East Coast SBT Habitat Report
Jason Hartog and Alistair Hobday
AFMA Report 14, October 30, 2012
Summary
The most recent 3-day SST composite is from October 27, 2012 (i.e. includes data between October 26-28)
and illustrates the general ocean situation off eastern Australia (Figure 1) with the surface currents added to
aid interpretation. Eddies and the strength of the East Australia Current (EAC) are emphasized by this
overlay. The predicted locations of the SBT habitat from the Habitat Prediction Model are shown in Figure 2.
The southward flow of the EAC has warmed a much broader region when compared to the previous report
(Figure 1) and warm water can now be seen close to shore south to 34°S. Due to this continued southern
flow, buffer habitat inshore is present south to Ulladulla and OK habitat offshore to 35°S (Figure 2). Core
habitat is still present inshore in the area south of Ulladulla, and it is expected that this area will warm and
become buffer habitat in the next month (Figure 3).
The seasonal forecast and climatology (Figures 3 and 4) also strongly indicate a southern expansion of the
OK and buffer habitat zones in the coming weeks as the EAC strengthens inshore.
Model Coverage
For this SBT season, AFMA have requested the model to be run in an “inshore” mode (out to 155°E) and in
“regular” mode (habitat preference extending to 170°E). The shelf region has been blocked with a mask for
distribution to stakeholders. The offshore and inshore climatology are shown in Figure 4. The inshore mode
climatology has more variability as it is focusing on the most dynamic part of the EAC, and this variability is
seen in the width of the buffer zone climatology in the winter months when the EAC is retreating and
advancing rapidly.
Seasonal Forecast
Forecasts of the position of the SBT habitat zones using the POAMA (Predictive Ocean Atmosphere Model
for Australia) model (http://poama.bom.gov.au/), developed by Bureau of Meteorology (BoM) is shown in this
report. While POAMA is a coarser resolution model than the one we use for the habitat nowcasts (Figure 2),
the model can provide managers some information about the coming months of SBT habitat distribution. We
have verified the skill of POAMA for this purpose (Hobday et al 2011) and this report provides operational
forecasts for SBT habitat zones out to 5 months (Figure 3). Our published analysis suggests that the skill of
the forecast deteriorates after 3 to 4 months, and so projected habitat locations more than three months into
the future should be interpreted with caution. These projections may help managers and fishers plan their
operations over and above using the climatology alone.
1
East Coast SBT Habitat, AFMA Report
Figure 1. High-resolution 3-day composite SST image for the most recent model run. The 200 m depth
contour is also depicted. 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. The images from the previous report is shown below for comparison
2
East Coast SBT Habitat, AFMA Report
Figure 2. Habitat nowcast: 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 to the side for comparison. The 200 m depth segment of the shelf is masked out. The major fishing ports have been added to aid
interpretation.
a) Current Report
b) Previous Report
3
East Coast SBT Habitat, AFMA Report
Figure 3: Seasonal forecast: Distribution of zones based on percentage distribution of SBT habitat from the
habitat prediction model using POAMA temperature fields based on Scenario 1 (80%: 15%: 5%). The 200 m
depth segment of the shelf is blacked out. The thick dark line on the current forecast shows a contour
analysis of the operational nowcast core zone. The thick dark line on the 1 to 5 month forecasts shows a
contour analysis of the current forecast to aid understanding of how the core zone will be changing when
compared to the current POAMA forecast. The arrows on the right side of each panel give an indication of
whether the core zone is moving north or south when compared to the previous month’s forecast.
4
East Coast SBT Habitat, AFMA Report
Figure 4: Climatology showing the mean position of the buffer zone throughout the year is indicated by the yellow band and is based on an analysis of satellite SST and subsurface temperature from 1994 to 2010 (to 170°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. The red stars show the location
of the core zone in this climatology for the 1 to 5 month forecasts.
a) Regular mode: coast to 170°E
b) Inshore mode: coast to 155°E
Scenario 1 Core and Buffer Zone Edges
-24
-26
-26
-28
-28
-30
-30
Latitude
Latitude
Scenario 1 Core and Buffer Zone Edges
-24
-32
-34
-36
-34
-36
-38
-38
Buffer Zone Climatology (1994-2011)
Buffer Zone 2012
Maximum Extent Any Year
-40
-42
Jan
-32
Apr
Jul
Month
Oct
Jan
Buffer Zone Climatology (1994-2011)
Buffer Zone 2012
Maximum Extent Any Year
-40
-42
Jan
Apr
5
Jul
Month
Oct
Jan
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. One habitat preference scenario is now used based on “Percent Habitat Distribution”.
This is known as Scenario 1: 80%: 15%: 5% (core zone: buffer zone: ok zone)
Until the middle of July, tag observations within 70 days of the analysis date will be considered
(e.g. May 2 ± 70 days). This changes to 30 days after that date, as in previous years. The
reason for this is that there is limited data in the early part of the year to condition the model.
Thus, the current habitat model is conditioned on a pop-up tag dataset consisting of 71 tags for
the years 2001-2009 (7656 observations at this time of year). This year we have included data
from SBT tagged in New Zealand, and we acknowledge MFish in New Zealand for the use of
these data. Analysis of the data suggests that these animals are suitable to provide additional
information on habitat preference in the study area. 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.
This same methodology is used to generate the habitat forecast shown in Figure 3, with the SST
and sub surface temperature field being replaced by temperature depth fields obtained from the
POAMA model from the Bureau of Meteorology.
The climatology (Figure 4) compares the average latitudinal position of the buffer zone so far this
year with its average position (based on tuna habitat preferences and a 17-year analysis of SST
from 1994 to 2011). The climatology is calculated using the subsurface model. Note that the
width of the buffer in Figure 4 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 core zone predictions from the
seasonal forecast are shown as red stars on Figure 4. POAMA is not eddy resolving, so there
will be dynamic features of the EAC that are not captured in the seasonal forecast. This effect of
this is that there are small differences in the core zone prediction (Figure 3a), but overall there is
skill in the predictions obtained using POAMA (Hobday et al 2011). The “northerly jump” in the
climatology beginning about April is influenced by limited tag data in this period: the model uses
the limited SBT data from the first portion of the year (Figure 5), and 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.
6
East Coast SBT Habitat, AFMA Report
Figure 5: 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
2008
2009
All Years
1000
500
0
Jan
Apr
Jul
Oct
Jan
7
East Coast SBT Habitat, AFMA Report
Summary of reports
Report
Report sent
from CSIRO
Date of Data
used in
Model
Port visit
April 27, 2012
April 23-23, 2012
1
May 17, 2012
May 13-15, 2012
Date
decision
made by
AFMA
Date lines
implemented
by AFMA
Line positions
May 18,2012
May 21, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 35°30’
S with the coast.
Comments
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 36°30’ S
with the coast.
2
May 31, 2012
May 27-29, 2012
3
June 12, 2012
June 8-10, 2012
No Change
June 18, 2012
June 21, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 35°30’
S with the coast.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 36°30’ S
with the coast.
8
East Coast SBT Habitat, AFMA Report
4
June 26,2012
June 22-24, 2012
June 27, 2012
June 28, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 32°30’
S continuing out to longitude 154°E then continuing
southeast to intersection of 35°S and 155°E and then
east along latitude 35°S .
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 35°30’ S
with the inshore Buffer Zone at 150°56.8’ and
extends to the east.
Inshore Buffer Zone: There has been an inshore
Buffer Zone implemented on the western side of the
Core Zone from the coast out to the approximate
position of the 1000 fathom line and extending south
to the NSW/Vic border.
n/a
July 3, 2012
July 5, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 33°00’
S with the coast continuing southeast to intersection
of 35°S and 155°E and then east along latitude 35°S .
No report sent, but discussion
between managers and fishers
leading to more regular updates
(weekly) and reanalysis of inshore
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 34°00’ S
with the inshore Buffer Zone at 151°54.50’E and
extends to the southeast to the intersection of
35°30’S and 155°00’E then continuing east along
latitude 35°30’S.
Inshore Buffer Zone: No Change
9
vs offshore catch rates
East Coast SBT Habitat, AFMA Report
5
July 10,2012
July 6-8, 2012
July 10, 2012
July 12, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 32°
30’S with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 33°30’ S
with the inshore Buffer Zone and extends to the
southeast to the intersection of 35° S with 155° E then
continues east along latitude 35° S.
Inshore Buffer Zone: No Change
6
July 24, 2012
July 20-22, 2012
July 24, 2012
July 26, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 34°
30’S with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 35° S with
the inshore Buffer Zone and extends to the southeast
to the intersection of 35°20’ S with 154° E then
continues east along latitude 35°20 S.
Inshore Buffer Zone: No Change
7
August 7, 2012
August 3-5, 2012
August 7, 2012
August 9, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 34° S
with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 35° S with
the inshore Buffer Zone and extends to the southeast
to the intersection of 35°30’ S with 152°20’ E then
continues south to the intersection of 36°20’S with
152°15’E then east along latitude 36°20 S.
Inshore Buffer Zone: No Change
10
East Coast SBT Habitat, AFMA Report
n/a
August 14,2008
August 16,2008
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 34°30’
S with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 35°30’ S
with the inshore Buffer Zone and extends to the east
to the intersection of 35°30’ S with 152°20’ E then
continues south to the intersection of 36°20’S with
152°20’E then east along latitude 36°20 S.
8
August 21, 2012
August 17-19,
August 22, 2012
August 24, 2008
2012
No report sent, but discussion
between managers and fishers
leading to more regular updates
(weekly) and reanalysis of inshore
vs offshore catch rates
Buffer Zone: Unchanged
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 35°S with
the inshore Buffer Zone and extends to the east to the
intersection of 35°S with 152°20’ E then continues
south to the intersection of 36°20’S with 152°20’E
then east along latitude 36°20 S.
9
August 28,2012
August 24-26,
No Change
2012
10
September 3, 2012
August 30 –
September 13,
September 1,
2012
No Change
2012
11
September 18, 2012
September 14-
September 18,
16, 2012
2012
September 20, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 34° S
with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 34°30’ S
with the inshore Buffer Zone and extends to the east.
12
October 2, 2012
September 27-
No Change
29, 2012
11
East Coast SBT Habitat, AFMA Report
n/a
October 9,2012
October 11, 2012
Buffer Zone: The northern boundary of the Buffer
Zone commences at the intersection of latitude 35°30’
S with the coast and extends to the east.
Core Zone: The northern boundary of the Core Zone
commences at the intersection of latitude 36°00’ S
with the inshore Buffer Zone and extends to the east.
13
October 16, 2012
October 12-14,
No Change
2012
14
October 30, 2012
October 26-28,
2012
12
East Coast SBT Habitat, AFMA Report
References
Hobday AJ, Hartog J, Spillman C, Alves O 2011 Seasonal forecasting of tuna habitat for dynamic spatial management. Canadian Journal of Fisheries and
Aquatic Sciences. 68, 1-14.
Hartog J, Hobday AJ, Matear R, Feng M (2011) Habitat overlap of southern bluefin tuna and yellowfin tuna in the east coast longline fishery - implications for
present and future spatial management. Deep Sea Research Part II 58, 746-752.
Hobday AJ, Hartog JR, Timmis T, Fielding J (2010) Dynamic spatial zoning to manage southern bluefin tuna capture in a multi-species longline fishery. Fisheries
Oceanography 19, 243253.
Hobday AJ, Flint N, Stone T, Gunn JS (2009) Electronic tagging data supporting flexible spatial management in an Australian longline fishery. In 'Tagging and
Tracking of Marine Animals with Electronic Devices II. Reviews: Methods and Technologies in Fish Biology and Fisheries'. (Eds J Nielsen, JR Sibert,
AJ Hobday, ME Lutcavage, H Arrizabalaga and N Fragosa) pp. 381-403. (Springer: Netherlands)
Hobday AJ, Hartmann K (2006) Near real-time spatial management based on habitat predictions for a longline bycatch species. Fisheries Management &
Ecology 13, 365-380.
13