What Can Marine Mammal Photo-Identification Tell Us?

We use photos to identify, catalog, and study marine mammals. These photos provide important information about marine mammals such as:

• Population size and trends
• Range and distribution
• Habitat use and site fidelity
• Diet and feeding behavior
• Reproduction, life span, and social structure
• Health: body condition, disease, and wound healing
• Environmental threats 
• Human threats

Population Size and Trends

An important goal of photo-identification research is to develop abundance estimates, something very similar to a human census. An abundance estimate is the inferred number of individuals in a population. One way to calculate this estimate is using capture-mark-recapture methods. For small terrestrial species, this process involves capturing a portion of the population and marking individuals in some fashion (often with a band, tag, or tracking device), releasing them back into the wild and then returning to the site again at a later time to capture another set of animals that may include individuals previously marked (recapture). 

For many aquatic species like marine mammals, physically capturing and marking individuals is not feasible. Instead, we use a modified method called capture-recapture using photo-ID. Instead of applying a mark to the animal, we take photographs of individuals in a population and identify natural markings on their bodies that are unique to each. This is the “capture” part of the process. During the “recapture” phase, more photos are taken at a later date. These could include resightings of animals seen during the first “capture” survey and some may be “captured” for the first time. We estimate the population size based on models that incorporate the resighting rates of animals. These estimates take into account the proportion of animals in the population that are “marked” (those with nicks and notches) versus clean or “unmarked” animals. These types of analyses allow us to monitor population trends over time which are very valuable to management and conservation of the species.

Learn More:

• Patterns of association and distribution of estuarine-resident common bottlenose dolphins in North Carolina 

• Survival, density and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill

Range and Distribution

Once we identify individual animals using photo-ID, we can use subsequent sighting locations to study their movement patterns. Visual observations documented by photo-ID provide information on the range and distribution of individuals within a population. A population is a group of individuals of the same species that interbreed with each other in a given area, and each species may contain one or more populations. Examining each location an individual was sighted provides information as to the geographic area in which that individual travels. We then compare catalogs between areas to determine whether or not the individuals have been seen in other photo-ID survey areas. 

Some species have large geographical ranges. For example, one sperm whale was identified from photographs taken in the Bahamas and the same animal was found in a photo-ID catalog from the Azores—more than 3,000 miles away! 

Alternatively, comparing photos from multiple regions helps us determine if there are separate populations. For example, if we compare photos from several bays, sounds, or estuaries and only find a small number of matches, or none at all, it’s likely that there are unique populations in each location. We can further investigate this using physical characteristics and genetics. Recently, scientists used these three tools together (photo-ID, morphometrics, and genetics) to not only identify a unique population of whales, but an entirely new species—the Rice’s whale!

Learn More:

• Long Range Longitudinal Movements of Sperm Whales in the North Atlantic Ocean Revealed by Photo-Identification
• Using Photo-Identification and Genetic Data to Examine Fine-Scale Population Structure of Common Bottlenose Dolphins in the Estuarine Waters Surrounding Savannah, Georgia
• Common bottlenose dolphin abundance and distribution patterns in St. Andrew Bay, Florida, USA

Habitat Use and Site Fidelity

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Tracking individuals with photo-ID provides information about an animal’s habitat use and site fidelity. Site fidelity is a term used to describe an individual’s tendency to routinely spend time in a particular location or area. For example, an individual may prefer to hunt regularly in certain areas and rest often in another. We would therefore consider that animal to have high site fidelity to those two habitats. Animals may be photographed and observed feeding, traveling (migrating), mating, or with newborn calves more often in certain areas, which tells us which specific behaviors take place in a particular habitat. Habitat use may vary seasonally and depend on natural factors such as the presence of predators and prey, or human influences such as noise pollution and vessel traffic. Sudden changes or long-term shifts in habitat use may alert us to environmental changes, threats or disturbances in the habitat. NOAA Fisheries uses this scientific information to minimize interactions between marine mammals and various industries like wind, shipping, aquaculture, tourism, construction, and commercial fishing when the animals are using certain habitats at different times of year.

Learn More:

• Seasonal abundance and site fidelity of bottlenose dolphins in Mississippi Sound

Diet and Feeding Behavior

Photo-ID surveys provide opportunities to observe animal behavior. During surveys, we may encounter animals that are feeding, which tells us about their prey and habitat use. For example, rorqual whales, like humpback and minke whales, migrate seasonally to certain areas to feed. These whales have been routinely documented in certain geographical areas exhibiting feeding behavior. Their feeding strategy involves taking in mouthfuls of water filled with small fish, krill, or plankton then pushing the water out through their baleen plates with their tongue while retaining the food in their mouth. Certain populations of bottlenose dolphins chase fish, like mullet, onto mud banks and briefly strand themselves while catching them. These behaviors are documented with photos and written observation. Since photo-ID can be used to identify individuals and mom-calf pairs, we can also use this method to document evidence of social learning where certain behaviors are observed and imitated within and among social groups.

Knowing the type of prey a species feeds upon, the strategies it uses to catch the prey, and where the animals find their prey are important data that can be collected during photo-ID surveys. These data are provided to conservation managers who are tasked with protecting prey resources, minimizing potential threats in feeding grounds and evaluating potential industry projects to ensure the plans will not prevent animals from accessing their prey source.

Learn More:

• Observations of a benthic foraging behavior used by common bottlenose dolphins in Barataria Basin, Louisiana, USA
• A common bottlenose dolphin prey handling technique for marine catfish in the northern Gulf of Mexico
• Killer whales attack a school of pantropical spotted dolphins in the Gulf of Mexico

Reproduction, Lifespan, and Social Structure

Reproduction 

The ability to track marked individuals through long-term photo-ID projects can provide information about calving intervals and calf survival. When an adult is photographed with a calf on multiple, consecutive occasions, it is likely an adult female with her offspring. Collecting images of mother and calf pairs provides knowledge on how long calves stay with their mother, as well as how long it takes for a certain species to reach a mature reproductive age.

From photo-ID surveys, scientists have learned that:  

• Common bottlenose dolphins reproduce about every 2–3 years
• Common bottlenose dolphin calves stay with their mom for 2–6 years
• Sperm whales produce a calf every 5–7 years
• Sperm whale calves stay with their mom between 4 and 21 years
• Female sperm whale calves mature faster than males
• Male sperm whale calves stay with their moms longer than females

Life Span

Researchers also use photo-ID to document when individuals are born and when they die. This helps us determine the average lifespan for marine mammal species. Information about a population’s reproductive timing and success, maturation rates, and lifespan allows managers to assess a species' vulnerability to population decline or extinction. Several photo-ID studies have provided a wealth of information for shorter-lived marine mammals like common bottlenose dolphins—which commonly live at least 40 years. 

Learn More:

• Reproductive outcome and survival of common bottlenose dolphins sampled in Barataria Bay, Louisiana, USA, following the Deepwater Horizon oil spill

Social Structure

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Photo-ID research provides us with information about the social structure of marine mammals. Social structures may vary by species, population, and location. For example, some species, like large sei whales are routinely photographed in smaller social groups of one to five animals, but smaller cetaceans, like spinner dolphins, often travel in much larger groups of a few hundred or more. 

For some species, like the common bottlenose dolphin, we investigate social bonds using photo-ID to determine which individuals spend the most time together. Bottlenose dolphins have been known to form male pair-bonds in which two or three males meet as juveniles and form a strong attachment to each other, often choosing to travel with each other for their entire life! Other species like pilot whales and sperm whales form social groups consisting of related females. In these groups, you may see one or more sets of grandmothers, mothers, and offspring routinely traveling together.

Learn More:

• Fine-scale social and genetic structure of common bottlenose dolphins in the Barataria Basin, Louisiana, USA

Health: Body Condition, Disease, and Wound Healing

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Tracking individuals over time allows us to document and monitor health and the development of skin diseases, the healing process of wounds, and the overall body condition of an animal. For example, in the photos above, animal #144 was first photographed on August 2, 1994. In November, 2013 the animal was photographed with some whitish-raised areas on the leading edge of the dorsal fin. The animal was photographed again in March 2019 and the white raised areas had spread lower on the fin and down onto the animals’ sides, giving us information on the timing of the disease progression.

The same process is used to understand wound healing. The above photos show Biscayne Bay animal #218 in September 2007 with a healing shark bite wound and then again three months later in December 2007 with a healed scar. Both animals #144 and #218 were photographed again during recent surveys in Biscayne Bay. Using photo-ID, we can get a sense of the prevalence of these threats to the population as well as the survival rate.

Photo-ID also provides insight on overall health and body condition, and is sometimes the first indication of an issue. For example, if we see a thin animal that looks “bony”, the animal may be having trouble eating or digesting its food. If several animals in the population appear thin at the same time, this may indicate a decrease in food availability or other health threat. If we document a pattern of animals in a population appearing thin only during a certain time of the year, this changing body condition may be a normal part of their life cycle. Having long-term photo documentation of individuals in a population allows us to develop a baseline for comparison and helps researchers and managers quickly recognize health threats and act accordingly.

Environmental Threats

Marine mammals are regularly impacted by changes to their environment. Some changes may be subtle and occur over extended periods of time such as climate change and changing water temperatures; others may be more sudden and severe as in large storm events like hurricanes and tropical storms, algal blooms, or freshwater influx—sometimes associated with extreme freshwater discharge from watersheds. Photo-ID research helps us track how these environmental changes may affect marine mammals. 

Hurricanes and Large Storm Events

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Large storm events can cause severe flooding. During these instances, marine mammals can become displaced, especially coastal species like bottlenose dolphins. Areas that are not normally accessible to marine mammals may become covered in several feet of water from excessive rainfall and storm surge. Animals may then be pushed into these areas by storm surge or swim into these areas before the water recedes. For example, animals have been reported in areas with no access under normal conditions such as drainage ditches/canals, enclosed lakes/ponds, or even on flooded private property located along these areas. They may also be discovered up-river, quite far from their normal habitat. If the animal can be identified by comparison to local photo-ID catalogs, it provides information about the animal’s natural home range. Knowing their home range allows us to assess the probability that the animal would find its way home while the area is still flooded or where to release it if it needs to be rescued and relocated. 

Learn More:

• Displaced dolphins: Post-hurricane Response

Algal blooms

Algae range from single-celled organisms to multicellular simple plants and occur naturally in aquatic environments, often acting in a key role as the primary producer at the base of the ecological food web. Sometimes these algae start to multiply exponentially which can have harmful effects on humans and marine life—this is known as a harmful algal bloom. These blooms can sometimes harm whales, dolphins, and manatees. In the southeast region of the United States, the three most common types of harmful algal blooms are caused by Karenia brevis, otherwise known as “red tide”; cyanobacteria or blue-green algae; and Aureoumbra lagunensis, also known as “brown tide.” Algal blooms can have both indirect and direct impacts on the survival of marine mammals. Some blooms deplete oxygen levels in the water killing off seagrass, invertebrates, and fish. This may indirectly affect marine mammals by depleting food sources. In other cases, the algae can produce toxins that directly affect the nervous and respiratory systems of marine animals and lead to mortality. Either can lead to an unusual mortality event.  

Photo-ID surveys are used to document individual habitat use prior to, during, and after algal blooms. We look for shifts in home ranges and foraging areas. Identifying individuals that may have stranded and died during an algal bloom sometimes allows us to categorize the cause of death. We also include the stranding date in the photo-ID catalog as part of the animal’s life history. Knowing which individuals have died allows us to flag their ID number in the catalog so that it will not be used for future matching purposes.

Learn More:

• Comparative analysis of three brevetoxin-associated bottlenose dolphin mortality events in the Florida panhandle region (USA)

Freshwater Impacts

Marine mammals rely on salt water habitats in oceans, estuaries or lagoons. Common bottlenose dolphins regularly inhabit several estuaries and lagoons in the Southeast. These dolphins can withstand brief periods of time in low-salinity water and are occasionally observed up rivers, away from their usual, more salty habitats. Sometimes, dolphins may be displaced to more freshwater areas during floods or high tide and may not be able to retreat back to saltwater habitats when the water recedes. Freshwater discharge into estuaries, lagoons, and coastal ocean waters can decrease salinity and pose a threat to marine mammals. When dolphins are exposed to excess fresh water, they can develop a suite of health issues such as  skin lesions, pale skin, or internal injury, which may lead to poor body condition or death.  

Pale skin, peeling skin and skin lesions are external impacts that may be photographed during routine photo-ID surveys. Identifying the impacted individuals using photo-ID methods allows us to document the number of individuals in the population that are impacted by freshwater intrusion. We use this information to estimate marine mammal survivability, healing rates, or mortality rates after a freshwater intrusion event. 

Human Threats

We also use photo-ID surveys to document evidence of human interactions. This gives us a better understanding of the threats these animals encounter such as vessel and fishery interactions, and marine debris. Sometimes, we capture photos of entangled animals. This allows us to quickly notify our Marine Mammal Health and Stranding Response Program. This team will closely monitor the animal to determine if the entanglement is life threatening, and if it warrants intervention.  Photo-id also helps us understand the rate of human interactions especially in comparison with other studied populations.  This information is important to managers in knowing where to direct resources and efforts to reduce threats to the most impacted or vulnerable populations. 

Vessel Interactions

Our photo-ID surveys allow us to document fresh wounds or scar patterns likely attributed to vessel interactions. For example, the photo above on the right shows parallel scars on this dolphin’s tail which appear to be from a boat propeller strike. While these instances allow us to recognize specific individuals, they also highlight the importance of studying these animals and the threats they face from human activities. 

Interacting with Marine Mammals

It is illegal to harass marine mammals in the wild, which can occur when people closely approach, follow, or interact with the animals, causing a change in their behavior. This includes touching, attempting to feed, feeding, or getting in the water to swim with them. Human activities that cause harassment of the animals are violations of the Marine Mammal Protection Act, which carries civil and criminal penalties. Our photo-ID surveys are conducted under scientific research permits that allow us to approach the animals safely and carefully to limit disturbance, in accordance with the Marine Mammal Protection Act. If you see dolphins in the wild, put your vessel in neutral and give the dolphins at least 50 yards of distance.  Never feed or attempt to feed a wild dolphin, it is dangerous for both you and the dolphin.

Fishery Interactions

During photo-ID surveys, we sometimes observe marine mammals swimming near commercial or recreational fishing vessels or interacting with fishing gear. We have also encountered dolphins and whales entangled in line, rope, and netting. This is reported to our Marine Mammal Health and Stranding Response Program staff who provide instructions for the appropriate response. If the entangled animal is one that has been recorded before, their previous sighting locations can be used to help inform potential disentanglement response efforts —another benefit of our photo-ID catalogs. Photos obtained of entangled animals also sometimes allow scientists to identify the gear type the animal is entangled in, giving managers insight to potential interaction rates with certain fisheries and information on how to better minimize these interactions in the future.

Marine Debris

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Marine debris is any human-made material that ends up in our waterways like microplastics, soda cans, plastic bags, larger discarded items, and more. Marine mammals can become entangled in some of these items like discarded ropes, fabric, or plastic which can become embedded in the animal’s skin as it grows. In addition, animals often ingest discarded plastic items and bags, which can lead to serious internal injury—like tearing the digestive tract—and causing blockages. These situations can prevent proper digestion and eventually lead to death. 

What Can You Do?

If you see a trapped, injured, or dead marine mammal, please immediately call trained responders. Across the Southeast Region, from North Carolina to Texas, call (877) WHALEHELP, (877-942-5343). Do not attempt to move, feed, or intervene with the animal(s) in any way. If possible, wait with the animal at a safe distance until a trained responder returns your call. Be prepared to describe the animal’s size, color, and physical characteristics, provide the animal’s exact location, and provide a photo taken from a safe distance.