Determining an Effective Method to Limit Bird Use of Aquaculture Structures as Perching Sites in New Brunswick

 

By

Isabelle J. Thériault¹, Kevin Burke¹ & Luc A. Comeau²

¹ New Brunswick Professional Shellfish Growers Association, 278 A, Pêcheurs Av., Shippagan, New Brunswick, Canada, E8S 1J6

² Department of Fisheries and Oceans, Gulf Fisheries Centre, P.O. Box 5030, Moncton, New Brunswick., E1C 9B6

 

Submitted to

Aquaculture Management, Department of Fisheries and Oceans

Within the Aquaculture Innovation and Market Access Program

 

March 26th, 2009

TABLE OF CONTENTS

• Summary
• Introduction
• Material and Methods
• Study sites
• Deterrent products
• Installation of the devices and observations of the birds
• Statistics
• Results
• Bird abundance
• Devices effects
• Discussion
• Acknowledgements
• References

List of Figures

Figure 1   Photographs of a) “Irri-Tape” commercial product and b) device with “Irri-Tape” firmly attached on floating pockets in the Bay of Caribou (photographs by Leon Lanteigne).

Figure 2   Commercial product « Gator Guard » of the company Bird-X (www.bird-x.com).

Figure 3   Average abundance (± standard error) of birds with all species and double-crested cormorants (Phalacrocorax auritus) observed on floating bags in the untreated site (UT), on treated site with no devices (ND) and on treated site with devices (WD) in the Bay of Caribou.

Figure 4   Average abundance (± standard error) of birds with all species, double-crested cormorants (Phalacrocorax auritus) and common terns (Sterna hirundo) observed on floating bags in the untreated site (UT), on treated site with no devices (ND) and on treated site with devices (WD) in the Bay of St-Thomas. Error bars represent typical errors.

Summary

In numerous bays off New Brunswick, coastal birds are roosting regularly on floating oyster bags. Droppings left on the floating bags by the birds raised sanitary and visual concerns for many oyster growers. The holographic tape “Irri-Tape” and the alligator heads “Gator Guard” were used as the visual dissuasive devices for the birds on the floating oyster bags in two bays in New Brunswick. The “Irri-Tape” devices were effective to diminish the number of birds in the Bay of Caribou, especially for the double-crested cormorant (Phalacrocorax auritus), which was the most abundant species at this site at the time of this study. On the other hand, the “Irri-Tape” devices did not appear effective towards the birds in the Bay of St-Thomas. The only observation made with “Gator Guard” devices seemed to show that the devices were not effective to deter birds from floating bags. The doubtful effectiveness of the devices to deter birds from floating bags and the brittleness of the “Irri-Tape” devices are not viable options for the oyster industry.

Introduction

The oyster growing industry in New Brunswick is in full expansion since the last decade. Recently, the majority of the oyster growers rear their oysters in suspension with floating gear such as the floating oyster bags. However, suspension culture gears provide a roosting platform for many coastal birds (Comeau et al., 2006). Droppings left by the birds on aquaculture gears raised concerns related to the sanitary aspect of oysters and to the general public image.

In 2004, the industry adopted a preventive approach about the concerns and following the recommendations of the regulatory agencies. Since then, the oysters are completely immersed and thus inaccessible to the birds for 14 to 30 days before they are placed on the market.  According to some growers, this option is not economically viable because it takes more labour to do the work and it prolongs the production cycle. By taking note of this information, it would be desirable to find new ways to reduce birds roosting on aquaculture gear.

Several methods exist to deter birds from roosting sites, but most of them are either ineffective or impossible to apply in shellfish farming for logistic reasons. These methods include fences and nets (Rowland, 1995), deterrent chemicals for the birds senses of smell and taste (Avery et al., 1996; Bleating et al., 1997; Blackwell et al., 2001; Cotterill et al., 2004; Harpaz & Clark, 2006), pyrotechnic devices (Mott et al., 1998, Cook et al., 2008), the use of raptors (Baxter et al., 2006) and even hunting (Blackwell et al., 2000; Bechard & Mark-Reyes, 2003). One method was proven efficient to limit birds perching on aquaculture gears. Comeau et al. (2009) provided spikes named as AntiCormoTM on the buoys of OysterGroTM floating oyster cages so that the cages does not serve as perching places for the birds. However, the application of this system to the floating bags remains problematic for reasons linked to its rearing techniques.

The commercial product “Irri-Tape”, a holographic tape, has been proven to be efficient to deter woodpeckers from house sidings (Harding et al., 2007). This tape could serve as an inexpensive, practical, effective and environmentally friendly method to deter bird for floating oyster bags. Furthermore, the alligator heads “Gator Guard” publicized by the company Bird-X Inc. seemed to have a potential to deter birds from oyster floating bags. The objective of the following study was to deter birds from oyster floating bags in eastern New Brunswick with the commercial products “Irri-Tape” and “Gator Guard’.

Material and methods

Study sites

The study took place in two bays from July to August 2008: 1) the Bay of Caribou, near Shippagan (New Brunswick, Canada) and 2) the Bay of Saint-Thomas near Saint-Thomas-of-Kent (New Brunswick, Canada) (fig. 1). Every bay of the study contained a treated site and an untreated one. The treated site was used to test the dissuasive visual devices whereas the untreated one was only used to register the number of birds during that time. There was about 500 m separating the treated site from the untreated site. The study sites were selected according to the rarity of the aquaculture activities so that birds were not influenced by the presence of floating gears from other aquaculture sites. Abundance of birds such as the double-crested cormorant (Phalacrocorax auritus), the common tern (Sterna hirundo) and the herring gull (Larus argentatus) frequently observed on floating oyster bags (St-Onge et al., 2007) was also a selection criteria.

Deterrent products

The commercial product used to reduce the number of birds perched on the floating bags was the “Irri-Tape” (Bird-X, Inc., Chicago, Illinois) made of a polyester film 51 mm in width and 50 µm thick (fig. 2a). This ribbon holographically printed can reflect sunrays and makes flapping sounds when let free in the wind, which can scare the bird when it gets close. The device used was made with 61 cm long pieces of “Irri-Tape” attached at each tip of 4 horizontal metal poles on a vertical metal structure put together and attached on a floating bag with hog rings and bungee ropes (fig. 2b).

Figure 1.  Photographs of a) “Irri-Tape” commercial product and b) device with “Irri-Tape” firmly attached on floating pockets in the Bay of Caribou (photographs by Leon Lanteigne).

The second product used to reduce the number of birds perching on oyster floating bags was the « Gator Guard » (Bird-X, Inc., Chicago, Illinois) (figure 2). This device in the shape of an alligator head (25" long x 11" large x 7" height) is fabricated with a sun and weather proof material. It is also destined to cover up to a maximum of 1 acre (0.4 hectare) of field. The alligator head devices were attached on a rope with an anchor so it can float and move with the wind at the water surface.

Figure 2.  Commercial product « Gator Guard » of the company Bird-X.

Installation of the devices and observations of the birds

For each of the treated and untreated sites, four longlines of 50 Vexar bags (85 cm X 44 cm X 9 cm) were installed in parallel and 15 m separated each line. Buoys were installed on the lateral side of bags in the Bay of St-Thomas, whereas in the Bay of Caribou, buoys were installed directly on the top side of the bag so the bag itself is submerged 3 cm under water. The oyster grower who supplied the bags in the Bay of Caribou was convinced that the modified bags lowered the number of birds on those, in spite of the lack of scientific evidence (see Comeau et al., 2009). In order to reproduce rearing conditions, 7 kg of American oysters (Crassostrea virginica) were used to fill the bags in the Bay of Caribou. In the Bay of St-Thomas, the oyster larval deposit is normally high, which could have caused an undesirable collection of oyster spats on live oysters belonging to the oyster grower. For this reason, 7 kg of soft-shell clam shells (Mya arenaria) were used to fill the bags instead of live oysters.

Within each bay, an observer was designated to follow the bird abundance on the sites. Before any observations, the observer checked from the shore if there were human activity presence since those could have influenced the number of birds on the sites. Then, the observer approached the site discreetly by kayak and observed the birds using binoculars. Only the birds which were perched on the floating bags, including the buoys on the bags, were identified and numbered. An observation of birds lasted one hour, with four counts made once every 15 minutes. The bird count used for the analysis was the maximum number of individuals found at any time during an hour of observation. The observations took place from 6:00 am to 7:30 pm under best weather conditions, i.e. with the wind speed lower than 25 km/hr and no precipitations. The observations were done only when the devices were functional. The devices were thus repaired as soon as possible when seen broken.

At the start of the experience, none of the devices were installed on the treated site to confirm the presence of birds. After these controlled observations, the devices were installed in the treated site. One “Irri-Tape” device was installed on a bag of each longline and its position was selected at random. However, observers noticed that the birds seemed to settle at the ends of the longlines. Thus, one “Irri-Tape” device was added at each longline end on the treated sites, which made a total of 12 devices per treated site. For the alligator heads “Gator Guard”, those were installed at the extremities of each longline. The experiment ended when the devices were withdrawn from the sites.

Statistics

Since only one observation was made with the “Gator Guard” devices during this study, it was not possible to make statistical analyses with those data.

According to Kolmogorov-Smirnov and Shapiro-Wilk normality tests, data related to the observations with the “Irri-Tape” devices were not normally distributed (P < 0.05), even after transformations. However, the analysis with Box-Liung Statistic shows that there is no evidence of autocorrelation between observation points of each time series of the study (P > 0.05), which means that the bird counts were independent from one another. Thus, the abundance of the birds could be gathered by site (untreated, treated with no device, treated with devices) in each bay. The non-parametric test Mann-Witney (α = 0.05) was used to compare abundance of birds on the treated site with no devices and the one with devices present in each bay.

Results

Bird abundance

The double-crested cormorant (74.5%) was the prevalent species in Bay of Caribou, whereas in the Bay of St-Thomas, two species prevailed, the double-crested cormorant (46.5%) and the common tern (50.7%). It should be noticed that the common terns were totally absent from the Bay of Caribou sites. In term of absolute numbers, there were more birds present on the bags in the Bay of St-Thomas than in the Bay of Caribou.

The absence of autocorrelation in the time series indicates that the abundance of the birds in Bays of Caribou and St-Thomas had not decreased to a significant degree over time. Thus, the birds were constantly in the area and there was no effect of migration on the abundance of the birds at the time of the study.

Devices effects

Results of statistical tests indicate that “Irri-Tape” devices on the treated site of the Bay of Caribou significantly reduced the number of all bird species (P = 0.001) as well as the number of double-crested cormorants (P = 0.005). In fact, there were 5.4 times fewer birds on the treated site with the devices present than at this same site without them. However, in the Bay of St-Thomas, the devices did not significantly reduce the number of all bird species (P = 0.070), double-crested cormorants (P = 0.653) and common terns (P = 0.192). In fact, common terns were 3.8 times more numerous on the treated site with the devices than on this same site without them.

Figure 3.  Average abundance (± standard error) of birds with all species and double-crested cormorants (Phalacrocorax auritus) observed on floating bags in the untreated site (UT), on treated site with no devices (ND) and on treated site with devices (WD) in the Bay of Caribou.

Figure 4.  Average abundance (± standard error) of birds with all species, double-crested cormorants (Phalacrocorax auritus) and common terns (Sterna hirundo) observed on floating bags in the untreated site (UT), on treated site with no devices (ND) and on treated site with devices (WD) in the Bay of St-Thomas. Error bars represent typical errors.

The bird observers from each bay noticed that the double-crested cormorants tended to perch at the extremities of the longlines in all sites. Moreover, these cormorants seemed to avoid the “Irri-Tape” devices during the first week after its installation by perching the farthest away possible from those. Then, one week later, the birds seemed to get closer to the devices. The observers also reported that the devices broke often during storms or high winds. The tapes broke, central stem of the device bended and the device fell on its side. Furthermore, the tapes had to be replaced regularly since they were losing their shining after a while.

As for the only observation with the “Gator Guard” devices, the bird observers reported that the birds completely ignored the presence of the alligator head devices. In fact, the double-crested cormorants, which composed all the birds on the floating bags at that moment except for the presence of Great Blue Heron (Ardea herodias), were swimming very close from the devices without being bothered by these.

Discussion

This study indicates that there is a prevalence of the double-crested cormorants (Phalacrocorax auritus) perched on the floating oyster pockets, as noticed in other studies carried out in eastern New Brunswick (Comeau et al., 2006; St-Onge et al., 2007; Comeau et al. 2009). The cormorants are recognized for roosting close to the aquaculture activities, especially if the reared species are edible (Glahn et al., 2000; Dorr et al., 2004; Roycroft et al., 2007). Since the oysters are protected from the birds in floating bags, it is possible that the cormorants benefit from this artificial platform mainly to rest close to their fishing sites and far from the predators.

In the Bay of St-Thomas, the common terns (Sterna hirundo) were almost as abundant as the double-crested cormorants. The high abundance of terns in that bay can partly be explained by their closeness of one of the largest colonies of common terns in the Maritimes which is in Kouchibouguac, New Brunswick (Erskine, 1992). In fact, this nesting site is approximately 40 km from the Bay of St-Thomas. However, their absence on bags in the Bay of Caribou can be explained by the buoys installed above the bags which allowed the complete immersion of the bags 3 cm under water. This depth is probably too deep for the common tern which has a rather short tarsus at 19 to 21 mm long (Schodde & Mason, 1974).

Birds with all species, including the double-crested cormorants, avoided being on the bags of a site where there were “Irri-Tape” devices in the Bay of Caribou. This means that the devices were effective to reduce the number of birds roosting on the floating bags in this bay, particularly for the cormorants. However, since experiment trials were carried out over a short period of time, it is not possible to extrapolate these results for spring, early summer and late fall where strong migrations of several species of birds normally happens in eastern New Brunswick.

In the Bay of St-Thomas, the “Irri-Tape” devices did not decrease the abundance of birds with all species, double-crested cormorants and common terns. The low abundance of cormorants on the treated site does not allow concluding that the devices were ineffective since very few cormorants were present on this site before the devices were even installed. However, the common terns were present in large numbers on the bags of the treated site. These birds tend to gather in large numbers outside their nesting sites to mutually preen their feathers, particularly after the nesting period (Palestis & Burger, 1998). In fact, terns probably showed this behavior at the time of the observations since the nesting period must have been already over. Moreover, it is possible that this social behavior let them let their guard down as for their anti-predatory vigilance (Palestis & Burger, 1998), which would explain their lack of reaction toward the deterrent devices in place.

As for the “Gator Guard” devices, they do not seem efficient to deter birds from oyster culture floating bags, according to the only observation made in St-Thomas Bay. It is possible that birds from eastern New Brunswick do not know the danger linked to alligators. Indeed, the double-crested cormorants which do not migrate very far in the south in winter did not have the instinct to react face to the fake alligator heads present on the oyster culture site since they most likely never saw any.

Although the “Irri-Tape” devices has potential in reducing the number of double-crested cormorants present on the oyster culture floating bags, the brittleness of the devices and time required to repair them are not very practical aspects for oyster growers. Indeed, these tapes did not seemed resistant to climate conditions found typically in aquaculture sites in eastern New Brunswick. Furthermore, the installation “Gator Guard” on oyster culture sites devices is not an option to deter birds from oyster culture floating bags. Future studies will be necessary to develop a system which could significantly decrease all bird species on the oyster bags and which would ask for only a minimum of maintenance so that the system can be functional over a prolonged period.

Acknowledgements

Thanks to Paul Savoie and Léon Lanteigne for installing the devices and counting the birds. Thanks also to Rhéal Savoie (Bouctouche Bay Industries) and Léon Lanteigne for their help in the conception of the deterrent devices. This study was financed by the Aquaculture Innovation and Market Access Program (AIMAP) from the Department of Fisheries and Oceans Canada in partnership with the New Brunswick Professional Shellfish Growers Association.

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