Potential Source Of Mortality Research Articles

THE ANTILLEAN MANATEE IN THE NORTH OF MARACAIBO LAKE (VENEZUELA): DISTRIBUTION, AND CONSERVATION ISSUES

In Venezuela, Antillean manatees (Trichechus manatus manatus) have declined mainly due to habitat loss and degradation, but other threats to the species persist. The objective of this work was to investigate the manatee distribution and conservation issues in Maracaibo Lake, Venezuela. Aiming to collect evidence on manatee presence, we conducted 404.14 hours of boat-based surveys and observations from the shore during 2003, 2004, 2009, and 2010. Environmental parameters were collected in areas where manatees were observed including pH, temperature, dissolved oxygen, salinity, transparency, and depth. Also, we recorded plants or algae that could serve as potential food for manatees. We developed 96 informal and opportunistic talks with local fishermen, to gather information about manatee occurrence, boat traffic, and people’s perception of the species. Finally, we reviewed published and unpublished documents containing information on manatees in Maracaibo Lake. The resulting database contains information on 39 sightings and 13 reports of dead manatees. The known causes of death were poaching, vandalism, boat collision, and entanglement in fishing nets. The Maracaibo Lake offers many suitable habitats for manatees, but also faces a wide array of conservation problems that represent critical threats to this endangered subspecies. Long-term monitoring of this population and potential sources of mortality is highly needed.

Viral infection impacts the 3D subcellular structure of the abundant marine diatom Guinardia delicatula

Viruses are key players in marine ecosystems where they infect abundant marine microbes. RNA viruses are emerging as key members of the marine virosphere. They have recently been identified as a potential source of mortality in diatoms, a group of microalgae that accounts for roughly 40% of the primary production in the ocean. Despite their likely importance, their impacts on host populations and ecosystems remain difficult to assess. In this study, we introduce an innovative approach that combines automated 3D confocal microscopy with quantitative image analysis and physiological measurements to expand our understanding of viral infection. We followed different stages of infection of the bloom-forming diatom Guinardia delicatula by the RNA virus GdelRNAV-04 until the complete lysis of the host. From 20h after infection, we observed quantifiable changes in subcellular host morphology and biomass. Our microscopy monitoring also showed that viral infection of G. delicatula induced the formation of auxospores as a probable defense strategy against viruses. Our method enables the detection of discriminative morphological features on the subcellular scale and at high throughput for comparing populations, making it a promising approach for the quantification of viral infections in the field in the future.

American eel state of buoyancy and barotrauma susceptibility associated with hydroturbine passage

American eel are likely to encounter and pass through hydropower turbines, particularly during the downstream spawning migration, where exposure to stressors can potentially lead to injuries and mortality. Previous research has recovered dead eels downstream of hydropower facilities and, for some fish, injuries were easily attributed to blade strike; however, others showed no external signs of injury suggesting that other stressors, such as rapid decompression may be a potential source of mortality. For this research, yellow– and silver-phase American eel were held and allowed to acclimate to 172 kPa (absolute pressure) in hyper/hypobaric hydro-chambers for about 1 d. After acclimation, the state of buoyancy was determined prior to exposure to a rapid decompression simulating pressures encountered during hydroturbine passage. Fish were then examined for signs of barotrauma. Eel did not attain a state of neutral buoyancy but rather maintained negative buoyancy suggesting that eels, and possibly other benthic species, likely maintain a state of negative buoyancy to facilitate occupancy on or near the substrate. Additionally, eel were found to be resilient to rapid decompression, displaying no instantaneous mortality and minimal injuries, suggesting that barotrauma is not likely a major concern for American eel passing downstream through hydroturbines.

Survival of cougars caught in non‐target foothold traps and snares

ABSTRACTCougars (Puma concolor) occupy mountain ranges throughout the Great Basin, Nevada, USA, where legal trapping of bobcats (Lynx rufus) is common and some non‐target captures of cougars in bobcat traps occur. Such incidental capture of cougars is an undocumented source of mortality because some cougars die from injuries several weeks after release from traps. We examined cause‐specific mortality and the effects of capture of cougars in bobcat traps on annual and overall (7‐year) survival during 2009–2015. We captured 48 cougars, of which we followed 33 until death. We estimated average annual survival rates for adult cougars and assessed the relative effects of sex, season, and long‐term effects of non‐target capture of cougars in foothold traps on estimated survival of adults using a nest survival model in Program MARK. We incorporated a time‐varying covariate to assess the long‐term effect of capture in non‐target foothold traps on survival of adult cougars. Average annual survival of non‐trapped females and males, regardless of trapping history, was significantly greater than females with a history of capture in a non‐target foothold trap; however, once partitioned across age, sex, and capture status, sample sizes were small. Our results suggest that capture in non‐target foothold traps decreases survival of adult female cougars directly by causing injuries that eventually result in mortality, and indirectly by increasing susceptibility to other forms of mortality. Mortality of adult females during the 7 years of our study caused by non‐target trapping was similar to hunting among radio‐marked female cougars, and this potential source of mortality has been unaccounted for in harvest objectives and harvest data for cougars without radio‐collars. Given anthropogenic sources of mortality accounted for 100% of recorded mortality of adult females, mortality from non‐target trapping is likely additive to other sources of mortality in our study area. We recommend regulatory agencies consider the possibility of unintentional take and potential for reduced long‐term survival of females where these large fields are sympatric with bobcats, and trapping of bobcats with foothold traps is a legal activity. Moreover, we suggest wildlife managers record information about the trapping incident, to include trap type, trap size, trap set type, location, number of days since last check, and type and severity of injuries when releasing incidentally captured cougars to inform future management decisions. Addressing other anthropogenic sources of mortality resulting from conflict with humans and road mortalities will be increasingly important as the human population expands into cougar habitat. © 2018 The Wildlife Society.

Moose (Alces alces) predation by eastern coyotes (Canislatrans) and eastern coyote × eastern wolf (Canislatrans×Canislycaon) hybrids

It has been widely assumed that coyotes (Canis latrans Say, 1823) are incapable of killing adult moose (Alces alces (L., 1758)) and previous studies of coyote predation support this assumption. However, eastern coyotes and eastern coyote × eastern wolf (Canis lycaon Schreber, 1775) are larger than western coyotes and appear to rely on larger prey in some areas. We used a combination of GPS telemetry, genetic analysis, and field investigation to test the hypothesis that eastern coyotes and coyote × wolf hybrids are capable of preying on adult moose in central Ontario. Our hypothesis was supported, as we documented four definitive cases of eastern coyotes and (or) eastern coyote × eastern wolf hybrids killing moose ≥1.5 years old. Predation by coyotes and coyote × wolf hybrids probably does not represent a threat to moose population viability in central Ontario, but our results suggest that researchers and managers in other areas with declining moose populations that are sympatric with eastern coyotes and (or) coyote × wolf hybrids should consider coyote predation as a potential source of mortality.

Rare or just unknown? The occurrence of the giant devil ray (Mobula mobular ) in the Adriatic Sea

Summary The presence of the giant devil ray (Mobula mobular) in the Adriatic Sea was evaluated based on new records collected through field research, information from interviews with fisherman and marine biology experts, and a review of existing data from the literature and Internet sources. Presented are 14 new records of 20 individual giant devil rays collected between 2008 and 2011, doubling the number of animals recorded in the Adriatic in the previous 125 years. In total, 28 records of 42 giant devil rays exist for the Adriatic to date. The cryptic life history of the species, its pelagic distribution and lack of systematic data collection have resulted in a low number of historical records. The results suggest that the species is not as rare as previously considered. Occurring mainly in the central and southern Adriatic Sea from early spring to early autumn, its appearance coincides with the general increase in local prey abundance. Interaction with fisheries is identified as a source of potential mortality, and the monitoring of multi-gear schemes should be carried out at the regional level. Further research on the distribution and abundance of the giant devil ray is crucial for the elaboration of any effective conservation strategy for this endangered species.

Positive feedback between microclimate and shrub encroachment in the northern Chihuahuan desert

Woody plant encroachment is affecting vegetation composition in arid grasslands worldwide and has been associated with a number of environmental drivers and feedbacks. It has been argued that the relatively abrupt character (both in space and in time) of grassland‐to‐shrubland transitions observed in many drylands around the world might result from positive feedbacks in the underlying ecosystem dynamics. In the case of the Chihuahuan Desert, we show that one such feedback could emerge from interactions between vegetation and microclimate conditions. Shrub establishment modifies surface energy fluxes, causing an increase in nighttime air temperature, particularly during wintertime. The resulting change in winter air temperature regime is important because the northern limit of the dominant shrub in the northern Chihuahuan Desert, Larrea tridentata, presently occurs where minimum temperatures are sufficiently low to be a potential source of mortality. Using freezing responses from published studies in combination with observed temperature records, we predict that a small warming can yield meaningful changes in plant function and survival. Moreover, we also suggest that the effect of the change in air temperature on vegetation depends on whether plants experience drought during winter. Thus, in the Chihuahuan region a positive feedback exists between shrub encroachment and changes in microclimate conditions, with implications for the response of this ecosystem to regional changes in temperature and precipitation.

Low incidence and limited effect of the oyster pathogen dermo (Perkinsus marinus) on an artificial reef in Delaware's Inland Bays

Delaware's Inland Bays comprise a large estuarine system with a restricted access to the Atlantic Ocean (Indian River Inlet). As part of a local oyster stock enhancement and restoration effort, we conducted a survey for the protozoan pathogen Perkinsus marinus (Dermo) in oysters from a newly established reef. Using standardized methods for the polymerase chain reaction (PCR) amplification of the non-transcribed spacer (NTS) region, we were surprised to find no detectable titers of this pathogen in the 30 oysters sampled in the first year of the project. The detection threshold of the PCR coupled with chemiluminescent detection was 30 fg P. marinus NTS DNA. We were able to detect a trace presence of this pathogen in a few hard clams (Mercenaria mercenaria) from the same locale, indicating that a Perkinsus sp. was present in the Inland Bay system. Subsequent monitoring of the reef system using a fluid thioglycollate assay over 3 yr revealed no epizootic outbreaks of this pathogen within the planted oyster population. Two large mortality episodes that did appear in the oyster population were attributable to abiotic conditions and not pathogen exposure. This study emphasizes that all potential sources of mortality in the environment are important to consider when designing oyster seeding projects. In the Delaware Inland Bays, P. marinus does not appear to have a large enough oyster host population to become a significant disease threat at present. Because of the low parasite incidence levels in the Inland Bay system in 2000, the James Farm oyster reef restoration project presents an ideal model system to follow the population dynamics between an oyster-host population and a latent or reservoir pathogen population.

TERRESTRIAL HABITAT USE BY NESTING PAINTED TURTLES IN LANDSCAPES WITH DIFFERENT LEVELS OF FRAGMENTATION

As part of a comprehensive study of the effects of landscape change on the demography of aquatic turtles, we investigated the use of upland habitats by adult female painted turtles (Chrysemys picta) during the nesting season. We intentionally selected three ponds that were surrounded by a range of land uses and development (e.g., road density ranged from 0.9 to 7.3 km/km2). Terrestrial locations of transmitter-equipped turtles (n = 8) and unmarked females that were incidentally encountered (n = 10) were recorded to: i) determine the distance traveled to nesting habitat, ii) estimate the frequency that female turtles crossed roads to reach nesting habitat, and iii) examine how the abundance of potential nesting habitat affected distance traveled. Average straight-line distance from shoreline to the site a female turtle was encountered ranged from 54 to 115 m for the three ponds. We estimated that marked turtles made five road crossings and two turtles were killed by vehicles. Distance traveled was negatively correlated with the abundance of nesting habitat near a pond. Although adult females are probably less vulnerable when nesting occurs near pond shores, nests created near pond edges may be more vulnerable to predation. As a result, providing additional nesting habitat away from roads and other potential sources of mortality may enhance recruitment among local turtle populations.

THE LIKELY CAUSE OF EXTINCTION OF THE TREE SNAIL ORTHALICUS RESES RESES (SAY)

The Stock Island tree snail, Orthalicus reses reses, went extinct in its native range in the Florida Keys in 1992. Fortunately, O. r. reses has been introduced elsewhere and further reintroductions are currently planned. Before these reintroductions are implemented, it is important to try and determine which factors were most likely to have caused the decline and extinction. While habitat destruction was probably the ultimate reason why there were so few tree snails, it is likely that an interaction of habitat fragmentation and the invasion of an exotic predator caused the final decline that lead to the extinction in 1992. We examined the last 93 O. r. reses shells to infer cause of death. In addition, using surrogate Florida tree snails, Liguus fasciatus, we conducted experiments on two previously unstudied causes of mortality: predation by red imported fire ants, Solenopsis invicta, and mortality from falls caused by wind. We found that the majority of the last O. r. reses shells were intact, indicating that mammalian and bird predation were not the greatest causes of mortality. Mortality caused by wind knocking tree snails onto the rocky hammock substrate appeared to be a potential source of mortality, but few of the tree snails exhibited signs of breakage. Mortality from fire ants appears to be one of the most likely causes of the recent decline and extinction of O. r. reses. Experiments indicated that in a semi-natural enclosure, fire ants were capable of killing all ages of L. fasciatus, even during aestivation. Fire ants are currently found throughout the last known habitat of O. r. reses and were first discovered in this area at the time of the decline.

ヒラメ人工種苗放流技術の開発に関する基礎的研究 ＩＩＩ 鳥取県沿岸浅海域に放流したヒラメ人工種苗の被食

Stomach contents of piscivorous fishes were examined to investigate their predation pressure on hatchery-reared Japanese flounder released in the coastal areas of Tottori Prefecture (1989-1991). Released flounder were taken frequently by 1-age group Japanese flounder, bartail flathead and sea bass primarily during the early days after release. We observed few incidences of predation on wild flounder juveniles by piscivorous fishes in the same study area. This suggests that reared juveniles are more vulnerable to predation than wild flounder due to behavioral differences. Abundance of 1-age group Japanese flounder and flathead in the area was estimated from May to July by counting by divers. Cumulative predation estimated from stomach content analysis and abundance of predatory fishes accounted for a substantial part of the estimated mortality. Other potential sources of mortality, particularly predation by nocturnal predators, are discussed.

Walleye and Sauger Predation on Paddlefish in Lake Sakakawea, North Dakota

Abstract Predation by walleye Stizostedion vitreum and sauger S. canadense on paddlefish Polyodon spathula was noted in Lake Sakakawea, North Dakota. Percid predation on paddlefish was detected at two of three sampling stations in September and at one sampling station in October. In October, 73% of the percids with identifiable food contained at least one paddlefish. Total length of ingested paddlefish ranged from 36 to 52% of percid total lengths. When designing stocking programs, fisheries managers should consider percid predation as a potential source of mortality of stocked paddlefish.

Quantification of Loss and Change in Floridian Reef Coral Populations

Six coral reef locations between Miami and Key West were marked with stainless steel stakes and rephotographed periodically between 1984 and 1991. The monitored areas included two photostations in the Looe Key National Marine Sanctuary, two photostations in the Key Largo National Marine Sanctuary, and two photostations in the Biscayne National Park. Stations were monitored for species number, percent cover, and species diversity of the scleractinian and hydrozoan stony corals. Monitoring began in 1984 for photostations in the National Marine Sanctuaries and in 1989 for stations in the National Park. All six areas lost coral species between the initial survey year and 1991. Survey areas lost between one and four species; these losses constituted between 13% and 29% of their species richness. Five of the six areas lost live coral cover. Based upon photographs taken repeatedly at these locations, net losses ranged between 7.3% and 43.9%. In the one station showing an increase in coral cover, the increase was only for the canopy branches of Acropora palmata ; understory branches of this same species lost surface area at the same rate as canopy branches gained area. For most of the common species, there was a reduction in the total number of living colonies in the community, and a diminution in the number of large, mature colonies. Throughout the study period, there was no recruitment to any of the photostations by any of the massive frame building coral species. Mortality of this magnitude is often associated with hurricane damage, but in this survey the losses occurred during a period without catastrophic storms. Sources of mortality identifiable in the photographs include (1) black band disease and (2) “bleaching” other potential sources of mortality are also considered. We conclude, for our survey areas, that loss rates of this magnitude cannot be sustained for protracted periods if the coral community is to persist in a configuration resembling historical coral reef community structure in the Florida Keys.

Pesticide Residues in Fulvous Whistling-Ducks from South Florida

Thirty fulvous whistling-ducks (Dendrocygna bicolor) collected during 1984-85 from the Everglades Agricultural Area (EAA) of south Florida were analyzed for organochlorine and organophosphate contaminants. Contaminants were detected in 30 livers and 14 of 15 breast muscles examined. Eighteen contaminants were found. Levels of detected pesticides were below those known to pose direct threats to birds and humans; however, recent illegal use of some compounds was indicated. Sources of contamination were local but also may have been from areas outside the United States. J. WILDL. MANAGE. 53(4):1052-1057 Organochlorine and organophosphate pesticides have been used extensively for insect and rodent control on agricultural lands, and remain a source of concern relevant to impacts on wildlife resources (Fleming et al. 1983, Flickinger et al. 1986). Some of these pesticides and their metabolites are toxic, often stable in the environment, and are potentially hazardous to wildlife. For example, pesticide contamination can limit reproduction and/or survivability of waterfowl (Babcock and Flickinger 1977, Cooke 1973, White and Stickel 1975). Further, pesticide-contaminated waterfowl could pose a health risk to people who harvest and consume them. Hall (1987) stressed the need for investigations into potential wildlife reductions in regions of heavy pesticide use (i.e., agricultural areas). Due to extensive agricultural industry, the EAA in south Florida has a high rate of pesticide use. Indeed, Palm Beach County, which comprises a large portion of the EAA, uses more kg of restricted-use pesticides than any other county in Florida (Pestic. Rev. Counc. Meet., 2 Dec 1982, Exhibit 3). Rice farming and summer flooding of fallow fields in the EAA is used to control soil subsidence, insects, and nematodes, and create attractive waterfowl habitat for fulvous whistlingducks. Coincident with development of commercial rice production in the EAA, which began in 1977 (Rohrman and Alvarez 1984), the species became established as a permanent resident in south Florida (Turnbull et al. 1989). Rice culture is important to the ecology of fulvous whistling-ducks, especially during the breeding season (Bolen and Rylander 1983). However, fulvous whistling-ducks are highly se sitive to many pesticides that have been used on rice (Flickinger and King 1972, Flickinger et al. 1986). Thus, pesticide contamination is a potential source of mortality and/or reduced rep oductive success in fulvous whistling-ducks because of their close association with an intens vely farmed agricultural area. No information exists on possible pesticide contamination of waterfowl in the EAA. This information is important because of the recent establishment of a waterfowl management area in t e EAA. Our objectives were to determine p sticide levels in fulvous whistling-ducks from the EAA and determine whether levels pose a risk to the ducks or humans harvesting them. F. Montalbano, III and D. H. Brakhage provided collection assistance. D. R. Eggeman, E. L. Flickinger, and D. H. White reviewed an earlier draft of this manuscript. Appreciation is extended to D. J. Forrester for providing laboratory facilities and assistance. STUDY AREA AND METHODS Located immediately south and east of Lake Okeechobee, the EAA consists of about 305,000 ha of diked and drained Everglades habitat that were converted to agricultural production (Fig. 1). The primary crop has been sugarcane, with about 150,000 ha grown annually (Rohrman and Alvarez 1984). Since 1979, about 3,500 ha of rice also have been produced annually (Rohrman and Alvarez 1984; Fla. Game and Fresh Water Fish Comm. file data, Okeechobee). We collected 21 fulvous whistling-ducks on 15 November 1985 in an EAA rice field; 20

Responses to predators of cultured and wild red abalone, Haliotis rufescens, in laboratory experiments

Hatchery-spawned and reared abalone that are placed onto subtidal reefs to enhance native populations often suffer a high mortality. A potential source of mortality is behavioral differences of cultured and wild abalone. Controlled observations and factorial experiments in the laboratory were used to examine abalone behavior and mortality rate due to three predators — crabs, sea stars and lobsters — on small reefs in laboratory tanks. Two abalone types — cultured and wild — and two age/size classes, 0+ (8–20 mm shell length) and 1+ (25–50 mm), were used. Abalone types differed in their movement patterns, with wild animals moving rapidlyto concealed positions within the reefs and most cultured abalones remaining in their original positions for several hours. Over all experiments, there were differences in predation rates by crabs, lobsters and sea stars, with crabs consuming the most abalone and sea stars the least. Significantly more cultured than wild abalone were consumed in an experiment in which different combinations of predators were present. No consistent differences were seen in the consumption of the two size classes of abalone. Animals fresh from the hatchery suffered significantly higher mortality and were more sluggish in their responses to predators than hatchery-reared abalone that had been acclimated to laboratory conditions. The results suggest, however, that cultured abalone may acclimate relatively quickly to a new environment, which may be useful for future attempts at transplanting these animals.