Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1, Canada.
Science (Impact Factor: 31.48). 03/2007; 315(5820):1846-50. DOI: 10.1126/science.1138657
Source: PubMed

ABSTRACT Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

Download full-text


Available from: Julia K Baum, Jul 05, 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sharks are apex predators and keystone species that have a profound influence on the ecology and food-web dynamics of coral reefs and epipelagic marine ecosystems. However, sharks are being heavily overfished compromising the health of the world’s reefs and pelagic environments. Although Indonesia is the world’s largest and most diverse coral reef ecosystem, information on the exploitation of sharks in this region is scarce. Results of DNA barcoding of shark fin revealed two alarming findings: (1) a rarity of reef sharks that should dominate Indonesia’s coastal ecosystems, and (2) a fishery that targets endangered sharks. The diversity and number of threatened species recovered in this study highlights the urgent need for improved regulation and control of Indonesia’s shark fishery.
    Fisheries Research 04/2015; 164(April 2015):130-134. DOI:10.1016/j.fishres.2014.11.003 · 1.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Rationale Individual foraging behavior is an important variable of predators commonly studied at the population level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods. Methods We determined the isotopic composition (δ13C and δ15N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values. Results There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ15N values of S. zygaena vertebrae, with lower values in the first group of samples. Conclusions Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology.
    Rapid Communications in Mass Spectrometry 03/2015; 29(9):821-829. DOI:10.1002/rcm.7169 · 2.64 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Oceanic top predators are the subject of studies by researchers under the international Climate Impacts on Oceanic Top Predators (CLIOTOP) program. A wide range of data sets have shown that environmental conditions, such as temperature and marine productivity, affect the distribution and biological processes of these species, and thus the activities of the humans that depend on them. In this special issue, 25 papers arising from the 2nd CLIOTOP symposium, held in Noumea, New Caledonia in February 2013 report the importance of realistic physical descriptions of oceanic processes for climate change projections, demonstrate a wide range of predator responses to historical climate variability, describe new analytical approaches for understanding the physiology, behaviour and trophodynamics, and project future distributions for a range of species. Several contributions discuss the implications for conservation and fisheries and show that resolving ecosystem management challenges and conflicts in the face of climate change is possible, but will require attention by decision-makers to issues that are broader than their traditional mandate. In the coming years, an increased focus on the development of management options to reduce the impacts of climate change on top predators and their dependent industries is needed.
    Deep Sea Research Part II Topical Studies in Oceanography 02/2015; 113. DOI:10.1016/j.dsr2.2015.01.013 · 2.76 Impact Factor