East Coast SBT Habitat Report
Jason Hartog and Alistair Hobday
AFMA Report 8, August 23, 2011
Summary
The most recent 3-day SST composite is from August 20, 2011 (i.e. includes data between August 1921) 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 emphasized by this overlay. The predicted locations of the SBT habitat from the Habitat Prediction
Model are shown in Figure 2.
The eddy to the south of Sydney identified in previous reports is no longer present and has been
replaced by cool water flowing from the south (Figure 1). Although a little weaker than in the last
report, the EAC is still flowing south from 28°S to 34°S (Figure 1). Off the coast of Coffs Harbour, for
example, this area is classified as buffer habitat (Figure 2a). Inshore, there is a large region of core
habitat extending north to 32°S along the coast, and this area has increased in size since the last
report (Figure 2b). Offshore, the water temperature has continued to cool, creating a large, continuous
area of core and buffer habitat (Figure 2a).
The SBT core and buffer habitat is in line with the regular long term climatology (Figure 4a). The
inshore mode climatology also suggests that the core habitat is in line with the long term average. The
seasonal forecast suggests that the northern edge of the core zone in the inshore region will still be
further south this season than the long term average (Figure 4b). Both the seasonal forecast (Figure 3)
and the long term climatology (Figures 4a and 4b) suggest that the core zone is at its maximum extent
for the season and we expect this zone to move south in the coming weeks as the EAC strengthens.
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 the first 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.
The forecasts in this report indicate that the habitat zones are likely to be typical for the remainder of
the season. The habitat zones now begin to move south for the next few months (in line with the
climatology in Figure 4). These zones are projected to be comparable to an average year for both the
regular mode (Figure 4a), and inshore mode (Figure 4b) for the next 2 to 3 months. These projections
may help managers and fishers plan their operations over and above using the climatology alone.
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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 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 SST image from the previous report is shown below for comparison.
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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
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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 months forecast.
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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
-32
-32
Latitude
Latitude
Scenario 1 Core and Buffer Zone Edges
-24
-34
-34
-36
-36
-38
-38
Buffer Zone Climatology (1994-2010)
Buffer Zone 2011
Maximum Extent Any Year
-40
-42
Jan
Apr
Jul
Month
Oct
Buffer Zone Climatology (1994-2010)
Buffer Zone 2011
Maximum Extent Any Year
-40
Jan
-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 56 tags for
the years 2001-2007 (4900 observations at this time of year). No SBT tags are available yet from
2008-2010. 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 16-year analysis of SST
from 1994 to 2010). 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 a lack of tag data in this period: the model uses
the limited SBT data from the first portion of the year (Figure 5), 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.
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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.
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East Coast SBT Habitat, AFMA Report
Summary of reports
Report
1
Report sent
from CSIRO
May 19, 2011
Date of Data
used in
Model
May 15-17,
2011
Date
decision
made by
AFMA
May 19, 2011
Date lines
implemented
by AFMA
May 21 2011
Line positions
Core Zone: The northern boundary of the
Core Zone commences at the intersection
of latitude 37°S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 36°30´S with the coast.
2
May 31, 2011
May 27-29,
2011
May 31, 2011
June 3, 2011
Core Zone: The northern boundary of the
Core Zone commences at the intersection
of latitude 36°30´S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 36°S with the coast.
3
June 15, 2011
June 11-13,
2011
June 15, 2011
June 18, 2011
Core Zone: The northern boundary of the
Core Zone commences at the intersection
of latitude 34°S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 33°S with the coast.
4
June 28, 2011
June 24-26,
2011
June 28, 2011
July 1, 2011
Core Zone: The northern boundary of the
Core Zone commences at the intersection
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Comments
First SBT interaction
East Coast SBT Habitat, AFMA Report
Report
Report sent
from CSIRO
Date of Data
used in
Model
Date
decision
made by
AFMA
Date lines
implemented
by AFMA
Line positions
Comments
of latitude 34°30´S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 34°S with the coast.
July 4, 2011
July 8, 2011
Core Zone: The northern boundary of the
Core Zone commences at the intersection
of latitude 34°30´S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 33°30´S with the coast.
5
July 12, 2011
July 8-10,
2011
July 13, 2011
July 15, 2011
Core Zone: The northern boundary of the
Core Zone commences at the intersection
of latitude 34°S with the coast.
Buffer Zone: The northern boundary of the
Buffer Zone commences at the intersection
of latitude 33°S with the coast.
6
July 26, 2011
July 22-24,
2011
July 26, 2011
July 29, 2011
No Change
7
Aug 9, 2011
Aug 5-7,
2011
Aug 9, 2011
Aug 12, 2011
No Change
8
Aug 23, 2011
Aug 19-21,
2011
9
Buffer line adjusted in
between regular report
update.
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.
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