Get Email Updates

Get Text Alerts

Sign up for recreational and commercial text alerts

Highlights

“Stranding” is an event where a marine animal comes ashore or near the shore. In order to encompass the many different scenarios by which this occurs, the definitions of “stranding” include:

 

  • An event in the wild where a marine mammal or sea turtle is found dead on the beach or shore or floating in US waters.
  • When a marine mammal or sea turtle is alive on the beach or shore, but unable to return to the water due to sickness or injury or some other obstacle.
  • When a marine mammal or sea turtle is in the water, but is unable to return to its natural habitat without assistance.
 

Strandings can be classified according to which animal is in distress, and what type of stranding is occurring, two equally important factors that determine how experts respond to the situation. Some types of strandings are specific to certain animals.

Types of strandings in the Northeast include:

  • Single Stranding
This occurs when a single individual is found along the beach or onshore, or floating dead in U.S. coastal waters. This is the most common type of stranding. Single strandings have been observed for pinnipeds, small cetaceans, large whales and sea turtles. For certain animals that are amphibious, like pinnipeds, it is very hard to distinguish a stranded animal from one that is resting on the shore. In the case of pinnipeds, stranding responders often monitor an animal for several hours or days to determine its condition.
 

 

 


 
  • Mass Stranding
This occurs when two or more animals strand at the same time and in close proximity to each other. A mass stranding can contain just a few animals to hundreds, sometimes thousands. This type of stranding commonly occurs in communal animals, such as small cetaceans, and may include one or several species. Cape Cod is known to be a mass stranding hotspot within the Northeast region.
  • Unusual Mortality Event
In certain circumstances, there is an increase in the magnitude of strandings or in the mortality rate of a specific species. This magnitude can represent an increase in frequency, age class or some other atypical stranding occurrence. This type of event usually occurs on a larger scale. Often these mass die-offs are attributed to disease or biotoxins. The Marine Mammal Protection Act defines an Unusual Mortality Event (UME) as “a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.” In order for an event to be declared a UME, the relevant data needs to fit into one (or more) of seven criteria. The stranding data is reviewed by an independent group of scientists to determine whether the event is in fact, a UME. If it is determined to be a UME, then NOAA is federally mandated to research the cause of the stranding events. In order to facilitate this, funds are made available to promote this research.
  • Out of Habitat
Situations occur when marine mammals and sea turtles are observed in areas known to be outside their normal tolerance range. Examples include Arctic seals in Florida, manatees in the North Atlantic and beluga whales migrating south of Canada. All of these occurrences are classified as Out of Habitat situations. Many times these occurrences do not result in the animal actually stranding. However, sometimes the animals do need our assistance in order to be returned to their natural environment. In most circumstances, the animal(s) will be monitored by trained stranding responders and veterinarians to ensure that it is not critically ill, and often the animal will require no assistance to return to their optimal range.
  • Oil Spill
When an oil spill occurs, due to the density difference between oil and water, the oil will remain at the surface of the water, forming a “slick.” Any animal that needs to pass through this layer, to breathe for instance, will become covered in oil. The oil is toxic and will affect their internal and external physiology. It is imperative that the animal becomes de-oiled as soon as possible. While this may not be classified as a stranding, stranding network officials typically respond to these animals.

Seasonality of Strandings in the Northeast

Strandings occur year-round in the Northeast Region. However, there are trends that are observed due to the seasonality of the animals’ movements and migration patterns.

  • Winter
Winter sees the migration of the so-called “ice” seals down from the Arctic. Ice seals (hooded and harp seals) are so dubbed due to the fact that they are pupped on the ice floes of the Arctic. Most of these animals have a very short nursing time. Hooded seals are known for having the shortest lactation period in the animal kingdom, only 4-5 days!! After they are pupped, the juveniles travel south. This is a very difficult time for them, as they are learning how to hunt and fend for themselves. They are often seen on the beaches and shores from December through March. Many of these animals may just need to rest onshore to gain strength while others may need medical attention.
 

 

 

Throughout the winter months, certain areas of the Northeast will see an increase in the frequency of mass strandings of dolphins. The causes of mass strandings are still unclear; however Cape Cod typically sees mass strandings of highly social species, such as pilot whales, common dolphins and Atlantic white-sided dolphins.
  • Spring

Spring sees the return of the North Atlantic right whales to their feeding grounds in the Great South Channel and Cape Cod Bay. Right whales are very slow moving and have a tendency to remain at the surface. These behaviors make them particularly susceptible to vessel strikes and gear entanglements.

During the spring months, harbor porpoises are more likely to be inshore and, consequently, strandings increase during this time.

Pupping season for the resident harbor and grey seal populations occurs in the spring. During the nursing period, the mother frequently must leave the pup on a beach while she goes to forage. If a person interacts with this pup while it is on the beach, the mother may abandon it. This abandonment is the cause of many seal pup strandings. Trained stranding responders will often monitor a seal pup for at least 24 hours in order to determine if the mother will return. Later in the spring, juvenile animals that have recently been weaned will often be seen on shore, as they are learning to survive on their own.
 

 

In the spring, sea turtles return to the Northeast Region, but remain in the Mid-Atlantic waters of Virginia, Maryland, Delaware and New Jersey. They are first seen in Virginia in early May, as they migrate to foraging grounds. During this time, the first strandings and entanglements of the season are observed.
 

 

  • Summer
During the late spring and early summer, other large whales (humpback and sei) migrate into the area. This migration increases the frequency of stranded animals, both in the water and on the beach. The presence of these large, often slow moving animals also triggers an increase in incidents of gear entanglements and vessel strikes.
In the summer, sea turtles continue their northern migration and are commonly found in New England waters, as far north as Massachusetts. Leatherback sea turtles have a slightly larger range than the hard-shelled turtles and are commonly found in Maine and Canadian waters during the summer months. The presence of these animals is marked by an increase in observed entanglements and vessel strikes.
  • Autumn

During the autumn months, most of the migratory animals start to leave the area, however we will get reports of strandings as they migrate down the coast.

In the late autumn, as the water temperature drops, sea turtles begin to travel south to the warmer waters of the tropics and sub-tropics. Unfortunately, some of them do not leave the area before the temperatures drop, resulting in cold stun strandings. These temperature-related strandings often begin in October and continue through to December or January.

 

 

During this time, we will also see cases where an animal got caught or blundered into an area outside of their tolerance range, such as a manatee up the Hudson River or a beluga in Cape Cod Bay. These events are often classified as Out of Habitat situations. Usually, the only action taken is to monitor the animal so it is not injured by vessel or fishery activity.
Stranding Reasons
The reason for strandings can divided into two main categories: natural and human related (anthropogenic).

 

Natural:

 

  • Failure to Thrive
For most marine mammals, mortality is high for the young. Once the animal survives its first year or two, chances of long-term survival increase.
 
  • Disease
Most wild animals will carry a burden of parasites; many of which are relatively harmless. However, if an animal becomes immunocompromised due to stress or infection, these parasitic infestations can turn into life-threatening conditions. Wild marine mammals and sea turtles are also periodically plagued by bacterial or viral infections that can affect some part of the population.
  • Biotoxins
Some marine algae produce chemicals that are toxic to many animal species, such as saxitoxin and brevitoxin. In humans, the reaction to these toxins is commonly referred to as shellfish poisoning. Marine mammals and sea turtles can also suffer from this poisoning through a process known as bioaccumulation or biomagnification. These toxins will be consumed by marine herbivores, such as filter feeders or zooplankton. Usually, these toxins are not metabolized, but instead are stored in the animal’s tissues and then will get passed up the food chain as these animals in turn are consumed. These toxins get more concentrated as they are passed up the food chain and can be fatal to animals that feed higher up in the food chain.
  • Predation

Even though marine mammals are mostly considered to be top predators, they can also be preyed upon. Often the predator will be another marine mammal or shark. Typically, the individuals that suffer from predation are the young, the old and those weakened by disease or injury.

Sea turtles are subject to predation throughout their life cycle, but especially in the early stages of life. Sea turtle eggs, which are laid in nests along beaches, are vulnerable to predation by a variety of land mammals, birds and reptiles, as well as human poaching. As hatchlings, sea turtles are extremely vulnerable to land based predators immediately after they emerge from the nest and while finding their way to the water. After they reach the water, they are subject to predation by a variety of fishes (including sharks), reptiles and marine mammals.

 

  • Old Age
Marine mammals and sea turtles have a high mortality rate when they are young. If they can learn to avoid anthropogenic threats and to hunt, they will likely live through their adulthood. Once they pass through their prime adult years, their mortality will increase again.
 
  • Environmental Conditions
Serious weather conditions can adversely affect stranding numbers. If a bad weather system comes through, animals can become disoriented and wash ashore. An extreme example of this is hurricanes; however the Nor’easters of the winter can also have a similar effect.
  • Rock ingestion (Pinnipeds only)
This is a common phenomenon seen amongst pinnipeds (seals) only. These animals have been known to strand and eat rocks or sand. The reasoning for this behavior is not fully understood.
  • Infanticide (Dolphins only)
Infanticide is defined as the act of killing infants. This tactic has been documented in certain mammal populations, such as lions. It is often used to stop the females from nursing, which will bring them into estrus more quickly. Within marine mammals this behavior has been observed amongst bottlenose dolphins along the U.S. eastern seaboard and in Scottish waters.
  • Cold stun (sea turtles only)
Cold stunning is a phenomenon that occurs only in sea turtles. Sea turtles are cold-blooded animals, meaning they are unable to regulate their own internal body temperature. In late autumn, as water temperatures continue to drop in the Northwest Atlantic Ocean, turtles begin to migrate south to warmer waters off the Southeast U.S. and Caribbean. During this period some animals, typically juveniles, are unable to migrate soon enough and suffer from a hypothermic reaction. When this happens their heart rate, circulation, and mobility decrease, and they are often found floating in the water or stranded on local beaches. If these animals are left untreated, they likely will not survive.

Anthropogenic:

  • Bycatch: Entanglement or Capture in Fishing Gear
Marine mammals and sea turtles are susceptible to entanglement or impingement in fixed fishing gear (e.g. pot, gillnet, and pound net gear), both commercial and recreational. These entanglements can vary in degree from minor to life threatening. If the entanglement is life threatening, human intervention is often required to free the animal. This intervention can be both risky and dangerous for both the animal and the disentanglement team.
 

 

Marine mammals and sea turtles are also susceptible to incidental catch in the nets or other mobile commercial gear types (e.g. trawl nets and dredges). This bycatch is unintentional; however it is classified as a “take” under the Marine Mammal Protection Act (MMPA) and Endangered Species Act (ESA). Depending on circumstances and the fishery involved, the animals may be captured alive and released, but often they suffocate and drown in the nets. Many U.S. commercial trawl vessels are required to have turtle excluder devices (TED) installed in their trawl nets, allowing for turtles to escape from the net, rather than becoming caught. The use of TEDs has significantly reduced the number of sea turtle mortalities in trawl fisheries.

 

  • Ship or Vessel strikes
Vessel strikes are a serious threat to marine mammals and sea turtles and have been documented to cause serious injury and mortality. Unfortunately, many collision cases go undocumented because when an animal is struck, it is killed instantaneously and the carcass subsequently sinks.
 
  • Harassment
Harassment can occur in many different forms. The Marine Mammal Protection Act (MMPA) defines “harassment” as any act that has the potential to injure or to disturb by causing a disruption of behavioral patterns such as breeding, migrating, breathing, nursing, feeding or sheltering. An example of harassment is when a seal is resting on a crowded beach and, people or their pets will surround the animal. Harassment can also occur on the water when vessels crowd a whale or dolphin. All of these events can stress an animal. If the animal is already compromised in some other way (e.g. a cut or an infection) this added level of stress can exacerbate the animal’s condition and may cause it to strand.
 

 

  • Ingestion of man-made debris
Very often, trash bags and other garbage get blown out to the ocean. This trash will float at the surface and can be mistaken for food by other animals. Once ingested this garbage can adversely affect the physiology of these animals.
 
  • Contaminants
Oil spills can have catastrophic effects on marine mammals and sea turtles. Not only are animals covered with a slick oil that may have detrimental effects on the ability to swim or forage, but the inhalation of the fumes associated with oil spills can cause degenerative effects within the body. Other contaminants, such as organochlorines, are also being linked to marine mammal mortality.
  • Deliberate Illegal Activities: Gunshot
The Northeast region observes several cases per year of animals that have been illegally shot. This is in direct violoation of the Marine Mammal Protection Act (MMPA) and the Endangered Species Act (ESA), and violators are prosecuted.
  • Pup abandonment
Prior to being weaned the marine mammal pup and the mother will remain in close proximity to each other. During this time, the pup will feed on the mother’s milk. However, intermittently, the mother will need to replenish her energy by foraging offshore. She will leave her pup on the shore as it does not have the strength to swim with her. If the pup is approached by a person, the mother will not return while there are people surrounding it. The pup will then run the risk of being abandoned by the mother. If the pup is abandoned at this point, it will not survive.
  • Noise/Acoustic trauma
The effect of underwater noise is still not completely understood. Stranded cetaceans have been observed with acoustic trauma, such as bleeding in the inner ear and brain. More work is required to determine if there is any significant correlation.

Decisions on the Beach:

Any of the above threats may cause an animal to strand. The stranding network aids and assists these animals once they become disabled. There are three primary principles that the stranding network takes into account when determining a course of action:

  1. The health of the responders and general public is paramount
  2. The need to ease the animal’s suffering
  3. The health of the wild population must not be jeopardized

Once trained stranding technicians arrive on scene, they will survey the site and the animal and make an assessment of the animal’s health.

When assessing LIVE animals, the decisions may appear to be complex, but essentially involve one or more of the following actions:

  • No Action: Leave the animal alone (Pinnipeds only)
Pinnipeds will often “haul out” on the shore. This is part of their natural behavior. They do this to rest or to maintain their internal body temperature. The determination of whether the animal is sick or not, or if a pup has truly been abandoned often requires an observational period. Within the Northeast, a 24-48 hour monitoring period has been established for all pinnipeds that appear to be stranded. This gives the animal a chance to be reunited with its mother or to perform other activities that brought it to the beach. However, if the animal is severely injured or otherwise in need of critical aid, this monitoring period is not followed.
 

 

  • Relocation
Sometimes an animal has found itself in a difficult situation, like a seal on a crowded beach or a dolphin on the bay side of Cape Cod. It can happen that these animals are disoriented or being harassed. In these cases it is in the animal’s best interest to be moved out of harm’s way. An animal may be tagged to ensure that it can return to its natural habitat.
  • Rehabilitation
The ultimate goal of rehabilitation is to release the animal back into the wild. If an animal is deemed unhealthy and in need of intervention, it may be brought in for rehabilitation. Rehabilitation space is another issue that must be considered. Within the Northeast, there are nine Rehabilitation centers. Only a few organizations are able to admit cetaceans, while others are only able to rehabilitate pinnipeds or sea turtles. Organizations within the network are in constant communication with each other to determine where rehabilitation space is available. Unfortunately, there is not always space available requiring the network to consider alternative actions such as euthanasia or relocation.
 

 

 

  • Euthanasia
The well-being of the stranded animal is one of the stranding network’s top priorities. If the condition of a stranded animal is deemed too poor, sometimes the best action for the animal is to ease its suffering. This decision is never approached lightly, and all other options are weighed prior to making this determination. When chosen as the best course of action, euthanasia is always performed under the direction of a trained veterinarian.

For more information on the stranding program, please contact NERStranding.staff@noaa.gov