(Presented by: Stacey Ellison and Tara Mae Goodrich)

• An animal’s ability to use sound is strongly constrained by environmental factors.
• Medium determines where sound will travel and to what extent it will be transformed.
• Communication over short distances are usually of graded repertoires.
• Communication over long distances are of discrete repertoires.

• This depends on signal frequency, source and receiver depth, sound-speed profiles (SSP’S), water depth, biomass, bottom variability, surface roughness.
• Shallow water environments place unique constraints on sound transmission.

• Effects become most relevant over long distances.
• Baleen whales transmit sounds over the longest distances.
• Blue and fin whale sounds have been detected from as far away as 1600 km.

• To use computational methods to examine how shallow-water environments constrain sound transmission by the Megaptera novaeangliae (humpback whale).

• The humpback whale is one of the only whales that can sing for extended periods of time.
• The sounds are 190 dB sounds that can be heard day and night from 10-20 hours for several months in a year.
• Lone males make these sounds and are sometimes accompanied by other males. The reason for this lone singing and the fact that it is only males is not really known. Some theories are that the average male may sing to recruit other males because his chances of getting closer to a female will increase. Another theory is that the whales’ song is a form of pronouncing fitness (Chadwick, 1999).
• Sound behavior varies as a function of gender, season, year, social context, geographic location, and the individual. As with their social behavior. The whales exhibit very peculiar social behavior while in groups. One such behavior is the exhibition of lateralized behavior. Do the whales prefer one side rather than the other? In 1995 a study was done and showed that the whales had a strong bias for a specific jaw side, usually the right (Clapham et al., 1995).

• The Humpback lives in shallow waters.
• During summer feeding seasons they are in high latitudes near continental shelf.
• In fall and winter (mating season) they are in lower latitudes warmer waters.
• They vocalize during whole cycle but mostly in the winter mating months.

• Sound in water is relative to temperature, salinity, and pressure versus depth in water.
• Sound in mixing layer,which is 50-140 meters in depth, slowly increases as a function of depth due to increasing pressure.
• The next layer is the thermocline, and in Hawaii it is 275-365 m.
• The speed in these has been recorded to 1530-1535 m/s in these two layers.

• Sediments help to regulate sound.
• Soft sediments are penetrable and remove significant fractions of energy.
• Sandy bottoms tend to be more reflective.
• Singers are often found in regions of smoother bottoms.

• This variable depends on time of day, location, season, wind speed, bottom conditions, and the extent of biological and manmade sound production in the area.
• Noise levels can vary by 10-20 dB from one day to the next.
• These are the same factors that control transmission loss.
• Whales songs and large boats contribute to this ambient noise. Large boats can pose serious danger for these large organisms.
• The drilling also may have a huge affect on the songs of the humpbacks. The dangers can be anywhere from behaviorial disturbances to deafness. This article written by Robbin (1997) talks about Scripps University emitting short 195 decibel sounds six times a day for 10 years. This will be used to measure Global Warming.
• Another source of Sound is the Acoustic Thermometry of Ocean Climate (ATOC) which is a 2 year study that creates a humming noise that travels all over the ocean. Many people are quite wary that this sound will affect the behaviors of marine mammals especially the singing whales. A study that was completed by Jocelyn Kaiser (1995) indicates that these animals may have a short term problem with hearing but there is no permanent damage.

• The whales have control as to how their sounds sound and project across a certain area.
• The whale’s choice of certain areas could be passed on genetically or by experience or by any combination of the two.
• The vast number of whales in given areas that have certain characteristics proves.
• Three things contribute to the maximum sound produced is source level, beam pattern, and frequency range used by whales.

• Source Level: The intensity of the sound radiated by a projector at a standard distance from the source.
• Beam Pattern: Directional Variability
• Frequency Range: 144-190 dB for Humpbacks and the average range over 20 years is 155-185 dB.

• Source energy close to source are modeled as spherical. TL=20 log r.
• Source energy at medium ranges spread between spherical and cylindrical. TL=15 log r.
• Source energy at long ranges modeled as cylindrical. TL=10 log r.

• Models are based on solutions of wave equations.
• There are several approaches to solving the wave equation, including: the ray theory, normal-mode theory, spectral methods, and the parabolic equation model.
• Normal-mode theory well-suited for humpbacks.

• The frequency that achieves the maximum propagation range, given a particular environment and source depth.
• Different features of the environment affect transmission loss at different frequencies.

• Optimum frequencies were tested both theoretically and empirically by Jensen and Kuperman and they produced similar results.
• The results suggest that for humpbacks to maximize propagation range in shallow water, they would need to produce sounds (1) with frequencies between 50 to 800 Hz, (2) at mid-depth in water between 30 to 300 m deep, and (3) over bottoms consisting primarily of sand and silt.

• Lower-frequency vocalizations will propagate longer distances than higher-frequency vocalizations.

• Suggestions are based on the following:
• The fact that attenuation of sound by seawater increases with increasing frequency.
• Lower-frequency signals are produced at levels equal to or greater than higher-frequency signals.
• Attenuation in the water channel is the primary determinate of how far different frequencies will propagate in shallow water.

• In Hawaii tests were completed by Jenson and Kuperman to see optimum frequencies that whales can sing in. Their data is what the researchers used to correlate the data in this experiment.
• The parameters that were looked at were: water depth, bottom type, and sound-speed profiles in the water channel.
• They used a single, homogenous bottom layer, the source was placed at mid-depth, and averaged the propagation loss over the water column for each receiver range.
• Optimum frequencies were calculated from depths of 20-400m, bottom types with clay-silt to chalk-limestone.

• Sound speed profiles for winter and summer were calculated.
• The sound-speed was calculated at 20, 40, 60, 100, 200, and 300 meters of depth.
• Constant salinity of 35 ppt and a constant temperature of 25^oC.
• The bottom was 50 m of sand and silt over basalt.
• The sound was set at 1.02 c.

• This graph gives the depth profile of the sound-speed.
• Shear-speed and compressional attenuation factors were compensated.
• Their numbers after manipulation were very close to the original data and the optimum frequencies were not significantly different.
• Dependence of optimum frequency on source depth, water, and thermocline depth.
• Current analyses tested for optimum frequencies using a simulated pattern.
• 20 frequencies were run between 0 and 4000 Hz, calculated at the 200 mark.
• At the 200 mark there is a 50 to 60,000 m and 50 receiver depths between surface and the bottom.
• Each row was then fit to a Logarithmic curve (TL = a log r).

• Many of the numbers correlate to the previous experiment by Kuperman and Jenson.
• The differences could be due to the fact that K&J put the source at mid-depth so the source and water depth were exactly the same and Mercado did not.

• The current simulations showed the optimum frequencies increased as the source moved away from the mid-depth position.
• Water depth did not seem to interfere with the frequencies (r= -.12)
• Source depth seems to be the main factor with an r factor of -.80.
• R-value for receiver depth and source depth correlate with a 0.96, whereas receiver depth and transmission loss correlate only to a 0.70.
• Lastly a deeper thermocline yields lower optimum frequencies and slightly lower values.
• Transmission Changes as a function of source depth and frequency
• When the source is 5m deep there is no evidence of optimum frequency but at 15 m depth the 74-dB contour shows a bulge near the optimum frequency of 17,090 Hz.
• At 30 m there is an alternating curve towards and away from the optimal frequency.
• Basically optimal frequency only always occurs when the receiver and source are at the same depth.

• Preliminary Calculations used Greens Function to assess the numbers. This is how the environmental standards were decided upon.
• The depth was 60 m and the source and receiver were at 15 m at ranges from 1-5 km.
• The width of the bands was from 50 –475 Hz.
• At 2 km there is a clear trough near 180 Hz. This indicates the channel acts as a Band-stop filter.

• The simulations of sound propagation have revealed several constraints on humpback whales’ use of sound:
• First, humpback whales cannot increase the distance their sound travels just by using lower frequencies.
• Second, source depth was found to be a critical determinant in optimum frequency, optimum receiver depth, and maximum propagation range.
• Finally, the results seem to suggest that most humpback whale songs are not acoustically optimal for long-range propagation.

• Possible reasons for discrepancies are:
• The current model is limited in that it does not account for the effects of scattering by the ocean surface or bottom, or the effects of bottom gradients.
• The model does not include measures of bathymetry, bottom composition, and sound-speed fields.

• Environmental constraints may not be the reason for the lower frequencies of the humpbacks’, but they can explain why there is such a range of frequencies.
• When the sounds of the humpback are lower they produce more harmonically related higher-frequencies.
• To maximize the range the singers choose an acoustic channel based on water depth, bottom sediments, and whether there is a thermocline or not.
• Humpback whales could also affect propagation range by modulating the spectral and energetic properties of the sounds they produce.

• Simulations based on normal-mode theory predict:
• How far a singer’s sound will propagate will be a function of the frequencies produced, depth of singer, and environmental factors
• The optimal receiving depth will be equal to source depth
• The bandwidth of near-optimum frequencies will increase with increasing water depth
• Distortions caused by propagation can potentially provide useful information about the position of the source.

• It is quite obvious that the coastal waters are polluted, but many people do not know by what. In Maine, there was an extreme case of poisoning from dinoflagellate toxin. There were 14 whales that were fatally poisoned by these microscopic organisms. The dinoflagellates worked rather quickly, anywhere from hours to days to completely kill the large mammal. The microorganisms were thought to have been picked up by the whale by eating a certain type of mackerel. These whales are not only being restricted by their everyday surroundings but by species that are in abundance for any number of reasons (Geraci et al., 1989).

Robbins, E. 1997. Whale Watch. E Magazine. 28-37.

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