Bioaccumulation of Some Metals and Metalloids in Laughing Gulls (Leucophaeus atricilla): Increases in Mercury and Decreases in Selenium from 2019 to 2022/2023

The elements in blood normally reflect the levels in prey, indicating a recent exposure. Laughing gulls (Leucophaes atricilla) eat mainly horseshoe crab eggs (Limulus polyphemus) in the spring in Delaware Bay, New Jersey. The levels of arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and selenium (Se) in the blood of laughing gulls foraging on crab eggs were examined in Delaware Bay to provide information on a species that is normally a generalist, and to determine if the levels of these elements were similar in 2019 and 2022/2023, were intercorrelated, and were related to those in crab eggs. Hg increased from 2019 (136 ± 31 ng/g) to 2022/2023 (473 ± 75 ng/g), while Cd and Se decreased. There were some significant correlations among elements and a close relationship between the element levels in blood and those in crab eggs collected in the same month (except for As). The levels differed between laughing gulls and three species of shorebirds for As and Cd. The elements in the blood of gulls and shorebirds should be similar because they eat mainly the same eggs in the same places. A significant proportion of laughing gull blood samples had levels of Hg and Se that were above the levels associated with adverse effects, which requires further examination.

Some metals and metalloids in the blood of three species of shorebirds increase while foraging during two-week migratory stopover in Delaware Bay, New Jersey

Most migratory shorebird species are declining, some are endangered, and some may be vulnerable to contaminants on long distance travel between wintering grounds and high latitude breeding grounds. We examined whether shorebirds accumulated trace elements at the Delaware Bay (New Jersey) stopover by testing the null hypothesis that there was no difference in the levels of arsenic, cadmium, chromium, lead, mercury, and selenium in blood of three species of shorebirds collected early in their stopover compared to levels in blood collected about two weeks later near the end of the stopover, before departing for breeding grounds. There were significantly higher levels of all metals and metalloids in the blood of ruddy turnstone (Arenaria interpres) later in May than earlier. There were seasonal increases in blood levels of arsenic and selenium for all three species. Chromium and lead levels also increased in red knots (Calidris canutus). These increases occurred although the birds were only present for about two weeks. Levels of arsenic, mercury, and lead in knots and selenium in sanderlings (Calidrris alba), exceeded reported effects levels. These results have potential implications for studying the refueling physiology, energetics, and feeding behavior of migratory shorebirds. However, they also suggest cause for concern because the increased contaminant loads occur in a short period, and the high metal level bolus received all in a few days may result in adverse effects.

Metal Levels in Delaware Bay Horseshoe Crab Eggs from the Surface Reflect Metals in Egg Clutches Laid beneath the Sand

Understanding variations in metal levels in biota geographically and under different environmental conditions is essential to determining risk to organisms themselves and to their predators. It is often difficult to determine food chain relationships because predators may eat several different prey types. Horseshoe crab (Limulus polyphemus) eggs form the basis for a complex food web in Delaware Bay, New Jersey, USA. Female horseshoe crabs lay thumb-sized clutches of eggs, several cm below the surface, and often dislodge previously laid eggs that are brought to the surface by wave action, where they are accessible and critical food for migrant shorebirds. This paper compares metal and metalloid (chromium [Cr], cadmium [Cd], lead [Pb], mercury [Hg], arsenic [As] and selenium [Se]) concentrations in horseshoe crab eggs collected on the surface with concentrations in eggs from clutches excavated from below the sand surface, as well as examining metals in eggs from different parts of the Bay. The eggs were all collected in May 2019, corresponding to the presence of the four main species of shorebirds migrating through Delaware Bay. These migrating birds eat almost entirely horseshoe crab eggs during their stopover in Delaware Bay, and there are differences in the levels of metals in blood of different shorebirds. These differences could be due to whether they have access to egg clutches below sand (ruddy turnstones, Arenaria interpres) or only to eggs on the surface (the threatened red knot [Calidris canutus rufa] and other species of shorebirds). Correlations between metals in clutches were also examined. Except for As and Cd, there were no significant differences between the metals in crab egg clutches and eggs on the surface that shorebirds, gulls, and other predators eat. There were significant locational differences in metal levels in horseshoe crab eggs (except for Pb), with most metals being highest in the sites on the lower portion of Delaware Bay. Most metals in crab eggs have declined since studies were conducted in the mid-1990s but were similar to levels in horseshoe crab eggs in 2012. The data continue to provide important monitoring and assessment information for a keystone species in an ecosystem that supports many species, including threatened and declining shorebird species during spring migration.

Variation in resource use between adult and juvenile Semipalmated Sandpipers (Calidris pusilla) and use of physiological indicators for movement decisions highlights the importance of small staging sites during southbound migration in Atlantic Canada

Semipalmated Sandpipers (Calidris pusilla) are Arctic-breeding shorebirds that use staging sites in Atlantic Canada during their annual migration to South America. The Bay of Fundy has long been recognized as a critical staging site for migrating Semipalmated Sandpipers and supports a large prey base. The diet of adult sandpipers in the Bay is flexible but the diet of juveniles, which arrive later, is not well documented. Comparatively little is known about the prey base and how it is utilized by sandpipers at sites in Atlantic Canada outside the Bay. Plasma metabolite measures can provide useful insight to assess habitat quality for sandpipers and have not yet been measured in Semipalmated Sandpipers in Atlantic Canada. To address these knowledge gaps we sampled shorebird habitat to estimate invertebrate availability in the Bay of Fundy and the Northumberland Strait. Concurrently, we collected blood samples from adult and juvenile sandpipers for analysis of plasma metabolite levels and isotopic estimates of dietary niche in both regions. We found that sites on the Northumberland Strait hosted a more diverse and variable prey base than sites within the Bay of Fundy, and that sandpipers were selective when foraging there, appearing to prefer bivalves. Juveniles may occupy a broader dietary niche than adults along the Northumberland Strait, though appear to gain weight as efficiently. Sandpipers sampled along the Northumberland Strait had higher plasma triglyceride concentrations than those within the Bay of Fundy, which may suggest differences in fattening rate or dietary fat intake. Sandpipers that had lower triglyceride concentrations on the Northumberland Strait were more likely to move into the Bay of Fundy, while sandpipers with high triglyceride values tended to remain on the Strait. These data suggest that sandpipers made movement decisions within the region depending on their physiological state. Our results suggest adult and juvenile Semipalmated Sandpipers successfully use a variety of staging habitats in Atlantic Canada. This is an encouraging finding for sandpiper conservation in the region, but also indicates that maintaining access to a broad variety of staging habitats is critical, supporting calls for stronger conservation measures throughout the region.

Seasonal and inter-annual variation in exposure to peregrines (Falco peregrinus) for southbound western sandpipers (Calidris mauri)

BACKGROUND

The western sandpiper (Calidris mauri) is an early southbound migrant species in North America. The 'peregrine avoidance' hypothesis proposes that this timing evolved to reduce exposure to their main predator, the peregrine (Falco peregrinus), along the Pacific flyway.

METHODS

I evaluate this hypothesis based on 16 years of near-daily (June - October) measures of peregrine presence made on the Fraser River estuary, a major stopover in the Pacific northwest.

RESULTS

Exposure to peregrines is lowest for the earliest southbound western sandpipers, and rises steeply as peregrines en route from northern breeding areas begin to arrive in late July or August. Peregrine arrival timing varies greatly between years, shifting in step with the onset of spring along coastal Alaska. Peregrine presence on the Fraser estuary on any date is higher in years with earlier spring onset. On the median adult sandpiper passage date (day-of-year 198) this increases 17-fold over the inter-annual range between the earliest and latest peregrine arrival dates.

CONCLUSION

The pattern of strong and predictable changes in the seasonal pattern of danger quantified here provides a further test of the hypothesis that danger affects migratory timing. Western sandpipers appear to anticipate the exposure level of southward migration, perhaps because they are able to observe spring onset on their Alaskan breeding grounds. They adjust the duration of parental care and length of the breeding season to keep the date of migratory departure from the Arctic relatively invariant in spite of large interannual variation in spring onset. While underway they also adjust aspects of migratory behavior. These observations support the 'peregrine avoidance' hypothesis, and suggest that western sandpipers are able to counter, at least partially, the higher migratory danger of early spring years.

Ecocultural attributes are important components of perceptions of the importance of coastal beaches of conservation concern

Sandy beaches along coasts and bays are prime real estate for houses and condominiums, marinas, recreation, and tourism for people living in urban and suburban areas within a hundred km of coasts. Human encroachment and disturbance can be a determinant of success of animals in human-impacted systems, particularly shorebirds. Understanding perceptions of people visiting critical habitats can aid in conservation of shorebirds and associated ecosystems, as well as improving the human experience. This paper examines valuation of ecological resources and ecocultural attributes of visitors to 9 beaches on the New Jersey shore of Delaware Bay during a shorebird migratory stopover period. Ecocultural attributes are those cultural activities or experiences that require an intact ecosystem to be optimal, including activities of recreational, aesthetic or spiritual importance. Using a Likert scale, interviewees (N = 279) rated the importance of shorebirds and/or horseshoe crabs Limulus polyphemus, ambiance, existence, aesthetics, the beach itself, and recreational activities (photography, birding, and fishing) to the Bay and to their experience. Although shorebirds/crabs were rated as most important (mean rating well over 4.0 out of 5); ecocultural attributes (ambience, existence, aesthetics, the beach itself) were rated higher (rating well over 3) than recreation, hardcore or casual birding, photography (mean rating around 3) and fishing (rating less than 2). Although some ratings of these resources and attributes were positively correlated, many values for birds and/or crabs were not correlated with the ecocultural attributes. Women rated most resources and ecocultural attributes higher than did men, and older people rated them higher than younger interviewees. It was unexpected that the ecocultural attributes played so heavily in the attractiveness of the beach. The importance and implication of these findings are discussed for management and conservation of these beaches, including the importance of ecocultural resources within a context of local community involvement.

Bird Migration at the Edge – Geographic and Anthropogenic Factors but Not Habitat Properties Drive Season-Specific Spatial Stopover Distributions Near Wide Ecological Barriers

Stopping-over is critical for migrating birds. Yet, our knowledge of bird stopover distributions and their mechanisms near wide ecological barriers is limited. Using low elevation scans of three weather radars covering 81,343 km2, we quantified large-scale bird departure patterns during spring and autumn (2014–2018) in between two major ecological barriers, the Sahara Desert and Mediterranean Sea. Boosted Regression Tree models revealed that bird distributions differed between the seasons, with higher densities in the desert and its edge, as well as inland from the sea, during spring and a predominantly coastal distribution in the autumn. Bird distributions were primarily associated with broad-scale geographic and anthropogenic factors rather than individual fine-scale habitat types. Notably, artificial light at night strongly correlated with high densities of migrants, especially in the autumn. Autumn migrants also selected sites located close to water sources. Our findings substantially advance the understanding of bird migration ecology near ecological barriers and facilitate informed conservation efforts in a highly populated region by identifying a few high-priority stopover areas of migrating birds.

Migration distance affects how closely Eurasian wigeons follow spring phenology during migration

BACKGROUND

The timing of migration for herbivorous migratory birds is thought to coincide with spring phenology as emerging vegetation supplies them with the resources to fuel migration, and, in species with a capital breeding strategy also provides individuals with energy for use on the breeding grounds. Individuals with very long migration distances might however have to trade off between utilising optimal conditions en route and reaching the breeding grounds early, potentially leading to them overtaking spring on the way. Here, we investigate whether migration distance affects how closely individually tracked Eurasian wigeons follow spring phenology during spring migration.

METHODS

We captured wigeons in the Netherlands and Lithuania and tracked them throughout spring migration to identify staging sites and timing of arrival. Using temperature-derived indicators of spring phenology, we investigated how maximum longitude reached and migration distance affected how closely wigeons followed spring. We further estimated the impact of tagging on wigeon migration by comparing spring migratory timing between tracked individuals and ring recovery data sets.

RESULTS

Wigeons migrated to locations between 300 and 4000 km from the capture site, and migrated up to 1000 km in a single day. We found that wigeons migrating to more north-easterly locations followed spring phenology more closely, and increasingly so the greater distance they had covered during migration. Yet we also found that despite tags equalling only around 2% of individual's body mass, individuals were on average 11-12 days slower than ring-marked individuals from the same general population.

DISCUSSION

Overall, our results suggest that migratory strategy can vary dependent on migration distance within species, and even within the same migratory corridor. Individual decisions thus depend not only on environmental cues, but potentially also trade-offs made during later life-history stages.

Chromosome-level genome assembly of the coastal horseshoe crab (Tachypleus gigas)

Horseshoe crabs, represented by only four extant species, have existed for around 500 million years. However, their existence is now under threat because of anthropogenic activities. The availability of genomic resources for these species will be valuable in planning appropriate conservation measures. Whole-genome sequences are currently available for three species. In this study, we have generated a chromosome-level genome assembly of the fourth species, the Asian coastal horseshoe crab (Tachypleus gigas; genome size 2.0 Gb). The genome assembly has a scaffold N50 value of 140 Mb with ~97% of the assembly mapped to 14 scaffolds representing 14 chromosomes of T. gigas. In addition, we have generated the complete mitochondrial genome sequence and deep-coverage transcriptome assemblies for four tissues. A total of 26,159 protein-coding genes were predicted in the genome. The T. gigas genome contains five Hox clusters similar to the mangrove horseshoe crab (Carcinoscorpius rotundicauda), suggesting that the common ancestor of horseshoe crabs already possessed five Hox clusters. Phylogenomic and divergence time analysis suggested that the American and Asian horseshoe crab lineages shared a common ancestor around the Silurian period (~436 Ma). Comparison of the T. gigas genome with those of other horseshoe crab species with chromosome-level assemblies provided insights into the chromosomal rearrangement events that occurred during the emergence of these species. The genomic resources of T. gigas will be useful for understanding their genetic diversity and population structure and would help in designing strategies for managing and conserving their stocks across Asia.

Seasonal Variation in Reproduction of Horseshoe Crabs (Limulus polyphemus) from the Gulf Coast of Florida

AbstractThe timing of reproduction is often governed by environmental variables, such as temperature or rainfall. Understanding how environmental variables affect mating dynamics is necessary to predict how systems and populations may adapt to changing environmental conditions and is crucial for management of threatened species. The American horseshoe crab (Limulus polyphemus) ranges from the Yucatan to Maine in distinct populations that differ in their timing of reproduction; while most populations have only one breeding period during the spring, some southern populations have two breeding periods. Here we discuss seasonal patterns of reproduction in a Florida Gulf coast population where horseshoe crabs have two periods of breeding: one in the spring and another in the fall. We used environmental measurements, spawning surveys, mark-recapture, and measurements of adult traits and spawning behavior to compare reproductive parameters between the two spawning seasons over three years. We then evaluated whether environmental conditions affect fall and spring horseshoe crab nesting patterns similarly and whether fall and spring horseshoe crabs should be considered two separate populations. We found significant differences in environmental conditions across seasons and in a wide variety of horseshoe crab traits and nesting parameters. Furthermore, environmental conditions affected nesting behaviors of fall and spring horseshoe crabs differently. However, some individuals spawn during both seasons, suggesting that trait differences may be attributable to environmental effects during development or seasonal plasticity, rather than genetic differences, although further study is necessary. Finally, our results suggest that management practices should be tailored to each population, because environmental conditions may have different effects even on genetically similar groups.

Multiple habitat use by declining migratory birds necessitates joined-up conservation

Many species depend on multiple habitats at different points in space and time. Their effective conservation requires an understanding of how and when each habitat is used, coupled with adequate protection. Migratory shorebirds use intertidal and supratidal wetlands, both of which are affected by coastal landscape change. Yet the extent to which shorebirds use artificial supratidal habitats, particularly at highly developed stopover sites, remains poorly understood leading to potential deficiencies in habitat management. We surveyed shorebirds on their southward migration in southern Jiangsu, a critical stopover region in the East Asian Australasian Flyway (EAAF), to measure their use of artificial supratidal habitats and assess linkages between intertidal and supratidal habitat use. To inform management, we examined how biophysical features influenced occupancy of supratidal habitats, and whether these habitats were used for roosting or foraging. We found that shorebirds at four of five sites were limited to artificial supratidal habitats at high tide for ~11-25 days per month because natural intertidal flats were completely covered by seawater. Within the supratidal landscape, at least 37 shorebird species aggregated on artificial wetlands, and shorebirds were more abundant on larger ponds with less water cover, less vegetation, at least one unvegetated bund, and fewer built structures nearby. Artificial supratidal habitats were rarely used for foraging and rarely occupied when intertidal flats were available, underscoring the complementarity between supratidal roosting habitat and intertidal foraging habitat. Joined-up artificial supratidal management and natural intertidal habitat conservation are clearly required at our study site given the simultaneous dependence by over 35,000 migrating shorebirds on both habitats. Guided by observed patterns of habitat use, there is a clear opportunity to improve habitat condition by working with local land custodians to consider shorebird habitat requirements when managing supratidal ponds. This approach is likely applicable to shorebird sites throughout the EAAF.

A new parameterization for integrated population models to document amphibian reintroductions

Managers are increasingly implementing reintroduction programs as part of a global effort to alleviate amphibian declines. Given uncertainty in factors affecting populations and a need to make recurring decisions to achieve objectives, adaptive management is a useful component of these efforts. A major impediment to the estimation of demographic rates often used to parameterize and refine decision-support models is that life-stage-specific monitoring data are frequently sparse for amphibians. We developed a new parameterization for integrated population models to match the ecology of amphibians and capitalize on relatively inexpensive monitoring data to document amphibian reintroductions. We evaluate the capability of this model by fitting it to Oregon spotted frog (Rana pretiosa) monitoring data collected from 2007 to 2014 following their reintroduction within the Klamath Basin, Oregon, USA. The number of egg masses encountered and the estimated adult and metamorph abundances generally increased following reintroduction. We found that survival probability from egg to metamorph ranged from 0.01 in 2008 to 0.09 in 2009 and was not related to minimum spring temperatures, metamorph survival probability ranged from 0.13 in 2010-2011 to 0.86 in 2012-2013 and was positively related to mean monthly temperatures (logit-scale slope = 2.37), adult survival probability was lower for founders (0.40) than individuals recruited after reintroduction (0.56), and the mean number of egg masses per adult female was 0.74. Our study is the first to test hypotheses concerning Oregon spotted frog egg-to-metamorph and metamorph-to-adult transition probabilities in the wild and document their response at multiple life stages following reintroduction. Furthermore, we provide an example to illustrate how the structure of our integrated population model serves as a useful foundation for amphibian decision-support models within adaptive management programs. The integration of multiple, but related, data sets has an advantage of being able to estimate complex ecological relationships across multiple life stages, offering a modeling framework that accommodates uncertainty, enforces parsimony, and ensures all model parameters can be confronted with monitoring data.

Metal Levels in Blood of Three Species of Shorebirds during Stopover on Delaware Bay Reflect Levels in Their Food, Horseshoe Crab Eggs

Understanding the relationship between metal level in predators and their prey is an important issue, and is usually difficult to determine because animals eat a variety of organisms. However, shorebirds that stop over during spring migration along Delaware Bay (New Jersey) stay for only 2–3 weeks, and eat mainly horseshoe crab (Limulus polyphemus) eggs. In this paper, we examine the relationship between metal levels in horseshoe crab eggs, and blood and feather levels of metals in red knot (Calidris canutus rufa; n = 30), sanderling (Calidris alba; n = 20) and semipalmated sandpiper (Calidris pusilla; n = 38) from Delaware Bay. There is a rich literature on metal levels in feathers. For all three species, the levels of arsenic, cadmium, chromium, lead and mercury in blood were highly correlated with the levels of metals in the eggs of horseshoe crab (17 pooled samples). This indicates that the levels in the blood of these shorebirds quickly reflect levels in their prey (horseshoe crab eggs), while metals in the feathers were not correlated with the levels in eggs. Semipalmated sandpipers had the lowest levels of arsenic in blood and the highest levels of arsenic in feathers, compared to the other species. At Delaware Bay, semipalmated sandpipers have a diet higher in marsh invertebrates than the other species, which may account for the differences. The levels of cadmium and chromium in blood were significantly higher in knots than other species; knots only ate horseshoe crab eggs. For all of the metals except arsenic, the ratio of levels in blood/feathers was similar among species. For arsenic, the ratio of levels in blood/feathers were significantly lower in semipalmated sandpipers than in the other species, by an order of magnitude.

Metal Levels in Shorebird Feathers and Blood During Migration Through Delaware Bay

We investigated levels of arsenic mercury, lead, cadmium, and chromium in Red Knot (Calidris canutus), Semipalmated Sandpipers (Calidris pusilla), and Sanderling (Calidris alba) migrating through Delaware Bay, New Jersey to determine if contaminant levels are likely to be causing negative effects on the populations of these shorebirds, to compare among species, and to explore differences among individuals collected early and late during their migration stopover. We analyzed blood and feathers, both nonlethal ways of exploring contaminants in birds. Blood contaminant analysis provides a direct measure of recent dietary exposure, whereas feathers reflect body burden at the time of feather molt. We found some differences among species and between early and late samples. Levels of Hg and Pb were higher in Sanderling blood collected early (36.52 ± 8.45 and 145.00 ± 12.56 ng/g ww respectively) compared with later (16.21 ± 6.03 and 33.60 ± 4.05 ng/g ww respectively) during the migration stopover. Blood Pb levels of Sanderling in the early period were higher than those of the other two species (75.38 ± 15.52 ng/g ww in Red Knot and 42.39 ± 8.42 ng/g ww in Semipalmated Sandpipers). Semipalmated Sandpipers had lower blood As levels than the other two species (254.33 ± 40.15 and 512.00 ± 66.79 ng/g ww early and late respectively) but higher feather levels (914.01 ± 167.29 and 770.00 ± 116.21 ng/g dw early and late respectively), and their blood As was higher in the later sampling period compared with the early sampling period. Arsenic levels in shorebird tissues were relatively high and may reflect levels in horseshoe crab eggs, their primary diet item in Delaware Bay. In Red Knot, blood Cr levels were elevated in the later samples (572.17 ± 62.82 ng/g ww) compared to the early samples (382.81 ± 95.35 ng/g ww) and to the other species. The mean values of the metals analyzed were mostly below effect levels-the level that has a measurable negative impact-although relatively high As levels in Semipalmated Sandpiper feathers and some high levels of Pb need to be further explored.

Updating movement estimates for American black ducks (Anas rubripes)

Understanding migratory connectivity for species of concern is of great importance if we are to implement management aimed at conserving them. New methods are improving our understanding of migration; however, banding (ringing) data is by far the most widely available and accessible movement data for researchers. Here, we use band recovery data for American black ducks (Anas rubripes) from 1951-2011 and analyze their movement among seven management regions using a hierarchical Bayesian framework. We showed that black ducks generally exhibit flyway fidelity, and that many black ducks, regardless of breeding region, stopover or overwinter on the Atlantic coast of the United States. We also show that a non-trivial portion of the continental black duck population either does not move at all or moves to the north during the fall migration (they typically move to the south). The results of this analysis will be used in a projection modeling context to evaluate how habitat or harvest management actions in one region would propagate throughout the continental population of black ducks. This analysis may provide a guide for future research and help inform management efforts for black ducks as well as other migratory species.

Population size and stopover duration estimation using mark-resight data and Bayesian analysis of a superpopulation model

We present a novel formulation of a mark-recapture-resight model that allows estimation of population size, stopover duration, and arrival and departure schedules at migration areas. Estimation is based on encounter histories of uniquely marked individuals and relative counts of marked and unmarked animals. We use a Bayesian analysis of a state-space formulation of the Jolly-Seber mark-recapture model, integrated with a binomial model for counts of unmarked animals, to derive estimates of population size and arrival and departure probabilities. We also provide a novel estimator for stopover duration that is derived from the latent state variable representing the interim between arrival and departure in the state-space model. We conduct a simulation study of field sampling protocols to understand the impact of superpopulation size, proportion marked, and number of animals sampled on bias and precision of estimates. Simulation results indicate that relative bias of estimates of the proportion of the population with marks was low for all sampling scenarios and never exceeded 2%. Our approach does not require enumeration of all unmarked animals detected or direct knowledge of the number of marked animals in the population at the time of the study. This provides flexibility and potential application in a variety of sampling situations (e.g., migratory birds, breeding seabirds, sea turtles, fish, pinnipeds, etc.). Application of the methods is demonstrated with data from a study of migratory sandpipers.

Developing objectives with multiple stakeholders: adaptive management of horseshoe crabs and Red Knots in the Delaware Bay

Structured decision making (SDM) is an increasingly utilized approach and set of tools for addressing complex decisions in environmental management. SDM is a value-focused thinking approach that places paramount importance on first establishing clear management objectives that reflect core values of stakeholders. To be useful for management, objectives must be transparently stated in unambiguous and measurable terms. We used these concepts to develop consensus objectives for the multiple stakeholders of horseshoe crab harvest in Delaware Bay. Participating stakeholders first agreed on a qualitative statement of fundamental objectives, and then worked to convert those objectives to specific and measurable quantities, so that management decisions could be assessed. We used a constraint-based approach where the conservation objectives for Red Knots, a species of migratory shorebird that relies on horseshoe crab eggs as a food resource during migration, constrained the utility of crab harvest. Developing utility functions to effectively reflect the management objectives allowed us to incorporate stakeholder risk aversion even though different stakeholder groups were averse to different or competing risks. While measurable objectives and quantitative utility functions seem scientific, developing these objectives was fundamentally driven by the values of the participating stakeholders.

Mercury, Lead, Cadmium, Arsenic, Chromium and Selenium in Feathers of Shorebirds during Migrating through Delaware Bay, New Jersey: Comparing the 1990s and 2011/2012

Understanding temporal changes in contaminant levels in coastal environments requires comparing levels of contaminants from the same species from different time periods, particularly if species are declining. Several species of shorebirds migrating through Delaware Bay have declined from the 1980s to the present. To evaluate some contaminants as cause for the declines, we examine levels of mercury, lead, cadmium, arsenic, chromium and selenium in feathers of red knot (Calidris canutus, N = 46 individuals), semipalmated sandpiper (Calidris pusilla, N = 70) and sanderling (Calidris alba, N = 32) migrating through Delaware Bay, New Jersey, USA, from 1991 to 1992 (N = 40), 1995 (N = 28), and 2011–2012 (N = 80) to determine if levels have changed. We found: (1) arsenic, chromium, and lead increased in red knot and decreased in semipalmated sandpiper; (2) cadmium decreased in semipalmated sandpipers; (3) mercury decreased in red knot and sanderlings; (4) selenium decreased in red knot and increased in semipalmated sandpipers. In 2011/2012 there were significant interspecific differences for arsenic, mercury and selenium. Except for selenium, the element levels were well below levels reported for feathers of other species. The levels in feathers in red knots, sanderling, and semipalmated sandpipers from Delaware Bay in 2011/2012 were well below levels in feathers that are associated with effect levels, except for selenium. Selenium levels ranged from 3.0 µg·g⁻¹ dry weight to 5.8 µg·g⁻¹ (semipalmated sandpiper), within the range known to cause adverse effects, suggesting the need for further examination of selenium levels in birds. The levels of all elements were well below those reported for other marine species, except for selenium, which was near levels suggesting possible toxic effects.

The Red Knot (Calidris canutus rufa) decline in the western hemisphere: is there a lemming connection?

Numbers of Western Atlantic Red Knots (Calidris canutus rufa (A. Wilson, 1813)) have declined since 1980, with a sustained downward trend observed after 1998. Because the reproductive output of a closely related Eurasian subspecies (Calidris canutus islandica (L., 1767)) is known to be low when lemming numbers are low, and because lemming cycles in Fennoscandia were recently interrupted, we investigated the relationship between the rodent cycle in arctic Canada and numbers of C. c. rufa migrating through the United States. Shooting records from Cape Cod in the 1800s and Red Knot counts on the Delaware Bay from 1986 to 1998 cycled with 4-year periods. Annual peaks in numbers of Red Knots stopping in the Delaware Bay in 1986–1998 occurred 2 years after arctic rodent peaks more often than expected at random. The results suggest that the reproductive output of C. c. rufa was linked to the rodent cycle before the Red Knot decline. There is no evidence that such a link existed after 1998. These findings are consistent with the hypothesis that an interruption of the rodent cycle in Red Knot habitat could have been a driver in the recent Red Knot decline. Field studies in the Arctic are needed to further investigate this hypothesis.