies From Bohol, Philippines [Paper presentation]. World Ecotourism Colloquium, Sarawak, Malaysia. https://www.researchgate.net/profile/Stuart-Green-6/publication/273452955_ Marine_Ecotourism_Community_Participation_Case_Studies_From_Bohol_Philippines/links/5502a8190cf2d60c0e64263f/Marine-Ecotourism-Community-Participation-Case-Studies-From-Bohol-Philippines.pdf

Hadi, S., Andayani, N., Muttaqin, E., Simeon, B., Ichsan, M., Subhan, B., & Madduppa, H. (2020). Genetic connectivity of the scalloped hammerhead shark Sphyrna lewini across Indonesia and the Western Indian Ocean. PLoS ONE, 15(10). https://doi.org/10.1371/journal.pone.0230763

Rigby, C.L., Dulvy, N.K., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N., Romanov, E., Sherley, R.B. & Winker, H. 2019. Sphyrna lewini. The IUCN Red List of Threatened Species 2019: e.T39385A2918526.

Kaijiura, S., & Holland, K. (2002). Electroreception in juvenile scalloped hammerhead and sandbar sharks. Journal of Experimental Biology, 205, 3609–3621.

Muriana, C., Vasconcelos, B., Leandro, R., Malavasi, C., Amorim, A., Rici, R., Maria, D., Miglino, M., & Ferreira, A. (2017). Morphological Study of the Eye Bulb of the Hammerhead Shark, Sphyrna lewini (Elasmobranch: Carcharhinidae). International Journal of Morphology, 35(1), 287–292.

Quintanilla, S., Gomez, A., Marino-Ramirez, C., Sorzano, C., Bessudo, S., Soler, G., Bernal, J., & Caballero, S. (2015). Conservation Genetics of the Scalloped Hammerhead Shark in the Pacific Coast of Colombia. Journal of Heredity, 106, 448–458. doi:10.1093/jhered/esv050

Wells, R., TinHan, T., Dance, M., Drymon, M., Falterman, B., Ajemian, M., Stunz, G., Mohan, J., Hoffmayer, E., Driggers, W., & McKinney, J. (2018). Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead. Frontiers in Marine Science, 5(321). https://doi.org/10.3389/fmars.2018.00321