Habitat Mapping

1
Habitat Mapping
2
Historical Fisheries Surveys

• Little knowledge of habitat types prior to
  surveys
• Random (or systematic grid) selection of survey
  sites
• Habitat-based surveys now a possibility

3
Heceta Bank ExampleNasby-Lucas et al.

• Habitat mapping using multibeam sonar
• Ground-truthing and fish counts using a
  submersible
• Establish fish density-habitat relationships
• Estimate fish abundance using habitat types as
  strata

4
Multibeam sonar

• Several (often 50-127) receiving beams
• High (3 degree) resolution along-ship
• Depth resolution 1 of water depth
• Lateral resolution 5-10 of water depth
• swath width about 4X water depth in shallow
  water
• Enables complete coverage of bottom (mowing the
  lawn)

5
(No Transcript)
6
Sonar Output

• Bathymetry (precise)
• Backscatter strength (guess at habitat type)
• Georeferenced using GPS
• Results in grids with a resolution of 5-10m

7
Submersible

• Two-man Delta (little yellow submarine
• Old positioning and georeferencing (Loran )
• Groundtruth sonar habitat classifications
• Count fish in a 2.3m wide transect
• direct observation
• video camera record

8
Fish Counts

• Species ID often difficult
• Fish must be near-bottom
• Avoidance?
• Attraction?
• gear bias a problem with any survey gear

9
ArcInfo/ArcView

• Dynamic segmentation using route
• Allowed linkage of submersible and sonar data
• Allowed identification of 8 habitat patches

10
(No Transcript)
11
Heceta-Clear Habitat Preferences

• Yellowtail rockfish, juvenile rockfish and
  lingcod on rock-ridge habitat
• Dover sole, rex sole and thornyhead on mud (weak
  backscatter)
• Sharpchin,rosethorn,greenspotted on mixed
  habitat (pebble, cobble,boulder--strong
  backscatter)

12
(No Transcript)
13
Heceta Bank-Conclusions

• Habitat types distinguishable using sonar,
  followed by groundtruthing
• Fish density observations from submersible
  extrapolated (by habitat strata) far more
  accurate than random sampling of entire bank
• Pilot project, but shows great potential
• Similar methodology in San Juans (Lab)