Tuesday, August 23, 2011

Bullfrog Battles

The Pender Island Farmers Institute and the Pender Island Conservancy are working together to initiate an American Bullfrog education campaign and eradication project on Pender Island with the assistance of Stan Orchard, a conservation biologist who’s company works almost exclusively on bullfrog eradication and control efforts in the greater Victoria area. Stan and his assistant have made a preliminary visit over two nights to survey and remove bullfrogs from some Pender Island ponds. In an interview with The Islands Independent, Stan Orchard said Pender Island is a good candidate for eradication which he estimates could take about five years. He believes it is possible because of the surrounding salt water so reintroduction could only occur if humans brought them back or if all sources are not found. It is hard to estimate the total cost of such a project, based on the experiences of other communities in the Victoria area. This could actually cost much more than initially estimated, since the bullfrogs have spread over a large area of North Pender since their introduction into a residential pond about fifteen years ago.
Stan Orchard and assistant catching a bullfrog on Pender

The American bullfrog is native to the east coast of the US, Ontario and Quebec and harvesting is restricted in some states because they taste so good. They are a common and popular part of the landscape in their home range. Bullfrogs came to British Columbia as a food source back in the early 1930's. After frog farm ventures failed, many bullfrogs were released. In later years bullfrogs were also part of classroom projects and could be sourced through garden supply outlets for residential ponds and water features. They were brought to some Gulf Islands, notably Lasqueti in the1930's for farming, to Salt Spring and more recently to Pender Island for a residential pond in the mid 1990's.

There are concerns that native amphibians are being reduced in numbers by the giant frogs, either through predation, competition for habitat, or by the introduction of disease. The large adults will eat anything that crosses their path and fits into their mouth, like birds, rodents, ducklings. This concern led to a research project studying the effect of the American Bullfrog on the native Pacific tree frog and the red-legged frog in Victoria area ponds by Dr. Purnima Govindarajulu while she was a PhD candidate at the University of Victoria. Through her research, she found that although American bullfrogs have been in the Victoria area since the 1930s-1960s, they exploded in numbers since the 1990's because of changes to the landscape that favoured the bullfrog. This included the alterations of wetlands to permanent ponds by agriculture and also by beavers, and the popularity of residential ponds, coupled with the loss of habitat for our native species. She recognizes that most eradication efforts after bullfrog introduction have not been successful, so she recommends education and prevention, and the enhancement of habitat for native frogs as a long term plan.

Dr. Govindarajulu  is now an amphibian/reptile/small mammal specialist with the Terrestrial Conservation Science Section of the BC Ministry of Environment. Through interviews with other amphibian specialists worldwide, she has reinforced her view that large scale eradication is very long term, very expensive and labour intensive. The scientific literature supports this, especially if bullfrogs are established and have spread in an area. In an interview with The Islands Independent, Dr. Govindarajulu emphasized that she is not against bullfrog control and says that communities and individuals need to determine what they are trying to achieve, whether it be to improve the conservation benefits for native species or the reduction of noise. Early removal of adult bullfrogs in April and May will certainly help in controlling noise and reducing the adult predation on native frogs, but there is also a balancing act with the removal of the primary predator of the juvenile bullfrogs

Work in BC is ongoing, with projects in the Okanagan and the Fraser Valley, looking at both eradication programs and range extension. Work on habitat restoration and long term landscape level projects are needed. It is known that if ponds dry up, bullfrogs can’t breed, so Dr. Govindarajulu recommends the construction and enhancement of temporary ponds as refuge habitat for native species. She recommends that property owners should take a site specific approach to control bullfrogs while enhancing native frogs. This could include draining ponds at the end of summer, increase plantings around ponds, fencing off irrigation ponds, as some examples. We need to also recognize that there are some predators that can help with bullfrog control, notably dragonflies, mink, otter, raccoons, herons, kingfishers and bullfrogs themselves. Bullfrogs are often described as tasting like chicken, which could make them a nutritious target for the racoons and mink in the Gulf Island, notorious lovers of all things chicken flavoured.

Beavers may be responsible for range expansion and can create habitat for both bullfrogs and native amphibians. In the Merville area, bullfrogs are in the ponds but with the adjacent intact forests, the native frogs have also persisted. In such a dry climate as the Gulf Islands many people have dug ponds - for livestock watering and irrigation, for water collection during the wetter winter months, accidentally creating an ideal habitat for the bullfrogs.

Dr. Govindrajulu has said that it is best to prevent them coming at all – as a warning to those Gulf Islands who do not yet have bullfrogs - be vigilant. If bullfrogs are introduced do something right away to get rid of them. We waited too long on Pender to make it an easy process. Now there are those who want to eradicate, and others who think we need to pick our battles carefully and plan our strategies accordingly. In a perfect world with unlimited volunteer energy and time and unlimited funds, it would still be a challenge to eradicate the island of bullfrogs. They have a head start on us. They are made to invade - their adaptation to their environment, their size, their fecundity with over 20,000 eggs laid at a time, their lack of selective taste buds with a huge mouth to eat almost anything, and their ability to move up to 5 km per year by travelling ditches and roadways gives them a big advantage. Some places outside their normal range lack enough predators to control them, and not many people in our neck of the woods have a taste for them. There is a chance with education to prevent the spread or learn how to manage frog habitats to favour the native frogs. At the very least, islands that do not have them can learn from this example.

1 comment:

  1. Update - Where have the bullfrogs gone? Late in the spring I would hear bullfrogs plopping into our ponds as I walked the water's edge. Then summer came and poof - no bullfrogs. No deep throaty noises at night. Some people spotted the odd frog dead by the road. But what happened to the invasion? On our farm, something made them go away. And we didn't do anything to remove or kill them.