Dolphin jumping

Bottlenose Dolphins of the St. Johns River

This post has been curated in conjunction with the “Highlights” section of the 2018 St. Johns River Report bringing attention to bottlenose dolphin (Tursiops truncates) inhabitants of the St. Johns River. Bottlenose dolphins utilize areas of the St. Johns River from the mouth to further upriver, going up to 35 miles away. Unfortunately, as human presence increases along the St. Johns River, we bring forth an elevated threat to these creatures, with anthropogenic pollution becoming a major focus as of late. As a marine mammal, bottlenose dolphins can be considered a bioindicator for anthropogenic toxins given their longer life span and ability to accumulate these toxins in their fat stores((Bossart G.D. 2006. Marine mammals as sentinel species for oceans and human health. Oceanography. 19(2): 134-137)). Harmful algal blooms that are caused by anthropogenic pollutants such as excess nitrates and phosphorus have been found to contribute to Unusual Mortality Events (UMEs) regarding bottlenose dolphins in the St. Johns River.

Excess growth of algae, otherwise known as eutrophication, can be triggered by an increase in inorganic nutrients in aquatic systems, as well as an increase in surface water temperature, light intensity, and susceptibility to grazers((Bukaveckas P., Franklin R., Tassone S., Trache B., Egerton T. 2018. Cyanobacteria and cyanotoxins at the river-estuarine transition. Harmful Algae. 76(2018): 11-21)). Some species of Blue-green algae, or cyanobacteria, have been found to possess cyanotoxins, further affecting aquatic wildlife and humans. Common toxins produced by these algae are microcystins and nodularins (MC/NODs). These are hepatoxic cyanotoxins that can be related to health issues in mammals such as dermatitis, immune system impairment, and respiratory issues. More recently, a study found that lesions on a stranded resident of the St. Johns River contained algal mat growth and presence of MC/NODs in liver tissue via the MMPB technique, which is used to detect free-forms of these toxins((Brown A., Foss A., Miller M.A., Gibson Q. 2018. Detection of cyanotoxins (microcystins/nodularins) in livers from estuarine and coastal bottlenose dolphins (Tursiops truncatus) from Northeast Florida. Harmful Algae. 76(2018): 22-34)).

Dolphin with skin lesions

So how can we help these aquatic mammals? The presence of bottlenose dolphins in the St. Johns River, as well as other aquatic creatures, is dependent upon our treatment of the River. We must work to reduce the amount of pollution that occurs in our River, whether it be trash that finds its way into the River via various tributaries, or nutrient pollution from inorganic fertilizers and agricultural runoff. Additionally, we must refrain from too much human contact and harmful interactions of the dolphins with debris, fishing line, and boat traffic in the St. Johns River. By protecting and investing in the health of our River, we in turn protect its inhabitants for the years to come. Learn more about this sentinel species in the St. Johns River, and other factors affecting the health of the river, by visiting the State of the River Report website.

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