1998 was a year of more intensive effort than previous years because it included monitoring by three groups: Meetz and Beckman's annual investigation, BioDiversity's summer-long research, and NPS personnel. Many locations were resurveyed if there was suspicion of missed juveniles or nesting activity in an effort to acquire the most complete information possible of territorial pairs and chicks. This combined effort substantially increased the accuracy of the survey, and recommendations have been made to continue this accuracy in subsequent years.
Forty-seven of the Island's interior lakes and 33 locations along the Lake Superior shoreline were surveyed between 26 July and 3 September 1998 either by boat, canoe, kayak, or walking along the shoreline.
Adult loons were recorded on 29 of the 47 interior lakes (62%) and 29 of the 33 Lake Superior sites (88%). Juvenile loons were present on 14 of the interior lakes (30%) and 13 of the Lake Superior sites (39%), and totaled 41. Productivity among the 52 pairs was 0.8 young/pair, higher than in the previous two years. This productivity rate is slightly above the range considered necessary for a loon population to sustain itself (range=0.5-0.79 young/pair). The average productivity of the 9-year loon survey (.64) is also within the range of sustaining the population. Ten pairs successfully raised twins in 1998, 5 on inland lakes and 5 on lake Superior. The total of 52 adult pairs is above the average of 44 for Isle Royale, and the total of 41 juveniles is notably above the average of 28.
When looking at productivity since the beginning of the formal Isle Royale monitoring program (1990-1998), it would appear that a regular 2-3 year cycle is occurring.
Beginning in 1991, a small number of Common Loons nesting on Lake Superior shoreline have been individually color-marked with leg bands and sampled (blood and feathers) for mercury and other trace metals. The mercury sampling in 1998 expanded to include Sargent Lake and several others that recorded elevated levels of fish mercury. Loons are a good bioindicator of mercury as they are obligate fish eaters (mercury accumulates in the aquatic environment), long-lived (adult survivorship of Lake Superior adults is 94%), and feed their young only from the natal territory.
The BioDiversity group is developing an atlas of territory delineation for Common Loons on Isle Royale. This atlas will improve the accuracy of NPS monitoring efforts and will be useful in management actions regarding loons.
Suggestions to improve nesting success of loons in high-use areas includes increased educational efforts to paddlers and powerboaters about loon nesting requirements, and the potential closure of known nesting areas to human use until approximately early July of each year. Natural Resource Management staff has already begun work on loon education projects for the 1999 season.
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