Alewives migrate into freshwater from the ocean to spawn, but can stay and survive in freshwater. They have been a problem in Lake Champlain, after their introduction in 2003, because they compete with native fish species and eat eggs of other fish. They also provide an insufficient diet for Lake Trout and Atlantic Salmon, causing a decline in native species. Some practices for control used in the Great Lakes, that could also be used in Lake Champlain, would be the introduction of a predator species, such as Chinook salmon and steelhead/rainbow trout. These fish also provide fun for anglers, as Chinook salmon can become quite large in size.
One of the larger effects of Alewives on Lake Champlain is its destruction of the zooplankton community. Since Alewives main food source is the zooplankton, they can cause a drop in zooplankton numbers, which in turn can effect the inner workings of the lake. By eating large amounts of zooplankton, algal blooms can occur because their are not enough zooplankton to keep algae in check. Water clarity and and nutrient dynamics of the Lake are then altered from the algal blooms.
Alewives, as stated before, can cause a large problem when they feed on the eggs of native fish, such as the Lake Trout. Feeding on the eggs can be a bigger problem than food competition, and can cause mass mortality in native fish. In a study of Lake Ontario, Alewives were found to cause a 100% mortality in Lake Trout fry in near-shore regions where Alewives were common. If Alewives are not controlled and monitored, Lake Trout in Lake Champlain may see the same fate.
Looking at the map to the left, one can see the red areas around the Lake Champlain basin, showing that Alewives have been introduced to our area. On the map one can see how they are native to coastal areas since they only come into freshwater to spawn, but now they have made it far upstream and become invasive in areas including Lake Champlain.Map from: http://www.greatlakesfisherman.com/gallery/files/1/alewiferange.gif
"Vermont Lakes and Ponds- Alewife." Vermont Dept. of Environmental Conservation. N.p.
,Nov. 2011.Web. 11 Apr. 2012. <http://www.anr.state.vt.us/dec/waterq/lakes/htm/ans
/lp_alewife.htm>.
One should note that the introduction of a natural predator into an unnatural environment could have equally adverse effects as the alewives themselves. Although this form of biocontrol is a viable option it must first be tested and observed as to not disrupt the ecology of Lake Champlain further , or any other water system for that matter.
ReplyDeleteI have had first hand experience dealing with thiamine deficiency in lake trout fry. I worked down at the Rubenstein lab for Ellen Marsden over the last couple months taking care of lake trout fry. Some of lake trout fry populations were from hatchery broodstock, which were fed a normal diet with thiamine, while other populations were from lake trout from the lake. Normally lake trout feed on rainbow smelt which contain thiamine. Alewives have replaced rainbow smelt as the primary food source in Lake Champlain. We observed post-emergent mortality trends between thiamine deficient fry, and broodstock fry. Studies have not been finished, but thiamine deficient populations showed higher mortality through simple first hand observations. With the lack of lake trout recruitment, it is apparent that thiamine deficiency due to an alewife diet is effecting post-emergent mortality of lake trout.
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