In this case, when alewives go into the winter and they don't have enough fat reserves stored up, they tend to go into the spring really stressed. Many of the alewives now kicking the bucket are ones that hatched late last summer and were smaller and weaker than their brethren born earlier, Burzynski explained. Members of the herring family, alewives are not native to Lake Michigan, which is also at the root of their annual die-off. After the St. Lawrence Seaway opened, alewives began to make their way to Lake Michigan from the Atlantic Ocean, arriving in the late 1920s and early 1930s. They're just not a tough fish.
Any fish can be susceptible to rapid changes in water temperature, but alewives even more so.
Surface water temperatures in Lake Michigan have been slightly colder than normal for this time of year, around 58 to 60 degrees, Burzynski said, and it's taking longer to warm up. Wind direction also helps decide the final resting place of dead alewives. Winds from the east and southeast will push dying alewives on to the Wisconsin shore. During the 1960s, so many dead alewives littered Wisconsin's beaches that bulldozers were needed to scoop them up. That die-off was caused by an overabundance of the fish that outstripped their food supply, Burzynski said.