THE OREGON DRAGONFLY AND DAMSELFLY SURVEY

The following is exerpted from a letter sent to the U. S. Forest Service in June, 1994

The summer of 1991 I began a project to study the longevity and distribution of individuals of three species, Aeshna palmata, Aeshna umbrosa and Aeshna interrupta, around the lake. Dragonflies in the genus Aeshna are commonly known as Blue Darners. They are large strong flying insects. The males spend most of their adult life on the wing patrolling the shoreline for ovipositing females and feeding on mosquitos and other small insects. The females usually only come to the water to mate and to oviposit in emergent vegetation and the soft wood of floating logs. Todd Lake has very little emergent vegetation so they oviposit exclusively in logs most of which are found at the shallow south end of the lake near the outlet stream. The nymphs take two years to develop and stay most of that time hiding in cracks in floating and submerged wood. They are predators, feeding on mosquito larvae and other aquatic insects.

The method I used to track individual dragonflies was to capture them and mark their wings with a series of dots using bright colored, fast drying felt-tip paint markers. They were then released. Different colors were used to designate each marking period and unique dot patterns allowed the identification of individuals. I marked approximately 350 A. palmata, 150 A. umbrosa and 100 A. interrupta. All marked specimens were male. My estimates are that only 5% to 10% of Aeshnas seen at the lake are females. I also estimate that 10% to 25% of the males at the lake were marked, although this estimate may be high. The study showed that many marked dragonflies were still flying after four weeks and a few were still observed after seven weeks. I do not know if the relative number of individuals of each species marked was due to differences in population densities or because some species are easier to capture than others.

In 1992 the populations of two species, A. umbrosa and A. interrupta, plummeted while the A. palmata population appeared to remain stable. I was only able to capture and mark twelve A. umbrosa and no specimens of A. interrupta were observed or captured. At Todd Lake the emergence of Aeshna nymphs into adults is dependent on weather conditions and how early in the season the snow melts, but in general A. palmata emerges first between mid June and mid July. A. umbrosa begins emerging about two weeks later, followed in another week or two by A. interrupta. The winter of 1992 was mild and spring was early, so emergence began early also. By early July A. palmata was mostly emerged and A. umbrosa was ready, but before they could three commercial nymph collectors "harvested" most of them for fishing bait. These three individuals told me they were professional river guides on the Deschutes. Their technique was to roll over floating logs or lift submerged logs to the surface and then walk along the log and pick off all the nymphs clinging to it. They each had a one gallon milk jug with the top cut off hanging around their neck on a cord. When the jug was full the nymphs were transferred to an icechest. The icechest was filled with many thousands of nymphs. They were taking all the nymphs they found, even the very small first year ones, as well as the ones that were so close to emergence that they would die before they could possibly be used for bait. Many also probably died from the stress of overcrowding and Oxygen deprivation. They referred to the nymphs variously as mayfly nymphs, stonefly nymphs and "helgramites".

The winter of 1993 was severe followed by a cold, wet spring and summer. Dragonfly emergence was delayed and the nymph harvesters were able to collect most of them before any emerged. I spoke to one individual I observed collecting about the impact the activity was having on the dragonfly population and that a "special use permit" from the U. S. Forest Service was probably required. He expressed concern that he might be damaging the population but the next weekend he was back and claimed to have obtained a permit. He seemed embarrassed to see me and left quickly. In 1993 I observed only a few dozen Aeshnas flying at Todd Lake.

I originally became aware that dragonfly nymphs were being harvested commercially in 1986 when Dr. Norm Anderson, Professor of Aquatic Entomology at Oregon State University, brought it to my attention. He asked my opinion whether the harvesting activities at Crane Prairie Reservoir and other nearby lakes was having a negative impact on dragonfly populations. At that time I really did not think the populations could be severely affected because of the vast amount of habitat available. The practice has continued for over a decade now and as the market has grown and accessible picking grounds have been depleted the harvesters are exploiting more lakes each year. Todd Lake has served their purposes ideally the past two years because the majority of the nymphs are concentrated in shallow water at on end of the lake. There is the added benefit that because the elevation is higher the nymphs emerge later, thus extending the period that they are available. The higher elevation may be a barrier that isolates Todd Lake from rapid re-population from nearby lower elevation lakes. There is the possibility that the dragonfly populations at Todd Lake may be isolated enough to have developed unique genetic adaptations to their habitat. The three species in question will undoubtedly re-populate if left alone, but their "Todd Lake uniqueness" may already be lost.

Dragonflies are important members of aquatic invertebrate communities, preying on vast quantities of mosquitos and other insects and in turn being consumed by fish, amphibians and birds. The large scale removal of them from these ecosystems, especially the smaller lakes has unpredictable consequences, but I can not believe they will be positive.

I recommend that harvests at Todd Lake and other small lakes be totally banned and that bans be ordered on other Deschutes National Forest lakes until studies can determine the impact of this practice. Signs should be posted prominently at each lake and all bait merchants and river guides should be informed of the areas that are off limits. If harvesting is allowed to continue, it should be carefully regulated on National Forest Service lands and "special use permits" should be required. I do not believe it is necessary to regulate individuals involved in small scale scientific collecting or anglers collecting a few nymphs for their own use.

ACTIONS TAKEN BY THE U. S. FOREST SERVICE

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