DOI: 10.5061/dryad.ht76hdrqk
title: Data from: Seasonal flexibility in energy stores of Hudson Bay beluga whales: Insights from blubber lipid analysis

description: During the primary feeding season, marine mammals often accumulate fat
 reserves, primarily in the form of blubber. Despite the
 ecological significance of feeding, uncertainty remains surrounding the
 timing of energy store accumulation in Hudson Bay beluga whales
 (Delphinapterus leucas (Pallas, 1776)). Blubber samples were collected
 from whales hunted by Inuit along the whale’s migration route, from 2015
 to 2021 (excl. 2018). Sampling occurred in spring and fall, assumed to
 represent feeding in winter and summer, respectively. We analyzed blubber
 for lipid content and adipocyte size, two related indices of lipid
 dynamics, across three blubber sections (outer, middle, and inner). We
 found interannual variability in the season with the highest fat content,
 with some years showing higher lipid content in spring than fall. While
 adipocyte size did not differ seasonally, minima were observed in 2017 and
 2019. Fat stores differed across blubber sections, with the highest lipid
 content and largest adipocytes in the middle section. The observed
 seasonal variation indicates there is no consistent season in which Hudson
 Bay beluga whales predominantly accumulate fat. Consequently, building
 energy stores in the form of blubber may not be the primary driving force
 behind the beluga whale’s migration between the wintering and summering
 areas.
description: The dataset includes data on 53 Hudson Bay beluga whales
 harvested near Sanikiluaq, Nunaut. Primary analysis was on lipid content
 and adipocyte size, used to evaluate the primary feeding season of these
 whales. Subsamples of blubber were collected from the outer, middle, and
 inner sections of the blubber. The data includes when the whale was
 harvested (year, month, season), genetically determined sex, and lipid
 content measured during fatty acid analysis. Histological analysis was
 conducted to obtain adipocyte size (average area). Age of the individuals
 was determined using teeth. Note: The blubber was seldom present down to
 the muscle. Blubber length represents the length of the blubber available
 and not necessarily the blubber depth of the whale. 
 Teeth were aged by Matson's Laboratory. 
 Sex was determined genetically at the Freshwater Institute
 (Fisheries and Oceans Canada) with DNA extracted from skin tissue (Qiagen
 DNeasy Kit) and analyzed following PCR procedures described in Rosel
 (2003). Lipids were extracted by placing ~0.5g of
 blubber in 7 mL of chloroform for a minimum of 24 hours. After, 3.5 ml of
 methanol with 0.01% butylated hydroxytoluene (BHT) was added and vortexed.
 The blubber was compressed to extract the lipids, and the remaining tissue
 was removed. Next, 2.6 mL of NaCl was added to the tube and vortexed. The
 lower phase containing the chloroform and lipids was extracted and placed
 in anhydrous sodium sulfate to remove excess water, which was subsequently
 rinsed with chloroform twice. Chemicals were obtained from Fisher
 Scientific Canada, Greenfield Global, and Avantor (previously VWR). The
 remaining solvent was evaporated using a nitrogen stream evaporator
 (N-EVAP) with silver beads (Organomation ©, USA) at 25-30°C. The final
 lipid mass was recorded and compared to the initial blubber sample weight
 to calculate the percent lipid content of the initial wet
 sample. Histological Analysis: Samples were no more
 than 0.4 x 1.5 x 2 cm in size, with the longest measurement parallel to
 the skin. ). The samples were placed in Falcon tubes with 50 ml of 10%
 neutral buffered formalin and fixed at room temperature on a shaker for a
 minimum of 48 hours. The samples were subsequently transferred to 50 ml of
 70% ethanol for shipping to The Centre for Phenogenomics (Toronto, ON),
 where histological analysis was conducted. The samples were processed,
 embedded, cut, stained, scanned, and analyzed by the lab. Samples were
 embedded using the maximum surface area, cut to their standard 4 µm,
 stained using an H&E stain (Harris hematoxylin and eosin Y; Table
 S2), and scanned with a Hamamatsu NanoZoomer at 20x magnification. Images
 were analyzed using an algorithm typically used to measure vacuoles, but
 was instead used to measure the area of the fat cells. 
description: # Data from: Seasonal flexibility in energy stores of Hudson Bay beluga
 whales: Insights from blubber lipid analysis Dataset DOI:
 [10.5061/dryad.ht76hdrqk](10.5061/dryad.ht76hdrqk) ## Description of the
 data and file structure Blubber samples were collected and provided by
 Inuit from Sanikiluaq, Nunavut, during beluga whale subsistence harvests
 2015-2021. ### Files and variables #### File:
 Belanger_etal_2025_SupplementalFile_Data.csv ##### Variables * BelugaID:
 Beluga whale individual * Blubber Length (cm): Measured in centimeters
 (cm) perpendicular to the skin, to the end of the longest part of the
 blubber. This represents the end of the blubber sample available, and not
 necessarily the full blubber depth, as muscle was seldom present. *
 Blubber Section: All cut in ~ 1cm3 * Outer - 1 cm subsample starting from
 the skin, along the depth of the blubber * Middle - 1 cm subsample, 0.5 cm
 on each side of the midpoint of the blubber length (e.g., 5cm blubber
 depth, middle sample is cut from centimeter 2 to 3) * Inner - 1 cm
 subsample starting from the end of the blubber, along the depth of the
 blubber * Season: * Fall - Blubber collected from September 8th to
 November 16th * Spring - Blubber collected from May 26th to July 1st *
 LabSex: Genetically determined sex from tissues * F = Female * M = Male *
 Year_harvested: Year that the beluga whale was harvested by hunters *
 Month_harvested: Month that the beluga whale was harvested by hunters *
 Lipid_Weight (g): Final chemically extracted lipid weight.  * Lipid
 Content Proportion: Proportion of blubber subsample used in fatty acid
 analysis that is made up of lipids (chemically extracted). Histological
 Analysis * CellCount: Number of cells measured within the square analysis
 area (see Q - TotalAnalysisArea 𝝁m^2) * TotalCellArea (𝝁m^2): Total area
 of all the measured cells within the analysis area * AvgArea
 (𝝁m^2): Average area of all the cells measured within the analysis area
 for that sample. * AvgDiameter (𝝁m): Average diameter of all the cells
 measured within the analysis area for that sample * AvgPerimeter
 (𝝁m): Average perimeter of all the cells measured within the analysis area
 for that sample * AvgRoundness: 1 is perfect roundness * AvgCircularity: 1
 is perfect circularity * TotalAnalysisArea (𝝁m^2): Size of the square
 analysis area.  * Age: Age of the beluga whale in years, determined with
 teeth. * Body_length (cm): Body length of the beluga whale sampled.
 Measured by hunters from the rostrum (beak) to the fluke (tail) notch. NA
 - Analysis was not performed