Fish Biomass: Northwestern Hawaiian Islands versus Main Hawaiian Islands:

a lesson on the Scientific Method and caring for the environment

STUDENT PAGE

Question: How does the biomass (amount) of fish in the Northwestern Hawaiian Islands (NWHI) compare to the biomass of fish in the main Hawaiian Islands (MHI)?

Hypothesis:

If I were an ichthyologist (a scientist who studies fish) and I studied the biomass of fish in Hawai’i using REA (Rapid Ecological Assessment) and other techniques, then I predict (circle your choice below)…

…the NWHI fish biomass would be the same as the MHI.

…the NWHI fish biomass would be greater than the MHI.

…the NWHI fish biomass would be less than the MHI.

Materials:

Small motorboat with towboards waterproof data tables transect rope

SCUBA gear pencil video camera

Thermometer depth recorder GPS unit

Methods:

1. TOWBOARD TEAM
• Use the motorboat to get to an ocean area around a Hawaiian island that is about 20 feet deep.
• Send two SCUBA divers into the water as a “Towboard Team.”
• The divers will be pulled through the water while holding onto “towboards” connected by rope to the stern (back) of the boat. One diver will be off the starboard (right) side of the boat; the other will be off the port (left) side. The towboards are flat boards that have data tables, thermometers, depth recorders and GPS units attached.
• The divers will record data about fish, coral, etc. while being pulled over a 3-kilometer long path over the seafloor.

2. FISH TEAM

· Using the information gathered by the Towboard Team, choose areas for doing more complete fish surveys, using the technique of Rapid Ecological Assessment (REA) as described here.

· Use the boat and GPS unit to get to a selected area.

· Anchor a 25-meter long rope on the shallow ocean seafloor; this is called a “transect line.” Put two more transect lines at different places, but nearby.

· Send three SCUBA divers into the water.

· The first two divers will swim along the transect counting the number of fish of each species that are over 20 cm long; the divers will only count the fish that are within 2 m on either side of the transect.

· When the divers get to the end of the transect, they will turn around and swim back. This time they will count the fish of each species that are under 20 cm.

· The third diver has two jobs:

--Stay in one spot. Within a radius of 10 m, count the number of large (over 25 cm), fast-moving fish in each species. Do this in 3 different spots, for a total of 4 surveys.

--Use a video camera to record the “general scene,” showing kinds and sizes of individual fish, as well as size of fish schools.

· In summary, at each GPS Fish Team location, a team of 3 divers will conduct 3 transect line surveys and 4 stationary counts.

Results:

1. It will take many days, months, and even years to gather REA data about fish from all the Hawaiian Islands!!
2. At last, you and other ichthyologists, have enough data to make calculations and comparisons on the fish biomass among all the Hawaiian Islands! Look at the data table “Average Biomass of Fish in the Hawaiian Islands.”
3. Notice that the data lists the islands in alphabetical order. To be able to reach conclusions, to answer your question at the start of this lesson, you need to graph the data.

Conclusion:

1. It is a scientist’s responsibility to analyze, or think about the data, in the Conclusion section.
2. Based on the data, as shown in your graph, how would you answer the question that you started with, “How does the biomass (amount) of fish in the Northwestern Hawaiian Islands (NWHI) compare to the biomass of fish in the main Hawaiian Islands (MHI)?”
3. Based on the data, was your hypothesis right or wrong?
4. What recommendation would you make?--
• The NWHI should be completely closed to fishing of any kind, at least until scientists can better understand the cause of the fish biomass and dynamics in the NWHI.
• The NWHI should be completely open to fishing; any species of fish, of any size, can be caught at any time of year, with any kind of fishing gear.