Many questions can be answered using photo identification as a tool. Some information that is commonly gathered from fluke photo ID data is outlined below, along with theoretical scenarios to help illustrate the concept.
Migration and Movements
We can learn about migration destinations of specific whales, and about the maximum transit time for migration. Also, movements within an area can be determined, and habitat preferences can be seen.
Example: If a whale was identified in Alaska on Nov 8 and then re-sighted in the Hawaii islands on Dec 11 of the same year, we can assume that the maximum time this whale spent migrating was 32 days.
Breeding/Foraging Site Fidelity
We can learn the breeding and foraging preferences of individuals, and determine tendencies humpbacks may have to return to the breeding and foraging (feeding) regions where their mothers initially brought them when they were a calf.
Example: If a mother and calf pair were sighted off Maui, Hawaii during winter, then in Lynn Canal, Alaska for the summer feeding months, it would be possible to monitor these areas in future years to see if this calf maintained those site preferences.
Kin/Social Relationships
We can learn if whales form long-term social bonds or associations and/or if they have long-term recognition and preference for association with kin (relatives).
Example: With good fluke IDs of a mother and calf, it would be possible, through continued monitoring, to identify a mother who retained an association with a former calf (her offspring). Or, similarly, two unrelated animals who maintained a long term association.
Age/Longevity
We can learn a minimum age for each whale based on the date of the first fluke photo taken of each animal. And, if the first fluke photo was taken when the whale was a calf, the exact number of years in age is known. We call these ‘known age whales.’
Example: If a whale was photographed in the winter of 1983, you can assume that the whale is at minimum 25 years old in 2008.
Calving Intervals
By documenting mother and calf pairs, we can learn about the reproductive success and frequency in females.
Example: If a female whale is seen frequently (with multiple sightings each year), it is possible to look at the years she has a calf and document the intervals between offspring. This type of information can be important in extrapolating the overall reproductive rate of the population.
Migration and Movements
We can learn about migration destinations of specific whales, and about the maximum transit time for migration. Also, movements within an area can be determined, and habitat preferences can be seen.
Example: If a whale was identified in Alaska on Nov 8 and then re-sighted in the Hawaii islands on Dec 11 of the same year, we can assume that the maximum time this whale spent migrating was 32 days.
Breeding/Foraging Site Fidelity
We can learn the breeding and foraging preferences of individuals, and determine tendencies humpbacks may have to return to the breeding and foraging (feeding) regions where their mothers initially brought them when they were a calf.
Example: If a mother and calf pair were sighted off Maui, Hawaii during winter, then in Lynn Canal, Alaska for the summer feeding months, it would be possible to monitor these areas in future years to see if this calf maintained those site preferences.
Kin/Social Relationships
We can learn if whales form long-term social bonds or associations and/or if they have long-term recognition and preference for association with kin (relatives).
Example: With good fluke IDs of a mother and calf, it would be possible, through continued monitoring, to identify a mother who retained an association with a former calf (her offspring). Or, similarly, two unrelated animals who maintained a long term association.
Age/Longevity
We can learn a minimum age for each whale based on the date of the first fluke photo taken of each animal. And, if the first fluke photo was taken when the whale was a calf, the exact number of years in age is known. We call these ‘known age whales.’
Example: If a whale was photographed in the winter of 1983, you can assume that the whale is at minimum 25 years old in 2008.
Calving Intervals
By documenting mother and calf pairs, we can learn about the reproductive success and frequency in females.
Example: If a female whale is seen frequently (with multiple sightings each year), it is possible to look at the years she has a calf and document the intervals between offspring. This type of information can be important in extrapolating the overall reproductive rate of the population.
Age of First Successful Reproduction
We can learn at which age female whales give birth to their first calf by observing the first year a known age whale has a calf with her. Due to the breeding strategy of humpback whales, it is not possible to observe the father of a calf, and therefore is not possible to use photo ID as a method to learn the age of sexual maturity for male whales.
Example: If a whale is sighted and photographed as a calf in 1995, and then seen later in 2004 with a calf, it can be assumed that the age of first successful reproduction was a maximum of 9 years.
Population Estimates
Photo ID can be used to determine an estimate for the number of whales in a given population using a basic mark-recapture analysis. The principle behind a mark-recapture study can be seen using a simple closed population (meaning no individuals leave or enter, including no births or deaths). A subsample of this population is taken and “marked” then released. The “mark” in this instance is the photograph taken of the flukes as an identifier for each individual whale. A second subsample is later taken after the population has had sufficient time to mix and reorganize. The re-sighted individuals are considered “recaptured”. Using a complex calculation based on the ratio of marked and unmarked whaled “captured” or documented, an estimate of the number of individuals in this population can be determined.
We can learn at which age female whales give birth to their first calf by observing the first year a known age whale has a calf with her. Due to the breeding strategy of humpback whales, it is not possible to observe the father of a calf, and therefore is not possible to use photo ID as a method to learn the age of sexual maturity for male whales.
Example: If a whale is sighted and photographed as a calf in 1995, and then seen later in 2004 with a calf, it can be assumed that the age of first successful reproduction was a maximum of 9 years.
Population Estimates
Photo ID can be used to determine an estimate for the number of whales in a given population using a basic mark-recapture analysis. The principle behind a mark-recapture study can be seen using a simple closed population (meaning no individuals leave or enter, including no births or deaths). A subsample of this population is taken and “marked” then released. The “mark” in this instance is the photograph taken of the flukes as an identifier for each individual whale. A second subsample is later taken after the population has had sufficient time to mix and reorganize. The re-sighted individuals are considered “recaptured”. Using a complex calculation based on the ratio of marked and unmarked whaled “captured” or documented, an estimate of the number of individuals in this population can be determined.