Occurrence, Distribution and Abundance of Cetaceans Off the Western Eyre Peninsula in the Great Australian Bight

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‘This is the peer reviewed version of the following article: Bilgmann, K., Parra, G. J., & Möller, L. M. (2017). Occurrence, distribution and abundance of cetaceans off the western Eyre Peninsula in the Great Australian Bight. Deep Sea Research Part II: Topical Studies in Oceanography. https://doi.org/10.1016/ j.dsr2.2017.11.006 which has been published in final form at https://doi.org/10.1016/j.dsr2.2017.11.006

Occurrence, distribution and abundance of cetaceans off the western Eyre Peninsula in the Great Australian Bight

Kerstin Bilgmann, Guido J. Parra, Luciana M. Möller

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PII: S0967-0645(17)30364-8 DOI: https://doi.org/10.1016/j.dsr2.2017.11.006 Reference: DSRII4348 To appear in: Deep-Sea Research Part II Received date: 28 June 2017 Revised date: 25 September 2017 Accepted date: 7 November 2017 Cite this article as: Kerstin Bilgmann, Guido J. Parra and Luciana M. Möller, Occurrence, distribution and abundance of cetaceans off the western Eyre Peninsula in the Great Australian Bight, Deep-Sea Research Part II, https://doi.org/10.1016/j.dsr2.2017.11.006 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Occurrence, distribution and abundance of cetaceans off the western Eyre Peninsula in

the Great Australian Bight

Kerstin Bilgmanna,b,c*, Guido J. Parraa, Luciana M. Möllera,b aCetacean Ecology, Behaviour and Evolution Lab (CEBEL), Biological Sciences, Flinders

University, GPO Box 2100, Adelaide, SA 5001, Australia. bMolecular Ecology La at Flinders University (MELFU), Biological Sciences, Flinders University,

GPO Box 2100, Adelaide, SA 5001, Australia. cSchool of Biological Sciences, Faculty of Science, Macquarie University, Sydney, NSW 2109,

Australia. [email protected] [email protected] [email protected], [email protected]

*Corresponding author. School of Biological Sciences, Faculty of Science, Macquarie

University, Sydney, NSW 2109, Australia.

Abstract

This study provides the first assessment of the occurrence, distribution and abundance of cetaceans in shelf and coastal waters off the western Eyre Peninsula, eastern Great Australian

Bight, South Australia. We undertook aerial line-transect surveys to estimate the abundance of common dolphins, and to assess the occurrence and distribution of other small and large

cetaceans. Two along shore surveys were also flown to assess occurrence of endangered southern right whales in coastal waters. Five cetacean species were detected: seven southern right whales, three humpback whales, one minke whale (unknown species), 71 schools of short- beaked common dolphins, and 14 schools of bottlenose dolphins. Abundance of common dolphins was estimated to be 20,000-22,000 using distance sampling methods with densities of

0.67-0.73 dolphin/km2. Comparisons or shot-beaked common dolphin densities off the Eyre

Peninsula in the eastern GAB with other regions around the world show that shelf waters off the

Eyre Peninsula represent an important habitat for common dolphins.

Keywords: marine ecology, conservation, coastal waters, continental shelves, biodiversity, aerial survey, distance sampling, dolphin, whale.

1. Introduction

The Great Australian Bight (GAB) off southern Australia is central to the longest stretch of southwards facing coast in the southern hemisphere and is of major oceanographic importance linking tropical waters of the Indian Ocean and temperate waters of the Pacific Ocean

(Petrusevics et al. 2009). The continental shelf of the GAB is up to 200 km wide and is the location of the world’s only upwelling system in a northern boundary current (Middleton and

Cirano 2002). High levels of marine biodiversity are found in the GAB across numerous taxa

(e.g. Shepherd 1991, Poore 1995), and the region is recognized as an area of conservation significance for rare and endangered marine mammals (Edyvane 1998). A minimum of 27 cetacean species occurs in the GAB, including the endangered southern right whale (Eubalaena australis) (Burnell and Bryden 1997, Bannister 2001, Kemper et al. 2005, Kemper et al. 2008).

Anthropogenic activities have the potential to impact marine biodiversity and the distribution and abundance of species. In the region off the western Eyre Peninsula impacts on cetaceans may

occur through disturbances from offshore oil exploration and fishery interactions. Firstly, the offshore South Australian Bight Basin represents one of the world’s last under-explored

Cretaceous basins with potential for large accumulations of petroleum (Government of South

Australia 2015). The upstream petroleum sector (exploration and production) in Australia is expected to grow rapidly over the next decade due to an increasing demand for energy resources (Government of South Australia 2015). Secondly, commercial fisheries operate in shelf waters off the western Eyre Peninsula including the purse-seine fishing of the South

Australian Sardine Fishery (SASF); the gillnet fishery of the Southern and Eastern Scalefish and

Shark Fishery (SESSF); and the midwater trawl fishery of the Small Pelagic Fishery (SPF).

Commercial fishing in the eastern GAB and in waters off the western Eyre Peninsula is ongoing and the purse-seine fishery for sardines, for example, has undergone a large scale expansion in

South Australia (Goldsworthy et al. 2013). The purse-seine fishery commenced in 1991 and it is today Australia’s largest fishery by catch volume (Goldsworthy et al. 2013).

Despite the increase of anthropogenic activities in the region off the western Eyre Peninsula and adjacent areas in South Australia, little is known about the occurrence, distribution and abundance of cetaceans in the region. For example, information on the distribution and abundance of endangered southern right whales in waters west of Eyre Peninsula to date is mainly derived from two long-term studies; an aerial program from Cape Leeuwin to Ceduna

(Bannister 2011), and a land-based program in the Great Australian Bight Marine Park

(GABMP) (Burnell 2008). These studies have shown that southern right whales aggregate in several coastal regions along the GAB, west of Eyre Peninsula, with the Head of Bight (South

Australia) being recognized as an important breeding and nursery ground (Burnell and Bryden

1997, Bannister 2011, DSEWPaC 2012, Mackay and Goldsworthy 2015). Bottlenose dolphins

(Tursiops spp.) and short-beaked common dolphins (Delphinus delphis delphis; Linnaeus

1758) are also regularly sighted off the western Eyre Peninsula (e.g. Kemper et al. 2005,

Bilgmann et al. 2007, Bilgmann et al. 2011, Bilgmann et al. 2014) but no estimates of density and abundance have been undertaken.

The aim of this study was to investigate the occurrence, distribution and abundance of cetacean species in coastal and shelf waters off the western Eyre Peninsula in the eastern GAB, South

Australia, using aerial surveys and distance sampling methodology. We present sighting data and distributional maps for all sighted cetaceans, and estimates of abundance for short-beaked common dolphins, the most frequently sighted cetacean species in the region.

2. Material and Methods

2.1 Survey Design

2.1.1 Line transect survey

Aerial surveys were flown off the western Eyre Peninsula in July and August 2013 covering

2,236 km of transect effort. Transects were aligned north to south, and spaced 15 km apart between Ceduna (32°14’S, 133°42’E) and Coffin Bay (34°43’S, 135°36’E) (Figure 1). Transects start and end points were at the coastline and the 100 m depth contour, respectively, and extended to a maximum of 136 nautical miles (252 km) from the coast over the Australian continental shelf. Although the transects were not exactly perpendicular to the coastline and the end points well inside the study area boundaries, we do not believe these have caused significant data biases. Each transect was flown once, alternating between north-south and south-north flights. Flights took place between 23 July and 8 August 2013, the peak season for southern right whale occurrence off southern Australia (Burnell and Bryden 1997, Bannister

2001, DSEWPaC 2012). Surveys were conducted from a Partenavia, twin-engine, six-seat, high-wing aircraft commonly used for aerial cetacean surveys (e.g. Dawson et al. 2008). All line-

transects were flown at an altitude of 500 feet (152.4 m) and speed of 100 knots (185.2 km/h) in good sighting conditions of wind speed less than 15 knots (i.e. Beaufort sea state ≤ 3). The survey team consisted of four people: the pilot (front-left), the survey leader (front-right), and two observers (rear-right and rear-left) looking out either side of the plane through flat windows that allowed them to view down to a 70 degree angle. Communication between survey leader and observers took place via aviation headsets connected to a four way intercom and recorded on a digital voice recorder. The observers called out declination angles to sightings as they came abeam using inclinometers and reported data on species, group size and sighting conditions

(i.e. Beaufort sea state, glare severity and angle, visibility, cloud cover and turbidity). The survey leader entered survey effort data, sighting conditions and sighting data called by the observers, together with time stamp signals of positions from a GPS system. Data were entered and stored in a handheld computer using the software CYBERTRACKER and a sequence specifically designed for cetacean aerial surveys. Surveys were flown in ‘passing mode’, which means that survey effort was not suspended to circle back when a sighting was made, except when species identification and/or school size was uncertain. In such cases a circle back procedure was initiated and effort was suspended to circle the general location of the animals and confirm species identification. Survey was then resumed at the location on the transect line where survey effort had previously been suspended.

2.1.2 Coastal survey

For the coastal survey two along shore transects were flown. The first transect followed the coastline within one nautical mile from shore in order to scan the area between the transect and the shore line, replicating the survey design of Bannister (2011) for studying the occurrence of southern right whales. In several coastal regions between Cape Leeuwin in Western Australia

and Ceduna in South Australia, southern right whale cows about to give birth or with newborn calves are frequently seen close to shore (Bannister 2011). The along shore transect aimed to assess southern right whale occurrence beyond the area previously surveyed by Bannister

(2011) (i.e. between Ceduna and Coffin Bay). The second transect followed the 40 m depth contour approximately parallel to the coast. The area around the 40 m bathymetry was chosen because it covers waters at medium depth, and at greater distance from shore, which may be utilized by southern right whales to travel from offshore feeding grounds to calving grounds at the Head of Bight (31°30’S, 131°10’E) (Bannister 2011), and/or Fowlers Bay (31°59’S,

132°34’E), the latter a historically significant whaling location.

The coastal surveys were conducted with the same Partenavia aircraft and observer team as the line-transect survey (pilot, observer leader and two observers) and followed the same protocols. Line transect locations were plotted with the Garmin software HOMEPORT 2.2.3

(Garmin Ltd.) and uploaded onto an aviation GPS in the Partenavia aircraft. During flights the pilot followed the survey track, and line tracking was checked by the observer leader throughout the flight. Both transects were flown at 1,000 feet (304.8 m; twice the altitude of the line transect survey design) and 100 knots (185.2 km/h) to replicate the survey design of (Bannister 2011).

2.2 Data analysis

2.2.1 Line-transect survey

Abundance was estimated only for those species with sufficient number of sightings (i.e. n >

~60, see Buckland et al. 2004 for details). Analyses were conducted in DISTANCE 6 (release 2) using Conventional Distance Sampling (CDS) and Multiple Covariate Distance Sampling

(MCDS) (Thomas et al. 2010). In the CDS engine, we used uniform, half normal and hazard rate detection functions, and in the MCDS engine half normal and hazard rate, and combined these with different adjustment terms (cosine, hazard rate, simple polynomial, hermite polynomial).

Best fit model(s) were selected based on the lowest Akaike Information Criterion (AIC)

(Buckland et al. 2001, Burnham and Anderson 2002). These combinations of key functions and adjustment terms have shown to perform well in similar studies (Thomas et al. 2010).

Goodness-of-fit was also performed for each model assessing quantile-quantile (q-q) plots,

Kolmogorov-Smirnov test, and Cramer von Mises statistics for exact data (Buckland et al. 2001,

Thomas et al. 2010).

While CDS is suitable for simple data analyses, MCDS allows for modeling the detection probability as a function of variables other than distance that may contribute to heterogeneity in detection probabilities (Borchers et al. 1998). These covariates are entered through the scale parameter of the key function (via a log link function), which means that the covariates are assumed to influence the ‘scale’ of the detection function but not its ‘shape’ (Buckland et al.

2001, Thomas et al. 2010). When detection on the track line is not certain, this is important because methods can be biased if detection probabilities vary among schools (Borchers et al.

1998). MCDS analysis allows for inclusion of explanatory variables (covariates: Beaufort sea state, cloud cover, visibility impacted by glare, and school size) that may influence abundance estimation. Availability bias (the bias that occurs when an observer misses an animal because it is submerged) was addressed using data from focal follows of schools of short-beaked common dolphins conducted with a helicopter in a region adjacent to the study area off the eastern Eyre

Peninsula, in similar water clarity and water depth ranges as in the line-transect survey. Focal follows of 10-15 min in length were flown at the same altitude as the line transect survey (500 feet; 152.4 m). Dolphin school size estimates and dolphin behaviours (travelling, milling, feeding and resting) were recorded for each focal follow. Any apparent reactions to the helicopter

presence during focal follows were also recorded. Dolphin schools were selected to cover a range of different school sizes that were typically encountered in the survey area.

2.2.2 Coastal surveys

Southern right whale counts from the coastal surveys were also compared to counts of these animals between Cape Leeuwin in Western Australia and Ceduna in South Australia recorded from1993 to 2010 as part of a long-term research program reported in (Bannister 2011). The coastal survey data were not used in the line-transect calculations of density and abundance.

3. Results

3.1 Line-transect survey

In total, an area of 29,822 km2 was covered off the western Eyre Peninsula in South Australia, between Ceduna (to the west) and Coffin Bay (to the east), between 23 July and 8 August 2013.

Information on the number of schools/pods, and individuals sighted for each cetacean species during the line transect survey is shown in Table 1. The most commonly sighted cetacean species was the short-beaked common dolphin, with 59 schools sighted (Figure 3). The short- beaked common dolphin was the only species that resulted in sufficient sightings for abundance estimates in DISTANCE. Other cetacean species sighted during the line transect survey were the bottlenose dolphin (Tursiops sp.) (Figure 4), southern right whale (Eubalaena australis), humpback whale (Megaptera novaeangliae), and minke whale (Balaenoptera sp.) (Figure 5,

Table 1). Bottlenose dolphins sighted in this study were likely to be the Burrunan dolphin form

(australis-type) based on their small body size, light coloration, relatively small school sizes of

≤30 individuals and close distance to shore (<12 km) (Bilgmann et al. 2007, Charlton-Robb et al.

2011, Charlton-Robb et al. 2014). The Burrunan dolphin (Tursiops australis) has been described

as a new dolphin species occurring in southern Australian coastal waters (Charlton-Robb et al.

2011), however the validity of this species has not yet been recognized (SMM Taxonomy

Committee, 2016). The larger, more robust, and with darker coloration, common bottlenose dolphin (Tursiops truncatus), although previously recorded in offshore waters of this region, was likely not observed during these surveys (based on our observations of morphological differences between the Burrunan dolphin form and the common bottlenose dolphin as explained above). It is also known from previous genetic studies that bottlenose dolphins inhabiting coastal areas between Ceduna and Coffin Bay belong to the Burrunan dolphin form, as opposed to the common bottlenose dolphin or Indo-Pacific bottlenose dolphin (Tursiops aduncus) (Bilgmann et al. 2007, Möller et al. 2008).

Position of the sightings detected during the line transect survey were calculated by adjusting for perpendicular distance from the transect line using geometric functions in Excel, which incorporated declination angle, bearing and the GPS location on the transect line when the sighting was abeam (Lerczak and Hobbs 1998) (Figure 3 and 4). Estimates of abundance where calculated only for short-beaked common dolphins. Common dolphin school sizes recorded during the line transect survey (using the same school size bins as in Figures 3 and 4) are displayed in Figure 6.

To determine availability bias and to calculate g(0), 19 helicopter focal follows of common dolphin schools were flown on 8 and 9 February 2012. During 16 of the 19 focal follows, common dolphins of different school sizes (2-50 individuals) and behaviours (travelling, milling and feeding) were sighted, and these did not seem to show any apparent reactions to the circling helicopter. In three focal follows of dolphin schools, however, mild reactions to the helicopter presence were observed (Table 2). Calculations of availability bias showed common dolphin schools were visible from the air 94% of the time when percentage was averaged

across the 19 focal follows. We therefore incorporated g(0)=0.94; g(0)SE=0.02 into the analysis of abundance based on these estimates of availability bias.

3.1.1 Estimates of abundance

The data was left-truncated at a perpendicular distance of 130 m to account for an obstructed view down to the transect line, and right-truncated at a distance of 420 m to remove outliers, and thus improve model fit (see Buckland et al. 2001, Thomas et al. 2010). Right-truncation of

420m was chosen because 1) it removed 5% of the extremely distant sightings as recommended by Buckland et al. (2001), and 2) it was the least amount of right-truncation (with the most data included) among those estimates that resulted in similar values of abundance and confidence intervals. The latter was determined by undertaking a range of different right- truncation distances trialed in an initial preliminary analysis (data not shown). The summary statistics of the detection function models are shown in Appendix A. For the CDS analysis, comparisons of AIC from all permutations of the detection functions and potential adjustment terms resulted in the uniform key function with the cosine adjustment term showing the lowest

AIC (Figure 7). The estimated strip width for the uniform key function with cosine adjustment term was 129.93 m, resulting in an estimated short-beaked common dolphin density of 0.73 dolphin/km2 (CV = 0.28) and an estimated number of individuals of N = 21,884 (95% CI= 12,602

-38,003) (Appendix A).

In the MCDS analysis we used the same right and left truncation of the data as for the CDS analysis. The following covariates were added one at a time, and tested if they improved model fit (i.e. if the AIC decreased): Beaufort sea state, cloud cover, glare and school size (cluster size). Each covariate added to any possible combination of key function and adjustment term led to convergence failure. Adding more than one covariate at a time also led to convergence

failure, and was therefore disregarded. Any step undertaken to facilitate convergence (for example, setting the number of adjustment terms manually to zero) did not improve convergence. As recommended in such cases, we only considered null models (no covariates) for model selection, and disregarded the models with convergence failure (see Buckland et al.

2001). Summary statistics are displayed in Appendix A.

Results from the CDS and the MCDS analyses using the same combination of key function and adjustment term resulted in the same estimates. Similar to the CDS criteria for model selection, we selected the best fit model based on the lowest AIC among the null models (all converged).

Since the uniform key function (selected for CDS) is not available in the MCDS engine, the results from the best fit model of CDS and MCDS, including the abundance estimates, differed slightly. However, the same results were produced when the same models were used (see summary statistics in Appendix A). The half normal key function fitted the data best in the

MCDS analysis (lowest AIC), regardless of the adjustment term used, and all three possible combinations of adjustment terms with the half normal key function led to the same values

(Appendix A). The fitted detection function is given in Figure 8. The estimated strip width for the half normal function with any of the adjustment terms was 147.36 m, and the estimated short- beaked common dolphin density was 0.67 dolphin/km2 (CV = 0.31). Number of individuals was estimated at N = 20,214 (95% CI = 11,067 - 36,921). Models with hazard rate key functions produced outputs that differed only slightly from those of the half normal key functions

(Appendix A).

3.2 Coastal surveys

The 1-nautical mile (1-nm) from shore transect of 498 km length was flown in a southeast to northwest direction on 24 July 2013. The 40-m depth contour transect of 393 km length was flown in the opposite direction, from northwest to southeast, on 7 August 2013. On the 1-nm

transect the only cetacean species detected were the southern Australian bottlenose dolphin and the short-beaked common dolphin. While on effort for the 40-m depth transect, we detected the humpback whale and the short-beaked common dolphin.

4. Discussion

This study provides the first systematic coastal and shelf survey, and assessment of the occurrence and distribution of cetaceans off the western Eyre Peninsula in the eastern Great

Australian Bight (GAB), out to the 100 meter isobath during the austral winter. It also provides the first abundance estimates for short-beaked common dolphins in the region. The results provide a valuable contribution for a better understanding of the importance of this region to cetaceans.

Altogether, five cetacean species were detected. The most sighted cetacean species for both the line-transect and coastal surveys was the short-beaked common dolphin. The second most commonly sighted dolphin species was the bottlenose dolphin of the Burrunan form (australis- type). Short-beaked common dolphins were mainly distributed in shelf waters, while bottlenose dolphins of the Burrunan form were sighted closer to shore. The abundance calculated for short- beaked common dolphins resulted in estimates of approximately 22,000 individuals and density of 0.73 dolphin/km2 using Conventional Distance Sampling. Estimates using Multiple Covariate

Distance Sampling were only slightly lower, with an abundance of approximately 20,000 individuals and density of 0.67 dolphin/km2.

While these are the first estimates of dolphin abundance for the region, they only provide estimates of minimum abundance because the design of our line transect survey had limitations that are likely to have impact upon our ability to detect cetaceans. First, logistic and time constraints did not allow for a higher number of line transects to be flown over the survey area with closer line spacing than the 15 km between transects used here. Second, surveys were flown using a single observer platform (one observer on each side of the plane) rather than a

double observer platform (two independent observers on each side of the plane), thus we could not correct abundance estimates for perception bias (the bias that occurs when an observer misses a sighting due to human error) (Buckland et al. 2001). However, we were able to improve abundance estimates by adjusting for availability bias. Despite this adjustment, abundance estimates are still likely to be slightly negatively biased because of perception bias.

Large-scale abundance estimates for short-beaked common dolphins have previously been conducted in several regions around the world, including Eastern Atlantic shelf waters

(Hammond et al. 2002, Hammond et al. 2013), off the southern Californian coast (Douglas et al.

2014; Campbell et al. 2015), and in the eastern and western Mediterranean Sea (Cañadas and

Hammond 2008, Cañadas and Vázquez 2017). Common dolphin densities off the western Eyre

Peninsula in the eastern GAB (0.67–0.73 dolphin/km2) were similar to those determined by ship- based line-transect surveys (0.71 dolphin/km2) off southern Californian waters (Campbell et al.

2015) and considerably higher to those obtained from aerial and shipboard line-transect surveys in European Atlantic shelf waters (Hammond et al. 2013). The aerial line-transect surveys in

European Atlantic shelf waters were undertaken over a large area (364,771 km2) divided into several survey blocks, and short-beaked common dolphins there were sighted in only about half these blocks, with densities ranging between 0.012 and 0.302 dolphin/km2 (see Hammond et al.

2013). Similar to our study, aerial line transect-surveys reported in Hammond et al. (2013) were corrected for availability bias, but not for perception bias. In both regions, the eastern Atlantic

(European waters) and eastern Pacific (off the Californian coast), short-beaked common dolphins were mainly distributed in continental shelf waters. In our study off the western Eyre

Peninsula, common dolphins were also found in continental shelf waters, although to a large extent distributed only in waters up to the 100m depth contour and rarely beyond this depth range.

In the Mediterranean Sea, short-beaked common dolphins appear to have undergone a steep decline in numbers over recent decades, which led to the Mediterranean common dolphins

being listed as endangered in the IUCN Red List of Threatened Species (UNEP/IUCN 1994,

Forcada and Hammond 1998, Bearzi et al. 2003, Cañadas and Vázquez 2017). The Alboran

Sea of the western Mediterranean still holds the highest densities of common dolphins compared to all other surveyed areas in the Mediterranean basin (Cañadas and Hammond

2008, Cañadas and Vázquez 2017). In the Alboran Sea, the estimated average common dolphin density was 1.01 dolphins/km2 (95%CI = 0.80 to 1.19) calculated using spatial modelling of data from boat-based cetacean surveys (Cañadas and Hammond 2008), which is higher than the densities of 0.67-0.73 dolphin/km2 estimated for our study area. However, the Alboran Sea is the last region of the Mediterranean where common dolphins are still abundant, and the species has almost or completely disappeared from other regions of the Mediterranean (Bearzi et al. 2003, Cañadas and Vázquez 2017).

Overall, comparisons or shot-beaked common dolphin densities off the Eyre Peninsula in the eastern GAB with other regions around the world show that shelf waters off the Eyre Peninsula represent an important habitat for common dolphins.

Globally threats to marine and land mammals are high, and generally higher in marine mammals compared to land mammals (Shipper et al. 2008). This is likely driven by processes such as accidental mortality and pollution and is often spatially distinct (Schipper et al. 2008).

Impacts of climate change have also been shown to be a considerable current and future threat to marine predators, including dolphins (Hobday et al. 2015, Cañadas and Vázquez 2017,

Robbins et al. 2017). The main potential threats for dolphins in southern Australia are human induced, such as for example operational fishery interactions, entanglements in debris, coastal development and pollution (Gales et al. 2003, Robbins et al. 2017). Entanglement and mortalities of cetaceans in fishing gear, in particular short-beaked common dolphins, have occurred as a result of shared use of the highly productive waters of the eastern GAB by both cetaceans and fisheries (Hamer et al. 2008, Kemper et al. 2008, AFMA 2013, 2015a). Short-

beaked common dolphins, in particular, are subject to operational interactions with fisheries including the purse-seine, gillnet and midwater trawl fisheries that operate off the western Eyre

Peninsula and adjacent regions (Hamer et al. 2008, AFMA 2011, 2013, 2015a,b,c). Hamer et al.

(2008) discovered high interaction rates of common dolphins with the purse-seine fishery for sardines off southern Australia, with 1728 estimated encirclements and 377 mortalities between

November 2004 and June 2005. Dolphin mortalities in gillnet and midwater trawl fisheries have only recently been discovered (mainly short-beaked common dolphins; see AFMA 2012,

2015a,b,c, Department of the Environment 2016). In recent years, several measures have been implemented to mitigate dolphin-fishery interactions off southern Australia including 1) an

Industry Code of Practice for mitigating operational interactions of the South Australian Sardine

Fishery (SASF) (Hamer al. 2008, Ward et al. 2015); 2) temporary closures of a region with high interaction rates to gillnet fishing in South Australia, and establishment of an adjacent dolphin monitoring zone (AFMA 2011, 2013); 3) requirements for gillnet fishers to independently respond to dolphin interactions by moving their fishing operations at least five nautical miles away when catching a dolphin, before fishing is allowed to resume (AFMA 2014, 2015a); and 4) a bycatch trigger limit in the Small Pelagic Fishery (SPF) with six monthly zone closures to trawling if a dolphin is caught (AFMA 2015b, 2016). For the SASF, these measures have led to a reduction in reported and observed bycatch of dolphins (Ward et al. 2015).

The cumulative impact of the different fisheries on the dolphin populations off southern

Australia, including the one off the western Eyre Peninsula, together with other anthropogenic impacts such as pollution and/or habitat degradation, remains unknown. Short-beaked common dolphins off the western Eyre Peninsula are particularly likely to interact with fisheries that operate there due to the dolphins’ distribution and regular occurrence in the region. Mitigation of these interactions is required and needs to consider the separate short-beaked common dolphin populations identified for southern and eastern Australian waters (Möller et al. 2011, Bilgmann et al. 2014). Short-beaked common dolphins are known to exhibit fine-scale genetic structuring

in these regions, which may make them vulnerable to anthropogenic impacts on a population level. These dolphins are mesopredators that tend to be affected by bottom up and top down effects in an ecosystem (Kiszka et al. 2015), thus they are an important species of the eastern

GAB ecosystem.

Along the southern and eastern Australian coasts, both short-beaked common dolphins and bottlenose dolphins (Tursiops spp.) exhibit fine-scale genetic structuring (Bilgmann et al. 2007,

Möller et al. 2007, Bilgmann et al. 2008, Wiszniewski et al. 2010, Möller et al. 2011, Bilgmann et al. 2014, Charlton-Robb et al. 2014). The short-beaked common dolphins that are distributed in waters off the western Eyre Peninsula belong to a population that is genetically differentiated from the short-beaked common dolphin populations to the east and west (see Bilgmann et al.

2014). Bottlenose dolphins off the western Eyre Peninsula belong to a genetic population that shows marked genetic differentiation from the one in Spencer Gulf (individuals from both regions belong to the Burrunan form) with their boundary coinciding with a temperature and salinity front at the mouth of the gulf (Bilgmann et al. 2007). While the bottlenose dolphins of the

Burrunan dolphin form in our survey were restricted to waters <12km from shore, short-beaked common dolphins were broadly distributed in shelf waters in a range of different water depths out to the 100 m depth contour, the southern boundary of our study area. Both short-beaked common dolphins and bottlenose dolphins of the Burrunan form, due to their fine-scale genetic structuring, are potentially sensitive to regional anthropogenic impacts. However, dissimilarity in the distribution of the two species may cause them to be differently at risk to potential anthropogenic impacts.

Adjacent to the surveyed waters off the western Eyre Peninsula, multiple petroleum exploration permits were granted to independent oil companies in the offshore Bight Basin between 2011 and 2013, covering an area of approximately 82,600 km2 in waters of up to 4,600 m deep

(Government of South Australia 2015). The approximate center of this petroleum exploration

area is located around 300 km southwest of Ceduna (BP 2013). Deep water drilling for petroleum includes risks of significant environmental impact, and potential oil spills can lead to an increased toxin load to the marine environment, habitat degradation and potentially to cetacean deaths (e.g. Exxon Valdez oil spill, Ehrenfeld 1990, Estes 1991, Deepwater

Horizon/BP oil spill, Machlis and McNutt 2010, Williams et al. 2011). Underwater sound from seismic surveys in the area may also lead to disruption of normal cetacean behavior (McDonald et al. 2006, Weilgart 2007). Anthropogenic activities in the region may be of concern if they lead to habitat degradation, cetacean habitat displacement and/or cetacean mortality. Data from this study can therefore be used to inform risk assessments of potential anthropogenic impacts on cetaceans off the western Eyre Peninsula in the eastern GAB.

A relatively low number of southern right whales was sighted throughout our survey between

Ceduna and Coffin Bay. The few southern right whales we detected suggest that the surveyed region did not represent a core area of use for this species at that time. However, as the species continues to recover from 19th and 20th century whaling, it is possible that some of these areas will become more frequently used by the whales. Currently, our data indicate that at least some southern right whales may use the eastern GAB for transiting from feeding grounds to coastal aggregation sites at the Head of the Bight and/or Fowlers Bay. Monitoring southern right whales in Australian waters is a requirement to meet the objectives of the Conservation Management

Plan for the Southern Right Whale 2011-2021 (DSEWPaC 2012). While the southern right whale population recovers and expands, monitoring is required of potentially emerging areas of southern right whale usage, such as the eastern GAB, as the whales may be exposed to human disturbance in the area (DSEWPaC 2012, Mackay and Goldsworthy 2015). Threats to southern right whales include human induced impacts such as vessel collisions, anthropogenic noise

(shipping, industrial and seismic surveys), commercial fishing entanglements and coastal

development (Kemper et al. 2008, DSEWPaC 2012); and climate variability and change

(DSEWPaC 2012).

The detection of three humpback whales and one minke whale during our study shows that the region between Ceduna and Coffin Bay is also used by other whale species during winter.

Whales, including southern right whales, were seen in both shelf and coastal waters. Since aerial surveys are ‘snap shots’ of temporal and spatial distribution of animals, other species that were not seen during this study may also utilize the area, and species that were detected may be found in different habitats at different times (MacKenzie et al. 2002, Martin et al. 2005,

Iknayan et al. 2014, Dénes et al. 2015).

During the coastal surveys we only detected humpback whales, short-beaked common dolphins and bottlenose dolphins of the Burrunan form. Although coastal transects where flown during the peak season for southern right whales (July/August; e.g. Burnell 2001, Bannister 2011,

Mackay and Goldsworthy 2015), this species was not observed close to shore. This is in contrast to the relatively large number of whales at aggregation sites along the coast west of

Ceduna. There, numbers of southern right whales ranged from 167 - 782 individuals between

1993 and 2009 (Bannister 2011). Helicopter surveys in the Head of Bight region, west of our study area, resulted in a count of 206 and 121 southern right whales in July and August, respectively (Mackay and Goldsworthy 2015). Although we did not detect southern right whales during our along shore transect, a study conducted by Watson et al. (2014) in late August of the same year, and using similar methods, detected eight southern right whales (including a female/calf pair) between Coffin Bay and Ceduna. The region between Ceduna and Coffin Bay may be more utilized by southern right whales towards the start and end of the peak season when whales transit to and from the aggregation sites. A recent satellite telemetry study of southern right whales with tags deployed in September 2014 at Head of Bight recorded two

whales moving southwards and one moving west, but none moving east (Mackay et al. 2015) into our study region. If southern right whales are found in the surveyed region between Ceduna and Coffin Bay more frequently in different years of their 3-4 year calving intervals remains unknown. Furthermore, availability bias may have occurred for southern right whale sightings during our aerial survey, which potentially leads to an underestimate of numbers. Southern right whales are generally easy to detect in shallow coastal waters with sandy bottom substrate, but in deeper waters and over darker coloured rocky reef bottom substrate the ability to detect a whale may be reduced.

6. Conclusions

We sighted five cetacean species in coastal and offshore waters off the western Eyre Peninsula during the austral winter: short-beaked common dolphins, bottlenose dolphins of the Burrunan form (australis-type), southern right whales, humpback whales and a minke whale. Short- beaked common dolphins appear to be particularly abundant in the region, and the shelf waters of the eastern GAB likely represent an important habitat for this species. The bottlenose dolphin of the Burrunan form was the second most commonly sighted cetacean species and was restricted to areas <12km from shore. The dissimilar distribution and ecology of these two dolphin species may result in them showing different levels of sensitivity to regional anthropogenic impacts. Sightings of endangered southern right whales were low compared to previous studies west of Ceduna, suggesting that the surveyed region did not represent a core area of use for this species during our study period. Our data however indicate that some southern right whales may use the eastern GAB for transiting from feeding grounds to coastal aggregation sites at the Head of the Bight and/or Fowlers Bay. As the species continues to recover from whaling, it is possible that some of these areas will become more frequently used by this species.

Acknowledgements

This study was funded as part of the Great Australian Bight Research Program, a collaboration between BP, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), the

South Australian Research and Development Institute (SARDI), the University of Adelaide, and

Flinders University. The Program aims to provide a whole-of-system understanding of the environmental, economic and social values of the region; providing an information source for all to use. We are thankful for the administrative support provided by Flinders Partners Pty Ltd,

South Australian Research and Development Institute and the Commonwealth Scientific and

Industrial Research Organization. We are thankful for the logistical support provided by

Observair and its Chief Pilot Brad Welch. We also thank Shae Small and Juliette Coudert for field assistance. The research was conducted under Flinders University and Southern Adelaide

Health Service Animal Welfare Committee approval (#E326) and DEWNR, SA research permit

(#E25889-3).

Appendix A Summary statistics of the Conventional Distance Sampling (CDS) and Multiple

Covariate Distance Sampling (MCDS) analyses in DISTANCE. Model(s) with lowest AIC (best fit models) are marked with a black frame. AIC = Aikaike Information Criterion; ESW = Effective

Strip Width; EDR = Effective Detection Radius; D = Density; N = Abundance Estimate; CV =

Coefficient of Variance; df = degrees of freedom.

CDS Key Function_Adjustment Delta AIC ESW/ D 95% Confidence %C N %C df 95% Term_Truncation AIC EDR Interval V V Confidence Interval 572. 147.3 0. 0.3 202 31. 93. 1106 369 CDS_Hn_Cos_LT130_RT420 1.63 26 6 67 0.37 1.23 1 14 05 66 7 21 570. 129.9 0. 0.2 218 28. 83. 1260 380 CDS_Un_Cos_LT130_RT420 0 62 3 73 0.42 1.26 8 84 29 23 2 03 572. 147.3 0. 0.3 202 31. 93. 1106 369 CDS_Hn_HP_LT130_RT420 1.63 26 6 67 0.37 1.23 1 14 15 66 7 21 573. 182.2 0. 0.3 193 34. 93. 377 CDS_Hr_SP_LT130_RT420 2.81 43 8 64 0.33 1.26 5 83 57 12 9945 75

MCDS Key Function_Adjustment Delta AIC ESW/ D 95% Confidence %C N %C df 95% Term_Truncation AIC EDR Interval V V Confidence Interval 572. 147.3 0. 0.3 202 31. 93. 1106 369 MCDS_Hn_Cos_LT130_RT420 1.63 26 6 67 0.37 1.23 1 14 15 66 7 21 572. 147.3 0. 0.3 202 31. 93. 1106 369 MCDS_Hn_SP_LT130_RT420 1.63 26 6 67 0.37 1.23 1 14 15 66 7 21 572. 147.3 0. 0.3 202 31. 93. 1106 369 MCDS_Hn_HP_LT130_RT420 1.63 26 6 67 0.37 1.23 1 14 15 66 7 21 573. 182.2 0. 0.3 193 34. 93. 377 MCDS_Hr_Cos_LT130_RT420 2.81 43 8 64 0.33 1.26 5 83 57 12 9945 75 573. 182.2 0. 0.3 193 34. 93. 377 MCDS_Hr_SP_LT130_RT420 2.81 43 8 64 0.33 1.26 5 83 57 12 9945 75 573. 182.2 0. 0.3 193 34. 93. 377 MCDS_Hr_HP_LT130_RT420 2.81 43 8 64 0.33 1.26 5 83 57 12 9945 75

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Figure 1. Map of the study area indicating aerial survey line transect layout. Transects were numbered from 1-11, west to east. Effort on transect was paused when flying over headlands and/or islands. The grey triangle west of the study area shows the location of the main aggregation site for southern right whales (Eubalaena australis) off South Australia at the Head of Bight.

Figure 2. Map of the study area indicating the layout of the two coastal transects. The 1-nautical mile from shore transect is displayed in a continuous black line and the 40 meter depth contour transect in a dashed line. The grey triangle west of the study area shows the location of the main aggregation site for southern right whales (Eubalaena australis) off South Australia at the

Head of Bight.

Figure 3. Sightings of short-beaked common dolphin (Delphinus delphis) schools (n = 71) off the western Eyre Peninsula in the Great Australian Bight, South Australia, during aerial surveys conducted in July/August 2013. Sightings from line transects are displayed in black circles and from coastal transects in black stars. Circle and star size increases proportionally with the number of individuals in schools, pooled into school size bins (1-5; 6-10; 11-20; 21-30; 31-40;

41-50; and 51-60 dolphins). Locations of sightings from line transects were adjusted for perpendicular distance to the transect line.

Figure 4. Sightings of bottlenose dolphin (Tursiops cf. australis) schools (n = 14) off the western

Eyre Peninsula in the Great Australian Bight, South Australia, during aerial surveys conducted in July/August 2013. Sightings from line transects are displayed in black circles and from coastal transects in black stars. Circle and star size increases proportionally with the number of individuals in schools, pooled into school size bins (1-5; 6-10; 11-20; 21-30 dolphins). Locations of sightings from line transects were adjusted for perpendicular distance to the transect line.

Figure 5. Sightings of southern right whales (Eubalaena australis; n = 7), humpback whales

(Megaptera novaeangliae; n = 3), minke whale (Balaenoptera sp.; n = 1) and whale of unidentified species (n = 1) off the western Eyre Peninsula in the Great Australian Bight, South

Australia, during aerial surveys conducted in July/August 2013. Locations of sightings from line transects were adjusted for perpendicular distance to the transect line.

Figure 6. Frequency of school sizes of short-beaked common dolphins (Delphinus delphis) spotted during aerial line transect surveys (on effort sightings) off the western Eyre Peninsula,

South Australia in July/August 2013. Dolphin schools were pooled into school size bins of 1-5;

6-10; 11-20; 21-30; 31-40; 41-50; and 51-60 dolphins.

Figure 7. Detection function plot for short-beaked common dolphin (Delphinus delphis) sightings from line-transect surveys off the western Eyre Peninsula, South Australia

(Conventional Distance Sampling method, uniform key function with cosine adjustment model;

Buckland et al. 2001). Dashed lines show left-truncation at 130 m and right-truncation at 420 m.

Figure 8. Detection function plot for short-beaked common dolphin (Delphinus delphis) sightings from line-transect surveys off the western Eyre Peninsula, South Australia (Multiple

Covariate Distance Sampling method, halfnormal key function with cosine adjustment model

without inclusion of covariates; Buckland et al. 2001). Dashed lines show left-truncation at 130 m and right-truncation at 420 m.

Table 1. Summary of cetacean sightings recorded during line transect surveys (11 equally spaced transects) and coastal surveys (1-nautical mile from shore and 40 m depth contour transect) off South Australia, between Ceduna and Coffin Bay. Number of schools/pods and number of individuals sighted are given for each species. Three bottlenose dolphin sightings, detected close to shore while off transect, were also added to the coastal survey counts.

Cetacean species sighted Number of schools/pods Total number of sighted individuals (direct Line- Coast Total count or best transec al number of estimate) t survey survey sightings s

Short-beaked common 59 12 71 722 dolphin (Delphinus delphis)

Southern Australian 6 8 14 107 bottlenose dolphin (Tursiops cf. australis)

Dolphin species uncertain 6 3 9 25

Southern right whale 2 1 3 7 (Eubalaena australis)

Humpback whale 1 1 2 3 (Megaptera novaeangliae)

Minke whale (Balaenoptera 1 0 1 1 sp.) Whale species uncertain 1 0 1 1

Table 2. Summary data for 19 focal follows of schools of short-beaked common dolphins off southern Australia using a helicopter. For each school sighing the table shows the focal follow number, species ID, school size, behaviour, reaction to helicopter, time followed, time visible and % visible from the helicopter, and g(0) for each follow. The bottom line shows the total time schools were followed, the total time schools were visible from the helicopter, and the average g(0) across the 19 focal follows including standard error (SE).

Focal Species ID School Behaviour Reaction Time Sum % Visible/ g(0) follow size to followed visible focal follow Helicopter hh:mm:ss hh:mm:ss

1 Common 40 Feeding None 0:10:30 0:10:30 100.00 1.00 dolphin 2 Common 15 Travelling None 0:10:33 0:10:33 100.00 1.00 dolphin 3 Common 8 Milling None 0:10:21 0:09:11 88.75 0.89 dolphin 4 Common 15 Travelling None 0:10:35 0:10:04 96.11 0.96 dolphin 5 Common 22 Travelling None 0:10:07 0:10:07 100.00 1.00 dolphin 6 Common 33 Travelling Mild 0:10:27 0:10:27 100.00 1.00 dolphin 7 Common 18 Feeding None 0:10:15 0:09:23 91.57 0.92 dolphin 8 Common 19 Feeding None 0:10:06 0:09:32 94.41 0.94 dolphin 9 Common 5 Travelling None 0:10:07 0:09:15 91.46 0.91 dolphin 10 Common 4 Travelling None 0:10:19 0:07:25 71.90 0.72 dolphin 11 Common 25 Feeding None 0:10:14 0:10:14 100.00 1.00 dolphin 12 Common 20 Travelling None 0:10:18 0:09:59 96.91 0.97 dolphin 13 Common 11 Feeding Mild 0:10:30 0:10:08 96.51 0.97 dolphin 14 Common 18 Travelling Mild 0:10:36 0:10:36 100.00 1.00 dolphin 15 Common 50 Travelling None 0:11:01 0:10:24 94.39 0.94 dolphin 16 Common 6 Travelling None 0:11:35 0:10:51 93.68 0.94 dolphin 17 Common 25 Feeding None 0:10:59 0:10:59 100.00 1.00 dolphin 18 Common 25 Travelling None 0:10:13 0:10:13 100.00 1.00 dolphin 19 Common 2 Feeding None 0:15:38 0:09:55 63.43 0.63 dolphin

TOTAL Common 3:24:24 3:09:46 Average g(0) Dolphin 0.94 Standard Error 0.02