Cowichan Estuary Habitat Mapping and Oyster Population Assessment. Cowichan Stewardship Round Table

Transcription

1 Cowichan Estuary Habitat Mapping and Oyster Population Assessment Presentation at Cowichan Stewardship Round Table June 21, 2018 By Dr. Goetz Schuerholz 1

2 More than 8000 drone photos taken stitched together for base map 2

3 Flight lines of drone northern section 3

4 Sample of 3D Point Cloud model ( three dimensional coordinate system, a set of data points in space) south of Westcan divide Point cloud data were used to: - create custom geospatial elevation models, - apply contours to orthophotos, - generate new 3D models; - direct measurement tool. 4

5 Digital Elevation Model Now Available for 95% of the Estuary Digital elevation model DEM of the Salt Marsh South of Westcan Terminal Rd. Ducks Unlimited Property and reclaimed salt marsh 5

6 Ortho-mosaic created for estuary at 2-4cm resolution Zoomed Out Orthophoto Magnified Object (see arrow in opposite image) 6

7 Polygonal Mesh with Image Texture 3D models will be posted on a free, web-based viewing platform along with annotations to help explain CERCA s work and the ecological processes of the estuary. 7

8 Example of interactive web-based annotated 3-D model with resolution 2 to 7 cm 8

9 Training Session 9

10 Estuary Habitat Mapping 1. Aerial photo- and 3-D drone imagery interpretation ; 2. Identify habitat polygons delineated on base; map/orthophoto (DFO Protocol; M. Wright &Associates); 3. Ground-truthing of habitat polygons by CERCA team: geo-referencing polygons; random sampling of each habitat polygon using one square meter sample plots; 4. Processing field data and finalizing habitat map. 10

11 Survey Blocks Used for Ground-truthing Habitat Types of Mudflats and Oyster Survey (Low Tides) V VI VII IV III VIII II I I = 18 August II = 19 August III = 20 August IV = 21 August V = 22 August VI = 01 September VII = 02 September VIII = 03 September 11

12 Intertidal Survey for Habitat Mapping (DFO Protocol) 1. Substrate Types (recorded as percent areal coverage). 2. Marine Plants Marine algae (green algae, red algae, brown algae), recorded as percent areal coverage. 3. Sessile Animals Invertebrates permanently attached to substrate as part of their life history (e.g. barnacles, oysters), recorded as percent areal coverage estimates. 4. Motile Animals (crabs numbers counted ) 12

13 13

14 14

15 15

16 16

17 17

18 Sample of Waypoints Taken (Geo-referencing Habitat Polygons via Hand-held GPS) 3 18

19 19

20 Geo-referencing eelgrass distribution 20

21 21

22 22

23 Distribution and Size of Estuary Habitat Types (DFO Protocol) Habitat Type Total Area (m2) Total Area in ha % Gravel (silt, sand, gravel) 225, Mud Flat (organic layer 2 to 30 cm) 4,566, Low Intertidal Vegetation 76, Mid Intertidal Salt Marsh 779, High Intertidal Salt Marsh 107, Large Woody Debris 2, Bedrock Anthropogenic 1,000, Marine Riparian 213, Oyster Bed (mostly on gravel bars) 62, Eelgrass (on sand/silt) 179, Grand Total 7,214,

24 24

25 Past (right) and current (left) eelgrass distribution in the Estuary 25

26 Cowichan Estuary Oyster Research 26

27 ECOLOGICAL IMPORTANCE Oyster: a recognized Keystone species! providing habitat to numerous species (e.g. barnacles, crabs, invertebrates etc.); purifying water (one mature oyster filters up to 2.5 gallons of water/ hour; fast growing (i.e. 2-3cm/a); highly prolific + long life expectancy of up to 30 years; significant carbon busters (i.e. 12% of shell composed of carbon); 27

28 28

29 29

30 30

31 31

32 Impacts of Log Booms on Largest Oyster Bed of Cowichan Estuary 32

33 Destruction of Oyster Bed North of Log Transport Channel 33

34 Oyster Beds North and South of Westcan Estuary Divide 34

35 Results of Mature Oyster Inventory Total area of oyster beds North of Causeway (square m) 47,952 Total number of oysters 10cm and larger 3,297,740 Total number of oysters between 5-10cm Total number of crabs sheltered by oysters 1,859,180 9,451,470 Total area of oyster beds South of Causeway (square m) 14,500 Total number of oysters 10cm and larger 57, 928 Total number of oysters between 5-10cm 435, 000 Total number of crabs sheltered by oysters 290,000 Grand total area of oyster beds (square m) 62,452 Grand Total number of oysters 10cm and larger 3,355,668 Grand Total number of oysters between 5-10cm 2,294,180 Grand Total number of crabs sheltered by oysters 9,741,470 35

36 Oyster status South of causeway compared to North of causeway South: Larger mud-habitat areas Significantly less oysters Significantly younger specimens 36

37 Economic Value Oysters account for 80 per cent of all of B.C.'s farmed shellfish by weight and around 40 per cent of its value, with the small-butworld-famous fishery (worth some $33 million annually) a mainstay of the Gulf Island and Vancouver Island economies. BC s oyster production represents approximately 45% of Canada s total oyster production; on average 14,000 tonnes/a produced in BC; annual average farm-gate value of oyster is $2-7/dozen (oyster bar value $25/dozen!); number of marketable oysters in estuary approximately 5,258,348; at $5/dozen total current market value of the estuary oyster population approximately $2,190,978 37

38 Key Values of Current Estuary Oyster Population filtering approximately 141,246,200 gallons of water/day (at high tide); approximately 2.5 metric tons of carbon sequestered; total current farm-gate value of marketable oysters approximately $2,190,