Feeding habits of minke whales in Korean waters

Transcription

1 Feeding habits of minke whales in Korean waters Jung Hyun Lim 1, Zang Geun Kim 2, Kyung-Jun Song 1, Hyeok Chan Kwon 1, Seok Gwan Choi 2, Yong-Rock An 2 and Chang-Ik Zhang 1 1 Pukyong National University, Korea 2 Cetacean Research Institute, National Fisheries Research and Development Institute, Korea

2 Introduction Study on minke whales in Korean waters is not so sufficient. In spite of conducting various studies, the majority of study was concentrated to distribution and abundance and also these studies were not yet systematically organized for conservation and management. Furthermore, there was no report on feeding habits of minke whales in Korean waters until now.

3 Introduction Objectives of this study To investigate feeding habits of minke whales in Korean waters Possibility of changes in dominant prey species according to growth condition and season To understand ecological role of minke whales

4 Japan/East Sea Bycaught sites of minke whales in Korean waters

5 Sample size Year Sample size % Unidentified Total

6 Analysis process of stomach contents

7 Methods Relative frequency (RF) RF = (N i / N all ) 100 N i = number of stomachs containing prey species i N all = total number of stomachs Relative weight (RW) RW = (W i / W all ) 100 W i = weight of prey species i W all = total weight of all prey species Combined Rank Index (CRI) (Pitcher, 1981) CRI = rank of RF rank of RW

8 N=31 40 n=10 Frequency (%) n=5 n=7 n=3 n=1 n=1 n=2 n=1 n=0 n= ~ ~ ~ ~ ~ ~ ~ ~ ~ ~9.0 Length (m) Size distribution of minke whales collected in Korean waters from 2000 to 2007

9 Results Prey species Common name Species name Crustaceans Euphausiacea Euphausia pacifica Southern rough shrimp Trachysalambria curvirostri Amphipoda Unidentified amphipods Fishes Pacific anchovy Engraulis japonicus Big-eyed herring Sardinella zunasi Horse mackerel Trachurus japonicus Yellow goosefish Lophius litulon Cephalopods Common squid Todarodes pacificus Mimika bobtail Euprymna morsei

10 Prey species (crustaceans) A B C A: Euphausia pacifica B: Trachysalambria curvirostri C: Unidentified amphipods

11 Prey species (fishes) A B C D A: Engraulis japonicus B: Sardinella zunasi C: Trachurus japonicus D: Lophius litulon

12 Prey species (cephalopods) A B A: Todarodes pacificus B: Euprymna morsei

13 Relative importance in terms of CRI N RF W (g) RW Rank of RF Rank of RW CRI Crustaceans Euphausiacea , Southern rough shrimp Unidentified amphipods Fishes Pacific anchovy Big-eyed herring Horse mackerel Yellow goosefish Unidentified fishes Cephalopods Common squid Mimika bobtail Unidentified cephalopods Unidentified Unidentified remains Total 18,

14 Composition of prey species Frequency Cephalopods 6% 4% Unidentified 31% Fishes Crustaceans 59%

15 Composition of prey species Weight Cephalopods 2.5% 1.8% 12.8% Fishes Unidentified Crustaceans 82.9%

16 Number of prey species Number of prey species Prey species Total N % 1 Euphausiacea Pacific anchovy Unidentified amphipods Total Euphausiacea + Unidentified fishes Pacific anchovy + Big-eyed herring Common squid + Horse mackerel Pacific anchovy + Unidentified fishes Unidentified fishes + Unidentified cephalopods Total E + PA + YG + SRS + MB + UF* Total Unidentified Unidentified remains Total Number of samples * E: Euphausiacea, PA: Pacific anchovy, YG: Yellow goosefish, SRS: Southern rough shrimp, MB: Mimika bobtail, UF: Unidentified fishes

17 Composition of prey species by length Frequency 100% n=5 n=10 n=7 n=3 n=1 n=1 n=2 n=1 n=0 n=1 Stomach contents (%) 80% 60% 40% 20% 0% 4.0~ ~ ~ ~ ~ ~ ~ ~ ~ ~9.0 Length (m) Crustaceans Fishes Cephalopods Unidentified

18 Composition of prey species by length Weight 100% n=5 n=10 n=7 n=3 n=1 n=1 n=2 n=1 n=0 n=1 Stomach contents (%) 80% 60% 40% 20% 0% 4.0~ ~ ~ ~ ~ ~ ~ ~ ~ ~9.0 Length (m) Crustaceans Fishes Cephalopods Unidentified

19 Composition of prey species by year Frequency Stomach contents (%) 100% 80% 60% 40% 20% 0% n=3 n=8 n=10 n=2 n=1 n= Year Crustacea Pisces Cephalopoda Unidentified

20 Composition of prey species by month Frequency Stomach contents (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% n=7 n=3 n=5 n=2 n=6 n=4 n=0 n=6 n=1 n=1 n=0 n= Month Crustacea Pisces Cephalopoda Unidentified

21 Discussion Feeding habits Minke whales seem not to prefer specific prey species. Role of minke whales in marine ecosystems Feed on several kinds of fishes in addition to small crustaceans Play an important role in this area as top predators Further research is needed To estimate ecological role of minke whales in Korean waters through studies on feeding habits and ecosystem modeling

22 Changes in prey species according to growth condition, year and month Further research is needed To investigate the possibility of changes in dominant prey species of minke whales in Korean waters according to growth condition, year and month using more samples Comparison with other studies on the feeding habits of minke whales

23 Limitations of this study Insufficient to investigate the feeding habits Sampling areas did not fully cover the whole habitat of minke whales. Thus, the whole habitat area should be covered in the future study. Further study Detailed investigation based on DNA analysis from stomach contents

24 Summary This is the first study on feeding habits of minke whales in Korean waters. 3 Crustaceans, 4 Fishes and 2 Cephalopods were identified. Euphausia pacifica was the most important prey species of minke whales in Korean waters.

25 Thank you

26 Kim et al. (2007)

27 Age distribution N=31 Number of individual Age (year) Na (2005)

28 The annual change and commercial catch n=2 n=8 n=9 n=1 n=1 n=7 Unknown Amphipoda Pacific anchovy Euphausiacea Frequency (%) Year Catch (M/T) 160, ,000 80,000 Pacific anchovy Common squid Chub mackerel Hairtail Spanish mackerel Horse mackerel 40, Year The annual change in relative frequency of prey species of minke whales and commercial catch in the East Sea.

29 Scientific whaling in Japan Tamura and Fujise (2002)

30 Composition of prey species by year Weight Stomach contents (%) 100% 80% 60% 40% 20% 0% n=3 n=8 n=10 n=2 n=1 n= Year Crustacea Pisces Cephalopoda Unidentified

31 Composition of prey species by month Weight Stomach contents (%) 100% 80% 60% 40% 20% 0% n=7 n=3 n=5 n=2 n=6 n=4 n=0 n=6 n=1 n=1 n=0 n= Month