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North and South Atlantic albacore (Thunnus alalunga) stocks assessment ICCAT WG ALB, 26 Sept., 2007

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Ex. Report ALB SCI-017 North and South Atlantic albacore (Thunnus alalunga) stocks assessment ICCAT WG ALB, 26 Sept., 2007 Multifan Inputs for ALB Assessment, March 2007 SCI-030 /2007 Detail Albacore stock assessment, July 2007- SCI-036 /2007 ALB- Atlantic Biology

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slide1
Ex. Report ALB SCI-017

North and South Atlantic albacore (Thunnus alalunga) stocks assessment

ICCAT WG ALB, 26 Sept., 2007

Multifan Inputs for ALB Assessment, March 2007 SCI-030 /2007

Detail Albacore stock assessment, July 2007- SCI-036 /2007

slide2
ALB- Atlantic Biology
  • Stock structure for assessment: North and South stocks in the Atlantic ocean separated at 5º and Mediterranean stock. Intermingling of Indian and Atlantic oceans needs research.
  • Present knowledge on habitat distribuition by size, spawning areas, maturity based on limited studies mostly from past years.
  • Revised vB growth equation was estimated for South Atlantic stock based on aging dorsal fin ray section
  • Vertical distribution: immature at sub-surface above thermocline in summer. Adult distribution at wider range from surface to ~ 300m depth.
slide4
Catch trend Northern stock ALB

1930-2005 years

1975 VPA

LL

TROL

BB

slide5
Fisheries indicators in North Atlantic

Overall description

  • Targeting immature and sub-adults (50- 90 cm FL) by surface fisheries in the North Eastern Atlantic from Azores Is. to northern lalitude (SW Ireland) and Bay of Biscay areas, during spring, summer and autumn.
  • Targeting immature and adult albacore (60-130 cm FL) by longline fisheries in Central and Western Atlantic waters all year round.
  • Catch was extended back to 1930 after revision for stock assessment.
  • Trend: declining began in 1986 due to reduction of traditional surface fleets (Troll and Baitboat) and longline fleets. Stabilization observed in the 90´s due to incorporation of new fleets (drifnets & mid-water pair pelagic trawl). Maximun catchof 38,063 t registered in 1993. Followed by the lowest on record of 22,685 t in 2002. Since then and steady increase until reaching a peak of 36,077 t in 2006.

LL

TROL

BB

slide6
Surface Fisheries

Gears: troll, baitboat, mid-water pair pelagic trawl (MWPT).

Main fleets involved: EC (Spain, France Portugal and Ireland)

In 2006 the surface fishery represented the 86 % of total catch in North stock

EC-France MWPT reported the highest catch of recent years in 2005, but decreased the 30 % in 2006.

EC-Ireland MWPT catch has decreased since 2002.

EC-Spain increased the baitboat catch by 49% respecting 2005 catch and the troll catch in 2006 was similar to 2005 level.

LL

Longline Fisheries

BB

Longline catches decreased in 2006, due to a decrease of landings by Chinese-Taipei fleet of 60% compared to 2005 caused by decline in fishing effort.

slide7
Catch trend Southern stock ALB

1956-2005 years

LL

LL

BB

LL

BB

slide8
Fisheries indicators in South Atlantic

Overall description

Targeting immature and sub-adults (70- 90 cm FL) by surface fisheries in the South Eastern Atlantic in coastal waters of Namibia and South Africa from October to May.

Targeting adult albacore (> 90 cm FL) by longline fisheries in Northeast coast off Brazil (5ºS-20º S) and over the South Atlantic area by longline fleet from Chinese-Taipei Central all year round.

Trend: total reported catch in 2006 was 24,375 t , an increase of about 5,000 t respect 2005. TheChinese –Taipei catch increased in 2006 to 12,293 t. As for Brazilian catches, the Chinese –Taipei vessels (incluidng Belize and St. Vincent flagged boats ) stopped fishing for Brazil in 2003, then albacore was only caugth as by-catch in the SWO and Trop target longline fisheries, reaching 267 t.

The decreased of albacore in 2006 in inshore waters of South Africa and unfavorable foreign currency has caused a reduction in number of active baitboat vessels.

LL

TROL

BB

slide9
Catch trend Mediterranean stock ALB

1964 -2005 years

Main Fleets

Longline

Other Surf

LL

LL

BB

LL

BB

  • Reported catches in 2006 were 5,874 t, an increased with respect to 2005.
slide10
Assessing the State of Atlantic stocks

Background

  • Thorough revision of North and South Atlantic stock data: Task I and Task II, was done and more robust method was implemented to analyse Catch-at-Size (CAS) information.
  • Historical Catch for North Atlantic stock was recovered and incorporate to the analyses up to 1930.
  • Catch rates analyses were reviwed and new model applied for some longline fleets resulting in better fit to data.
  • Substantial work was undertaken to implement new methods which do not assume that CAA is known whitout error, to assess the albacore stocks.
  • This new implemented method provided the opportunity to evaluate a range of hypothesis:

- how the fisheries operated over time and their impact in the population ?

LL

LL

BB

LL

BB

slide11
ALB- North stock. Total Catch-At-Age (CAA)

1 to 8+ age group

Bubble size proportional to number of fish

slide12
ALB- North stock. Catch-At-Age (CAA) by Fishery

1 to 8+ age group

LONGLINE FLEETS

Target Ch-TAI

By-catch USA

By-catch

By-catch JPN

SURFACE FLEETS

Target BB ESP

Target TR ESP

Target OTHER

Bubble size proportional to number of fish on each fleet

slide13
ALB- North CPUE time series

Surface

TR fleet

Longline

Taiwan LL target

slide14
ALB-N- Recruitment and Spawning stock

Age 1- recruit

MFCL model

2005 high but uncertain

1930- 2005

MFCL model

SSB ~ ¼ Max in 40´s

slide16
ALB- North State of stock

SSB has decreased to one fourth of the SSB in the highest level in the 40´s

Recruit decreased from the 60´s until 2004. In 2005 the estimated recruitment is high ~ 60´s, but magnitude is uncertain.

The stock rebuild to levels near BMSY (SSB 20% below MSY) vs 2000 assessment when SSB 50% below MSY

Current F is 50% above F msy

Estimates of MSY varied over time as a combination of surface and longline fisheries with changing selectivity pattern over time period.

MSY for 3 recent years ~ 32.000 t , but over time ranged from 26.000 t to 34.00 t.

slide17
ALB- North Atlantic

Fishing trajectory and 2005 status

status in 2005

1930-2005 evolution of relative biomass and fishing mortality estimated trajectory relative to MSY

slide18
ALB- North Atlantic

Uncertainty of 2005 status determination

2005 status

F/Fmsy =1.5

B/Bmsy = 0.81

slide19
ALB- N- Projections

2006 CATCH of 36.000 t

32.000 t

TAC of 34.500 t

VPA

relative SSB (SSB/SSBMSY)for scenarios of cte catch 2008 -2020

Projected Current catch for 2006 & 2007

slide20
ALB- N- VPA Projections scenarios

assuming strong year class

32.000 t TAC

34.500 t TAC

relative SSB (SSB/SSBMSY)for scenarios of cte catch 2008 -2020

Projected Current catch for 2006 & 2007

slide21
ALB- South stock. Total Catch-At-Age (CAA)

1 to 8+ age group

Bubble size proportional to number of fish

slide22
ALB- South stock. Catch-At-Age (CAA) by Fishery

1 to 8+ age group

LONGLINE FLEETS

Target Ch-TAI

Target and By-catch BRA

By-catch JPN

SURFACE FLEETS

Target BB SA

Target BB NAM

Target OTHER

Bubble size proportional to number of fish on each fleet

slide23
ALB – South CPUE time series

Longline

Taiwan

Target

Surface

Baitboat

slide24
ALB- South Atlantic

Fishing trajectory and 2005 status

slide25
ALB- South Atlantic

Uncertainty of 2005 status determination

2005 status

F/Fmsy =0.63

B/Bmsy = 0.9

slide26
ALB- South State of stock

Last assesmment was done in 2003

Longline CPUE ´show a declining trend at the begining of time series, less marked in the recent period. Thos indices traget adult albacore.

Surface CPUE´s (Baitboat) target mostly immature albacore and no trend is seen.

Current SSB has declined 25% from unfished SSB.

Accordingly it is likely that in 2005 SSB is about 90% of Bmsy and F is 40% below F msy

Estimates of current MSY is around 33.300 t and Replacement yield is around 29.000 t, current catch 24.460 t is below.

slide27
ALB- S- Projections

10 years projections

BMSY

SSB over time trend and 80% confidence bounds

Projected cte catch = 25.000 t

slide28
ALB- N MANAGEMENT Rec.
  • Current TAC is 34.500 t
  • 2005 and 2006 catches have been above
  • Projections indicate that stock will not recover from overfished state if catch level remain > 30.000 t
  • If strong year class enters the fishery the stock would recovered faster

ALB- S MANAGEMENT Rec.

  • Current TAC is 29.900 t
  • 2Recent catches have been below
  • Projections indicate that catches at 2006 level will recover the stock from overfished state
  • Current management scheme is sufficient for recovery of South stock
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