Fishing Articles
The Saline Wedge
Drought does affect the movement of fish in the
estuarine environment
Timothy Kusherets
There is a balance of temperature, oxygen, salinity,
and water in an estuary that is achieved before salmon can migrate from
the marine environment into rivers and streams. When this balance is
not achieved a form of toxicity takes place forcing salmon to either
rush up stream or out to deeper seawater. When a drought plagues an
estuary it becomes ripe to develop an uneven wedge of water between
the two environments causing temperatures to rise, oxygen to deplete,
and an abrupt increase in salinity (It is especially important in estuaries
since water does not easily turnover and circulate). In most cases the
introduction of freshwater (rivers, streams, and runoff) into saltwater
creates a water column that forces saltwater nearer the seabed and freshwater
closer to the surface creating a sort of wedge before mingling further
out to sea. Any given area that suddenly becomes devoid of fish, during
extended periods of high-pressure, is probably suffering from the dilemma
of an increase of the "saline wedge" but though fish may have moved
out they can be tracked even if the movement drives them miles from
the estuary. Given the option of dying at sea or spawning salmon will
migrate up those waterways that offer the ability to spawn even if is
not their place of birth. Scientists have observed this phenomenon for
years while recreational fishermen remain largely uninformed. During
a drought not only does the temperature of the estuary rise but heat
depletes the necessary oxygen level of both environments, driving fish
that have begun the process of transition from salt to freshwater upriver,
and those that have not out of the area. Fishermen are left to assume
that the run of fish was both small and short and abandon the estuary
and go to other places to fish. Backtracking the migration of the run
is the first thing anglers should consider before leaving the area entirely.
Tides and large freshwater ways are the main
variables to watch when backtracking. Strong tides during drought conditions
transport salmon in the direction of the ebb tide. Salmon will not resist
the pull of tides greater than 7 to 10 feet of movement. Follow the
direction of the offshore current and fish the very first large system
you find. Almost any map will show rivers and the larger the river the
more likely you are to find holding fish. Drought does affect the movement
of fish in the estuarine environment but those movements can be tracked
by simple observations of weather and tides when fishing in proximity
to smaller rivers and streams. The applications of the saline wedge
work in any estuary. When fish go off the bite, during natal stream
migration, ask yourself about the saline wedge.
© Timothy Kusherets, 2004/09
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