Ecological role of common minke whales in the southwestern East Sea (Sea of ) ecosystem during the post-commercial whaling moratorium period

By Kyung-Jun Song* and Chang Ik Zhang

Abstract The structure of the southwestern East Sea ecosystem and the role of common minke whales (Balaenoptera acutorostrata) in this ecosystem during the post-commercial whaling moratorium (post-CWM) period (1986-2007) were examined using an Ecopath model. Results showed that catch and biomass of common squid was the highest in this ecosystem (catch=0.302 t/km2, biomass=1.031 t/km2). Although this ecosystem consists of primary producers, primary consumers, secondary consumers and terminal consumers, most taxonomic groups were classified as secondary consumers. Common minke whales were classified as terminal consumers along with apex predators. The trophic level of common minke whales in this ecosystem was estimated at 3.34, and the mean trophic level of this ecosystem was estimated as 2.91. The relative contribution of common squid to the total energy flow at trophic level III, which includes common minke whales, was the highest (72.0%). However, the relative contribution of common minke whales at this trophic level was low (1.3%) compared to other taxonomic groups. This study is one of the first to address anthropogenic impacts (commercial whaling) on the trophic role of common minke whales in the East Sea, and it could potentially be used to understand the importance of common minke whales to this ecosystem within a context of potential biological removal (PBR).

*Corresponding Author E-mail: [email protected]

Pacific Science, vol. 68, no. 2 October 24, 2013 (Early view)

Introduction

Common minke whales (Balaenoptera acutorostrata) are widely distributed from the equator

to the polar regions (Jefferson et al. 2008). In the western North Pacific, two stocks are

recognized, the East Sea-Yellow Sea- stock (J stock) and the Okhotsk Sea-West

Pacific stock (O stock) (IWC 1983). Common minke whales in Korean waters, which are from J

stock, are the most abundant baleen whale in this area, with a population size of 5,841

individuals (95% confidence interval: 2,835-12,032) during August and September of 1989 and

1990 (Buckland et al. 1992). Their locations of highest abundance correspond with the

continental shelves parallel to shore (Cho et al. 2003), with southward migrations to breeding

areas occurring in winter, and return migrations occurring to northern feeding areas in the

summer (Gong 1988).

Common minke whales were extensively hunted until the moratorium on commercial whaling

began in 1986 (Kim 1999). During the commercial whaling period, the total recorded catch

numbers from 1962-1986 were 13,734 whales, with a peak of 1,033 in 1973 (Kim, 1999).

Although common minke whales in Korean waters were protected for more than 23 years after

this moratorium, they continued to be anthropogenically threatened by the fishing industry

bycatch in this area (Song 2010, Song et al. 2010, Zhang et al. 2010, Song 2011, Song 2013).

Several studies have been conducted in the past on the ecological role of common minke

whales, including on their feeding habits (Haug et al. 1996, Konishi et al. 2009), prey preferences (Lindstrøm and Haug 2001, Murase et al. 2007) and functional response (Smout and

Lindstrøm 2007). These studies showed that common minke whales are top predators that feed on commercially important fishes, especially small pelagic fishes such as Japanese , in addition to small crustaceans such as euphausiids and thus play an important top-down ecological role in the marine ecosystem. In particular, some studies also reported that common

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minke whales showed prey selection for Japanese anchovy in the western North Pacific (Murase et al. 2007).

The roles of marine mammals in the marine ecosystem were investigated by using a variety of

ecosystem models, including the Ecopath model, in many regions of the world (Mori and

Butterworth 2006, Morissette et al. 2006, Lindstrøm et al. 2009). All these studies indicated that

ecosystem models are important for the purpose of the investigation of the ecological roles of

marine mammals. In particular, a mass balance ecosystem model, the Ecopath model, is

normally used to investigate the ecosystem structure and function (Walters et al. 1997,

Christensen et al. 2000).

Recent fisheries management studies that include cetaceans are based on ecological interactions among various taxa in the ecosystem (Walters et al. 1997, Christensen et al. 2000).

Thus, it is important to consider an ecosystem approach to fisheries in order to sustainably

maintain fisheries resources in addition to cetaceans, including common minke whales. The

ecological role of common minke whales in the post-moratorium East Sea ecosystem is poorly

understood due to a paucity of investigations (Zhang and Yoon 2003, Zhang et al. 2007).

The objective of our study was to examine the structure of the southwestern East Sea ecosystem and the role that common minke whales have played during the post-commercial whaling moratorium (post-CWM) period (1986-2007).

Material and methods

Data collection

The study area used for our ecosystem modeling was in the southwestern East Sea (Sea of

Japan), an area of approximately 193,000 km2, which includes Korea-Japan provisional fishing

zones (Fig. 1). The East Sea is located east of the Korean peninsula, between Korea and Japan.

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The average water depth and the total area of the East Sea are 1,700 m and 1,000,000 km2, respectively. There is approximately a total of 960 km of coastline in the East Sea. This area is one of the most productive areas in Korean waters compared with other areas (Kim and Kang

1998).

Species abundance and distribution information for this area were investigated with a survey of the relevant literature (NFRDI 1994, Park and Choi 1997, NFRDI 1999, NFRDI 2000). A time series of the catch data from 1986 to 2007 was obtained and analyzed from databases within the

Ministry for Food, Agriculture, Forestry and Fisheries (MIFAFF) in Korea (MIFAFF 1987-

2008). The catch data of each taxonomic group was calculated from the sum of the average catch of each species within each group, including the bycatch of common minke whales during this period (Kim et al. 2004, Kim 2008).

The grouping of species in this area was conducted by using the self-organizing mapping

(SOM) method, which is a neural network pattern recognition technique (Lek and Guegan 1999).

An artificial neural network (ANN), which is a black box approach that has a great capacity for predictive modeling, is a non-linear mapping structure based on the function of the human brain.

All characters describing an unknown situation should be presented to the trained ANN, and the prediction is then given in a self-organizing map. Based on the method of Lek and Guegan

(1999), a total of nine variables were used to classify species, including mobility (weak, medium, strong), body size (small, medium, large, very large), bone type (soft bone, hard bone, mollusk, carapace), habitat depth (epipelagic, pelagic, semi-demersal, demersal), body shape (spindle, flat, streamlined), habitat type (surface, bottom, sand/mud, rock, sand/rock, sandy bottom, nektonic), feeding type (filter feeding, beak/tooth), longevity (0-5, 5-10, 10-15, over 15 years) and food type (herbivorous, omnivorous, carnivorous).

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Data analysis

The structure of the southwestern East Sea ecosystem and the role of common minke whales in

this ecosystem during the post-CWM period (1986-2007) were examined using an Ecopath model (Christensen et al. 2000) (Fig. 2). This period was selected to investigate the potential

effect of the CWM in 1986 on this ecosystem. The Ecopath model is based on two equations.

The first, a mass-balance equation, described how the production rate of each group (i) is divided

into components. This is fulfilled using the following equation,

Pi = Yi + Bi·M2i + Ei + BAi + Pi·(1-EEi) (1)

where Pi is the total production rate of group i, Yi is the total catch rate of group i, Bi is the

biomass of group i, M2i is the total predation rate of group i, Ei is the net migration rate of group

i, BAi is the biomass accumulation rate of group i, Pi·(1-EEi) is the other mortality rate of group i

and EEi is the ecotrophic efficiency, i.e., the fraction of the production that is utilized within the system for predation or export, of group i. The second equation balances the input and output energy of all groups in the model by accounting for energy flows.

Consumption = Production + Respiration + Unassimilated food (2)

The input parameters of the catch (C), biomass (B), production to biomass (P/B) ratio and

consumption to biomass (Q/B) ratio were estimated for each taxonomic group classified by

SOM. The biomass (B) of common minke whales was calculated from the abundance and

average body weight (Trites and Pauly 1998, Park et al. 2009). In particular, a shipboard sighting

survey using the line transect method was conducted to estimate the abundance of common

minke whales in this area, and the abundance was estimated using the DISTANCE program

(Buckland et al., 1993). The biomass (B) of other groups was calculated from the B=C/F

relationship (C=catch, F=instantaneous coefficient of fishing mortality which is associated with

fishing activity). The biomass (B) of zooplankton and phytoplankton was calculated using

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previously published information (Kang et al. 2000). Since the production to biomass (P/B) ratio

is equal to the biomass-averaged total mortality, it was calculated from the instantaneous

coefficient of total mortality (Z), which consists of fishing mortality and natural mortality

(NFRDI 1994, NFRDI 2000). Due to a lack of data for the Q/B ratio in this area, it was assumed to be the same as that of the Bering Sea ecosystem, because the temperature and species composition of the Bering Sea ecosystem are relatively similar to those of the southwestern East

Sea ecosystem compared with other areas (Trites et al. 1999). The diet composition of common minke whales was calculated from direct observation of the forestomach contents of common minke whales incidentally bycaught during fishing operations in Korean waters from 2000 to

2008 in our other study. The diet composition of other taxonomic groups was calculated from several scientific papers and reports on prey species of each taxonomic group (NFRDI 1994,

NFRDI 1999, NFRDI 2000).

Results

Ecosystem structure

Nine variables (i.e. mobility, body size, bone type, habitat depth, body shape, habitat type,

feeding type, longevity and food type) were used to classify species in the southwestern East Sea ecosystem. As a result, they were classified into 14 taxonomic groups by a SOM method, except for zooplankton, phytoplankton and detritus. In particular, a total of four species, specifically

Japanese anchovy ( japonicus), Pacific saury (Cololabis saira), walleye pollock

(Theragra chalcogramma) and common squid (Todarodes pacificus), were subjectively classified as single taxonomic groups because of their importance as prey species for common minke whales (Table 1).

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The input parameters of the catch (C), biomass (B), production to biomass (P/B) ratio and consumption to biomass (Q/B) ratio for each taxonomic group are shown in Table 2. The catch and biomass of common squid was the highest in this ecosystem during the post-CWM period

(catch=0.302 t/km2, biomass=1.031 t/km2). The diet composition for each species group is shown in Table 3.

Although the southwestern East Sea ecosystem consists of primary producers, primary consumers, secondary consumers and terminal consumers, most taxonomic groups were classified as secondary consumers (Fig. 3). Common minke whales were classified as terminal consumers along with apex predators. The trophic level of common minke whales in this ecosystem was estimated to be 3.34 during this period (Table 4), and the mean trophic level of this ecosystem was estimated to be 2.91.

Ecosystem function

The relative contribution of common squid to the total energy flow at trophic level III, which includes common minke whales, was the highest (72.0%) (Fig. 4). However, the relative contribution of common minke whales at this trophic level was low (1.3%) compared to other taxonomic groups.

Discussion

The results from our model suggested that the structure of the southwestern East Sea ecosystem during the post-CWM period was similar to that reported by previous studies (Zhang and Yoon 2003, Zhang et al. 2007), including the result that most taxonomic groups were also

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classified as secondary consumers. However, our results concerning the ecological role of

common minke whales in this ecosystem are not directly comparable with these previous studies

because in those cases common minke whales were not analyzed as an independent taxonomic

group.

Our calculated trophic level value (3.34) for common minke whales was similar to the value

(3.40) for common minke whales in other geographic areas (Pauly et al. 1998). Other studies

involving the stomach contents of common minke whales in our study area show that the

proportion of macrozooplankton, including krill, was slightly higher than those in published reports of other areas (Kasamatsu and Hata 1985, Kasamatsu and Tanaka 1992, Tamura et al.

1998, Tamura and Fujise 2002). Because of the higher proportion of macrozooplankton in stomach contents of minke whales in our study, the trophic level of common minke whales in

this area is slightly lower than those of published reports of other areas (Pauly et al. 1998).

Generally, baleen whales tend to feed on mainly small crustaceans like krill, while toothed whales tend to feed on several kinds of fishes, crustaceans and cephalopods, although there is some variation in the composition of prey species according to the region (Horwood 1990). Our result show that the trophic level of common minke whales in this area (3.34) was lower than that of the finless porpoise (Neophocaena phocaenoides) in the Yellow Sea (4.21) (Park et al.

2002). Due to the common ’s baleen feeding habit, the trophic level of common minke whales in this area is probably lower than those of other predatory fishes as well as of the finless porpoise.

Self-organizing mapping is a valuable method for grouping and visualizing species according to their ecological characteristics (Lek and Guegan 1999). Zhang et al. (2007) also reported the utility of this method for grouping species, and they used seven variables, specifically the mobility, body size, bone type, habitat depth, body shape, habitat and feeding type, to classify

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species. Our study used nine variables, including longevity and food type, to classify species

because we aimed to generate a grouping that better represents the trophic structure in our study

area.

Even though an Ecopath model can be used to study the ecosystem structure and function, the

accuracy of the modeling of an ecosystem mainly depends on the input parameters including the

biomass (B), production to biomass (P/B) ratio and consumption to biomass (Q/B) ratio.

Consequently, more accurate data need to be obtained regarding the input parameters which

generally require extensive time and effort. A limitation of our model was that the data on the top

predators (e.g., sharks and whales), including the biomass and prey composition, was sparse.

Previous studies on the structure of the southwestern East Sea ecosystem also had this limitation

(Zhang and Yoon 2003, Zhang et al. 2007). Therefore, future work using similar Ecopath models

may require more information on the top predators in order to have more realistic applications

toward the management and conservation of common minke whales in the North Pacific.

Acknowledgements

We wish to acknowledge the many volunteers who reported bycatch events of common minke

whales in Korean waters. We thank Mr. Hyeok Chan Kwon and Dr. Jong-Hee Lee (Pukyong

National University, Republic of Korea) for their assistance with the Ecopath and SOM analysis.

This research was supported by a grant from the Cetacean Research Institute, National Fisheries

Research and Development Institute in Republic of Korea.

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Table 1. Classification of groups by species in the southwestern East Sea ecosystem Biota Group name Sharks and whales Apex predator Small sharks Birds Seabirds Fishes Japanese anchovy Pacific saury Walleye pollock Small pelagic fish Large pelagic fish Semi-demersal fish Benthic demersal fish Cephalopods Common squid Cephalopods Benthos Benthic feeders Epifauna Infauna Gastropods Algae Benthic algae Plankton Zooplankton Phytoplankton Other Detritus

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Table 2. Basic input parameters for the post-CWM model Production/ Consumption/ Habitat area Biomass Catch Biomass Biomass (fraction) (t/km2) (t/km2) (/year) (/year) Apex predator 1.000 0.003 0.280 11.156 - Common minke whale 1.000 0.031 0.280 8.331 0.002 Small sharks 1.000 0.000 0.280 11.156 0.000 Seabirds 1.000 0.006 0.800 60.000 - Japanese anchovy 1.000 0.036 0.630 3.650 0.029 Pacific saury 1.000 0.021 1.250 3.650 0.017 Walleye pollock 1.000 0.074 0.600 5.487 0.034 Common squid 1.000 1.031 3.200 10.667 0.302 Small pelagic fish 1.000 0.089 1.610 3.650 0.073 Large pelagic fish 1.000 0.025 1.000 3.145 0.010 Semi-demersal fish 1.000 0.049 0.934 2.226 0.031 Benthic demersal fish 1.000 0.042 0.910 2.611 0.027 Cephalopods 1.000 0.044 3.200 10.667 0.013 Benthic feeders 1.000 0.298 0.934 7.690 0.103 Epifauna 0.050 0.109 1.051 5.777 0.041 Infauna 0.050 0.041 0.863 12.000 0.018 Gastropods 0.050 0.167 1.156 5.777 0.065 Benthic algae 0.050 0.569 10.000 - 0.014 Zooplankton 1.000 12.740 5.545 22.000 - Phytoplankton 1.000 13.062 718.754 - - Detritus 1.000 - - - -

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Table 3. The estimated proportions of prey eaten by predators in the post-CWM model Prey\Predator 1 2 3 4 5 6 7 8 9 1 Apex predator 2 Common minke whale 0.015 3 Small sharks 0.005 4 Seabirds 5 Japanese anchovy 0.062 0.079 0.100 0.001 0.0002 6 Pacific saury 0.019 0.030 0.001 0.0001 7 Walleye pollock 0.239 0.383 0.010 0.001 8 Common squid 0.356 0.120 0.100 0.051 0.082 9 Small pelagic fish 0.010 0.053 0.027 0.100 0.100 0.100 0.015 0.001 0.020 10 Large pelagic fish 0.005 0.008 11 Semi-demersal fish 0.009 0.014 0.007 12 Benthic demersal fish 0.019 0.017 0.001 13 Cephalopods 0.037 0.100 14 Benthic feeders 0.224 0.100 0.100 0.100 0.012 15 Epifauna 0.017 0.033 0.016 0.001 16 Infauna 0.010 0.020 0.010 0.0001 17 Gastropods 0.074 0.147 0.001 18 Zooplankton 0.868 0.700 0.800 0.800 0.839 0.9317 0.8519 19 Benthic algae 0.003 0.008 20 Phytoplankton 0.017 21 Detritus 0.019 SUM 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

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Table 3. Continued Prey\Predator 10 11 12 13 14 15 16 17 18 1 Apex predator 2 Common minke whale 3 Small sharks 4 Seabirds 5 Japanese anchovy 0.061 0.005 0.009 0.005 6 Pacific saury 0.018 0.001 0.002 0.001 7 Walleye pollock 0.030 0.034 0.020 8 Common squid 0.219 0.063 0.110 0.008 0.003 9 Small pelagic fish 0.300 0.101 0.050 0.020 10 Large pelagic fish 0.023 0.004 0.003 0.002 11 Semi-demersal fish 0.030 0.028 0.015 12 Benthic demersal fish 0.015 0.007 0.005 13 Cephalopods 0.083 0.004 0.060 14 Benthic feeders 0.097 0.100 0.253 0.322 0.082 15 Epifauna 0.016 0.028 0.034 0.064 16 Infauna 0.013 0.023 0.028 0.053 17 Gastropods 0.043 0.075 0.092 0.172 18 Zooplankton 0.282 0.494 0.250 0.598 0.698 0.171 0.130 19 Benthic algae 0.001 0.289 0.338 20 Phytoplankton 0.003 0.159 0.333 0.331 0.762 21 Detritus 0.001 0.128 0.092 0.667 0.331 0.108 SUM 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

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Table 4. Estimated trophic levels in the southwestern East Sea ecosystem for the post-CWM model

Group name Trophic level Apex predator 4.17 Common minke whale 3.34 Small sharks 3.95 Seabirds 3.09 Japanese anchovy 3.24 Pacific saury 3.24 Walleye pollock 3.13 Common squid 3.07 Small pelagic fish 3.08 Large pelagic fish 3.76 Semi-demersal fish 3.47 Benthic demersal fish 3.46 Cephalopods 3.48 Benthic feeders 3.18 Epifauna 2.50 Infauna 2.00 Gastropods 2.00 Zooplankton 2.02 Benthic algae 1.00 Phytoplankton 1.00 Mean trophic level 2.91

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Fig. 1. Study area for ecosystem modeling in the southwestern East Sea ().

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Fig. 2. Flowchart of the steps and processes for conducting ecosystem modeling.

Fig. 3. Estimated trophic levels and relative biomass of species in the southwestern East Sea ecosystem for the post-CWM model.

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Fig. 4. Relative contribution (%) of species to the total energy flow (throughput) at trophic level

III in the southwestern East Sea ecosystem.

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Literature Cited

Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Laake. 1993. Distance sampling:

estimating abundance of biological populations. Chapman and Hall, London.

Buckland, S. T., K. L. Cattanach, and T. Miyashita. 1992. Minke whale abundance in the

northwest Pacific and the Okhotsk Sea, estimated from 1989 and 1990 sighting surveys.

Rep. Int. Whal. Comm. 42:387-392.

Cho, I. H., P. N. Halpin, and Z. G. Kim. 2003. Spatial and temporal patterns of minke whale

distributions off the east coast of Korea. J. Kor. Soc. Fish. Res. 6(1):53-71.

Christensen, V., C. Walters, and D. Pauly. 2000. Ecopath with Ecosim: A User's Guide. UBC

Fisheries Centre and ICLARM Vancouver, Canada and Penang, Malaysia.

Gong, Y. 1988. Distribution and abundance of the Sea of Japan-Yellow Sea-East China Sea

stock of minke whales. Bull. Nat. Fish. Res. Dev. Agen. 41:35-54 (In Korean).

Haug, T., U. Lindstrøm, K. T. Nilssen, I. Rottingen, and H. J. Skaug. 1996. Diet and food

availability for northeast Atlantic minke whales, Balaenoptera acutorostrata. Rep. Int.

Whal. Comm. 46:371-382.

Horwood, J. 1990. Biology and Exploitation of the Minke Whale. CRC Press Inc., Florida.

International whaling commission. 1983. Report of the Sub-Committee on minke whales. Rep.

Int. Whal. Comm. 33:91-122.

Jefferson, T. A., M. A. Webber, and R. L. Pitman. 2008. Marine mammals of the world.

Academic Press, London.

Kang, S. K., S. Kim, and S. W. Bae. 2000. Changes in ecosystem components induced by

climate variability off the eastern coast of the Korean Peninsula during 1960-1990. Prog.

Oceanogr. 47:205-222.

18

Kasamatsu, F., and T. Hata. 1985. Notes on minke whales in the Okhotsk Sea-West Pacific area.

Rep. Int. Whal. Comm. 35:299-304.

Kasamatus, F., and S. Tanaka. 1992. Annual changes in prey species of minke whales taken off

Japan 1948-87. Nippon Suisan Gakkaishi 58(4):637-651.

Kim, S., and S. K. Kang. 1998. The status and research direction for fishery resources in the East

Sea/Sea of Japan. J. Kor. Soc. Fish. Res. 1(1):44-58 (In Korean).

Kim, Y. H. 2008. A study on the characteristics of minke whale (Balaenoptera acutorostrata)

bycatch in Korean waters. MS thesis, Pukyong National University, Busan (In Korean).

Kim, Z. G. 1999. Bycatches of minke whales in Korean waters. J. Cetacean Res. Manage. 1

(Supp):98-100.

Kim, Z. G., Y. R. An, H. Sohn, and C. I. Baik. 2004. Characteristics of minke whale

(Balaenoptera acutorostrata) by-catch in Korean waters. J. Kor. Fish. Soc. 6(2):173-182 (In

Korean).

Konishi, K., T. Tamura, T. Isoda, R. Okamoto, T. Hakamada, H. Kiwada, and K. Matsuoka.

2009. Feeding strategies and prey consumption of three baleen whale species within the

Kuroshio-Current Extension. J. Northwest Atl. Fish. Sci. 42: 27-40.

Lek, S., and J. F. Guegan. 1999. Artificial neural networks as a tool in ecological modelling, an

introduction. Ecol. Model. 120:65-73.

Lindstrøm, U., and T. Haug. 2001. Feeding strategy and prey selectivity in common minke

whales (Balaenoptera acutorostrata) foraging in the southern Barents Sea during early

summer. J. Cetacean Res. Manage. 3:239-249.

Lindstrøm, U., S. Smout, D. Howell, and B. Bogstad. 2009. Modelling multi-species interactions

in the Barents Sea ecosystem with special emphasis on minke whales and their interactions

with cod, herring and capelin. Deep Sea Res. II 56:2068-2079.

19

Ministry for Food, Agriculture, Forestry and Fisheries (MIFAFF). 1987-2008. Statistical

Yearbook of Agriculture, Forestry and Fisheries of Korea. Ministry for Food, Agriculture,

Forestry and Fisheries (In Korean).

Mori, M., and D. S. Butterworth. 2006. A first step towards modelling the krill-predator

dynamics of the Antarctic ecosystem. CCAMLR Sci. 13:217-277.

Morissete, L., M. O. Hammill, and C. Savenkoff. 2006. The trophic role of marine mammals in

the northern Gulf of St. Lawrence. Mar. Mamm. Sci. 22:74-103.

Murase, H., T. Tamura, H. Kiwada, Y. Fujise, H. Watanabe, H. Ohizumi, S. Yonezaki, H.

Okamura, and S. Kawahara. 2007. Prey selection of common minke (Balaenoptera

acutorostrata) and Bryde's (Balaenoptera edeni) whales in the western North Pacific in

2000 and 2001. Fish. Oceanogr. 16:186-201.

National Fisheries Research and Development Institute (NFRDI). 1994. Commercial Fishes of

the Coastal and Offshore Waters in Korea. National Fisheries Research and Development

Institute. Ye-Moon Publ. Co. (In Korean).

National Fisheries Research and Development Institute (NFRDI). 1999. Commercial Molluscs

from the Freshwater and continental Shelf in Korea. National Fisheries Research and

Development Institute. Ku-Deok Publ. Co. (In Korean).

National Fisheries Research and Development Institute (NFRDI). 2000. Ecology and Fishing

Ground of Major Commercial Species in the Korean EEZ. National Fisheries Research and

Development Institute. Ye-Moon Publ. Co. (In Korean).

Park, C., and J. K. Choi. 1997. Zooplankton community in the front zone of the East Sea of

Korea (the Sea of Japan): 1. species list, distribution of dominant taxa, and species

association. J. Kor. Fish. Soc. 30(1):225-238 (In Korean).

20

Park, K. J., C. I. Zhang, Z. G. Kim, and H. Sohn. 2002. Feeding habits and trophic level of

finless porpoise, Neophocaena phocaenoides in the Yellow Sea. J. Kor. Soc. Fish. Res. 5:52-

63 (In Korean).

Park, K. J., Y. R. An, Z. G. Kim, S. G. Choi, D. Y. Moon, and J. E. Park. 2009. Abundance

estimates of the minke whale, Balaenoptera acutorostrata, in the East Sea, Korea. J. Fish.

Aqua. Sci. 42(6):642-649 (In Korean).

Pauly, D., A. W. Trites, E. Capuli, and V. Christensen. 1998. Diet composition and trophic levels

of marine mammals. ICES J. Mar. Sci. 55:467-481.

Smout, S., and U. Lindstrøm. 2007. Multispecies functional response of the minke whale

Balaenoptera acutorostrata based on small-scale foraging studies. Mar. Ecol. Prog. Ser.

341:277-291.

Song, K. J. 2010. Population ecological characteristics of minke whales (Balaenoptera

acutorostrata) in Korean waters. Ph.D. thesis, Pukyong National University, Busan.

Song, K. J. 2011. Status of J stock minke whales (Balaenoptera acutorostrata). Anim. Cell Sys.

15(1):79- 84.

Song, K. J. 2013. Potential areas for whale watching in Korean waters. Tourism Mar. Environ.

8(4):213-219.

Song, K. J., Z. G. Kim, C. I. Zhang, and Y. H. Kim. 2010. Fishing gears involved in

entanglements of minke whales (Balaenoptera acutorostrata) in the East Sea of Korea. Mar.

Mamm. Sci. 26(2):282-295.

Tamura, T., and Y. Fujise. 2002. Geographical and seasonal changes of the prey species of

minke whale in the Northwestern Pacific. ICES J. Mar. Sci. 59:516-528.

21

Tamura, T., Y. Fujise, and K. Shimazaki. 1998. Diet of minke whales Balaenoptera

acutorostrata in the Northwestern part of the North Pacific in summer, 1994 and 1995. Fish.

Sci. 64(1):71-76.

Trites, A. W., and D. Pauly. 1998. Estimating mean body masses of marine mammals from

maximum body lengths. Can. J. Zool. 76:886-896.

Trites, A. W., P. A. Livingston, S. Mackinson, M. C. Vasconcellos, A. M. Springer, and D.

Pauly. 1999. Ecosystem change and the decline of marine mammals in the eastern Bering

Sea: testing the ecosystem shift and commercial whaling hypotheses. Fisheries Centre

Research Reports 7(1):106 p.

Walters, C., V. Christensen, and D. Pauly. 1997. Structuring dynamics models of exploited

ecosystems from trophic mass-balanced assessments. Rev. Fish Biol. Fish. 7: 139-172.

Zhang, C. I., and S. C Yoon. 2003. Effects of climatic regime shift on the structure of marine

ecosystem in the southwestern East Sea during the 1970s. J. Kor. Fish. Soc. 36(4):389-401

(In Korean).

Zhang, C. I., K. J. Song, and J. H. Na. 2010. Estimation of mortality coefficients and

survivorship curves for minke whales (Balaenoptera acutorostrata) in Korean waters. Anim.

Cell Sys. 14(4):291-296.

Zhang, C. I., S. C Yoon, and J. B. Lee. 2007. Effects of the 1988/89 climatic regime shift on the

structure and function of the southwestern Japan/East Sea ecosystem. J. Mar. Sys. 67:225-

235.

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