Oceanographic conditions in the JARPNII survey areafrom 2000 to 2013 using FRA-ROMS data
MAKOTO OKAZAKI1, MASACHIKA MASUJIMA1, HIROTO MURASE2 AND KENJI MORINAGA2
1

National Research Institute of Fisheries Science, Fisheries Research Agency (FRA), 2-12-4 Fukuura, Kanazawa,
Yokohama, Kanagawa 236-8648, Japan
2 National Research Institute of Far Seas Fisheries, Fisheries Research Agency (FRA), 2-12-4 Fukuura,
Kanazawa, Yokohama, Kanagawa 236-8648, Japan
ABSTRACT
Oceanographic conditions in the JARPNII survey area were study by using FRA-ROMS data. FRA-ROMS is an ocean forecast
system developed by Fisheries Research Agency (FRA) based on Regional Ocean Modeling System (ROMS). Changes in area(km2) of four water types (Oyashio, cold, warm and Kuroshio) by each month (April-September) in JARPNII survey area from2000 to 2013 was investigated. There was no statistical significant trend for the area except the cold water in September. Negativevalues of annual mean the Pacific Decadal Oscillation (PDO) index were dominant in the period from 2000 to 2013. Generally, sea
surface temperature in the western North Pacific is high in the negative phase of the PDO. The results of this study indicated that
overall oceanographic conditions in the JARPNII survey area from 2000 to 2013 were relatively stable although year to year
variations and spatial heterogeneity of distribution of water types were observed.

INTRODUCTION
The second phase of the Japanese Whale Research Program under Special Permit in the North Pacific (JARPNII)
has been conducted since 2000. The survey in the first two years (2000 and 2001) was conducted as a feasibility
study and then it has been conducted as a full scale research since 2003. The survey area was set in the western
North Pacific. Main target species of JARPNII are common minke (Balaenoptera acutorostrata), Bryde’s (B.
edeni), sei (B. borealis) and sperm (Physeter microcephalus) whales The southern, northern, eastern and westernboundaries of the survey area were 35°N, the boundary of the economic exclusive zone (EEZ) claimed by countries
other than Japan,170°E and the eastern coastline of Japan, respectively. The offshore component of JARPNII has
been conducted mainly from May to September. The coastal component off Sanriku and Kushiro has been
conducted mainly in April and September, respectively.
The northern part of the survey area is under the influence of the Oyashio (a subarctic western boundary
current with cold, low-salinity water) whereas the southern part is under the influence of the Kuroshio and its
extension (the subtropical western boundary current with warm, high-salinity water). The area between the
Oyashio and the Kuroshio is called the Kuroshio-Oyashio or subarctic-subtropical transition (interferential) zone
(Fig. 1).
The Kuroshio-Oyashio ecosystem is habitats for commercially important species such as Japanese sardine(Sardinops melanostictus), Japanese anchovy (Engraulis japonicus), Pacific saury (Cololabis saira), chubmackerel (Scomber japonicus) and Japanese common squid (Todarodes pacificus) and their population dynamics
are influenced by both environmental conditions and fisheries (Yatsu et al., 2013). It is recognized that bothclimatic and biological regime shifts occurred in the North Pacific Ocean. Commercial catch histories of pelagic
fishes have shown drastic fluctuation and quasi-decadal species alterations so-called species replacement in thewestern North Pacific since the 1950’s (Yatsu et al. 2001). Species replacement is a form of a biological regime
shift. Although there are many definition of regime shift, the study group of fisheries and ecosystem responses torecent regime shift under PICES defined regime shift as “a relative rapid change from one decadal-scale period ofa persistent state to another decadal-scale period of persistent state” (King, 2005).Based on climate indices suchas the Pacific Decadal Oscillation (PDO) index, various scientific literatures reported that regime shifts were
occurred in North Pacific around 1925, 1947, 1977 and 1998 in recent decades (King, 2005; Overland et al., 2008).
Responses of pelagic biological organisms to climatic regime shifts were reported including copepods (Tadokoro
et al., 2005), Japanese anchovy, Japanese sardine, Pacific saury and mackerel (Takasuka et al., 2008; Tian et al.,
2004; Yatsu et al., 2008). It is expected that fluctuation of oceanographic conditions and prey abundance affectspatial distribution and feeding habits of whales.
In this paper, it is investigated that whether oceanographic conditions in the JARPNII survey area werechanged from 2000 to 2013 by using FRA-ROMS data. FRA-ROMS is an ocean forecast system developed by
Fisheries Research Agency (FRA) based on Regional Ocean Modeling System (ROMS). Trends of annual meanof PDO index and North Pacific Index (NPI) from 1900 and 2015 are also used to investigate whether decadal

1scale climatic change is occurred in the period. The Niño 3 SST anomaly index (1949-2015) is also used as anindicator of El Niño-Southern Oscillation (ENSO) events.
MATERIALS AND METHODSMonthly mean water temperature at 100 and 200 m deep in the entire JARPNII survey area from April to
September were prepared using data extracted from FRA-ROMS. Four water types were classified based onfollowing criteria:

Oyashio water: Area where water temperature at 100 m deep is lower than 5°C
Cold water: Area where water temperature at 100 m deep is higher than 5°C and lower than 10°C
Warm water: Area where water temperature at 100 m deep is higher than 10°C and water temperature at
200 m deep is lower than 14°C
Kuroshio water: Area where water temperature at 200 m deep is higher than 14°C
The criteria is conventionally used by FRA for the purpose of oceanographic and fisheries forecast. Area (km2) bywater type in each month from 2000 to 2013 were calculated by using the data. Trends in area by water types were
investigated by using ordinal linear regressions.
Annual mean PDO index from 1900 to 2015 was calculated using monthly data available from“http://research.jisao.washington.edu/pdo/” [accessed on 6 October 2015]. The PDO index is the leading principal
components (PC) from an un-rotated empirical orthogonal function (EOF) analysis of monthly “residual” North
Pacific sea surface temperature (SST) anomalies, poleward of 20°N (Mantua and Hare, 2002). Causes of PDO are
yet to be determined, but it is assumed that it is related to other climate events such as changes in Aleutian Low
Pressure (ALP) and ENSO events. It has been described that decadal change in PDO is related to biological regime
shift in the North Pacific as mentioned above.
NPI anomalies in winter in the same period was provided by the Climate Analysis Section, NCAR,
Boulder, USA,(Trenberth and Hurrell, 1994) [accessed on 15 October 2015]. The NPI is the area-weighted sea
level pressure in the North Pacific bounded by 30°N, 65°N, 160°E and 140°W. NPI anomalies in winter is linked
to the ALP. Positive NPI is related to weak ALP while the negative is related to strong ALP. Water temperature
in Oyashio is low in the negative phase of NPI while it is high in the positive phase.
The Niño 3 SST index available from Japan Meteorological Agency (http://www.data.jma.go.jp) wasused in this paper [accessed on 19 November 2015]. The area bounded by 5°N, 5°S, 150°W and 90°W is termed
as “Niño 3” and the SST anomalies in the area is used as a indictor of ENSO events. It is considered as El Niño
when the index is positive phase while it is considered as La Niña if the index is negative.
RESULTS AND DISCUSSION
Maps of water types from April to September by each year (2000-2013) are shown in Figs. 2-15. Trends of area(km2) by water types in each month from 2000 to 2013 are shown in Fig. 16. No statistical significant trend at 5%
level was detected except the cold water in September. The results indicated that overall oceanographic conditionsin the JARPNII survey area from 2000 to 2013 were relatively stable, although year to year variations and spatial
heterogeneity of distribution of water types were observed.
Negative values of annual mean PDO index were dominant in the period from 2000 to 2013 (Fig. 17). It
can be considered that JARPNII from 2000 to 2013 was conducted in the negative phase of PDO index, although
the index recorded in the future is required to make formal conclusion. Sea surface temperature in the eastern
Pacific is high in the positive phase while that in the western Pacific is low (Fig. 18). Vice versa is true for thenegative phase. It can be considered that JARPNII from 2000 to 2013 was conducted in warm water temperate in
the context of long term oceanographic conditions. Positive values of NPI were dominant from 2000 to 2013 andimplied warm water temperate in the JARPNII area (Fig. 19). Generally, NPI showed opposite phases of PDO
index. However, there were some discrepancies between these two indices. The discrepancies might be caused by
ENSO events (Fig. 20). It seems that ALP is prone to ENSO events in comparison with PDO index. In contrast,
PDO index could capture longer term climate change in the North Pacific though relationship among these indicesis yet to be determined.
Overall, the results of this study implied that JARPNII from 2000 to 2013 were conducted relatively
stable oceanographic conditions. The future survey conducted in the different regime will enhance ourunderstanding how biological organisms including whales response to regime shift in the western North Pacific.

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REFERENCES
King, J.R (Ed.). 2005. Report of the study group on fisheries and ecosystem responses to recent regime shifts. PICES Scientific Report 28, 162pp.
Mantua, N.J. and Hare, S.R. 2002. The Pacific Decadal Oscillation. J. Oceanogr. 58: 35-44.
Overland, J., Rodionov, S., Minobe, S. and Bond, N. 2008. North Pacific regime shifts: Definitions, issues and recent transitions. Prog.
Oceanogr. 77: 92-102.
Tadokoro, K., Chiba, S., Ono, T., Midorikawa, T. and Saino, T. 2005. Interannual variation in Neocalanus biomass in the Oyashio waters of
the western North Pacific. Fish Oceanogr. 14:210-222.
Takasuka, A., Oozeki, Y. and Kubota, H. 2008. Multi-species regime shifts reflected in spawning temperature optima of small pelagic fish in
the western North Pacific. Mar. Ecol. Prog. Ser. 360: 211-217.
Tian, Y., Ueno, Y., Suda, M. and Akamine, T. 2004. Decadal variability in the abundance of Pacific saury and its response to climatic/oceanic
regime shifts in the northwestern subtropical Pacific during the last half century. J. Mar. Syst. 52:235-257.
Trenberth, K. and Hurrell, J. 1994. Decadal atmosphere-ocean variations in the Pacific. Clim. Dyn. 9: 303-19.
Yatsu, A., Aydin, K. Y., King, J. R., McFarlane, G. A., Chiba, S., Tadokoro, K., Kaeriyama, M. and Watanabe, Y. 2008. Elucidating dynamic
responses of North Pacific fish populations to climatic forcing: Influence of life-history strategy. Prog. Oceanogr. 77:252-268.
Yatsu, A., Chiba, S., Yamanaka, Y., Ito, S., Shimizu, Y., Kaeriyama, M. and Watanabe, Y. 2013. Climate forcing and the Kuroshio/Oyashio
ecosystem. ICES J Mar Sci. 70:922-933.
Yatsu, A., H. Nishida, M. Ishida, A. Tomosada, T. Kinoshita and T. Wada. 2001. Trajectories of catch and stock abundance of dominant small
pelagic fishes and common squid with some related environmental indices around Japan. PICES Sci. Rep. 18:175-178.

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Fig. 1. Schematic map of oceanographic conditions around JARPNII survey area.

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Fig. 2. Water temperature at 100 m deep from April to September in 2000. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 3. Water temperature at 100 m deep from April to September in 2001. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 4. Water temperature at 100 m deep from April to September in 2002. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 5. Water temperature at 100 m deep from April to September in 2003. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 6. Water temperature at 100 m deep from April to September in 2004. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 7. Water temperature at 100 m deep from April to September in 2005. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 8. Water temperature at 100 m deep from April to September in 2006. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 9. Water temperature at 100 m deep from April to September in 2007. Four water types (Oyashio, cold,
warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 10. Water temperature at 100 m deep from April to September in 2008. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 11. Water temperature at 100 m deep from April to September in 2009. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 12. Water temperature at 100 m deep from April to September in 2010. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 13. Water temperature at 100 m deep from April to September in 2011. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 14. Water temperature at 100 m deep from April to September in 2012. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 15. Water temperature at 100 m deep from April to September in 2013. Four water types (Oyashio,
cold, warm and Kuroshio) are shown in the maps. Red lines represents the survey area of JARPNII.

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Fig. 16. Trends in area (km2) by water types (Oyashio, cold, warm and Kuroshio) within the survey areafrom April to September in the period of JARPNII (2000-2013).

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Fig. 16. (Continued)

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Fig. 16. (Continued)

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Fig. 17. Annual mean of Pacific Decadal Oscillation (PDO) index from 1900 to 2015. Monthly PDO data
available from “http://research.jisao.washington.edu/pdo/” (accessed on 6 October 2015) are used to
calculate annual mean. Climate regime shift indicated in several published papers are also shown in the
figure (see main text for the details). Note: Sea surface temperature in the eastern Pacific is high in thepositive phase while that in the western Pacific is low. Vice versa is true for the negative phase.

22Fig 18. Schematic maps showing sea surface temperature (SST), sea level pressure (SLP) and surface windstress anomaly in the positive and negative phases of Pacific Decadal Oscillation (PDO) Index. The maps
are available from http://research.jisao.washington.edu/pdo/graphics.html. Sea surface temperature in theeastern Pacific is high in the positive phase while that in the western Pacific is low. Vice versa is true forthe negative phase.

23Fig. 19 North Pacific Index (NPI) in winter from 1900 to 2015. The data were provided by the Climate
Analysis Section, NCAR, Boulder, USA, (Trenberth and Hurrell, 1994) [accessed on 15 October 2015].
Climate regime shift indicated in several published papers are also shown in the figure (see main text forthe details). NPI winter anomalies in winter is linked to the ALP. Positive NPI is related to weak ALP while
the negative is related to strong ALP. Temperature in Oyashio is low in the negative phase of NPI while itis high in the positive phase.

24Fig. 20. The Niño 3 SST anomaly index from 1949 to 2015 Data were available from Japan Meteorological
Agency (http://www.data.jma.go.jp) [accessed on 19 November 2015]. It is considered as El Niño when
the index is positive phase (orange) while it is considered as La Niña (blue). Climate regime shift indicatedin several published papers are also shown in the figure as black lines (see main text for the details).

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