Investigating the Beach
As with the other Sea Keeping exercises, investigating the beach
offers a range of opportunities. Start with the easy ones and
select activities that are appropriate to the participants and
the schedule. Some projects might be done as a special project,
others could be a class project. Most lend themselves to adjusting
the effort from easy to challenging.
- Map the beach. Starting with a copy
of a Council map of the beach, add landmarks. Indicate key points
with measurements (using measured lengths of rope, bearings, triangulation,
tape measures). Where do pipes, rivers, or other sources of water
enter the beach? Are there stormwater drains that empty onto the
beach? When were they installed? What do they drain? Are there
underground springs? Give your map to someone else to test it.
Can they find the same landmarks and places? Indicate North on
the map and enter the latitude and longitude co-ordinates, and
the name(s) of the beach. Indicate the horizontal profile of the
beach and type of sand in different zones. Is the beach sheltered
or exposed to large waves? Record this information.
- One of the measurements you will try to determine is the total
number of shellfish per unit area of the beach. This means working
out the number of square meters of the area measured. First, you
will need to work out the scale of your map. The first step is
to go to the beach and actually measure the distance between two
obvious landmarks that are located on the map or on the aerial
photograph. Next, photocopy the map (or tracing of an aerial photograph)
using graph paper with 1-mm squares in the paper tray. Measure
the distance between your two landmarks on the map (say 50-mm)
and divide this into the real world measurement (say 200 metres
or 200,000-mm). This yields the scale of the map, (4,000 to 1
or one millimetre equals 4 metres). Count up the 1-mm squares
within the area measured to get the total area of the sampled
area in square millimetres and convert this to square metres using
the map scale. For example, if the area measured contained 4000
square millimetres and if each square millimetre represented 4
meters by 4 meters as in our example, the total zone measured
would be 64,000 square metres.
- Look for old photographs of the beach taken by people in the
community or in a local library or museum. Can you find (from
landmarks in the photos) where the photos were taken from? Can
you take a photo from the same place again to show the changes?
Are there old survey maps of the beach? How do the very old maps
compare with the beach today? Obtain aerial photographs of the
beach - perhaps covering a long time span to see changes in the
beach and surrounding countryside. Trace the differences on paper
or in a computer to animate the changes and make them easy to
- What kinds of shellfish live on your beach? Look for dead
shells as these will indicate what species live nearby. If there
is an ancient Maori midden site near your beach you might look
at the species they collected from the beaches years ago and compare
them with shells that are present now. Do not disturb the midden,
however, simply look at the shells on the surface. Is the midden
marked on Department of Conservation maps? If not, you can notify
them of its existence. Does the local Iwi know of the midden?
- Use a good shell identification book to help you identify
the shells and other creatures. Plan a systematic search for living
shells, looking in likely and unlikely places. If you see holes
in the sand, you might have to dig 10-15 cm down to find the clams.
Perhaps you can take an experienced clam digger with you. Look
for big shells and baby shells.
- Shellfish live in groups, called beds. When you find a bed,
sketch its boundaries on the map and note the kind of habitat
the particular species likes in the Beach Keeper Log Book. (How
can you be sure they are in the right place on the map? Will you
use bearings, landmarks, triangulation?).
- What other features of the beach can you map? Is there algae
growing on the sand or rocks? What kind of algae is it? Some algae,
like green sea lettuce, is considered a possible indicator of
pollution. Are there crabs? Where are they located and what do
they feed on?
- Once you have a good map of the beach and some knowledge of
the shellfish, you are ready to begin your shellfish census.