Research methods used to study whales and dolphins

Scientists use many different methods to study whales and dolphins in the wild. Below is a brief summary of the most common methods used with a few illustrations.  Of these, only a few are easily combined with whale watching, but managers, tour operators and whale watchers alike may be interested to learn more about how researchers learn about whales and dolphins and their conservation needs. 

Boat surveys to study distribution and habitat use:  Meticulously recording the whale and dolphin observations that are made during vessel-based surveys in a particular study area can provide insight into which species are present and at which time of year.  Sightings can be recorded in a non-systematic manner, as is often the case when sightings are recorded from whale watching vessels, or studies can be carried out more systematically, with planned transects that provide even coverage of the target area.  A more systematic approach allows researchers to draw conclusions about where the whales or dolphins are NOT present as well as where they are present.  Only through such a systematic approach can robust conclusions be drawn about the animals’ preferred habitats.

One of the most commonly used research methods, particularly in areas where little is known about the species or whales or dolphins that are present, or their population numbers is the Line transect method.  Researchers define their study area (often a bay, or a strip of coastal waters) and design a method to cover that area as systematically as possible with evenly spaced parallel transects or zig-zags.  They then use a research vessel to navigate these transect lines and record all of the whales and dolphins that they observe as they go along.  By comparing encounter rates (e.g. how many whales are observed per kilometre or per hour searched) in different seasons or in parts of the study area, researchers can also understand whether there are seasonal patterns to the animals’ distributions, or whether certain species prefer shallow or deep habitats, rocky or sandy bottomed areas, rivermouths or open water, etc.  This data can be used to help managers decide where to conduct dolphin watching activities, where to create marine protected areas for whales and dolphins, and where environmental impact assessments for marine or coastal activities need to take whales and dolphins into account.  Data from dolphin watching vessels can be used to perform similar analysis if the vessels are also able to supply information on their daily tracks or search effort, as well as their sightings.  But whale-watching tracks are likely to be biased toward the known ‘hotspots’ for whales².  Line transect methods can also be used to generate abundance estimates (see below for more detail).

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Photo identification: Individual whales and dolphins can be recognized over time using photos of either the undersides of their tail flukes³, their dorsal fins⁴ or, most recently, in the case of bottlenose dolphins, underwater photos of their faces⁵.   In well-studied populations, such as the humpback whale feeding grounds in Alaska and the Gulf of Maine, or the bottlenose dolphins of Sarasota Bay, some individual whales and dolphins have been monitored for over 40 years⁶.  By monitoring where individuals are observed form one season or one year to the next, observing when they have calves with them, and documenting how long it takes calves to reach adulthood and independence, researchers can learn about important aspects of different species’ life history, growth and reproduction. By comparing the photo-identification catalogues in different study areas, researchers can establish connections between feeding and breeding grounds of migratory species like whales⁷, or determine whether or not there is any movement and exchange between neighbouring populations of the same species⁸.    Photo identification is one of the research methods most effectively combined with whale watching, as has been the case, for example, in the Gulf of Maine, where whale watching data has contributed to over 75 peer-reviewed scientific papers on humpback whales and other species. The species accounts in this handbook include examples of photos used in the identification of individuals of each featured species. This may inspire whale watch operators, guides, and perhaps even tourists with good zoom lenses and good photography skills to use their next whale watching trip as an opportunity to contribute to science and conservation.

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Genetic Sampling:  Genetic sampling is becoming an increasingly important tool to understand whales and dolphins and their conservation needs.  Samples can be collected opportunistically from dead or live stranded or entangled animals, or from the bits of sloughed skin that remain on the surface of the water after a whale breaches⁹.  In dedicated genetic sampling surveys researchers use poles tipped with scrubbers¹⁰, crossbows¹¹ or modified paxarms guns loaded with hollow-tipped darts to collect skin samples from free swimming whales or dolphins. The samples can be used to determine the sex of the sampled animal¹² and its relationship to other sampled animals in the population (e.g. parents, offspring, siblings)¹³. At a population level, with an adequate number of samples, scientists can determine whether a group or population of sampled animals are related to another (neighbouring) group¹⁴, or whether they comprise a discrete or isolated population¹⁵, or possibly a new sub-species¹⁶ or species¹⁷.  Genetic sampling is not easily combined with whale watching, as it only preformed under strict permitting conditions that allow the close approaches necessary for sampling, and requires highly experienced research staff.

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Satellite tagging and time-depth recorders:  It is impossible to follow individual animals with a boat 24 hours a day for extended periods of time. To better understand the movement and behaviour of individual whales, researchers apply satellite tags or sensors that either adhere to whales’ skin with a suction cup or are temporarily anchored into the blubber just under the skin¹⁸.  Time–depth sensors can measure the depth and duration of whales’ dives and provide important information on their feeding locations and behaviours¹⁹.  Satellite tags transmit signals that reveal whales’ positions at regular intervals and provide insight into their long range movements beyond the areas and time frames in which they can be directly observed by researchers.  Satellite telemetry data has yielded valuable and sometimes surprising information about migratory whales.  The time and distance between transmitted positions allows researchers to determine when and where whales are swimming quickly and in transit, and where they slow down to either feed, rest, or socialize^20-22.  Some satellite telemetry studies have also demonstrated connections between feeding and breeding grounds^23,24 or migratory routes that researchers would not have otherwise suspected existed^20,25.  Satellite tagging is also not easily combined with whale watching, as it requires specialist equipment, highly experienced personnel, and close approaches to whales only possible under special permit.  In some areas, such as the Antarctic, however, cruise ships that host researchers are able to launch small inflatable vessels manned only by the research team for satellite tagging purposes.

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Acoustic studies:  Another means of learning about whales’ and dolphins’ whereabouts or behaviour when they cannot be directly observed is through acoustic monitoring. Underwater microphones called hydrophones can be used in conjunction with boat surveys to detect and record whale vocalizations or (in the case of humpback whales) song.  They can also be towed from vessels to detect the presence of whales or dolphins in poor visibility conditions (e.g. at night), and can be effective to detect deep diving species that rarely reveal themselves at the surface.  Passive acoustic monitoring through the placement of rugged stationary underwater recording devices with long-life batteries can allow researchers to monitor the presence of different whale and dolphin species year round, and detect daily or seasonal patterns in their presence or vocalizations.

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Estimating population size:  While knowing how many whales or dolphins are present in a particular area is one of the most important questions to address for management and conservation, it can be one of the most difficult to answer.   How do researchers count animals that spend most of their time under the water and occupy areas extending hundreds of square kilometers? The two most commonly used methods are:

1. Line transect: With a more rigorous application of the line transect methods above, researchers can us the information on how many whales or dolphins they directly observed on each transect to calculate the density of whales or dolphins in the whole study area²⁶.  In order for this to yield a robust estimate, the transects need to provide an even coverage of the different types of habitat in the survey area, and observers need to be well trained and meticulous in their observations and data recording procedures. This is not easily combined with whale watching. 
2. Mark-recapture: In addition to yielding information on the life histories of individual whales, photo-identification data can be used to generate population estimates by using formulas to calculate the total population based on the proportion of animals that are re-sighted (photographed or ‘captured’) from one survey or field season to the next^27,28.   The underlying concept can be explained with the following analogy:  the chances of bumping into the same people from one day or one year to the next as you walk down the road are much higher in a small village of 200 inhabitants than they are in New York City.  Similarly, if you take photographs of whales in your study area and keep seeing the same whales from one survey to the next, the chances are that you are dealing with a small population rather than a large one.  Photos collected from whale watching platforms can contribute to mark-recapture studies, but researchers need to account for the possible bias that may result if whale watching tours are returning to the same area day after day, year after year.  Repeated re-sights of known individuals in the same small area may yield a misleadingly small population estimate – akin to estimating the human population size of New York City based on repeated re-sights of the loyal customers you run into regularly at a particular Starbucks rather than walks around the whole city.

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Stranding analysis:  In some locations logistics, funding, or security constraints make it difficult or impossible to conducted dedicated cetacean surveys at sea.  In these places information about whales or dolphins that have washed up onto shore may provide some of the only available data about the occurrence and distribution of different species²⁹.  Even in areas where boat-based cetacean surveys are possible, the examination of stranded animals can provide insight into the occurrence of rarely observed species, causes of mortality, and can provide access to valuable tissue samples for genetic analysis and stomach contents for analysis of diet and prey³⁰.  Whale watching operators and members of the public can play an important role in alerting researchers and authorities to the presence of live or dead strandings, either on beaches or at sea.

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