Gulf of Maine Council

Resources

Gulf of Maine Library Collection

Identification of Important Habitats in the Lower Casco Bay (Maine) Watershed

Table 1. Calculations to Combine Habitat Scores for the Evaluation Species

SEQUENCE OF STEPS:

1) Habitat Qualtity Rating by Species: assign habitat values according to environmental conditions, needs of each species and observed levels of use (see relevant Chapters by species); scored on 0 - 8 scale.

2) Gulf of Maine Council Rating by Species: determine index score reflecting the rank of the evaluation species on the Gulf of Maine Council list (based on economic, environmental, and institutional factors; scored on 0 - 8 scale. <see ranked list>

Evaluation Species

Species Rating

Species Rating Scores*

(values indexed on 0-8 scale)

eelgrass

7.2

shellfish (average of scores, 4 spp.)

7.2

cordgrass

6.9

eagle

6.5

roseate tern

6.4

seabirds (average of scores, 2 spp.)

6.3

shorebirds (average of scores, 2 spp.)

6.3

waterbirds (average of scores, 3 spp.)

6.1

marine worms (average of scores, 2 spp.)

6.1

fishes (average of scores, 9 spp.)

5.6

wading birds (great blue heron)

5.1

*indexed so highest rating on the list (66)= 8.0

3) Abundance / Scarcity Rating by Species: rate habitats or habitat components inversely to their abundance; score on 0.5 - 8 scale.

Habitat / Component

Habitat Area

(in 30 m sq cells)

Relative Abundance Value**

(apportioned by component)

Abundance Scores***

(values indexed on 0.5-8 scale)

eelgrass

35509

6.3

1.7

shellfish beds

99874

2.2

1.3

cordgrass

15281

14.6

2.2

eagle nest areas

163

1368.6

8.0

roseate tern nesting

118

945.2

7.2

roseate tern foraging

23359

4.8

1.6

seabird nesting

1760

63.4

3.3

seabird foraging

129294

0.9

1.0

shorebird nesting

976

114.3

3.9

shorebird foraging

5989

18.6

2.3

waterbirds

223078

1.0

1.0

marine worms

25991

8.6

1.9

freshwater and anadromous fishes

60127

3.7

1.5

wading bird nesting

856

130.3

4.1

wading bird foraging

175486

0.6

0.9

** Relative Abundance Value = number of cells in most abundant habitat / (number of components x number of cells in a particular habitat component)

*** Abundance Score = Relative Abundance Value ^.2875

4) Combining Ratings for Each Species: Habitat Quality Rating x Gulf of Maine Council Rating x Habitat Abundance Rating. Potential Scores per Species: (8 x 8 x 8) = 1 to 512; Actual Scores: 1 to 429.

5) Combining Scores for Final Map: for each grid cell sum scores for all species from step (4)