How Invasive Species are Introduced and Spread

Invasive species are sometimes introduced intentionally to provide benefits to ecosystems and society. Examples of intentional introductions include:

• habitat restoration activities
• authorised fish stocking
• biological control of pests
   

Unintentional introductions often pose a more serious problem. The ways invading species are unintentionally introduced and spread include:

Scientists estimate that 65 per cent of the aquatic invasive species present in the Great Lakes – including the zebra mussel, round goby and the spiny water flea – have been brought in by ocean-vessels.

• release of ballast water from ocean-going ships and hull fouling (e.g. spiny waterflea)
• escape from fish farms (e.g. bighead, silver and black carp in the U.S.)
• opening of canals and waterways (e.g. sea lamprey)
• use of live bait (e.g. round goby)
• release or escape from aquarium or water gardens (e.g. fanwort)
• release from live food fish trade (e.g. bighead carp)
• unauthorized fish transfers or stocking (e.g. native species such as bass and pike)
• recreational boating and movement of equipment and gear (e.g. zebra mussels)
• Internet and mail ordering

Ships are by far the most significant way invasive species are introduced to the Great Lakes – ballast water accounts for the majority of foreign species introductions.

Photography
Large ship image from iStockPhoto.com