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The first type of dolphin that I researched is the rough-toothed dolphin, Steno bredanensis. It is generally between 7Õ6Ó and 9Õ long and will weigh between 285 and 350 pounds. The back, pectoral fins, caudal fin and flanks are grey-black with pink or white spots while its snout and stomach are white (Sylvestre). The characteristic feature of a rough-toothed dolphin is its Òconical head and slender noseÓ (wikipedia.org). This species eats pelagic cuttlefish if it lives in the Gulf of Mexico or Florida regions. To identify this species in the field, it is necessary to note that the melon and dorsal fin are visible when swimming. Their pods range from 3-20 individuals and it will move in herds of 50 to several hundred, as it is a very social species. One can also identify the rough-toothed dolphin from its acquaintances; it can be spotted traveling with tuna, bottlenose dolphins, spotted dolphins, spinner dolphins and short-finned pilot whales (Sylvestre).
The second type of dolphin we could see is the FraserÕs, or Sarawak, dolphin Lagenodelphis hosei. This species is generally between 7Õ6Ó and 8Õ6Ó in length and will weigh between 140 and 185 pounds average, but can be up to 300 pounds. It has a short and rounded snout and small dorsal, pectoral and caudal fins. The FraserÕs dolphinÕs back is dark grey, and the stomach is white and sometimes tinged pink. Its characteristic feature is two parallel stripes location on the flanks; the upper stripe is creamy white, starts above and ahead of the eye and ends by narrowing at the base of the tail while the lower stripe is black or dark grey and runs from the eye to the anus. Its throat and chin are white while the upper jaw, pectorals, caudal and dorsal fins are black. FraserÕs dolphin has a diet of octopus, crabs, shrimp and pelagic fish. Because its hunting is carried out at immense depth, this specieÕs feeding relies only on echolocation, which uses sonar to detect the location of its meal (Sylvestre). ÒIn echolocation, a dolphin strings clicks together in bursts of sound called click trains. Click trains form sound waves that leave a dolphinÕs headÉ When click train sound waves hit an object, they bounce off the objectÕs surface. The waves race back toward the dolphinÓ (Walker 19). When one sees this type of dolphin in the wild, it can be identified by certain characteristics. FraserÕs dolphins are aggressive swimmers and surround themselves with foam when surfacing. They are quick and sometimes jump out of the water, but not acrobatically like other species will. FraserÕs dolphins generally stay away from boats. They travel in pods of seven or eight, herds up to 300 individuals, and can be seen with false killer whales, striped dolphins, spotted dolphins, spinner dolphins and sperm whales (Sylvestre). This species is also subject to mass strandings, which scientists believe is abnormal. According to wikipedia.org, Ògroups of stranded dolphins have been found as far afield as France and Uruguay. However these are regarded as anomalous and possibly due to unusual oceanographic conditions, such as El Ni–o.Ó I wondered if perhaps these oceanographic conditions did something to interfere with the dolphinsÕ echolocation sonar and caused them to think the shoreline was farther away than it was. I researched this question more using multiple books and internet sources, but I could not find any more information on the stranding of FraserÕs dolphin.
The third type of dolphin I researched is the common dolphin, Delphinus delphis. I discovered that there are actually two types of common dolphins: the short-beaked common dolphin and the long-beaked common dolphin. The exact type of this species is determined by its location and the length of its beak. The short-beaked variety is the species that we will have a chance to see in Key Largo and San Salvador. The common dolphin is, on average, a length of 6Õ6Ó, with a maximum of 8Õ6Ó and weighs between 200 and 300 pounds. It has a long and slender body with a snout that is also long and thin. Its back is very dark, almost black, and its throat and stomach are white. The upper jaw is very dark while the lower jaw is light. The common dolphin prefers a diet of migratory fish such as anchovies, herring and sardines. When in the field, one can identify the common dolphin by its behavior. It will emerge several times a minute to breathe (usually every 20-30 seconds) but can remain submerged for up to 8 minutes. It often zigzags and jumps while swimming for no particular reason, and this species likes to play in the bow waves of boats (Sylvestre). According to wikipedia.org, Òan intriguing theory suggests that dolphins 'bow-riding' on very large whales was the origin of bow-riding on boats.Ó This species is also subject to mass strandings like FraserÕs dolphin, but there is no reason for this occurrence that scientists can discern. The common dolphin sticks to pods of around 10 and will travel in herds up to 100, often with striped dolphins (Sylvestre).
One of my two favorite dolphins that I could potentially see on this field study is the Atlantic spotted dolphin, Stenella plagiodon. It is an average of 6Õ6Ó in length with a maximum of 7Õ6Ó and weighs between 240 and 265 pounds. Its snout is ÒdetachedÓ from the rest of the head, making it easily discernable from the melon, unlike RissoÕs dolphin. The most interesting part of this species to me is that its coloring varies with age. Young calves are light in color, comparable to the bottlenose dolphin, but when maturity starts, the dolphins begin having spots. The adult is generally completely blue with a darker back, white spots and dark fins. Much like humans and age spots, the Atlantic spotted dolphin literally has spots that occur with age. Its diet consists of small fish like herring and anchovies as well as octopus. Other than its noticeable spots, one can identify this species in the field by the fact that it rarely jumps out of the water, but will emerge slowly and cautiously. It often moves in pods of 10 and herds of 50. [Information from Sylvestre] While researching this type of dolphin, I became very excited about the prospect of spotting this species because Òthere have been reports of a solitary individual living off the coast of San Salvador in the Bahamas who appears to appreciate human companyÓ (Sylvestre 89). I hope to find this dolphin this year since I did not last summer!
My other favorite species of dolphin that I researched is the striped dolphin, Stenella coeruleolba. It measures 7Õ9Ó in length on average but could reach 8Õ2Ó with an average weight of 240 to 250 pounds and 310 pounds as the maximum. It has a slender body with a distinct snout, but less so than the common dolphin. It has a dark gray and brown to bluish grey back with lighter-colored flanks and a white stomach. The eyes are circled in black, which begins the stripes that lead to the pectoral fins and the anal area. It feeds primarily on sardines and anchovies, but will also consume shrimp and octopus in small quantities. Its major identifying characteristic is its stripes, but one can also identify it in the wild because it jumps acrobatically often up to 20 feet high and will sometimes land on its side. Striped dolphins are also attracted to the bow waves of ships and will often play in them. Its pods are generally between 10 and 20 individuals (Sylvestre).
The spinner dolphin, tropical Atlantic Ocean form, Stenella longirostris, is yet another type of species we could identify on this trip. Its average length is 5Õ10Ó but can be a maximum of 6Õ6Ó, and its weight is around 180 pounds. Spinner dolphins have a dark grey back with lighter flanks and a white stomach, as well as a long snout, the tip of which is black. It eats mesopelagic fish (it will dive up 200 feet to feed) and octopus. This species can be found in the AtlanticÕs tropical waters and the Gulf of Mexico. It does not fear boats and will accompany them for a half hour or more to play, generally in a pod of three to five (Sylvestre). Spinner dolphins are one of the most acrobatic species of dolphins and Òperforms impressive jumps, and it is said to be able to rotate seven times on a longitudinal axis during a single jumpÓ (Sylvestre 95).
The Clymene dolphin, Stenella clymene, is an average length is 5Õ10Ó with a maximum of 6Õ6Ó and weighs between 165 and 200 pounds. It has a Òlong black cape, starting at the melon and running down to half of the caudal peduncle, which spills over a little onto the flanksÓ (Sylvestre 98). It also has a grey stripe from the snout, over the eyes and joining the caudal peduncle, a white stomach, eyes circled in black and the tip of its snout, lips and fins are black (Sylvestre). Clymene dolphins feed on small fish, especially Lanternfish, Òwhich it eats at half-depth during the day, or at night when these fish come to the surfaceÓ (Sylvestre 99). In the wild, Clymene dolphins spin and jump and move in small groups. Not much research has been done on this species, so much of its behavior is unknown (Sylvestre).
The most widely-known species of dolphins is probably the bottlenose dolphin, Tursiops truncatus, as this is the type that many people will have seen in zoos, aquariums and maybe even had the chance to swim with on family vacations. Bottlenose dolphins are an average length of 10Õ and can be up to 13Õ; weigh an average of 440 pounds, but can be up to 1,430 pounds; have a slender body with a well-defined snout, and the major identifying characteristic of this species is that its lower jaw is longer than the upper jaw. Bottlenose dolphins have a medium to dark grey back with lighter flanks and a white or pink stomach. They eat catfish, eels, rays, shrimp, crabs, octopus and small sharks, and in captivity, they consume between 13 and 33 pounds of food per day. This is a very friendly animal, which will occasionally play in a boatÕs waves, but is very cautious of motor boats. They travel in groups of hundreds and split off into smaller groups of 12. Bottlenose dolphins are also seen with RissoÕs dolphins and will mate with them in the wild, which is the only interspecies mating that has been discovered so far (Sylvestre).
One last species of dolphin that lives in the coastal Florida and Bahamas region is RissoÕs dolphin, Grampus griseus, which measures an average of 10Õ with a maximum length of 14Õ. Its average weight is 660 pounds but has been known to reach 1,500 pounds. This species has a sturdy body getting slender past the dorsal fin, a huge melon with a depression from the forehead to the mouth and an unpronounced snout. Much like the Atlantic spotted dolphin, RissoÕs dolphinsÕ coloring depends on age: an adult has a dark grey body with a long white area on the throat, chest and stomach with black fins, while the young have a yellowish head and are lighter-colored than adults. Older RissoÕs dolphins are easily identified by numerous white scars appearing on its skin. These scars are the result of other dolphins or sharks trying to bite the individual, and they generally get more scars with age. RissoÕs dolphins feed on cephalopods and occasionally fish. This is a very interesting species in that it surfaces to breathe about every 6 seconds, but can make its apnea last for up to a half hour (Sylvestre). Like the spinner dolphin, this type jumps acrobatically when in groups and Òpractices Ôspy hoppingÕ by holding itself vertically in the water, with its head and flippers above water levelÓ (Sylvestre 105). Spy hops are an acrobatic movement in which the dolphin has its head out of the water to look around (Wild About Dolphins 11). This is a very timid species which will swim alone, in couples or in groups of five or more, often with spinner dolphins, northern right whale dolphins, long- and short-finned pilot whales and bottlenose dolphins. [Information from Sylvestre]
While researching the different species of dolphins located in the Key Largo and San Salvador region, I learned much about the different ways that dolphins will play and communicate with one another, as well as humans. Along with spy hopping, dolphins also practice porpoising, which is Òtraveling along in and out of the waterÓ, and will often jump out of the water completely (Wild About Dolphins 11). Dolphins are able to jump Òby swimming very fast under the surface, then turning suddenly so their speed carries them up into the airÓ (Wild About Dolphins 21). One of the major ways the dolphins communicate with one another is using whistles and clicks. Humans can hear the whistles, and so captive dolphins will use these to communicate with their trainers as well (Walker). ÒDolphins may whistle to warn of danger, to call for help, or to identify themselves, rather like humans introducing themselves by nameÓ (Cerullo 16). Dolphins also groan, bark, squeal and mew, which humans can also hear. Another way that dolphins communicate with one another is by using their bodies. ÒThey smack the water with their tails and flippers. They snap their jaws. When they are really excited, some dolphins even leap out of the waterÓ (Stahl 25).
When expanding this paper, I had to wonder about the evolution of a species such as this. Dolphins are one of the many marine mammals that live in the waters of the Atlantic and close relatives include whales and porpoises. According to sources such as Science Daily, an e-journal, there are three major characteristics that point to the reality that dolphins were once land mammals before making the journey to sea: they use lungs to breathe air from the surface as opposed to gills filtering oxygen through water, the bones in their fins resemble that of human hands and the way their spine moves is more characteristic of a mammal which runs as opposed to swims. Old theory suggests that whales, a member of the cetaceans, were at one point related to hoofed animals such as the hippopotamus and this is where cetaceans truly began (Science Daily). While DNA evidence over the past decade has suggested that a hippo is, in fact, the closest living relative to todayÕs whales, this has been challenged in recent months by other scientists who view fossils as being the better indicator of a family tree (Science Daily). This debate is still currently continuing as one side states that by using DNA, whales and hippos are closely linked while one side states that by using fossils, modern whales are more closely related to the Indohyus, an acient pig (Science Daily). The more recent discovery of pakicetids has helped to suggest even further that cetaceans began as land mammals, and the pakicetid has been called the earliest whale, which was linked due to its ears. ÒThe structure of the auditory bulla is formed from the ectotympanic bone only. The shape of the ear region in Pakicetus is highly unusual and only resembles the skulls of whales. The feature is diagnostic for cetaceans and is found in no other speciesÓ (wikipedia.org).
Even more recently, the discovery of Ambulocetid in 2000 and again in 2004 in the country of Pakistan is remarkable. The creature resembles a mammal-like crocodile that is thought to be a stage between pakicetid and todayÕs cetaceans. It is clearly an amphibian-like creature as its hind legs appear to be more adapted to swimming as opposed to walking or running, and it most likely got around the way that todayÕs sea otters do, by floating on their backs (Science Daily). From here, early cetaceans evolved into protocetids, which were highly amphibious creatures who had adaptations for both marine and land life (wikipedia.org). While it is still unclear whether or not the animal had flukes like modern-day cetaceans, it is clear that it is a more aquatically-adapted mammal when compared with Ambulocetid. Their anatomy also suggests that this particular mammal gave birth on land, which shows that it was still living life partly out of the water. In 1840, the discovery of Basilosaurus was made, and it was mistaken for a reptile when it was actually a fully marine-adapted cetacean (wikipedia.org). Early cetaceans such as Ambulocetid or Pakicetid used well-developed hind legs to move about on land (Science Daily), but todayÕs cetaceans do not have these for the most part. In some cases, the genetic coding for this specific characteristic can misfire and cause some to have miniature hind legs also known as ÒatavismÓ, or a setback in evolution (wikipedia.org). Another major skeletal evolution for cetaceans is the location of their nostrils. The earliest cetaceans had them on their snouts, but due to nasal drift, the nostrils have evolved upward to be on the top of the skull and into the modern blowhole used for breathing (wikipedia.org). The ears also have moved inward to become the melon for echolocation as opposed to using ears for hearing (wikipedia.org).
One major topic that kept surfacing when I was searching for information about dolphins was the fact that the United States Navy uses dolphins for various missions, called ÒmarksÓ (MK), through a program called the Navy Marine Mammal Program (NMMP). This project began in the 1950Õs and was highly classified until the early 1990Õs, which caused a lot of speculation and rumors to come about (NMMP website). They Navy only uses bottlenose dolphins and sea lions to work on these missions to mark sea mines and divers because the animals can make repeated deep dives unlike human divers, as they do not experience any side effects from decompression. According to the NavyÕs website, sea mines are designed specifically so that sea life cannot set them off, only large ships, so that makes the trained animals perfect for these missions, which include: Òprotecting ports and Navy assets from swimmer attack, locating and attaching recovery hardware to expensive exercise and training targets, and locating potentially dangerous sea minesÓ (NMMP website). There are three missions for which dolphins are the preferred animal because their biological sonar is better than any manmade sonar in use today. In MK 4 Marine Mammal System (MMS), they are essential in Òdetecting and/or marking the location of sea mines that are tethered off the ocean bottomÓ (NMMP website). For MK 7 MMS, Òdolphins are trained to detect and/or mark the location of mines sitting on the ocean bottom or buried in sedimentÓ (NMMP website). MK 8 MMS is a human and dolphin team that Òallows troops to quickly identify safe corridors for the initial landing of troops ashoreÓ (NMMP website). The final mission that dolphins are used for also utilizes the help of sea lions. In MK 6 MMS, the two animals work together for force protection as they Òeffectively protect piers, ships, harbors and anchorages against unauthorized swimmers, SCUBA divers, closed-circuit divers and swimmer delivery vehiclesÓ (NMMP website). These teams have been deployed for both the Vietnam War in 1971 and in Bahrain in 1986, as well as being used currently in Operation Iraqi Freedom (NMMP website). Currently, the dolphins are not being trained to actually attack any person or ship, only to identify potentially dangerous objects, but Òthe idea of them as last lines of dense against underwater terrorists was broached very seriously in the months and years immediately after 9/11Ó (MSNBC).
The use of marine mammals by the U.S. Navy has many benefits, but it might also have one major negative effect. As the single largest provider of research publications on dolphins and many other marine mammals, the U.S. Navy prides itself on the research it has done over the years to learn more about the nature of the bottlenose dolphin. The program is currently researching preventative veterinary care for dolphins, which could lead to many advantages for the bottlenose dolphins living in captivity around the world. While all of the information that the Navy provides to the public shows that it takes excellent care of its animals, many animal rights activists still have their doubts. The de-classification of the operation has helped to stifle many of the negative concerns about the welfare of the dolphins; especially since the Navy has stated the different lengths it goes to protect the health of their animals. ÒIn response to charges that the program abused the animals, the presidentially appointed Marine Mammal Commission investigated the program in 1988 and 1990. The Commission reported that the allegations were not only false, but that the NavyÕs care of its marine mammals was ÔexemplaryÕÓ (NMMP website). Another major research topic that the U.S. Navy is looking into today is the bioacoustics of the bottlenose dolphin. According to their website, Òthe NMMPÕs Biosonar Program has constructed the worldÕs first biomimetic sonar to try to emulate dolphin sonar and incorporate search strategies that are specifically effective in the noisy near shore environment.Ó While this seems like a fantastic accomplishment for our military, I could not help but to let my mind wander to an article I had found on the Bahamas Marine Mammal Research Organisation website. This article was a scientific research article based on a mass stranding incident that occurred on March 15, 2000, which coincided with a U.S. Navy sonar test.
According to the article, this was one of the largest mass strandings of cetaceans ever recorded, as it included 15 animals of four different species, with the major concern on beaked whales. While one dolphin was included in this stranding, the article focused more on the beaked whales because of the effect these sonars had on their internal organs and their own sonar. After denying the fact that there was sonar testing occurring on this day for multiple weeks, the U.S. Navy finally admitted to the testing, and the labs began their examinations of the specimens. ÒOn June 14, 2000, a NOAA Fisheries status report of preliminary findings of postmortem examinationÉ indicated that there was evidence of injuries consistent with an intense acoustic or pressure eventÓ (Balcomb 6). One year later, NOAA Fisheries issued another report that stated they had no final conclusions as of yet, but the pattern that the stranding followed indicated that there must be Òa source or intense pressure or acoustic energy moving from south to north through the Northwest Providence ChannelÓ and no source other than the NavyÕs test of sonars fit this description, so team believed the mass stranding to be the effect of this test (Balcomb 7). While the animals who were stranded appeared to be externally doing well, the team found that internally, they had been hemorrhaging, which followed the same description as a mass stranding two years earlier in Rum Cay. The veterinarian who conducted the examination of those two species stated that Òhe believed they Ôlost sonar controlÕ. The muscle mass and internal organs evidenced Ômassive hemorrhageÕÓ (Balcomb 8). All of the scientific evidence points to the use of the NavyÕs sonar to be the reason for the mass stranding in 2000. The article continues discussing the level of noise that was considered safe for marine mammals, but proves that the safe level is actually Òone hundred trillion times noisierÓ than the normal noise level around the area (Balcomb 8), and that Òthe whalesÕ sensitivity was not only behavioral, it was physiological and could reasonably be expected whenever similar received levels of similar frequencies of similar duration occurÓ (Balcomb 11).
Reading that article made me wonder what type of effect this new biomimetic sonar would have on the population of marine mammals in the testing sites, and especially the potential negative effect it could have when it is in use. While I could not find anymore information specifically depicting the NavyÕs use of the sonar so far, I can only imagine the type of negative effects it is having on the marine population when its old sonars have wreaked so much havoc in the past. This will definitely be a subject worth following in the future to see the potential failure of the sonar. I also have to wonder if perhaps this sonar will be better than other sonars because it was based on the natural biosonar of the bottlenose dolphin. Perhaps because it is biomimetic, it will not cause any harm to the marine mammal population; it could be less ÒnoisyÓ than other sonars. According to an article on www.nationaldefensemagazine.org, scientists are creating this sonar to help prevent these negative effects from happening, but the project does not have enough funding to be fully put to use yet.
Dolphins are definitely an interesting subject to study because many people know a little bit about dolphins, and maybe have had the chance to swim with them at some point, but I was able to learn a lot more about dolphins and the specific species native to the Bahamas Islands and the Key Largo, Florida, region. I hope to have the chance to spot a few on this field study and on future trips to the beach. It was also very interesting to have the opportunity to learn about such a controversial topic that deals with these magnificent animals. I am looking forward to reading more articles about the NavyÕs use of dolphins and their biomimetic sonar they are constructing right now.
Works Consulted
Balcomb, K.C. & Claridge, D.E. (2001) ÒA Mass Stranding of Cetaceans Caused by Naval
Sonar in the Bahamas.Ó Bahamas Journal of Science, 01/05: 2-12.
Cerullo, Mary M. Dolphins: What They Can Teach Us. Dutton ChildrenÕs Books, New York:
1999.
Davies, Nic. Natural World: Dolphins; Habitats, Life Cycles, Food Chains, Threats. Raintree Steck-Vaughn Publishers, Austin and New York: 2000.
Davies, Nicola. Wild About Dolphins. Candlewick Press, Massachusetts: 2001.
ÒEarly Whales Give Birth on Land, Fossil Find RevealsÓ Science Daily: 4 Feb 2009. Available ÒEvolution of Cetaceans.Ó Science Daily. Available online at ÒEvolution of Cetaceans.Ó Available online at ÒIs the Hippopotamus the Closest Living Relative to the Whale?Ó Science Daily: 19 March Jean, Grace. ÒDolphinÕs Brain Holds Secret to More Sophisticated SonarÓ April 2008. ÒNew Fossils Suggest Whales and Hippos are Close KinÓ Science Daily: 20 Sep 2001. Stahl, Dean. Dolphins. The ChildÕs World, Inc., Minnesota: 2001. ÒU.S. Navy Sonar Linked to Whale Strandings, Environmental Scientists ArgueÓ Science Daily: Walker, Sally M. Nature Watch: Dolphins. Lerner Publications Company, Minneapolis: 2008.
For Further Info on this Topic, Check out this WWW Site: www.bahamaswhales.org.
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