Ken Dahler, Taylor Ferreira and Ryan Glew(Team 11)

Problem StatementA growing Double-crested Cormorant

population is affecting sport fish populations as well as destroying island nesting habitat in Lake Champlain.

GoalsEvaluate why cormorant populations have

begun to grow so rapidly in the Lake Champlain basin.

Investigate how the increasing cormorant population is effecting the local fish populations

Look at what effects cormorants impose on island nesting sites.

ObjectivesTo assess the ecological risks associated with increasing

Cormorant populations, with focus on habitat destruction and alteration, fish consumption, and competition among piscivorous birds.

To identify factors that influenced the drastic increase of cormorants in the Lake Champlain basin.

To identify if and how Cormorants destroy habitat and how that affects other island nesting species.

Determine how cormorants impact sport fishing in Lake Champlain, and how they affect fish populations.

Review case studies and current legislation on management techniques to develop a management plan on how mitigate the negative effects of this species.

Double-crested CormorantOne of 40 species of CormorantsInhabits rivers, lakes and costal

areas in North America. Can weigh between 2.6 to 5.5

lbs. Body length between 28-35 in.Wingspan of between 45-52 in.

(Hatch and Weseloh 1999)

Feeding BehaviorSurface divers, they forage underwater for fish. Fully-webbed feet propel their slim bodies on dives up to

60 feet deep. Chases prey underwater, grabbing them in their bill.

(USFWS, 2009)

(Hatch and Weseloh 1999)

Cormorant fishing on the Nagara River, Japan

Nuisance Species AquaculturePerch on boats and docks

Destruction of private propertyKill nesting trees (aesthetics) Non-charismatic speciesPredate game fish?

Findings

Historic Populations• Archaeological records show skeletal remains of

Double-Crested Cormorants from native American sites that date 500-5000 years old.

• Remains found throughout all of continental US and into Canada

• Records indicate higher populations before English settlement

• Late 1800s – early 1900s = big decrease• Early 1900s – mid 1900s = increase• 1960s and early 1970s = decrease• Since 1970s = increase

(Wires, Cuthbert 2005)

Range

(Hatch and Weseloh 1999)

Regional Population Growth

• Since 1970s:• Great Lakes cormorant populations

increased at annual rate of 29% (Weseloh et al. 2006)

• Coastal New England population increased at annual rate of 6% annually (Krohn et al 1995)

• Where is Lake Champlain located…?

Lake Champlain Population Growth

• 1970s: Cormorants = rare visitors• 1981: First nest observed • 1981 – late 1990s: population has

shown annual increase of 21%

(Duerr 2007)

Population Misconceptions• Cormorant populations are

higher now than ever• Cormorant populations are

expanding to “new” territories

Factors that Influenced Population Growth• 1969: Canada bans the use of DDT• 1972: US bans the use of DDT (Hatch and

Weseloh 1999)

• 1972: Cormorant protected under Migratory Bird Treaty Act (Hatch 1984)

• Catfish farms help decrease overwinter mortality

• Fishermen overharvest large predatory fish in Lake Champlain…increase in smaller fish populations (Allan Strong)

Effects on Vegetation• Cormorants are colonial nesting birds• Remove sticks and leaves from trees and

shrubs to use as nesting material• Slows growth and increases mortality of

vegetation• Acidic guano that kills trees and ground

shrubs

(Sullivan et al. 2006)

Change in forest cover on Middle Island, Lake Erie, due to cormorant nesting between

1995 and 2001. Hebert et al. 2005

~1,000 nests

~4,000 nests

Effects on Other Bird Species• When cormorants inhabit a new location, they

will often nest with other colonial waterbirds (Allan Strong)

• Habitat destruction by nest construction and guano often displaced other native island-nesters (Duerr 2007)

• Early arrival to nesting sites can directly displace other birds looking to establish nests (Allan Strong)

Lake Champlain• YOUNG ISLAND/ FOUR

BROTHERS:– Snowy Egrets– Cattle Egrets– Black-crowned Night

Herons– Ring Billed Gulls– Greater Black-backed Gulls

• MISSISQUOI NWR– Great Blue Herons

• BIXBY ISLAND– Black-crowned Night

Herons• POPASQUASH ISLAND

– Common Terns* (Endangered)

(Audobon Vermont 2010)

http://valdodge.com/wp-content/uploads/2008/03/leslie-spit-cormorant-trees-0822m.jpg

http://www.wildlife-research-team.org/cormorants.jpg

http://artzi.invianet.com/autumn/Cormorant4.jpg

Effects on Fish WARNING: DISTURBING PICTURE ON

NEXT SLIDE!!

Effects on Fish

(Lake Champlain Fishing Forum)

•Cormorants are opportunistic foragers that consume the most abundant fish species available. (Allan Strong)

Effects on Fish:(Lake Oneida, NY)

(Rudstam et al. 2004)

Effects on Fish: (Lake Champlain)

Duerr (2007) conducted research from 2001 to 2002 examining the stomach contents of cormorants in Lake Champlain.

Collected 154 cormorants for diet analysis From these samples, 2,255 fish of 21 species were

identified. Most common prey items identified were Yellow Perch

and Rainbow Smelt Yellow Perch being the most abundant prey item by

mass (78%) These results suggest that cormorants may have a

negative effect on the Lake Champlain Yellow Perch population, such that they did in Oneida Lake.

(Duerr 2007)

What are the effects on sport fishing?

Should sport fishermen really be concerned?

Cormorants do consume large quantities of yellow perch

Do not commonly feed on the larger sport fish

However...

Management Options

Non-Lethal Methods of Control

Harassment: Nest or Egg destructionEgg OilingMonofiliment barriers

HarassmentPyrotechnic DevicesAutomatic ExploderAlarm or Distress

callsLightsWater-Spray devicesHuman EffigiesHarassment patrols

Images from scaregun.com

Nest and/or Egg DestructionForm of HarassmentDestroying nests and/or eggs is a viable

option in harassing birds to relocate a new nest

If done too early in the breeding season, birds have opportunity to build new nest, and lay a 2nd clutch (not useful)

Egg OilingKills embryos before they have opportunity to

develop.What does putting oil on an egg do?With What?Why is this method so effective?Egg Flotation Test

Egg oiling is very effective

Table from Johnson et. Al 2000

Monofilament barriersHave a variety of applications from

aquaculture to agricultureCan be as simple as 1-5 lines being stretched

over a small field, pond or island and tied off.Can also be a complex grid system with 6-12”

grid squares.Makes travel difficult for large birds

Wire Barrier SystemsThe Picture to the left and bottom are from Popasquash Island, and shows the wire barrier system in place there to reduce the number of cormorants from landing and nesting there. Established to protect the Common Tern.

Images from Beckett 2008

Monofilament BarriersPopasquash Island: has an experimental

monofilament barrier established with lines tied between metal stakes and small shrubs

Discourages and reduces the ability of Cormorants and Other large birds from landing.

This method is proving to be affective against cormorants due to their size and poor agility, but is not as inhibiting for terns and other small agile birds.

Popasquash Island Is a very small

island between Swanton and st. Albans VT

It is home to one of the few breeding habitats for the endangered common tern

Try to keep cormorants off of the island

Popasquash Island Grid SystemThis Diagram Shows the approximate grid system created on Popasquash Island. The darker lines on the northern side of the island represent areas where enclosures were created for common terns to nest in. Image from Beckett 2008.

Lethal Management OptionsThe last resort, populations have become to

large, or destructive and a large number of individuals need be removed from the area.

The right to use lethal control must be issued by the USFWS, after a representative from the service has come and completed a full site assessment and determined that non-lethal control is no longer effective.

If lethal control is instituted, there are 2 acceptable methods

The use of non-toxic lead free shot must be usedAsphyxiation

ConclusionsPopulations have exploded over the past 30 yearsPopulations may be lower than they historically

were, but they are high compared to recent records (past 30 years)

It appears they are re-colonizing old breeding grounds, rather than expanding to new territory

Populations have boomed since DDT banScience suggests cormorants are not

detrimentally affecting bait or sport fish populations

They do destroy island nesting sites, making them uninhabitable for other island nesters

RecommendationsWe recommend the use of non-lethal harassment

techniques Egg Oiling Monofilament barriers Human Patrols at nesting sites

The lake Champlain population is not large or destructive enough to warrant lethal management, but it could be an option in the future if populations continue to grow exponentially

Outlook for the FutureMore information needed on

population size and nesting locations.

Non-lethal options should be explored before lethal techniques are used.

Issue of social versus biological carrying capacity should be addressed.

Summary: Problem Statement: A growing Double-crested

Cormorant population is affecting sport fish populations as well as destroying island nesting habitat in Lake Champlain.

Goals: Evaluate why cormorant populations have begun to grow so rapidly in the Lake Champlain basin. Investigate how the increasing cormorant population is effecting the local fish populations. Look at what effects cormorants impose on island nesting sites.

Conclusion: Increasing cormorant populations are affecting small island nesting sites, and possibly diminishing sport fish populations.

Audubon Vermont. (2010). Lake Champlain Colonial Waterbird Database. from < ://vt.audubon.org/colonialWaterbirds.html> Accessed 23 March 2010.

Beckett, Sean. 2008. Assessing Endangered Lake Champlain Common Tern Predator Deterrent Systems via Video Surveillance. VINS Environmental Science Research Fellowship. Pp. 1-21 August 2008.

Duerr, A.E. (2007). Population Dynamics, Foraging Ecology, and Optimal Management of Double-crested Cormorants on Lake Champlain. Dissertation to the Faculty of the Graduate College of the University of Vermont. May, 2007.

Green Mountain Audubon center: 255 Sherman Hollow Road. Huntington, VT 05462 (802)434-3068

Hatch, J.J. (1984). Rapid Increase of Double-crested Cormorants Nesting in Southern New England. American Birds38:984-988.

Hatch, J. J., and D. V. Weseloh. (1999). Double-crested cormorant (Phalacrocorax auritus). Account 441 InA. Poole and F. Gill, editors. The Birds of North America, The Academy of Natural Sciences, Philadelphia, Pennsylvania, and The American Ornithologists’ Union, Washington, D.C. USA.

Hebert, Craig E., Jason Duffe, Chip Weseloh, and Ted Senese. "Unique Island Habitats May Be Threatened by Double-Crested Cormorants." The Journal of Wildlife Management 69.1 (2005): 68-76. Web.

Johnson, J.H., Ross, R.M., Farquhar,J. March 1, 2000. The effects of Egg oiling on Fish Consumption by Double-Crested Cormorants on Little Galloo Island, Lake Ontario. New York State Department of Environmental Conservation, Watertown, NY 13601

Krohn W. B., R. B. Allen, J. R. Moring and Hutchinson A. E. (1995). Double-Crested Cormorants in New England: Population and Management Histories. Colonial Waterbirds, 18(Special Publication 1): 99-109.

Rudstam, L.G., VanDeValk, A.J., Adams, C.M., Coleman, J.T.H., Forney, J.L., Richmond, M.E., and (2004). Cormorant Predation and the Population Dynamics of Walleye and Yellow Perch in Oneida Lake. Ecological Applications.14(1), 149-163.

Strong, Allan. Personal interview. 24 Mar. 2010.

Sullivan, K. L., Curtis, P. D., Chipman, R. B. and McCullough, R. D. (2006). The Double-Crested Cormorant: Issues and Management. Retrieved from Cornell University Cooperative Extension. Department of Natural Resources, Cornell University, Ithaca, New York. < http://wildlifecontrol.info/pubs/Documents/Cormorant/Cormorant.pdf>

United States Department of Agriculture, Bird Predation and Its Control at Aquaculture Facilities in the Northeastern United States, Animal and Plant Health Inspection Service, APHIS 11-55-009 Issued June 1997

Wires, L.R., F.J. Cuthbert, D.R. Trexel and A.R. Joshi. (2001). Status of the Double-crested Cormorant (Phalacrocorax auritus) in North America. Final Report to USFWS < ://library.fws.gov/Bird_Publications/cormorant_status01.pdf>