There have been no range-wide population estimates made for the weedy seadragon and further research and monitoring are needed to determine population size and trends.
To date, there has been no range-wide population estimates made for the weedy seadragon, but several local studies have occurred. Further research and monitoring are needed in order to determine population size and trends in abundance for this species.
One study conducted at five sites near Sydney and Hobart from 2001-2007 and 2003-2004, respectively, found densities of 10 to 70 animals per hectare, with significant declines at three of the five sites. These declines however were not directly attributable to anthropogenic causes, but it is likely given that pollution and invasive species are of concern in the area. Further research is needed to quantify human impacts on the species and to tease them apart from natural cycles and disease outbreaks.
In South Australia, a possible contraction in area of occupancy has been mentioned. Historical records exist from benthic surveys in Gulf St. Vincent in the 1965–1971 period, where reportedly “numerous weedies were observed” in northern Gulf St. Vincent, adjacent to the city of Adelaide. No sightings in this area have been reported to Dragon Search during the late 1990s and early 2000s.
Admittedly the lack of recent sightings might be due to the lack of popular diving spots in the northern gulf, and the lack of systematic surveys in recent years. However, the occurrence of seadragons might have been affected by significant habitat degradation and loss recorded since the 1960s in this part of the gulf. In particular, large areas of seagrass have been lost in waters deeper than 10 meters south of a line between Ardrossan and Port Prime.