A new study led by the New England Aquarium is providing insight into North Atlantic right whale calf survival, growth rates, and life history, demonstrating the power of genetic sampling for this critically endangered species.
The study, published in the journal Mammalian Biology, analyzed all North Atlantic right whale calves born between 1988 and 2018 and categorized the animals based on genetic samples and photo identification. The researchers focused on 13 case studies of right whales that required genetics to track their life history data. Scientists were able to determine the ages of 12 whales, matched 11 with their birth mothers, and determined that four calves previously thought to be dead had in fact survived.
"It is often difficult to document the tremendous variation in the behavior and development exhibited by animals in the wild. The results of this study have changed what we know about the separation time between a mother and calf as well as calves' physical development, all crucial information for a critically endangered species that numbers less than 350 individuals," said lead author Philip Hamilton, Senior Scientist at the New England Aquarium's Anderson Cabot Center for Ocean Life.
For 40 years, the whales' histories have been tracked using the North Atlantic Right Whale Catalog, an extensive photo-identification database curated by scientists at the Aquarium. Individual North Atlantic right whales are distinguished by photographs of the natural markings on their head, called callosities, as well as scars on their bodies. Because calves' callosities take months to develop, they are generally identified by their close association with their mothers in the calving grounds off the southeast United States between December and March.
"If a calf remains with its mother until its callosity is identifiable and there are adequate photographs of the pair together, the calf can be added to the Catalog along with its known age and parentage," said Hamilton. "However, if the calf is separated from its mother early or is not adequately photographed, its age and parentage are unknown. That is where genetic sampling comes in."
More than 80 percent of cataloged right whales have been genetically sampled. For this study, biopsy efforts focused on calves in a given year, other whales recognized in the field that were known to have not been previously sampled, and whales that could not be identified in the field. Right whale photographs were collected throughout the whales' migratory range in all months of the year, and all photographic data was submitted to the New England Aquarium for processing.
The biopsy samples were then sent to Saint Mary's University in Halifax, Nova Scotia, where Drs. Tim and Brenna Frasier conduct genetic analyses. These analyses have been developed over several decades for better understanding the genetics of this species, as well as for use in population monitoring, such as the genetic identification of individuals, linking parents and offspring, and for assessing other patterns of relatedness.
"Through these collaborations, the impact of integrating the genetic and field research is much larger than just the sum of the parts, and is leading to a much richer understanding of this species than either approach could provide on its own," Dr. Tim Frasier said.
"Because they are completely independent identification techniques, the genetic and photo-identification databases serve as excellent quality checks for each other," Hamilton said.
The research showed that it is not uncommon for mothers to be seen without their calves in the feeding grounds for short periods of time as early as April, and some calves associate with different mothers for short periods. The data reveals that mothers and calves are seen apart from each other in the feeding grounds off New England and Canada in 10 to 40 percent of all spring and summer sightings. Prior to this study, calves were assumed to have died if their mothers were always alone on the feeding grounds during the calf's birth year. Using genetics and photo identification, four calves thought to be dead were discovered to be alive; two of the four weaned earlier than the expected 10 to 12 months.
In one case study, female right whale "War" (Catalog #1812) was sighted alone in the feeding ground off of Massachusetts in May 2004, calling into question if her calf was alive. A biopsy sample from "Seadragon" (Catalog #3680) three years later determined that the calf had indeed survived. Another case study examined unnamed Catalog #3970, a whale born in 2009 and genetically sampled in January 2009 as a calf on the calving grounds with mother "Braces" (Catalog #3320). Braces and her calf were last seen together in mid-February of 2009. Four months later in mid-June, researchers spotted a young whale alone on the feeding ground 1,000 miles to the north. That whale remained alone through mid-September when it was genetically sampled. When the genetics were reviewed, scientists learned that the young whale was Braces' calf of the year that had separated from his mother when he was only 7 to 8 months-old.
The study ultimately underscores the importance of utilizing both photographs and genetics from young marine mammals, as well as decomposed carcasses, to accurately capture individual life history data.
"Genetically sampling animals early in their lives before they disperse or separate from their mothers provides an important means of individual identification at a time when photo-identification is not as reliable," Hamilton said. "All of this information is critical to help save this species from the brink of extinction."
The study involved researchers from five organizations and agencies. To collect the genetic samples, Hamilton worked with Lisa Conger of NOAA Fisheries, Clay George of the Georgia Department of Natural Resources, and Katharine Jackson of the Florida Fish and Wildlife Research Institute, among others. Tim Frasier and Brenna Frasier of Saint Mary's University processed the genetic samples. NOAA Fisheries funded the field sampling efforts, with recent support for the genetic analysis funded by Fisheries and Oceans Canada.
As part of a multi-year, multi-million-dollar grant led by Saint Mary's University and the Aquarium, the genetic samples collected from right whales will be used to quantify the impact of inbreeding on reproductive success and to identify the long-term negative consequences of non-lethal entanglements in fishing gear.
Cite This Page: