Sampling with Toxicants

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Sampling with Toxicants

• Chapter 10
• Fisheries Techniques

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Toxicants have been used since the 1930s to
sample fish communities and to remove
undesirable species. Rotenone was the 1st of
several piscicides used by fisheries biologists
in NA. it is a naturally occurring compound
that can be synthetically produced. Often
used for control of nuisance species renovatio
n and reclamation. Lopinot (1975) estimated
piscicides were applied to 47,000 ha in 12
states in the midwest between 1963-72. during
the same time period 6,800 km of streams were
treated.
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Piscicides were often used to try and control
common carp. This practice has ended due to poor
results. In the 1950s a synthetic cpd.
(3-trifluoromethyl-4-nitrophenol (Abbrev. TFM)
was found. It effectively killed sea lamprey
larvae. A 2nd chemical (Bayluscide) was also
used to kill sea lamprey larvae. Widely used
in Great Lakes tributaries for control of
lampreys. Also in the 1950s, using toxicants
to sample fish communties became popular.
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Currently, only 4 compounds are registered with
the federal govt. for use as piscicides
rotenone antimycin TFM
Bayluscide Of these 4 registered piscicides, TFM
and Bayluscide are registered for use only as
a lampricide for sea lamprey control. Concentrati
ons of these 2 can be applied with limited damage
to other species because the concentrations
required are below the lethal level for most
other species.
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10.2.2 Rotenone Is derived from the roots of
species of trees in the genera Derris and
Lonchocarpus. Native peoples have used this
to capture fish for a long time. It is
extremely toxic to fish usually kills all but
the most resistant species (gar, bullheads,
bowfin) mode of action is disruption of
cellular respiration. Applied as 1.0 mg/L
conc. Of a 5 rotenone formulation. When
applied in reccd. Doses, rotenone does limited
harm to bugs, crayfishes, and mollusks. IT IS
toxic to tadpoles metamorphosing amphibians
at gt0.01 mg/L
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- Toxicity of Rotenone is affected by
environmental factors turbidity
temperature pH - Toxicity is greatest in warm
(gt20 C), acidic, clear waters with little
vegetation. -Rotenone does not persist long in
the environment. At 23 C the half life is
less than 1 day. - Rotenone can be neutralized
with strong oxidizing agents like potassium
permanganate. -Rotenone is now applied as a
liquid, but was originally applied as a
powder. - COSTS - about 13 per 1000 m3 as
powder/ 35 for 5 liquid.
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10.2.3. Antimycin Mode of action is also to
interfere with cellular respiration. Similar
environmental influence as for rotenone,
except temperature has little effect on
toxicity. Costs are similar to liquid rotenone
(35 per 1000 m3).
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10.3 Toxicants and Public Relations
Inflicting death on 1000s of fish can have a
negative influence on public relations.
Information is the key. Clear explanation for
the rationale for application of the toxicant
will help minimize bad PR. Studies have shown
public sentiment changed when they realized
large sampling or reclamation projects resulted
in improved fishing. Public concerns can be
alleviated if the public perceives important
info is being used and it will go to protect or
enhance a fishery. Piscicides are tightly
regulated. Wont be shipped unless proof of
training in use is provided.
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10.4 USE OF TOXICANTS IN RESEARCH AND
MANAGEMENT SURVEYS 10.4.1 Lacustrine (lake)
habitats Cove Sampling - treating of small
embayments or coves with rotenone. The
resulting data on standing crops permitted
analysis of relationships between fish
production and other factors. For example
Jenkins (1982) modeled fish biomass as a fcn. Of
MEI (morphedaphic index T.D.S./mean depth).
Cove sampling is still common in SE US.,
typically conducted in mid- late-summer.
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Cove sampling is done by selecting a site and
blocking it off with a block net. Usually
these block nets are 100 m long and 6-9 m deep.
Nets are usually 6 mm bar mesh to keep fish in
the cove. Volume of water in the cove is
estimated (see Box 10.1 in text) and rotenone is
applied to achieve a 3-mg/L concentration.
Remember 3 L to treat 1000 m3.
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Usually a gas powered pump is used to apply
the rotenone
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Alternatively, a venturi pump mounted off the
prop on an outboard motor is used for application
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Rotenone can be dispersed outside of the cove by
wind, currents. Springs, etc. To counteract
this, potassium permanganate can be hung in 1
kg bags outside the block net to neutralize the
toxicant.
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After applying rotenone, fish begin to surface
and are netted by personnel in boats. BUT, not
all fish surface following application of
rotenone. Estimating non-recovery Three
methods- 1. Release of tagged fish into cove
prior to sampling. 2. Multiple day pick-ups 3.
Bottom nets
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WVDNR found on average, a 1-d pickup gets about
75 of fish that would have surfaced (in lock
sampling) over 3-days. (S. Morrison,
WVDNR). Bayley Austin (1990) found in ponds
coves efficiency was high for large fish (gt150
mm TL) in warm (gt 25 C) water, but was low for
small fish in cool water.
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Sampling Efficiency for some species in Cove
Samples.
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Primary purposes of cove samples are to provide
total number and biomass of each species. A
secondary goal may be to get info on the size
structure of populations.
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Block Net Sampling is often done in lakes without
coves. Here, biologists enclose an area of water
(often _at_ 0.4 ha) with a block net of about 64 m
on a side. Each corner is anchored with a
weight. Wegener Ring is a 0.0004 ha circular
net of 0.5 - 1.8 m depth. The ring is thrown by
1-2 people from shore or from a boat. Then 10-15
ml of rotenone are applied and fish are
dipnetted, taken to shore and processed. After
dipnetting, the net is fished like a seine to
collect any remaining fishes. This ring is
effective in shallow-water habitats and up to 15
samples can be collected in an 8-h day.
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The Wegener Ring...
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Shoreline sampling. A small mesh net is deployed
from shore like a haul seine and then anchored at
both ends on shore. Rotenone is applied and fish
sampled.
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Navigation locks- Commonly used by WVDNR on the
Ohio, Mon. and Kanawha Rivers to sample fish
communities. Lock is partially filled and
closed. Rotenone applied and fish recovered. A
key limitation of the method is that samples
cannot easily be replicated. Also difficult
where there is only a single lock since the lock
must remain closed for _at_ 24 h. Rivers and
Streams. Place block nets up and downstream of
area to be sampled. Rotenone applied from
upstream area. Fish are dip-netted. Strong
oxidizing agent is applied to neutralize the
rotenone during and after the survey.
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Use of Toxicants in Reclamation and Fish Control
Activities reclamation in uncommon now. Has
been used most often (recently) for
re-habilitation of small urban fisheries to
shift community from carp/undesireable to
desireable fishes.
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Selective Removal of Target Species We have
already discussed use of toxicants to control
sea lampreys. Sometimes used to reduce shad
populations, can be done because shad are
susceptible to 0 low (0.1 mg/l) conc.
That generally dont harm other species.
poisoned feed pellets have been used to kill
carp. in the SE US rotenone is applied to
shallow littoral areas 2-4 weeks after bluegill
or bass hatch to reduce stunted Centrarchid
populations.