RELEVANCE OF THE SCIENTIFIC WORK OF SEIJI OHSUMIRELEVANCE OF THE SCIENTIFIC WORK ON
CETACEANS OF DR. SEIJI OHSUMILuis A. PASTENE and Hidehiro KATO
Institute of Cetacean Research, Toyomi-cho 4–5, Chuo-ku, Tokyo 104–0055, Japan

Dr. Seiji Ohsumi, ‘Seiji’ as he was known by colleagues and friends, passed away on 2 November
2019 at the age of 89 years. It was a sad day for his family, friends and for all of us who knew andworked with him; without a doubt it was a sad day for cetacean science as well. During his memorialservice held on 23 December 2019, many messages were received from colleagues and friends fromboth Japan and abroad. Most of those messages mentioned Seiji as a kind and true gentleman, a person that enjoyed meeting people at social events, a great cetacean scientist, and a person whose energy
and enthusiasm for research remained undiminished until the end. We agree with that characterizationof Seiji very much.
Seiji was a skilled debater with a deep command of the scientiﬁc issues. His opinions were always
based on updated knowledge and good scientiﬁc information, and he strongly defended his ideas.
During the meetings, people could have passionate discussions and disagreements with him over someissues. However, he never became angry and it was common to see Seiji outside the meetings displaying great courtesy to those same colleagues. Seiji enjoyed social events including parties very much,and saw those events as opportunities to hear and learn from people from diﬀerent research areas,
cultures or countries. At the very domestic level he saw the small parties as an opportunity for younger
people to express their opinions, knowing that they were unable to express such opinions in more formal meetings.
Here we would like to focus on the scientiﬁc work conducted by Seiji. First, we brieﬂy outline his
professional career and then we highlight some of his most relevant scientiﬁc contributions.
Brief outline of professional career• Born on 12 July 1930 in Gunma Prefecture, Japan.
• Graduated in 1948 from the Science Course at the Niigata Public High School under the former educational system.
• Completed pre-graduate studies in 1951 at the Faculty of Agriculture, the University of Tokyo.
• Published his ﬁrst study in English in 1954 in collaboration with some colleagues. The study wastitled ‘On the sexual maturity of the sei whale of the Bonin waters’ under his original name Seiji
Kimura (Nishiwaki et al., 1954).
• Completed post-graduate studies in 1958 at the Faculty of Agriculture, the University of Tokyo. The
title of his doctoral dissertation was ‘A study on age determination of the ﬁn whale’ (Ohsumi, n.d.).
• Became a member of the Whale Research Institute (WRI) in 1958. In his early days at the WRI, Seiji
was mainly engaged in ﬁeld work at numerous places where commercial whaling occurred as well inlaboratory work and analyses of samples he collected. In this period, he worked under the supervision of the late Prof. Masaharu Nishiwaki and Dr. Hideo Omura.
• Became a member of the Population Dynamics and Statistics Division of the Tokai Regional Fisheries Research Laboratory in 1966.
• Became Head of the Unit for Cetacean Population Studies at the government’s Far Sea Fisheries Research Laboratory (FSFRL) in 1967.
• Became Director General of the FSFRL between 1988 and 1991.
• Became a member of the board of directors of the Institute of Cetacean Research (ICR) in 1991.
• Became Director General of the ICR between 1995 and 2003.
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• Became a Senior Scientiﬁc Adviser of the ICR in 2004.
• Became Adviser Emeritus at the ICR from 2015 until he passed away in 2019.
Scientiﬁc contributions
Seiji was a proliﬁc researcher with over 700 scientiﬁc articles and publications on cetacean biology
and ecology, conservation and management, and whaling issues, among other subjects. He regularlypresented his work at scientiﬁc meetings as well as in public forums.
Apart from his specialized scientiﬁc publications and lectures in the ﬁeld of natural and appliedscience that targeted scientists, he considered it important that the general public was aware of cetacean conservation and management, and consequently spent considerable time preparing articles andtalking to the general public on those topics. He was especially skilled at writing and talking in a waythat was understandable for diﬀerent kinds of audiences. This is reﬂected in the large number anddiversity of his written publications and articles on cetaceans, whaling, whale conservation and management, and whale food culture, prepared during his productive life (see also his bibliography in thisissue):• Specialized papers published or presented at scientiﬁc meetings: 286• Books and book contributions: 58• Reports and booklets: 40• Geiken Tsushin (Whales Research Institute/Institute of Cetacean Research (WRI/ICR) Quarterly
Newsletter published in Japanese since 1948): 100• Miscellaneous: 257
Some relevant studies
The scientiﬁc work of Seiji was mainly focused on the assessment and management of large whales
as well as with the natural history of this group of animals.
Seiji conducted the work on assessment and management largely in the context of the work of theScientiﬁc Committee of the International Whaling Commission (IWC/SC), the international organization in charge of the conservation and management of the large whales. The IWC/SC is recognized as
the most skilled group of specialists in the ﬁeld of whale assessment and management, and Seiji was
one of its leading members for over ﬁve decades. Seiji was engaged in the assessment and management of several large whale species, including ﬁn (Balaenoptera physalus), sei (B. borealis), Bryde’s(B. edeni), common minke (B. acutorostrata), Antarctic minke (B. bonaerensis), and sperm (Physetermacrocephalus) whales of both hemispheres. Seiji’s contributions to the biological knowledge andassessment of these species were enormous, and these contributions are reﬂected in many publicationsin the specialized journal of the IWC.
As in other groups of marine living resources, age and reproductive data are essential for assessment through the application of population dynamic models. Seiji not only applied models to assess
diﬀerent populations and species of large whales but also investigated the scientiﬁc basis of some ofthe essential data used in those models. One of the most remarkable examples is the work he conducted to determine the age of ﬁn whales based on their earplugs (Ohsumi, 1964).
By the time of the publication of this work, several approaches were available to estimate the ageof the ﬁn whale, namely body length, stage of growth, number of ovulations, white scars (Mackintosh and Wheeler, 1929); baleen plates (Ruud, 1940); crystalline lens (Nishiwaki, 1950), and earplugs (Purves, 1955). Seiji believed that the laminations found in the core of earplugs were the best
approach to determine age because the laminations were considered to form periodically and werepresent in both males and females throughout the whale’s lifespan and earplugs are relatively easy tocollect and prepare for reading (Ohsumi, 1964).
The main scientiﬁc question at that time was on the frequency of deposition of the earplug lami-6

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RELEVANCE OF THE SCIENTIFIC WORK OF SEIJI OHSUMInations, which was considered to be biannual (Laws and Purves, 1956). Seiji examined this matterin further detail by using biological material of a number of ﬁn whales taken in both the Antarctic
and the North Paciﬁc. He used three approaches to address the question above: examination of age
characters from recaptured whales (mark-recaptured whales), comparison of results among diﬀerent
approaches, and an examination of the population dynamics on the age composition based on earplug
laminae readings.
After detailed analyses and examination he stated the following: that ‘it will be concluded that theannual accumulation rate of earplug lamination must be less than two, probably near one, and averageannual ovulation rate will be under one, probably near 0.5, although there are individual and racialvariations. In addition, the average age at sexual maturity will be older than 5 years, probably 9–11years. Of course, there are individual variations in the age of sexual maturity’ (Ohsumi, 1964).
The conclusions above regarding the annual deposition rate of earplug laminations had strong implications for the assessment and management not only of ﬁn whales but of several other balaenopterid species where earplugs were subsequently used for determining the age, e.g., Antarctic minke
whales. In his 1964 publication, Seiji recommended that ‘the standardization of the reading of earplug
lamination should be established….’. Subsequent work on Antarctic minke whales and other species
have beneﬁted from the early studies of Seiji, and standardization has been conducted thoroughly inrecent years. Age data based on earplugs have also been very useful in the calibration of molecularmethods being developed to determine age in the Antarctic minke whales.
In the ﬁeld of natural science there are many contributions from Seiji not only on large baleen
whales but also on odontocetes. Here we would like to highlight the investigation he made on theschool structure of sperm whales (Ohsumi, 1971).
Ohsumi (1971) studied the structure of sperm whale using biological information obtained fromthree complete schools taken in coastal waters of Japan (1) and pelagic waters of the Southern Hemisphere (2). Information examined included the number of whales forming a school, size distribution,
sex ratio, sexual maturity, physical maturity, age distribution and sexual condition of whales which
form a school.
Based on detailed analyses, Seiji proposed the following hypothesis on the formation of sperm
whale schools, in which the behavioral foundation of sperm whales is considered to be a maternalfamily group.
• The fundamental form of a sperm whale school is the ‘nursery school,’ which is composed of mature
females and calves nursed by mature females.
• Immature males and females are also nursed by mature females until the time of sexual maturity.
• The average size of school was estimated to be 27.1 whales, and half of them are mature females.
• A nursery school moves as a tightly united school and remains as a family for long time.
• Some immature whales leave the nursery school after weaning to form ‘juvenile schools.’• After attainment of puberty, all males gradually leave the nursery school. Males at puberty form
‘bachelor schools.’• Socially mature males or bulls form a small ‘bull school’ or live alone. Most bulls are considered tolive as solitary animals.
• Bulls struggle with each other to join a nursery school in the breeding season, and the winning bulland the nursery school form the so-called ‘harem.’
Seiji also estimated that the number of mature females served by a bull in a harem was 14 on average.
This study was not only important in understanding the natural history of sperm whales but it wasalso useful for their assessment. In particular, parameters important for assessment include the numberof mature females with which a bull mates and the ratio of number of males/mature females; information on both was obtained in Seiji’s study (Ohsumi, 1971).
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Special awards
His scientiﬁc and dissemination work on cetaceans and whaling was recognized with numerous
awards including the following:• The Order of the Sacred Treasure, Gold Rays with Rosette (2002).
• The Royal Norwegian Order of Merit (2006).
• Special Award of the Mammal Society of Japan (2011).
Some ﬁnal thoughts
Seiji’s scientiﬁc contribution to the knowledge of cetaceans is enormous. He made contributions
not only in the ﬁeld of basic biology and ecology of cetaceans but also contributed substantially inthe assessment of several species, which was translated into appropriate policies of conservation andmanagement. He was a hard worker in the ﬁeld, in the laboratory (Fig. 1), in the analyses, and in thepreparation of scientiﬁc communications. He was very skilled at expressing his ideas and studies
through written and oral presentations, which were understandable to diﬀerent audiences. We werefortunate not only to share with him the same institute and discuss together research plans and results,
but also share social events that Seiji enjoyed very much. In particular many colleagues and friends
with Japanese knowledge appreciated his beautiful Japanese sentence expressions. His enthusiasm forthe study of cetaceans was evident throughout his life as he was assisting the ICR until the very last
moment before his death. His enthusiasm, energy, productivity and courtesy should be an example forthe younger cetacean scientists, especially for those working at the ICR.
References
Laws, R. M. and Purves, P. E. 1956. The ear plug of the Mysticeti as an indication of age with special reference to the North
Atlantic ﬁn whale. Norsk Hvalfangst-Tid. 45 (8): 413–425.
Mackintosh, N. A. and Wheeler, J. F. G. 1929. Southern blue and ﬁn whales. Discovery Rep. 1: 257–540.
Nishiwaki, M. 1950. Determination of the age of Antarctic blue and ﬁn whales by the colour changes in crystalline lens. Sci.
Rep. Whales Res. Inst. 4: 115–161.
Nishiwaki, M., Hibiya, T. and Kimura, S. 1954. On the sexual maturity of the sei whale of the Bonin waters. Sci. Rep.
Whales Res. Inst. 9: 165–177.
Ohsumi, S., n.d. A study on age determination of the ﬁn whale. Doctoral Thesis, The University of Tokyo. UTokyo Repository. doi: 10.15083/00078951.
Ohsumi, S. 1964. Examination on age determination of the ﬁn whale. Sci. Rep. Whales Res. Inst. 18: 49–88.
Ohsumi, S. 1971. Some investigations on the school structure of sperm whales. Sci. Rep. Whales Res. Inst. 23: 1–25.
Purves, P. E. 1955. The wax plug in the external auditory meatus of the Mysticeti. Discovery Rep. 27: 293–302.
Ruud, J. T. 1940. The surface structure of the baleen plates as a possible clue to age in whales. Hvalrådets Skrifter 23: 1–24.

Fig. 1.

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Dr. Seiji Ohsumi counting growth laminae in a whale earplug at ICR (August 5, 2010).
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