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THE
PROBLEM WITH HABITAT BANKS, THERMAL BANKS, TEMPERATURE TARGETS AND
FLOW TARGETS
Any
fisheries management plan for the Delaware River tail water trout
fishery that is based on habitat banks, thermal banks, temperature
targets and flow targets depends on the accuracy and timeliness of a
bewildering number of assumptions, predictions and monitoring ability.
In order to be effective, such a plan needs to accurately
monitor, on a continuing basis, water and air temperature and flow
conditions at a number of locations AND be able to predict, far enough
in advance, the effect that a certain amount of water at a particular
temperature and flow will have on a living resource tens of miles
downstream, tens of hours later.
Even more problematic is the ability to estimate, a year or
more in advance, how much water should be allocated to these banks.
EFFECT
OF NON-MONITORED TRIBUTARIES AND WEATHER
The temperature and flow of tributaries and
springs within the three main tributaries have a profound but
unmeasured effect on the temperature and flow in the designated trout
management sections. The
Delaware River system spans hundreds of miles.
Local weather conditions have important, unpredictable and
often un-recorded effects on the waters under consideration.
MONITORING
AND LOCATION OF GAGES
Water temperatures and flow change rapidly
as a function of the amount of water being released from the
reservoirs and local weather conditions.
On any particular summer day, one tributary may be receiving
mostly cold water from releases whereas another tributary may consist
almost entirely of flow from unmonitored tributaries to that stream.
In order for a system based on temperature and flow targets to
be effective, the location of key temperature and flow gages must not
only be calibrated frequently for accuracy, they must be located in
places that adequately reflect conditions that are of significance to
the resources to be protected.
PREDICTION
AND LAG TIME
Reliance on a bank or portion thereof to be
released to prevent undesired consequences to a living resource
requires a bewildering ability to be able to predict the time,
duration, and amount of water that needs to be released, and is
dependent upon many unknown or unpredictable conditions and effects.
For example, if a reservoir is spilling and water is being
withdrawn (diverted) from the system, the manager needs to be able to
predict the effect such withdrawal will have on the amount being
spilled and the rate at which the amount that is spilling will change
during the release. He
needs to be able to predict how much the water will be heated by
exposed rocks during transit time (a function of existing flow and
weather) and how long it will take to reach the target (a function of
amount of release, distance to target, and the existing flow before
release). Releases from
major tributaries such as the Lackawaxen River and Mongaup are highly
unpredictable but profoundly effect the flow at Montague, N. J.
AIR TEMPERATURE AND CLOUD COVER
Although the air temperature is an
important factor, the greatest heat gain to a river system occurs by
the absorption of sunlight by the rocks in the bottom of the stream,
especially on shallow riffles. Even
on comparatively cool days, when the sun is high in the sky, as in
June, a great amount of solar energy is absorbed by the rocks through
the relatively transparent water and then conducted to the water from
below. Although part of
this prediction can be inferred by weather forecasts, there can be
considerable variation from day to day and is highly unpredictable.
The amount of heat that is absorbed by the substrate changes
throughout the summer, being greatest in June when the sun is highest
in the sky and then decreases throughout the summer, as air
temperatures climb. Consequently
the water temperatures in the designated trout management sections
rise and fall rapidly and sporadically throughout the summer on a
daily basis.
. ASSUMPTIONS
A system based on temperature and flow
targets assumes that the temperature and flow targets chosen are
biologically important to the target organisms and that these targets
reflect optimum conditions for the entire system, not just at the
target location. Because the trout are able to move and their behavior is
strongly affected by water depth, velocity and temperature, all of
which vary widely throughout the entire system, the ability to
calculate a specific set of temperature and flow criteria, best for
the trout fishery, let alone the complex array of aquatic organisms
that may have important ecological significance, is highly problematic
at best. It is by no
means given that in a system as large and complex as the Delaware
River that any such combination of temperature and flow targets could
ever be judged as being best for the system as a whole.
Temperature targets of 72F and 75 F are
based on mortality rates of individual trout held in isolation.
They are not intended to, nor do they adequately reflect the
impact on the ecosystem much less the various populations of wild
trout. Temperature
strongly affects not only the physiology of trout but their behavior
as well. Above 68 F, trout can no longer feed efficiently.
At this temperature trout begin to move in search of cooler
water. This movement
affects the social hierarchy of the trout and causes excess
expenditure of energy just at the time at which the fish can no longer
feed efficiently. If
temperatures are allowed to gradually increase and flows are not
artificially changed over an unpredictable and erratic period the
trout will instinctively move in search of cool water.
This may be upstream, or even downstream if coldwater refuges
exist downstream at nearby springs or tributaries.
ASSUMPTION
THAT PULSED RELEASES ARE BENEFICIAL TO THE TROUT
If the water is artificially and temporally
lowered the behavior of the trout is unnaturally altered to the
detriment of the population as a whole.
Instead of moving to cooler water, the trout may be temporarily
induced to stay in a potentially lethal location.
Then, when the flows are reduced and temperatures once again
begin to rise, the trout may not be able to negotiate shallow riffle
areas in search of cooler water.
Sudden and brief pulses of cold water in a lotic (running
water) environment are unnatural and are found nowhere in a natural
system. No aquatic
organisms have ever been exposed to such an environment naturally and
therefore have never become adapted to cope with such conditions. Pulses of cold water cause fish and invertebrates to behave
unnaturally and undoubtedly to the detriment of both.
ASSUMPTION
THAT THE DROUGHT OF RECORD STARTS TOMORROW
The easiest way to reduce the risk of
running out of water is to assume the drought of record starts
tomorrow. But a fisheries management plan that is subject to such a
constraint necessarily constrains the ecosystem to permanent drought
conditions. In natural
systems, aquatic organisms undergo periods of scarcity and abundance
depending on the weather that particular year.
A system based on the most extreme drought conditions condemns
the ecosystem to perpetual drought regardless of the actual climatic
conditions.
ENFORCEABILITY
Temperature and flow targets are just that,
targets. They are not
mandatory requirements, and require a good-faith willingness to be
met. Failure to meet such
targets carries with them no consequences other than the impact on the
resource. To be
effective, such a system needs to carry with it the force of law with
penalties for failure of adherence.
It is unlikely that any system that relies on so many
variables, unknowns, day to day monitoring and un-testable assumptions
could ever gain the authority of law or regulation.
AN
ALTERNATIVE
A SYSTEM BASED ON AVAILABILITY OF WATER ON A
REAL-TIME BASIS AND ACCEPTABLE RISK, IN WHICH A SPECIFIED AMOUNT OF
WATER IS RELEASED AS A FUNCTION OF STORAGE AND TIME OF YEAR (PROBABILITY
OF REFILL) ELIMINATES VIRTUALLY ALL OF THE “PROBLEMS” DISCUSSED
ABOVE. SUCH A
SYSTEM NEED NOT INCREASE THE FREQUENCY OR PROBABILITY OF
“DROUGHT”, IS MUCH MORE BENEFICIAL TO THE AQUATIC ORGANISMS IN THE
RIVER AND IS EASY
TO IMPLEMENT.
GIVE THE AQUATIC ORGANISMS THE AMOUNT OF WATER
THAT IS AVAILABLE TODAY AND THEY WILL TAKE CARE OF THEMSELVES.
Robert Bachman, Ph.D
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