of water varies from place to place, we can match the “chemical signature” of a particular water body to the chemical makeup of the otolith to determine where the fish traveled during its entire life. To reveal movements of
flounder into and out of freshwater habitats, we mea- sured concentrations of the trace element barium in the otoliths. Barium concentra- tions are generally high in fresh water and comparatively low in sea water. Therefore, if barium concentrations in part of an otolith are high, we can con- clude that the fish resided in fresh water at the time that part of the otolith was formed. We analyze bari- um using a computer-controlled laser system. First, we select the path for the laser to take across the otolith. As the laser moves across the otolith, it blasts off tiny pieces of material from the otolith. These pieces are carried to an
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55 percent of the fish never entered fresh water at all, while the remaining 45 per- cent entered fresh water at least once. Taking their entire lifetime into consid- eration, 59 percent of the flounder used fresh water at some point. Of those individuals that
instrument that measures the concen- tration of barium and other chemical elements. With the help of local fishermen, we
collected otoliths from more than 250 juvenile and adult southern flounder, and these otoliths revealed interesting insight into the migration patterns of southern flounder in Texas. We found that, on average, individual fish spent 15 percent of their first year of life in fresh water. Some individuals, how- ever, spent most of their time in fresh water. During their first year of life,
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did enter freshwater habitats, there were many different migration patterns. Some individuals made one quick
trip into fresh water, while other individ- uals stayed there for a while. Some indi- viduals entered fresh water, then moved back into the bay or estuary, before re - turning to fresh water a second or even third time. Some individuals moved into fresh water quickly after hatching, while others spent time in the bays and estuaries before moving into fresh water. The main message we found is that
not all flounder are doing the same thing when it comes to using freshwa- ter habitats. There were two distinct
TIDE
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