6. SOUND PRODUCTION AND DETECTION
177
1968) used avoidance conditioning to demonstrate auditory thresholds.
In the common perch, Perca fluviatilis, the lowest threshold was about
-14 dB pb at 100 Hz, and the curve rose sharply to f35 dB pb at 50 Hz,
and almost +45 dB pb at 200 Hz. In the pike perch, Lucioperca Sandra,
thresholds were about 0 to $5 dB pb from 50 to 200 Hz, rising to $60
dB pb at 800 Hz. The audiogram for the stone perch, Acerina cernuu, was
similar in shape to that of the pike perch, but consistently about 10 dB
higher, It is possible, as in the case of the cod, that these percids may be
primarily sensitive to displacements mediated by the lateral line.
Deserving special mention is the attempt by Kritzler and Wood
(1961) to determine a complete audiogram in the bull shark, Curcharhinus leucm. Their data, based upon positive reward conditioning, ranged
in threshold values from +lo dB pb at 100 Hz, to a low level of about
-15 dB pb 400-600 Hz, to over +lo dB pb at 1400 Hz. Considering
the fact that the shark has no swim bladder and therefore receives all
sounds either through direct conduction to the inner ear or by way of
the lateral line system, these low thresholds are quite remarkable. This
may serve to indicate that an air chamber need not function as the main
transducer in sound reception, and the acoustical difference between the
water medium and the bone or cartilage of the neurocranium may be
sufficient to permit detection of frequencies up to 1000 Hz.
The above report by Kritzler and Wood (1961) was the first behavioral study of hearing in any elasmobranch fish, although the ability
of sharks to detect and respond to acoustic signals has long been known
(Parker, 1910a). Interest in the hearing of sharks has, of course, been
spurred by practical aspects of dealing with attacks of these animals on
human beings. Many of the problems in experimental work on the hearing of sharks have been summarized by Wisby et al. (1964), and Backus
(1963). In a preliminary report, D. R. Nelson and Gruber (1963) reported that they were able to attract sharks in open sea conditions to a
sound source playing back recordings of low frequency pulses, similar
to those produced by a struggling, wounded fish.
Davies et a2. (1963) conditioned four species of sharks to respond to
sounds and obtained data on response to both pure tones and octaves of
broad-band noise. The results gave a fairly flat audiogram curve ( + l o
dB pb) from 50 to 7000 Hz. The pressure levels ranged from +5 to +2S
dB pb, and the lowest sensitivities of the animals were within a few
decibels of the background noise levels at the tested frequencies. The
authors concluded that the sharks are capable of determining the location
of the sound source but are not capable of any significant frequency discrimination. These results should be considered as highly preliminary
177
1968) used avoidance conditioning to demonstrate auditory thresholds.
In the common perch, Perca fluviatilis, the lowest threshold was about
-14 dB pb at 100 Hz, and the curve rose sharply to f35 dB pb at 50 Hz,
and almost +45 dB pb at 200 Hz. In the pike perch, Lucioperca Sandra,
thresholds were about 0 to $5 dB pb from 50 to 200 Hz, rising to $60
dB pb at 800 Hz. The audiogram for the stone perch, Acerina cernuu, was
similar in shape to that of the pike perch, but consistently about 10 dB
higher, It is possible, as in the case of the cod, that these percids may be
primarily sensitive to displacements mediated by the lateral line.
Deserving special mention is the attempt by Kritzler and Wood
(1961) to determine a complete audiogram in the bull shark, Curcharhinus leucm. Their data, based upon positive reward conditioning, ranged
in threshold values from +lo dB pb at 100 Hz, to a low level of about
-15 dB pb 400-600 Hz, to over +lo dB pb at 1400 Hz. Considering
the fact that the shark has no swim bladder and therefore receives all
sounds either through direct conduction to the inner ear or by way of
the lateral line system, these low thresholds are quite remarkable. This
may serve to indicate that an air chamber need not function as the main
transducer in sound reception, and the acoustical difference between the
water medium and the bone or cartilage of the neurocranium may be
sufficient to permit detection of frequencies up to 1000 Hz.
The above report by Kritzler and Wood (1961) was the first behavioral study of hearing in any elasmobranch fish, although the ability
of sharks to detect and respond to acoustic signals has long been known
(Parker, 1910a). Interest in the hearing of sharks has, of course, been
spurred by practical aspects of dealing with attacks of these animals on
human beings. Many of the problems in experimental work on the hearing of sharks have been summarized by Wisby et al. (1964), and Backus
(1963). In a preliminary report, D. R. Nelson and Gruber (1963) reported that they were able to attract sharks in open sea conditions to a
sound source playing back recordings of low frequency pulses, similar
to those produced by a struggling, wounded fish.
Davies et a2. (1963) conditioned four species of sharks to respond to
sounds and obtained data on response to both pure tones and octaves of
broad-band noise. The results gave a fairly flat audiogram curve ( + l o
dB pb) from 50 to 7000 Hz. The pressure levels ranged from +5 to +2S
dB pb, and the lowest sensitivities of the animals were within a few
decibels of the background noise levels at the tested frequencies. The
authors concluded that the sharks are capable of determining the location
of the sound source but are not capable of any significant frequency discrimination. These results should be considered as highly preliminary