Using photo-ID as a tool to study beluga whales
Photo-Identification (photo-ID) is an effective, non-invasive tool that allows researchers to study individual beluga whales long term. Photo-ID is used to study population estimates (how many whales there are), distribution/movement patterns (where the whales go), age/longevity (how old are they and how long do they live), kin and social structure (who is related to whom and who hangs out together), and reproductive information (which whales are reproducing, how often, and calf survival).
The goals of the Cook Inlet Beluga Whale Photo-ID Project are to conduct research and education that contribute to the recovery and conservation of beluga whales in Cook Inlet and to provide information to help manage human activities that might affect the belugas. Using boat and shore-based surveys of Upper and Middle Cook Inlet the Photo-ID Project photographically tracks individual beluga whales identified by natural markings. The CIBW Photo-ID Project has conducted over 500 surveys between 2005-2019, identifying ~450 individuals in the Right-Side Catalog, ~475 in the Left-Side Catalog and ~100 whales in the Dual Catalog (whales that are identified on both their right and left-sides). We believe that the CIBW photo-ID catalog contains a majority of the population. Over time, sighting histories are compiled for each known individual and researchers are able to learn more about the distribution, habitat use, social structure, reproduction and mortality of the Cook Inlet beluga whales.
Photo-ID: What Have We Learned From a Long Term Data Set?
Distribution and Habitat Use
Using the sighting histories of individual Cook Inlet beluga whales (CIBWs), we have been able to examine residency and movement patterns of CIBWs.
We have found that CIBWs encountered during the ice-free months were not distributed uniformly throughout Cook Inlet or within the designated critical habitat, but were instead found seasonally in distinct areas where they aggregate in large groups of both sexes and all age-classes as they rear calves and feed. These areas, namely the Susitna River Delta, Chickaloon Bay, Turnagain Arm, and Knik Arm, and the general corridors connecting them, represent important beluga habitat that may warrant focused management attention and protection efforts due to the presence of large numbers of endangered belugas engaged in critical activities.
Although CIBWs cluster in seasonal hotspots, the sighting histories of individual CIBWs indicate that CIBWs do not display fidelity to any single area of Cook Inlet, but move throughout the entire study area and their movements are highly influenced by tidal state.
2005-2018 CIBW sighting history from CIBW Photo-ID land- and boat-based surveys.
Reproductive Natural History
There is little, to no, historical baseline data available for the reproductive parameters (i.e., birth rates, inter-birth intervals, age of first and last reproduction, age of calf independence, etc.) of Cook Inlet belugas, yet this information is extremely important in making population assessments and developing recovery plans.
It has been an overarching goal of the CIBW Photo-ID Project to use the long-term photo data set to fill data gaps to contribute to the management and recovery of this endangered population, specifically looking at the seasonality of reproduction, the distribution of groups containing calves and the number of identified mothers and calves in the catalog, inter-birth interval, period of maternal care/association, and age of first and last reproduction.
During each survey we document group location, size, and composition including presence of calves(dark gray, relatively small (3/4 total length of adult or smaller, and photographed near lighter-colored adult), and neonates (newborns, estimated to be hours to days old with visible fetal folds and often a “peanut-shaped” head and/or dark eye ring). All photographs taken during a survey were later processed and sorted into individual belugas.
Photos of identified belugas were classified as presumed mothers if they appeared in the same uncropped photo frame with a calf or neonate alongside them. Sighting records for presumed mothers included information on when the mother was photographed with and without a calf, as well as information on the relative size of the calf. If a presumed mother was seen with a calf in multiple years, and the calf appeared larger every year, it was assumed to be the same calf maturing (the majority of photographed calves cannot be identified as individuals because they are either not well marked with the long-lasting marks used for photo-id, or they are not photographed with enough of the body above water to allow marks to be seen).
Identified whales were classified as a possible mother if they appeared in the same uncropped photo frame with a calf near but it was ambiguous of which whale the calf belonged to.
Seasonality and Occurrence of Reproduction
In 2008, the CIBW Photo-ID Project began differentiating calves from neonates. Neonates were observed from early July through mid-October,with the first neonates always being observed at the Susitna River Delta and often coinciding with the largest beluga groups of the year. During the entirety of the CIBW Photo-ID Project, three possible beluga births have been documented. Two births were observed in the month July in the Susitna River Delta, and one was observed in September in Turnagain Arm.
Distribution of Groups Containing Calves and Neonates
Calves (ages 0-5 years old) were seen in all survey zones, months, and years. Groups with calves occurred in same general locations as groups without calves and calf counts were highest in the Susitna River Delta. Neonates (0-2 months old) were observed in all survey zones and groups with neonates occurred in same general locations as groups without neonates.
Reproductive females and inter-birth interval, period of maternal care/association, and age of first and last reproduction
We classify belugas as presumed mothers when there is a photograph taken of an individual with a closely associated calf. In the dual-side catalog, 56% of the individuals are classified as presumed mothers, 47% are presumed mothers in right-side catalog, and 43% are presumed mothers in the left-side catalog. There are 15 known individuals that are of known female sex (known from genetic, stranding and tagging data). 10 of these females are classified as presumed mothers, and 1 is classified as a possible mother.
Data combined from photo-ID, satellite tagging and tooth aging data sets indicate that the minimum female reproductive period of CIBWs is from age 13-47 (Shelden et al. 2019, Shelden et al. 2019, Vos et al. 2019) and may be younger.
31 presumed mothers from the dual-side data set were photographed over a 13-year period of time, producing 1-5 calves each. The inter-birth interval ranged from as little as 2 years, to 3-5 years, and for some, as long as 13 years.
The estimated period of maternal association between identified calves and identified mother is 3-5 years. There have been some mother photographed simultaneously with a newborn calf and an older calf.
We recognize that photo-ID methods most likely underestimate the number of presumed mothers and that confirmed-sex females with longer sighting records more likely to be classified as mothers. Mother-calf associations were made at the level of the photo frame and we are working on ways to improve our ability to identify calves by their own, quickly changing marks. This will allow us to examine how often calf and mother are photographed in the same group. Photographic tracking of individuals provides important insight into reproductive natural history of this population and basic parameters needed for more complex population models.
Shelden KEW, Burns JJ, McGuire TL, Burek-Huntington KA, Vos DJ, Goertz CEC, O’Corry-Crowe G, Mahoney BA (2019) Repro-ductive status of female beluga whales from the endangered Cook Inlet population. Marine Mammal Science early online: DOI:10-1111/mms.12648.
Shelden KEW, Goetz KT, Hobbs RC, Hoberecht LK, Laidre KL, Mahoney BA, McGuire TL, Norman, SA, O’Corry-Crowe G, Vos DJ, Ylitalo GM, Mizroch SA, Atkinson S, Burek-Huntington KA, Garner C (2018) Beluga whale, Delphinapterus leucas, satellite-tagging and health assessments in Cook Inlet, Alaska, 1999 to 2002. NOAA Technical Memorandum NMFS-AFSC-369.
Vos DJ, Shelden KEW, Friday NA, Mahoney BA (2019) Age and growth analyses for the endangered belugas in Cook Inlet, Alaska. Marine Mammal Science 36(1):293-304.
Calf and neonate distribution maps 2005-2018 based on CIBW Photo-ID surveys. Click on image to make larger.
We combined data from the photo-ID database with data from 95 reported CIBW carcasses during the 2005-2017 study period in order to discern any patterns in age, sex, geographic range, month, and cause of death (COD). We also used cessation of resightings of individuals in the photo-id catalog to estimate the number of unreported deaths in the population.
Looking at the data associated with the 95 beluga carcasses, reported between 2005-2017, 96% of strandings were reported during the ice-free season and 87% of the strandings were reported in Upper Cook Inlet. Mortality during the other six months of the year and in other locations throughout the range of the CIBW is likely under-represented due to low detection and reporting.
Demographic Patterns and cause of death (COD)
Dead female and male belugas were reported at the same rates. Reported mortality was greatest for adults of reproductive age, followed by calves, with subadults being the lowest reported group. There are no adults older than 49 years in the stranding dataset (Vos et al. 2019). If belugas can live to 70 years, where are the oldest adults?
Trauma from live-stranding was the predominant known COD, but only for ~33% of the examined deaths. Other CODs were choking on prey, pneumonia, and blunt trauma (Burek-Huntington et al. 2015). It is unknown what is causing most of the other deaths and the live-strandings.
Presumed dead vs confirmed dead CIBWS
We used cessation of resightings of individuals in the photo-id catalog to estimate the number of unreported deaths in the population (Figure presumed dead). A whale was presumed dead the time when the individual was last photographed was greater than ten years. A ratio of presumed dead to confirmed dead CIBWs was created (see table below). The 2005-2017 stranding data suggest that the average CIBW mortality rate is at minimum 2.2%, but our analysis suggests that it could be closer to 8.8-14.1%when you multiply 2.2% by the ratio of presumed dead to known dead.
Literature Cited: Burek-Huntington, K. A., Dushane, J. L., Goertz, C. E., Romero, C. H., & Raverty, S. A. (2015). Morbidity and mortality in stranded Cook Inlet beluga whales Delphinapterus leucas. Diseases of Aquatic Organisms, 114(1), 45–60.
Vos, D. J., Shelden, K. E. W., Friday, N. A., and Mahoney, B. A. (2019). Age and growth analyses for the endangered belugas in Cook Inlet, Alaska. Marine Mammal Science, Advanced online publication. https://doi.org/10.1111/mms.12630.
Standing locations and time frame of 95 beluga carcasses reported 2005-2017. Click on image to see full size.
Distribution of the maximum number of years between photographic sightings of identified individuals in the Cook Inlet beluga whale photo-id catalogs 2005-2017, according to catalog side (n=422 individuals in the right-side catalog and n=429 individuals in the left-side catalog). A gap of 0 years indicates an individual was photographed in consecutive years. Numbers in boxes represent the 12 dead photo-identified individuals shown above the number of years between when the individuals were photographed dead and when last photographed alive.
Ratio of presumed dead (based on the period of timebetween resightings of ten years or more) to confirmed dead CIBWs.
-Habitat protection and regulation of anthropogenic activities with the potential to affect CIBWs should not be considered in isolation, but rather the cumulative effects of all activities in the range of CIBWs and their potential to affect the entire population must be taken into account due to what appears to be the broad use of all areas of Upper Cook Inlet by the majority of CIBWs.
-Sighting histories and distribution data have identified the critical areas and seasons for calving and calf rearing. Management of human activities during these periods is reccomended.
-CIBWs also face natural threats such as mass strandings and predation events. These stranding events have been reported to occur more often in Turnagain Arm and Knik Arm than elsewhere in Cook Inlet(NMFS 2008b). If a mass-stranding event were to occur at the Susitna Delta in July, this could have catastrophic consequences because the entire population, including calving females, appears to congregate here during this time to feed. Photo-id has provided evidence that most or all of the individuals in the CIBW population use these areas at some time during the year, which underscores the
threat that such events pose to the entire population, and should prompt managers to have site-specific
stranding response plans ready to activate should such events occur.
-More CIBW carcasses need to be detected, reported, photographed, and necropsied to determine true mortality patterns and rates so that trends may be understood and reversed.