1. Project Title: Use of Reefrafts to Create Habitat for Birds and Fish
2. Contacts
Hans Blokpoel
Environment Canada, Canadian Wildlife Service, 49 Camelot Drive, Nepean, Ontario K1A 0H3
Tel.: (613) 952-2410; FAX: (613) 952-9027
Scott Jarvie
Metropolitan Toronto and Region Conservation Authority, 5 Shoreham Drive, Downsview, Ontario M3N 1S4
Tel.: (416) 661-6600, ext. 312; FAX: (416) 661-6898
3. Agencies Involved
Metropolitan Toronto Parks and Properties
4. Restoration Goal
To provide nesting habitat for Common Terns and shelter for fish.
5. Project Type
Construction of reefrafts and their installation at suitable locations. Reefrafts are floating wooden platforms with strips of plastic snow fence hanging down from the bottom of the platform.
6. Background and Rationale
Common Terns at the Toronto waterfront have been declining sharply in numbers due to encroachment of their nesting areas at the Eastern Headland by nesting gulls and by vegetation. For terns, the presence of large numbers of gulls constitutes an impairment to the use of their traditional nesting habitat. Traditionally, Common Terns have been a highly visible component of the avifauna of the Toronto Waterfront.
During the 1990 breeding season a project was undertaken to construct and install large wooden rafts for use as nesting habitat by Common Terns. Attracted by wooden painted decoys and suitable substrate, common terns immediately colonized the rafts and fledged chicks. The project continued in 1991 and 1992, again with excellent results. The only drawback of the project was the need to remove the rafts before freeze-up (to prevent damage) and to reinstall them in the spring when the terns first started to return from their wintering grounds in South America. In 1993 tests were carried out with "reefrafts" that differed from the original tern raft in that (1) reefrafts use floatation materials that can withstand ice pressure (thus obviating the need to remove and reinstall the raft), and (2) an artificial reef made out of plastic was suspended below the raft to create habitat for fish. Electrofishing under, near, and away from the reefrafts in the summer/fall of 1993 and 1994 showed that the reefrafts were used by fish. Common Terns used the reefrafts during 1993 and 1994 to the same extent as they used the original nesting rafts during 1990-1992.
7. Regulatory Considerations
a) Environmental assessment: probably not required.
b) Safety aspects: the rafts should be installed in accordance
with regulations to prevent
boating accidents.
8. Criteria
Common Terns prefer insular sites for nesting (to prevent predation by ground predators) and they prefer open substrate with little and low vegetation (Blokpoel et al. 1978). Common Terns are fairly "manageable" in that they readily colonize new areas and respond to decoys.
Fish of several species readily use the overhead shelter provided by the platforms as well as the additional protection offered by the reefs.
9. Project Design
After installation of the reefrafts, we added earth, sand, pebbles, and driftwood to create a suitable nesting substrate for the Common Tern. Once chicks became mobile we added a ramp to each reefraft that allowed chicks that might fall off the reefraft to get back on to it. Reproductive success of the terns was monitored by regular visits to determine fates of eggs and chicks.
The "reefs" were attached to the bottom of the reefraft when it was being assembled during installation in the water. Fish use of the reefrafts was monitored by electrofishing.
10. Implementation
During 1990-1994, the numbers of original rafts and reefrafts were as follows:
Eastern Headland Trout Pond, Toronto Islands
1990 4 Original Rafts -
1991 4 Original Rafts -
1992 4 Original Rafts -
1993 2 Original Rafts & 2 Reefrafts 1 Reefraft
1994 2 Original Rafts & 2 Reefrafts 1 Reefraft
Original rafts and reefrafts were 5 ¥ 5 m. The nesting substrate was spread evenly and had a depth of 2.5-5 cm. Further information on design and effectiveness of the original rafts are given in Dunlop et al. (1991, 1992); further information on the reefrafts is provided by McNicholl et al. (1995) and Jarvie and Blokpoel (1993).
11. Degree of Environmental Intervention
Although no studies were undertaken, we believe that the original rafts and reefrafts did not have any negative effects on the local biotic communities or on the abiotic aquatic environment.
12. Costs
Materials and labour to construct one reefraft: $3 500
Costs to transport, launch, install and anchor a reefraft: variable
Costs to monitor effectiveness (= biological assessment): variable
Costs for annual maintenance: variable
13. Biological Assessment
Original rafts and reefrafts were routinely visited to monitor nesting chronology and reproductive success of Common Terns (Dunlop et al. 1991; McNicholl et al. 1995).
Electrofishing was carried out under/near the original rafts, under/near the reefrafts, and in open water (control) in 1993 (Jarvie 1993) and 1994 (Jarvie 1994).
14. Measures of Success
The project had excellent results for Common Terns in that during 1991-1994 at least 50 chicks fledged from each raft (or reefraft) in each year.
Success rating for birds: 4
The project appears also successful for fish, but unfortunately electrofishing was carried out on only three occasions so the supporting data are limited. The number of fishes caught on those three occasions was as follows:
Mean Range at/under reefraft 13.3 0-30 at/under original raft 9.5 5-19 control (open water) 5.7 0-13 Success rating for fish: 4
15. Key References
Blokpoel, H., Catling, P.M., and Haymes, G.T. 1978. Relationship between nest sites of Common Terns and vegetation on the Eastern Headland, Toronto outer Harbour. Can. J. Zool. 56: 2957-2061.
Dunlop, C., Blokpoel, H., and Jarvie, S. 1992. Nesting rafts as a management tool for a declining Common Tern (Sternahirundo) colony. Colonial Waterbirds 14: 116-120.
Dunlop, C., Blokpoel, H., and Jarvie, S. 1991. Guidelines for the construction and assembly of nesting rafts for Common Terns. 6p. (Unpublished report)
Jarvie, S. 1993. Results of electrofishing during the summer and fall of 1993. (Unpublished report)
Jarvie, S. 1994. Results of electrofishing during the summer and fall of 1994. (Unpublished report)
McNicholl, M.K., Blokpoel, H., and Jarvie, S. 1995. Ecology of Common Tern nesting on rafts along the Toronto Waterfront, 1991-1993. (In preparation)
Correct citation for this contribution:
Blokpoel, H., and Jarvie, S. 1995. Use of reefrafts to create habitat for birds and fish, p.51-54. In J.R.M. Kelso and J.H. Hartig [editors]. Methods of modifying habitat to benefit the Great Lakes ecosystem. CISTI (Can. Inst. Sci. Tech. Inf.) Occas. Pap. No. 1.