Developmental Changes in the Morphology of Western North Pacific Bryde’s Whales (&amp;lt;i&amp;gt;Balaenoptera edeni&amp;lt;/i&amp;gt;)

Takeharu Bando,Gen Nakamura,Yoshihiro Fujise,Hidehiro Kato

doi:10.4236/ojas.2017.73026

Abstract

Developmental changes in the body proportions of western North Pacific Bryde’s whales (Balaenoptera edeni) were investigated by examining the proportion of each body part to the total body length. The head and chest region increased to a certain body length; subsequently, the length of head region stabilized, and that of the chest region decreased. The length of the abdominal region remained constant to a certain body length and subsequently showed a marked increase, and that of the tail region decreased consistently. The length of dorsal fin and flukes decreased consistently, whereas that of the flippers remained constant to a certain body length and subsequently decreased. The relative growth pattern determined by an allometric analysis was positive for the head region but negative for the lower body part, flippers, flukes, and dorsal fin. Both sexes demonstrated the same growth pattern, but the coefficients differed. This is the first study to investigate developmental changes in the body proportions of Bryde’s whales using more than 700 specimens covering a wide body length range. We believe that the results of this study will contribute to various research fields, including taxonomy, phylogeny, and feeding ecology of this species.

Highlights

The body proportions of animals differ according to their adaptation to the environment [1]
This study aimed to investigate developmental changes in the body proportions and sex-based differences in the growth pattern of western North Pacific Bryde’s whales using more than 700 specimens covering a wide body length range
Measurements related to the head region (Eye, Ear, SKL, and SKW) showed similar trends; they increased to a particular body length and stabilized

Summary

Introduction

The body proportions of animals differ according to their adaptation to the environment [1]. Developmental changes in body proportions have been reported for some Balaenoptera species, such as blue (Balaenoptera musculus), fin (B. physalus), and sei (B. borealis) whales [3] [15] [16] [17] These studies have shown species-specific growth patterns, such as an increase in the length of the head region associated with a decrease in the length of the tail region in blue and fin whales [15] but no obvious trend in sei whales [16]. The prey species of Balaenoptera species range from planktonic crustaceans (copepods and krill) to schooling fishes, depending on the species [18] [19] [20] [21] They feed using a unique system called “lung feeding” in which they engulf a large mass of water with prey and extrude only the water by filtering the prey items using their baleen plates [22]. The high energy cost of “lung feeding” and the necessity to create sufficient swimming speed leads to an optimum body proportion based on the feeding habits and body size (growth stage) of each individual [23] [24] [25]

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