Caspian Terns Hydroprogne Caspia Research Articles

Recovery of Coded Wire Tags at a Caspian Tern Colony in San Francisco Bay: A Technique to Evaluate Impacts of Avian Predation on Juvenile Salmonids

AbstractWe recovered coded wire tags (CWTs) from a colony of Caspian terns Hydroprogne caspia on Brooks Island in San Francisco Bay, California, to evaluate predation on juvenile salmonids originating from the Sacramento and San Joaquin rivers. Subsamples of colony substrate representing 11.7% of the nesting habitat used by the terns yielded 2,079 salmonid CWTs from fish released and subsequently consumed by terns in 2008. The estimated number of CWTs deposited on the entire tern colony was 40,143 (ranging from 26,763 to 80,288), once adjustments were made to account for tag loss and the total amount of nesting habitat used by terns. Tags ingested by terns and then egested on the colony were undamaged, and the tags’ complete numeric codes were still identifiable. The CWTs found on the tern colony indicated that hatchery Chinook salmon Oncorhynchus tshawytscha trucked to and released in San Pablo Bay were significantly more likely to be consumed by Caspian terns than Chinook salmon that migrated in‐river to the bay; 99.7% of all tags recovered were from bay‐released Chinook salmon. Of the CWTs recovered on the tern colony, 98.0% were from fall‐run Chinook salmon, indicating a higher susceptibility to tern predation than for the spring run type. None of the approximately 518,000 wild Chinook salmon that were coded‐wire‐tagged and released in the basin were recovered on the tern colony, suggesting that the impacts on wild, U.S. Endangered Species Act–listed Chinook salmon populations were minimal in 2008. Overall, we estimate that 0.3% of the approximately 12.3 million coded‐wire‐tagged Chinook salmon released in the basin in 2008 were subsequently consumed by Caspian terns from the Brooks Island colony. These results indicate that CWTs implanted in juvenile salmon can be recovered from a piscivorous waterbird colony and used to evaluate smolt losses for runs that are tagged.Received January 25, 2010; accepted December 13, 2010

Impact of the Potholes Reservoir Caspian Tern Breeding Colony on Out‐Migrating Juvenile Salmonids in the Mid‐Columbia River

AbstractWe examined the foraging behavior and diet of Caspian terns Hydroprogne caspia breeding at Potholes Reservoir, Washington, in 2003, 2005, and 2006, and we developed a bioenergetics model to estimate impacts on juvenile salmonids Oncorhynchus spp. from Columbia River stocks. Potholes Reservoir Caspian terns mostly foraged on local fish (68–97% of tern bill loads) rather than traveling to the Columbia River. Our model suggested that only 8,913–94,139 juvenile salmonids were consumed, representing 0.02–0.38% of the salmonids available to Caspian terns. Local foraging is probably explained by higher net profitability of Potholes Reservoir fish prey. Columbia River steelhead O. mykiss were the only juvenile salmonids that were energetically comparable with local Potholes Reservoir fish, mostly due to their high energy density and relatively large size. Passive integrated transponder tag analyses showed that Potholes Reservoir Caspian terns preferred steelhead (predation rates = 0.42–1.06%) to all other salmonid stocks (coho salmon O. kisutch = 0.09–0.36%; subyearling Chinook salmon O. tshawytscha = 0.009–0.040%; yearling Chinook salmon = 0.05–0.17%). Given the proposed reduction in nesting habitat at East Sand Island (ESI; where the current Caspian tern population consumes 3.6–5.3 million juvenile salmonids annually), we estimated the impact on salmonid stocks that would occur if ESI Caspian terns relocated to Potholes Reservoir. Depending on diet scenario, 100% relocation could result in juvenile salmonid consumption between 2.2 and 6.6 million fish, with lower values being much more likely, making Potholes Reservoir the colony location of least likely impact among all sites within the Columbia River drainage. We suggest that selection of sites for ESI relocation should be based on scientific evidence combining a quantitative approach, such as bioenergetics modeling linked to prey population growth rate.

Waterbirds of Lake Eyre, Australia

Few data exist on abundance and diversity of waterbirds on Lake Eyre in the arid zone of Australia. We report extremely high densities of waterbirds during a study over an eight-month period, August 1990–February 1991. At least thirty species were seen during aerial surveys, and nine previously unrecorded species were sighted on the lake. Numbers were highest in December when more than 300 000 waterbirds, including 135 000 shorebirds, were estimated. These figures were considered to underestimate true abundance by 50%. Australian pelicans Pelecanus conspicillatus (448 nests), silver gulls Larus novaehollandiae (4754 nests) and Caspian terns Hydroprogne caspia (about 80 nests) nested on one of the islands. Only silver gulls and Caspian terns were successful. Historical records indicate that some flooding of the lake bed occurs every year. These results show the importance of this wetland to waterbird conservation in Australia.

Planar chlorinated hydrocarbons (PCHs) in colonial fish-eating waterbird eggs from the Great Lakes

Reproductive impairment of double-crested cormorants ( Phalacrocorax auritis) and Caspian terns Hydroprogne caspia) has recently been observed in the Great Lakes of North America. Planarchlorinated hydrocarbons (PCHs), which include polychlorinated biphenyls (PCBs), polychlorinated dibenzo- p-dioxins (PCDDS), and polychlorinated dibenzofurans (PCDFs), are believed to be at least partially responsible for the increased incidence of teratogenesis and embryonic mortality. The objective of this study was to assess the potency of the PCH mixtures in egg extracts from these colonial waterbirds. The relative potency of the egg extracts was assessed by their ability to induce cytochrome P-450-dependent ethoxyresorufin O-deethylase (EROD) in H4IIE rat hepatoma cells. The magnitude of the response was compared with EROD induction in cell cultures by a standard, 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). The TCDD-equivalents derived by this bioassay concur with residue analysis and biological data, in that the highest TCDD-equivalents were found in waterbird egg composites from areas with greater PCH concentrations and more severe reproductive effects. Significant concentrations of PCHs were detected in all sites tested; the range of TCDD-equivalents in the waterbird eggs was 49–415 pg/g, uncorrected for extraction efficiencies. The evidence is strong for at least a partial role of PCHs as causal agents in the reproductive impairment of fish-eating waterbirds from the Great Lakes of North America.

Establishment of Colonies of Caspian Tern Hydroprogne caspia by Deserting Flights in the Northern Gulf of Bothnia

Establishment of Colonies of Caspian Tern Hydroprogne caspia by Deserting Flights in the Northern Gulf of Bothnia