Ecological Importance of Sharks

Why might these roles be important to ecosystems?

The research reveals sharks may be especially important when preying upon longer-lived species, maintaining specialized diets of a limited number of prey species, or preying upon species that have their own important ecological roles. 

• Direct predation on prey
  • There are few empirical data to support this mechanism for influencing prey population sizes, with the exception of some pinniped populations (although most appear unaffected by predation rates).
  • Some studies of reefs and time series analyses from fisheries suggest prey populations are lower when shark populations are greater, but these patterns often have alternative explanations or cannot partition an effect of shark predation from that by large teleosts; furthermore these correlations could be due to changes in shark predation rates combined with behavioral effects.
  • Recent studies suggest white shark predation on sea otters in areas where kelp cover is low likely is responsible for limiting range expansion by otters and kelp.White shark predation on otters, however, is not important in well-developed kelp forests.
  • Evidence for major cascading effects of shark loss in open oceans is relatively weak and may not be large because of similar roles played by large bony fish and rapid reproduction of prey taxa;but they could play roles we are not necessarily measuring or capturing in models like facilitating aerial predators or transporting nutrients.
  • The lack of current evidence does not preclude this as important in some locations or under certain conditions (e.g., periods of food stress for prey), but there are multiple studies suggesting that shark direct predation is not likely to affect prey population sizes in the systems where those studies occurred.While often considered top predators, the majority of elasmobranchs are mid-level predators and have diets and roles that likely overlap with large bony fishes reducing the probability of large effects on prey. 
• Behavioral or physiological responses in prey
  • A large body of evidence shows that prey taxa – from small fish to marine mammals – change their behavior in response to risk from sharks, but the consequences for wider ecosystems is only documented in a few key locations so far.
  • In Shark Bay, Australia, a multi-decade study has shown pervasive effects of sharks on behavior of prey and that these behavioral effects cascade to the structure of seagrass communities and enhances resilience to climate disturbance; the presence of sharks facilitates the development of structurally complex seagrass meadows with high habitat value and sequestration of carbon;the generality of the Shark Bay study is unknown, but loss of tiger sharks combined with turtle population increases suggests that tiger sharks are a critical species in multiple situations.
  • On coral reefs, the presence of sharks may result in spatial variation in algal and coral cover based on the relative safety of different microhabitats; more studies of indirect effects of risk on reefs is needed.
• Changing the behavior of competitors
  • There is growing evidence that sharks might influence populations of teleosts that are competitors on reefs.The consequences of these interactions more broadly is poorly known.
  • Sharks on reefs and in estuaries can feed in habitats that are distant from those where they spend considerable amounts of time.This means they can transport considerable amounts of nutrient and possibly fertilize the primary producers in the areas where they reside but do not forage.  While the links across habitats have been established the ecological importance of this nutrient transport is currently unclear.
• Bioturbation
  • Elasmobranchs can excavate huge quantities of sand while feeding, but the ecological importance of sediment turnover is still poorly known.
• Facilitating other species
  • While elasmobranchs may facilitate other taxa, (e.g. serving as parastite scratching posts for fish or protecting small fish by hunting big fish) the importance of these interactions is poorly known.
• Providing food for others
  • Studies of predator diets have shown some where sharks or their relatives are critical prey items.Examples span from other sharks to killer whales.  In some situations, it is unclear if these predators would be able to switch to other prey sources successfully if elasmobranch prey were to decline.

The Scientists

• Mike Heithaus
  Executive Dean and Marine Ecologist, Florida International University

  
  Mike Heithaus has spent his career studying the ecological role of sharks including two decades in Shark Bay, Australia. As a marine ecologist, he specializes in predator-prey interactions and the ecological importance of sharks and other large marine species. He is on a mission to unlock the secrets of our oceans by deploying cutting-edge technology including drones and animal-borne cameras. Helping to shape shark and ocean conservation, his work in Shark Bay is the most detailed study of the ecological role of sharks in the world and has been used as the underpinning for affecting positive policy changes. 

  Sharing his passion for science, Heithaus has been involved in the production of more than 30 natural history documentaries, including many featured on National Geographic’s Shark Fest and Discovery’s Shark Week. He also hosted National Geographic's Crittercam television series. He has co-written two high school science textbooks and is an author on national K-8 science programs. 

  At FIU, he is the executive dean of the College of Arts, Sciences & Education and professor of Biological Sciences. He previously served as executive director of the School of Environment, Arts and Society and director of the Marine Sciences Program. He has authored or co-authored more than 200 peer-reviewed journal articles and book chapters and co-edited five books on the biology of sharks and their relatives. 

  Heithaus is an Explorers Club fellow, member of the Science Advisory Committee for Pew Environment’s Global Shark Program, serves as the associate editor of Frontiers in Marine Science, and is an inaugural member of the Academy of Science, Engineering and Medicine of Florida board of directors. He also serves on the Zoo Miami Foundation Board of Directors and chairs the Education Committee. Prior to joining FIU, Heithaus was a scientist at Mote Marine Laboratory’s Center for Shark Research. He also worked with National Geographic’s Remote Imaging Department where he conducted studies using their Crittercam. He received a B.A. in Biology from Oberlin College in 1995 and completed his Ph.D. at Simon Fraser University in 2001.

  

• Yannis Papastamatiou
  Shark Behavior Ecologist and Associate Professor, Florida International University

  
  With more than 100 research publications, Yannis Papastamatiou is one of the world’s leading shark behavioral ecologists. Papastamatiou’s use of new tag technologies on species ranging from pelagic oceanic whitetips to home-ranging reef sharks has advanced the field of predator ecology and led to evidence-based marine protected area zoning. His work has appeared on National Geographic and BBC. Papastamatiou has over 1,500 dives and is certified in most forms of scientific and technical diving. He is interested in the ecology of mesophotic reefs and in the use of technical diving for underwater exploration. A native of London, Papastamatiou has conducted research in California, Florida, Hawaii, South Africa, French Polynesia, Japan, Mexico and throughout the Mediterranean and Northern Pacific Ocean. He earned an undergraduate degree from the University of Southampton, master's from California State University, Long Beach and a Ph.D. in Zoology from the University of Hawaii at Manoa.
  

  

• Simon Dedman
  Postdoctoral Scientist, Florida International University

  
  Simon Dedman is a research scientist at Florida International University and has spearheaded the use of machine learning tools for movement studies on sharks, rays, and tuna, authoring multiple papers on the drivers of animal movement, and developing two software packages which make it faster and easier for scientists to turn tracking data into results and management advice. His work helps us understand where animals go, when, and why; how species inhabit different areas based on sex and age; and what causes changes in population sizes. From working as the UK’s fisheries quota manager to his Ph.D. in spatial management of skates and rays in the Irish sea, Dedman has experience and a holistic understanding from hands-on shark tagging, to modeling, to management advice, to the management and the enforcement interface with the fishing industry. From London via academic appointments and industry roles in England, Scotland, Ireland, The Bahamas, and California, his ongoing work is to use causal models to reveal whether sharks are more crucial to coral reefs, or vice versa.

   
• Jerry Moxley
  Postdoctoral Scientist, Florida International University

  Jerry Moxley is a conservation ecologist at Florida International Univeristy who specializes in studies on the abundance, movement, and behaviors of marine megafauna. Working with sharks and marine mammals, he examines how both direct and indirect species interactions influence the recovery of protected species and affect broader patterns of ecosystem recovery. On both east and west U.S. coasts, he has investigated how marine mammal interactions modulate the ecological importance of white sharks in food webs. This includes how direct non-trophic impacts on sea otters affected range expansion processes and interfered with refuging behavior, how predation risk influenced seal space use and movement, and how threatening killer whales induce dramatic behavioral responses in white sharks and redistributed their predation pressure. In his research, Dr. Moxley employs quantitative approaches with field-based tagging and monitoring programs to create integrative understandings about species recovery and ecosystem restoration. He received his Ph.D. in marine ecology and conservation from Duke University, and previously completed a post-doctoral fellowship at the Monterey Bay Aquarium.  

   

  
• Co-Authors of Ecological roles and importance of sharks in the Anthropocene Ocean

  Matias Braccini, Western Australia Fisheries and Marine Research Laboratories

  Jennifer E. Caselle, Marine Science Institute, University of California, Santa Barbara

  Demian D. Chapman, Mote Marine Laboratory

  Joshua Eli Cinner, University of Sydney

  Erin M. Dillon, University of California, Santa Barbara and Smithsonian Tropical Research Institute

  Nicholas K. Dulvy, Simon Fraser University

  Ruth Elizabeth Dunn, Lancaster University and the Lyell Centre, Heriot-Watt University

  Mario Espinoza, Universidad de Costa Rica

  Alastair R. Harborne, Institute of Environment, Florida International University

  Euan S. Harvey, Curtin University

  Michelle R. Heupel, University of Tasmania and Australian Institute of Marine Science

  Charlie Huveneers, Flinders University

  Nicholas A.J. Graham, Lancaster University

  James T. Ketchum, MigraMar, Pelagios Kakunjá and Centro de Investigaciones Biológicas del Noroeste

  Natalie V. Klinard, Dalhousie University

  Alison A. Kock, Cape Research Center at South African National Parks and South African Institute for Aquatic Biodiversity

  Christopher G. Lowe, California State University, Long Beach

  M. Aaron MacNeil, Dalhousie University

  Elizabeth M.P. Madin, University of Hawai'i at Mānoa

  Douglas J. McCauley, University of California, Santa Barbara

  Mark Meekan, Australian Institute of Marine Science

  Amelia C. Meier, University of Hawai'i at Mānoa

  Colin A. Simpfendorfer, University of Tasmania and James Cook University

  M. Tim Tinker, University of California, Santa Cruz and U.S. Geological Survey

  Megan Winton, Atlantic White Shark Conservancy

  Aaron J. Wirsing, University of Washington