Removing sharks from marine ecosystems has been demonstrated to have detrimental effects on marine ecosystems. Early work by Sala et al demonstrated that coral reefs with apex predators like sharks had more coral cover and healthier ecosystems. Dr. Stuart Sandin* of the Scripps Institution of Oceanography and his collaborators concluded that sharks play a vital role in maintaining the health of coral reefs. Removing these predators through overfishing sets off a cascade of effects that ripple through the food chain.
A decrease in the Caribbean shark population is met by an increase in its prey, the grouper fish. The expanding grouper population takes parrotfish, normally responsible for clearing coral of algae, in greater numbers. This could explain why algae now dominates many degraded reefs in the Caribbean. It also shows how the systematic elimination of one species—a key link in a complex web of relationships—can destabilize the entire ecosystem. Dr. Sala and his work is featured in our film Shark Stewards of the Reef, including the impacts of shark finning on global shark populations.
These cascade effects have the potential to permanently alter the ecosystem and impact local economies dependent on fisheries and ecosystem services.
Another study off the coast of North Carolina, USA, suggests that overfishing sharks like blacktip sharks has led to the complete collapse of a century-old bay scalloped fishery that supported the local community. The removal of local large sharks caused their main prey, the cow nose ray, to soar in numbers and expand into areas that were previously too risky to forage. The rays decimated the scallop populations in the area to a point beyond which, combined with ongoing fishing pressure, they may not be able to recover.
Saving Sharks Saves Ocean Health
CASCADING EFFECTS OF THE LOSS OF APEX PREDATORY SHARKS FROM A COASTAL OCEAN Science 30 March 2007: Vol. 315 no. 5820 pp. 1846-1850 .
*Sandin, S., A., Smith, J. E., DeMartini, E. E., Dinsdale, E. A., Donner, S. D., Friedlander, A. M., Konotchick, T., Malay, M., Maragos, J. E., Obura, D., Pantos, O., Paulay, G., Richie, M., Rohwer, M., Schroeder, R. E., Walsh, S., Jackson, J. B. C., Knowlton, N., Sala, E. 2008. Baselines and degradation of coral reefs in the Northern Line Islands. PLOS One 3(2): 1-11.
A compilation of References on the Importance of Sharks to Marine Ecosystems
1 – Pauly, D. 1995. Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology and Evolution 10: 430.Sheppard 1995
2 – Sheppard, C. 1995. The shifting baseline syndrome. Marine Pollution Bulletin 30: 766-767.
3 – Robbins, W. D., Hizano, M., Connolly, S. R., J. H. Choat. 2006. Ongoing collapse of coral-reef shark populations. Current Biology 16: 2314-2319.
4 – Sandin, S., A., Smith, J. E., DeMartini, E. E., Dinsdale, E. A., Donner, S. D., Friedlander, A. M., Konotchick, T., Malay, M., Maragos, J. E., Obura, D., Pantos, O., Paulay, G., Richie, M., Rohwer, M., Schroeder, R. E., Walsh, S., Jackson, J. B. C., Knowlton, N., Sala, E. 2008. Baselines and degradation of coral reefs in the Northern Line Islands. PLOS One 3(2): 1-11.
5 – Stevenson, C., Katz, L. S., Micheli, L. F., Block, B., Heiman, K. W., Perle, C., Weng, K., Dunbar, R., Witting, J. 2006. High apex predator biomass on remote Pacific Islands. Coral Reefs 26: 47-51.
6 – Ricker, W. E. 1946. Production and utilization of fish populations. Ecological Monographs 16: 373-391.
7 – Jennings, S., Kaiser, M. (1998) The effects of fishing on marine ecosystems. Advances in Marine Biology 34: 201-
8 – Jennings, S., Reynolds, J. D., and Polunin, N. V. C. 1999. Predicting the vulnerability of tropical reef fishes to exploitation with phylogenies and life histories. Conservation Biology 13: 1466-1475.
9 – Pitcher, T. J. 2001. Fisheries managed to rebuild ecosystems? Reconstructing the past to salvage the future. Ecological Applications 11: 601-617
10 – Dulvy, N. K., Polunin, N. V. C. 2004b. Size structural change in lightly exploited coral reef fish communities: evidence for weak indirect effects. Canadian Journal of Fisheries and Aquatic Sciences 61: 466-475.
11 – Friedlander, A. and De Martini, E. E. 2002. Contrasts in density, size, and biomass of reef fishes between the northwestern and main Hawaiian Islands: effects of fishing down apex predators. Marine Ecology Progress Series 230: 253-264.
12 – Birkeland, C. and Friedlander, A. M. 2001. The importance of refuges for reef fish replenishment in Hawai’i. Hawaii Audubon Society, 19 pp.
13 – Pala, C. 2007a. Conservationists and fishers face off over Hawaii’s marine riches. Science 317: 306-307.
14 – Richie, M., Rohwer, M., Schroeder, R. E., Walsh, S., Jackson, J. B. C., Knowlton, N., Sala, E. 2008. Baselines and degradation of coral reefs in the Northern Line Islands. PLOS One 3(2): 1-11.
15 – Starmer, J., Asher, J., Castro, F., Gochfeld, G., Gove, J., Hall, A., Houk, P., Keenan, E., Miller, J., Moffit, R., Nadon, M., Schroeder, R., Smith, E., Trianni, M., Vroom, P., Wong, K., and Yuknavage, K. 2008. The state of coral reef ecosystems of the Commonwealth of the Northern Mariana Islands. Pages 427-463 in Waddell, J. E. and A. M. Clarke (eds.) The state of coral reef ecosystems of the United States and Pacific Freely Associated States: 2008. NOAA Technical Memorandum NOS NCCOS 73.
16 – Wilkinson, C. (ed.) 2008. Status of coral reefs of the world: 2008. Global Coral Reef Monitoring Network, Townsville, Australia. 298 pp.