2. Biodiversity

Sea snakes, although the most diverse group of marine reptiles, have received relatively little scientific attention.⁴²⁷ There are two groups of sea snakes: the amphibious sea kraits and the marine ‘true’ sea snakes.⁴²⁷ True sea snakes produce live young and are entirely marine, never venturing onto land. Offshore marine species retain traits from their terrestrial ancestors, such as needing to drink fresh water obtained from lenses that form on the surface of the ocean after rainfall.^428,429 Sea snakes are important ecologically as predators and have been used as bio-indicators for cryptic species of fish.⁴²⁷

The Region forms part of a global hotspot of sea snake diversity that encompasses northern Australia and the Indonesian–Malaysian archipelago. Sixteen species of true sea snakes have been recorded in the Region, and 14 maintain permanent breeding populations.⁴³⁰ Most are benthic foraging species, but different species are associated with different habitats.⁴³¹ The highest density and diversity of sea snakes are found in the central and southern Reef, and species like the olive sea snake and spine-bellied sea snake are commonly recorded in inshore bays and fringing reefs along the Queensland coast.⁴²⁷

Sea snakes have a low reproductive output and limited dispersal capability limiting their potential for population recovery and recolonisation when populations are affected.^432,433 Studies on sea snake movements on the Reef have shown that some species are highly attached to specific reefs, for example, olive sea snakes ⁴²⁷ and turtle-headed sea snakes ⁴³⁴ do not venture far from their home reef. During the mating season, males increase their movements to find females on the same reef, and seasonal aggregations of sea snakes are often observed in areas with large populations.⁴²⁷ The limited capability of sea snakes to disperse between reefs can result in highly fragmented populations ⁴³⁵ such as found in the Swain Reefs and Pompey Reef complex in the southern region.⁴²⁷

Long-term population trend data are severely limited. Densities of sea snakes at Marion Reef, east of Airlie Beach, declined by more than 80 per cent between 2012 and 2017,⁴³⁶ whereas populations in other areas (for example, Cleveland Bay) are considered stable.⁴²⁷ The extent and underlying causes of population declines remain uncertain. Most species of sea snakes are considered to be at medium risk from interactions with trawl fisheries in Queensland, and bycatch mitigation strategies to quantify and reduce mortalities are being advanced in collaboration with industry.⁴³⁷ 

Despite reported declines in some locations, the lack of systematic population monitoring means the status of sea snakes in the Region remains uncertain. Based on the limited available evidence, the condition of sea snakes in the Region is inferred to be stable.