Prior to the 1970s the double-crested cormorant (DCCO) was declining along with another large fish eater the bald eagle. Toxins, especially DDT, appeared to be the culprit in both cases. In some areas like the Great Lakes, DCCOs suffered an 80 percent loss in population.
But things began to change in the 1970s. A US Fish and Wildlife Service report lists five reasons for the resurgence of the DCCO. They are:
• Ban on DDT (1972) and other pesticide reduction regulation. Prior to this time (but post WWII) widespread use of DDT occurred. Cormorants accumulated high levels of DDT through their food supply, which interfered with reproduction. Depressed populations began to increase after DDT was banned.
• In 1972 the DCCO was added to the Migratory Bird Treaty Act protected bird list. Before 1972, federal legislation did not prevent killing or harassment of cormorants during their annual cycle. Some states also provided special protection for DCCOs around this time.
• Human induced changes (e.g. accidental and intentional introduction of exotics; over fishing; changes in water quality) in aquatic communities in the breeding range.
• Development of aquaculture (e.g. catfish farms) in the south (especially Mississippi Delta region) that provided a new food source.
• Creation of additional breeding and foraging habitat (e.g. reservoirs, dredge spoil islands).
To most people of my generation and younger this resurgence of DCCOs looks like an invasion, however the USFWS report states, “...recent population increases may represent recovery towards historical (presettlement) levels in certain regions. In some areas where the DCCO has been documented as a recent breeder, the species is actually re-colonizing after an absence of 50 to 300 years.”
The DCCO is a large (length 27 inch, wingspan nearly four feet) dark (brown to greenish black) bird with an orange throat pouch, long tail and webbed feet. It gets its name from the tufts of feathers adults have over their eyes. Sexes look alike.
While the DCCO breeds from Alaska and Nova Scotia to Mexico and the Bahamas its breeding range is divided into five distinct geographical areas — Canada, U.S. interior, northeast Atlantic coast, southern U.S., Pacific Coast and Alaska. The USFWS documents an increase in breeding populations in three of these areas. They do not have sufficient data to detect trends along the Pacific Coast and Alaska. Numbers have also increased across wintering grounds.
While many people are thrilled to see this native species making such a marked comeback, many are not. The increase in cormorants has also created an increase in human-cormorant conflicts.
The primary areas of contention are among commercial and sports fishermen and aquaculture farmers. When commercial and sports fishermen look out and see a flotilla of cormorants they often see competition. However, most studies have found that cormorants, in natural waters, do not have a significant impact on sport or commercial fishes. Cormorants may have a negative impact in areas that depend on stocking of game fish.
Cormorants can create problems in areas of intense aquaculture. One 2000 study estimated that wintering cormorants in the Mississippi delta likely cost catfish farmers more than $5 million annually. There also appears to be a correlation between the increase in catfish farms and an increase in winter cormorant populations in Mississippi, Alabama and Arkansas.
In October 2003 the USFWS released a Final Rule and Record of Decision regarding the management of DCCOs. The ruling gives states more flexibility in managing cormorants.
The good news is DCCOs have made a wonderful recovery with populations approaching historical proportions. The bad news is DCCOs have made a wonderful recovery with populations approaching historical proportions.