Uncovering genetic secrets of Atlantic White-sided and White-beaked Dolphins
Amongst the majestic large whales inhabiting the waters off Longue-Pointe-de-Mingan are some smaller-bodied cetaceans that are no less dynamic and mysterious. Although they do not always get as much attention as the massive blue whales and acrobatic humpbacks, the Atlantic white-sided (Lagenorhynchus acutus) and white-beaked (L. albirostris) dolphins are some of the most colorful and energetic marine mammals in the aquatic world. Despite their eye-catching appearance, relatively little is known about these animals. The habitat ranges for both species are thought to largely overlap, generally spanning across the North Atlantic and along the northern coastlines of eastern North America and western Europe. In the western North Atlantic (WNA), the white-beaked dolphin is generally considered to be more northern and offshore compared to the white-sided dolphin although both are believed to occur over the continental shelf slope.
Both species have been seen on numerous occasions within the Gulf of St. Lawrence. Based on MICS sighting records dating back to 1982, the white-sided dolphin has been observed more regularly, predominantly coming into the area in August and September, hot on the heals of the white-beaks, which are most often seen in July and trail off by mid-September.
Both species are relatively abundant within the North Atlantic, however very little is understood about the genetic relationships among individuals within each species across, and on either side of, this broad ocean basin. For instance, for Atlantic white-sided dolphins very few individuals have been observed on the Atlantic side of Nova Scotia, possibly setting the scene for separate, genetically distinct populations north (in the Gulf of St. Lawrence) and south (in the Gulf of Maine) of this area. In the eastern North Atlantic (ENA), recent studies have shown some levels of very low population structure for both species throughout the waters of the U.K. and into the Norwegian Sea. But scientists don't know if the animals within the WNA are the same or are composed of one or more genetically distinct population compared to their ENA counterparts. Evidence based on sighting, stranding, and morphological data suggest that neither species is one large panmictic population across their entire habitat range, however very little genetic work has been done to corroborate this, especially in the WNA.
Because these dolphins inhabit relatively cold, northern waters they are potentially at a greater risk for negative impacts from global climate change. Furthermore, in the WNA mortalities for both species have been attributed to incidental takes by commercial and recreational fisheries and even from subsistence hunting off Newfoundland, Labrador, and Greenland. In the face of these anthropogenic and other natural threats, it is important to identify the presence, or lack of, distinct populations so that we can better understand the impact these various types of threats might have.
Dr. Vollmer in the field attempting to get a biopsy from Atlantic white-sided dolphins (left) and processing samples back at the Laboratory of Analytical Biology at the Smithsonian Institution (right).
Nikki Vollmer, a postdoctoral fellow with the National Oceanic and Atmospheric Administration (NOAA) and the Smithsonian Institution, is trying to shed some light onto the genetic mysteries of these Lagenorhynchus species. Dr. Vollmer has already obtained hundreds of samples of both species and has partnered with MICS to try to obtain the first ever biopsy samples from free-ranging dolphins in the Gulf of St. Lawrence. Interestingly, this semi-enclosed habitat has been suggested to harbor a genetically unique population of Atlantic white-sided dolphins, however this hypothesis has never been genetically investigated. Overall, her research will improve understanding of which population(s) is/are being detrimentally affected by commercial fisheries, help predict possible impacts of climate change and will contribute to the future conservation and accurate management of these charismatic marine mammals.