Species Distribution Mapping

Using our DGPS-positioned, towed video camera, we collect imagery of the seabed along a series of transects. Shown below is a typical series of video transects for a survey site.

An example of video transect lines.
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The georeferenced benthic videos are annotated, and all observational data are entered into a database. The observations for both flora and fauna species can then be mapped as a series of points in a GIS program. The image below shows an example of data for a single species plotted on a map.

Species point data.
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Range maps for flora and fauna are generated using the fixed kernel density estimation procedure.

• Definition: The kernel density estimation procedure is a way of estimating the probability density function of the species' distribution. As an illustration, given data about the location and abundance of some individuals of a population, kernel density estimation makes it possible to extrapolate the entire geographical range of the population.
• Definition: A probability density function is a statistical function that shows how the individuals in a population are distributed. It represents the probability of finding an animal within a defined area.

Observations are weighted by abundance (or coverage). For each organism, a 95% volume contour is generated (see below). This consists of a polygon covering a geographical area in which 95% of the estimated population is expected to be found.

95% volume contour.
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Another method of representing the distribution of a species is to use a density map. This map has the darkest shading where species' density is highest. Percent volume contours can be overlaid on the density map to show where the estimated population levels are expected to be found (see image below).

Species distribution map.
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