How to Study Big Fish in Hawaii

To start, let’s see what you already know…..

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?

Let’s meet the “big guys”!

Tiger shark or Mano (as sharks are named in Hawaiian)

White-tipped Reef Shark

Black-tipped Reef Shark

Galapagos Shark

Ulua (otherwise known as Trevally or Jacks)

There are several species of Ulua in Hawaii

Grey Snapper or Uku

Hawaiian Black Grouper or Hapu`u

• These fish are found in deep water near Hawaiian reefs

• They have unfortunately become quite scarce

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"

To understand the role of apex predators, scientists need to understand reef ecosystems as a whole

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

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.

Of course safety is a consideration!

If a researcher feels the behavior of nearby predatory fish is unsafe they get out of

the water as quickly as possible.

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

Click hereto see the “big fish in action”

Close the movie frame when the movie is finished

Sometimes these fish change their behavior when divers are in the water –

they may become aggressive

Researchers may conduct observations while swimming a transect

They may count the number of certain species present

There are times when they have to make estimations

Many species of apex predators feed at night and most swim much faster

than humans.

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

Results are gathered from a receiving station and analyzed

This study by Carl Meyer et al shows the movements of giant trevally near two islands of the

Papahānaumokuākea Marine National Monument

This is the Giant Trevally or Ulua

Sharks are baited, surgically implanted with tracking devices and immediately released – a

technique developed by researcher Kim Holland

Sharks have also been fitted with underwater video cameras that also collect data on movements of fish –

these cameras are called “crittercams”

Scientists also can take tissue samples from sharks and other large fish

without killing them

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

The stomach content of fish can be studied – the fish does not, however, survive this method

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)

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.

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

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