S4: May.16 Second International Symposium on Effects of Climate Change on World Oceans, Yeosu, Korea, 13- May, 1. Synchrony in the abundance trends of spear squid Loligo bleekeri in the Japan Sea and Pacific Ocean with special reference to the latitudinal differences in response to the climate regime shift Yongjun Tian 1, Kazuya Nashida and Hideo Sakaji JSFRI, Fisheries Research Agency (FRA) 1
Outline Background:spear squid Abundance trends in the north and south stocks both in Pacific and the Japan Sea and, their responses to the climate regime shift Impact of fishing Conclusions
Life History of Spear Squid with Oceanographic Features Spear squid Loligo bleekeri Pair Trawler Japan Sea Set net Pair Trawler Single Trawler Pacific Ocean Fisheries are different in the south and north areas. Fishing grounds in the south and north are affected by warm and cold currents, respectively. Growth and ヤリイカ Age Male: 长枪乌贼 3cm in one year; Female: cm in one year Life Span 1 year old Spawning Season Winter-Spring Distribution Coastal waters 3
Catch (tons) Catch (ton) Catch (ton) 16,, 1, 15, 8, 1, 4, Catch trend of spear squid in Japan Japan Sea Total Catch in Japan Pacific Japan Sea 5, 1978 198 1986 199 1994 1998 6 1 6, 1978 198 1986 199 1994 1998 6 1 5, 4, 3,, 1, Pacific North South North South Catch from the south area declined largely since 199s, suggested impact of the late 198s regime shift? (Tian et al., 8, 9). Japan Sea Pacific 1978 198 1986 199 1994 1998 6 1 4
Objectives To identify the variability in the abundance both in Pacific and the Japan Sea and the impact of the late 198s regime shift. To identify and compare the variation patterns in the north and south stocks (latitudinal difference) To unravel the mechanism causing the latitudinal differences in different stocks. 5
Data Source and Analysis Fisheries data: Catch data for trawl and set net. Abundance Index: s were estimated by areas and fisheries. Water Temperature (WT) in the Japan Sea: winter 5m WT used as indicator of TWC WT in Pacific: 1m WT (spring, averaged for 37-41 N) in the north and 15 m WT in the south (spring, costal Obs. St.3,in Kochi Pref.) 6
Catch and : Pacific (kg/haul) (kg/haul) 1 8 6 4 5 15 1 5 Iwate (Single Trawler) Iwate (PairTrawler) Bousou (Single Trawler) North 1978 198 1986 199 1994 1998 6 1 South Central (Single Trawler) South (Single Trawler) South (Pair Trawle)r 5 4 3 1 3 5 15 1 5 Catch (tons ) Catch (tons) Abrupt change around in 199 Increase in the North but decline in the south since 199 Different trend between north and south 1978 198 1986 199 1994 1998 6 1 Latitudinal difference 7
Catch and : Japan Sea Catch (tons) Catch (tons) 5 4 3 1 16 1 8 4 Catch (Set Net, Aomori Pref.) South Catch (Pair Trawler) Abundance index () North 1975 198 1985 199 1995 5 1 1975 198 1985 199 1995 5 1 1 8 6 4 15 1 5 (tons/unio) Abundance index Similar pattern with Pacific Higher in the North but lower in the South since 199s Different trend between north and south 8
6 4 vs. WT: Pacific North (Single Trawler) 15 1 South (Pair Trawler) (kg/haul) (kg/haul) 5 5 4 1975 198 1985 199 1995 5 1 1975 198 1985 199 1995 5 WT WT Anomalies ( ) 1 1 Spring WT Anomalies (Apr. Jun.) 4 41N WT Anomalies ( ) 4 3 1 1 Spring WT Anomalies(Apr Jun.) 15m 3 3 1975 198 1985 199 1995 5 1975 198 1985 199 1995 5 Cold Warm Cold Warm 9
WT (tons/fisheries unio) 3 (Set Net, Aomori Pref.) 1 WT in the north during warm regime was 9 1 closely to WT in the south 6 during cold 3 regime, suggesting the optimal habitat 1 temperature shifted from the south to the 3 3 6 north during warm regime. 1975 198 1985 199 1995 5 1975 198 1985 199 1995 5 WT Anomalies ( ) 1 1 vs. WT: Japan Sea North Spring WT Anomalies (Apr. Jun. ) (kg/haul) Same WT Anomalies ( ) 15 1 1 (Pair Trawler) Winter WT Anomalies (Jan. Mar.) South 3 5mWT 1975 198 1985 199 1995 5 5mWT 1975 198 1985 199 1995 5 Cold Warm Cold Warm 1
Fishing impact:a case study for the south stock in the Japan Sea Abundance index (same trend as catch and ) changed around 199. Estimated Fishing Mortality by DeLury Model x 15 e d In e c n1 a d n u b A 5 Abundance Index STARS-defined trend Linear trend y = -3.964x + 11.9 R =.74 1975 198 1985 199 1995 5 Cold Year Warm P =.1 L = 15 H = 1 n t ie fic e o c lity rta o m g in h is F 16 14 1 1 8 6 4 Cold 1975-79 198-84 1985-89 199-94 1995-99 - Warm Fishing mortality increased during warm-regime, accelerated the collapse of spear squid stock. Tian (9): Fish. Res.,1,78-85 11
Fishing impacts: effort in Pacific Fishing Effort (hauls) Fishing Effort (hauls) 1 9 8 7 6 5 4 3 1 4 35 3 5 15 1 5 Pacific: North 岩手 1そう 岩手 そう 房総 1そう 1978 198 1986 199 1994 1998 6 1 Pacific: South 中部 1そう 南部 1そう 南部 そう 1978 198 1986 199 1994 1998 6 1 Fishing effort declined during 199s both in the south and north of Pacific, indicating that the long-term catch trends were not depended on fishing effort. Cold Warm 1
Summary Decadal variability with large interannual variations in the abundance (abrupt change around 199). Synchrony in the Japan Sea and Pacific Ocean strongly suggests environmental impacts (rather than fishing). Variability in the abundance corresponded well to WT, indicating the impact of the late 198s regime shift. Opposite variation patterns between north and south stocks indicate the latitudinal difference in response to the climate regime shift: the optimum habitat shifted from the south to north during warm regime. Under an un-favorable thermal regime, fishing mortality can increase even with declining fishing effort, and accelerates the collapse of the stock. 13