Changes in Abundance and Spatial Distribution of Southern Bluefin Tuna

Changes in Abundance and Spatial Distribution of Southern Bluefin Tuna Tom Polacheck April 2008

Acknowledgements Paige Eveson Dale Kolody Marinelle Basson Bill Hearn John Gunn Sophie Bestley Alistair Hobday Jessica Farely Grant West taggers, crews of the tagging vessels Liaison officers Data managers Australian, Japanese and Taiwanese Fishing industry And a multitude of others (including a large number of funding sources) Salvador Dali

SBT Background Species Long-lived (up to age 40), with age at maturity 8+ years Highly migratory, with distribution spanning southern ocean from South Africa to New Zealand Single spawning ground in northeast Indian Ocean south of Indonesia During austral summer, juveniles found in coastal waters south of Australia age 0-2 commonly found south of Western Australia (WA) age 1-4 commonly found off South Australia in Great Australian Bight (GAB) During austral winter, juveniles found in deep oceanic waters age 2+ found from South Africa to NZ age 1 less certain, some caught off WA sub-adult and adult spend winter in temperate (mainly ocean waters) and adult migrate to tropical spawning grounds in winter. May not spawn every year.

SBT Background Fishery Multiple fishing fleets, gear types and countries Juveniles harvested by: Australian surface fishery (primarily purse seine and pole-and-line) operating in coastal waters south of Australia in austral summer Japanese, Taiwanese and Korean longline fleets operating on high seas and NZ EEZ (joint venture) and in Australia EEZ in 1990s mainly during austral winter Major changes in SBT fishery: Largest catches in early 1960s on the spawning grounds and large juvenile catches in 1970s Collapse of surface fishery off NSW in late 1970s Restrictive quota introduced in 1980s (1984 for Australia, 1989 for longline) Qutoa reductions in 1980s and switch from canning to sashimi market resulted in fishing off WA decreased substantially (thus reducing catch of age 1 dramatically) doesn t exist now. Introduction of farming in 1992 resulted in continual increase of purse seine operations in GAB, so that PS catches have dominated Australian catches since 2000

SBT Background Available Data Conventional tagging experiments conducted in 1960s (1959-1969), 1970 s1980 (1983-84), 1990s (1991-1997) and 2000s (2001-2007) Arial Surveys in the Great Australian Bight Catch data CPUE Japanese longline, Taiwanese, NZ longline Size data of varying quality on catches back to 1950-60s Direct age data for Indonesian (spawning ground catches since 1995) NOTE: Highsea s longline catch, effort, and size compromised by large IUU fishing (assumed to be largely Japanese) since at least the early 1990s; Reliability of size data from surface fishery is in question since advent of farming

SBT Background Tagging experiment Major conventional tagging experiments conducted in 1960s (1959-1969), 1980 (1983-84), 1990s (1991-1997) and 2000s (2001-2007) A total of ~206,000 tags released and ~24,000 recovery 20 30 40 50 60 70 80 90 100 110 120 130 140 150E 30 30 2004 SBT Archival Tagging average length (cm) > 100 20 20 1990s and 2000s 98-100 were similar in design (multi-year/multi-cohort) and 95-98 < 95 tagging 10 methods 10 Number No.16 Most deployments N from pole and line in WA, SA and NSW N (only in 0 No.10 No. 9 0 S No. 1 S 1960s) with some longline releases 10 10 in 1990s and 2000s 20 20 30 30 40 40 50 50 20 30 40 50 60 70 80 90 100 110 120 130 140 150E Longline recovery rates similar to pole and line but not used here Three periods of archival tag deployments (1993-1995, 1998-2000 and 2002-2007)

2000 1996 1984 Estimated Annual SBT Catch OVercatch (t) 16000 14000 12000 10000 8000 6000 4000 2000 0-2000 IUU Catches based on Market Statistic Percent 280 230 180 130 80 30-20 2004 25000 20000 15000 10000 5000 0 Catch (t) -4000 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 Year Case 1 Case 2 Adapted from CCSBT SAG 2006 1992 1988 Year Case 1 Case 2 Official Catches

Spawning stock biomass (thousand tonnes) Overall Population Trends: scenario modelling i.e. Integrated Statistical Catch at age model for assumptions about IUU catches 800 600 400 200 SB1989 SB2004 9925 m future catch CCSBT SAG 2006 Recruitment (millions) 0 2 4 6 80 2 4 6 8 Scenario c CCSBT SAG 2006 overcatch 14925 9925 4925 1980 1990 2000 2010 20201980 1990 2000 2010 2020 Year CCSBT/08/09/27 0 1970 1980 1990 2000 2010 2020

New Zealand Longline CPUE by Age and Cohort

SBT Growth changes over time

Overall Population Trends: Summary Largest catches in 1960 and generally decline Large IUU catches in 1990-2005 period compromise catch, size data and main tuning index (Japanese longline CPUE) Despite problem of large IUU catches in 1990, all analyses suggest that spawning stock estimated to have continually declined since the beginning of subtantial commerical fisheries in late 1950s (perhaps currently 5-15% of 1960 level) Recruitment decline since early 1960/70 Assessment suggests strong stock/recruitment level but with periods of large positive and negative anomolies (possible regime shifts) and assessment results are compatabile with a wide range of productivity/steepness Apparently some very small recent cohort (2000-2002)

Juvenile Distribution Movements and Migration: Decadal Changes1960s-2000 s 70 80 90 100 110 120 130 140 150E 30 20 10 N 0 S 10 20 WA 30 40 70 80 90 100 110 120 130 140 150E 50 GAB NSW

Conventional Tag Returns from Releases in the 1990s Release Location WA SA Tas All Returns <3 months Japanese Longline Return 3-6 months 6-9 months >12 months Release and recovery location

Typical Long Term Movement Pattern most released and recovered in Australian Waters -31-31.5 Archival tag releases 1998-2000 and recapture locations (n=24) Release Recapture -32-32.5-33 Latitude ( S) -33.5-34 -34.5-35 -35.5-36 126 127 128 129 130 131 132 133 134 135 136 Longitude ( E) Release and recovery location

Current Understanding of Juvenile SBT Migration Pathways in the 1990s Synthesis of: archival tag data conventional tagging data catch data (length frequency and cpue)

Movements and Migration: Decadal Changes 1960s-1990 s

Australian Surface Catches by Region Total Catches Catch (millions of fish) 0.0 0.5 1.0 1.5 NSW WA SA No Surface Fishery off NSW since 1983 but juvenile schools basically not seen ever since and evidence of subsequent increase in juvenile in winter longline catches in Tasman Sea and end of WA surface fishery (previous source for NSW fish) 1950 1960 1970 1980 1990 2000 Year Age 3 LL CPUE Tasman Sea Observation indicated juvenile schools common in NSW prior to commercial fishery (1940-50 and earlier)

NSW Surface Fish Age Composition October December 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1982 0% 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 o 1 2 3 4 5 6 7 November January 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1977 1978 1979 1980 1981 1982 1983 1984 0% 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1975 1976 1977 1978 1979 1980 1981 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8

1960s Tag Releases and Returns Release Years Fisher Scientist 1959-1969 Unknown tagger Number released 17616 12771 13967 1959-1966 1967-1969 Number returned 5172 786 603 Return rate 0.294 0.062 0.043 Number released 1338 12285 13884 Number returned 134 706 592 Return rate 0.100 0.057 0.043 Number released 16278 486 83 Number returned 5038 80 11 Return rate 0.309 0.165 0.133

Return Locations from 1960s Tag Release Release Years Recapture Location Release Location SA NSW TAS High Seas 1959-66 WA 222 123 1 94 SA 116 17 0 124 NSW 20 182 0 34 TAS 3 1 0 2 1967-69 WA 56 43 0 34 SA 63 111 0 20 NSW 27 1440 1 43 TAS 0 0 0 1 (Only for releases at liberty more then 270 days)

Geographic Location of Longline Returns from 1960 Tag Releases Release Recapture Longitude Location <115 115-145 >145 WA 66 27 35 SA 61 25 58 NSW 12 7 58 TAS 0 0 3 Indian Ocean Tasman Sea

Geographic Location of Longline Returns from 1960 & 1990 Tag Releases 1960 Release Recapture Longitude Location <115 115-145 >145 WA 66 27 35 SA 61 25 58 NSW 12 7 58 TAS 0 0 3 1990 WA SA 291 406 49 107 183 665 Indian Ocean Tasman Sea

Pre -1980 Juvenile Distribution and Migration Ages 0-1 Ages 2-5

Movements and Migration: Decadal Changes 1990s-2000 s 350 GAB Surface Fishery Catches 300 250 Catch (numbers) 200 150 100 50 0 1992 1994 1996 1998 2000 2002 2004 2006 2008

AGE 1 RELEASES (age 2-4 recaptures) WA RELEASES GAB RELEASES 1990s -50-40 -30-20 -10 0 2.2% 7.1% 86.0% 4.6% N = 25890 R = 8.7% -50-40 -30-20 -10 0 2.6% 4.5% 77.1% 15.0% N = 3005 R = 8.9% 0 50 100 150 0 50 100 150 2000s -50-40 -30-20 -10 0 1.6% 9.2% 87.3% 1.3% N = 7590 R = 4.0% -50-40 -30-20 -10 0 5.1% 7.6% 87.3% 0.0% N = 394 R = 20.1% 0 50 100 150 0 50 100 150 Conventional Longline Returns 1990s versus 2000 s

AGE 2 RELEASES (age 3-4 recaptures) WA RELEASES GAB RELEASES 1990s -50-40 -30-20 -10 0 5.2% 5.6% 79.9% 8.9% N = 3339 R = 8.1% -50-40 -30-20 -10 0 3.1% 6.0% 77.5% 13.3% N = 19538 R = 10.0% 0 50 100 150 0 50 100 150 2000s -50-40 -30-20 -10 0 1.6% 9.1% 88.2% 0.3% N = 7478 R = 17.2% -50-40 -30-20 -10 0 0.6% 4.0% 94.6% 0.6% N = 5889 R = 21.6% 0 50 100 150 0 50 100 150 Conventional Longline Returns 1990s versus 2000 s

AGE 3 RELEASES (age 4 recaptures) WA RELEASES GAB RELEASES 1990s -50-40 -30-20 -10 0 0.0% 0.0% 100.0% 0.0% N = 88 R = 1.1% -50-40 -30-20 -10 0 3.5% 6.7% 73.4% 16.4% N = 12902 R = 4.6% 0 50 100 150 0 50 100 150 2000s -50-40 -30-20 -10 0 0.0% 11.8% 88.2% 0.0% N = 182 R = 9.3% -50-40 -30-20 -10 0 0.9% 4.4% 93.9% 0.5% N = 4984 R = 8.6% 0 50 100 150 0 50 100 150 Conventional Longline Returns 1990s versus 2000 s

Percent of longline returns that were from the Tasman Sea Japanese Longliners All Longliners 60 60 50 50 40 40 Percent 30 Percent 30 20 20 10 10 0 1 2 3 4 0 1 2 3 4 Age Age 1990s 2000s 60 50 Japanese Effort In Tasman Sea 70% 60% Japanese Catch In Tasman Sea Percent 40 30 20 effort 50% 40% 30% Age 3 Age 4 10 0 1968 1974 1980 1986 1992 1998 2004 Year 20% 10% 0% 1968 1974 1980 1986 1992 1998 2004 Year

2000 Archival Tag East-West Movements WA Releases High Sea Releases GAB Releases 0 0 0 100 100 100 200 200 200 300 300 300 Day 400 Day 400 Day 400 500 500 500 600 600 600 700 700 700 800 800 800 0 30 60 90 120 150 180 Longitude 0 30 60 90 120 150 180 Longitude 0 30 60 90 120 150 180 Longitude

Archival Tag East-West Movements 1998-2000 Releases 1993-1995 Releases 2002-2005 Releases 0 0 50 50 0 100 100 100 150 150 200 day 200 250 day 200 250 Day 300 400 300 300 500 350 350 600 400 400 700 450 0 30 60 90 120 150 180 450 0 30 60 90 120 150 180 800 0 30 60 90 120 150 180 Longitude longitude longitude

Archival Tag East-West Movements East Maximum Longitude Year 145 >145 1993 2 0 1994 6 2 1995 11 5 1998 9 7 1999 6 2 2000 5 3 2002 2 0 2004 8 0 2005 13 1 2006 1 0 2007 1 0 Total 64 20 Maximum Longitude Year <65 >65 1993 0 2 1994 3 5 33% 1995 1 15 17% 1998 1 15 1999 3 5 4% P<0.001 West 2000 2 6 2002 0 2 2004 1 7 2005 0 14 2006 0 1 2007 0 1 Total 11 73 4% P<0.01

Sea Surface Temperature 1990-2006 Tas SGB EIO Average sea surface temperature for May-August

Where are the 1 year old WA Fish???

Release Length of Fish Tagged and Release Length for those Fish that were Recaptured 1990s: releases 2000s: Releases Frequency 0 2000 4000 6000 8000 10000 40 60 80 100 120 Release length (cm) 1990s: recaptures Frequency 0 5000 10000 15000 40 60 80 100 120 release length 2000s: Recaptures 0 200 400 600 800 1000 0 500 1000 1500 40 60 80 100 120 40 60 80 100 120 release length Release length (cm)

Comparison of Length at Release for Recaptures by Purse Seiners and Longliners Purse Seine Recaptures Longline Recaptures 0 200 400 600 0 20 40 60 40 60 80 100 120 length at release 40 60 80 100 120 length at release

AGE 1 RELEASES (age 2-4 recaptures) WA RELEASES GAB RELEASES 1990s -50-40 -30-20 -10 0 2.2% 7.1% 86.0% 4.6% N = 25890 R = 8.7% -50-40 -30-20 -10 0 2.6% 4.5% 77.1% 15.0% N = 3005 R = 8.9% 0 50 100 150 0 50 100 150 2000s -50-40 -30-20 -10 0 1.6% 9.2% 87.3% 1.3% N = 7590 R = 4.0% -50-40 -30-20 -10 0 5.1% 7.6% 87.3% 0.0% N = 394 R = 20.1% 0 50 100 150 0 50 100 150

Comparison of the number and percent of tags recovered by age and release location. Age at Release Release Location Number Recovered Number Released Percent Recovered 1 GAB 153 1161 13.2% WA 460 16570 2.8% 2 GAB 2435 13745 17.7% WA 1432 8314 17.2%

Juvenile SBT Migration Pathways 2000 s???????????

Juvenile SBT Migration Pathways 1990 s vs 2000 s 1990s??????????? 2000s

Why No Juveniles in the Tasman? Hypotheses: Environmental Changes Fishery Effect (similar to NSW collapse)

Where are the 1 year olds? Environmental Changes? WA: Mean monthly SST GAB: Mean monthly SST WA.SST[, 1] 15 16 17 18 19 20 21 December January January February February March March April GAB.SST[, 1] 16 17 18 19 20 21 December January January February Jan February March March April Mar 1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 1994:2008 1994:2008

Why No Juveniles in the Tasman? Hypotheses: Environmental Changes Fishery Effect (similar to NSW collapse)

Fishing Mortality Rates: 1990s vs 2000s experiments F at age 3 1.2 1.0 0.8 F 0.6 0.4 F at Age 4 0.2 1.2 0.0 1.0 1992 1994 1996 1998 2000 2002 2004 2006 2008 Year 0.8 age 1 releases age 2 releases 1990 Brow nie F 0.6 0.4 Estimates utilize year specific reporting rate estimates and individual tagger shedding rate 0.2 0.0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year age 1 releases age 2 releases age 3 releases 1990 Brownie

First year recaptures of fish released in December in the Great Australian Bight Fishing Year Release Age Number Released Number Returned Percent Returned Est. Percent Caught 2003 2 894 13 1.5 2.3 3 3004 283 9.4 14.6 4 242 32 13.2 20.5 2004 2 3187 75 2.4 4.9 3 978 234 23.9 49.6 4 27 7 25.9 53.8 2005 2 2760 33 1.2 3.3 3 308 32 10.4 28.6 4 130 11 8.5 23.3 5 68 12 17.6 48.6 2006 2 1887 15 0.8 3.7 3 2442 179 7.3 34.1 (no allowance for tag shedding)

Same Year Recaptures of December Releases in the Great Australian Bight (GAB) 2003 Recoveries From December Releases 2003 December Releases 2002/2003 Fishing Season Latitude -35-34 -33-32 -31 0 10 20 30 40 50 60 130 131 132 133 134 135 136 Longitude 2006 Recoveries From December Releases 2005 December Releases 20 40 60 80 100 120 Day of Capture since Dec. 1 Day of capture since December 1 2005/2006 Fishing Season Latitude -35-34 -33-32 -31 0 10 20 30 40 130 131 132 133 134 135 136 Longitude 20 40 60 80 100 120 Day of Capture since Dec. 1 Day of capture since December 1

Aerial Survey in Great Australian Bight 32 S 34 S 36 S Nullarbor + Ceduna 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Port Lincoln 128 E 130 E 132 E 134 E 136 E + + REL ABUND 0.0 0.5 1.0 1.5 2.0 2.5 Aerial Survey Index Mean and 95 CI 1994 1996 1998 2000 2002 2004 2006 Index standardized for sighting conditions and observer effects Catch (numbers) 350 300 250 200 150 100 GAB Catches 50 0 1992 1994 1996 1998 2000 2002 2004 2006 2008

Aerial Survey in Great Australian Bight: Within season depletion 250000 Within season depletion = Feb. Index/Jan. Index (monthly indecies are predicted values based corrected for sighting conditions and observer effects) Catch through February 200000 150000 100000 50000 250000 200000 1.40 1.20 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 Within Seaon Depletion Catch through Feb 150000 100000 50000 1.00 0.80 0.60 0.40 0.20 Feb index/jan Index 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 0.00 catch depletion

Where are the 1 year old WA Fish??? Hypotheses High tagging mortality rates or high dependent tag loss Same tagging protocol and many of the same taggers both between WA and GAB and between 1990s and 2000s High rates of survival during the first few months of release based on accoustic tags Non-mixing and change migration/movements 1 year olds found in the GAB as compared to those found in WA are preferentially found at older ages in the high seas winter feeding grounds where longlining occurs no differential is seen in the return rates for 2 year old fish tagged in the WA or the GAB If non-mixing, WA fish are not only not going to the GAB, but are also not going to areas where the longline fishery is operating. Change and High Natural Mortality Rates no direct evidence for this Accoustic tagging in WA indicates high survival during the 3 months after tagging ~80% of the 1 year olds tagged in WA would have to have died in order to yield the same return rate as the 1 year olds tagged in the GAB

Juvenile SBT Migration Pathways Pre and Post 1980 Post 1980 Pre 1980

Juvenile SBT Migration Pathways 1990 s vs 2000 s 1990s??????????? 2000s

Juvenile SBT Migration Pathways Pre and Post 2010??? 1990s?????? Post 2010?

Summary - juvenile Current fishing mortality rates for age 3 and 4 fish found in the GAB appear extremely high and are substantially greater then in the1990s Tagging return data are not consistent with the estimated size/age distribution of catches in the GAB Movement and migration patterns of juvenile SBT have changed between the 1960 and 1980/90 and between the 1990 s and 2000s There is an unexplained difference in the return rates for age 1 fish tagged in WA and GAB in the 2000s that was not apparent in the 1990s where are all the 1 year old fish? High fishing mortality rates and changes in juvenile movement patterns were associated with the collapse of the NSW juvenile component of the SBT stock in late 1970s. Is this being repeated in GAB??

Changes in Adult Distribution??

Japanese Vessel Reported Longline Effort Number of Year s Fished 000 W 050 E 100 E 150 E 50 S number 140 120 100 80 60 40 20 0 69 75 81 87 93 year first fished last fished Large area with no data in most years Steady reduction in Area fished The total number of five degree squares that had been fished at least once prior to the end of a given year and the total number of squares that were never fished after that given year.

Adult Japanese Longline CPUE by Area

Changes in targeting or species replacement?? 100 Percent 80 60 40 20 30 35 40 45&50 0 69 73 77 81 85 89 93 97 Year The proportion of the total catch of SBT, Bigeye and Yellowfin tuna that was SBT by latitudinal bands

Concentration Profiles for Japaness Longline 1969-1978 1979-1988 relative CPUE 1.0 0.5 0.0 1 6 11 16 rank relative CPUE 1.0 0.8 0.6 0.4 0.2 0.0 1 6 11 16 rank 1989-1997 relative C PU E 1.0 0.5 0.0 1 6 11 16 rank

Japanese Area 10 CPUE Area 10 CPUE - Pre and post 1986-30 -35-40 Pre 1986 Post1986 Post 1986 effort/no catch -45-50 -70-65 -60-55 -50-45 -40-35 -30-25 -20

Summary - adult Data for analysing changes in adult distribution are limited and problematical Interpretation of available data is confounded by changes in fishing effort distributions and operational/management changes plus issues of data reliability No strong evidence for large, major shift/contraction but note above Some suggestions of some possible substantive changes as well as finer scale changes in use of space

Why No Juveniles in the Tasman? Environmental Changes

Decadal Reported Effort & Catch By Ocean Effort Catch

Data Issues: Proportion of Catch or Tag Returns by Age for a Cohort Age 4 Catch Data Age 4 Catch Data Catch Data Age 3 Tag Returns Age 2 Tag Returns Age 3 Age 3 Tag Returns Age 2 Age 1 2 3 Age 1 Releases 2002 Cohort Age 1 2 3 Age 2 Releases 1 2 3 Age 1 Releases 2003 Cohort

Age Structure of Indonesian Spawning Ground SBT Catches Correspondence to very low escapement from surface fishery in 1980-84 and subsequent increase escapement as a result of restrictive quotas on surface fishery Recent lack of older fish due to high recruitment to spawning stock or fishing effects???? Based on annual ALK derived from direct aging of otoliths

Japanese Nominal Longline CPUE by Age

Fishing Mortality From Tagging: Reporting Rate Estimates Australian Farm Returns Tag Seeding Re-releases Reporting Rate Vector 2002/2003 2003/2004 2004/2005 2005/2006 A0 0.65 0.55 0.42 0.22 A1 1.00 1.00 1.00 1.00 A2 1.00 0.79 0.62 0.34 A3 0.65 0.55 0.42 0.30 A4 1.00 0.79 0.62 0.47 A5 0.47 0.47 0.47 0.47 A6 0.67 0.67 0.33 0.33