Hikaru Watanabe’s research while affiliated with National Research Institute of Far Seas Fisheries and other places

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Publications (23)


Biogeography of small odontocetes in relation to wide-scale oceanographic structure in the North Pacific Ocean
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March 2016

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84 Reads

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21 Citations

Fisheries Oceanography

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Makoto Okazaki

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Hikaru Watanabe

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Tomio Miyashita

Information regarding the distributional patterns of top predators is undoubtedly important for the monitoring and management of marine ecosystems. Nevertheless, previous knowledge on the distributional patterns of cetacean species in relation to physical oceanography is usually limited to a small fraction of each species' range because of their vast distribution and infrequency of encountering many species. We carried out comprehensive analyzes on the distributions of small odontocetes covering almost the entire North Pacific Ocean. Using data from over 300 000 nautical miles (≈ 555 600 km) of dedicated sighting surveys and 7000 school sightings of 14 small odontocete species, which have accumulated for approximately a quarter of a century, we describe interspecific habitat differences in small odontocetes with respect to physical oceanography. Multivariate analyzes were used to discriminate the 14 species into four ecological groups: (i) Subtropical Domain species; (ii) Subarctic Boundary species; (iii) Transitional Domain species; and (iv) Subarctic Domain species. By comparing environmental variables in their habitats with variables indicative of water mass and frontal structures, the four species groups were further divided into several subgroups. Groups at higher latitudes comprised fewer species than those at lower latitudes, while species diversity was maximal at lower and intermediate latitudes. Our findings indicate that large-scale oceanographic structures are important determinants for the present patterns in biogeography and species diversity of small odontocetes.


Variability in reproductive investment of skipjack tuna (Katsuwonus pelamis) in relation to the ocean–climate dynamics in the tropical eastern Indian Ocean
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  • Publisher preview available

August 2012

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50 Reads

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4 Citations

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Hikaru Watanabe

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[...]

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Makoto Okazaki

The Indian Ocean is characterised by significant climatic and oceanographic variability such as the seasonal monsoon and the decadal and inter-annual oscillation of the Indian Ocean Dipole (IOD). Understanding the effects of ocean–climate variability on marine top predators is important for both fisheries and ecosystem management. To test the hypothesis that variability in surface and subsurface temperature affects the annual reproductive cycles of skipjack tuna (Katsuwonus pelamis) in the tropical eastern Indian Ocean, we examined the seasonal and inter-annual variations of the gonadosomatic index (GSI) and determined hatch date by using otolith microstructure analysis. The GSI tended to be higher in January–February during the north-eastern monsoon when seawater cooling at the subsurface layer is induced by the seasonal inflow of the South Equatorial Countercurrent (SECC). The mode of the hatch-month distribution was also detected in that season. The generalised linear model (GLM) resulted in a dome-shaped quadratic relationship, with a peak GSI between 24°C and 26°C occurring at a depth of 50 m during austral summer. These findings indicate that seasonal monsoons and associated changes in oceanographic conditions strongly affect the energy-allocation pattern of skipjack tunas.

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Habitat and prey selection of common minke, sei, and Bryde’s whales in mesoscale during summer in the subarctic and transition regions of the western North Pacific

May 2012

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106 Reads

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17 Citations

Fisheries Science

This study represents the first quantitative analysis of the characteristics of the distribution areas and stomach contents of common minke whale Balaenoptera acutorostrata, sei whale B. borealis, and Bryde’s whale B. edeni in relation to oceanographic and prey environments in mid summer in the western North Pacific. Common minke whales were distributed within subarctic regions and the northernmost region of the transitional domain, coinciding with the main habitat of their preferred prey, Pacific saury Cololabis saira. Sei whales were mainly found in the northernmost part of the transition zone and showed prey preference for Japanese anchovy Engraulis japonica, which was significantly more abundant in the main distribution area of the whale than in its adjacent areas. “Hot spots” of Bryde’s whales were found in several regions of the transition zone between the subarctic boundary and the Kuroshio front. This whale species preferred Japanese anchovy as prey, for which the distribution density was significantly higher in the main distribution area of the whale than in the adjacent areas. These results indicate that the summer distributions of Pacific saury and Japanese anchovy greatly influence the distributions of these whale species, suggesting that the whales’ habitat selection is closely related to their prey selection.


Feeding ecology of the swordfish Xiphias gladius in the subtropical region and transition zone of the western North Pacific

December 2009

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98 Reads

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34 Citations

Marine Ecology Progress Series

This is the first time a quantitative analysis has been carried out on feeding habits of swordfish Xiphias gladius (n = 455), mainly ranging from 1200 to 2100 mm in eye-fork length, in the western North Pacific. Based on these data, we examined the feeding ecology of this species in relation to its seasonal south-north migration between subtropical and transition waters. The main X. gladius prey size was 80 to 500 mm, and the size spectrum of the prey shifted to a smaller range from spring to summer. In winter and spring, X. gladius was distributed in the subtropical region and fed mainly on the winter-spring cohort of neon flying squid Ommastrephes bartramii, followed by Pacific pomfret Brama japonica. In summer and autumn, X. gladius migrated to the transition zone between the Kuroshio front and subarctic boundary and fed mainly on the winter-spring cohort of O. bartramii, which also migrates into the transition zone from the subtropical region in Summer. Other common prey species in summer and autumn were the gonatid squid Gonatopsis borealis and the myctophid fish Diaphus gigas, which are endemic to transition and/or subarctic regions. B. japonica almost disappeared from the stomachs of X. gladius during these seasons because this species migrates in summer into the subarctic region, north of the range of X. gladius. Therefore, seasonal changes in stomach contents of X. gladius could be explained by the difference in seasonal south-north migration patterns between predator and prey. The seasonal south-north migration of X. gladius seems to be a feeding migration, following the migration of the winter-spring cohort of O. bartramii.


Acoustic characterization of biological backscatterings in the Kuroshio‐Oyashio inter‐frontal zone and subarctic waters of the western North Pacific in spring

November 2009

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52 Reads

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33 Citations

Fisheries Oceanography

The acoustic characteristics of biological backscattering in the western North Pacific were studied to verify expert knowledge on species composition in the echosigns. The survey was conducted in the Kuroshio-Oyashio inter-frontal zone and the subarctic waters in April 2003. The species composition of backscatterings was identified by using midwater trawl, Isaacs-Kidd midwater trawl and Bongo net. The differences of mean volume backscattering strengths between 120 and 38 kHz (ΔMVBS120−38) were calculated for the backscatterings. Six types of backscatterings were classified based on the results of net samples and the ΔMVBS120−38. The ΔMVBS120−38 of each group was as follows: copepods 13.7–17.3 dB, krill 11.6–15.3 dB, Japanese anchovy −1.6 to 1.1 dB, a myctophid, Diaphus theta−0.8 dB, sand lance 6.1 dB and larvae and juveniles of pelagic and mesopelagic fish −9.6 to −4.0 dB. The results suggest that biological backscatterings in the Kuroshio-Oyashio inter-frontal zone and subarctic waters of the western North Pacific in spring can be characterized by using ΔMVBS.


Diet and sexual maturation of the neon flying squid Ommastrephes bartramii during autumn and spring in the Kuroshio–Oyashio transition region

March 2008

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51 Reads

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25 Citations

Journal of the Marine Biological Association of the UK

Diet and sexual maturation were examined in the winter–spring cohort of the neon flying squid, Ommastrephes bartramii, during its southward migration through the Kuroshio–Oyashio transition region of the western North Pacific. The main prey items are micronektonic animals and small pelagic fish, which were abundantly distributed throughout the study area. Among the prey species, O. bartramii was dependent on the Japanese anchovy Engraulis japonicus, which also migrate from the northern to southern transition region during the winter, and the micronektonic squid Watasenia scintillans throughout the study period. Other common prey items were Gonatopsis borealis, Diaphus theta, and Ceratoscopelus warmingii from October to November or December, and Tarletonbeania taylori after December. These dietary changes can be explained by the difference in the seasonal north–south migration patterns of the predator and prey species. Male sexual maturation progressed throughout the season, and most individuals were fully mature in January. In contrast, most of the females were immature throughout the study period. The feeding strategy of the squid in relation to their seasonal north to south migration and sexual maturation was discussed.


Feeding habits of the blue shark, Prionace glauca, and salmon shark, Lamna ditropis, in the transition region of the Western North Pacific

June 2007

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183 Reads

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92 Citations

Reviews in Fish Biology and Fisheries

We describe the feeding habits of 70 blue sharks (Prionace glauca) and 39 salmon sharks (Lamna ditropis) caught at 0–7m depth at night by research drift gillnets in the transition region of the western North Pacific during April–May of 1999 and 2000. Blue sharks of 50–175cm total length fed on a large variety of prey species, consisting of 24 species of cephalopods and 16 species of fishes. Salmon sharks of 69–157cm total length fed on a few prey species, consisting of 10 species of cephalopods and one species of fish. Important prey for the blue sharks were large, non-active, gelatinous, meso- to bathypelagic cephalopods (e.g., Chiroteuthis calyx, Haliphron atlanticus, Histioteuthis dofleini and Belonella borealis) and small myctophid fishes. Important prey for the salmon sharks were mid-sized, active, muscular, epi- to mesopelagic squids (e.g. Gonatopsis borealis, Onychoteuthis borealijaponica and Berryteuthis anonychus). Our results suggest that blue sharks feed on cephalopods mainly during the daytime when they descend to deep water. Salmon sharks may feed opportunistically with no apparent diurnal feeding period. Blue sharks and salmon sharks have sympatric distribution in the transition region in spring; they have different feeding habits and strategies that reduce competition for food resources.


Prey selection of common minke (Balaenoptera acutorostrata) and Bryde's (Balaenoptera edeni) whales in the western North Pacific in 2000 and 2001

February 2007

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56 Reads

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50 Citations

Fisheries Oceanography

A study of common minke and Bryde's whales was conducted in the western North Pacific in the 2000 and 2001 summer seasons to estimate prey selection of cetaceans as this is an important parameter in ecosystem models. Whale sighting and sampling surveys and prey surveys using quantitative echosounder and mid-water trawl were carried out concurrently in the study. Biomasses of Japanese anchovy, walleye pollock and krill, which were major prey species of common minke and Bryde's whales, were estimated using an echosounder. The results suggested that common minke whale showed prey selection for Japanese anchovy while they seemed to avoid krill in both the offshore and coastal regions and walleye pollock in the continental shelf region. Selection for shoaling pelagic fish was similar to that in the eastern North Atlantic. Bryde's whale showed selection for Japanese anchovy in August 2000 and July 2001, while it showed prey selection for krill in May and June in 2001.


Diel vertical migration of squid in the warm core ring and cold water masses in the transition region of the western North Pacific

June 2006

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369 Reads

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80 Citations

Marine Ecology Progress Series

We examined the diel vertical migration of squid (dorsal mantle length 21 to 490 mm) in warm core ring (WCR) and cold water mass (CW) areas in the transition region of the western North Pacific. A total of 28 squid species belonging to 23 genera, 2 octopus species from 2 genera, and 1 vampyrmorph Vampyroteuthis infernalis were captured from depths of 20 to 700 m by day and night sampling using a commercial otter trawl. Three patterns of diel vertical migration were recognized for 11 of the squid species. (1) Migrant, in which day and night habitats are clearly separated with peak abundance deeper than 300 m during the day and shallower than 300 m at night: Gonatopsis borealis, Gonatus berryi, Gonatus onyx, Eucleoteuthis luminosa, Onychoteuthis banksii, Ehoploteuthis chunii, and Watasenia scintillans. (2) Semi-migrant, in which part of the population migrates to the upper 100 m at night from its daytime habitat of 500 to 600 m, while the remainder of the population mainly remains in the daytime habitat: O. borealijaponica. (3) Non-migrant, in which the habitat is consistently distributed below 400 m: Histioteuthis dofleini, Belonella borealis, and H. inermis. Horizontally, E. luminosa, E. chunii, and H, inermis were restricted to the WCR, while other species were distributed in both the WCR and CW areas in the transition region. Among the vertically migratory and semi-migratory species, nighttime distribution depth was similar between WCR and CW for O. banksii, but was deepened by upper layers of warm subtropical waters in the WCR for G. borealis, G. berryi, W, scintillans, and O. borealijaponica. We also examined day-night habitat temperature ranges for these 11 species.


Feeding habits of albacore Thunnus alalunga in the transition region of the central North Pacific

August 2004

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43 Reads

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39 Citations

Fisheries Science

The feeding habits of albacore Thunnus alalunga (fork length: 48.9–76.2 cm, n = 132) were examined from late spring to early autumn in relation to its northward migration in the transition region between the subtropical and subarctic fronts in the central North Pacific. Samples were collected at night using surface gill nets or during daytime pole-and-line surveys in 2001 and 2002. During May and June, albacore fed mainly on Japanese anchovy Engraulis japonicus, which accounted for 27.2%, 67.0%, and 45.5% of the total stomach contents by number (Cn), wet weight (WW), and frequency of occurrence (F), respectively, and secondarily on the subarctic gonatid squid Gonatopsis borealis (Cn, 15.8%; WW, 10.8%; F, 28.8%). From July to September, albacore continued to depend on Japanese anchovy (Cn, 48.2–52.8%; WW, 79.9–95.2%; F, 27.8–85.4%). These results corresponded well with the remarkable rebound of the Japanese anchovy stock since the 1990s. Gonatopsis borealis, the main squid prey from May to June, almost disappeared from the stomachs of albacore from July to September, probably due to the northward migration of this squid to subarctic waters in summer. The feeding impact of albacore on the Japanese anchovy stock in the transition region was conservatively estimated to be from 1400 to 2100 tons per day from late spring to early autumn.


Citations (19)


... Short-finned pilot whales are widely distributed in both hemispheres in tropical, subtropical and warm-and cold-temperate waters in the North Pacific (Olson 2018). In the Western North Pacific, their main habitats exist along the Kuroshio current including Kuroshio waters, Kuroshio extension waters and Kuroshio-Oyashio mixed water regions (Kanaji et al. 2015b(Kanaji et al. , 2016Kanaji, Okazaki, and Miyashita 2017) (Figure 1). The population inhabiting the Kuroshio-Oyashio mixed water regions is recognized as a genetically and morphologically distinct population from those other waters and is commonly called Tappanaga or the northern form (Kasuya, Miyashita, and Kasamatsu 1988;Wada 1988;Kasuya and Tai 1993;Miyazaki and Amano 1994). ...

Reference:

Recovering or Still Depleted? Updated Population Assessment of Tappanaga , a Northern Local Population of Short‐Finned Pilot Whales ( Globicephala macrorhynchus ) off the Coast of Japan
Biogeography of small odontocetes in relation to wide-scale oceanographic structure in the North Pacific Ocean
  • Citing Article
  • March 2016

Fisheries Oceanography

... Sebastine et al. (2011) reported that monounsaturated FAs (predominantly 18:1) are the most abundant FAs of Watases lanternfish. Seo et al. (1996) has reported that 16:0 acid and DHA are the major FAs in tropical myctophids, whereas 18:1 (n-9) and 16:0 are the predominant FAs in temperate species. These previous studies are largely consistent with our results, and indicate that differences of FA profiles among micronekton could largely be caused by differences in ambient water temperature. ...

Characterization of Lipids in Myctophid Fish in the Subarctic and Tropical Pacific Ocean
  • Citing Article
  • June 1996

Fisheries Science

... The oceanographic characteristics in this research (SST, chl-a, sal, wav, win and cur) were the natural explanatory variable in explaining skipjack CPT relationships. This is consistent with other researches within Indonesia and the regions (Kuo-Wei et al., 2017;Kanaji et al., 2012;Zainuddin et al., 2013). For instance, there was a relationship between skipjack tuna CPUE and SST in Brazilian waters (Andrade and Garcia, 1999;Andrade, 2003). ...

Variability in reproductive investment of skipjack tuna (Katsuwonus pelamis) in relation to the ocean–climate dynamics in the tropical eastern Indian Ocean

... It spans more than 8000 km across the North Pacific, and seasonally moves north and south by about 1000 km, between 30-35°N in the winter to about 40-45°N in the summer (Polovina et al., 2001). During surveys between 2008 and 2021 Bryde's whales were present in waters between 35-40°N in July to August (Hakamada and Matsuoka, 2016;Katsumata and Matsuoka, 2022), and were following the distribution of juvenile Japanese sardine and anchovy, which move north with the TZCF in spring and summer (Watanabe et al., 2012;Sasaki et al., 2013). However, Murase et al. (2016) deployed satellite tags on two Bryde's whales Histogram of the intercall intervals calculated for the manually annotated HARP data. ...

Habitat and prey selection of common minke, sei, and Bryde’s whales in mesoscale during summer in the subarctic and transition regions of the western North Pacific
  • Citing Article
  • May 2012

Fisheries Science

... Due to specimen damage, squid whose sex or ML could not be determined were excluded from the analysis. Maturity stages were assigned following the criteria used for the Japanese flying squid Todarodes pacificus, which is closely related to O. bartramii and belongs to the same family Ommastrephidae (Yatsu et al. 1998;Sakurai et al. 2003;Watanabe et al. 2008). Based on the maturity stage, each male was classified as immature, maturing, or mature. ...

Diet and sexual maturation of the neon flying squid Ommastrephes bartramii during autumn and spring in the Kuroshio–Oyashio transition region
  • Citing Article
  • March 2008

Journal of the Marine Biological Association of the UK

... También se han efectuado investigaciones en migraciones diarias verticales nocturnas, en el crecimiento y en la fisiología de su tapetum reflectante (Fujita et al., 1995;Bigelow et al., INTRODUCCIÓN 1995;Takei et al., 2003). Se alimenta principalmente de anfípodos, cefalópodos y peces (Pearcy et al., 1993;Watanabe et al., 2003Watanabe et al., , 2006. En B. japonica se han realizado algunos estudios parasitológicos con énfasis en cestodos, digeneos y crustáceos (Pearcy et al., 1993;Pozdniakov, 1993;Gibson, 1996;Moles, 2007 Los macroparásitos presentan selección a un área específica del pez hospedero (Le Roux et al., 2011). ...

Feeding habits of Pacific pomfret Brama japonica inthe transition zone of the central North Pacific
  • Citing Article
  • April 2003

Fisheries Science

... 2-20 cm, living in the ocean twilight zone, are important components of pelagic ecosystems (Brodeur and Yamamura, 2005). Because of their small size and swimming ability, micronektonic fish represent intermediate trophic links in marine pelagic food webs between zooplankton and organisms at higher trophic levels, such as predatory fish, seabirds, and marine mammals (Watanabe et al., 2009;Duffy et al., 2017). Micronektonic fish are regarded as one of the most abundant marine organisms whose global biomass is estimated to be much greater than 1,000 million tons (Irigoien et al., 2014;Proud et al., 2017Proud et al., , 2019 with high diversity and niche segregation in terms of prey preference and distribution depth (Hopkins and Gartner, 1992). ...

Feeding ecology of the swordfish Xiphias gladius in the subtropical region and transition zone of the western North Pacific
  • Citing Article
  • December 2009

Marine Ecology Progress Series

... The micronekton community in the environmental water was not observed in either our study or previous studies focusing on the feeding habits of B. splendens; however, the dominant prey in our study (A. quadrispinosa, P. prehensilis, E. chunii, C. calyx, S. gracilis, and G. elongatum) were common species in the Kuroshio area (Kikuchi & Omori, 1985;Sassa, 2019;Terazaki et al., 1994;Watanabe et al., 2006). Therefore, B. splendens could be an opportunistic feeder, as pointed out by Watari et al. (2017), and the micronekton community in the circumjacent environment would be the key to identifying basin-scale differences in gut contents. ...

Diel vertical migration of squid in the warm core ring and cold water masses in the transition region of the western North Pacific
  • Citing Article
  • June 2006

Marine Ecology Progress Series

... Especially myctophid fishes are major prey items of adult squids (Lipiński and Linkowski 1988;Quetglas et al. 1999;Phillips et al. 2001;Watanabe et al. 2004;Merten et al. 2017). Due to efficient predation, squids can exert topdown control on their prey during times of high occurrence (Clarke 1996;Quetglas et al. 1999;Boyle and Rodhouse 2005;Coll et al. 2013). ...

Feeding habits of neon flying squid Ommastrephes bartramii in the transitional region of the central North Pacific

Marine Ecology Progress Series

... We used some biological datasets, including body length, sex, weight of testis, and number of ovulations. Based on Kishiro et al. (2010) and Yoshida et al. (2009), a male with a testicle weighing more than 290 g and a female with at least 1 corpus luteum or albicans in the ovaries were regarded as sexually mature. Left earplugs were collected by using gelatin, and right earplugs were collected by using a standard procedure. ...

Cruise report of the Second phase of the Japanese Whale Research Program under Special Permit in the western North Pacific (JARPN II) in 2009 (Part II) - Coastal component off Kushiro
  • Citing Article