J-STAGE Advance published date: October 20, 2021

MINKE WHALE MUSCLE COMPOSITION ASSESSMENT BY NIR SPECTROSCOPYPRELIMINARY USE OF NEAR-INFRARED
SPECTROSCOPY TO ESTIMATE THE BIOCHEMICALCOMPONENTS OF THE MUSCLESOF THE ANTARCTIC MINKE WHALE
BALAENOPTERA BONAERENSIS
Kenji KONISHI* and Tsutomu TAMURA
Institute of Cetacean Research, 4–5 Toyomi-cho, Chuo-ku, Tokyo 104–0055, Japan*Corresponding author: konishi@cetacean.jp

Abstract
The energetic condition of whales is an important information to understand their energy
demand to sustain their migration and reproductive success. However, basic energetic information based on biochemical components (protein, lipid, sugar, and water) and calorimetricdata are limited, particularly in small baleen whales such as the minke whale. This study
reports the biochemical components of the muscle tissues of 61 Antarctic minke whales (Balaenoptera bonaerensis) of diﬀerent sexes and sexual maturity using near-infrared (NIR) spectroscopy. Prior to sample analysis, a calibration curve based on a standard chemical analysis
was installed in the NIR analytical equipment. The dorsal muscle tissues from Antarctic minke
whales contain approximately 0.5%–0.6% lipid, 26% protein, and 73% water, suggesting thatthe dorsal muscle contains a small amount of lipid and a high proportion of water. These proportions were similar between sexes and sexual classes. The proportions of lipids in the dorsal
muscle of Antarctic minke whales are likely to be lower than those of other baleen whales,such as sei (B. borealis) and ﬁn (B. physalus) whales, and this requires further investigation.
Key words:

lipid contents, nutritional condition, muscle tissue, Antarctic minke whale.

The information about the nutritional indices of baleen whales is important to evaluate their energetic conditions and energy demand to sustain their migration and reproductive success. The information on their biochemical components, such as protein, lipid, sugar, and water, and calorimetricdata are necessary to estimate the total energy deposit of individuals and evaluate their nutritionalindices. The biochemical components of large whales, such as ﬁn (Balaenoptera physalus) and sei(B. borealis) whales, were previously reported (Arai and Sakai, 1952; Lockyer et al., 1984, 1985;
Aguilar and Borrell, 1990).
This biochemical composition diﬀers among whale species, and it also varies with the season,
body size, reproductive status, and organs (Lockyer et al., 1984, 1985; Aguilar and Borrell, 1990).
Therefore, species-speciﬁc biochemical information is needed to estimate their energy deposits using
tissues that function as a lipid deposit. However, little information is available for Antarctic minke
whales (B. bonaerensis). The biochemical components and lipid contents of Antarctic minke whales
were previously reported from the aspect of food nutrition (Ito et al., 1993, 1998; Iida et al., 1998).
The biochemical components of the “red meat” from three Antarctic minke whales (a mature male, animmature female, and a >30-year-old female) were reported by Iida et al. (1998). The lipid contentsof the dorsal muscle at the level of the dorsal ﬁn (regarded as red meat) and tail (regarded as lipid-rich“tail meat”) were examined in 29 males and 23 females (Ito et al., 1998). Although fat tissue suchas blubber function as lipid deposit, muscle mass represents a greater proportion in terms of weight
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Fig. 1. Near-infrared spectrometer CA-HM (Joy World Paciﬁc Co. ltd.) and a terminal PC. The solid muscle
samples were homogenized using a food processor and a portion the (approximately 25 g) was set for analysis
on a saucer at the lower right slot.

(Gunnlaugsson et al., 2020). Therefore, it is important to determine the biochemical components of
their muscle tissues to calculate the total energy contents and their function for energy storage.
In this study, near-infrared (NIR) spectroscopy was used to determine the biochemical componentsof the muscle tissues of Antarctic minke whales. While conventional methods analyze the samples
only for a single component, NIR spectroscopy allows simultaneous measurements of multiple biochemical components, optimizing the use of samples. However, this NIR technique needs a calibration
based on a regression model to predict the biochemical properties based on spectral data (Prieto etal., 2017).
The NIR technique was used to estimate the biochemical components of the muscle tissues from61 Antarctic minke whales sampled during the austral summer of 2016/17 under NEWREP-A (NewScientiﬁc Whale Research Program in the Antarctic Ocean). Muscle tissues were sampled from thedorsolateral muscle at the level of the dorsal ﬁn. To reduce the seasonal eﬀect on the analyses of thebiochemical components during the summer feeding period, the samples from a limited time period in
the survey season were used (December 15–January 5). The samples involved 25 immature males, 14
mature males, 17 immature females, and ﬁve pregnant females.
The muscle samples were scanned using an NIR spectrometer, CA-HM (Joy World Paciﬁc Co.,
Ltd.; Fig. 1). Before the analysis, a calibration curve set for whale muscles was prepared (Fig. 2). Thisﬁgure shows the plots of the values of protein, lipid, and water components from conventional chemical analyses and NIR spectroscopy. The muscle tissues from Antarctic minke whales and North Paciﬁc
sei whales were used for this calibration. This calibration curve was ﬁt using these values and installedin the spectrometer.
The muscle samples were homogenized using a food processor, and a sub-sample (approximately25 g) was set on a saucer dedicated for NIR spectroscopy (Fig. 3). In both conventional chemical analyses and NIR spectroscopy, the white ﬁbrous parts, such as perimysium, were not removed from themuscle sample since these are muscle components. However, the results were expected to vary slightly by homogenizing the muscle samples.
The summary of the NIR analysis of the dorsal muscle at the level of the dorsal ﬁn of Antarctic

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Cetacean Popul. Stud. (CPOPS), Short noteVol. 3, 2021, 281–285MINKE WHALE MUSCLE COMPOSITION ASSESSMENT BY NIR SPECTROSCOPYFig. 2. Comparisons of biochemical components between laboratory-based and near-infrared (NIR) analyses
to set a standard curve of the whale muscles for NIR spectroscopy. Left, protein; center, lipid; right, water.
The muscle samples from Antarctic minke and North Paciﬁc sei whales were used. The gray bands represent
the 95% conﬁdence intervals.

Fig. 3. Homogenized muscle of an Antarctic minke whale set on a saucer before analysis on the near-infraredspectrometer. The white ﬁbrous parts were included in the analysis.

minke whales is listed in Table 1. On average, the muscle tissues contain approximately 0.5%–0.6%
lipid, 26% protein, and 73% water, showing that the muscle consists of a very small amount of lipid
and a high percentage of water in all maturity stages. The lipid compositions are similar among sexes
and sexual maturity/classes. The results of Iida et al. (1998) are similar to the results of this study (Table 1). Ito et al. (1998) also showed that the lipid content of the dorsal muscle at the level of the dorsal
ﬁn was approximately 1.1% in Antarctic minke whales sampled in the austral summer of 1990/91 (Table 1). This lipid content in muscle tissues was slightly higher compared to the results of the present
study. However, the energy storage diﬀers among years and seasons (Konishi et al., 2008; Konishi andCetacean Popul. Stud. (CPOPS), Short noteVol. 3, 2021, 281–285

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107.05
25.58
0.48
0.10
72.84
—3.41

Calorie (kcal)
106.03
3.54
Protein (g)
25.08
0.45
Lipid (g)0.59
0.22
Sugar (g)0.10
0.00
Water (g)
73.23
0.63
Ash—
—
Lateral blubber thickness at
3.33
0.61
the level of dorsal ﬁn (cm)Half girth at the level of
163.28 18.27
umbilicus (cm)Sample size
25
14

212.00

mean

SD

mean

10.70

6.22
0.82
0.37
0.00
1.13
—
0.44

SD

Mature male

Immature male

2.28
0.35
0.15
0.00
0.43
—
0.47

SD

17

166.29 19.14

104.18
24.82
0.50
0.10
73.58
—
3.22

mean

214.20107.61
25.45
0.60
0.10
72.85
—
3.10

mean

5

9.91

3.33
0.47
0.17
0.00
0.63
—
0.66

SD

Immature female Pregnant female

1—

—
24.10
0.70
0.15
74.40
0.92
—

1—

—
24.00
0.30
0.36
74.60
1.65
—

1—

—
24.40
0.36
0.14
74.50
0.90
—

Mature Immature Mature
malefemale female

Iida et al. (1998)

—

—
—
1.14
—
—
—
—

Male

29

—

—
—
0.57
—
—
—
—

SD

—

—
—
1.11
—
—
—
—

23

FemaleIto et al. (1998)

—

—
—
0.5
—
—
—
—

SD

Table 1. Summary of the calorie content and biochemical components (per 100 g) of the muscles of Antarctic minke whales. For comparative purposes, the data fromthe results of Iida et al. (1998) and Ito et al. (1998) based on conventional analyses are also indicated.

KONISHI AND TAMURA

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MINKE WHALE MUSCLE COMPOSITION ASSESSMENT BY NIR SPECTROSCOPY

Walløe, 2015), and this diﬀerence may suggest a possible seasonal and yearly variation of lipid contents in the muscles of Antarctic minke whales.
The lipid contents of the dorsal muscles of ﬁn and sei whales exceeded 3% on average. The musclesin the anterior body part at the level of the ﬂippers have less accumulated lipids compared to those in
the middle and posterior parts of the body (Lockyer et al., 1985). Given this, the muscles of Antarctic
minke whales seem to have less lipid contents than those of large baleen whales. However, to conﬁrm
this, further comparative analyses among baleen whale species should be conducted using the same
methodology while strictly considering the body parts from where the muscle samples are obtained.
The application of NIR spectroscopy to estimate the biochemical components of whale tissues isuseful and practical to determine the basic information about the energetics of baleen whales. The useof techniques, such as NIR, which allows analysis of multiple components from a single sample, is ofparticular utility in the case of baleen whale samples, which are limited and diﬃcult to access.
Acknowledgements

We are most grateful to the researchers on board of Nisshin-Maru for their assistance in biological sampling during the2016/17 NEWREP-A survey. We also would like to thank two anonymous reviewers for their useful comments to improve
this paper. The NEWREP-A program was conducted with permission from the Fisheries Agency, Government of Japan.

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Received: January 28, 2021
Accepted: June 30, 2021
Published online: October 20, 2021

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