2. Biodiversity

An estimated 18 species of dolphin occur in the Region. Dolphins are important top‑level predators that feed on a variety of fish, crustaceans, shellfish and squid. Dolphins can concentrate contaminants in their tissues; high levels of contaminants can be an indication of ecosystem stress. Economically, dolphins are important to tourism and recreational users as iconic marine megafauna. Dolphins are also deeply significant to the culture of many Traditional Owners communities with cooperative fishing having been geographically widespread in eastern Australia 510 and rock paintings of dolphins found across northern Australia.⁵¹¹ Two species of dolphin are culturally significant for the Mandubarra Traditional Owners as indicators for assessing Sea Country health.⁷⁶

Four dolphin species are known to reside in the Region year-round. The spinner dolphin is found from the coast to the eastern boundary of the Region. The other 3 species, the Australian snubfin dolphin, Australian humpback dolphin, and the Indo-Pacific bottlenose dolphin, inhabit inshore waters. Another 14 species are occasionally sighted in the outer waters of the Reef. Data for these species and the extent to which they are resident within the Region are limited. All dolphin species within the Region are protected by legislation.

There are no Region-wide abundance assessments for Australian humpback and snubfin dolphins, and estimates for discrete populations show they occur in generally low numbers (less than 150 individuals) at low densities.⁵¹² Population sizes of bottlenose and spinner dolphins in Great Barrier Reef waters are unknown and no trend data exist for any of the 4 coastal dolphin species. 

All 4 resident dolphin species are long lived (multiple decades). They have low reproductive rates (single calf and long intervals between births) and are late to reach sexual maturity (approximately a decade).^512,513 These characteristics make individual populations particularly vulnerable to threats causing mortality, such as drowning due to entanglement.⁵¹⁴ All shark control nets have been removed from the Marine Park, while ¹³¹ drumlines are allowed under permit. Gillnet fishing will be phased out by 2027. Eight strandings of dolphins have been reported in the past 5 years, the majority found washed up on beaches.⁴⁶¹ 

Anthropogenic activities vary widely across the Queensland coastline, resulting in a broad range of potential stressors for coastal species. The main stressors include habitat loss and degradation through disturbances from boating activities, underwater noise and an increase in the severity of extreme weather events (for example, cyclones and floods) caused by climate change. As port development and floods are expected to increase along the Queensland coastline over the coming decades, concerns about the vulnerability of inshore dolphins are increasing.⁵¹⁵ Offshore dolphin species are less likely to be exposed to nearshore threats but remain vulnerable to anthropogenic climate change. 

Overall, due to multiple and cumulative threats, populations of some dolphin species within the Region are inferred to have continued deteriorating since 2019.