Robert D. Barber Introduction
Gomphus apomyius (IMAGES) is a rare dragonfly inhabiting small, sand-bottomed streams. It was discovered in Burlington County, New Jersey, in the 1950's and later described from specimens taken in Texas (Donnelly, 1966). The population in New Jersey appears to be in decline. They can no longer be found at the site where the types were taken, and a second formerly healthy population appears to be declining as well. There has been considerable development and disturbance in both of these watersheds. One male was taken at a new site in Ocean County in 1994, but the extent of that population is unknown. I am only aware of seven states where the species has been recorded: New Jersey, Virginia, North Carolina, Alabama, Mississippi, Louisiana, and Texas. It is listed by the New Jersey Natural Heritage Program as G4 - S1
The following are notes on a population found in sections of three counties in New Jersey beginning on 21 May 1995. Their presence was detected by finding exuviae (IMAGE) on three streams whose watersheds interconnect. I suspect that all emergence had taken place within the preceding two days. Torrential rains on 18 and 19 May would have detached exuviae from the exposed locations where they were found. I searched the area for exuviae on 13 May and found no G. apomyius. All exuviae were removed from collecting sites at each visit. Five visits between 21 May and 4 June indicated that peak emergence probably occurred between 21 and 25 May. Only three exuviae were located after 1 June.
Habitat and Distribution
Exuvial evidence indicates that this is a fairly large population of G. apomyius, but greater numbers are found at particular sections of stream corridor. All streams where exuviae were found enter or exit a large lake, but they do not occur on the lake. Most emergence took place at open sunny areas along the stream corridors. Few were found where the streams had a closed canopy The lake out-fall stream widens and deepens at about 5 kilometers downstream. No exuviae were found in this section. Primary habitat appears to be shallow, low gradient, gently flowing streams, generally one meter or less in depth. The width varies considerably but is generally from about five to seven meters. Most of the bottom is fine sand with intermittent pockets of muck and submerged logs. In some sections, there are small bays that open up into open boggy Tussock-Grass marshes off the stream corridor. A few exuviae were also found at a large pond-like area with very turbulent water just below a spillway. There are quiet pools and backwaters around the periphery with pockets of muck and some sandy areas. The bottom substrate in the main flow area is course gravel and pebbles. Where this area enters the stream it is nearly impounded by a large gravel bar. Exuviae were found attached to rootlets and moss, partially submerged logs, twigs of fallen branches, Arrow Arum, Cattail, grasses, ferns, Decadon verticulatus, and two concrete bridge abutments. Most were found very close to the water edge. Two exceptions were one over a meter above the water line on a bridge abutment, and one over one-half meter from the stream on bare ground.
By 28 May, a few flying G. apomyius were seen in the immediate vicinity of the largest numbers of exuviae. They were seen perched on High Bush Blueberry, Red Maple branches, or occasionally on leaves of Arrow Arum hanging over the stream in open sunny areas. These perches were shared with numbers of Calopteryx dimidiata. Newly emerged tenerals were seen flying high up into the swamp canopy. Others were seen coming down from the canopy for a quick dip in the stream, and immediately returning to the canopy high above the stream corridor. None could be found using upland areas or sand roads outside the swamp corridor, a common practice of other species emerging from the stream during the post-emergence feeding period. I suspect that the entire flight period is spent in proximity to the stream corridor. By 2 June, adult males were being seen patrolling the streams with more frequency, and on 3 June two females were seen ovipositing in the stream. On this date only two exuviae could be located in the most productive area. One female was ovipositing in the shade of some overhanging bushes very close to the stream bank, making repeated passes tapping her abdomen in the water over the same area. She then made a right angle turn and a few quick taps as she flew rapidly across the stream and up into the trees. I was alerted to a second female by observing a male hanging vertically from a bridge abutment. About a meter from him, a female was also perched vertically, but holding her abdomen horizontally, rapidly vibrating her wings. After a short period she flew to the water below and began ovipositing within a few centimeters of the bridge. She repeated this process three times within twenty minutes. Males were still patrolling, and females ovipositing on 24 June, but none were found on 4 July
Threats to Population Stability
The prime habitat for this population is protected by a Nature Conservancy preserve, and I see no immediate threat to this population. A large twin-span bridge over prime habitat was built in 1973, and apparently had no lasting impact on the population. Numerous exuviae were found on this bridge abutment. Large section of two of these streams are heavily used by canoeist during warmer months, but I suspect this has little or no impact. The localization of large numbers in relatively small sections of stream corridor, indicate that a major disturbance in one of these areas could have a major impact on the entire population of a particular stream. Of all of the exuviae picked up during the monitoring period (184), 68 percent (126), were found in an area about 30 meters in length. It may be notable that there is no development at all along the sections of stream corridor with the largest population. Two areas that appeared to be prime habitat receives multiple stockings of non-native trout in April and May, and is very heavily used by fishermen during the emergence period. These areas are also heavily used by bathers during warmer months. Only two exuviae were found there and were located immediately upstream of the heavily used area.
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