Sidescaner Trace

Conclusion

Citations

Introduction

Methods & Materials

Notes

FALMOUTH BENTHIC HABITAT MAP

Using Sidescan and Video Data Transects

Conditions

Date:

Time:

Location:

Latitude:

Longitude:

Wind Speed:

Sea State:

Cloud Cover:

Vessel:

High water:

Low water:

26/06/13

8:54 GMT

Pendennis Point

50˚08’541N

005˚02’532W

2

Calm

2/8

Viking

07:15 GMT

14:10 GMT

Introduction to the Geophysics practical

The aim of the Geophysics practical was to create a habitat map by combining multiple layers of information. Habitat maps are necessary to provide a greater knowledge of the sea bed and, in particular, areas in need of protection. This is important as conservation and management schemes require an understanding of the marine habitats in the area in which they are working. The Fal Estuary is a good example of an area in need of a detailed habitat map for multiple industries to refer to. Grab samples could not be taken due to new legislation.

Equipment used:

1. Sidescan Sonar

2. Video

Poster (Click)

Kelp covered Rock

The areas identified as rock from the sidescan showed strong backscatter and shadowing with a height range of 0.78m to 5.68m. These values are greater than that of ripples.  The video showed kelp in boundaries A, E and F. The holdfast of Kelp requires a hard substrate to anchor itself confirming rock as the bedform.

Mixed Sediments

The majority of the surveyed area was identified using a sidescan and video output, as mixed sand and coarse gravels. An Admiralty Chart of Pendennis Point was used as confirmation.

Citations:

[1] Hall-Spencer, J. 2005. Ban on Maerl extraction. Marine Pollution Bulletin. 50, 121.

[2] Langston, W. J. et al. 2006. Characterisation of the European Marine Sites in South West England: The Fal and Helford Candidate Special Area of Conservation (cSAC). Hydrobiologia 555, 321–333.

[3] Deeble, M. & Stone, V. 2009. A port that could threaten marine life in England’s Fal Estuary. Oryx 19, 74.

Notes

Small sections of the seabed were not sampled due to the research vessel drifting off course during the transects (see key)

Conclusion:

In conclusion, various mapping techniques and external references (Admiralty charts), have allowed for an assessment of the bedforms around Pendennis Point. It was established that the surveyed area showed a combination of hard substrata with kelp interactions (A, B, C, E, F and G), mixed sediment (D and H) and coarse mixed sands and gravels.

Introduction:

The Fal estuary is a site of ecological importance due to the high diversity of habitats, including maerl beds[1] and eel grasses and as such is a  Special Area of Conservation (SAC)[2]. Due to this conflicting views have risen with regards to dredging plans and recent restrictions have been put in place on boat anchorages and certain scientific surveying methods. A habitat map is required to identify the areas suitable for dredging and to prevent further destruction of important habitats[3].

Materials and Methods:

• A suitable survey area was located using Admiralty charts.
• Sidescan sonar was used to create an acoustic oblique image of the seafloor, the frequencies used were 100kHz and 415kHz. Video recording equipment was towed behind the boat. Together, these were used to characterise the main bedforms and physical habitats.
• Due to new legislation, a video transect was used for ground truthing instead of grab samples.
• Seven transects were made in the area between 50˚08.446’N, 005˚02.813’W and 50˚08.420’N, 005˚02.420’W with one additional video transect (Start: 50˚08’2994N and 005˚02’4272W).

• Only a small video transect, across the edge of the sidescan transects, was taken which limited confirmation of the sidescan data. A time restriction meant multiple video transect could not be taken. More would been beneficial for identification purposes.