The University of Michigan Biological Station (UMBS) was founded in 1909.
Great Lakes Coastal Waterbird Survey: Cormorants and Colony Co-Nesters
Do large colonies of double-crested cormorants reduce populations of recreational and commercially important fish? These birds, which staged a remarkable come-back in the Great Lakes after being nearly wiped-out by DDT in the 1960s, are now considered a nuisance species by many anglers and are the subject of intense controversy. With funding from the US Fish and Wildlife Service, scientists based at UMBS have surveyed the distribution and abundance of cormorant nests during the period 1977-2014 to quantify the cormorant breeding population and inform whether action is necessary/desirable to actively reduce their numbers.
In the 1960’s, the Great Lakes population of double-crested cormorants was devastated by DDT, which thinned their egg shells to the point that they broke under the weight of the incubating parent. After the chemical was banned and the species was listed for protection under the Migratory Bird Treaty Act of 1918, the bird rebounded. Now, however, anglers consider cormorants a nuisance species and a serious threat to recreational and commercial fish species. In response, in 2005, notwithstanding the paucity of research to determine if culling would be necessary or desirable, state agencies began to issue depredation permits to reduce their numbers.
Do these birds really hurt fish stocks? This is a just-restored population of birds that used to fly over the area in the hundreds of thousands! On the other hand, much has changed environmentally in the Great Lakes over the years that perhaps has tipped the previous balance: alewife populations have declined dramatically in the 1980’s, for example, and these fish were previously an important part of the cormorant diet.
And if the birds are truly the cause of significant decline in fish like walleye and perch, should they be actively managed? What does the trend in Great Lake cormorant numbers look like? Has the culling undertaken over the past decade been successful? Or has the population of cormorants reached a carrying capacity that will naturally modulate numbers through density-dependent mechanisms such as competition for nesting sites?
To answer these questions, USFWS funded scientists based at UMBS from 1977-2014 to survey changes that were occurring in the distribution and abundance of cormorant nests in the US Great Lakes. Researchers scrutinized trends at multiple geographic scales ranging from the entire Great Lakes to much smaller localized groups of sites and analyzed the data at two temporal scales, allowing for finer-scale analysis of the time period after 2005, when active culling had become widespread. They found that the breeding population increased until the early 2000s and declined thereafter, a pattern that coincided with the onset of active control measures, but that could also have been precipitated naturally as the population of birds reached carrying capacity. Nest abundances at the smaller geographic scale were too variable to illuminate patterns. Researchers recommended continuing a complete census of nesting cormorants in the Great Lakes on a biennial basis to provide much-needed insight into lethal and non-lethal management options for USFWS.
In 2017, a federal court judge ruled that USFWS lacked sufficient understanding of cormorant abundance and impact to justify killing them and suspended the Agency’s authority to issue depredation permits until it learned more, reinforcing the importance that scientific data must play in this important wildlife management decision.