Changes in Abundance and Spatial Distribution of Southern Bluefin Tuna

Transcription

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

2 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

3 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.

4 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

5 SBT Background Available Data Conventional tagging experiments conducted in 1960s ( ), 1970 s1980 ( ), 1990s ( ) and 2000s ( ) Arial Surveys in the Great Australian Bight Catch data CPUE Japanese longline, Taiwanese, NZ longline Size data of varying quality on catches back to s 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

6 SBT Background Tagging experiment Major conventional tagging experiments conducted in 1960s ( ), 1980 ( ), 1990s ( ) and 2000s ( ) A total of ~206,000 tags released and ~24,000 recovery E SBT Archival Tagging average length (cm) > s and 2000s were similar in design (multi-year/multi-cohort) and < 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 in 1990s and 2000s E Longline recovery rates similar to pole and line but not used here Three periods of archival tag deployments ( , and )

7 Estimated Annual SBT Catch OVercatch (t) IUU Catches based on Market Statistic Percent Catch (t) Year Case 1 Case 2 Adapted from CCSBT SAG Year Case 1 Case 2 Official Catches

8 Spawning stock biomass (thousand tonnes) Overall Population Trends: scenario modelling i.e. Integrated Statistical Catch at age model for assumptions about IUU catches SB1989 SB m future catch CCSBT SAG 2006 Recruitment (millions) Scenario c CCSBT SAG 2006 overcatch Year CCSBT/08/09/

9 New Zealand Longline CPUE by Age and Cohort

10 SBT Growth changes over time

11 Overall Population Trends: Summary Largest catches in 1960 and generally decline Large IUU catches in 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 ( )

12 Juvenile Distribution Movements and Migration: Decadal Changes1960s-2000 s E N 0 S WA E 50 GAB NSW

13 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

14 Typical Long Term Movement Pattern most released and recovered in Australian Waters Archival tag releases and recapture locations (n=24) Release Recapture Latitude ( S) Longitude ( E) Release and recovery location

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

16 Movements and Migration: Decadal Changes 1960s-1990 s

17 Australian Surface Catches by Region Total Catches Catch (millions of fish) 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) Year Age 3 LL CPUE Tasman Sea Observation indicated juvenile schools common in NSW prior to commercial fishery ( and earlier)

18 NSW Surface Fish Age Composition October December 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% % Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 o November January 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% 0% % Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8

19 1960s Tag Releases and Returns Release Years Fisher Scientist Unknown tagger Number released Number returned Return rate Number released Number returned Return rate Number released Number returned Return rate

20 Return Locations from 1960s Tag Release Release Years Recapture Location Release Location SA NSW TAS High Seas WA SA NSW TAS WA SA NSW TAS (Only for releases at liberty more then 270 days)

21 Geographic Location of Longline Returns from 1960 Tag Releases Release Recapture Longitude Location < >145 WA SA NSW TAS Indian Ocean Tasman Sea

22 Geographic Location of Longline Returns from 1960 & 1990 Tag Releases 1960 Release Recapture Longitude Location < >145 WA SA NSW TAS WA SA Indian Ocean Tasman Sea

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

24 Movements and Migration: Decadal Changes 1990s-2000 s 350 GAB Surface Fishery Catches Catch (numbers)

25 AGE 1 RELEASES (age 2-4 recaptures) WA RELEASES GAB RELEASES 1990s % 7.1% 86.0% 4.6% N = R = 8.7% % 4.5% 77.1% 15.0% N = 3005 R = 8.9% s % 9.2% 87.3% 1.3% N = 7590 R = 4.0% % 7.6% 87.3% 0.0% N = 394 R = 20.1% Conventional Longline Returns 1990s versus 2000 s

26 AGE 2 RELEASES (age 3-4 recaptures) WA RELEASES GAB RELEASES 1990s % 5.6% 79.9% 8.9% N = 3339 R = 8.1% % 6.0% 77.5% 13.3% N = R = 10.0% s % 9.1% 88.2% 0.3% N = 7478 R = 17.2% % 4.0% 94.6% 0.6% N = 5889 R = 21.6% Conventional Longline Returns 1990s versus 2000 s

27 AGE 3 RELEASES (age 4 recaptures) WA RELEASES GAB RELEASES 1990s % 0.0% 100.0% 0.0% N = 88 R = 1.1% % 6.7% 73.4% 16.4% N = R = 4.6% s % 11.8% 88.2% 0.0% N = 182 R = 9.3% % 4.4% 93.9% 0.5% N = 4984 R = 8.6% Conventional Longline Returns 1990s versus 2000 s

28 Percent of longline returns that were from the Tasman Sea Japanese Longliners All Longliners Percent 30 Percent Age Age 1990s 2000s Japanese Effort In Tasman Sea 70% 60% Japanese Catch In Tasman Sea Percent effort 50% 40% 30% Age 3 Age Year 20% 10% 0% Year

29 2000 Archival Tag East-West Movements WA Releases High Sea Releases GAB Releases Day 400 Day 400 Day Longitude Longitude Longitude

30 Archival Tag East-West Movements Releases Releases Releases day day Day Longitude longitude longitude

31 Archival Tag East-West Movements East Maximum Longitude Year 145 > Total Maximum Longitude Year <65 > % % % P<0.001 West Total % P<0.01

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

33 Where are the 1 year old WA Fish???

34 Release Length of Fish Tagged and Release Length for those Fish that were Recaptured 1990s: releases 2000s: Releases Frequency Release length (cm) 1990s: recaptures Frequency release length 2000s: Recaptures release length Release length (cm)

35 Comparison of Length at Release for Recaptures by Purse Seiners and Longliners Purse Seine Recaptures Longline Recaptures length at release length at release

36 AGE 1 RELEASES (age 2-4 recaptures) WA RELEASES GAB RELEASES 1990s % 7.1% 86.0% 4.6% N = R = 8.7% % 4.5% 77.1% 15.0% N = 3005 R = 8.9% s % 9.2% 87.3% 1.3% N = 7590 R = 4.0% % 7.6% 87.3% 0.0% N = 394 R = 20.1%

37 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 % WA % 2 GAB % WA %

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

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

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

41 Where are the 1 year olds? Environmental Changes? WA: Mean monthly SST GAB: Mean monthly SST WA.SST[, 1] December January January February February March March April GAB.SST[, 1] December January January February Jan February March March April Mar : :2008

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

43 Fishing Mortality Rates: 1990s vs 2000s experiments F at age F F at Age Year 0.8 age 1 releases age 2 releases 1990 Brow nie F Estimates utilize year specific reporting rate estimates and individual tagger shedding rate Year age 1 releases age 2 releases age 3 releases 1990 Brownie

44 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 (no allowance for tag shedding)

45 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 Longitude 2006 Recoveries From December Releases 2005 December Releases Day of Capture since Dec. 1 Day of capture since December /2006 Fishing Season Latitude Longitude Day of Capture since Dec. 1 Day of capture since December 1

46 Aerial Survey in Great Australian Bight 32 S 34 S 36 S Nullarbor + Ceduna Port Lincoln 128 E 130 E 132 E 134 E 136 E + + REL ABUND Aerial Survey Index Mean and 95 CI Index standardized for sighting conditions and observer effects Catch (numbers) GAB Catches

47 Aerial Survey in Great Australian Bight: Within season depletion Within season depletion = Feb. Index/Jan. Index (monthly indecies are predicted values based corrected for sighting conditions and observer effects) Catch through February Within Seaon Depletion Catch through Feb Feb index/jan Index catch depletion

48 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

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

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

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

52 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??

53 Changes in Adult Distribution??

54 Japanese Vessel Reported Longline Effort Number of Year s Fished 000 W 050 E 100 E 150 E 50 S number 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.

55 Adult Japanese Longline CPUE by Area

56 Changes in targeting or species replacement?? 100 Percent & Year The proportion of the total catch of SBT, Bigeye and Yellowfin tuna that was SBT by latitudinal bands

57 Concentration Profiles for Japaness Longline relative CPUE rank relative CPUE rank relative C PU E rank

58 Japanese Area 10 CPUE Area 10 CPUE - Pre and post Pre 1986 Post1986 Post 1986 effort/no catch

59 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

60

61 Why No Juveniles in the Tasman? Environmental Changes

62 Decadal Reported Effort & Catch By Ocean Effort Catch

63 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 Age 1 Releases 2002 Cohort Age Age 2 Releases Age 1 Releases 2003 Cohort

64 Age Structure of Indonesian Spawning Ground SBT Catches Correspondence to very low escapement from surface fishery in 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

65 Japanese Nominal Longline CPUE by Age

66 Fishing Mortality From Tagging: Reporting Rate Estimates Australian Farm Returns Tag Seeding Re-releases Reporting Rate Vector 2002/ / / /2006 A A A A A A A