How to Study Big Fish in Hawaii
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Transcript of How to Study Big Fish in Hawaii
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How to Study Big Fish in Hawaii
To start, let’s see what you already know…..
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Answer these pre-assessment questions:
• List the “big fish” you think are associated with Hawaiian reefs.
• What role(s) do you think these fish play in the reef ecosystem?
• How specifically, do you think scientists discover the answers to the first two questions?
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Let’s meet the “big guys”!
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Tiger shark or Mano (as sharks are named in Hawaiian)
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White-tipped Reef Shark
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Black-tipped Reef Shark
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Galapagos Shark
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Ulua (otherwise known as Trevally or Jacks)
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There are several species of Ulua in Hawaii
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Grey Snapper or Uku
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Hawaiian Black Grouper or Hapu`u
• These fish are found in deep water near Hawaiian reefs
• They have unfortunately become quite scarce
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These fish and related species are the apex predators of the reef!
• Apex predator species are often at the end of long food chains, where they have a crucial role in maintaining the health of ecosystems.
• The term "apex predator" has been defined in terms of trophic levels.
• Trophic levels are "a group of organisms that occupy the same position in a food chain"
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To understand the role of apex predators, scientists need to understand reef ecosystems as a whole
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Understanding Reef Ecosystems is a Work in Progress
• Scientists are currently studying reef organisms and their interactions all over the world
• They are still finding previously unidentified species in the islands northwest of Hawaii that comprise the Papahānaumokuākea Marine National Monument
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Understanding the role of apex predators in reef ecosystems is
obviously a complicated undertaking!
• How would you study the “big fish” of the Hawaiian reefs?
• How could you determine what and how much they eat?
• Brainstorm specific methods now.
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Of course safety is a consideration!
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If a researcher feels the behavior of nearby predatory fish is unsafe they get out of
the water as quickly as possible.
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Researchers who study fish need to be comfortable in the water
• They need to know how to snorkel and SCUBA
• They often handle camera and video equipment
• They also record observations underwater on waterproof paper
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Click hereto see the “big fish in action”
Close the movie frame when the movie is finished
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Sometimes these fish change their behavior when divers are in the water –
they may become aggressive
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Researchers may conduct observations while swimming a transect
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They may count the number of certain species present
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There are times when they have to make estimations
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Many species of apex predators feed at night and most swim much faster
than humans.
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Did you think of any methods to learn about these fish that don’t involve direct
human observation?
• One method being used on an increasing basis it the radio-tagging of these species
• A small radio transmitter is attached to the fish (or surgically implanted)
• Scientists are able to track the fish as it moves through the ocean
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Results are gathered from a receiving station and analyzed
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This study by Carl Meyer et al shows the movements of giant trevally near two islands of the
Papahānaumokuākea Marine National Monument
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This is the Giant Trevally or Ulua
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Sharks are baited, surgically implanted with tracking devices and immediately released – a
technique developed by researcher Kim Holland
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Sharks have also been fitted with underwater video cameras that also collect data on movements of fish –
these cameras are called “crittercams”
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Scientists also can take tissue samples from sharks and other large fish
without killing them
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Scientists can learn a lot from a tissue sample!
• DNA can be extracted and studied for a number or things including relationships between individuals and populations of a fish species
• Genes with known functions (or malfunction) can be identified and determined present or absent in individual fish
• The metabolism of the fish can be better understood
• Fatty acids can be analyzed to determine to a certain extent what the fish are eating
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The stomach content of fish can be studied – the fish does not, however, survive this method
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Scientists use statistical methods, mathematical models and graphic displays to better interpret and share their findings
Figure 2. Geographic pattern of apex predator biomass density (t ha-1) at the 10 emergent Northwestern Hawaiian Island (NWHI) reefs surveyed during September/October 2000, 2001 and 2002 (DeMartini and Friedlander 2004)
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Think critically, how sure can a researcher be that their findings are conclusive?
• Is the sample (number) of fish they observed or studied representative?
• Are there important behaviors as yet unobserved?
• Does the presence of a diver affect fish behavior?
• Reflect on these questions and record your thoughts on your worksheet.
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Scientists are careful about interpreting their findings
• Scientists don’t say that they “prove” things or discover “facts”
• They analyze the data and are careful to note that it is based only on a sample of fish
• Most scientists who study fish understand that there are still an enormous number of unanswered questions
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Acknowledgements
• Photos by James Watt and Andy Collins • Kim Holland Shark Lab at the Hawaii Institute
of Marine Biology• Carl G. Meyers, Kim M Holland and Yannis P.
Papastamatiou for the ulua movement research and graphics
• Alan Friedlander and Lisa Wedding for the apex predator biomass research and graphic
• Wikipedia for definition of apex predator