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.

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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.

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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.  

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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.

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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.

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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.

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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.

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Literature cited:

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.

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