GREEN WATER AND SILVERSIDES
By Dr. Joe Richardson
Not to creep anybody out, but when you’re out there waist-deep in
Tybee’s surf, you wouldn’t believe all the little fish around you. Don’t worry,
they won’t hurt you, but as abundant as they are, it’s amazing that you
never notice them. Although we don’t eat them, they are very important
ecologically. With their tiny mouths, they feed on tiny, microscopic algae and
animals (plankton); and then they are big enough to be food for pan size fish
and birds. Those bigger fish and birds would never be able to eat things as
tiny as plankton.
As the water warms up this month, more and more different species of
small fish will show up in the surf zone eating plankton. Some of them, such
as little Bumpers, finger Mullet, and baby Pompano, are just youngsters of
what will become larger fish. But one of the most abundant and year round
resident species is the Silverside. They only grow to be about 3 inches long,
so they remain an important plankton eater their entire lives.
One of the main reasons you never notice Silversides swimming around
you is because of their color pattern. They are green on top, and their belly
side is shiny white. Although they swim close to the surface, when you look
down on them, their green backs blend in with the green water, so you don’t
see them. And if you were underwater looking up at them, you wouldn’t
notice them because their shiny white belly blends in with the shiny white
surface. Lots of our inshore fish, even larger ones like Spanish Mackerel,
26 TYBEE BEACHCOMBER | JULY 2018
Bluefish, and adult Mullet have this color pattern of green on top and shiny
white below, to help them become almost invisible in our green inshore
water. This type of coloration is called counter shading.
A Silverside gets its name from the mirror-like silver band running along
each side. There are a few ideas about why this highly reflective stripe is an
advantage. One is that many species of fish that live close together in schools
have shiny reflective parts so that when a member of the school moves one
way (e.g. to the right), everybody in the school can easily see the change in
reflection and also move to the right. This visual communication allows the
whole school to move at once as a coordinated unit. Another explanation
why schooling fish, especially small ones like Silversides, have shiny parts
is to confuse predators such as Bluefish and Spanish Mackerel when they
charge into a school. As the Silversides flee for their life, scattering in all
directions, those silver stripes reflect flickers of light going on and off all
around the predator and hopefully distract it from being able to target any
one individual.
For a little fish, it has a number of good adaptations (little mouth for little
food, color pattern, and silver stripes). And now that I think about it, maybe
that is why it is so abundant around here!
Dr. Joe Richardson is a retired marine science professor with 35+ years of
research and teaching experience along GA and the southeastern coast and
Bahamas. Besides research, he conducts Tybee Beach Ecology Trips year
round (www.TybeeBeachEcology.com) and frequently posts pictures of what
they are finding on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe
/(www.TybeeBeachEcology.com)