Many of you that fish the local club tournaments are aware that the DNR collects information about the fish you weigh in.
Julie Vecchio was a graduate student working
with the DNR and she had put
together this informative document.
|South Carolina Department of Natural Resources|
|"So, what ARE those crazy DNR people doing to our fish?"|
inshore fisheries section of SCDNR keeps track of age, reproductive status,
and populations size of several recreationally important estuarine and near-shore
fish species in South Carolina.
We do this through a variety of means.
We do our own fisheries-independent sampling using both trammel nets and electrofishing techniques. We also have a freezer-fish program in which people leave the wracks of fish they have caught for us in freezers throughout the coastal area.
In addition, we use structures from the fish you catch and bring into tournaments. It is important for us to examine all specimens brought in, not just the biggest ones.
These species include:
Fish Lengths and Weights:
Each fish is measured to
the nearest millimeter for
Total Length and Standard Length.
It is then weighed to the
Otoliths are the internal ear bones of the fish.
Every fish has 3 pairs of otoliths. Most of the time, scientists use the sagittal otoliths to age fish, mostly because they are the biggest and easiest to find, see, and examine under a microscope.
are calcium secretions within the head of the fish, and they grow as the
fish grows. Most fish grow through their lives. Therefore, their otoliths
grow with them
throughout their lives.
Each day, the fish lays down an extremely tiny layer of new calcium on the outside of the otolith.
This is a whole otolith of
a Spotted Seatrout
This is a sectioned Red Drum otolith. The space from one bright
band to the next is counted
as a year of growth.
This fish is 7 years old.
the fish that we care about live in coastal waters, they encounter seasons
where the water is warmer and seasons where the water is colder. Generally,
during colder months, the fish grow more slowly than during warmer months.
The daily layers are laid down closer together during colder months. When examined as a whole, the otolith appears to have layers to it, one compact layer, followed by one diffuse layer. When examined, one compact layer, plus one diffuse layer equals one year of growth.
one year of growth.
we examine enough of these otoliths,
we can find out how old the fish within the population are.
marine and estuarine bony fish reproduce
by getting together in large groups and
spraying huge numbers of eggs and sperm into the water.
When the eggs and sperm meet in the water column,
they fertilize. However, each fish species
reproduces during a specific time of year.
Fish do not have external genitalia.
This means that we cannot tell if they are
males or females by looking at them from the outside.
We must cut them open to find out if they are males or females, and to find out if they are able to reproduce.
gonad look like this
gonad look like this
|Bringing it all together|
putting this information together, we can tell how large the
fish are within the population, how old those same fish are,
and whether those individuals are able to reproduce.
This is very important information for several reasons.
First, it is important to know about the life history of fisheries species.
This helps us to determine at what size and age they
can be harvested from the population while doing the least
amount of damage to future generations.
In addition, we can tell whether a group of fish is in
danger from overfishing. Classic signs of overfishing include
fish that are smaller than they used to be at a certain age,
and fish that are maturing earlier than they used to.
If fisheries scientists notice these things about a species,
they will know that the stock of fish is probably being overfished.
If scientists are monitoring a species and notice that it
is being overfished, they may be able to change
harvest regulations and and prevent the
species from becoming extinct.
|Life histores of the fish we study|
Drum enter the estuary as eggs and are washed into shallow nursery areas
by currents. The spend the first few years of their lives living and feeding
within the estuary.
Males become sexually mature between
3 and 4 years of age, 25 inches total length,
and about 8 pounds.
Females mature later, between 4 and 5 years
of age, 30 inches total length,
and about 10 pounds.
Both males and females move out of
the estuary into the ocean at about
the time when they mature.
Red drum have been aged to over 35 years of age.
All red drum within the slot limit are immature fish.
Most spotted seatrout live to only a few years old. However, a few have been aged to over 10 years.
Seatrout spend their entire
lives within the estuary. The adults spawn between May and August within the estuary,
and eggs enter small nursery creeks.
Spotted seatrout take approximately
one year to mature. Both males and females are approximately 10 inches long and weigh
about ½ pound when they become sexually mature. However, after this, females begin growing much faster than males.
For example, a 3 year old female would be approximately 17 inches long and
weigh about 2 ½ pounds.
A 3 year old male would be approximately 15 inches long and weigh about 1 ½ pounds.
This size difference continues
throughout their lives.
Flounder spawn in offshore waters during the late fall, early winter months.
The eggs drift in offshore waters,
hatching into larvae that are about ½ inch long when they finally get to shallow nursery areas within the upper estuaries.
When they are tiny, flounder begin life
looking like normal fish, with an eye
on each side of their head.
As they grow, the right eye migrates
to the left side of the head.
By about ½ inch long, they have both eyes on the left side of their head.
Females grow rapidly
and may reach 12 inches by the end of the first year.
Males may be only
8 to 10 at one year.
Julie...Thanks, this is great information!...Janell