Waterbird Colonies of Georgian Bay and the North Channel, Lake - PowerPoint PPT Presentation

The Changing size of Colonial Waterbird Colonies of Georgian Bay and the North Channel, Lake Huron between 1995 and 2015. Observations made when sampling for the 2015 status of contaminants and vitamin A in double-crested cormorants. by James P. Ludwig and F.E. ‘Ted’ Ludwig II

Vitamin A Study: Rank Order of Circulating Vitamin A.  Lake & Region 1991 2015  Lake Ontario AOC 7 (16) 8 (150)  Western Lake Erie 8 (13) 7 (249)  Saginaw Bay AOC - 6 (256)  Lake Superior AOC - 5 (345)  Northern Lake Michigan 5 (36) 4 (533)  Northern Green Bay 6 (33) 2 (686)  Eastern Lake Erie - 3 (674)  Georgian Bay 2 (123) 1 (841)  Lake Superior 1 (255) -  Mean Concentration ppb 76 466 +613%

OVERALL VITAMIN A STATUS  THE PATTERN OF DEPRESSED VITAMIN A IN BIRDS FROM THE AOCs IS THE SAME AFTER 24 YEARS.  TH ABSOLUTE CONCENTRATION OF VITAMIN A HAD INCREASED BY MORE THAN SIX FOLD.  THE INCREASE IS VERY LIKELY OWING TO DIET AS GOBIES REPLACED ALEWIVES IN THE FOOD WEB.  HOPE TO REPEAT IN 2016 ADDING IN OTHER AOCs AND MORE REFERENCE AREAS IN LAKE SUPERIOR.

Research Design in 2015  Repeat the sampling from the same colony sites sampled in a 1991 pilot study.  Suspected that DCCOs had shifted to some new sites with culling, egg oiling programs in place since 2004.  Some regions (Straits of Mackinac, North Channel) had no large chicks to sample; sampled 4 AOCs.  Substituted nearby sites whenever possible.  Coverage area included at least one site in every GL.

Northern Georgian Bay DCCOs: Changed nesting Numbers. Island Site 1995 2015 West Rock 2,350 0 Erie Shingle 550 250 Snake Island 0 450 Gull Island 1,450 140 SW Gull Rocks 780 unknown Totals 5,230 840 Percentage 100 16 84% decline

North Channel, LH DCCO Nests: Colony sites west to east Island Site 1995 2015 Bird 125 0 Middle Grant 800 250 Herbert 860 0 Talon Rocks 200 0 West 1,900 0 Batture 300 0 96% decline Cousins 1,050 0 Egg 625 0 SW Gull Rock 450 0 Elm 960 69 Flat Point Reef 480 unknown West May Island Reef 200 0 Heywood Rocks 150 0 Totals 8,100 319

Caspian Tern Colonies in Lake Huron Island Site 1995 2015 St. Marys River 95 15 Cousins 285 0 Elm 189 39 Papoose 265 0 Gull 0 0 abandoned 1992 SW Gull Rocks 205 nd appeared 1992 Halfmoon 0 0 abandoned 1991 Totals 1,039 54 (95% decrease)

Other Observations or Impressions: Lake Huron: North Channel & Georgian Bay.  The very few DCCOs seen were roosting, not nesting, at most sites that were used in 1995.  Every Herring Gull colony visited had very few live chicks or fledglings except Erie Shingle.  Common terns that were exceedingly rare in 1995 appear to have recovered somewhat. Large colonies were seen at Cousin and Elm Islands, probably more than a thousand nests total. A possible indication of a resurgence in emerald shiners after alewife decline.

Other Observations or Impressions: Lake Michigan 1995 - 2015  Two of four DCCO colonies off the Garden Peninsula abandoned 2015, fewer nests in remaining colonies.  Beaver islands DCCO colonies reduced in number and size except at Hat Island.  Apparently all Michigan colonies of Caspian terns were abandoned except Bellows Island in 2015. One colony in Wisconsin. Lake Michigan nests down >80%.  Herring Gull reproduction very depressed except possibly at Bellows Island in Grand Traverse Bay.

Change in two Decades  Relocation to inshore islands from more pelagic sites.  Populations shift to more productive bay areas in L H.  Our observations consistent with report of DCCO colonies relocating to inshore areas of Georgian Bay between 2003 and 2004.  Probably owing to alewife collapse and gobies arrival.  Food propelled diving cormorants (and possibly diving ducks) much less affected than surface feeding species , except common terns. aka ‘the minnow gull’.  Herring gulls depressed; Ring-bills maintaining numbers owing to agricultural food supplies.

Changes to come?  Cormorants will prosper owing to available gobies.  Most other water bird species will suffer owing to the collapse of surface-available fish (alewives) unless they feed elsewhere: common terns feeding on the emerald shiner and ring-billed gulls feeding on insects and earthworms in farmed fields are the exceptions.  Other species likely at risk in LH colonies – herons.  Species expanding are white pelicans and American egrets. How and why is a complete mystery!

Research needed in 2016 – 2017 to guide Lake Huron Management?  A thorough and complete colonial waterbird survey. A subsampling strategy will not suffice because the colonial waterbird species move from site to site.  An inventory of all known waterbird nesting sites.  Description of the current diets of important species: Cormorants should be the top priority. Caspian Tern and Herring Gull productivity & diet data are lacking since the invasions of mussels & gobies and the alewife collapse have restructured their food webs.

Assignment: REPLACE SPECULATION and MODELS with REAL DATA.  ADAPTIVE MANAGEMENT has been based on models.  Effective ADAPTIVE MANAGEMENT requires real data based on field observations and measurements. We are at a potential ‘fork in the road’. Do we return to the old ways of doing field work to observe and measure changes in the Great Lakes, or do we make assumptions and default to models for our management paradigm? Models are cheap to develop, easy to generate, but hard to verify. Field work is difficult, often dangerous time consuming and expensive, but gives accurate data, whereas models are speculative projections at best [WAGs]. Which path will we follow?