Vanessa Brown, Gene Smith, and Briana Weldon

[Editorial note from Dr. Young: Technically, the term "mass stranding" refers to a large group or pod of cetaceans which come ashore as a group, alive and apparently healthy, but usually end up dying on the beach. The term "die-off event" refers to an unusually large number of animals which strand one at a time (although often many per day), often dead or dying, over a fairly defined geographic area and over a period of days, weeks, or even months in severe cases. Mass strandings are still very mysterious, while die-off events usually have a well-defined cause, such as an epidemic or red tide event. The paper below refers to both categories as "mass strandings."]

Mass stranding is defined as a group of cetaceans that have become beached or trapped in water too shallow to allow the animals to survive. This is generally one species , but occasionally mixed species that are stranded together in one area of coastline. There are several possibilities to why mass strandings occur. Some of the more popular ideas are presented in this paper.

There are many reasons why these cetaceans strand, and below are some of the reasons we think marine mammals, particularly cetaceans, strand in big groups. The first reason why strandings of great proportions occur is by illnesses. Some illnesses include viral diseases, bacterial diseases, and internal parasites. The three viral diseases that make a huge impact on cetaceans are dolphin pox, hepatitis B, and the deadly morbillivirus. Dolphin pox is also known as ‘tatoo’ which demonstrates predominant lines of hyperpigmentation of the epidermis which is located on the dorsal body, flippers, fins, and the fluke. Hepatitis B has periods of inactivity, and shows anorexia, and icturus. The morbillivirus is seen in the pulmonary, and central nervous systems as lesions (Moeller; 1998). Some of the bacterial diseases are erysipelothrix rhusiopathidae, pseudononas infection, edwardsiella, salmonella, staphylococcus, clostridial disease, and klebsiella. Erysipelothrix rhusiopathidae is a skin disease, and if it is left untreated the cetacean will die. Pseudononas infection causes serious ulcers in dolphins, and can be transmitted to humans through cuts and abrasions. Edwardsiella causes hemorrhaging, and salmonella is a great concern in many marine mammals. Staph is usually seen in captive dolphins along with cases of pneumonia. Clostridial disease produces gas build up in dolphins, and klebsiella is associated with pneumonia in cetaceans. Internal parasite cause a great concern in cetaceans, and an example is stenurus which is a common nematode. This is located in the pulmonary parenchyma, and causes nodules which are filled with this parasite. This parasite will migrate, and fill the tympanic bullae.

Another reason why we think mass standings occur is because of geomagnetic disturbances. This causes cetaceans to make mistakes in geomagnetic topography. This is caused by disorientating the pattern of movement. This also indicates that cetaceans are using geomagnetic time information to reset a ‘biological travel clock’ (Moeller; 1998).

Other additional reasons for mass strandings are predation from other marine mammals, pollution and human intervention (from river runoff, oil spills, litter, poisoning, , and fishing nets), sonar testing (from LFAS, and acoustic), environmental effects (such as El Nino, salinity, and temperature changes), and finally, last but not least, behavioral changes such as feeding patterns of cetaceans. Even though these are our reasons of why mass strandings and single strandings occur there is no single cause of why. This leaves a wide range of other reasons open to individuals.

Little is known about much of cetacean biology due to their aquatic existence. Mass strandings and single strandings provide a unique opportunity to study cetaceans. The Natural History Museum is one example of an organization that has a marine mammal stranding program, that has been studying cetaceans since 1960. Knowledge gained from detailed necropsies provide insights to possible causes of mass strandings.

The real value of necropsies becomes apparent when the records add up to view asegment of the population that strands on our beaches. Recent recordings of mass strandings of cetaceans around the world have been linked to the possible causes which were mentioned previously.

For instance, a mass stranding of the Cuvier’s Beaked Whale in May 1997 was recorded. It is believed that the mass stranding coincided closely in time and location with military tests; of an acoustic system for submarine detection being carried out by the North Atlantic Treaty Organization (NATO).

From the morning of the 12th of May 1997 to the afternoon of the 13th of May, 12 recorded beaked whales were stranded alive along the coast of Kyparissiakes Gulf (Frantzis, 1998). Frantzis found that sound detecting system trials, had been performed by NATO research vessel from 12:00a.m. on the 11th of May to 12:00a.m. on the 15th of May, a period that encompassed the mass stranding. It was officially declared that the area where the sea trials had been carried out enclosed all the coordinates of the stranding points.

The Low frequency Active Sonar (LFAS) tests may have panicked or harmed the hearing of the whales in the Mediterranean, causing them to lose their way and die. It is suggested that noises travel hundreds of kilometers underwater and may have also been responsible for a dozen whales that beached in Greece in 1996.

Only seven mass strandings of Cuvier’s Beaked Whales, where more than 4 were stranded, have been reported worldwide since 1963. After necropsies of the stranded whales in 1997, Frantzis, could not find any abnormalities or wounds and that they had recently eaten. Frantzis also calculated that the probability of the latest stranding not being due to the LFAS tests was less than 0.07% (Frantzis, 1998). The LFAS tests may have damaged the cetaceans hearing, in which the whales use for navigation causing them to strand.

Geomagnetic disturbance of cetaceans as mentioned previously, is a possible reason for mass strandings. Cetaceans make the key mistakes, which results in live strandings at some distance from the shore. The disturbances implied by the analyses fit well with the existence of major choice points in the geomagnetic topography of the usual migration routes. It is believed that live strandings are associated with geomagnetic disturbances (Klinowska, 1985).

Seventy-one dolphins were stranded alive on Cape Cod, Massachusetts. Knapp, a spokeswoman for the New England Aquarium, led the recovery and rescue attempts and believes that Cape Cod has the most mass strandings of dolphins anywhere in the world. Only 16 to 18 of the stranded dolphins were able to be herded back to sea (Knapp, 1998). Geomagnetic disturbance is a possible cause for this case of mass stranding. The topography and the coastline of Cape Cod may have influenced this mass stranding.

Human intervention and pollution are also potential causes for mass strandings. In 1994, 11 sperm whales were beached alive on the Island of Sanday in Orkney, North Scotland. All the animals died a short while after. Necropsies of the whales were performed and no cephalopod flesh or fish remains were found which suggested that most of the whales had not been feeding prior to the stranding (Stantos, 1995).

Sperm whales are rare in the North Sea and sightings of more than one animal are exceptional. The sperm whales may have been members of a single group as they are known to stay and travel together. Fishing activities may have significantly influenced the mortality of cetaceans. The sperm whales in this example may have been affected by certain fishery and were in search of a food resource in a different place.

Another example of a fishery having an affect on cetaceans is a mass stranding on the Galician coast (north-west of Spain), from 1993 to 1994, where 65 small cetaceans were stranded. The stranded species were: 41 common dolphins, 7 long finned pilot whale, 5 bottlenose dolphins, 5 Risso’s dolphins, 4 harbor porpoises and 3 striped dolphins. The stomach contents of each of the species were examined. Most of the species examined had been feeding in coastal waters. For example many of the common dolphins, normally thought of as living inshore waters had been feeding on gobies which are offshore fish. Many of the fish species eaten are of importance to human fisheries, but there are currently insufficient data to adequately quantify possible impacts on fisheries.

In 1987, during a 5 week period in November, 14 Humpback whales, Megaptera novaeangliae, died in Cape Cod after eating Atlantic mackeral, Scomber scombrus, containing saxitoxin (STX), a dinoflagellate neurotoxin responsible for paralytic shellfish poisoning in humans and whales (Geraci et. al, 1989). It is believed that the toxin accumulated in the Gulf of St. Lawrence and delivered it to the Gulf of Maine and Cape Cod Bay in the fall of 1987.

The planktonic toxins move through the food chain and is eventually consumed by the cetaceans. This planktonic toxin offers new insights into natural mortality and strandings of marine mammals.

Environmental effects such as El Nino, salinity and temperature changes are also recognized as potential causes of mass strandings. The Texas Marine Mammal Stranding Network (TMMSN), predicts a bad year for strandings in 1998 along the Texas Gulf, due to stormy weather patterns brought about by the El Nino phenomenon. Dr. Graham Worthy, from (TMMSN) believes that the El Nino weather pattern is expected to bring a cold, stormy winter to the Gulf coast which will increase the likelihood of marine mammal strandings, especially live strandings. There has already been an increase in the number of strandings in December 1997. This increase in Texas strandings last December was almost twice that of the 1996 and may be indicative of what can be expected in 1998 (TMMSN, 1998). Though most of the animals are unfortunately not found alive, the research provided by studying them provides valuable insight into the coastal environment.

According to the Texas Marine Mammal Stranding Network (1998) March has historically been the most active stranding month along the Gulf coast of Texas. According to the Marine Mammal Stranding Network (1998) there have been several strandings of cetaseans since June 27,1998. The majority of these strandings have been harbor porpoises. Strandings usually correlate with migration patterns. The strandings that we saw earlier in the semester were probably some of the same groups that were found stranded earlier in the year. Animals die of natural causes at all times of the year. Also any diseases that may be affecting these animals would cause deaths most of the year. The statistical data to support these ideas is not complete because few strandings can be identified with a definite cause.

The true reason for mass strandings of cetaceans is not known. As more data is accumulated on the distribution and timing of cetacean strandings the answer may draw near. The answers may lie in necropsies of stranded animals which are being performed as often as posible. There may not be one factor causing mass strandings, there may be several factors combined. As the number of cetacean strandings are increasing there is a noticeable change in weather patterns. For examlpe, El Nino, and a relationship between the two. With the number of strandings that occur with no known reason, is it at all out of the question to think that these possible factors are just coincidental, and that there is no real reason for the mass strandings of cetaceans?

Frantzis, A. (1998). Does Acoustic Testing Strand Whales? Nature, vol. 392:6671.

Geraci, J.R. et al. (1989). Humpback Whales (megaptera novaeangliae) Fatally poisoned by Dionflagellate Toxin. Canadian Journal of fusheries and Aquatic Sciences, vol. 46:11.

Klinowska, M. (1985). Cetacean Live stranding Dates Relate to Geomagnetic Disturbances. Aquatic Mammals. vol. 11:3.

Knapp, S. (1998). Dolphin Death Toll Tops 70 on Cape Cod. Wellfleet.

Moeller, R.B. (1998). Diseases of Marine Mammals. United States Army Medical research Institute of Chemical defense.

Stantos, M.B. (1995). Diets of Sperm Whales Stranded in Scotland.

Texas Marine Mammal Stranding Network. (1998). <www.tmmsn.html>.

Texas Marine Mammal Stranding Network. (1998). Stranding Statistics. <www.tmmsn.org/strandings/statistics.html> .

Marine Mammal Stranding Center. (1998). Stranding Summary. <www.mmsc.org/blowhole/strandings.html> .

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