East Coast SBT Habitat, AFMA Report
East Coast SBT Habitat Preference Model Report
Alistair Hobday and Jason Hartog
CSIRO Marine and Atmospheric Research
AFMA Report 18, November 9, 2010
Summary
The most recent 3-day SST composite is from November 3, 2010 (i.e. includes data
between November 2-4) and illustrates the general ocean situation off eastern
Australia (Figure 1). The surface currents have been added to aid the interpretation.
Eddies and the strength of the East Australia Current (EAC) are made particularly
obvious by this overlay. The predicted locations of the SBT habitat from the Habitat
Prediction Model are shown in Figure 2.
The EAC has continued to warm and strengthen and there is a strengthening warm
eddy off the coast of Ulladulla (Figure 1). This has reduced the amount of core
habitat offshore in that region, now made up of OK habitat and a large buffer region
(Figure 2). Some cool water has been drawn northward along the edge of the eddy
near shore at Ulladulla, resulting in a small area of Core habitat in being present in
that area that was not present in the last report (Figure 2). The far offshore habitat
predictions have not changed significantly since the last report (Figure 2). The SBT
core habitat locations (lower edge of red ribbon) for this part of the year are further
south than the long term climatology (1994-2009, Figure 3). This is because the EAC
is further south than usual for this time of year.
Model coverage
As requested by AFMA for 2007, this report shows habitat preference extending to
170°E (previous reports in 2006 extended out to 160°E). This extension is to allow
consideration of the SBT habitat further east. The shelf region has been blocked with
a mask for distribution to stakeholders. Currents could also be shown on Figure 2, if
desired by AFMA managers.
Seasonal Forecast
The seasonal forecast of the position of the SBT habitat zone for the coming months
using the POAMA (Predictive Ocean Atmosphere Model for Australia) model
(http://poama.bom.gov.au/), developed by BOM scientists Oscar Alves and Claire
Spillman has been tested and a manuscript submitted (and a copy sent to Trent).
While POAMA is a coarser resolution model than the one we use for the realtime
forecasts, we think it can provide information to fishers and managers about the SBT
habitat distribution in coming months. We plan to indicate forecasts of boundary
location out to four months in the next season.
Hobday, A. J., J. Hartog, C. Spillman and O. Alves (in review). Seasonal forecasting
of tuna habitat for dynamic spatial management. Canadian Journal of Fisheries and
Aquatic Sciences.
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East Coast SBT Habitat, AFMA Report
Methods
The set of predictions of the extent of SBT habitat on the east coast of Australia are
based on analyses of current satellite sea surface temperatures (SST), sub-surface
temperatures from a CSIRO ocean model incorporating satellite sea surface height
data and pop-up tag temperature data for SBT. This model run uses the revised SynTS
3-D ocean product (introduced in 2006) which has improved depth resolution (more
layers to a depth of 200 meters: 25 compared with 17). Surface currents are shown on
the surface SST map to aid understanding of the ocean dynamics.
Only those tag observations within 70 days of the analysis date have been considered
(e.g. May 2 ± 70 days). Thus, the current habitat model is conditioned on a pop-up tag
dataset consisting of 56 tags for the years 2001-2007 (5032 observations at this time
of year). No SBT tags were deployed in 2008-2009. The pop-up tags provide
information about the sub-surface temperatures that the tagged SBT encounters in
addition to the SST. This report used SBT sub-surface temperature preferences in
combination with a sub-surface temperature oceanographic model to calculate the
probability of SBT presence at depths to 200 m. In waters shallower than 200 m the
depth integration is only to the maximum depth. These probabilities are then
combined over all depths to calculate the probability of SBT presence at a single
location.
The climatology (Figure 3) compares the average latitudinal position of the buffer
zone so far this year with its average position (based on tuna habitat preferences and a
14-year analysis of SST from 1993 to 2009). The climatology is calculated using the
subsurface model. Note that the width of the buffer in Figure 3 is due to a persistent
inshore filament of buffer water along the coast, and the offshore fraction outside the
core of the EAC. This has the effect of moving the most northern 5% of buffer pixels
used to calculate the habitat climatology much further north than is apparent in the
real-time prediction (e.g. Figure 2). The “northerly jump” in the climatology
beginning about April is influenced by a lack of tag data in this period: the model uses
the limited SBT data from the first portion of the year (Figure 4), then transitions to
using the bulk of data available after April. This discontinuity will exist until more
data from tags at liberty in February to April are collected.
One habitat preference scenario is now used based on “Percent Habitat Distribution”:
• Scenario 1 : 80% : 15% : 5% (core zone : buffer zone : ok zone)
Information from the observer program on SBT captures
• Report 1: None.
• Report 2: None.
• Report 3: None.
• Report 4: First SBT interaction in the ETBF.
• Report 5-18: None.
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East Coast SBT Habitat, AFMA Report
Figure 1. High-resolution 3-day composite SST image for the most recent model run. The image from
the previous report is shown below for comparison. The 200 m depth contour is also depicted. Note this
map extends to 170° E. The surface currents have been overlayed on this image to enhance
understanding of the ocean dynamics. The size of the arrows is proportional to current velocity, and
show the direction of water movement.
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East Coast SBT Habitat, AFMA Report
Figure 2. Distribution of zones based on percentage distribution of SBT habitat from the habitat
prediction model based on Scenario 1 (80%: 15%: 5%). The image from the previous report is shown
below for comparison. The 200 m depth segment of the shelf is blacked out. The dotted line at 160°E
shows the extent of previous analyses (i.e. 2006 and earlier). The major fishing ports have been added
to aid interpretation.
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East Coast SBT Habitat, AFMA Report
Figure 3: The mean position of the buffer zone from the sub-surface temperature model throughout a
year is indicated by the yellow band and is based on an analysis of satellite SST from 1993 to 2007 (to
160°E). The blue lines indicate the maximum northerly (5%) and southerly extent (5%) of buffer pixels
in any year. For the climatology the position of the buffer zone is estimated as the upper and lower 5%
of buffer pixels in the current year is depicted by the red band. This may not reflect the optimal
placement of the buffer zone, and is intended as a guide to the seasonal movements of the SBT habitat
preferences. Scenario 1 is the 80:15:5 habitat division.
Figure 4: The number of observations from pop-up tags that are used in the analysis during different
times of the year is shown below for each of the years during which the observations were obtained.
Observations Used per day
2500
Observations
2000
1500
2001
2002
2003
2004
2005
2006
2007
All Years
1000
500
0
Jan
Apr
Jul
Oct
Jan
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East Coast SBT Habitat, AFMA Report
Table 1. Summary of report delivery and line placement dates for 2010
Report
Report sent
from CSIRO
Date of Data used
in Model
Date decision
made by
AFMA
Date lines
implemented
by AFMA
Line positions
1
2
3
4
May 5, 2010
May 18, 2010
June 1, 2010
June 9,2010
May 1-3, 2010
May 14-16, 2010
May 27-29, 2010
June 4-6, 2010
NA
NA
NA
June 9, 2010
June 12, 2010
Core Zone: The northern boundary of the Core Zone will commence at the intersection
of latitude 36°00’ South with the coast, then continue due east.
Buffer Zone: The northern boundary of the Buffer Zone will commence at the
intersection of latitude 35°00’ South with the coast, then continue due east.
5
6
June 15, 2010
June 22, 2010
June 11-13, 2010
June 18-20, 2010
June 15, 2010
June 22, 2010
June 25, 2010
7
July 6, 2010
July 2-4, 2010
8
9
10
July 13, 2010
July 20, 2010
July 27, 2010
July 9-11, 2010
July 16-18,2010
July 23-25, 2010
July 13, 2010
July 20, 2010
July 27, 2010
11
August 3, 2010
July 30-August 1, 2010
August 3,2010
Core Zone: The northern boundary of the Core Zone will commence at the intersection
of latitude 32°30’ South with the coast, then continue due east to longitude 153o’00
East, the heading south easterly to the intersection of latitude 35o’00 South and
longitude 155o’00 East, then heading due east at latitude 35o’00 South.
Buffer Zone: The northern boundary of the Buffer Zone will commence at the
intersection of latitude 32°00’ South with the coast, then continue due east.
Core Zone: The northern boundary of the Core Zone will commence at the intersection
of latitude 32°30’ South with the coast, then continue due east.
Buffer Zone: The northern boundary of the Buffer Zone will commence at the
intersection of latitude 32°00’ South with the coast, then continue due east.
No change
No change
Core at 33°00’ S
Buffer at 32°30’ S
Core Zone: The northern boundary of the Core Zone commences at the intersection of
latitude 33°30’ S with the coast, then continues east to Longitude 153° E, then south east
to the intersection of 35°S and 155°E, then continues due east.
Buffer Zone: The northern boundary of the Buffer Zone commences at the intersection
of latitude 32°30’ S with the coast, then continues east to Longitude 153° E, then south
east to the intersection of 34°S and 155°E, then due east to 156° E, then north east to
31°S 158° E, then continues due east.
Core Zone: The northern boundary of the Core Zone commences at the intersection of
latitude 35° S with the coast then continues due East.
Buffer Zone: The northern boundary of the Buffer Zone commences at the intersection
of latitude 32°30’ S with the coast, then continues south east to the intersection of
Longitude 153° E and 34°S then due east to 156° E, then north east to 31°S 158° E, then
continues due east.
Core Zone: The northern boundary of the Core Zone commences at the intersection of
latitude 35° S with the coast then continues due East.
Buffer Zone: The northern boundary of the Buffer Zone commences at the intersection
of latitude 34° S with the coast, then continues due east.
No change
Core Zone: The northern boundary of the Core Zone commences at the intersection of
latitude 35 30 S with the coast then continues due East.
Buffer Zone: The northern boundary of the Buffer Zone commences at the intersection
of latitude 35 S with the coast, then continues due east.
11a
August 11, 2010
12
August 17, 2010
August 13-15, 2010
August 17, 2010
13
14
August 31, 2010
September 14, 2010
August 27-29, 2010
September 10-12, 2010
August 31, 2010
September 14,
2010
15
16
September 28, 2010
October 12, 2010
September 24-26, 2010
October 8-10, 2010
17
18
October 26, 2010
November 9, 2010
October 19-21, 2010
November 4-6, 2010
October 12, 2010
October 26,2010
Comments
Trent: Not starting lines till first SBT caught.
Core Zone: The northern boundary of the Core Zone will commence at the intersection
of latitude 36 30 S with the coast, then continue due east.
Buffer Zone: The Buffer Zone has been removed
No Change
Due to the first capture of SBT in the ETBF we will be implementing the SBT Zones this
week.
No change
There has been a reported capture of SBT in the ETBF and the SBT zones will be
implemented this week.
Special request by Trent due to indications of current change.
Special Request after full moon.
Lines moved south by 30 miles
The zones have been changed this week. The SBT core and buffer zones are now located
at:
No habitat model run
Buffer zone removed
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