Sound Production:
A variety of crustacean species are known to be soniferous, including: white shrimp, snapping shrimp, crabs, spiny lobsters, rock lobsters, and red-banded lobsters. In all of these species sound is produced by exoskeletal movement, such as; stridulation (rubbing) of two body parts, percussion of two body parts, or percussion of a body part and the substrate.

American lobsters produce simultaneous waterborne sounds and shell vibrations, using internal musculature. This mechanism, which is unique amongst was first hypothesized when Fish (Fish, J. 1966 Sound Production in the American Lobster. Crustaceana 11:105) he observed differences in the spectral qualities of American lobster sounds versus sounds from stridulatory sound producers. While sound production by stridulation (such as in spiny lobsters and many insects) typically consists of wide band sounds with no harmonic component, Fish observed low frequency (100-130 Hz in 6 animals), tonal, short duration sounds in the American lobster that are, in fact, most similar to sounds produced by rattlesnakes, some insects, such as cicadas and some teleost fish, such as toadfish.

The remotor muscle at the base of the large (second) antennae has previously been implicated in lobster sound production. The remotor muscle has been studied on a cellular anatomical level and vibrations have been recorded in association with muscle contractions. Besides being a putative sonic muscle, the remotor muscle serves to move the antennae.

Sound Detection:
While the morphology of putative acoustic receptors in crustaceans has received considerable attention, few studies have examined the physiological and behavioral responses of crustaceans to sound stimuli. In American lobsters our understanding of how they respond to sound is limited to one brief report published by Offut (Offut, G.C. 1970 Acoustic stimulous perception by the American Lobster. Experientia 26:1276-1278). Offut used cardiac assays to record changes in the heart rate of five juveniles in response to waterborne sound waves of 10-150 Hz. He found that they responded to sounds between 18.7 and 150 Hz by briefly stopping or dramatically slowing their heart rate (bradycardia). Bradycardia is a common response of lobsters to novel stimuli and it has also been observed in lobsters exposed to small changes in temperature and salinity.

Lobsters lack the air-filled cavities necessary for pressure detection, so they must detect acoustic signals with particle displacement receptors. Particle displacement receptors are most effective in sensing both vibrations, which directly move the sensory hairs, and sounds produced close to the receptor. Many benthic inhabitants, such as sea robins, haddock, oyster toadfish, and lobsters themselves produce low frequency sounds that could be detected by lobsters using particle displacement receptors.

From the "Biology of the Lobster Homarus americanus" by J.R. Factor, 1995.

Two types of putative acoustic receptors in the American lobster are hair-fan organs and hair-peg organs. Hair-fan and hair-peg organs are sensory hairs that have been implicated in low frequency waterborne sounds and water current detection in the European lobster, Homarus vulgaris. These receptors are widely dispersed on the anterior carapace, but are absent from the antennae and antennules. However, statocyst receptors have been identified on the antennules of American lobsters that respond to vibrations but not waterborne sounds (Cohen M.J. 1955 The function of receptors in the statocysts of the lobster Homarus americanusJ. Physiology 130:9-31). The location of acoustic receptors on a movable appendage is advantageous for locating and orienting toward sound or vibration sources (phonotaxis), which would be especially advantageous for lobsters during nocturnal foraging and social interactions.

Study Site

Based on our observations of approximately 24 videos obtained during the summers of 1998-2000, we have drawn a number of conclusions, a few of which are listed below. For more details about these studies see our first manuscript on the subject (Jury and Watson, 2001) in the Publication section of this website.

1. A large number of lobsters approach and enter traps, yet typically we only catch 1-3 per trap haul because the vast majority escape. We estimate that 10% of the lobsters that approach a trap enter, and of the ones that enter, only 6% are caught. Over 75% of the lobsters that escape the trap do so through the entrance. Video 1, on the right, shows a lobster escaping through the entrance to the kitchen.

2. Lobsters are very active around traps during the day, as well as the night. This confirms other field observations indicating that lobsters in their natural habitat are not as strickly nocturnal as previously thought.

3. Agonistic encounters around traps appear to limit entry and stimulate exits. Video 2 shows a large lobster chasing away smaller lobsters and then entering the trap. Small lobsters are very hesitant to enter, while larger lobsters tend to move right in like the one shown in this video.

4. Once in the trap, lobsters tend to "defend" the resource. Video 3 demonstrates this behavior. This also limits entry and it is probably one of the main behaviors that lead to trap "saturation".

Figure 1
Figure 1
Figure 2
Figure 2
Figure 3
Figure 3
Figure 4
Figure 4
Video 1 (click to play)
Video 2 (click to play)
Video 2 (click to play)

Preliminary Results from 2002

In the summer of 2002 we had four main goals:

  1. Measure the home range of lobsters by tracking them for at least 3 days.
  2. Determine if they exhibited homing behavior, naturally and if displaced.
  3. Measure the area of bait attraction.
  4. Determine if lobsters are nocturnal, diurnal, or neither.

During the past summer we tracked 36 lobsters for approximately 5-8 days each. Of these, 11 escaped from the mesocosm at some point during a typical 7 day trail, but some of these stayed in the area long enough to examine their behavior outside the mesocosm. In general, lobsters outside the mesocosm, that were in range of the telemetry system, moved about the same amount, and with the same general patterns, as they did when they were inside the mesocosm.

Many of the lobsters we tracked had some type of shelter affinity, even though their "shelters" were sometimes just pits in the sand (Figure 1). Occasion they would leave their shelters, move around within the mesocosm, and then return to the same location. Two example of this type of behavior are shown in Figure 3.

The data collected during the summer of 2003 were sufficient to make it possible to calculate the home range for a number of different lobsters. These calculations were performed using the Animal Movement Analysis Extension for ArcViewGIS. This extension was developed by Dr. Hooge and his colleagues. Based on our home range calculations so far, the typical home range of a lobster is 653.5 ± 149.4 m2. These home ranges are roughly 26% the area of the entire enclosure (2500 m2). An example showing how a home range was calculated is shown in Figure 4.

Although it is generally accepted that lobsters are nocturnal, the data we have collected so far does not support that view. We often observed lobsters moving about outside shelters during the day and many of the animals we tracked moved the same distance in the day as in the night (Figure 5).

One way we started to determine the area of bait attraction was to fish a single lobster trap, equipped with a transmitter, within the mesocosm. Because the local lobstermen were considerate enough to avoid dropping traps within the mesocosm, our trap was the only source of bait odor. On several occasions we were able to track lobsters approaching the trap (Figure 6) and, because the trap was also equipped with a video camera, we were also able to determine if they entered the trap or simply approached it. Based on these preliminary data lobsters appear capable of sensing a trap from distances of < ~ 10 meters. However, considerably more data are required before we can state with confidence that lobsters are attracted to bait from a certain distance away, taking into account major factors such as current speed and the activity or behavioral state of the lobster.

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