Manipulation of the feeding behaviour of diving ducks on mussel farms

Ross, Ben Paul (2000) Manipulation of the feeding behaviour of diving ducks on mussel farms. PhD thesis, University of Glasgow.

Abstract

Eider numbers in the North Clyde area remain quite constant throughout the winter, with an influx of birds, mainly juveniles, in the late summer. These birds subsequently disappear from the area either as a result of increased mortality or by competitive exclusion by adult birds. Attendance at a mussel farm in the area was highest throughout the winter, and male to female sex ratio was higher here than in other areas. Some breeding eiders from the North and West of Argyll move into the Clyde during the winter, but these represent only a small proportion of the wintering population. Eider wintering distribution can be influenced by aquaculture sites in some areas, although the effect on population growth is unclear.
The activity patterns of foraging eiders on natural mussel beds is strongly influenced by tidal height whereas on mussel farms there is no such effect. In wild-feeding flocks, different areas are utilised at differing periods of the tidal cycle, perhaps as a method of keeping a uniform optimal dive-depth. Birds feeding on natural mussel beds dived on average three times as frequently as those feeding on mussel farms, and so clearly had to work harder to meet energy requirements.
97% of Scottish mussel farmers contacted reported eiders as a pest species, and 21% also suffered damage from goldeneyes. Losses of stock to feeding eiders can be huge, and the fmancial cost considerable, averaging 14000 per farm per year (1994-1998). Attendance at farms tended to peak during early spring and late autumn. Many damage limitation measures were employed by farmers, with only one, netting, giving unambiguous success.
Worker presence on mussel farms decreased eider attendance by 95%. Chasing the birds by boat significantly reduced numbers of feeding eiders and goldeneyes in the short-term, by 91 and 51% respectively. This effect was short-lived, particularly with goldeneyes. There was also evidence to suggest that disturbance lowers the subsequent feeding rate of goldeneyes on mussel farms.
Laser light significantly reduced numbers of diving ducks on mussel farms, however its efficacy is reduced as ambient fight levels increase. As a result, its use is often restricted to periods around sunrise and sunset. Different populations of eiders showed significantly different sensitivities to laser light. Sequential trials of the laser fight on adjacent farms showed that birds were initially scared from one site to the next, but repeated regimes moved birds out of the area.
Trials of an Underwater Playback System (UPS), replaying recordings of chase-boat engines, gave significant reductions in eider numbers of 50-80%. A control trial with the playback of an unassociated noise gave no significant reduction in numbers. The mean return time of birds to the farm after chasing by boat also increased significantly during UPS trials. The long-term habituation of ducks to this system was negligible with occasional reinforcement by boat chasing.
On the basis of these scientific trials and observations,r ecommendations to mussel farmers are made in an advisory booklet (Appendix III). Netting designs are presented and possible use of UPS or laser light on farms is reviewed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QL Zoology; S Agriculture > SH Aquaculture. Fisheries. Angling
• Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
• Supervisor's Name: Furness, Professor Bob
• Date of Award: 2000
• Depositing User: Adam Swann
• Unique ID: glathesis:2000-79002
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Feb 2020 16:30
• Last Modified: 04 Feb 2020 16:30
• URI: https://theses.gla.ac.uk/id/eprint/79002