Aquatic Nuisance Species
These bug-eyed, green aliens are swimming towards your lands and waters!
In an earlier issue, we introduced the subject of alien species, including pike, zebra mussels and plants. In Alaska, aquatic nuisance species (ANS) may prove a greater threat than fresh-water or land based invaders. In their home waters, these species may be relatively harmless. If introduced into other areas, with the right conditions, these species can thrive as they have moved away from their natural predators. They may upset the ecosystem balance, prey on local species, reduce biodiversity, and impact subsistence.
ANS invasions have occurred for centuries in North American waters. The greatest source of ANS are transport ships from foreign ports. Historically, ballast waters have been the most common method of introducing foreign species to North American waters. ANS move attached to ship hulls, carried in ballast waters and transported by people. Other sources of introduction are economically based- including aquaculture, sport fish stocking, the bait business and aquarium trade.
With shorter shipping times and cleaner harbors, alien species may better survive travel to thrive in their new homes. San Francisco Bay is a prime example of an ecosystem heavily impacted by ANS. Through many activities, including shipping and oyster farming, it has continually been exposed to non-native species, and hosts more than 210 of them. Over the last decade, a new variety has arrived about every 12 weeks.
The European Green Crab and Atlantic Salmon are two species that Alaska may need to be watchful for.
European Green Crab was first introduced on the eastern seaboard in the 1700s. In 1985, it was found in San Francisco Bay, and has since spread along the California and Oregon coastlines. Currently, they are documented as far north as the Willipa bay in Southwest Washington.
They have the potential to spread rapidly along the Pacific coast, and are thought to be expanding their range by hitching rides on ocean currents or in ballast waters. They have wide tolerances in salinity and temperature. Their estimated range extends from Baja California to the Aleutians.
The green crab is voracious, and has been described as an eating machine. They have stronger and more maneuverable claws than other crabs. They like: barnacles, clams, oysters, mussels, worms, urchins, young Dungeness or red rock crabs, some plants and small fish. They live from three to five years, and adult males reach carapace widths of about three inches. Due to their small size, their use as human food is limited.
They have the potential to restructure the crab population in ecosystems that they become established in, as they feed on the larvae of other crab species, and can devastate their near shore nurseries. They like shallow water, out of range of octopus and other natural predators. The crabs natural habitat is under rocks, and in disturbed areas, making it difficult for the birds to keep them in check. They pose a direct threat to shorebirds, as they have similar diets. It has been rumored they were recently sighted in Ketchikan. The State of Alaska, Department of Fish & Game is setting out special green crab traps several coastal communities.
Atlantic Salmons introduction on the Pacific Coast has occurred relatively recently. Salmon farmers in British Columbia began producing Atlantic salmon in the mid-1980s. Currently, Atlantic salmon aquaculture industries are established in both BC and Washington. Theres no documentation of an established, naturally reproducing Atlantic salmon population, but there are signs this may be starting to occur.
If this does occur, there no doubt will be habitat competition with sometime already weak runs of Pacific salmon. There is also the possibility of disease introduction and habitat degradation around net-pen sites. Genetic mingling is not believed a threat because Pacific and Atlantic salmon are different species. Thousands of salmon are known to escape from BC pens. In these areas, habitat competition has been documented. Habitat degradation around the pens is a serious problem, but not one Alaska will face as fin fish farming is not allowed.
The virus ISA (Infectious salmon anemia) and sea-lice are present in some pen-reared salmon, and can easily spread through bays where they are being farmed. In New Brunswick, three bays were affected with ISA in 1996. Despite efforts to control the disease by slaughtering all fish from the infected areas, it has now spread to at least seven bays, and is believed endemic to the area.
Atlantic salmon look similar to king salmon, but with brown coloration and small, black, x-shaped spots. They also lack spots on their tails. They become weak after spawning, but don't always die like Pacific salmon.
It is generally not believed they could become established along the Pacific coastline, for past efforts of introduction in the last century failed. Despite this, there is the possibility they may become established in Pacific northwest streams. If you see this, please notify the nearest ADF&G office, or contact a local USFWS office.
If you have questions about ANS, or see non-indigenous animals, contact:
Mr. Bob Piorowski, Mariculture Program Coordinator, Alaska Department of Fish & Game. (907) 465-6150
Adelheid Herrmann, Fisheries Economic Development Coordinator, Representative on the Western Panel on Aquatic Nuisance Species (907) 246-8332
Jack Lorrigan, Tribal Biologist, Sitka Tribe of Alaska, Alternate on the Western Panel on Aquatic Nuisance Species (907) 747-3207
Gary Sonnevil, USFWS, Project Manager, (907) 262-9863.