Folklore

Table 7 reviews information on mortalities that were recorded within the Swan-Canning Riverpark from 2002-2008, and Figures 25-30 provide images for some of the mortalities. There were six mortalities recorded during this period, suggesting a stranding rate for carcasses of approximately one per year. This estimate is unlikely to reflect actual rates of mortality for several reasons. Firstly, dolphins resident in the Swan Canning Riverpark also range outside of the estuary, indicating that at least some deaths will occur in coastal areas, and carcasses of these animals may, for various reasons

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(e.g. drift, submersion, predation or scavenging by sharks), not be recovered or recorded. Secondly, mortality records are available for only a limited period of time and are somewhat limited by the opportunistic manner in which data were collected and carcasses recorded and recovered. Finally, there has been monitoring of dolphins within the Swan Canning Riverpark since 2003. Where continuous long-term studies occur rates of mortality can be estimated from the rate of disappearance for know individuals, i.e. when a known individual is not re-sighted for an extended period of time, this individual can be presumed to have died.

However, while this stranding rate has limitations, it does provide a baseline against which the 2009 mortalities can be compared, and indicates that the number and timing of mortalities in 2009 is anomalous, i.e. six deaths within five months, with three deaths of these deaths within three weeks of each other (5 June to 21 June 2009) and three other deaths within five weeks of each other (17 September to 25 October 2009).66As discussed in Section II (Introduction), the stranding data support the conclusion that the 2009 deaths constitute an unusual mortality event as defined by criteria developed to support the U.S. Marine Mammal Protection Act 1972.

Most of the records of dolphin mortalities in the Swan Canning Riverpark prior to 2009 contain little supporting information. Carcasses were also often recorded as being in an advanced state of decomposition. Four of the six recorded deaths (i.e. observations of stranded carcass) occurred in the October-November period. Post-mortem examination was undertaken in one instance (18 November 2007) and findings from that examination are reviewed in context with the 2009 mortalities (see below).

Two dolphins that died between 2002-8 exhibited skin lesions based on: (a) a single photographic image available (October 2003; Figure 25) and (b) photographic images and post-mortem examination (18 November 2007; Figure 26). The presence of these lesions and the timing of the two deaths (i.e. in October and November) suggest aetiologies potentially similar to that of the two adult females that died on 17 September and 25 October 2009. Although difficult to confirm from the image, Figure 25 suggests severe ulcerative-type lesions similar to those observed in the two 2009 females (but with much less of the body surface area affected). The carcass of the October 2003 mortality was recovered near Ascot, suggesting a possible association with use of the upper reaches of the Swan River, which tend to have brackish salinities during the winter-spring period. The female that died on 25 October 2009 was also observed near Ascot on 3 October 2009 with skin lesions present (Figure 28).

The presentation of the 18 November 2007 dolphin had certain commonalities with the two females that died on 17 September and 25 October 2009, particularly the presence of poxvirus-induced skin lesions. However, this individual did not have the extensive pattern of severe ulcerative skin lesions

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covering much of the body surface as was observed in the deaths of the two 2009 females. These commonalties and differences are discussed further below and in Section VI (Pathology).

Figures 27a and 27b are images of a dolphin mortality along the eastern shoreline of Freshwater Bay taken around 16 April 2006 (R. McCauley, Curtin University, personal communication). Images of the dorsal fin indicate that this dolphin is ‘Middy’, an adult male considered resident in the Swan Canning Riverpark from 2001-3. This appears to be the dolphin classified as the 7 October 2006 mortality in the November 2009 Situation Report on the dolphin mortalities in the Swan Canning Riverpark.67 The carcass was recorded as being in an advanced state of decomposition upon recovery at Freshwater Bay in October, but appears recently deceased (i.e. minimally decomposed) in the April images. The images indicate that the animal was in poor body condition (i.e. emaciated) and show a large abrasion-type wound along the dorsal surface anterior to the dorsal fin (i.e. a ‘degloving’ injury involving avulsion of the skin from the underlying tissue). This injury is indicative of being struck with (or grazed by) a broad sharp object, and may constitute an example of human-induced injury. However, this dolphin also had a shark attack wound on its ventrum (there are no images of the shark attack wound), and we cannot ascertain whether the degloving injury occurred prior or subsequent to the shark attack, or whether it may have occurred as a post-mortem event. Views of the genital region confirm the dolphin as a male, and the size and intensity of ventral speckling indicate that the animal was an adult.68

C. 2009 dolphin mortalities in the Swan Canning Riverpark

Appendix A5 contains the full post-mortem reports for the 2009 dolphin mortalities in the Swan Canning Riverpark, as well as findings from post-mortem analyses conducted for the 18 November 2007 mortality. A summary of this information is given below and represents a synopsis of the most significant findings. Section VI (Pathology) provides a more-detailed discussion of the pathology findings. The extent of post mortem decomposition/autolysis is represented by a ‘carcass condition code’ (as outlined by Pugliares et al. 2007).69 Figures 28-30 provide images of these dolphins (see also post-mortem reports in Appendix A5).

Six bottlenose dolphin deaths occurred within the Swan Canning Riverpark in 2009. The mortalities occurred in two clusters: (a) three deaths in June 2009 and (b) three deaths in September-October 2009. These deaths involved: two adult females [17 September, 25 October]; one adult male [9 October]; one male calf [5 June]; one juvenile male [8 June]; and one sub-adult/adult female [21 June]. Two of the dolphins [5 June and 9 October] were in an advanced state of decomposition at the time of recovery, and no post-mortem examinations were conducted. Post-mortem examinations were conducted for the other four dolphins. Additional analyses were also undertaken, including analyses to determine the

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concentrations of certain contaminants within dolphin tissue samples. Certain analyses have yet to be completed, in particular those involving viral pathogens. Post-mortem findings from the 18 November 2007 mortality were also considered.

Synopsis of post-mortem examinations of dolphins from Swan Canning Riverpark

2007

18 November Post-mortem at Perth Zoo Case No: AS-07-3710 Carcass condition code = 2 (fresh)

Adult lactating female in good body condition. Recovered by DEC at Bicton Baths.

Description

Numerous skin lesions present; the majority of the lesions were non-ulcerative, however some bordered a focally extensive ulcerative lesion immediately caudal to the blowhole.

Intracytoplasmic viral inclusion bodies detected in keratinocytes (skin cells of the outer epidermal layer), indicative of poxvirus infection (TSD).70

Lymphoid depletion noted histologically with fibrosis and calcification of the mesenteric lymph node chain, indicative of chronic exhaustion secondary to chronic inflammation.

2009 – June cluster

5 June MUVS Pathology No: 09/663

Carcass condition code = 3 (moderate decomposition) Male calf in good body condition.

Was observed dead on days previous with mother attempting to support the carcass.

Recovered by Swan River Trust in lower reaches.

Post-mortem analysis severely limited by advanced state of decomposition. Preliminary analyses of dental layering suggest a minimum age of 5 years.71

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8 June MUVS Pathology No: 09/637

Carcass condition code = 2-3 (fresh to moderate decomposition) Male juvenile in good body condition.

Recovered by Swan River Trust in lower reaches.

Preliminary analyses of dental layering suggest a minimum age of 3+ years.

Description

Fungal meningoencephalitis with intralesional fungal organisms consistent with

Aspergillus spp. (fungal infection of the brain).

Segmental jejunal (small intestinal) infarction likely secondary to spread of

Aspergillus within the bloodstream.72

Lymphoid depletion noted histologically.

21 June MUVS Pathology No: 09/664 Carcass condition code = 2 (fresh)

Female sub-adult/adult in good body condition.73

Recovered by Swan River Trust and Department of Transport (Marine Safety) near Ascot.

Preliminary analyses of dental layering suggest a minimum age of 16 years.

Description

Human induced injury: severe chronic fishing line entanglement of the right fluke.

Bronchopneumonia with intralesional fungi consistent with Aspergillus spp. (in addition to this, two types of opportunistic bacterial pathogens found on lung culture).

Kidney infection [one type of opportunistic bacterial pathogen found on kidney culture—identical to one of the two identified on lung culture, indicative of systemic haematogenous (via bloodstream) spread].

Lymphoid depletion noted histologically.

Septicaemia likely.

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2009 – September-October cluster

17 September Post-mortem at Perth Zoo Case No: AS-09-2912-F-V1 Carcass condition code = 2 (fresh)

Adult female in reasonable condition. Recovered by DEC south of Windan Bridge.74

Description

Numerous, extensive ulcerative skin lesions with intralesional opportunistic bacterial and fungal organisms noted histologically.

Intracytoplasmic viral inclusion bodies detected in keratinocytes, indicative of poxvirus infection (TSD).

9 October Adult male in good body condition.

Carcass condition code = 4 (advanced decomposition) Too decomposed to carry out post-mortem analysis. Recovered by Swan River Trust at Freshwater Bay.

25 October MUVS Pathology No: 09/1108 (‘Leeuwin’) Carcass condition code = 1 (fresh)

Aged female in poor body condition.

This animal identified as a known Swan resident from 2001-3. Died under observation at Waylen Bay (near Heathcote).

Was swimming abnormally before becoming stranded on the beach and dying. Recovered by Murdoch University, Curtin University, and Swan River Trust.

Description

Numerous, extensive ulcerative skin lesions with intralesional opportunistic bacterial and fungal organisms noted histologically.

Intracytoplasmic viral inclusion bodies detected in keratinocytes, indicating poxvirus infection (TSD).

Evidence of acute (recent) human induced injury – fishhook lodged in oesophagus, minor entanglement with minimal tissue laceration of the right pectoral fin.75

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