WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2022 27 only about 100 m of a narrow streambed in which water flow is maintained by a running faucet. The population is therefore highly vulnerable and establishment of additional populations on the island is a top priority. In November 2018, the Hawaii Department of Land and Natural Resources (DLNR) began a captive rearing and reintroduction program for M. xanthomelas in which eggs were collected from TAMC, hatched and reared in a laboratory, then released as last-stage immatures or adults into fish-free habitats. Large numbers of naiads could be successfully raised in the laboratory with low mortality. By 2020, DLNR had released over 1,000 captive-reared naiads at two locations: artificial ponds at Lyon Arboretum in the Koʻolau Range on East Oʻahu and a natural stream in the Waiʻanae Range on West Oʻahu. Unfortunately, neither reintroduction was successful, but for different reasons. At Lyon Arboretum, adult damselflies successfully emerged and mated, but were not attracted to the fish-free ponds that had been provided to them. Instead, they favored nearby taro patches that were heavily infested with mosquito fish., The site was considered nonviable because it was not feasible to remove fish from the taro patches. At the stream in the Waiʻanae Range, preliminary results were more promising. Damselflies were observed laying eggs in the fish-free, spring-fed stream. However, a second generation of damselflies was never observed at the site, possibly because it is located near the high elevation limit for this species and winter stream water temperatures dropped below the range of temperatures known to be suitable for the species at other sites. Since 2020, DLNR has continued to rear M. xanthomelas in captivity, and is now focusing on a third reintroduction site in northwest Oʻahu. Damselflies were released from June 2020 to June 2021. Monitoring of the site is ongoing, but damselflies have successfully produced a second generation, and a small population persists. DLNR is working with their US Army collaborators to enhance habitat at the site with the aim of increasing its carrying capacity. Improving Captive Rearing Methods for the Endangered Orangeblack Hawaiian Damselfly Kelli Konicek, William Haines, Katrina Scheiner and Cynthia King Captive rearing of M. xanthomelas naiads produced large numbers of naiads with a high survival rate, but naiads reared in the laboratory were much lighter than those observed in the wild. The reasons for this were unclear and DLNR staff were concerned that the pale coloration may increase naiads’ vulnerability to predation when they were released into the wild, or that it reflected a nutrient or mineral deficiency in the naiad’s diet or environment in the laboratory. Rearing methods were adjusted to test the effects of diet supplementation and substrate type on naiad developmental rates and pigmentation. To measure the effect of diet diversity, naids were fed a diet consisting of exclusively brine shrimp Artemia franciscana or a diet supplemented with a diversity of freshwater zooplankton cultured from the wild. Naiads fed a more diverse diet developed significantly faster but were only slightly darker than naiads fed only brine shrimp. To explore the roles of substrate color and composition, naiads were reared on six different substrates spanning a range of colors and textures. Substrate color had a much greater effect on naiad coloration, with naiads raised on dark backgrounds more closely matching the color of wild naiads than those raised on lighter backgrounds (Fig. 14). Based on these results DLNR has modified rearing protocols for this endangered insect. Naiads are now fed zooplankton and insect larvae to promote faster growth, and rearing cups are lined with dark gravel to produce a more camouflaged pigmentation. Because there was little previous work with mass rearing of damselflies, and no previous work on husbandry of the genus Megalagrion, the development of rearing protocols has yielded much valuable information on the life history of this rare insect. Now that researchers are able to produce rapidly thousands of healthy naiads, doors have been opened for conservation of Hawaiian damselflies. Now the limiting factor is not whether large numbers of individuals can be reared, but whether suitable reintroduction sites can be found or created. Notes Ann Gannam, Abernathy Fish Technology Center, U.S. Fish and Wildlife Service, 1440 Abernathy Creek Rd., Longview, WA 98632 Ryan Schloesser, Mote Marine Laboratory, Sarasota, FL 34236 rschloesser@mote.org Mary L. Moser, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric FIGURE 13. Adult male orangeblack Hawaiian damselflies at a reintroduction site (Photo: W. Haines, Hawaii DLNR-DOFAW). FIGURE 14. Naiads reared on white gravel (left) were significantly and noticeably lighter than those reared on black gravel (right) (Photo: K. Konicek, Hawaii DLNRDOFAW). ( C O N T I N U E D O N P A G E 2 8 )
RkJQdWJsaXNoZXIy MjExNDY=