Density_weight

The species of any one region has the following key property:

wS = Expected weight of an individual specimen of species S (kg)

This property can be seen on the Region Class Properties dialog box and defined using the Species Properties dialog box.

Then:

Where:

= Volumetric fish density in the region (kg/m3).
= Areal fish density in the region (kg/m2).
= Volumetric fish density in the region (fish/m3). See Density_number for method of calculation.
= Areal fish density in the region (fish/m2). See Density_number for method of calculation.

Note: Unit conversions for exported variables may be required when they are used in generic biomass algorithms.

Single beam vs. Multibeam

Echoview provides access to these results in different ways depending upon the type of analysis as follows:

Single beam data	Density_weight = ρwaS Units of kg/nmi2or kg/hectare are used (as specified in the Biomass area units box on the Export page of the EV File Properties dialog box) You must choose to export Density_weight on the Export page of the EV File Properties dialog box, or it will not be exported.
Multibeam data	Density_weight = ρwvS Units of kg/m3are used (as calculated above) Density_weight is always exported with analyses.

Density_weight calculation warning

In Echoview version 3.10 and 3.00 Density_number was calculated using pS to apportion the mean sv (rather than the specimen count) among the species. Version 3.20 and onwards correctly apportion the specimen count among the species defined. If you have used the Density_weight (or Density_number) variable in Echoview 3.10 or 3.00 your analysis results will differ in 3.20 and later. You must redefine pS (Proportion of fish of this species for region class on the Species Allocation dialog box).

Density_weight

Single beam vs. Multibeam

Density_weight calculation warning

See also