1

Survey of Sonar Test Sites, Phase 1, Literature Review

J.F Middleton, C.E James, J.L Luick, S. Goldsworthy, A. Tsolos, C.E.P Teixeira and L. Richardson

SARDI Publication No. F2011/000212-1 SARDI Research Report Series No. 566

ISBN: 978-1-921563-41-6

DSTO Contract No. 4500782641

SARDI Aquatic Sciences

PO Box 120 Henley Beach SA 5022

August 2011

Final Report for the Defence Science and Technology Organisation

2

Survey of Sonar Test Sites, Phase 1, Literature Review

Final Report for the Defence Science and Technology Organisation

J.F Middleton, C.E James, J.L Luick, S. Goldsworthy, A. Tsolos, C.E.P Teixeira and L. Richardson

SARDI Publication No. F2011/000212-1 SARDI Research Report Series No. 566

ISBN: 978-1-921563-41-6

DSTO Contract No. 4500782641

August 2011

3

This publication may be cited as: Middleton, J.F., James, C.E., Luick, J.L., Goldsworthy, S., Tsolos, A., Teixeira, C.E.P. and Richardson (2011). Survey of Sonar Test Sites, Phase 1, Literature Review. Final Report for the Defence Science and Technology Organisation. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2011/000212-1. SARDI Research Report Series No. 566. 67pp.

South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.sardi.sa.gov.au DISCLAIMER The authors warrant that they have taken all reasonable care in producing this report. This report has been through SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Chief, Aquatic Sciences. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it. © 2011 SARDI This work is copyright. Apart from any use as permitted under the Copyright Act 1968 (Cth), no part may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owner. Neither may information be stored electronically in any form whatsoever without such permission. Printed in Adelaide: August 2011 SARDI Publication No. F2011/000212-1 SARDI Research Report Series No. 566 ISBN: 978-1-921563-41-6 DSTO Contract No. 4500782641 Author(s): J.F Middleton, C.E James, J.L Luick, S. Goldsworthy, A. Tsolos,

C.E.P Teixeira and L. Richardson Reviewer(s): M. Doubell and R. McGarvey Approved by: T. Ward

Assoc Prof – Wild Fisheries Signed: Date: 23 August 2011 Distribution: Defence Science and Technology Organisation, SAASC Library, University

of Adelaide Library, Parliamentary Library, State Library and National Library Circulation: Public Domain

4

Table of Contents: Summary 9 Background 9

Data and Analyses 9 Additional Data Requirements – west zone, spring 14

1 Methodology 16 2 Sound Speeds 19 2.1 CTD Cast Data 19 2.2 Sea Surface Temperature (SST) data 35 2.3 Ocean Model Results 38 2.4 Ocean Glider Data 41 3 Monthly, Weekly, Hourly Sound Speed Variability 45 3.1 Month to Weekly Variability 45 3.2 Tidal Band Variability 46 3.3 Hourly Variability 47 4 Other Factors – Topography and Waves 48 4.1 Bottom Topography 48 4.2 Surface Wave Climatology 50 5 Other Factors – Marine Mammal Distributions 53 5.1 Australian Sea Lions 53 5.2 New Zealand Fur Seals 55 5.3 Blue Whales 57 5.4 Southern Right Whales 58 5.3 Other 61 6 Other Factors – Marine Vessel Activity 62 References 65

5

List of Tables: Table S.1 Key indicators for SONAR testing by zone 14 Table 1.1 Summary of data types, public access and web sites for download And/or description. Data that is not public domain is either private Research data or commercial in confidence 16

6

List of Figures: Fig S.1 Place names and the topography of the region including the 100 and 1000m isobaths 10 Fig S.2 The zones of study. The 20, 70, 300 and 5000m isobaths are indicated 11 Fig 1.1 The three regions used during analysis 17 Fig 2.1 Winter sound speed profiles for region 1 and the three zones 22 Fig 2.2 As in Fig 2.1 but for spring 23 Fig 2.3 As in Fig 2.1 but for summer 24 Fig 2.4 As in Fig 2.1 but for autumn 25 Fig 2.5 Winter sound speed profiles for region 2a (70 to 300m) and the three zones 27 Fig 2.6 As in Fig 2.5 but for spring 28 Fig 2.7 As in Fig 2.5 but for summer 29 Fig 2.8 As in Fig 2.5 but for autumn 30 Fig 2.9 Winter sound speed profiles for region 2b (300 to 5000m) and the three zones 31 Fig 2.10 As in Fig 2.9 but for spring 32 Fig 2.11 As in Fig 2.5 but for summer 33 Fig 2.12 As in Fig 2.5 but for autumn 34 Fig 2.13 A SST image illustrating very strong upwelling during summer 35 Fig 2.14 A SST image illustrating the relatively warm Leeuwin Current inflow during winter 36 Fig 2.15 SST image illustrating the relatively uniform temperatures during October (spring) 37 Fig 2.16 Output from the SARDIs numerical ocean model (Teixeira 2010) Obtained using forcing by a monthly atmospheric climatology and for summer (February 25th) 38 Fig 2.17 Output from the SARDIs numerical ocean model (Teixeira 2010) Obtained using forcing by a monthly atmospheric climatology and for autumn (April 20th) 39 Fig 2.18 Output from the SARDIs numerical ocean model (Teixeira 2010) Obtained using forcing by a monthly atmospheric climatology and for winter ( July 13th) 40 Fig 2.19 Output from the SARDIs numerical ocean model (Teixeira 2010) Obtained using forcing by a monthly atmospheric climatology and for spring (October 11th) 41 Fig 2.20 The Slocum glider path for 4 days in February 2010. 42 Fig 2.21 A 3D plot of temperature data for the glider path shown in Fig 2.20 42 Fig 2.22 The Slocum glider path for 10 days in November 2009 43 Fig 2.23 A 3D plot of temperature data for the glider path shown in Fig 2.22 44 Fig 2.24 A 3D plot of salinity data for the glider path shown in Fig 2.22 44 Fig 3.1 Time series of temperature and sound speed at the Reference Station, low pass-filtered with a cut-off period of 34 hours 45 Fig 3.2 Time series of temperature and sound speed at Coffin Bay, low pass-filtered with a cut-off period of 34 hours 46 Fig 3.3 Time series of temperature and sound speed at the Reference Station, band pass-filtered with cut-off periods of 10-26 hours (tidal band) 46 Fig 3.4 Time series of temperature and sound speed at the Coffin Bay, band pass-filtered with cut-off periods of 10-26 hours (tidal band) 47 Fig 3.5 Time series of temperature and sound speed at the Reference Station, high pass-filtered with a cut-off period of 4 hours 47

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Fig 4.1 Topographic gradient in the western zone as computed from 1000*/grad(h)/ with units meters/kilometre. The depth contours 50,70, 100, 200, 500 and 1000 m are shown 48 Fig 4.2 Topographic gradient in the central zone as computed from 1000*/grad(h)/ with units meters/kilometre. The depth contours 50,70, 100, 200, 500 and 1000 m are shown 49 Fig 4.3 Topographic gradient in the eastern zone as computed from 1000*/grad(h)/ with units meters/kilometre. The depth contours 50,70, 100, 200, 500 and 1000 m are shown 50 Fig 4.4 Significant Wave Height in summer 51 Fig 4.5 Significant Wave period in summer 51 Fig 4.6 Significant Wave Height in winter 52 Fig 4.7 Significant Wave period in winter 52 Fig 5.1 Breeding and haul-out areas for Australian sea lions and NZ fur seals (URS 2010) 54 Fig 5.2 Examples of raw satellite derived at-sea positions and modelled densities at sea for Australian sea lions (a,b) and NZ fur seals (c,d) 56 Fig 5.3 Distribution of blue whale sightings between 2002-2007 in the DSTO areas of interest (a), raw data from Gill et al (2011) 60 Fig 5.4 Feeding areas of Beaked, Sperm and other whales (URS 2010) 61 Fig 6.1 The number of boat days for the scalefish and lobster fisheries for the “summer” (November to April) and “winter” (May to October) periods 62 Fig 6.2 The number of boat trips for the sardine fishery for the “summer” (November to April) and “winter” (May to October) periods 63

8

List of Acronyms:

ANFOG: Australian National Facility for Oceanic Gliders AWD: Australian Warfare Destroyer CARS: CSIRO Atlas of Regional Seas – data set CSIRO: Commonwealth Scientific and Industrial Research Organisation CTD: Instrument to measure Conductivity, Temperature, Depth IMOS: Integrated Marine Observing System ISS: integrated sonar system MATLAB: a mathematical analysis package MB: Middleton and Bye (2007) – an extensive review of oceanography for the South Australian region. NOAA/NCEP: National Ocean and Atmospheric Administration/ National Center for Environmental Prediction (U.S. agencies) RAN: Royal Australian Navy SAIMOS: Southern Australian Integrated Marine Observing System SARDI: South Australian Research and Development Institute SONAR: Sound Navigation and Ranging SST: Sea Surface Temperature (satellite data) T&E: test and evaluation XBT: Expendable Bathythermograph

9

SUMMARY Background

The Royal Australian Navy (RAN) is currently acquiring three Air Warfare Destroyers (AWD) under

project SEA4000 and the acceptance process of these platforms will include at sea testing of the

integrated sonar system (ISS) suite. This report contributes to the identification of suitable at sea

locations in South Australian waters for this testing. The criteria for suitable locations include: being

near the build location of Adelaide, a relatively flat seafloor for about thirty kilometres, known

underwater acoustic conditions and variability, with as benign conditions as possible (such as

minimal frontal activity and constant sediment grain size) and contain minimal amounts of marine

mammal activity, regular fishing, and traffic routes. The water depths of interest are a shallow (70

to 200 m), intermediate (2000 to 4000 m), and a deep water site (5000 m).

This review and report was under contract 4500782641 and required a literature and database

search for information relevant to underwater acoustics for South Australian waters. The most

extensive set possible of temperature and salinity data was assembled from the archives of

CSIRO, IMOS and SARDI and includes data obtained from field surveys, tagged marine mammals,

fixed moorings, satellites and ocean model output. This report is limited to oceanographic

phenomena which affect the sound speed profile, seafloor slope, surface wave height, marine

mammal distributions, and fishing vessel distributions. Other significant parameters, including

sediment and sidescan data, are outside the scope of this report, however should be considered in

the selection of the testing locations.

Data and Analyses

To determine the best region and times for sonar test and evaluation (T&E), an analysis was made

of around 6,700 conductivity, temperature, and depth (CTD) casts and two years of CTD time

series to determine the acoustic properties of the South Australian (S.A.) region (Fig. S.1). These

data are supplemented by sea surface temperature (SST), ocean model output, wave and

topographic data and distributions of marine mammals and fishing vessel activity. The CTD data

consists of all that stored by CSIRO and SARDI up until June 2010 and represents the most

extensive database of its type for the region. The CTD time series (at two depths and sites) have

been collected by SARDI through its involvement in the Southern Australian Integrated Marine

Observing System (SAIMOS).

10

Fig. S.1. Place names and the topography of the region including the 200 and 1000 m isobaths. The +s denote the location of the SAIMOS Coffin Bay mooring (BC) and Kangaroo Island reference station (RS).

In order to determine the optimal area for sonar testing, we have split the region up into 3 zones as

shown in Fig. S.2.

The central shallow zone (136.25 to 138 oE, 70 to 300 m) encompasses southern Kangaroo Island

and is too small to provide the needed 30 km region of uniform topography due to the narrow and

steeply sloping shelf. In addition, it is also subject to dense water eddy outflows during winter that

are generally confined largely to the east of longitude 135.25 E and the bottom 10-20 m and flow

past the western side of Kangaroo Island. However glider data from this region in early November

2009 does indicate that gulf outflows can occur in late spring. During summer, cold, fresh water is

upwelled onto the shelf to the south of Kangaroo Island. This water follows the 70 - 100 m isobaths

and surfaces off the western Eyre Peninsula. Both the upwelled and winter dense water outflows

will affect sound speed on a seasonal and weekly time scale. Fishing vessel activity is also

significant in the central zone.

The east shallow zone (138 to 140 oE, 20 to 300 m) does provide a 30 km region of uniform

topography for shelf depths of 20 to 300 m. During summer, upwelling reaches the surface as a

massive cold water plume that extends from Portland (Victoria) to the west of Robe (139 oE). The

strong vertical and horizontal temperature gradients that result can vary on weekly to seasonal

time scales. In addition, the temperature and sound speed for the region in water depths less than

11

100 m is relatively under-sampled compared to the west and central zones. Indeed, dense bottom

water may be formed in the coastal regions during winter, although there is insufficient data to

determine if this occurs.

Fig. S.2. The zones of study. The 20, 70, 300 and 5000 m isobaths are indicated. (Note for the east zone, data will be included for shelf depths 20 to 300 m, while for the other zones, data will be included for shelf depths 70 to 300 m.)

The west shallow zone (135 to 136.25 oE, 70 to 300 m) appears to be the most suitable region for

T&E. A region 30 km in diameter exists for depths 70 to 300 m that has bottom slopes that are

generally less than 50 m/km. Moreover, the temperature and sound speed variability is least

during winter and spring suggesting that these months may be the most suitable for T&E of the

sonar.

During winter, dense water outflows from coastal regions may be found (Petrusevics et al., 2009)

although these are not apparent in the CTD profile data presented below. Over the shelf (70 – 300

m) the top 100 m of the water column is generally well mixed. Due to the effect of pressure, the

mean sound speed increases with depth. This results in an acoustic surface duct approximately

100 m thick.

During spring, atmospheric heating leads to temperatures and sound speeds that generally

decrease with depth. On average, the acoustic surface duct existing in winter is not found. Glider

data for the western zone in early November 2009 shows an anomalous upwelling of cold fresh

12

water in the bottom 30 m of the water column and over the 100 m isobath. This anomalous result

indicates the need for additional data and is an important phenomenon needing investigation.

For the shallow region over all zones and seasons, the mean temperature and sound speed

increase with depth from the surface to depths of 5 -10 m. This is attributed to atmospheric cooling

during winter and evaporation during summer. Thus, a narrow (5 – 10 m) surface duct is expected.

This narrow duct is not found offshore (water depths > 300 m).

For the deep region in all zones (>300 m) below the surface turbulent layer (Region 2b, fig 1.1)

there is little variability in sound speed within and between seasons. All data indicate a well defined

deep sound channel with axis at about 1100m. The strong linear increase in sound speed at

greater depths results from the increase in pressure. The lack of variability is expected at such

depths where atmospheric forcing of temperature and sound speed is minimal. The surface sound

speeds for each zone are close to 1510 m/s and imply a critical depth of about 3200 m for

convergence zone propagation.

For the deep region in all zones (>300 m) within the surface turbulent layer (Region 2a, fig 1.1) and

for all seasons, (with the possible exception of winter), the overlying waters generally have sound

speeds that increase towards the surface. Near surface sonar transmissions will therefore be

focused down into the deep sound channel.

For all regions, SST data and ocean model results indicate the sound speed to be spatially uniform

during spring which marks the transition between summer upwelling and wintertime cooling and

gulf outflows. During winter, spatial temperature increases of around 2 oC are found within the

Leeuwin Current compared to the other water over the shelf.

During summer and autumn, cold upwelled water lies below the 40 m deep surface mixed layer for

both the western and central zones. The strong decrease in temperature and sound speed with

depth within these two zones implies that an acoustic surface duct is rarely found.

Two years of CTD time series data in the western and central zones, shows that most of the sound

speed variability (18 m/s) is seasonal. The daily variability is less significant at around 3 -10 m/s

(10 – 20 day filter band). The sound speed variability under 1 day is less than 0.01 m/s, with no

internal wave activity found. So if the Leeuwin current, upwelling zones, storms, and salinity

currents can all be avoided, the sound speed should be fairly stable during the T&E trial. More

measurements would be needed to confirm this.

13

Sonar testing during September-October in the western zone may affect the N.Z. Fur Seals and

Australian sea lions which forage on the shelf and slope all year round. Whale activity in this region

is least in spring prior to November. Fishing vessel activity is generally minimal between May and

November and less in the western zone. Regular shipping routes do exist between Melbourne and

Adelaide, via Backstairs passage, and Adelaide and Perth, via the southern tip of the Eyre

Peninsula. Wave heights and periods are typically 2-3 m and 11-13 seconds with a swell directed

from the south-west. Wave heights can exceed 8 m, 1.3% of the time and 5 m, 17% of the time.

The above is summarised in Table S.1 below where key testing indicators are evaluated for each

zone. We conclude that testing in the west zone during spring (October) represents the optimal

choice. This is based upon:

a) the presence of a 30 km region of uniform topography

b) the smaller variability found in sound speed with depth

c) minimal upwelling and downwelling

d) minimal horizontal variability in temperature and dense water outflows

e) the overall uniformity of temperature and sound speed that is expected for spring – a

transition period between summer and winter

f) minimal marine mammal and fishing vessel activity.

In addition, selection of the western zone means that the T&E can lever off the extensive data sets

being collected by SAIMOS for this region. These include CTD surveys, moorings, marine mammal

and glider data.

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Indicator West Zone Central Zone East Zone

30 km region of topographic uniformity

Yes No Yes

Period of best sound speed uniformity

Spring Spring Spring

Other features: summer

Weak or no upwelled water except near Eyre Peninsula

Strong upwelled bottom plumes

Strong upwelled plumes (bottom and surface)

Other features:

winter

Dense bottom

water plumes are

not evident

Downwelled dense

water and eddies

(bottom)

Possible

downwelled

dense bottom

water

Marine Mammal

activity

Sea lions and

seals all year.

Blue whales

(Nov-May)

Sea lions and seals all

year.

Blue whales (Nov-May)

Sea lions and

seals all year.

Blue whales

(Nov-May)

Right whales

calve (May-Nov)

Fishing Vessel

activity

minimal May-

Nov.

minimal May-Nov.

(sig. KI-Eyre

Peninsula)

minimal May-Nov.

(sig. Robe)

Surface waves 2-3m height / 10-

13 s period

2-3m height / 10-13 s

period

2-3m height / 10-

13 s period

Table S.1. Key indicators for SONAR testing by zone.

Additional Data Requirements – West zone, spring

Additional data may be needed for T&E in the western zone in spring. The analysis below shows

that there are only 125 CTD casts for the region in spring as compared to 1064 for summer. The

glider data indicates the (unsuspected) possibility of upwelling in the region during early November.

Thus, there is a need to refine our understanding of the vertical and spatial variability of sound

speed for the region, through further glider missions and CTD survey work. These could be

designed to complement those undertaken by SAIMOS which runs 8 five-day field surveys each

year including one each in October and November. Three SAIMOS glider missions are run each

year between Kangaroo Island and the Eyre Peninsula. In addition, in collaboration with SAIMOS,

additional marine mammals could be tagged with CTDs to increase data coverage off the Eyre

Peninsula (see Fig. 5.2).

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In addition, further data is required to fully determine the temporal variability of sound speed. The

SAIMOS mooring data suggests that there is almost no variability at time scales shorter than 24

hours. However, this is based on data from only one or two CTDs at fixed depths that might not

resolve variations in the surface and/or bottom layers. We suggest the deployment of strings of

temperature loggers on fixed moorings that include the shelf (100 m) and shelf slope (300 m), for

at least 6 months to 1 year. These could be deployed in a complementary fashion to the 100

loggers that are being deployed by SAIMOS.

The above might also be complemented by direct estimates of sound speed propagation, through

the installation of acoustic transmitters and receivers. Design of such a system is beyond our

expertise.

In addition, it is imperative that the above field surveys, glider missions and moorings be

maintained through out the T&E of the SONAR system. As we have noted and show below, there

may be unexpected spatial and temporal variations in sound speed that arise from anomalous

oceanographic events (e.g., the November 2009 upwelling found for the western zone – section

2.4 below). Again, T&E in October-November can lever off the SAIMOS data streams and field

cruises which will continue to at least June 2013 and most likely beyond.

Finally, we note that it will also be possible to use SARDI’s ocean model to incorporate the data

collected and hind-cast for the period of T&E. Further developments of the model are undertaken

each year and are most promising. Thus, if sufficient effort is injected into improving the model,

especially for temperature, the model output could be coupled with an acoustic model to improve

the understanding of sound propagation during the T&E sonar trials.

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1 Methodology

A review has been made of relevant databases and information about the underwater

oceanographic environment within the region 34°S to 40°S and 135°E to 140°E (Fig. S.2). This

includes temperature and sound speed profiles, acoustic ducts (both seasonal to hourly variations)

as well as other oceanographic processes that may be important to sound speed.

Data type Public domain

Web site

CARS CTD (casts, XBT)

y http://www.marine.csiro.au/~dunn/cars2009/

Argo float CTD

y http://imos.org.au

SAIMOS CTD surveys

y http://imos.org.au

ANFOG IMOS glider data

y http://imos.org.au

SAIMOS Mooring data

y http://imos.org.au

Marine mammal data

n http://www.smru.st-andrews.ac.uk/Instrumentation/pageset.aspx?psr=288

SST data y http://www.marine.csiro.au/remotesensing/oceancurrents/index.htm

NOAA/NCEP wave data

y http://polar.ncep.noaa.gov/waves/download.shtml

Fishing vessel activity

n SARDI data

Table 1.1. Summary of data types, public access and web sites for download and/or description. Data that is not public domain is either private research data or commercial in confidence.

The relevant data bases were identified through our long experience in oceanographic research of

Australia’s southern shelves. In addition A/Professor John Middleton leads both the Oceanography

Program at SARDI and also SAIMOS which is made up of marine observing platforms that include

ship-based CTD surveys, moorings, ocean gliders and tagged marine mammals.

The data sources used in this report are listed in Table 1.1 along with a statement on public access

and web sites where the data can be downloaded and/or is described.

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The data is all quality controlled as required by CSIRO and IMOS. Only the marine mammal and

fishing vessel data are not public domain: the latter through commercial in confidence.

In addition, many of the comments on the physical oceanography are based on our knowledge of

the region summarised in the review paper Middleton and Bye 2007 (hereafter MB) and with

appropriate references to the environmental reports supplied by DSTO: SAXA (2004) and URS

(2010).

In order to analyse these data, three zones were chosen to group results: west (Eyre Peninsula),

central (Kangaroo Is.) and east (Robe) as shown in Fig. S.2. Within each zone we define three

regions by depth (Fig 1.1.):

a) Region 1 – shelf depths (70 to 300 m)

b) Region 2a – water depths 0 to 300 m above region 2b

c) Region 2b - shelf depths (300 to 5000 m)

NOTE: for the eastern zone, region 1 is defined to be shelf depths from 20 m to 300 m as

requested by DSTO.

Fig. 1.1. The three regions used during analysis (figure is not to scale).

We were also advised by DSTO that regions that would be most suitable for T&E would include:

a) minimal spatial and temporal sound speed variability of sound speed and over a 30 km

area.

b) that the sea floor variability be minimal over this region.

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c) that there is a focus on the shelf depths 70 (20) to 300 m.

In section 2, temperature and sound speed data are presented for these zones and regions and at

seasonal time scales. Snapshots of satellite SST data are presented along with Slocum glider

data.

In section 3, we present two years of SAIMOS mooring data to illustrate the monthly to hourly

variability of sound speed. In section 4, seasonal data for surface waves is given and the

topography and slope of the region discussed.

In sections 5 and 6, marine mammal and marine vessel activity and distributions are discussed.

These data will assist in determining the locations and times of T&E of the SONAR systems.

19

2. Sound Speeds

2.1 CTD Cast Data

All available temperature and salinity data was collated for the regions and up until June 2010. This

includes around 676 XBT profiles, 1,313 CTD casts (including ARGO float data) and 4,790 CTD

casts made by SARDI including 4,032 casts from seal-based CTDs: the non-SARDI data was

supplied by CSIRO Marine and Atmospheric Research. The total of over 6,700 casts provide

excellent coverage of the three zones and greatly exceeds that presented in the SAXA (2004)

report (p64-68).

Indeed, this is the largest data set assembled for this region. Both the SARDI and CSIRO supplied

data have been quality checked and temperature is accurate to within 0.05 oC. CTD data from

three Slocum glider missions were not included here due to time constraints.

The sound speed was calculated using the UNESCO standard (Fofonoff and Millard 1983) that

comes with the MATLAB analysis package. The formula is quite complicated, but in summary,

sound speed is only weakly dependent on salinity and so for the XBT data, a value of salinity of 35

ppt was adopted. Sound speed increases by about 3 m/s for every degree increase in temperature

and by about 1.1 m/s for every 100 m increase in depth (pressure).

We begin by first examining the number of casts made for each zone and by region and season

(Table 2.1). Region 2a (0 to 300 m) overlies region 2b (300 to 5000m) and the number of casts in

each is generally equal since both mostly result from the same CTD surveys. The total of regions 1

and 2 is given. By far, the most casts are made in autumn and then summer: the latter a reflection

of the general scientific interest in summer upwelling. The central zone is the most sampled (an

important upwelling area), although the number of casts in each zone exceeds 2000 most casts

come from region 1. For the eastern zone, most casts are from the shelf slope (shelf depths > 70

m) as indicated by the cast location maps in Figures 2.1 to 2.12. That is, relatively few casts (~ 30)

were taken on the shelf proper and for water depths 20 to 70 m.

Based on the cast numbers one might conclude that the sound speed results below would be more

accurate in summer and autumn. However, as discussed below, the water column tends to be well

mixed during winter and autumn so that the natural variability is smaller than in summer and

autumn.

20

zone region winter spring summer autumn

west 1 100 119 1064 504

2a 31 6 113 103

2b 31 6 112 103

Total (1+2) 131 125 1177 607

central 1 142 48 462 1834

2a 21 14 31 39

2b 21 14 31 39

Total (1+2) 163 62 493 1873

east 1 57 25 351 1352

2a 68 57 168 72

2b 68 57 166 72

Total (1+2) 125 82 517 1424

Table 2.1. Number casts for each zone and by region and season. Region 2a overlies region 2b and the number of casts is generally equal. The total cast numbers of regions 1 and 2 is given.

Plotted in Figures 2.1 to 2.12, are the sound speed C and its vertical gradient (positive values

indicate C increases with depth) and for winter, spring, summer and autumn.. The number of casts

is indicated in the bottom left of the lower panels. The locations of the casts are indicated in the

upper left panel along with the data source XBT, CTD (CARS/CSIRO) and CTD (SARDI). The solid

and dashed black lines in the profiles indicate the mean and mean ±2 standard deviations. In some

figures the sound speed gradient appears quite “spikey”. This is due to a lack of data rather than

errors in the data itself. To assist in determining the sign of the sound speed gradient, the zero line

is plotted in dark grey.

Results - region 1

Now consider the sound speed data for region 1: 70 to 300 m shelf depths for the west and central

zones and 20 to 300 m for the east zone.

The winter data (Fig. 2.1) indicate the least variability in C and dC/dz which may be expected given

winter time winds mix the water to 300 m or so through downwelling and cooling (MB). For sound

speed, 2 standard deviations is about 10 m/s. The sound speed itself is around 1510 m/s for each

of the three zones: see also SAXA (2004). Between depths of 10 to 100 m, the (mean) sound

speed increases with depth for all zones. This may result from the increase in C that is expected to

arise from increasing pressure (depth) and where temperature is uniform due to mixing. Thus, on

average a duct may be expected over the top 100 m. The scatter in both C and its gradient

indicates that this will not always be the case. At depths below 100m, the sound speed decreases.

21

An additional feature of the results for winter, and indeed all seasons, is that there is an abrupt

increase in mean speed between the surface and depths of 5 -10 m. During winter, this may be

due to atmospheric cooling and results in a narrow surface duct.

For spring (Fig. 2.2), the western and central zone data indicates that C decreases over most

depths and most rapidly over depths of 10 to 30 m. This results from an equivalent decrease in

temperature with depth where the surface is warmed by the springtime increase in atmospheric

heating. At depths of 70 to 300 m, little variability is found although not a lot of data is available. At

depths 50 to 110 m, the data for the sound speed gradient indicates it can often be positive so that

a duct can exist at these depths.

During summer, cold upwelled water is found at depths of 50 to 300 m in all three zones (MB). For

the western and central zones the water remains largely sub-surface and is overlain by very warm

water 20 oC that results from summertime heating. For the eastern zone, the cold water extends to

the surface as a plume from Portland to the NW of Robe (Fig. 2.13 below).

The impact on sound speed is similar for all three zones (Fig. 2.3). For both the central and

western zones, mean surface values of temperature and thus C are larger than for winter and

spring. In addition, the colder upwelled water leads to a significant decrease in sound speed over

depths of 30 to 50 m: the depth of the surface mixed layer corresponds to the minima in dC/dz at

about 40 m. While there is some scatter in dC/dz, the mean gradient is strongly negative over the

top 100 m indicating that a surface duct is not common. We note that there is again a notable

increase in C with depth and within 5 -10 m of the surface. Temperature also increases in a similar

way and this might result from evaporation due to generally low humidity and windy conditions

expected during summer. These results would suggest the existence of 5 – 10 m surface duct.

Finally, we consider the results for autumn (Fig. 2.4) that are qualitatively similar to those for

summer. After the upwelling and surface heating of summer, the winds and cooling act to mix the

warmer surface and colder upwelled waters. This occurs through the progression of individual

storms leading to a larger scatter in C and dC/dz than found in summer (or winter and spring).

The large scatter in summer and autumn suggests that winter or spring might be better months for

T&E.

22

Fig. 2.1. Winter sound speed profiles for region 1 and the three zones: West (red), Central (green) and East (blue). The region is shown schematically in the top right panel. The number of casts is indicated in the bottom left of the lower panels. The location of the casts is indicated in the upper left panel along with the data source XBT, CTD (CARS/CSIRO) and CTD (SARDI). The solid and dashed black lines denote the mean and mean ±2 standard deviations. The thick grey line in the mid-panels denotes zero sound speed gradient.

23

Fig. 2.2. As in Fig 2.1 but for Spring.

24

Fig. 2.3. As in Fig 2.1 but for Summer.

25

Fig. 2.4. As in Fig 2.1 but for Autumn.

Results - region 2a

Now consider the data for region 2a defined for water depths 0 to 300 m with seafloor depths of

300 m to 5000 m. This region is offshore and to the south of region 1 discussed above. Indeed, the

26

winter and spring results for sound speed (Figures 2.5 and 2.6) show again that there is relatively

little variability in sound speed. Notably, less cast data is available (Table 2.1), although the

surface duct found at depths 10 – 100 m is less pronounced than for region 1. For spring the rapid

decrease in C over the top 20 m found for region 1 is not found here: presumably surface heating

here is smaller than for the more northward, region 1.

For summer and autumn (Figures 2.7 and 2.8), the effects of surface heating are also evident in

the rapid decrease in sound speed C (and temperature) at the base of the surface mixed layer

(depth 50 m).

Unlike region 1, a surface duct within 5 – 10 m of the surface is not found.

Results - region 2b

Finally, we consider the deep water data for region 2b (300 to 5000 m) and which lies below region

2a (Figures 2.9 to 2.12). As is evident, there is little variability within and between seasons and

zones. All data indicate a well defined deep sound channel with axis at about 1100 m. The strong

linear increase in C at greater depths results from the increase in pressure. The lack of variability is

expected at such depths where atmospheric forcing of temperature and C is minimal.

The surface sound speeds for each zone is close to 1510 m/s. From Figures 2.9 to 2.12, this would

imply a critical depth of about 3200 m for convergence zone propagation.

With the exception of winter, the overlying waters (region 2a) have sound speeds that increase

towards the surface. Near surface SONAR emissions will therefore be focused down into the deep

sound channel.

27

Fig. 2.5. Winter sound speed profiles for region 2a (70 to 300 m) and the three zones West (red), Central (green) and East (blue). The number of casts is indicated in the bottom left of the lower panels. The location of the casts is indicated in the upper left panel along with the data source XBT, CTD (CARS/CSIRO) and CTD (SARDI). The solid and dashed black lines denote the mean and mean ±2 standard deviations. The thick grey line in the mid-panels denotes zero sound speed gradient.

28

Fig. 2.6. As in Fig 2.5 but for Spring.

29

Fig. 2.7. As in Fig 2.5 but for Summer.

30

Fig. 2.8. As in Fig 2.5 but for Autumn.

31

Fig. 2.9. Winter sound speed profiles for region 2b (300 to 5000 m) and the three zones: West (red), Central (green) and East (blue). The number of casts is indicated in the bottom left of the lower panels. The location of the casts is indicated in the upper left panel along with the data source XBT, CTD (CARS/CSIRO) and CTD (SARDI). The thick grey line in the mid-panels denotes zero sound speed gradient.

32

Fig. 2.10. As in Fig 2.9 but for Spring.

33

Fig. 2.11. As in Fig 2.9 but for Summer.

34

Fig. 2.12. As in Fig 2.9 but for Autumn.

2.2 Sea Surface Temperature (SST) data

35

To augment the above we consider several SST images that illustrate some large scale processes

that are considered important to sound speed variability.

In Fig. 2.13 SST data for strong summer upwelling illustrates an intense surface plume of very cold

(13 oC) water that is upwelled off the Bonney Coast (eastern zone) and off Coffin Bay (western

zone; 15 oC). Cold water is also found along the 100 m isobath for all three zones. The horizontal

temperature changes will also affect sound speed with rays bending into the cold water plumes

and away from the warmer gulf waters,

Fig. 2.13. A SST image illustrating very strong upwelling during Summer.

A second image (Fig. 2.14) is typical of winter and illustrates the flow of relatively warm Leeuwin

Current water from the west and into the region.

36

Fig. 2.14. A SST image illustrating the relatively warm Leeuwin Current inflow during Winter

A third image illustrates the SST in October after the Leeuwin Current has ceased and before the

onset of summer upwelling. The uniformity of temperature in the western and central zones is

strong and suggests, along with the CTD casts, that spring may provide the most uniform sound

speed conditions.

The above SST image (Fig. 2.13) highlights the strong spatial variability in surface temperatures

expected during summer. This variability is smoothed out in the monthly averages presented by

SAXA (2004; p61) and in any climatological data base.

37

Fig. 2.15. SST image illustrating the relatively uniform temperatures during October (Spring).

It is also worth noting that eddy activity for the region is relatively weak compared to regions such

as the Leeuwin and East Australian Currents. The white lines in the SST images denote altimetric

sea level height (0.1 m contour) while the arrows denote currents. These show that while cyclonic

and anticyclonic eddies do exist at the shelf edge, the speeds are typically less then 20 cm/s.

38

2.3 Ocean Model Results

The above data may be augmented by results from SARDI’s S.A. Regional Ocean Model. The

model has a 5 km grid resolution and has been partly validated (Middleton et al 2010) against the

data streams from the Southern Australian Integrated Marine Observing System (SAIMOS;

imos.org.au). The results were determined using forcing by a climatological meteorological data

(monthly means) of surface fluxes of momentum, heat and freshwater (Teixeira 2010). The model

was spun up over 2 years so as to reach a quasi-steady state. No forcing for the open boundaries

was used.

Model results are for summer (February 25th) and are presented in Fig. 2.16. In the top left and

right panels are bottom temperature and salinity. In the bottom left panel are the depth averaged

(oceanic) velocities with magnitudes indicated by the colour bar (m/s). In the bottom right panel are

the atmospheric forcing functions: net heat flux (into the ocean; watts/m2), evaporation less

precipitation (mm/d) and wind stress magnitude (Pa). The wind direction (WD) is indicated on the

bottom left panel.

Fig. 2.16. Output from the SARDI’s numerical ocean model (Teixeira 2010) obtained using forcing by a monthly atmospheric climatology and for Summer (February 25th).

39

Between January and 3rd March, the winds are from the S.E. and upwell cold (14-15 oC) fresh

water off the shelf near Kangaroo Island as illustrated by the model results in Fig. 2.16. The

upwelled water forms a plume along the 100 m isobath that appears to block the exchange of

water with Spencer Gulf. Water in the gulfs is hot (22 oC) and salty (38 ppt) and is formed as a

plume that migrates south from the head of Spencer Gulf. Upwelling can occur 4-5 times during

summer (MB) and is perhaps not “rare” as described in SAXA (2004). The climatological model

results here indicate that in an average sense, upwelling occurs between December and early

March (see also MB).

Fig. 2.17. Output from the SARDI’s numerical ocean model (Teixeira 2010) obtained using forcing by a monthly atmospheric climatology and for Autumn (April 20th).

After February, there is a net heat loss from the ocean and the shallow gulf waters get

progressively cooler. In addition, by the 20th April (Fig. 2.17), the winds are to the NE. The

upwelling is shut down and the dense gulf waters explode onto the shelf as a sequence of

Speddies (Spencer Gulf eddies; Teixeira 2010). These dense salty eddies are mostly confined to

the immediate east of longitude 136o (the central zone). These eddies flow out past Kangaroo

Island and to depths of 250 m or so (MB) and between April and August (Fig. 2.18). In addition,

SAIMOS data we have collected for the region indicates the dense saline outflows to be confined

largely to the bottom 20 - 30 m or so.

40

After August, the atmosphere begins to re-heat the ocean and by 11th October temperatures in the

western zone are largely uniform (15 oC) and well mixed in the vertical. The upwelling favourable

winds return in November.

Fig. 2.18. Output from the SARDI’s numerical ocean model (Teixeira 2010) obtained using forcing by a monthly atmospheric climatology and for Winter (July 13th).

The above would suggest that temperature and sound speed is generally uniform in the western

region during spring which corresponds to the transition period between summertime upwelling

and the wintertime outflows from the gulf.

41

Fig. 2.19. Output from the SARDI’s numerical ocean model (Teixeira 2010) obtained using forcing by a monthly atmospheric climatology and for Spring (October 11th).

2.4 Ocean Glider Data

The spatial variability (or otherwise) of water temperature (and sound speed) is illustrated by data

from two (SAIMOS) Slocum Glider profiles below. These gliders are programmed via satellite to

move towards preset way points of latitude and longitude, move up and down the water column as

they do so and collect CTD information along the way. Typically the gliders travel at speeds of

about 25-40 cm/s and surface every 4 hours. A typical 25 day mission can provide 3000 vertical

profiles of CTD data with a sample rate of order 4 seconds. Typically, this implies a vertical

resolution of order 1 m and horizontal resolution of 200 m.

The first set of temperature data comes from four days of the 2010 February mission with a path

(in red) shown in Fig. 2.20. The period was one of intense upwelling. The temperature data is

shown in the 3-dimensional plot Fig. 2.21 with coldest water (11.7 oC) in the bottom 20 m, and in

the central zone off Kangaroo Island. A well defined surface mixed layer (SML) of warm water (19 oC) is found above. The depth of the SML appears to vary along the glider path and over a scale of

10 km or so. However, this may be the result of cross shelf variations in temperature. An analysis

of the data is outside the scope of this report.

In either case such variability may be important to sound speed propagation and it is

recommended that additional glider missions be undertaken for the SONAR testing zone.

42

Fig. 2.20. The Slocum glider path for 4 days in February 2010. The glider profile began off Kangaroo Island on February 14th.

Fig. 2.21. A 3-D plot of temperature data for the glider path shown in Fig. 2.20. The horizontal axes are latitude and longitude and the vertical axis is depth (m). The temperature is indicated by the colour bar.

Six days of data from a spring, (November 2009, 4th-10th) mission are shown below. The path

again begins near Kangaroo Island (Fig. 2.22). Bottom temperatures are typically 13.5 to 14.5 oC

(Fig. 2.23), and 2 to 3 oC warmer than that found 3 months later (Fig. 2.21) and after the onset of

summertime upwelling. While vertical variations in temperature are smaller during November (3 oC), horizontal variations are comparable with those in summer and water within 20 m of the

43

bottom is 2 oC cooler in the west. The summer data (Fig. 2.21) shows near bottom water to be

cooler in the east due to upwelling.

The origin of the colder near bottom water in November and in the western zone may be localised

upwelling. A plot of the salinity data for the November mission (Fig. 2.24) shows the near-bottom

water in the west to be cold and fresh: a property of upwelling. In the east, the water is “warm” and

salty suggesting it to be residual dense water formed in Spencer Gulf during winter.

The apparent upwelling in the west during November is unexpected and not apparent in other

data, the ocean model output or in any previous studies (MB). It indicates that more data needs to

be obtained for the region and in particular the spring period when all other information would

indicate it to be the best time for T&E of the SONAR system.

Fig. 2.22. The Slocum glider path for 10 days in November 2009. The glider began off Kangaroo Island on November 4th.

44

Fig. 2.23. A 3-D plot of temperature data for the glider path shown in Fig. 2.22. The horizontal axes are latitude and longitude and the vertical axis is depth (m). The temperature is indicated by the colour bar.

Fig. 2.24. A 3-D plot of salinity data for the glider path shown in Fig. 2.22. The horizontal axes are latitude and longitude and the vertical axis is depth (m). The salinity (psu) is indicated by the colour bar. 3 Monthly, weekly, hourly Sound Speed Variability

45

3.1 Month to Weekly Variability

Almost 2 years of ADCP and CTD data is available from moorings off Kangaroo Is (Reference

Station) and Coffin Bay (Fig. 1.1). The temperature and salinity data has been low pass filtered (35

hr cut-off) and the results for sound speed and temperature at the upper and lower CTDs at the

Kangaroo Island Reference Station are shown in Fig. 3.1. The upper and lower CTDs are 40 m

and 100 m from the surface. At Coffin Bay, data is only available from a lower level CTD (100 m

from the surface).

The highest sound speeds and temperatures are found nearest the surface. During winter, the

water is well mixed and sound speeds are typically 1510 m/s. During summer, the cold, upwelled

water at the lower CTD lowers the sound speed to 1500 m/s. There is variability on a 10-20 day

scale of 3-10 m/s due to storms, mixing and heat exchange with the atmosphere.

Fig. 3.1 Time series of temperature and sound speed at the Reference Station, low pass-filtered with a cut-off period of 35 hours. Data in the upper pair of figures is from the upper level CTD (40 m from surface) and data in the lower pair of figures is from the lower level CTD (100 m from the surface).

46

Fig. 3.2 Time series of temperature and sound speed at Coffin Bay, low pass-filtered with a cut-off period of 35 hours.

The largest variability is clearly in the seasonal band. A similar result is found for the Coffin Bay

mooring (100 m depth) as shown in Fig. 3.2 above.

3.2 Tidal band variability

The data were then filtered with 10 and 26 hr period cut-offs so as to examine the variability in the

tidal band. The results for the lower CTD at Kangaroo Island (central zone) is shown in Fig. 3.3 and

the variability in temperature and sound speed is typically less than 0.01 oC and 0.01 m/s

respectively.

Fig. 3.3. Time series of temperature and sound speed at the Reference Station, band pass-filtered with cut-off periods of 10-26 hours (tidal band).

The results at Coffin Bay (western zone) are shown below in Fig. 3.4 and are very similar to those

at the Reference Station.

47

Fig. 3.4. Time series of temperature and sound speed at Coffin Bay, band pass-filtered with cut-off periods of 10-26 hours (tidal band).

3.3 Hourly Variability

The CTD data was finally high pass filtered with a cut-off of 4 hours. The CTD data was obtained

every 15 minutes. The results for the reference station are shown below (lower CTD). The

variability in temperature and sound speed is typically less than 2 X 10 –5 oC and 3 X 10 –5 m/s

respectively. This variability is due to noise since the CTD accuracy for temperature is 0.005 oC.

There is no evidence of significant internal waves activity as suggested by the SAXA (2004; p60)

although we agree that more data is needed to confirm this or otherwise.

Fig. 3.5 Time series of temperature and sound speed at the Reference Station high pass-filtered with a cut-off period of 4 hours.

The data at other sites (Coffin Bay) showed similar results.

48

4 Other factors – Topography and Waves

4.1 Bottom Topography

Plots of bottom slope and contours of depths are shown in Figures 4.1 to 4.3 for the western,

central and eastern zones respectively. The bottom slope for a depth h(x,y) is computed as 1000*

|grad(h)| with units meters/kilometre. The data source is the Australian Bathymetry and

Topographic Grid (June 2009, Geosciences Australia).

As shown, the western zone has an extensive region (~50 km) between the 70 m and 300 m

isobaths that has slopes less than 50 m/km (0.05)

Fig. 4.1 Topographic gradient in the western zone as computed from 1000* |grad(h)| with units meters/kilometre. The depth contours 50, 70, 100, 200, 500 and 1000 m are shown.

49

Fig. 4.2 Topographic gradient in the central zone as computed from 1000* |grad(h)| with units meters/kilometre. The depth contours 50, 70, 100, 200, 500 and 1000 m are shown.

The slope for the central region (Fig 4.2) between the coast and 200 m isobath is generally 50

m/km: near the 200 to 300 m isobaths it can be up to 350 m/km. In addition the region seaward of

the 70 m isobath that is uniform is smaller than that in the western zone. The seafloor in the

immediate vicinity of the head of du Couedic canyon (Fig S.1) (depths 100 m) appears to be

covered with meter high sponges that may absorb sound transmission (Currie and Sorokin 2011).

Based on one bottom grab, the sponge biomass was estimated at around 1 tonne per hectare

which is much higher than found elsewhere for comparable water depths in the Great Australian

Bight and off the Bonney Coast. Currie and Sorokin (2011) speculate that the high biomass may

be related to enhanced organic material associated with the wintertime dense water outflows from

Spencer Gulf.

The slope for the eastern zone is also small (Fig. 4.3), and the region bounded by the 20 to 300 m

isobaths is at least 50 km across and adequate for SONAR testing.

50

Fig. 4.3 Topographic gradient in the eastern zone as computed from 1000* |grad(h)| with units meters/kilometre. The depth contours 50, 70, 100, 200, 500 and 1000 m are shown.

4.2 Surface Wave Climatology.

The significant wave height and period for summer and winter were obtained from the

NOAA/NCEP wave climatology data with a resolution of 1 o latitude and 1.25 o longitude.

For summer the typical wave heights are 2.5 m for the central and western zone and 1.5 to 2.5 m

for the eastern zone (Fig. 4.4). The wave periods are 10-11 seconds (Fig. 4.5).

For winter wave heights are 2.5-3.5 m (Fig. 4.6) with wave periods 11 to 13 seconds (Fig. 4.7).

These results are augmented by the observations that were obtained south of Portland, Victoria

(Fig S.1) (water depth 1395 m) by Wood and Terray (2005) and for the April–September period of

2004. They found the waves to have a significant wave height of 3.7 m, period 13 s and to be

directed from the south-west. Wave heights exceeded 8 m for 1.3% of the time and 5 m for 17% of

the time.

51

50

50

50

100

100

200

500

1000

Sig. Wave Height: Summer

135oE 136oE 137oE 138oE 139oE 140oE 40oS

39oS

38oS

37oS

36oS

35oS

met

res

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Fig. 4.4 Significant Wave Height in summer.

50

50

50

100

100

200

500

1000

135oE 136oE 137oE 138oE 139oE 140oE 40oS

39oS

38oS

37oS

36oS

35oS se

cond

s

10

10.5

11

11.5

12

12.5

13

13.5

14

14.5

15

Fig.4.5 Significant Wave period in summer.

52

50

50

50

100

100

200

500

1000

135oE 136oE 137oE 138oE 139oE 140oE 40oS

39oS

38oS

37oS

36oS

35oS Sig. Wave Height: Winter

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Fig. 4.6 Significant Wave Height in winter.

50

50

50

100

100

200

500

1000

135oE 136oE 137oE 138oE 139oE 140oE 40oS

39oS

38oS

37oS

36oS

35oS

seco

nds

10

10.5

11

11.5

12

12.5

13

Fig. 4.7 Mean summer wave period in winter.

The spring and autumn results (not presented) lie between those for summer and winter and again

the significant wave heights and periods are around 2 -3.5 m and 11-12 seconds respectively. In

addition, SAXA (2004) provides plots of the monthly averaged combined sea and swell heights and

swell and wind-wave directions. The latter show the swell to be from the S.W. for most of the year.

The wind-waves come from the S.E. during summer and from the west during winter. The former

makes for a cork-screw motion of small vessels that during summer can make mooring

deployments and field surveys difficult (source: SAIMOS).

53

5 Other factors - Marine Mammal distributions

Two main groups of marine mammals occur in the DSTO study area, cetaceans (whales and

dolphins) and pinnipeds (seals). All marine mammals are protected species under the Australian

Government’s Environment Protection and Biodiversity Conservation Act 1999 (Cth) (EPBC Act),

and some species are listed as threatened. A recent publication has indicated that 23 species of

cetacean have been recorded from Gulf St Vincent, Investigator Strait* and Backstairs Passage*,

14 from live strandings; and five pinniped species (Kemper et al. 2008). Of all these marine

mammal species, only four are addressed here in detail; two resident (breeding) pinnipeds, the

Australian sea lion and the New Zealand fur seal and two large whale species, the blue and

southern right whale. These species are the only marine mammal species in South Australian

waters where there is some information on distribution and/or abundance, for at least for part of the

year.

5.1 Australian sea lions

Australian sea lions (ASL) (Neophoca cinerea) are listed as Threatened under the Environment

Protection and Biodiversity Conservation Act 1999 (Cth) (EPBC Act), as vulnerable under the

National Parks and Wildlife Act 1972 (SA), and as Endangered under the International Union for

the Conservation of Nature (IUCN) Red List.

The Australian sea lion is Australia’s only endemic seal species and its least numerous. It is unique

among pinnipeds in having a non-annual breeding cycle of 17 to 18 months (Gales et al. 1994).

Furthermore, breeding is temporally asynchronous across its range (Gales & Costa 1997; Gales et

al. 1994). There are 76 known locations where Australian sea lion pups have been recorded, 48 of

them in South Australia (Fig 5.2) where the species is most numerous (~86% of estimated pup

production), with the remainder (28 sites) in Western Australia (Goldsworthy et al. 2009). In South

Australia, pup production is estimated to be 3,119 per breeding cycle, leading to a population

estimate of 12,726 sea lions (Shaughnessy et al. in press).

54

Models describing the spatial distribution of at-sea densities of ASL in South Australia have been

based on extensive satellite tracking data sets from 210 individual deployments (157 adult females

from 17 colonies, 31 adult males from 9 colonies and 22 juveniles from 4 colonies) (Goldsworthy et

al. 2010).

* Investigator Strait and Backstairs Passage lie at the western and eastern ends of Kangaroo Island and the mainland.

Fig. 5.1. Breeding and haul-out areas for Australian sea lions and N.Z. fur seals (URS 2010). The blue circles denote sea lion haul out areas. The red and orange circles denote sea lion and NZ fur seal breeding areas respectively. The red dashed line denotes Australian fur seal breeding areas.

Telemetry data were derived from ARGOS linked platform transmitting terminals (PTTs), and from

fully archival or archival/ARGOS-linked GPS tags resulting in 100,934 satellite derived at-sea

locations (Goldsworthy et al. 2010). Some of these are presented in Fig. 5.2a. Statistical models

using data distributions were used to estimate the spatial distribution of foraging effort throughout

South Australia, following the methods outlined in Goldsworthy et al. (2010). The foraging depths of

adult females and males rarely exceed 120 m and 140 m, respectively (Goldsworthy et al. 2010).

Australian sea lions are resident and present year round in continental shelf waters. Tracking data

from individuals tracked over many months indicate animals have a high fidelity to foraging

grounds and that there is little seasonal variation in foraging locations. As such the density plot

presented in Figure 5.2b provides an indication of year-round distribution of foraging

effort/distribution.

55

5.2 New Zealand fur seals

Breeding areas for N.Z. fur seals are illustrated in Fig. 5.1. Estimates for the abundance of New

Zealand fur seals (Arctocephalus forsteri) (NZFS) in South Australia have been based on pup

production (Shaughnessy et al. 1994). Pup production estimates at most Kangaroo Island breeding

sites have been monitored annually since 1988, and other South Australian colonies less

frequently (Shaughnessy 2004; 2005; Shaughnessy & Dennis 1999; Shaughnessy & Dennis 2001;

Shaughnessy & Dennis 2003; Shaughnessy et al. 1994; Shaughnessy & Goldsworthy 2007;

Shaughnessy & McKeown 2002). Total annual pup production in South Australia has been

estimated to be 17,622, with most pups born at the Neptune and Liguanea Islands of the lower

Eyre Peninsula (~10,500 pups) and two southernmost headlands on Kangaroo Island (Cape du

Couedic and Cape Gantheaume, ~7,000 pups) (Goldsworthy et al. 2007; Goldsworthy & Page

2007). The total South Australian NZFS population is estimated to number ~83,860 seals

(Goldsworthy et al. 2007; Goldsworthy & Page 2007). Telemetry data on NZFS were derived from

ARGOS-linked platform transmitting terminals (PTTs) deployed on 64 seals (137 foraging trips)

from four colonies (Cape Gantheaume and Cape du Couedic [Kangaroo Is], North Neptune and

Liguanea Island) (Baylis et al. 2008a; 2008b; Baylis et al. 2005; Page et al. 2006). Some of these

data (those restricted to continental shelf waters) are presented in Figure 5.2c. Statistical models

using data distributions were used to estimate the spatial distribution of foraging effort throughout

SA, following the methods outlined in Goldsworthy et al. (in review; 2010).

NZFS undergo a marked transition in foraging behaviour as they mature. As pups, foraging activity

is localised to near-colony waters (Baylis et al. 2005), then shifts to oceanic (off-shelf) waters as

juveniles, and then contracts to mid-outer shelf waters in adult females and to slope waters in adult

males (Page et al. 2006) (Figures 5.2c,d). Given that most of the SA NZFS population occurs in

four main regions; Cape Gantheaume and Cape du Couedic (Kangaroo Island), the Neptune and

Liguanea Islands, there is a marked concentration of foraging effort in near-colony waters and

adjacent shelf and slope waters between south-east Kangaroo Island and south-west of the Eyre

Peninsula (Figure 5.2d). However, given the size of the South Australia NZFS population and

based on the foraging effort models developed, some degree of foraging effort occurs in all shelf,

slope and oceanic waters off SA. NZFS are resident in South Australia and animals forage in shelf,

slope and oceanic waters year-round, hence Figure 5.2c provides an indication of the density of

animals in shelf and slope waters year-round.

56

a. b.

c. d.

57

Fig. 5.2. (above) Examples of raw satellite derived at-sea positions and modeled densities at sea for Australian sea lions (a, b) and New Zealand fur seals (c, d). Only data from the coast to the 5000 m isobath have been included for New Zealand fur seal tracking data. The at-sea data and right-side density plots are derived from 17 sea lion colonies (where tagging has been done) while there are 48 colonies in the state. The known mammal numbers from untagged colonies are used to correct the density plots and the red (light blue) colours indicates areas from highest (lowest) density (no units). Green dots indicate the location of breeding colonies for each species. Bathymetry lines in bold represent 70, 1000, 2000, 3000 and 4000 m, DSTO areas of interest (west, central and east) are also presented. All data derived from Goldsworthy et al. (in review; 2010), and are indicative of year-round distribution and density.

5.3 Blue whales

The blue whale (Balaenoptera musculus) is listed as endangered species under the Australian

Government’s EPBC Act. Blue whales, thought to be pygmy blue whales (Balaenoptera musculus

brevicauda) aggregate to feed in a regional meso-scale seasonal cold water upwelling system

between the Great Australian Bight (GAB) and Bass Strait each year between November and May

(Gill 2002). Here, blue whales feed on patchy aggregations of krill (Nyctiphanes australis). Gill et

al. (2011) present data on the distributions of blue whales based on aerial surveys conducted over

six consecutive season between 2002 and 2007, in slope and shelf waters between south-west of

Kangaroo Island through to eastern Bass Strait. The timing of when blue whales reach their

feeding grounds, the duration and location of their foraging effort and timing of departure vary

markedly between seasons as a function of physical and biological oceanographic factors (Gill et

al. 2011). The locations of blue whale sightings within the DSTO study area from Gill et al.’s (2011)

study, are presented in Fig. 5.3a. Most of the survey effort south and south-west of Kangaroo

Island occurred during the 2003–04, 2004–05, and 2005–06 seasons, with most (65%) occurring in

2003–04 (Gill et al. 2011). The earliest sightings of blue whales in any seasons monitored by Gill et

al. (2011) was 13 November 2003 and 8 November 2004, each about one week after upwelling

onset. Most whales have departed the feeding grounds by late April (Gill et al. 2011).

Most (93%) of blue whale sightings in the eastern part of Gill et al.’s (2011) study area occurred in

depths ≤200 m. However, blue whales foraged in deeper water south and south-west of Kangaroo

Island. The mean depth of sighting south of Kangaroo Island was 150 m (±67 SD), significantly

shallower than west of Kangaroo Island (mean depth 389 m, ±299 SD) (Gill et al. 2011). It is

thought that some of the changes in the distributions of blue whales from east to west are a result

of physical oceanographic differences that affect the depth and distance from shore of nutrient-rich

water which underpins the distribution of krill. Gill et al. (2011) acknowledge that most of their

survey effort south and west of Kangaroo Island were concentrated on the outer shelf so they may

have missed whales in depths <50 m. More survey effort was expended west of Kangaroo Island,

where the 100 and 200 m isobaths diverge widely and the outer shelf has a gentler depth gradient.

Here, blue whales were found either side of the shelf break, some in very deep water. South of

Kangaroo Island where the outer shelf is steeper due to the proximity of the 100 and 200 m

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isobaths, Gill et al. (2011) found blue whale density (when accounting for survey effort) was higher

than west of Kangaroo Island.

5.4 Southern right whales

The southern right whale (Eubalaena australis) is listed as endangered under the Australian

Government’s EPBC Act. Right whale numbers were critically low world-wide at the beginning of

the 20th century following hundreds of years of hunting in the northern hemisphere and a briefer

but very intensive period of hunting in the southern hemisphere from the early 19th century.

Hunting pressure on right whales was intense because whalers considered the species were the

"right" whales to kill – the whales swam slowly, often hugged the shoreline, provided a great

quantity of oil, and floated when dead. In 1931, right whales were granted international protection

under a League of Nations convention intended to take effect in 1935, and then protected under

the International Whaling Commission (IWC) from its inception in 1946. However, commercial and

illegal, unreported and unregulated whaling continued up to the 1970’s, hindering recovery of the

species. The IWC imposed a moratorium on all commercial whaling from the 1985-86 season.

Population levels prior to exploitation are difficult to estimate but it has been suggested that for

right whales in the southern hemisphere the population was approximately 60,000 (DEH 2005).

Southern right whales inhabit sub-Antarctic waters where the main summer feeding grounds are

thought to be between 40° and 55° S, but have been documented in latitudes south of 60° S. The

species generally spends winters in warmer waters, with current strongholds off eastern South

America, South Africa, southern Australia, and in the vicinity of oceanic islands at Tristan da Cunha

and Auckland Island, New Zealand (DEH 2005).

Australian Southern Right Whales migrate seasonally between higher latitudes and mid latitudes.

They are regularly present on the Australian coast from about mid-May to mid-November. The

general timing of migratory arrivals and departures varies slightly on an inter-annual basis;

although exact migratory pathways are not well known (no satellite tracking has been undertaken

in southern coastal Australian waters). It is thought that right whales follow a circular,

anticlockwise migration pattern south of the Australian continent, which is supported by the

majority of within year coastal movements being in a westerly direction and between year coastal

movements being in an easterly direction (Burnell 2001). Within such an overall pattern it is likely

that the majority of individual whales make direct approaches to the coast as the relative

infrequency of sightings outside major calving areas is not consistent with a widely used near-

shore migratory pathway.

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Calving areas for right whales tend to be very close to the shore. The main calving areas in South

Australia are the Head of the Bight, Fowlers Bay, and Encounter Bay. Sleaford Bay near Port

Lincoln is also a regular aggregation and calving area. Two of these calving areas occur adjacent

to the DSTO study are, Encounter Bay and Sleaford Bay (Fig. 5.3b).

Aerial surveys of right whales between Western Australia and Ceduna (South Australia) have been

undertaken by John Bannister (Western Australian Museum) between 1993 and 2008. In August

2008, 702 animals were surveyed, including 236 cow/calf pairs, the highest number reported for

the region (Bannister 2008). The annual rate of increase is 6.4% (6.7% for cow/calf pairs). The

Australian population estimate of southern right whales is 2,400 (Bannister 2008).

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a.

b.

Fig. 5.3. Distribution of blue whale sighting between 2002-2007 in the DSTO areas of interest (a), raw data from Gill et al. (2011). Locations of southern right calving areas adjacent to the DSTO areas of interest (from DEH 2005). Blue whales distribution is indicative of the periods from November to May; southern right calving grounds indicative of use between mid-May to mid-November. 5.5 Other

61

URS(2010) provides further, albeit limited information, on other relatively rare species in SA

waters. Pygmy, dwarf Sperm whales, Sperm whales and Beaked whales are all found in the region

and notably along the continental slope (200 m isobath) as illustrated in Fig. 5.4 below. Little other

information is presented.

Fig. 5.4. Feeding areas (pale green) of Beaked, Sperm and other whales (URS 2010).

SAXA (2004; p91) provides an Australian-wide qualitative map of whale distribution that adds little

to the discussion above.

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6 Other factors – Marine Vessel Activity

SARDI has routinely collected statistics on fishing vessel activity. For scalefish and lobster fishing,

this data consists of the number of boat days for each month and for the one degree by one

degree squares shown in Fig 6.1. Boat days are defined by the number of boats multiplied by the

number of days spent at sea. Thus, 40 boat days could be one boat fishing for 40 days or four

boats, each fishing for 10 days. It is thus a good measure of vessel activity.

Fig. 6.1. The number of boat days for the scalefish and lobster fisheries for the “summer” (November to April) and “winter” (May to October) periods and for the one degree squares shown. Boat days are the number of boats times the number of days each spends at sea in the regions shown. Winter boat days are in brackets.

To increase reliability, we have averaged the number of boat days into a “summer” period

(November to April) and a “winter” period (May to October) and the boat days for these periods are

indicated in Fig. 6.1. The data is provided by the fishing industry to SARDI as part of their license

requirements and for the period November 2003 to October 2009 inclusive. The winter boat days

are in brackets and are clearly much less than for summer where the largest vessel activity occurs

off Robe (east zone), between Kangaroo Island and the Eyre Peninsula (mostly the central zone)

and inshore of the 70 m isobath and then the region to the south of Kangaroo Island (central zone).

Minimal vessel activity is found during winter for the west zone and offshore of the 70 m isobath

with a total of 19 boat days.

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Now consider similar data for the sardine fishery. The data supplied to SARDI is boat trips by

individual vessels each month. Data on the number of days at sea is not provided, but typically

might be 3-5 days per trip. The number of boat trips shown in Fig. 6.2 is for the summer and winter

periods defined above and again obtained for the period November 2003 to October 2009

inclusive. One degree squares that have no entries indicate no trips for these periods.

Clearly, most of the sardine vessel activity is confined to the region between Kangaroo Island and

the Eyre Peninsula with little activity in the west zone and none in the east zone.

Fig. 6.2. The number of boat trips for the sardine fishery for the “summer” (November to April) and “winter” (May to October) periods and for the one degree squares shown.

While the above data give “seasonal” variability, it is also worth noting that the fishing for scalefish

is least in winter (July and August) and fishing for sardines is least in August and September. The

Rock Lobster fisheries opens in October and activity maximal from then until May. This fishery

closes from June 1st. Data on the lobster fishery is commercial in confidence and unavailable.

These state based fisheries results are augmented by information regarding both state and

commonwealth fisheries from the Australian Fisheries Management Authority (SAXA 2004; p74-

76). The species, number of fishing permits and methods are listed. The spatial extent of those

listed is given in a qualitative form that illustrates that all of the three zones discussed here are

subject to fishing of the listed species.

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Shipping routes are also described in SAXA (2004; p76). We quote:

International shipping is relatively limited in the Great Australian Bight. The Adelaide Port Authority

estimates 35 merchant ships per month enter St Vincent’s Gulf to visit Port Adelaide, Port Stanvac

and Ardrossan. Vessel numbers approaching from the west are equal to the number approaching

from the east. Vessels from the west pass through Investigator Strait on the north side of Kangaroo

Island, while those approaching from the east almost always enter through Backstairs Passage on

the east side of Kangaroo Island. About 10 vessels per month cross SAXA to the south of

Kangaroo Island on route from Newcastle, Sydney, Port Kembla and Melbourne to ports in

Spencer Gulf. These vessels carry ore, metals, wheat, oil, sheep and general cargo.

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