Eelgrass Extent 2014 - Central Coast

Eelgrass extent mapped out for selected sites for the Hakai Outer Shores program. Polygons represent eelgrass beds digitized using underwater video. People involved: Luba Reshitnyk (boat operator and data producer), Ondine Pontier (field assistant and video analysis), Midoli Bresch (field assistant),Carolyn Knapper (field assistant), Ben Millard-Martin (field assistant)

Equipment: Splashcam pro, Field computer, Hakai Blue Refer to Video Habitat Mapping protocol.pdf at

Methods: Georeferenced video data were analyzed by Ondine Pontier with classification of video every 2 seconds for substrate and biological features in a hierarchical classification scheme in an excel spreadsheet. Data were sent to Luba Reshitnyk September 14th 2014. Video data were imported into ArcGIS and polygons were drawn around transect lines where eelgrass was present.

Goose Date Publish - November 27th, 2014 Date collected - August 16th, 17th, 18th 2014 Goose consists of 2 sites - Goose South 1 (GS1) and Goose South 2 (GS2). Depth was less than 20 m.

McMullins Date Publish - November 26th, 2014 Date collected - August 15th 2014. McMullins consists of two sites - McMullins North (MMN) and McMullins South (MMS). Depth did not extend beyond 15 m.

Triquet Date Publish - November 27th, 2014 Date collected - September 16th, 2014 More details:

Underwater video is an important tool for visualizing the seafloor. When georeferenced, video data can be used to create maps of floral and faunal marine biodiversity as well as groundtruthing satellite and sonar imagery. At the Hakai Beach Institute, underwater video habitat mapping is conducted aboard the Hakai Blue – a 23 foot aluminum vessel with a 250 HP outboard motor. At minimum a boat operator and a camera operator are needed. Ideally, a third person is present to look for submerged hazards and to replace the camera operator as needed.

Video data were collected on April 30th, May 1st, May 5th, May 23rdand May 24thaboard the Hakai Blue using a small colour underwater video camera (Deep Blue Pro, Ocean Systems Inc) mounted to a custom-made aluminum wing. Survey transects are shown in Fig. 1. Live video feed was visible via a field computer and allowed the camera operator to maintain the camera 1-2 m above the seafloor. This height provided an imagery swatch width of approximately 1-2 m. Video transects (n=75) were run both parallel and orthogonal shore and transect spacing was maintained between 50-100 m. Vessel speed was maintained below 1 knot during video surveys (greater speeds negatively impacted the quality of the video and the layback between the camera and the vessel). Video data collected from April 30th, May 1stand May 5thwere georeferenced using the GPS aboard the Hakai Blue while data collected on May 23rd-24th were geo-referenced using the Topcon GR5 operating in a differential GPS mode (to increase positional accuracy). Positional data were recorded every 2 seconds. Video and dGPS data were recorded directly to a field computer hard drive.

Video data were analyzed for the presence of eelgrass and the dominant seafloor substrate type (data for substrates not shown here). A semi-quantitative method was developed to distinguish between different densities of eelgrass within the video frame (Table 1) and included 5 classes – no eelgrass present, sparse cover (5-20%), moderate (20-60%), dense (60-80%) and very dense (>80%). After analysis, data were loaded into a GIS for visualization (ArcGIS 10.1, ESRI). A polygon was drawn around the classified transects to estimate the extent of the eelgrass present in Choked Passage.

There is a large eelgrass meadow present in Choked Passage approximately 1.3 km long and 500 m at its widest point (Fig. 1). The total surface area of eelgrass in Choked Pass is approximately 307000 m1(~93% of that is the single large meadow). Smaller patches are present in the northern part of the study site. A red algal epiphyte (Porphyra sp.) was evident in large portions of the eelgrass meadow.

While current high resolution bathymetric data are unavailable, depth of the eelgrass is between 6-9 m (below chart datum). The distribution of eelgrass density will be used in future analysis for comparison against diver surveys of eelgrass density. Based on the video data, the majority of eelgrass is occurring at a “moderate” density.

A total of 17.5 hours of video data were analyzed (two analysts working for 3 days).

Hakai Institute, Luba Reshitnyk, Keith Holmes, Ondine Pontier, Midoli Bresch, Carolyn Knapper, Ben Millard-Martin

Access and Use

Licence: Appropriate credit must be given to Hakai Institute and the authors of the dataset.

Data and Resources


Metadata Created October 26, 2018, 22:48 (UTC)
Metadata Updated October 26, 2018, 22:48 (UTC)
Reference Date(s) 2014-09-12 (Creation)
2015-10-11 (Publication)
Frequency of Update
Metadata Date November 24, 2017, 15:02 (UTC)

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Additional Info

Field Value
Contact Email
encoding utf8
metadata-language eng
progress completed
resource-type dataset
Responsible Party Hakai Institute (Point of Contact, Processor)
spatial-reference-system 3857