Ecological Archives A014-029-A2

Richard W.G. Caldow, Helen A. Beadman, Selwyn McGrorty, Richard A. Stillman, John D. Goss-Custard, Sarah E. A. Le V. dit Durell, Andrew D. West, Michel J. Kaiser, Kim Mould and Andrew Wilson. 2004. A behavior-based modeling approach to reducing shorebird–shellfish conflicts. Ecological Applications 14:1411–1427.

Appendix B. Details of the model parameters, their values and sources. Only those parameters for which it was necessary to gather site-specific values are shown here. All other parameters and their default values used in the model have been published in Stillman et al. (2000) and West et al. (2003). Unless otherwise stated, the parameter values presented here are the result of the authors’ direct knowledge of the system, observations, and measurements. Other sources are indicated by superscript numerals and details given at the foot of the appendix.

TIME AND ENVIRONMENTAL CONDITIONS

Parameter

Type

Values

Number of tidal stages

 

6 (high water, tide receding 1, tide receding 2, low water, tide advancing 1,

tide advancing 2)

Time of first high-water on full spring tides

 

00:00h

Duration of tidal stages (high tide first)

 

4h, 1h, 1.3444h, 3.7556h, 1.3444h, 1h

Mean daily temperature at Llanbedr (exemplary values shown for the first of each month over winter 1999–2000 only)

 

1 Sept 16.7oC, 1 Oct 12.5oC,  1 Nov 11.9oC, 1 Dec 10.0oC,  1Jan 7.9oC,1 Feb 8.2oC, 1 March 5.5oC

PREY PATCHES

Parameter

Type

Values

Number of patches

Commercial Mussel Lays

6 (lays 4, 5, 6, 7, 8 & Experimental lay (see Fig. 1))

Natural Mussel Beds

3 (beds 1, 2, 3 (see Fig. 1))

Upshore Flats

1 (see Fig. 1)

Fields

1

Patch areas (hectares)

Commercial Mussel Lays

1999–2000:

 Lay 4 27.6, Lay 5 42.3, Lay 6 23.3, Lay 7 19.0, Lay 8 15.0, Experimental Lay 1.44

2000–2001:

Lay 4 32.5, Lay 5 42.3, Lay 6 33.2, Lay 7 19.0, Lay 8 16.4, Experimental Lay 1.44

Natural Mussel Beds

1999–2000 and 2000–2001:

Bed 1 24.2, Bed 2 12.2, Bed 3 21.1

Proportion of each patch exposed at each tidal stage on full spring tides (high tide first).

Commercial Mussel Lays

Lay 4: 0.0 0.0 0.0 1.0 0.0 0.0
Lay 5: 0.0 0.0 0.0 1.0 0.0 0.0

Lay 6: 0.0 0.0 0.0 1.0 0.0 0.0
Lay 7: 0.0 0.0 0.0 1.0 0.0 0.0
Lay 8: 0.0 0.0 0.0 1.0 0.0 0.0
Experimental Lay: 0.0 0.0 0.0 1.0 0.0 0.0

Natural Mussel Beds

Bed 1: 0.0 0.0 1.0 1.0 1.0 0.0

Bed 2: 0.0 0.0 1.0 1.0 1.0 0.0

Bed 3: 0.0 0.0 1.0 1.0 1.0 0.0

Upshore Flats

0.0 1.0 1.0 1.0 1.0 1.0

Fields

1.0 1.0 1.0 1.0 1.0 1.0

Proportion of each patch exposed at each tidal stage on full neap tides (high tide first).

Commercial Mussel Lays§

Lay 4: 0.0 0.0 0.0 –0.538 0.0 0.0
Lay 5: 0.0 0.0 0.0 –0.538 0.0 0.0
Lay 6: 0.0 0.0 0.0 –0.538 0.0 0.0
Lay 7: 0.0 0.0 0.0 –0.538 0.0 0.0
Lay 8: 0.0 0.0 0.0 –0.538 0.0 0.0
Experimental Lay: 0.0 0.0 0.0 –0.538 0.0 0.0

 

Natural Mussel Beds

Bed 1: 0.0 0.0 0.9 0.9 0.9 0.0
Bed 2: 0.0 0.0 0.9 0.9 0.9 0.0
Bed 3: 0.0 0.0 0.85 0.85 0.85 0.0

 

Upshore Flats

0.0 1.0 1.0 1.0 1.0 1.0

 

Fields

1.0 1.0 1.0 1.0 1.0 1.0

Number of size classes

Mussels

13

Width of size classes (mm)

Mussels

20–24, 25–29, 30–34, 35–39, 40–44, 45–49, 50–54, 55–59, 60–64, 65–69, 70–74, 75–79, 80+

Size range of prey taken by birds

Mussels

25–60mm

Density (number m-2) of prey in each size class at the start of winter

Commercial Mussel Lays

September 1999:

Lay 4: 93.6 301.8 297.4 87.2 12.7 4.4 5.9 5.9 13.7 3.9 0.5 0.0 0.0
Lay 5: 13.7 4.9 6.0 12.0 20.2 47.5 97.8 83.6 29.0 9.8 1.1 0.6 0.0
Lay 6: 12.7 7.9 6.3 9.0 19.0 26.9 57.0 66.5 41.2 19.0 5.3 1.6 0.5
Lay 7: 257.4 206.4 114.2 74.2 117.4 110.3 83.9 81.3 47.7 21.3 5.8 0.7 0.0
Lay 8: 2.2 2.2 1.1 0.6 2.8 3.9 21.0 48.7 43.8 20.5 5.5 1.1 0.0
Experimental lay||: 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

September 2000:

Lay 4: 924.0 289.6 46.4 84.0 183.2 178.4 96.8 35.2 14.4 8.8 7.2 1.6 1.6
Lay 5: 1299.6 958.8 517.5 502.1 155.0 20.8 6.3 9.1 10.0 2.7 2.7 0.0 0.0
Lay 6: 1737.6 470.6 112.2 146.6 81.5 28.1 58.8 101.4 60.6 27.2 7.2 0.9 0.9
Lay 7: 698.4 285.3 53.6 90.7 92.7 61.6 47.0 55.0 40.4 16.6 2.0 0.0 0.0
Lay 8: 1595.0 462.3 56.6 44.1 25.0 2.9 10.3 14.0 19.1 13.2 5.9 0.7 0.7
Experimental lay: 43.4 281.3 934.3 1077.5 334.7 34.5 2.4 1.4 0.0 0.0 0.0 0.0 0.0

Natural Mussel Beds

September 1999:

Bed 1: 28.7 49.9 52.4 48.2 36.3 52.4 38.9 35.5 12.7 1.7 0.0 0.0 0.0
Bed 2: 15.6 18.2 26.8 32.0 37.2 70.9 74.4 70.1 42.4 16.4 1.7 0.0 0.0
Bed 3: 20.2 18.5 31.7 49.3 41.4 59.8 59.0 59.8 39.6 20.2 2.6 0.0 0.0

September 2000:

Bed 1: 21.2 26.9 38.2 45.3 30.4 37.5 48.8 33.3 16.3 7.8 1.4 0.0 0.0

Bed 2: 57.7 28.8 38.1 28.8 50.2 73.5 92.1 87.4 40.9 24.2 1.9 0.9 0.9

Bed 3: 13.3 13.3 15.0 22.5 34.2 30.9 60.9 83.4 54.2 26.7 6.7 1.7 1.7

Ash-free dry mass of an individual prey in each size class on each patch at start of winter (mg)

Commercial Mussel Lays

September 1999:

Lay 4: 14 52 134 270 457 684 933 1184 1422 1632 1806 1941 2035
Lay 5: 33 98 220 408 664 980 1341 1734 2141 2547 2941 3312 3653
Lay 6: 37 108 238 436 701 1025 1395 1794 2209 2623 3025 3405 3756
Lay 7: 25 73 162 306 509 775 1100 1480 1905 2369 2860 3370 3890
Lay 8: 31 78 161 289 472 717 1029 1412 1869 2399 3003 3680 4428
Experimental Lay||: 0 0 0 0 0 0 0 0 0 0 0 0 0

September 2000:

Lay 4:  8 41 124 276 494 760 1043 1310 1538 1710 1820 1871 1867

Lay 5: 12 47 124 257 453 706 1004 1329 1665 1993 2300 2576 2813

Lay 6: 23 66 148 285 490 776 1152 1624 2197 2873 3652 4531 5508

Lay 7: 12 45 117 244 435 689 1000 1354 1736 2130 2524 2901 3254

Lay 8: 20 45 89 161 270 427 645 938 1322 1816 2438 3209 4152

Experimental Lay: 43 84 151 255 413 643 968 1419 2032 2850 3925 5319 7105

 

Natural Mussel Beds

September 1999:

Bed 1: 42 113 231 393 587 800 1015 1220 1407 1568 1699 1801 1874
Bed 2: 40 103 212 370 576 826 1111 1423 1750 2086 2420 2748 3063
Bed 3: 23   82 202 389 634 912 1198 1467 1701 1889 2025 2110 2147

September 2000:

Bed 1: 21 67 154 287 458 654 860 1059 1241 1398 1524 1618 1680

Bed 2: 38 100 204 354 548 777 1033 1305 1585 1863 2132 2388 2625

Bed 3: 29 85 189 344 547 787 1050 1321 1587 1838 2066 2266 2434

Over-winter % decrease in ash-free dry mass of an individual mussel on each patch

Commercial Mussel Lays

Lay 4 37.2%, Lay 5 45.4%, Lay 6 54.2%, Lay 7 42.6%, Lay 8 39.8%,

Experimental Lay 40.0%

Natural Mussel Beds

Bed 1 34.4%, Bed 2 43.6%, Bed 3 41.8%

BIRD POPULATION

Parameter

Type

Values

Population size

All

4840 individuals

Number of age classes

 

3: juvenile (1st years), immature (2nd years), adult (3+ years)

Proportion of birds in each age class

 

Juvenile 0.02, immature 0.04, adult 0.94

Number of mussel feeding methods

 

2 (stabbers and hammerers)

Proportion of each age class with each feeding method (stabbers, hammerers)

 

Juvenile - 1.00, 0.00 Immature - 1.00, 0.00  Adult -  0.30, 0.70

Mass on 1st September (g)

Juvenile

530

Immature

550

Adults

550

Target mass

(days since 1st September - target mass (g) )

Juvenile

day 0 - 530g, day 196 - 530g

Immature

day 0 - 550g, day 167 - 550g, day 196 - 570g

Adult

day 0 - 550g, day 136 - 550g, day 196 - 625g

COMMERCIAL FISHING ACTIVITY

Parameter

Type

Values

Number of fishing types

All

2 (Hand gathering, Dredging)

Patch types fished

Hand gatherers

Natural Mussel Beds only

Dredgers

Commercial Mussel Lays only

Number of periods over which each fishing type is banned

Hand gatherers

0

Dredgers

1

First and last days of each ban (days after 1st September)

Dredgers

0 90 (i.e., no harvesting by dredging until 1st December)

Probability of fishing by each type on each day of week (Mon–Sun)

Hand gatherers (on natural beds)

1 1 1 1 1 1 1

Dredgers (on commercial lays)

1 1 1 1 1 1 1

Probability of fishing during the day by each type at each tidal stage (high tide first)

Hand gatherers (on natural beds)

0 0 0 1 0 0

Dredgers (on commercial lays)

1 0 0 0 0 0

Probability of fishing at night by each type at each tidal stage (high tide first)

Hand gatherers (on natural beds)

0 0 0 1 0 0

Dredgers (on commercial lays)

0 0 0 0 0 0

Stage of spring/neap cycle between which fishing by each type is possible

Hand gatherers (on natural beds)

0.00 – 1.00

Dredgers (on commercial lays)

0.00 – 1.00

Patches on which fishing by each type is allowed

Hand gatherers (on natural beds)

Natural Mussel Beds 1, 2, 3 (see Fig. 1)

Dredgers (on commercial lays)

Commercial Mussel Lays 4, 5, 6, 7, 8 (see Fig. 1)

Number of fishing units

Hand gatherers

3

Dredgers

2

Maximum time over which shellfishing occurs per tidal stage (h)††

Hand gatherers

2.44 (1999–2000), 1.05 (2000–2001)

Dredgers

2.01 (1999–2000), 3.08 (2000–2001)

Minimum fished size (mm)

Both

50

Area fished per hour (sq m)

Hand gatherers

11.4

Dredgers

800

Patch areas reduced by fishing activity

Hand gatherers

No (0)

Dredgers

Yes (1)

Minimum area fished (proportion of initial area)

Hand gatherers

0

Dredgers

0.1

Minimum fishable density of mussels (n/m)

Both

0

Fishing activity kills non-target size classes

Hand gatherers

No (0)

Dredgers

Yes (1)

INTAKE RATE ON SUPPLEMENTARY PREY

Parameter

Type

Values

Intake rate (mg ash-free dry mass 300s-1)

Upshore Flats

260 mg AFDM 300s-1

Fields

102 mg AFDM 300s-1

http://badc.nerc.ac.uk/data/ Download Met Office station data: Gwynedd, Llanbedr. Last accessed 13th January 2004.

No patch areas are necessary for either supplementary habitat (upshore flats and fields) because, as in all previous versions of the model, birds are assumed to achieve a constant intake rate when feeding in such supplementary areas that is affected neither by depletion nor interference.

§ The value of –0.538 for exposure over the low water tidal stage on a full neap tide is required to yield exposure patterns in the model that mimic reality i.e. on average commercial lays do not expose at all, even at low water, on approximately one third of tides.

|| Mussels were not laid on the Experimental Lay until April 2000.

Data provided by the SCAN ringing group.

†† The maximum time over which fishing by each type was allowed in the model was the parameter that was manipulated in trial simulations in order that the total annual harvest (number of mussels) of both hand gatherers on the natural beds and of dredgers on the commercial lays that was generated by the model matched the actual harvest in those seasons.

 

LITERATURE CITED

Stillman, R. A., J. D. Goss-Custard, A. D. West, S. E. A. le V. dit Durell, R. W. G. Caldow, S. McGrorty, and R. T. Clarke. 2000. Predicting mortality in novel environments: tests and sensitivity of a behaviour-based model. Journal of Applied Ecology 37:564–588.

West, A. D., J. D. Goss-Custard, S. McGrorty, R. A. Stillman, S. E. A. le V. dit Durell, B. Stewart, P. Walker, D. W. Palmer, and P. J. Coates. 2003. The Burry shellfishery and oystercatchers: using a behaviour-based model to advise shellfishery management policy. Marine Ecology Progress Series 248:279–292.


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