The ability to recognize individual animals, whether through the use of tags, bands, or naturally-occurring marks, facilitates the study of their demography and behavior.
Of all of the naturally-occurring marks on humpback whales, the pigment pattern on the ventral surface of the flukes is most commonly used to identify individuals. These patterns are present at birth, although they may be hazy in calves and other young whales. Dorsal fin shape is also helpful, as are persistent scars on any visible part of the body. In the Southern Hemisphere humpback whales can be matched based on the pigmentation patterns along their flanks.
This image (above right) shows the ventral fluke pattern of a humpback whale named "Patchwork". Matching a fluke photograph like this to a catalog of individuals takes good observational skills and patience. We focus on three things, in particular: pigmentation, distinctive marks and trailing edge shape. Taken together, these features of a humpback whale fluke are like a fingerprint, no two individuals are exactly alike.
Fluke pigmentation ranges from all white in some individuals to all black in other individuals, with the majority of individuals lying somewhere in between. When black pigmentation is present it may be limited to the core, or it may extend outward along the top and/or bottom of the flukes. Note that the yellow color on the flukes in the picture above is not pigment, but a temporary coating of diatoms (algae).
2. Distinctive marks or scars
It is helpful to focus on one or more specific marks or scars. Sometimes there are unusual or prominent shapes in the pigment, like the black blotch on the lower right side of the fluke shown above. Humpback whale flukes often have circular scars, linear scratches and other marks that make them distinctive.
3. Trailing edge shape
The trailing edge ranges from being perfectly smooth to having noticeable 'hills' and 'valleys'. Sometimes the 'hills' are quite round, but they can also be pointy. The trailing edge is a very useful tool when trying to match whales without distinctive pigment patterns (for example, whales with nearly all-black flukes).
The ease of matching depends greatly upon the quality of the photograph (distance and angle from the subject, as well as exposure). In addition, whales do acquire marks (scratches, nicks and notches) during their lifetime which can alter the appearance of the tail. Finally, a small proportion of whales experience substantial pigmentation changes that can make re-identification difficult. These types of changes generally occur within the first three years of life (see Carlson et al. 1990).
Now that you've learned the basics, you can give fluke matching a try. Click here to try our matching game.
Understanding genetic population structure is critical to the conservation of endangered species.
The program’s longest standing collaboration is with Drs. Per Palsbøll and Martine Berube (currently at Stockholm University). These geneticists are undertaking detailed molecular genetic analyses to identify first order relatives (mothers, fathers and siblings) based solely on skin samples. In large whale species, maternal relatedness can only be known by observation if an individuals seen in its year of birth when it is still dependent on its mother. Paternity can not be known by observation at all. The Humpback Whale Studies Program strives to obtain data from each individual Gulf of Maine humpback whale at least once in its lifetime to contribute to this important molecular genetic study. These and other genetic data are being used for detailed insight into population structure, population size and the mating system. Molecular genetic matching also allows individuals to be identified even after death, when distinguishing pigmentation has been lost.
Cetacean genetic data is generally obtained from skin samples. Pieces of naturally-sloughed skin can sometimes be collected from the water after a whale has been active (breaching, lobtailing or flippering) at the surface (see Clapham et al. 1993, "High energy behaviors in humpback whales as a source of sloughed skin for molecular analysis") Unfortunately, sloughed skin can only be collected on an opportunistic basis, may not be attribued to the correct individual when more than one whale is present, and does not always provide enough high quality DNA.
More commonly, skin samples are by biopsy sampling. In this procedure, a small tissue sample is obtained by firing a modified arrow from a cross bow (see above). When the arrow bounces off the whale, it retains tissue in the sampling tip and floats at the surface until it can be retrieved. PCCS and others have studied the reaction of whales to this procedure and do not believe that it causes significant harm in the short- or long-term. In fact, we observe the same range of reactions when a whale is missed entirely, indicating to us that most individuals are simply startled by the procedure (see Clapham et al. 1993, "Reactions of humpback whales to skin biopsy sampling on a West Indies breeding ground").
We also continue to develop other scientific uses of these tissues. Biopsy samples can now be used to measure contaminant loads, foraging preferences, pregnancy rates and even used to determine the age of an individual. See our publication list for recent examples.
Scar-based studies of entanglement
Entanglement in fishing gear is a source of injury and mortality to humpbacks, but its frequency is difficult to quantify. To address this problem, PCCS developed a technique for studying humpback whale entanglement based solely on body scarring and ground-truthed it against documented entanglement events. Since 1997, this research has provided annual information on Gulf of Maine humpback whale entanglement rates. We are now applying this approach in other areas, including as part of the first ocean-basin-wide study in the North Pacific for the SPLASH project. Our long-term studies of entangled humpback whales are also providing insight into impacts on survival and reproduction.
Example of a photograph used in scar analysis. Download field protocols here
The data for scar-based analyses consist of high quality photographs of the body where it meets the flukes (see image at right). Photographs are obtained while parallel to the whale and slightly ahead of its flukes during the terminal dive. PCCS codes these images to reflect the presence or absence of wrapping scars, notches and other injuries that are consistent with a prior entanglement.
Detailed field protocols for collecting appropriate data for humpback whale entanglement scar analysis can be downloaded here*.
*This file may take some time to download, depending on the speed of your connection.