Waterways Experiment station

Transcription

1 ,Evaluation of Seismic Sources for Repelling Sea Turtles from Hopper Dredges Final Report Submitted to the U.S. Army Corps of Engineers Waterways Experiment station by The Virginia Institute of Marine Science College of William and Mary Gloucester Point, VA by Soraya E. Moein John A. Musick John A. Keinath Debra E. Barnard Martin Lenhardt and Robert George Virginia Institute of Marine Science College of William and Mary May 1994

2 receptors. 1 Introduction Hopper dredges are an effective way to both widen and deepen channels to accommodate deep draft shipping traffic. These dredging operations are required to comply with the Endangered Species Act of 1973 (Dickerson et al., 1991, Studt, 1985). It has been found that sea turtles can be entrained and killed during normal dredging operations. The five species of sea turtles that occur in the southeastern united states which may be harmed by dredging operations are the loggerhead (Caretta caretta), the green (Chelonia m~das), the Kemp's ridley (Lenidochelys kemnii), the hawksbill (Eretomochelys imbricata), and the leatherback (Qermochelys coriacea). Because of their geographic distribution and life history attributes, the National Marine Fisheries Service (NMFS) has concluded that only the Kemp's ridley, the loggerhead, and the green sea turtle may be at risk by hopper dredging activities (Joyce, 1982). Due to the need to keep shipping channels open and the concern over the unacceptable mortality of sea turtles caused by hopper dredges, NMFS has suggested that repulsion from the hopper dredges could be one method to reduce the incidental take of sea turtles. We investigated the potential usefulness of pneumatic energy sources (air guns) to repel loggerhead sea turtles from dredge heads. This method assumes that sea turtles have the capacity to perceive these pulses, either through auditory or tactile

3 1982, 1969). frequencies. 2 until recently little research has been performed on the auditory behavior of sea turtles (Art et al., 1985, Crawford and Fettiplace, 1980, Lenhardt, 1981, Lenhardt and Harkins, 1983, Lenhardt et al., 1985}. Even 20 years ago it was not believed that turtles could hear. In order to repel sea turtles using pneumatic sources, intensity of sound, frequency range, and frequency modulation needed to stimulate the sea turtle's acoustic receptors must be determined. The anatomy of the sea turtle ear suggests that the turtle's middle ear is a compromise for sound conduction through two different media, bone and water. In bone conduction, the columella (middle ear bone) and the ear drum act as dampening devices, not as sound receptors (Lenhardt Lenhardt et al., 1983). Bone conduction limits the range of frequencies used by the sea turtle to low frequencies. Although much has been learned about the anatomy of the sea turtle ear, there are few published behavioral audiograms and all have been performed on the green turtle (Wever, 1978, Ridgeway, The frequencies tested on these turtles ranged from 50 to 2000 Hz. The results revealed limited variability in sound frequency range detectible by this species ( Hz). Green turtles displayed a high level of sensitivity at the low tone region of about 400 Hz. Moreover their range of sensitivity declined by a rate of 40 db per octave with an increase in Recent experiments using auditory evoked potentials in our laboratory have examined the auditory behavior of the loggerhead

4 thresholds, stimuli. attempt. However, 3 sea turtle. Evoked potentials are electric responses to the stimulation of the nervous system (Spehlmann, 1985). Consequently the threshold level (the minimum hearing level of the animal} can be determined by examining a repeatable waveform associated with the firing of the auditory nerve. In these series of experiments, tones of 500 Hz yielded the lowest with 250 and 750 Hz being the next most sensitive No animal responded to tones over 2000 Hz. Thus, consistent with the anatomical research, the effective range of hearing of the loggerhead sea turtle is low frequencies ( Hz). One study has been performed which used seismic air guns to to create a sound barrier for loggerhead turtles at the end of a canal of Florida Power & Light (O'Hara, 1990). The test results indicated that at 140 kg/cm2 the air guns were effective as a deterrent for a distance of about 30 m. one of the problelds encountered in this study was the reflection of sound by the canal walls. Consequently, the results may be ambiguous when related to open water stimuli. The Army Corps of Engineers (COE) has proposed to use pneumatic energy sources in the form of air guns to produce acoustic stimuli to repel sea turtles from hopper dredges. In the course of the air gun testing, parameters such as distance of the turtle from the air gun, chamber pressures, and firing rates were recorded. These data were subsequently used to assess the safety in utilizing this method to disperse sea turtles.

5 4 Furthermore, the behavior of the sea turtles were evaluated before and during discharge to evaluate effectiveness of the air gun in repelling sea turtles.

6 each, 5 Materials g.ng Methods A net enclosure (approximately 18 m x 61 m x 3.6 m; 3.8 cm bar) was erected in the York River, VA to contain the turtles The enclosure was stratified into two equal sections: near and far (Fig 1). Air guns, provided by the Army Corps of Engineers (COE), were positioned at each end of the net, and the two guns were calibrated to create equal seismic and auditory output. A hydrophone was positioned equidistant from the air guns to monitor the output. Ten loggerhead turtles were tested (Table 1), and seven of these were retested for a total of seventeen tests. A float was attached to the posterior end of the carapace of each turtle with a 3 m line so position could be monitored. For each test, a single loggerhead was placed in the enclosure and allowed to acclimate for one hour prior to exposure to stimuli. Air guns were initially discharged only when the turtles were near the center of the net so that there would be equal distance for movement toward or away from the sources. Three different decibel levels (175, 177, 179) were utilized twice resulting in six trials per test. A coin toss determined which air gun was to be used first. The air gun was discharged at 175 db every 5-6 seconds for 5 minutes, followed by at least 10 minutes of no emission. The other air gun was then discharged at the same decibel level for 5 minutes. After at least 10 minutes of no emission, the decibel level was increased to 177 db

7 Table 1. Tag numbers, dates captured and released, weight, and length of the eleven turtles tested with air guns in the YorkRiver. N/A = not available 6 Front Flipper Tag# DATE Captured DATE Released Weight (Kg.) Length (Curved, Notch to Notch) cm. ) QQZ406 QQZ407 QQZ426 QQZ427 QQZ429 QQZ430 QQZ437 QQZ438 QQZ441 QQC530 QQZ442 QQZ443 QQZ451 QQZ452 QQZ455 QQZ456 QQZ476 QQZ477 QQZ486 QQZ MAY 93 3 AUG JUN JUL 93 N/A N/A 8 JUN 93 3 AUG JUN AUG JUN JUL JUN JUL JUN JUL JUN JUL JUN JUL 93 N/A JUL 93 2 AUG

8 7 Figure 1. A representative drawing of the sections of the net used in the sea turtle acoustic response experiments in the York River, VA. Triangle = position of the air gun in use, the other air gun was at the opposite end of the enclosure.

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10 db. Secondly, and one of the air guns, randomly determined by a coin toss, was discharged for 5 minutes. After at least 10 minutes of no emission the other gun was discharged at the same decibel level for 5 minutes. This sequence of events continued until the turtle was exposed to six trials: the first two trials at 175 db, the third and fourth at 177 db, and the fifth and sixth at position and direction of movement of the turtle within the net was recorded every 15 seconds. The number of positions in the near and far sections during each trial were tallied Turtles were separated into two groups: the first time tested vs. the second time tested. Due to problems with either the upkeep of the air guns or unforeseen weather, not all the turtles were subjected to six trials. The data were used to compare the mean amount of time each turtle spent in the section of net away from each of the two air guns in order to infer whether differences existed between the air guns. A nonparametric two-sample t-test, the Wilcoxon paired sample test, was used (Zar, 1984). the observed response of each turtle to the emission of the air gun (observed number of positions in the section of net away from the gun) was compared to the expected (equal amount of time spent in both sections of the net) using the Wilcoxon test as a test of goodness-of-fit (Siegel and Castellani 1988). only the first trial data for each exposure were examined to determine the turtle's reaction on first

11 group. 9 encountering the air gun The possibility of habituation of the turtle to the stimulus over time was examined. The number of positions each turtle spent in the section of net away from the stimulus for each trial was analyzed using the nonparametric Friedman's test (Zar, 1984) Only data from those turtles which completed six full trials in a test were examined The amount of time for the turtle to respond to the initial firing of the stimulus ("response time") as well as the time taken to turn away from the stimulus ("turn time") were calculated for those turtles who were initially moving towards the stimulus prior to firing the air gun. The response time was defined as any perceived increase in speed of the turtle irrespective of direction. Turn time was the time from the first firing of the air gun until the turtle changed direction away from the airgun. Response time and turn time data were computed for the first three trials of those turtles in the first exposure Averages were computed for both response and turn times for each turtle. The same data were compiled for the distances from the air gun at which the turtle responded ("response distance") and turned ("turn distance") after the stimulus (Figs. 2-4) In order to monitor the health and to determine the effects of exposure to air guns on the experimental animals, blood was drawn prior to and within 24 hrs after each test and analyzed by a veterinarian for several standard parameters (Appendix I).

12 Furthermore, the hearing threshold levels were determined for 10 each turtle before, within 24 hours after each test, and approximately 14 days later using an auditory evoked potentials computer, the Nicolet spirit Portable (Appendix II

13 River, 11 Figure 2. Movement of turtle QQZ406/QQZ407 for the first trial of test 7 of the sea turtle repelling experiments in the York VA. Triangle = position of sound source; Open circle start of trial; Closed circle = end of trial; Open square = position taken every 15 seconds. Arrow = initial direction of movement of the turtle prior to exposure.

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15 12 Figure 3. Movement of turtle QQZ451/QQZ452 for the third trial of test 5 of the sea turtle repelling experiments in the York River, VA. Triangle = position of sound source; Open circle = start of trial: Closed circle = end of trial; Open square = position taken every 15 seconds; Arrow = initial direction of movement of the turtle prior to exposure

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17 13 Figure 4. Movement of the turtle QQZ426/QQZ427 for the third trial of test 2 of the sea turtle repelling experiments in the York River, VA. Triangle = position of sound source; Open circle := start of trial; Closed circle = end of trial: Open square := position taken every 15 seconds; Arrow = initial direction of movement of the turtle prior to exposure.

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19 Results 14 The Wilcoxon paired sample test found no significance between reaction to the two air guns. This unbiased response seen in both first exposure (T+ and T- > TO.O5(2)J.O) and second exposure (T+ and T- > TO.O6(2),7 The goodness-of-fit analysis found significant differences in the observed vs. expected for the first trial of the first exposure group (T- < TO.OS(2),3.0). However, the observed number of positions away from the gun in the first trial of the second exposure group was not significantly different than expected (T+ and T- > TO.O5(2),7). The Friedman analysis to examine for habituation effect found significant differences among the trials (X2> X20.0S,S) in the first exposure group (Fig 5). However, in the second exposure group, significant differences among the trials were found (X2 < X20.os,s) (Fig 6). The mean response time was 39.5 s (range s); mean turn time was 49.4 s (range s). Moreover, the average response distance was 20.8 m (range m) while the average turn distance was 15.0 m (range m) (Table 2)

20 ~ Table 2. Response time and distance and turn time and distance for those turtles in the first exposure group who were moving towards the air gun when initially fired. NR = no response. 15 Turtle/ Trial QQZ441/1 QQZ441/2 QQZ441/3 QQZ426/1 QQZ426/2 QQZ426/3 QQZ442/1 QQZ442/2 QQZ442/3 QQZ429/1 QQZ429/2 QQZ429/3 QQZ451/1 QQZ451/2 QQZ451/3 QQZ437/1 QQZ437/2 QQZ437/3 QQZ406/1 QQZ406/2 QQZ406/3 QQZ476/1 QQZ476/2 QQZ476/3 QQZ486/1 QQZ486/2 QQZ486/3 Initial Direction Response Time Turn Time Response Distance Turn Distance, Away Toward 65 s 65 s 1.5 m 1.5 m Away Away Toward Toward Away Away Toward 15 s 15 s 34.8 m 34.8 m 5 s 5 s 33.9 m 33.9 m s 8.2 m 6.6 m Away Toward 67 s 67 s 15.9 m 15.9 m NR Toward 75 s 97 s 15.9 m 1.5 m Away Toward NR Away Toward 20 s 37 s 11.3 m 1.7 m 135 s 150 s 13.4 m Toward 25 s 25 s Away Away* Away NR NR Away Toward Away 10 s 15 s 22.6 m 37.8 m 6.7 m 22.6 m 15 s 28.1 m 28.1 m

21 16 Turtle/ Trial Initial Direction Response Time Turn Time Response Distance Turn Distance QQZ455/1 Toward 20 s 50 s 24.1 m 4.4 m QQZ455/2 QQZ455/3 Toward Away 7 s 7 s 22.6 m 22.6 m Mean 39.5 s 49.4 s 20.8 m 15.0 m (range s) (range s) (range (~ange 1.5- m) 34.8 m) *Turtle initially moving away but still displayed perceivable immediate reaction to the firing of the airgun.

22 17 Figure 5. Number of positions in the near and far sections of the net for all turtles combined in the first exposure group of the sea turtle repelling experiments in the York River, VA.

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24 18 Figure 6. Number of positions in the near and far section of the net for all turtles combined in the second exposure group of the sea turtle repelling experiments in the York River, VA.

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26 guns. However, stimuli. 19 Discussion The first task was to test whether a significant difference existed in the response of the turtle to each of the two air Once establishing that response to these air guns was not statistically different, analysis of behavior was continued by combining data from the two air guns. On first exposure to the air guns (trial one), naive turtles occupied a significantly higher number of positions in the far section of net than expected by chance. This suggests an avoidance response to the air gun emissions. in the second exposure, no difference in observed and expected was seen. This response suggests that the turtles are habituating to the To pursue the idea of habituation, the response of each turtle in all the trials of each exposure group was analyzed. In the first exposure group, number of positions in the sections of the net were not the same for each trial. Turtles avoided the air gun in the first three trials, but did not avoid emissions in trials 4-6 (Figure 5). The second exposure group did not avoid the emissions throughout all six trials (Figure 6). This suggests that turtles are habituating to the stimuli after approximately three exposures, and do not loose this habituation over days of no exposure

27 away. distance. However, conditions. Do the turtles have enough time to avoid a dredge with an 20 air gun on the draghead emitting emissions every 5 s? Dredges operate at speeds up to 5 knots (or 2.57 ms-1. Mean response time was 39.5 s and in this time the dredge would be m However, turtles probably would not respond at that The average response and turn distances were 20.8 m and 15.0 m, respectively. A dredge travelling at 2.57 ms-j. would cover 13 m in the 5 s between emissions from the air gun. Using 15.0 m as a conservative distance at which turtles will respond to first encounters with a dredge, it appears the turtles would avoid the dredge. a turtle subsequently encountering a dredge mayor may not avoid the dredge. These preliminary results need to be further' explored to see how turtles would react under field If a turtle begins to respond to the emissions of the air gun 23.7 m away from the approaching dredge and continues to respond 23.7 m after the dredge passes, the turtle will be exposed. to 4 emissions from the air gun. A possible experimental design to address the question of habituation under normal dredge conditions in the field would be to expose the turtle to 4 emissions, allow the turtle to rest for several days and then expose the turtle to 4 more emissions. ultimately, the final phase of this study should be to use telemetry to track turtles' behavioral response to air gun emissions in the field.

28 examination. function. 21 Appendix I: The Effects of Repeated Acoustic stimuli on the Health of Cat:~ttg caretta INTRODUCTION In order to provide healthy subjects for acoustic studies, a sea turtle health assessment protocol (HAP) was developed. The individual components of the protocol were selected to provide a method of evaluating the animal's overall health by assessing the degree of function of each animal's various organ systems METHODOLOGY The values obtained in the HAP for each animal were compared to established normal values and observation. Animals with abnormal values were not used in the acoustic study. Those animals deemed healthy and employed in the study were reevaluated by repeating the HAP twenty-four to thirty-six hours post-exposure and again fourteen to twenty three days post ex]posure. The post-exposure HAP results were compared to the pre-exposure values to determine if the turtles were adversely effected by exposure to the stimuli. The HAP consisted of three parts. The first was a physical The turtles were examined for visible problems such as wounds, parasites, or damaged appendages. A neurological exam was performed. It consisted of an evaluation of righting reflexes, spatial positioning abilities, and ocular and iris The second component of the HAP consisted of blood

29 chemistry measurements. 22 Blood samples were drawn from each turtle's dorsal cervical sinus and preserved in lithium heparin tubes. The samples were refrigerated until they could be processed. All samples were processed less than twenty-four hours after being drawn. Hematology tests were performed manually using a modified unipette system. Plasma chemistries were performed on a Hitachi automated blood analyzer Hematology parameters were a white blood cell count (WBC) packed cell volume (PCV), and differential cell count. The various organ systems were evaluated by determining the following plasma chemistry: total protein, albumin, glucose, blood urea nitrogen (BUN), creatinine, lactic acid dehydrogenase (LDH), creatinine phosphokinase (CPK), alkaline phosphatase, serum glutamic oxalo-transaminase (SGOT), sodium (Na), chlorine (Cl), potassium (K), calcium (Ca), phosphorous (P), and magnesium (Mg). RESULTS Hematology and chemistry values, when compared to normal values (Table 1), determined in the HAPs of tested turtles (Table 2) showed some variations for each item tested. Only three items showed any change in the first post-test HAP that could indicate damaged tissue, or altered physiology. There was an increase in the CPK, an enzyme which may be released from damaged cells of

30 23 striated muscle, cardiac muscle, or brain tissue. The increase in the level of plasma CPK in study animals may indicate the

31 24 TABLE ONE PLASMA CHEMISTRY NORMALS Caretta carettg, wild juveniles, Chesapeake Bay TEST MEAN 3D RANGE PCV % WBC per cubic ml T. Protein g/dl Albumin g/dl Glucose mg/dl BUN mgjdl Creat mg/dl LDH u/l CPK u/l Alk Phos u/l SGOT u/l Na meq/l Cl meq/l K meq/l Ca mgjdl P mg/dl Mg mg/dl

32 25 TABLE TWO PLASMA CHEMISTRY VALUES Turtles Exposed to Acoustic stimuli TEST PRE-EXPOSURE MEAN STD DEV POST-EXPOSURE 1 MEAN STD DEV POST-EXPOSURE 2 MEAN STD DEV Glucose :;1.3 Protein Albumin p Ca Alk Phos CPk SGOT Na K Cl BUN Globulin Mg WBC PCV

33 response. enclosure. tissues, 26 presence of cellular necrosis. The glucose levels rose in the post-tested animals as did the WBCs. The elevation of these two values indicates a stress induced plasma cortisol The stressed turtles released cortisol from their adrenal glands which caused a rise in the plasma gluco$e and white blood cell counts of each turtle. It is impossible to determine whether these temporary responses resulted from the sound stimuli used in the experiments or from the handling required to place the animals in and out of the net There was a significant drop in BUN, but this is not an indication of a problem but rather that the animals had not eaten in several days. The values from the HAPs done fourteen to twenty-three days after the acoustic testing returned to the levels of the pre-testing HAPs. CONCLUSIONS The temporary alteration of post-test HAP values showed that turtles may have been affected by exposure to repeated acoustic stimuli, however the magnitude of the changes did not indicate any significant damage to the turtle's organs. The rapid return of the post test values to normal levels indicated that tissue alterations due to acoustic stimuli were only transitory. The information from the HAPs indicated that repeated exposure to acoustic stimuli caused minor, but reversible changes to the turtle's and can be used without endangering the animal.

34 vibrations. plugs. 27 Appendix II: Methods and results of auditory evoked potentials from loggerhead sea turtles Methods The technique of auditory evoked potentials has been used extensively in humans, especially in the examination of infant neural responses. This technique may also be employed on sea turtles, provided that additional energy is used to deliver sound through the vibrator, due to the turtle's substantially larger size. The turtles were suspended in the air or placed in a box to reduce extraneous Needle electrodes were placed on either side of the fronto-parietal plate on the dorsal surface of the head, a reference electrode in the skin immediately behind the skull over the extension of the supraoccipital, and a ground electrode in the inactive skin of the lateral neck. A computer capable of delivering stimuli and receiving bioelectric activity (Nicolet Spirit Portable) was used for attaining evoked potentials. This computer contains an input board with receptacles for the electrode connector Two channels, left and right, of elect:roencephalographic (EEG) activity were amplified (x20k), filtered ( HZ) and fed into the computer. Bioel.ectric activity was timed locked to the delivery of the stimulus (vibrator) secured over the eardrum and thus

35 stimulus. stimuli. [re: decreased, recorded by the computer with the same rate as that of the 28 Evoked pot.entials were extracted from the EEG by repeating and averaging single responses. Averaging reduces the components of the EEG unrelated to the stimulus (such as muscle contractions and other extraneous biological activity) so that responses can be clearly distinguished. (Spehlmann, 1985). The time window on the computer was set at 10 milliseconds stimuli were clicks composed of broadband frequency ( Hz) delivered through the bone vibrator strapped to the tympanum. The frequency response to the bone vibrator was obtained by coupling the vibrator to a piezoelectric film sensor and feeding the energy in to a real time spectral analyzer. From the spectral analyzer, we recorded the actual frequency found in the broadband click The intensity of the stimulus was manipulated, ranging from -36 to 6 db one gravity unit (g)]. Confirmation of the stimulation of the auditory nervous system with the use of this bone vibrator was through exam:ination of the EEG readouts produced by the computer. A positive wave at about 4.5 milliseconds was used as an index for determining threshold. If this wave decreased in amplitude and increased in latency as the stimulus intensity then the lowest intensity at which a visible wave at 4.5 milliseconds was observed was termed the threshold. Thresholds were obtained from the turtles before the

36 exposure. first testing sequence in the net, within 24 hours after 29 each test, and approximately two weeks after the last exposure Results to the airgun. Five of the turtles exhibited either; 1) a phase shift in their electroencephalogram or; 2) nonrepeatability in the recordings of their EEGs when tested within 24 hours after All evoked potential recordings reverted back to normal when tested two weeks after exposure (Fig. 7-8). DiscussiQn The shift in the EEGs as well as the nonrepeatability in the recordings of a few turtles' EEGs leads us to believe that air guns caused a change in the hearing physiology. Whether this change was related to the habituation effect which was observed after the third trial is unknown. However, in all cases, hearing capabilities of each turtle returned to normal by the end of two weeks and obviously demonstrated that the effect was temporary. The decibel level of the air guns was not unusually higher than the threshold level of turtles' hearing. Consequently, it is possible that this effect on the turtle's hearing could be a result of the particle motion of the near field. Validation of this hypothesis would require more research on the effect of particle motion on the hearing mechanism of sea turtles.,

37 VA. 30 Figure 7. An example of the phase shift seen in turtle QQZ429/QQZ430 of the sea turtle repelling experiments in the York River, Wave 1 and 2 were collected before the first testj.ng sequence with the air gun, wave 3 and 4 after the first test in the net, wave 5 and 6 after the second test in the net, and wave 7 and 8 were taken two weeks after the last test. The x-axis is time in milliseconds and the y-axis is amplitude in microvolts.

38 qq7a29. final 1.62nV 1.D~ 2.62uV l.dmscc 3.62nV l.dmsec 4.62uV l.dmsec 5.62uV l.dm= 6.62uV l.dm~ 7.62uV 1.Om.-~ 8.62uV 1.Omsec Wa.Ye

39 microvolts. 31 Figure 8. An example of normal evoked potential readings taken from the turtle QQZ486/QQZ487 of the sea turtle repelling experiments in the York River, VA. Wave 1 and 2 were collected before the first testing sequence with the air gun, wave 3 and 4 after the first test in the net, wave 5 and 6 after the second test in the net, and wave 7 and 8 were taken two weeks after the last test. The x-axis is time in milliseconds and the y-axis is amplitude in

40 ~..,r-'"'"' qqza86. fin1ll2 ABR Index wave ~1 r- 3~./-""""-"""-"'""'"""'--'-./'"'\ s 7 1/ """"'-'~"'~./ '"""""""" ~v, I~/I r I II I I I II 1.62uV l.dm~~ 2.62uV l.dms~ 3.62uV l.om.~ 4.62nV l.dmsec 5.62uV l.dm~ec -6.62nV l.om.'tc 7.62uV 1.Om~~ 8.62nV l.om.1ec

41 Art, Dickerson, Lenhardt, O'Hara, Ridgeway, Siegal, 32 Literatur~ Cited J.J., A.C. Crawford, R. Fettiplace, and P.A. Fuchs Efferent modulation of hair cell tuning in the cochlear of the turtle. J. Physiol. 360: Crawford, A.C. and R. Fettiplace The frequency selectivity of auditory nerve fibres and hair cells in the cochlear of the turtle. J. Physiol. 306: 79~125. D.D., J. Richardson, J. Ferris, A. Bass, and M. Wolff Entrainment of sea turtles by hopper dredges in Cape Canaveral and King's Bay ship channels. US Army Corps of Engineers Information Exchange Bulletin, Vol D Joyce, J.C Protecting sea turtles. The Military Engineer, No. 481, July-August, p Lenhardt, M.L Evidence for auditory localization ability in the turtle. J. Aud. Res. 21: M.L Bone conduction hearing in turtles J. Aud. Res., 22: Lenhardt, M.L., S. Bellmund, Marine turtle reception R. Byles, and J. Musick. of bone conducted sound J. Aud. Res. 23: Lenhardt, M.L. and S.W. Harkins Turtle shell as an auditory receptor. J. Aud. Res. 23: M.L., R.C. Klinger, and J.A. Musick Marine turtle middle-ear anatomy. J. Aud. Res. 25: J Avoidance responses of loggerhead turtles, Caretta caretta, to low frequency sound. Copeia. 2: Spehlmann, S Evoked Potential Primer: Visual, Auditory, somatosensory Evoked Potentials in Clinical Diagnosis. Butterworth-Heinemann: Boston. S.H. et. al turtle Chelonia mydas Hearing in the giant seaproc. Nat. Acad. Sci. 64:(3) S. and N.J. Castellan, Jr Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill, Inc.: New York, p

42 studt, J. F Amelioration of maintenance dredging impacts on sea turtles, Canaveral harbor, Florida, p In: W. N. witzell (ed.), Ecology of East Florida Sea Turtles. NOAA Tech. Rept. NMFS 53. Wever, E.G The Reptile Ear: Its structure and Function. Princeton University Press: Princeton. 33 Zar, J.H Biostatistical Analysis. Englewood Cliffs. 718 pp. Prentice Hall: