DEMOGRAPHIC PARAMETERS OF INDO‐PACIFIC BOTTLENOSE DOLPHINS (TURSIOPS ADUNCUS) AROUND MIKURA ISLAND, JAPAN

Abstract

Long‐term identification surveys were conducted using video records on Indo‐Pacific bottlenose dolphin (Tursiops aduncus) around Mikura Island, Tokyo, Japan. On 246 surveys, 3,996 min of video were recorded during each summer season from 1994 to 2001. Two hundred and twenty individuals were observed, including juveniles and neonates, that were not cataloged, but could be identified by association with their mothers. Over the eight‐year study period, the total number of identified and cataloged individuals was 169. The annual number of newly identified dolphins stabilized at ∼ 10 after 1995. In the middle of each research season, a plateau in the number of reidentified individuals was reached. Most of the dolphins were observed frequently–percentages of reidentified dolphins in adjoining years were greater than 86% and 62 individuals were seen consecutively during the eight years. There were no significant differences in the sex ratio between years. The sex ratio was skewed significantly towards male for subadults and towards female for adults. The survival rate of one‐year‐old calves was 86.7%, and the mean age at weaning was 3.5 yr. The calving interval averaged 3.4 yr among adult females. The mean annual birth, fecundity, and recruitment rates were 0.071, 0.239, and 0.068, respectively. Mikura Island is located in the pelagic ocean with no protected bay area existing around the island. Dolphins do not regularly inhabit any other locations besides Mikura within the Izu island chain. Thus, this island may be important core habitat of these dolphins.

Report of the Working Group on Population Parameters and Demography of Tursiops truncatus in the Southwest Atlantic Ocean

“…The result found is consistent with values reported for other populations of bottlenose dolphins worldwide (e.g. Wells and Scott, 1990;Kogi et al, 2004). Using the same dataset, mean annual birth rate (calculated as the proportion of calves born to the total population size) was estimated at 9% for the Patos Lagoon population (Fruet et al, 2015a), a result similar to that of the bottlenose dolphins from Moray Firth, Scotland (Wilson et al, 1999) and Fiordland, New Zealand (Haase and Schneider, 2001).…”

Pectoral fin contact as a mechanism for social bonding among dolphins

“…The lack of evidence for consistent dominance hierarchies could be related to sample size. That is, multi-year, detailed, lengthy observations of inter-individual interactions are available only from a few wild study populations (e.g., Connor & Krützen, 2015;Dudzinski et al, 2009;Elliser & Herzing, 2014;Kogi et al, 2004;Wells et al, 1987). Assuming dolphin social structure includes some level of dominance hierarchy, specific tactile affiliative behavior(s) might function as a tool to mitigate interactions to reinforce the relationship status among individuals in a group.…”

“…In several dolphin groups studied, it would seem that samesex, same-aged pairings represent the primary framework for the fission-fusion society with mixed-sex associations happening, but not as frequently; for example, Atlantic spotted dolphins, Stenella frontalis, in The Bahamas (Dudzinski, 1996;Elliser & Herzing, 2014;Herzing, 1997;Herzing & Brunnick, 1997); Indo-Pacific bottlenose dolphins, Tursiops aduncus, around Mikura (Kogi, Hishi, Imamura, Iwatani, & Dudzinski, 2004) and in Australia (Connor, 1992;; common bottlenose dolphins, T. truncatus, in the USA (Wells, 1991;Wells, Scott, & Irvine, 1987) and in The Bahamas (Rossbach & Herzing, 1999). Social tactile contact can be affiliative or agonistic (e.g., Connor, Mann, & Watson-Capps, 2006;Dudzinski, 1996Dudzinski, , 1998, and previous research suggests that at least some dolphins have preferred partners with whom they exchange contact (e.g., Connor et al, 1992;Connor, Smolker, & Bedjer, 2006;Dudzinski, 1998;Herzing & Brunnick, 1997).…”

“…Affiliative behaviors, especially tactile contact among dolphins, could be considered one form of currency used in the development of social bonds (Cords, 1997); many smaller delphinid species reside in fission-fusion societies (Kogi et al, 2004;Smolker, Richards, Connor, & Pepper, 1992;Wells et al, 1987). Small subgroups will mix to form larger groups for foraging or other activities before separating again into the same or different subgroups , with this multi-level socializing requiring complex cognitive abilities to keep track of individuals with whom one is familiar or not .…”

Factors influencing heterogeneity in female reproductive success in a Critically Endangered population of bottlenose dolphins

“…when a calf died shortly after birth). This problem is well recognised in other studies of calf survival in marine mammals , Kogi et al 2004, Currey et al 2009b). Failure to record a calving event in which the calf had died soon after birth would cause calf survival rates to be biased high.…”