Impact of Detonation Cord on
Northern
Pike (Esox lucius) and Aquatic Life
Northern pike (Esox lucius) is a rapidly growing, prolifically reproductive, predatory fish first documented in Lake Davis in August 1994. A review of the life history and biology of northern pike was prepared for CDFG by Lee (1999). Northern pike are considered an exotic nuisance species that pose a threat to protected native species of fish and wildlife throughout the Feather River watershed and the Sacramento/San Joaquin River system (CDFG 1997). The threat to native California riparian and aquatic resources cannot be understated.
Experience in Alaska and many western states indicates that uncontrolled northern pike populations in habitat similar to lake Davis can wipe out virtually all other species sharing habitat, resulting in a collapse of the aquatic ecosystem around the northern pike (Lee 1999). Species complexity is lost and the ecosystem tends to produce numerous stunted northern pike (CDFG 1997). Introduction of northern pike in the Sacramento/San Joaquin River system would likely result in the loss of numerous Evolutionarily Significant Units (ESU) of salmon, steelhead and other native species of fish and shellfish. The expansion of northern pike into the Delta could have extremely adverse effects on recreational and commercial fisheries for salmon (CDFG 1997).
Lake Davis was treated with rotenone in 1997 but northern pike were rediscovered in May 1999. The 1999 monitoring program resulted in the collection of 197 northern pike by electrofishing, 2 in box traps, and 35 by backpack electroshockers in Lake Davis tributaries (CDFG 2001). Most of the pike were caught in Mosquito Slough and Big Grizzly and Freeman Creeks.
Greatly increased monitoring efforts in 2000 resulted in the collection of 601 northern pike by 8 types of gear (CDFG 2001). Gill nets were responsible for collecting nearly half of the total northern pike catch. Electrofishing was the next most productive method for collecting northern pike.
In addition to the ongoing collecting efforts both public education and increased enforcement are being used to help prevent reintroduction into Lake Davis and distribution down stream of Lake Davis. Increased collecting effort in 2001 has resulted in over 4,500 northern pike being collected by the end of September 2001 using collection methods and intensities similar to those used in 2000 (CDFG 2001).
The use of explosives to eradicate unwanted fish is not unique to the Lake Davis project. Johnston (1957) conducted a series of experiments with dynamite to determine if explosives could be effectively used to remove concentrations of longnose gar, (Lepisosteus osseus), from large coastal streams in North Carolina. Explosives were found to be effective for that purpose. During the 20-day test, 12,707 longnose gar weighing a total of 47,142.3 pounds were removed using only 7 cases of dynamite. The total number of game fish killed during the operation was 1,197, weighing a total of 215.5 pounds.
The use of explosives to collect fish is not considered a "standard" fish sampling technique in the United States (Nielsen and Johnson 1983). However, explosives have been successfully used to conduct fishery surveys in a number of different aquatic habitat types (Bass 1977, Hesse 1979, Rasmussen 1984, Platts 1974). Detonation cord appears to be the explosive of choice by fishery professionals and has been successfully used in large rivers, small streams, canals, and in lakes.
Effectiveness of Detonation Cord
Detonation cord has been successfully used as a fish sampling technique in a number of stream studies (Bass 1977, Hesse 1979, Rasmussen 1984, Platts 1974). In at least one stream sampling study, detonation cord was found to be completely ineffective. Layher (1984) used detonation cord to collect fish from Stillwater Creek, Oklahoma. Three parallel strands of detonation cord were laid on the stream bottom equidistant from the stream bank and the stream center-line. No fish were killed. Electroshocking the area after the use of detonation cord resulted in the capture of fish that had apparently been unharmed by the detonation. They suggested that the mud and silt bottom absorbed much of the shock wave resulting in the lack of fish mortalities. Detonation cord will be suspended above the bottom in the Lake Davis project, mitigating for the attenuation effects of a soft bottom.
There are two studies that used detonation cord to sample fish populations in lakes that approximate conditions at Lake Davis (Metzger 1986, Bayley 1988). Metzger (1986) set parallel strands of detonation cord with a load of 50grains (gr.) PETN/ft.) at mid-water or deeper at intervals of 29.4 ft or less depending on specific site conditions (e.g., depth and vegetation) in areas blocked with netting. At two lake detonation sites, 60% (94 of 157) of tagged fish released into the blocked area were recovered. In two follow-up tests in two one-acre lakes with (mean depth = 9.2 + 5.6 ft.) sampled first with detonation cord, then with rotenone, an average of 89% of the total fish biomass collected was recovered after the detonations. When rotenone was applied first (mean depth = 7.4 ft. + 0.5 ft) an average of 68% of the total biomass was recovered after the toxicant treatment.
Bayley and Austen (1988) compared fish sampling efficiency of detonation cord with that of rotenone in warm- water impoundments, using detonation cord (50 gr. PETN/ft.) for their studies. When water depth exceeded 4.6 feet , the cord was suspended in mid-water from wooden floats attached to the cord at intervals of 31-feet. In shallower water, the cord was laid on the bottom. In ponds treated with detonation cord that were subsequently drained, an average of 19.7% (range, 14-23%) of the stocked fish were recovered live and in good condition (Approximately 90% mortality). No live fish were found in ponds treated with rotenone.
Effective Mortality Range of Detonation Cord
Metzger (1986) placed a variety of fish species on stringers at a depth of approximately 6 feet and exposed them to a single 77-feet long strand of detonation cord (50 gr. PETN/ft.) also placed at a depth of 6 feet. Experimental fish stationed within 21 feet of the detonation cord were killed instantly. The pressure wave produced 92% and 88% mortality at 24.7 and 27.8 feet, respectively. Fish not immediately killed at these distances were stunned and probably would not have recovered. No mortality occurred among control fish outside the blast area.
Linton (1985), evaluating fish mortality from geophysical exploration, exposed caged black drum (Pogonias cromis) and red drum (Sciaenops ocellatus) to an explosion from a 33-m strand of 1500gr PETN/ft detonation cord. They found 100% mortality of black drum at 3.09 feet from the strand in cages placed on the bottom in approximately 8 feet of water. At 34 feet, 71 feet, 142 feet, they found 70%, 40%, 90% experimental mortality, and 20% control mortality, respectively. Red drum mortality was 100% at 3.09 feet from the detonation cord but survival was 100% at the further distances. There was no control mortality. Black drum in surface cages placed 7.4 feet above the strand experienced 10% mortality; red drum had 0 mortality. The detonation cord was placed on the ocean bottom, which probably accounts for the low mortality observed. Much of the pressure was actually transmitted into the bottom sediments, the goal of geophysical surveys, and only a fraction of the pressure was transmitted into the water column.
Platts (1974) indicated that detonation cord has a potential for a total kill of fish within 10 to 15 feet of the cord providing there are no major barriers. However, there is no indication in his report that a testing program was conducted to establish the kill radius of the fish species being sampled. Platts (1974) and Platts et al. (1983) provided a table indicating strand number for various stream depths and widths for sampling programs in small streams (< 4th order).
Based on Metzger and Shafland (1986) and Bayley and Austen (1988), deployment of parallel strands of detonation cord (50 gr. PETN/ft.) set at intervals of 27.8 feet or less at mid-water depth would provide an effective kill zone for the Lake Davis northern pike control and containment program. The closer the parallel strands are set together, the higher the anticipated mortality zone. The proposed Phase 1 detonation cord mortality test blast (see project description)will greatly assist in establishing effective distances for the Lake Davis pike eradication program, considering the paucity of data on kill radius for detonation cord, and the complete lack of mortality data for pike.
The only study that attempted to evaluate the relationship between fish mortality and distance from a detonation cord charge was Linton et al. (1985). However, detonation cord was placed on the substrate in that study producing results that would be considerably different from the mid-water blasts proposed for Lake Davis. Metzer and Shafland (1986) found that five species of fish stationed within 21.6 feet of a single strand of detonation cord placed at mid-water depth were killed instantly upon detonation and 88% were killed at the maximum tested distance of 27.8 feet. This study was designed to evaluate the use of detonation cord for sampling fish. It doesn't provide information on the magnitude of mortality beyond 27.8 ft from the detonation cord explosion. However, it does indicate that all five species tested were killed at 21.6 feet.
Northern pike, or pike species in general, have not been used as test species in any explosive studies, let alone detonation cord impact studies. As such, there is no information on species-specific pike mortality. The only available information (Metzger 1986) would suggest that northern pike would probably also suffer 100% instantaneous mortality at 21.6 feet from a 50 gr. PETN/feet detonation cord mid-water explosion. Delayed mortality, approaching 100%, could occur to 86 feet from the detonation cord.
The use of detonation cord will provide a useful tool in the pike eradication program at Lake Davis. Use of detonation cord will have its highest potential for success in spawning areas where pike congregate. However, based on the best available information (i.e., Metzger, Bayley and Austen 1988), detonation cord will not be 100% effective in killing all the pike in the blast zone. As such, detonation cord should be used in combination with the pike-removal techniques currently being employed at Lake Davis, including electrofishing, gill and trap nets, and purse seining.
Based on the best available information, juveniles would be expected to have a higher mortality level than adults. Yelverton (1975) tested a number of different fish species and found that a higher impulse was required to kill larger fish (body weight) than small fish. This was true both within a species and between species tested.
There has not been a single published study on the effects of explosions on larval fish. If the larval fish have inflated airbladders, their mortality would be similar but somewhat greater than juvenile pike. If their airbladders have not inflated, they would be relatively immune to blast pressures. Mortality (100%) of larvae without inflated airbladders probably wouldn't extend beyond 7 feet from the detonation cord blast.
Kostyuchenko (1973) exposed anchovy, blue runner, and carucian carp eggs to a 1.7 oz. charge of TNT. The TNT charge produced structural abnormalities in the anchovy eggs at a distance of 6.2 feet to 61 feet from the source, in the blue runner eggs up to 31 feet away, and in the carucian carp eggs up to 16 feet away. Only 20% of the eggs used in the experiment survived at a distance of 6.2 feet, 58.2% at a distance of 61 feet; only at a distance of 61feet were there no sharp differences from the control. The proposal to use 50 gr. detonation cord is similar to the Kostyuchenko (1973) test charges and similar results would be expected at Lake Davis. Northern pike eggs should experience mortality between 60% and 100%, depending on the exposure distance from the detonation cord.
Other aquatic organisms
within the kill zone also have the potential of being injured or killed,
depending on the species exposed to the blast pressures. Underwater explosions produce a pressure
waveform with rapid oscillations from positive pressure to negative pressure
that results in rapid volume changes in gas-containing organs. In fish, for example, the swimbladder is the
most frequently damaged organ (Faulk and Lawrence 1973, Kerns and Boyd 1965,
Linton et al. 1985). It is subject to
rapid contraction and overextension in response to the explosive shock waveform
(Wiley et al. 1981). Fish that lack
swimbladders are extremely tolerant of underwater explosions (Goertner et al.
1994). Gas-containing organs (lungs,
stomach, and intestines) have also been implicated as a causative factor of
internal damage and mortality in humans exposed to underwater explosions
(Cameron et al. 1944, Ecklund 1943, Yaguda 1945) and in tests with other
mammalian species (Richmond et al. 1973).
Data on the effects of
underwater explosions on aquatic vegetation are very limited. Ludwig (1977) used explosives as a
"herbicide" to remove eelgrass (Zoster marina) to create a
channel within the Niantic Estuary at Waterford, Connecticut. Detonation cord placed on the estuary bottom
substrate produced a kill zone approximately 2 to 4 meters wide. During an eight-week period following the
explosions, the eelgrass experienced an orderly dieback. Ludwig (1977) hypothesized that the orderly
defoliation was the result of a disruption of the cellular structures within
the rhizomes. Smith (1996) examined the
effects of underwater explosions on two aquatic plant species (Ludwigia
peploides) and (Myriophyllum heterophyllum). Only (L. peploides)
suffered 100% mortality at the closest distance tested, 7-feet from a 4.4 lb.
charge of high explosives (a very large charge when compared to detonation
cord). Impacts beyond 7 feet were minor
for both species. Both species showed
rapid recovery within two weeks.
The northern pike
control and containment program will be conducted prior to emergence of aquatic
vegetation in Lake Davis. The timing of
the program should reduce the impacts to aquatic plant species in the blast
zones. Detonation cord will be
suspended in mid-water, reducing the pressure waveform transmitted into the
sediments, thus, reducing impacts to the root system. Should detonations occur during the growing season, damaged
aquatic plants would be expected to recover quickly.
There are eighteen
publications dealing with the effects of underwater explosive pressure waves on
aquatic invertebrates (Keevin et al. 1999).
A wide range of marine organisms have been tested (i.e., abalones,
oysters, crabs, shrimp, and lobsters).
There are no publications on aquatic insect larvae. The published studies indicate that marine
invertebrates are insensitive (in comparison to fish with swimbladders,
amphibians and reptiles, and aquatic mammals) to pressure related damage from
underwater explosion. Two freshwater
invertebrate groups have been studied, freshwater mussels and crayfish, and
have also been found to be insensitive to explosions (Keevin pers. comm.). The insensitivity of aquatic invertebrates
to explosive pressures may be due to the fact that all the species tested
lacked gas-containing organs that have been implicated in internal damage and
mortality in vertebrates.
Impacts to aquatic
invertebrates within the northern pike eradication zones are considered to be
minor. Unless aquatic invertebrates are
within approximately 7 feet of the detonation cord, no adverse impacts would be
expected. Detonation cord will be
suspended in mid-water, reducing the probability of being within the impact
zone. The pressure waveform transmitted
into the sediments from a mid-water detonation will also be minimized, thus,
reducing impacts to benthic invertebrates.
To date, there has not
been a single comprehensive study to determine the effects of underwater
explosions on either amphibians (i.e., frogs, salamanders) or reptiles (i.e.,
turtles, snakes) that defines the relationship between distance/pressure and
injury or mortality. There have been a
number of field observations demonstrating that turtles (sea turtles) are
injured and killed by underwater explosions (Gitschlag 1990, Gitschlag and
Herczeg 1994, Gitschlag and Renaud 1989, Gitschlag et al. 1996, Klima et al.
1988, O'Keeffe and Young1984).
Although untested,
amphibians and reptiles with air-containing organs probably have mortality
comparable to fish with swim bladders.
As such, organisms within the northern pike eradication zones would also
be killed.
Refer to the Reference section of the Initial Study.