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Seminar 27 June

SARDI SEMINAR SERIES 2013

Date:        Thursday 27 June
Time:        1pm
Duration:   ~ 30 mins
Location:   Lecture Theatre, SARDI Aquatic Sciences Centre, 2 Hamra Ave, West Beach
Catering:   lunch to follow
Speaker:    Dr Shane Roberts, PIRSA Fisheries and Aquaculture

 

South Australian marine mortalities, summer 2013: an overview

Roberts SD1, Bastianello SB2, Pyecroft S4, Wilkinson C2, Van Ruth P3 and Neverauskas V2

1Primary Industries and Regions SA, Fisheries and Aquaculture, Adelaide, SA 5000
2Primary Industries and Regions SA, Biosecurity SA, Glenside, SA 5065
3South Australian Research & Development Institute, Aquatic Sciences, West Beach, SA 5024
4University of Adelaide, School of Animal & Veterinary Science, Roseworthy Campus, SA 5371 


Abstract:

South Australia experienced an ongoing and widespread marine mortality event during the summer of 2013. Large numbers of dead fish in Spencer Gulf were reported on 3 March 2013. Over the next 2 months, numerous more reports were phoned in (FISHWATCH hotline) from across the State. These included fish (mostly small-bodied benthic species) and abalone kills, over 30 dead dolphins, large amounts of dead seagrass / macro-algae and species observed outside their normal range (e.g. a leatherback turtle).

An investigation was initiated at the first fish kill report, with data suggesting that the unusually high, fluctuating, water temperatures and evidence of elevated harmful algae concentrations were the likely cause. A similar ‘marine heat wave’ event was reported off Western Australia during 2010/11 (Pearce et al, 2011). However, public and media speculation fuelled conspiracy theories including desalination plants, underwater volcanoes to Fukushima nuclear radiation. An inter-governmental ‘task force’ was subsequently formed to ensure the separate investigations (fish, abalone, dolphin & water quality) were coordinated and appropriately resourced. 

Fish pathology and diagnostic examinations demonstrated prolonged stress (melanomacrophage aggregation in spleens and kidneys) and physical gill damage (proliferative branchitis, focal gill lesions, mucous cell hyperplasia and haemorrhagic inflammation). These pathologies would have impeded respiratory physiology of fish, compromised the immune system ultimately exposing some (weaker) fish to the observed terminal bacterial septicaemia. Pathology was mostly unremarkable in the abalone examined but pedal abscesses associated with bacterial infection was observed in some abalone. To date, there has been no evidence of exotic infectious diseases in either the fish or abalone examined. Diver and underwater video observations found that only a small percent of fish populations were affected.

The unusually high, and variable, water temperature (3-5°C above the historic average), was likely the primary factor in this marine mortality event. The plume of warm water across the State (satellite imagery) corresponded with the kill locations. Harmful (abrasive) algae (Chaetoceros coarctatus) were observed in water samples and likely contributed to fish mortalities. A separate investigation (Biosecurity SA and Department of Environment, Water & Natural Resources) into dolphin mortalities determined a morbillivirus outbreak as the underlying cause of mortality.