Assessing techniques for estimating the extent of mangroves: topographic maps, aerial photographs and Landsat TM images

Coastal habitats are critical to the sustained production of many fisheries . It is important, therefore, that fishery managers obtain accurate estimat es of the extent of these habitats. This study investigated three methods o f estimating the linear extent and area of mangroves ( commercially availab le topographic data, aerial photographs and Landsat Thematic Mapper satelli te imagery) in two regions in northern Australia: the Joseph Bonaparte Gulf ( in particular, the Berkeley and Lyne Rivers) with typically narrow fring es of mangroves (<50 m wide), and the Embley River on Cape York Peninsula, with much broader mangrove stands (50-1000 m wide). Ground-truthing verifie d that aerial photographs provided the most accurate estimates of extents o f mangroves in all rivers, because of their high spatial resolution (2 m). Landsat Thematic Mapper imagery gave good estimates of the area of habitats , but, because of the 30 m pixel resolution, it underestimated the linear e xtent in places where the mangrove fringe was narrow. Topographic data gave good estimates of the extent of mangroves where the forests were more exte nsive and less linear in shape, but were very poor otherwise at this scale. These findings have implications for the use of remote sensing techniques in ecological studies in these regions.