Differences in foods and feeding habits in common minke and sei whales in the western North Pacific based on samples under JARPN II survey project Ryosuke Okamoto1, Tsutomu Tamura2, Kenji Konishi2 and Hidehiro Kato2 1 Tokyo University of Marine Science and Technology, Japan 2 The Institute of Cetacean Research, Japan Aim of this Study 1.To clarify geographical and monthly changes in prey composition 2.To clarify changes prey prey composition with growth 3.To compare prey among whale species Feeding habits of minke and sei whale in the PICES area in conjunction with temporal and spatial variation 2006 Common minke whale Balaenoptera acutorostrata Body length : 8 m Body weight : 6 t Sei whale Balaenoptera borealis Body length : 14.5 m Body weight : 16 t Materials and methods The Second Phase of Japanese Whale Research Program under Special Permit in the western North Pacific (JARPNⅡ) Sampling location of common minke and sei whale Common minke whale 50°N Sei whale JARPN Ⅱ 2006 ● May to August ● From the Pacific coast of Japan to 170°E and north of 35N 40°N Western Central Eastern Sub-areas 140°E 150°E 160°E 170°E Sampling of stomach contents Stomach contents from each forestomach were weighed to the nearest 0.1 kg. A part of each stomach contents (sub-sample) was taken, weight and frozen or fixed in 10% formalin solution (for crustacean) for later analyses. Anchovies from a forestomach of sei whale Estimation of amount eaten by whales Identification of species Japanese anchovy Otolith (Japanese anchovy) Number of individuals for OL=4.1mm each prey species Measurement body (includes otolith weight of prey counting) Inverse of sub-sample Total amout of prey Results : Prey of common minke whale May-July June -July June-July 43 27 Western Central Eastern N=35 N=36 N=23 50°N 685.0 kg 412.8 kg 677.1 kg 88 57 63 Japanese anchovy Pacific saury Walleye pollock Other fishes Euphausiids 40°N Western : Japanese anchovy Central : Pacific saury and Japanese anchovy Eeastern : Pacific saury 30°N 140°E 150°E 160°E 170°E Monthly change of prey species (Common minke whale) WW,C,EM,E 100 W : Western C : Central 80 29 E : Eastern 60 Japanese anchovy 95 67 Pacific saury 40 73 Walleye pollock 20 Other fishes 19 Euphausiids Percent of prey weight 0 May June July (N=14) (N=44) (N=36) Prey of sei whale Japanese anchovy 4 June-July 3 June-August Pacific saury Other fishes 10 17 Euphausiids Central Eastern Copepods N=46 N=43 50°N 4064.3 kg 4715.2 kg 86 78 Western N=5 589.0 kg 100 40°N June-July Western : Japanese anchovy Central : Japanese anchovy and Euphausiids Eastern : Japanese anchovy and Euphausiids 30°N 140°E 150°E 160°E 170°E Monthly change of prey species (Sei whale) W : Western W,C,E W,C,E E 100 C : Central 11 12 E : Eastern 80 20 60 Japanese anchovy 86 84 Pacific saury 40 71 Other fishes Euphausiids 20 Copepods Percent of prey weight 0 June July August (N=36) (N=36) (N=22) Differences in prey composition by sexual maturity of whales (common minke whale) 100 13 80 15 40 Japanese anchovy 60 17 Pacific saury Walleye pollock Other fishes 40 Euphausiids 55 54 20 Percent of prey weight Chi-square test df=4 p<0.01 0 Immature Mature Determination of maturity on a ship (N=23) (N=71) ♂: Weight of testis (350 g) ♀: Number of corpus luteum and albicans Immature : Euphausiids and Walleye pollock Mature : Pacific saury Differences in prey composition by sexual maturity of whales (sei whale) 100 10 80 40 Japanese anchovy 60 Pacific saury Other fishes 93 Euphausiids 40 Copepods 49 20 Percent of prey weight Chi-square test df=4 p<0.01 0 Immature Mature Determination of maturity on a ship (N=28) (N=66) ♂: Weight of testis (900 g) ♀: Number of corpus luteum and albicans Immature : Euphausiids and Copepods Mature : Japanese anchovy Variations in prey composition by maturity Minke Sei Japanese anchovy 55% Japanese anchovy 49% Immature Euphausiids 15% Euphausiids 40% Walleye pollock 13% Copepods 10% Japanese anchovy 54% Mature Japanese anchovy 93% Pacific saury 40% Energy contents (kcal/ kg) Pacific saury 3140 High Japanese anchovy 1530 Walleye pollock 1110 Zooplankton (Euphausiids) 850 Low Perez (1994), Tamura (2003) Mature animals have a clear foraging strategy directed at species with higher caloric content. Comparison in foods and feeding habits between common minke and sei whales Geographical Monthly Maturity Minke Japanese anchovy Pacific saury Walleye pollock May June July Other fishes Euphausiids Copepods Sei W M E June July Aug Im Ma Comparison in foods and feeding habits between common minke and sei whales •Common minke and sei whales utilize different prey species in area, month • Prey shifts by growth stage in common minke and sei whales Common minke and sei whales play different roles on marine ecosystem of the western north pacific. Thank you for your attention List of prey species Common minke whale Sei whale Prey species % Prey species % occurrence occurrence Japanese 51% Japanese 38% Pacificanchovy saury 37% Pacificanchovy saury 12% Walleye pollock 2% Japanese sardine 2% Brama japonica 2% Vinciguerria 1% Japanese sardine 1% nimbaria Chub mackerel 1% Euphausiid 14% Euphausiid 7% Copepod 16% Daily prey consumption of minke and sei whale D = 206.25M0.783 , I = D / E Sigurjonsson and Vikingsson (1998) Energy contents (kcal/ kg) Japanese anchovy 1530 D : Daily energy requirement (kcal/day) Pacific saury 3140 M : Body weight of whales (kg) Walleye pollock 1110 I : Daily prey consumption (kg/day) Zooplankton (Krill) 850 E : Energy contents of prey species (kcal/kg) Average contents 1658 D Whale Maturity Mean body I (kg/day) weight (kg) (kcal/day) Immature 2,603 97,434 59 Minke Mature 5,165 166,620 101 Immature 13,709 357,824 216 Sei Mature 22,685 530,808 320 Differences in prey consumption between minke and sei whale D : Daily energy requirement (kcal/day) , I : Daily prey consumption (kg/day) Case 1 : All of prey composition is Pacific saury Case 2 : All of prey composition is Japanese anchovy Case 3 : All of prey composition is Zooplankton D I (kg / day) I (kg / day) I (kg / day) Whale Maturity (kcal/day) Case 1 Case 2 Case 3 Immature 97,434 31 64 115 Minke Mature 166,620 53 109 196 Immature 357,824 114 234 421 Sei Mature 530,808 169 347 624 Feeding on Pacific saury has the obvious advantages of saving time and energy, and facilitates efficient energy intake..