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Dolphin Research Update-10 year report

Dolphin Scientists, Chandra Salgado Kent and Delphine Chabanne have released a new research paper, combining 10 years of Dolphin Watch citizen science reports with scientific vessel surveys.

The aim of this study was to undertake a comparative analysis of spatial and temporal patterns of Indo-Pacific bottlenose dolphin (Tursiops aduncus) sighted in the Swan Canning Riverpark (Western Australia) collected from two survey modes (citizen science and scientific vessel surveys); and thereby inform management directly and plan for ongoing future monitoring. You can read a summary of the findings here or access the full paper here

 

Research into the Dolphins of the Peel-Harvey Estuary

Some exciting new research into Indo-pacific bottlenose dolphins in teh Peel-Harvey Estuary and adjacent coastal waters. 

Niche partitioning among social clusters of a resident estuarine apex predator (Prepared by Dr Krista Nicholson)

This study identified intra-population resource partitioning according to social structure in a resident estuarine dolphin population. The heterogeneity in space use and diet among social clusters may result in individuals being susceptible to different pressures and threats. The dolphins’ foraging behavior and trophic interactions identified them as an apex predator in the Peel-Harvey Estuary, with their collective minimum annual food intake (~ 200,000 kg) exceeding the annual fish biomass removed by commercial fishers. As top predators in the system, dolphins may suppress prey populations through consumption and as agents of intimidation by changing prey distribution and behavior. This study provides scientific basis for recognizing dolphins as an important component of the Peel-Harvey Estuary ecosystem.

Algae update for the Swan River

The Department of Biodiversity, Conservation and Attractions (DBCA) advises that elevated levels of algae have been detected in the Swan and Canning rivers. The algae can provide reddish-brown water discolouration and could influence fish kills upstream of Maylands to Middle Swan in the Swan River.

Elevated algae levels have also been detected in the Canning River from Shelley Bridge to Kent Street Weir. This algae can produce toxins that can impact fish by damaging their gills and in severe cases, may cause fish deaths. Blooms of this algae can also make river water appear a reddish-brown colour.

The long weekend weather forecast of hot weather and light winds could assist these algal blooms to grow. DBCA officers are continuing to monitor the blooms and will keep our key Riverpark stakeholders updated.

Information from members of the public is welcome. Anyone who sees dead or sluggish fish in the Swan and Canning rivers are asked to report this to FishWatch on 1800 815 507 and avoid swimming in that area.

The public is also advised to not collect dead fish and to prevent their dogs from consuming dead animals that may appear along the river foreshore.

Fantastic news for Fairy Terns

Some great news has arrived from Point Walter Spit. The vulnerable Fairy Tern which uses this habitat for nesting has recorded an estimated 150 nests with eggs or small chicks for this breeding season.

These migratory birds build their nests on the beach, leaving them exposed to disturbances such as humans and predators. If the birds are disturbed frequently, they may abandon their nests, resulting in nest failure. With the help and support from Department of Biodiversity, Conservation and Attractions and the City of Melville, several conservation management actions have improved nesting and breeding success, leading to a record number of breeding pairs being recorded at Point Walter Spit this season.

The breeding season is still in full swing, so please continue to avoid the spit for the next few months, to keep the area a safe habitat for these nesting birds.

Dolphin populations likely to be impacted by climate change

Freshwater Skin Disease (FWSD) is due to the detrimental effects of freshwater exposure in coastal bottlenose dolphins, and is an emerging cause of morbidity and mortality in many regions. We, for the 1st time, provide a case definition of this disease entity based on two Australian mortality events. The 1st affected Burrunan dolphins (Tursiops australis) in Victoria’s Gippsland Lakes in 2007 (a similar event is currently unfolding - see https://www.abc.net.au/.../burrunan-dolphin.../12900270). The 2nd event occurred in 2009 and affected the resident Indo-Pacific bottlenose dolphins (T. aduncus) in WA's Swan-Canning Riverpark. Simultaneously with the Gippsland Lakes event, the first outbreak of FWSD in US waters was recorded for common bottlenose dolphins (T. truncatus) entrapped in Lake Pontchartrain, Louisiana, USA, following Hurricane Katrina in 2007. However, the dermatopathology was not described for the US event, as post-mortem examinations were not conducted.

By contrast, the Australian events occurred where the resident populations were well documented by long-term and ongoing field ecology, population, and behaviour studies (including Citizen Science projects e.g. WA's River Guardians and Dolphin Watch programs); the waters inhabited by the dolphins were intensively monitored for physical and chemical parameters before, during and after the events; and when mortalities occurred, thorough and systematic post-mortem examinations were carried out. Based on these data, FWSD occurs when there is a sudden (over days) and precipitous (>25ppt to <5ppt) decrease in salinity, persisting for weeks to months. The skin lesions initially appear as patchy pale areas that progress to raised targetoid areas of ulceration and opportunistic colonisation by algae, diatoms, fungi and bacteria. In our paper we detail the gross and histological appearance of the characteristic skin lesions of FWSD. Death may ensue from fluid loss and electrolyte imbalance - because the ulcerative skin lesions are akin to severe third degree burns and often affect a large % of the body surface.

In Australia, the outbreaks followed resumption of seasonal rainfall following a prolonged drought that flooded the Gippsland Lakes (normally brackish to marine saline) with fresh water. In WA, unusually high winter-spring rainfall in the river catchments similarly turned a normally marine/brackish habitat to freshwater. In the Gulf of Mexico, USA, events have followed the heavy rainfall and storm surges in the aftermaths of Hurricanes Katrina and Harvey. Common to all events is a preceding extreme weather event - which are predicted to increase in frequency and severity with Climate Change. Therefore, FWSD is an emerging disease of cetaceans which we are likely to see increasing in frequency in vulnerable estuarine and coastal habitats that continue to be affected by worsening Climate Change.

The research paper is titled ‘Fresh water skin disease in dolphins: a case definition based on pathology and environmental factors in Australia’ published in Nature Scientific Reports. Read the full paper here.

Photo: Case 3 from the paper, a dolphin from Perth’s Swan-Canning Riverpark that died in 2009 (photo credit – Douglas Coughran, AM, DBCA)