• 한국수산과학회지
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• 제42권6호
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• pp.650-656
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• 2009

Recently, bottlenose dolphins have frequently appeared in coastal waters of the Jeju Islands. To determine whether these individuals belong to one or more pods, the Cetacean Research Institute (CRI) established visual and photo-identification surveys in the Jeju Islands from November 2007 to July 2009. During visual surveys, pods composed of 10 to 80 individuals were sighted mainly in the northeastern and northwestern of Jeju Islands. Eighty-nine individuals were identified and cataloged by photo-identification using natural nicks and notches on their dorsal fins. Thirty-six individuals were identified three times or more, and nine individuals were identified five times during seven surveys. One individual appeared in November 2007, August 2008, October 2008, April 2009, and July 2009. The results of our study confirm that these dolphins represent a coastal resident stock. Futhermore, we will establish dolphin abundance, management, and usage studies using continuous visual and photo-identification surveys.

• Fisheries and Aquatic Sciences
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• 제11권3호
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• pp.166-171
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• 2008

The feasibility of photo-identification techniques for the bottlenose dolphins from Jeju Island, Korea, and the potential for dolphin watching were simultaneously evaluated in this study. During the sighting survey, a pod of bottlenose dolphins composed of approximately 30 individuals was observed in the southwestern coastal area of Jeju Island. Among 35 suitable photographs, five bottlenose dolphin individuals were identified and cataloged using unique nicks and notches on their dorsal fins. This shows that the Jeju Island dolphins can be individually identified by the nicks and notches on their dorsal fins using photo-identification techniques. Furthermore, the Jeju Island population appears to be suitable for long-term population biology studies using this technique. The potential for dolphin watching around the island would be higher if more information on the seasonal distribution, movement, and residency of this population were obtained.

• Animal cells and systems
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• 제14권3호
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• pp.213-219
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• 2010

Bottlenose dolphins (Tursiops sp.) commonly inhabit Korean waters, including the coastal waters of Jeju Island. However, their taxonomic position was unclear because of the validity of this genus. The genus Tursiops has recently been determined to comprise two species: the common bottlenose dolphin (Tursiops truncatus) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus). To confirm the taxonomic position of bottlenose dolphins frequenting the coastal waters of Jeju Island, the external morphology and osteology of specimens from Jeju Island were examined. Photographs of free-swimming individuals were also used for determining external morphological characters. The cranial and meristic measurements fell within the ranges of T. aduncus. Osteological ratios were also consistent with those of T. aduncus. The presence of a prominent ventral spot was observed among some individuals. As a result, the dolphins mainly distributed in the coastal waters of Jeju Island were identified as Indo-Pacific bottlenose dolphins (T. aduncus) in terms of their cranial characters and ventral spotting. We propose a new Korean name, 'Nambang-keun-dol-go-rae'.

• 수산해양기술연구
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• 제59권4호
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• pp.399-406
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• 2023

This study presents an analysis of bycatch data concerning Pacific white-sided dolphins (Lagenorhynchus obliquidens) along the Korean coast from 2016 to 2021. A total of 503 bycatches were examined, encompassing data on year, month, body length, sex, latitude (N), longitude (E), and fishing gear. Bycatch was the most frequent in waters with a longitude of less than 130°E, particularly in the southern coastal region at a latitude of 35.5°N, with a higher likelihood of bycatch in lower latitudes. Since 2017, a decreasing trend in bycatches has been observed. The sex distribution of bycaught dolphins showed a predominance of males (40%), followed by females (31%), with an unclassified category at 29%, though no statistically significant differences were found (p > 0.05). Seasonal analysis indicated that bycatch predominantly occurred during the winter months, with significant monthly variations (p < 0.01). Pacific white-sided dolphins were primarily ensnared in gill nets and, to a lesser extent, in stationary nets. Statistical analysis by gear type revealed a significant preference for gill nets (p < 0.001). Considering body length composition in relation to latitude, it is suggested that Pacific white-sided dolphins may utilize the southern waters of the East Sea as a potential nursery ground, though this was not confirmed at a significant level, emphasizing the need for further in-depth monitoring and ecological investigations. Given that there are approximately 27 different types of gill nets associated with the majority of bycatches, more detailed research is warranted to divide these gear types into finer subcategories for estimating bycatch relationships, ultimately leading to the development of effective conservation and management strategies.

• Advances in Computational Design
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• 제1권2호
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• pp.175-194
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• 2016

Nature has provided inspiration for most of the man-made technologies. Scientists believe that dolphins are the second to humans in smartness and intelligence. Echolocation is the biological sonar used by dolphins for navigation and hunting in various environments. This ability of dolphins is mimicked in this paper to develop a new optimization method. Dolphin Echolocation Optimization (DEO) is an optimization method based on dolphin's approach for hunting food and exploration of environment. DEO has already been developed for discrete optimization search space and here it is extended to continuous search space. DEO has simple rules and is adjustable for predetermined computational cost. DEO provides the optimum results and leads to alternative optimality curves suitable for the problem. This algorithm has a few parameters and it is applicable to a wide range of problems like other metaheuristic algorithms. In the present work, the efficiency of this approach is demonstrated using standard benchmark problems.

• 한국수산과학회지
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• 제48권6호
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• pp.940-946
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• 2015

The Indo-Pacific bottlenose dolphin Tursiops aduncus commonly inhabits the coastal waters of Jeju Island, Korea. An investigation was conducted using data from vessel sightings and point sightings from land. During 40 days of vessel sighting surveys between 2007 and 2010, a total of 18 dolphin groups were encountered. The overall sighting rate was 0.01 group/n.m. Most Indo-Pacific bottlenose dolphins were sighted within 500 m of the northern coast of Jeju Island during surveys. Also, dolphin groups were observed 47 times during 109 days of shore-based surveys conducted between 2011 and 2015. The results of a dolphin distribution survey conducted in 2011 were generally similar to the results of previous surveys. However, there were no dolphin sightings from 2012 in Hanllim-eup, in the north-western part of the island, where dolphins were sighted frequently until 2011, whereas dolphin observations increased in the southern part of the island. The mean group size was 35.4 (SD=18.08) individuals. The most frequently sighted group size was 36-40 individuals. To conserve resident dolphins off Jeju Island, long term sighting surveys and environmental assessment are required to monitor their distribution patterns.

• 한국수산과학회지
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• 제49권6호
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• pp.875-882
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• 2016

The numbers of books, news articles, and documentary films on whales and dolphins have increased dramatically in Korea. The translation of 37 species with established Korean names, as reviewed and reported by Sohn et al. (2012), Kim et al. (2010), and Kim et al. (2013) in those books and public media, was not a problem. However, 52 cetacean species, which do not have proper Korean names, have been translated into Korean, causing confusion in the public. This short note suggests Korean translations for common names that have no Korean names based on the origins of the English common names, recent scientific information, and books on cetaceans.

• 한국수산과학회지
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• 제50권4호
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• pp.406-412
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• 2017

Vocalizations of the common dolphin Delphinus Delphis, were recorded from a single hydrophone while coastal visual survey was performed in the East Sea in March 2017. Like most Delphinidae, common dolphins produce whistles, echolocation clicks, and burst-pulsed calls, with repertoires that differ between species and geographically separated populations. This study focuses on using frequency analysis to classify sounds into three categories and to compare them with those of other common dolphin populations. The fundamental frequencies of the whistles were high in the 6 to 14 kHz range, while echolocation clicks were in the 40 to 90 kHz frequency band. These results are similar to high-energy distributions in the same frequency band in other regions. Based on this study of the acoustic characteristics of dolphins off the east coast of Korea, cetacean vocalizations can be classified using a database of cetacean sounds in Korea. In addition, this technique could improve data quality for visual whale surveys and could be applied to various other research subjects.

• Ocean Science Journal
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• 제43권4호
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• pp.175-182
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• 2008

Bottlenose dolphins are the only cetaceans regularly observed in the northern Adriatic Sea, but they survive at low densities and are exposed to significant threats. This study investigates some of the factors that influence habitat use by the animals in a largely homogeneous environment by combining dolphin data with hydrological and physiographical variables sampled from oceanographic ships. Surveys were conducted year-round between 2003 and 2006, totalling 3,397 km of effort. Habitat modelling based on a binary stepwise logistic regression analysis predicted between 81% and 93% of the cells where animals were present. Seven environmental covariates were important predictors: oxygen saturation, water temperature, density anomaly, gradient of density anomaly, turbidity, distance from the nearest coast and bottom depth. The model selected consistent predictors in spring and summer. However, the relationship (inverse or direct) between each predictor and dolphin presence varied among seasons, and different predictors were selected in fall. This suggests that dolphin distribution changed depending on seasonal forcing. As the study area is relatively uniform in terms of bottom topography, habitat use by the animals seems to depend on complex interactions among hydrological variables, caused primarily by seasonal change and likely to determine shifts in prey distribution.

• 한국수산과학회지
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• 제52권6호
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• pp.740-744
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• 2019

Pacific white-sided dolphins Lagenorhynchus obliquidens inhabit cool temperate waters; in Korean waters, they concentrate near the coast of Gangwon and Gyeongbuk from late autumn to early spring. We collected 15 individuals from Yeongduk, Gyeongju, Ulsan, and Busan between December 2018 and February 2019 and analyzed their stomach contents. Fresh prey items were identified to the species level, and residual stomach contents that were unidentified due to digestion were filtered through a sieve to find fish otoliths and cephalopod beaks. The most important prey items of Pacific white-sided dolphins were cephalopods, composing 68.0% of the diet by occurrence. Fishes were the second largest dietary component, making up 32.0% of the diet by occurrence. Of the cephalopod species consumed, Watasenia scintilans was the principal prey item.