Colony Location Research Articles

Spatial variation of mercury contamination in yellow-legged gulls (Larus michahellis) in the Western Mediterranean

Mercury (Hg) is a global pollutant of major concern in marine and coastal environments. In the Mediterranean Sea, Hg concentrations in biota are higher than in other seas, even when seawater concentrations are similar. Seabirds, as marine top predators, can reflect Hg contamination on a large spatial scale. By sampling seabirds at 17 different breeding colonies, we evaluated Hg concentrations of yellow-legged gulls (Larus michahellis) in the occidental Mediterranean basin in 2021 and 2022. More specifically, we investigated spatial variation of Hg contamination in both chicks and adults as well as associated toxicological risks through the use of blood and feathers, which reflect contamination over different periods of the year. The highest concentrations in chicks were found in Djerba (Tunisia) with blood Hg values of (mean ± SD) 1.69 ± 0.51 μg g−1 dry weight (dw). Adults were most contaminated in Djerba and Dragonera (Balearic Islands, Spain) with blood Hg concentrations of respectively 3.78 ± 2.54 and 5.25 ± 3.73 μg g−1 dw. Trophic ecology was investigated using stable isotope analyses (δ13C, δ15N and δ34S as proxies of feeding habitat and diet), and showed that spatial variation in Hg was mainly driven by foraging habitat in both chicks and adults. Low Hg concentrations were related to the use of anthropogenic food sources. An effect of colony location was also found, suggesting spatial differences in local environmental pollution transfer up to seabirds. Our results also supported the use of δ34S to discriminate between marine and continental foraging habitats in generalist seabirds. This study provides new insights onto the spatial distribution of Hg contamination in a widespread seabird, reporting some of the highest Hg values recorded for this species. Populations with highest concentrations are of potential concern regarding toxicological risks.

Mercury contamination and potential health risk to French seabirds: A multi-species and multi-site study

Mercury (Hg) is a naturally occurring highly toxic element which circulation in ecosystems has been intensified by human activities. Hg is widely distributed, and marine environments act as its main final sink. Seabirds are relevant bioindicators of marine pollution and chicks are particularly suitable for biomonitoring pollutants as they reflect contamination at short spatiotemporal scales. This study aims to quantify blood Hg contamination and identify its drivers (trophic ecology inferred from stable isotopes of carbon (δ13C) and nitrogen (δ15N), geographical location, chick age and species) in chicks of eight seabird species from 32 French sites representing four marine subregions: the English Channel and the North Sea, the Celtic Sea, the Bay of Biscay and the Western Mediterranean. Hg concentrations in blood ranged from 0.04 μg g−1 dry weight (dw) in herring gulls to 6.15 μg g−1 dw in great black-backed gulls. Trophic position (δ15N values) was the main driver of interspecific differences, with species at higher trophic positions showing higher Hg concentrations. Feeding habitat (δ13C values) also contributed to variation in Hg contamination, with higher concentrations in generalist species relying on pelagic habitats. Conversely, colony location was a weak contributor, suggesting a relatively uniform Hg contamination along the French coastline. Most seabirds exhibited low Hg concentrations, with 74% of individuals categorized as no risk, and < 0.5% at moderate risk, according to toxicity thresholds. However, recent work has shown physiological and fitness impairments in seabirds bearing Hg burdens considered to be safe, calling for precautional use of toxicity thresholds, and for studies that evaluate the impact of Hg on chick development.

Floods and fire ants, Solenopsis invicta (Hymenoptera: Formicidae): the Australian experience

AbstractThe rafting behaviour of the red imported fire ant, Solenopsis invicta, in response to flooding events is well documented, although studies generally have focussed on the mechanisms of raft assembly and the behaviour of the raft's occupants. Flooding as a means of dispersal of S. invicta is frequently mentioned in the literature, although there are few data on the distances travelled or how effective it is compared to natural flight. In Australia, S. invicta is a priority invasive species with a national eradication program operating for 23 years, focussed on the population in southeast Queensland, which currently encompasses more than 700 000 ha. Flooding presents a risk to the success of the program through extending the infestation area or recolonising successfully treated areas. We used the program's extensive spatiotemporal dataset of known fire ant colony locations to assess the effects of two significant flood events on the dispersal or displacement of S. invicta in Queensland. Results indicated that flooding did not spread S. invicta beyond the known boundaries of infestation but contributed to localised spread, particularly for sites with known polygyne infestations. This situation could change if the ant spreads to new river catchments. A novel method developed to assess the risk of S. invicta dispersal through flooding is presented, alongside program actions that can be applied to mitigate this risk.

Correcting detection bias in mapping the abundance of marine megafauna using a Mediterranean seabird as an example

Abstract Distance sampling surveys are extensively used to estimate the abundance of wide-ranging species but are prone to detection biases. This may be particularly acute for strip-transect protocols, which assume perfect detection. We examined this assumption by quantifying the detection probability of a declining seabird (Scopoli’s shearwater, Calonectris diomedea), with particular attention to time of day and observation conditions at sea. We found detection probability was negatively affected by sun glare but positively by cloud cover and considerably dropped during mid-day hours due to circadian changes in behaviour (reduced detectability while resting). This result urges for systematically assessing and correcting detection bias when using strip-transect data to derive abundance information. Here, we did so by building a detection-corrected presence-absence ensemble model and combining it with a compilation of colony sizes and locations. A Monte-Carlo simulation ensured uncertainty propagation within and across data sources. The corrected abundance map showed shearwaters were largely prevalent in the central Mediterranean, Tunisia hosting most of the population both at sea and at colonies (45% of the global population; 79% of breeding pairs). This first accurate map is an essential conservation tool, emphasizing the importance of transnational actions for such species, that know no political boundaries.

I need some space: solitary nesting Adélie penguins demonstrate an alternative breeding strategy at Cape Crozier

According to the ‘selfish herd’ hypothesis, most seabird species breed colonially so that individuals can decrease their risk of predation by forming compact groups. However, costs and benefits associated with colonial breeding may not be evenly distributed among individuals within a colony. At Adélie penguin colonies, individuals nesting on the periphery of subcolonies (distinct groups of nests) may experience higher rates of nest predation by south polar skuas, and thus the optimal aggregation pattern for Adélie penguins may be within groups that minimize the proportion of edge nests. Nevertheless, some penguins choose to nest solitarily, at significant distances from conspecifics. We tracked 50 of these “solitary-nesting” Adélie penguins at Cape Crozier, a large colony on Ross Island, during the 2021 nesting season and compared their breeding success to individuals nesting within subcolony boundaries. We found that both solitary and subcolony nests successfully raised chicks large enough to join crèches and left unattended by adults. However, chicks from solitary nests exhibited a rate of mortality more than six times higher during the transition from nest brooding/guarding to crèche stage. In the 2022 nesting season, we found that solitary nests which had previously hosted actively breeding penguins were more likely to be re-occupied. Solitary nesting therefore appears to be a less-successful alternative to breeding within subcolonies, but enough individuals could be successful with this approach to maintain the apparently disadvantageous behavior and effectively pioneer previously unused locations, possibly including eventual new colony locations.

‘Merchant Princes and Ocean Leviathans:’ the Uneven Development of the Overseas Mail, 1837–1880

ABSTRACT Over the nineteenth century, the global expansion of British trade and settlement were underwritten by a massive expansion of correspondence and communication networks. But while there are detailed studies of how the domestic Post Office developed in this era, how mail was carried between these colonial and international locations has not been fully investigated. This omission is striking because, as this article explains, the development of overseas mail services diverged significantly from the patterns of reform, cost-efficiency, and rationalisation described in histories of the domestic Post Office. Rather, the overseas mail grew through a set of unprecedented partnerships between the state and steamship companies that resulted in a surprisingly uneven postal network, which served an expanding collection of international and colonial ports but under highly variable conditions and costs. This article brings together postal records, Parliamentary debates, and the histories of steamship companies to explain how the overseas mail system developed between 1837 and 1880 as the power of private actors waxed and waned. It not only explains how a central utility of empire functioned but also provides insight on the operation of a key set of public-private partnerships in the nineteenth-century British world.

Inherited cultural diversity and wages: surname-based evidence

Abstract This article shows that inherited cultural diversity at the regional level generates a positive wage externality. We use administrative panel data on formally employed individuals in Rio Grande do Sul in Brazil from 2008 to 2013 and apply machine learning to infer the ancestry of workers from their surnames. We distinguish inherited diversity from birthplace diversity and use the plausibly exogenous location of former colonies to build an instrumental variable. The positive wage externality of inherited diversity withstands alternative explanations such as institutional quality, municipality size, human capital externalities, individual productivity differences, and sorting of workers.

Intra-colony spatial variance of oxyregulation and hypoxic thresholds for key Acropora coral species.

Oxygen (O2) availability is essential for healthy coral reef functioning, yet how continued loss of dissolved O2 via ocean deoxygenation impacts performance of reef building corals remains unclear. Here, we examine how intra-colony spatial geometry of important Great Barrier Reef (GBR) coral species Acropora may influence variation in hypoxic thresholds for upregulation, to better understand capacity to tolerate future reductions in O2 availability. We first evaluate the application of more streamlined models used to parameterise Hypoxia Response Curve data, models that have been used historically to identify variable oxyregulatory capacity. Using closed-system respirometry to analyse O2 drawdown rate, we show that a two-parameter model returns similar outputs as previous 12th-order models for descriptive statistics such as the average oxyregulation capacity (Tpos) and the ambient O2 level at which the coral exerts maximum regulation effort (Pcmax), for diverse Acropora species. Following an experiment to evaluate whether stress induced by coral fragmentation for respirometry affected O2 drawdown rate, we subsequently identify differences in hypoxic response for the interior and exterior colony locations for the species Acropora abrotanoides, Acropora cf. microphthalma and Acropora elseyi. Average regulation capacity across species was greater (0.78-1.03 ± SE 0.08) at the colony interior compared with exterior (0.60-0.85 ± SE 0.08). Moreover, Pcmax occurred at relatively low pO2 of <30% (±1.24; SE) air saturation for all species, across the colony. When compared against ambient O2 availability, these factors corresponded to differences in mean intra-colony oxyregulation, suggesting that lower variation in dissolved O2 corresponds with higher capacity for oxyregulation. Collectively, our data show that intra-colony spatial variation affects coral oxyregulation hypoxic thresholds, potentially driving differences in Acropora oxyregulatory capacity.

Movement patterns of foraging common terns (Sterna hirundo) breeding in an urban environment in coastal Virginia.

Nesting colonial seabirds are prime examples of central-place foragers, animals that must return to a central location (e.g., a breeding colony) after each bout of foraging. They must balance the costs and benefits of foraging with the need to return to their colonies frequently to form pair bonds during courtship, incubate, provision mates and offspring, and protect and rear young. For some populations, the loss and degradation of suitable breeding habitat due to human activities have necessitated the construction of new breeding sites and/or the restoration of previously occupied sites. South Island, which is part of the Hampton Roads Bridge-Tunnel (HRBT) complex in the Commonwealth of Virginia, U.S.A., is a human-created island that supported Virginia's largest mixed species seabird colony until 2020, when the expansion of the HRBT began and when all nesting seabirds were permanently excluded from the site. We studied the movement patterns of foraging common terns (Sterna hirundo) to determine how travel to and around foraging sites related to their colony location and to inform the siting and construction of a new breeding island. We tracked 18 individual common terns from 07 June to 29 June 2018, and we used a hidden Markov model to assign behavioral states and investigate common tern movements around the HRBT. Common terns spent more than half their time in the colony (58%), followed by time devoted to foraging (22%), and the remainder of their time was spent on outbound (15%) and inbound (5%) transit. Terns traveled as far as 98km from the colony, but on average foraged relatively close to South Island (13.6 ± 0.3km, mean ± 1 SD). Individuals tended to forage in the same locations, but there was variation among individuals. Flying to foraging sites uses energy during the already energetically costly breeding season, thus managers should prioritize placing a new colony site in a location that minimizes the distance traveled to the foraging locations frequented by the South Island birds while accounting for other life-history characteristics. These findings could help in the design and construction of new breeding sites or the restoration of current sites for other, related species, particularly for which these data do not exist.

Circumpolar assessment of mercury contamination: the Adélie penguin as a bioindicator of Antarctic marine ecosystems.

Due to its persistence and potential ecological and health impacts, mercury (Hg) is a global pollutant of major concern that may reach high concentrations even in remote polar oceans. In contrast to the Arctic Ocean, studies documenting Hg contamination in the Southern Ocean are spatially restricted and large-scale monitoring is needed. Here, we present the first circumpolar assessment of Hg contamination in Antarctic marine ecosystems. Specifically, the Adélie penguin (Pygoscelis adeliae) was used as a bioindicator species, to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury was measured on body feathers collected from both adults (n = 485) and chicks (n = 48) between 2005 and 2021. Because penguins' diet represents the dominant source of Hg, feather δ13C and δ15N values were measured as proxies of feeding habitat and trophic position. As expected, chicks had lower Hg concentrations (mean ± SD: 0.22 ± 0.08 μg·g‒1) than adults (0.49 ± 0.23 μg·g‒1), likely because of their shorter bioaccumulation period. In adults, spatial variation in feather Hg concentrations was driven by both trophic ecology and colony location. The highest Hg concentrations were observed in the Ross Sea, possibly because of a higher consumption of fish in the diet compared to other sites (krill-dominated diet). Such large-scale assessments are critical to assess the effectiveness of the Minamata Convention on Mercury. Owing to their circumpolar distribution and their ecological role in Antarctic marine ecosystems, Adélie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across Antarctic waters in the future.

Coral Detection, Ranging, and Assessment (CDRA) algorithm-based automatic estimation of coral reef coverage

Climate change poses significant threats to the health of coral reefs. The detection of coral coverage is a quantitative method for assessing the health of coral reefs. Valuable insights into the effects of climate change on coral reef ecosystems and the trends in coral reef development can be gained through the monitoring of coral coverage. However, traditional manual methods for estimating coral coverage are time-consuming and labor-intensive, limiting the scalability and efficiency of coral surveys. The field of automated processing for coral video imagery is currently limited, impeding the development of effective techniques for comprehensive coral monitoring and further hindering progress in coral ecosystem monitoring. To cope with these challenges, there is a crucial need for automated systems to efficiently handle large volumes of video data, thereby transforming imaging devices, such as underwater robots, into autonomous sensors capable of conducting reliable and comprehensive surveys. In response to this pressing issue, this study presents a novel video analysis approach, termed the Coral Detection, Ranging, and Assessment (CDRA) algorithm, which combines cutting-edge computer vision techniques including You Only Look Once version 5 (YOLOv5) object detection, binocular stereo vision, and tracking algorithms. The CDRA algorithm aims to analyze continuous video segments of coral reefs, enabling the identification, counting, and estimation of size and location of individual coral colonies. Experimental evaluations conducted in controlled pool environments demonstrated the high accuracy of the proposed method, with an average accuracy of 90.7% in estimating coral coverage at different locations. Moreover, field trials conducted in Xidao Island of China verified the effectiveness and robustness of the CDRA algorithm under varying water quality and lighting conditions. The findings of this study represent a significant step towards the development of reliable and automated techniques for coral reef detection, contributing to the advancement of coral reef conservation efforts.

From colony to fallout: Artificial lights pose risk to seabird fledglings far from their natal colonies

AbstractSeabirds are at risk of decline from multiple threats, including artificial light resulting in their grounding (“fallout”). Without evidence, it can be assumed that seabirds travel short distances from natal colonies to their fallout location, potentially to the closest light source. To test this, a case study on wedge‐tailed shearwaters (Ardenna pacifica, ʻUaʻu kani) fledging from the island of Oʻahu, Hawaiʻi was conducted. To assess fallout locations in relation to natal colonies, we affixed identification bands to 4648 chicks at nine natal colonies prior to fledging from 2018 to 2022. Distances between fallout location and natal colony were mapped and fallout location characteristics (radiance, elevation, distances to nearest coastline, road, and colony) were analyzed for 27 banded fledglings that were discovered post‐fallout. The distance between the natal colony and fallout location was significantly greater than the distance between the nearest colony and the fallout location. Fallout often occurred on opposite coastlines from the natal colonies and at substantial distances (x¯ = 24.91 km), with one fallout event recorded on a different island from the natal colony. Our results demonstrate that all artificial lights, regardless of proximity to seabird colonies, may pose a threat to seabird fallout and that fallout is often occurring far from natal colonies and in inconsistent patterns. Collaborative, large‐scale, and multi‐island light management alteration, particularly during fledging periods, is critical in recovering Pacific Island seabird populations. Actions such as these will benefit not only light‐sensitive species such as seabirds and sea turtles but also human health and night‐sky viewing.

Learning and innovation in urban yellow mongooses (Cynictis penicillata)

AbstractProblem‐solving and innovation have been studied extensively, yet urban animals are overlooked despite opportunities to innovate in urban areas. We studied problem‐solving in yellow mongooses (Cynictis penicillata) in an urban setting. Using novel puzzle box experiments, we investigated whether yellow mongooses could solve a task of increasing complexity in three locations with varying extents of anthropogenic interactions. Mongooses in a residential ecological estate took the longest time to solve the problem, whereas those frequenting a residential garden solved the problem the fastest. Mongooses solved the puzzle box problem at each of the four stages of complexity, but were the fastest during the least complex first stage, followed by the third stage and requiring more time in the second and fourth stages of complexity. Overall, the location of the mongoose colonies and the complexity of the task were the main correlates of the speed of solving the problem. Urban‐living yellow mongooses can interact with novelty in an anthropogenic environment and solve novel problems through innovation to obtain a food incentive.

Rampant asexual reproduction and limited dispersal in a mangrove population of the coral Porites divaricata.

Corals are critical to marine biodiversity. Reproduction and dispersal are key to their resilience, but rarely quantified in nature. Exploiting a unique system-a fully censused, longitudinally characterized, semi-isolated population inhabiting mangroves-we used 2bRAD sequencing to demonstrate that rampant asexual reproduction most likely via parthenogenesis and limited dispersal enable the persistence of a natural population of thin-finger coral (Porites divaricata). Unlike previous studies on coral dispersal, knowledge of colony age and location enabled us to identify plausible parent-offspring relationships within multiple clonal lineages and develop tightly constrained estimates of larval dispersal; the best-fitting model indicates dispersal is largely limited to a few metres from parent colonies. Our results explain why this species is adept at colonizing mangroves but suggest limited genetic diversity in mangrove populations and limited connectivity between mangroves and nearby reefs. As P. divaricata is gonochoristic, and parthenogenesis would be restricted to females (whereas fragmentation, which is presumably common in reef and seagrass habitats, is not), mangrove populations likely exhibit skewed sex ratios. These findings suggest that coral reproductive diversity can lead to distinctly different demographic outcomes in different habitats. Thus, coral conservation will require the protection of the entire coral habitat mosaic, and not just reefs.

Physical properties of the soil around the Lanka, Mirzamurad and Babatpur, Varanasi

The analysis of soil samples taken from the areas around the Lanka, Mirzamurad and Babatpur, Varanasi for evaluating its physical properties were carried out in the Department of Soil Science and Agricultural Chemistry Laboratory at the Institute of Agricultural Sciences, Banaras Hindu University, Varanasi during 2015. The bulk density, particle density, water holding capacity%, porosity%, particle distribution% and texture of these soil samples was determined by using standard methods. These soil samples were collected from Vaishnov nagar, Susuwahi, Newada, Gandh, Nasirpur, Agriculture farm, Sankat mochan colony, Naria, Sear govardhan and Karadhi locations of Lanka, Nayapur, Todarpur, Rupapur, Sheorampur, Tribhuvanpur, Bharkala, Dewapur khurd, Ram rathauna, Kasara and Pratappur locations of Mirzamurad and Chherapur, Narayandaspur, Dallipur, Tadi, Fattepur, Kathraon, Rajapur, Nindeva, belwa and khemapur locations of Babatpur, Varanasi. The result showing that bulk density (1.33) was recorded more in Pratappur location of Mirzamurad, particle density (2.60) in Vaishnov nagar location of Lanka, water holding capacity% (63.82) in Todarpur location of Mirzamurad, porosity% (54.49) in Belwa location of Babatpur, under particle distribution sand % (44.56) in Chherapur location of Babatpur, silt % (34 and 34) in Dewapur khurd and Ram rathauna location of Mirzamurad and clay% (35.44) were recorded more than other locations of Lanka, Mirzamurad and Babatpur of Varanasi.

The survival and growth of honey bee (Hymenoptera: Apidae) colonies overwintered in cold storage: the effects of time and colony location.

For over a decade, high percentages of honey bee colonies have been perishing during the winter creating economic hardship to beekeepers and growers of early-season crops requiring pollination. A way to reduce colony losses might be moving hives into cold storage facilities for the winter. We explored factors that could affect the size and survival of colonies overwintered in cold storage and then used for almond pollination. The factors were when hives were put into cold storage and their location prior to overwintering. We found that colonies summered in North Dakota, USA and moved to cold storage in October were larger after cold storage and almond pollination than those moved in November. Colony location prior to overwintering also affected size and survival. Colonies summered in southern Texas, USA and moved to cold storage in November were smaller after cold storage and almond pollination than those from North Dakota. The colonies also were smaller than those overwintered in Texas apiaries. Fat body metrics of bees entering cold storage differed between summer locations. North Dakota bees had higher lipid and lower protein concentrations than Texas bees. While in cold storage, fat bodies gained weight, protein concentrations increased, and lipids decreased. The decrease in lipid concentrations was correlated with the amount of brood reared while colonies were in cold storage. Our study indicates that in northern latitudes, overwintering survival might be affected by when colonies are put into cold storage and that colonies summered in southern latitudes should be overwintered there.

Bees reflect better on their ecosystem health than their products.

Beehives constitute a source of environmental contaminants because forager bees explore their habitat and unintentionally accumulate them while foraging for food. Therefore, this review paper investigated different bee species and products from 55 countries to identify how they can help environmental biomonitoring by giving an overview of the past 11 years. Thereby is presented in this study the beehive's use as a bioindicator for metals, analytical techniques, data analysis, environmental compartments, common inorganic contaminants, reference thresholds for some metal concentrations in bees and honey, and other factors over more than 100 references. Most authors agree that the honey bee is a suitable bioindicator to assess toxic metal contamination, and among its products, propolis, pollen, and beeswax are more suited than honey. However, in some situations, when comparing bees with their products, bees are more efficient as potential environmental biomonitors. Some factors such as the colony location, floral sources, regional effects, and activities surrounding the apiary influence the bees, and the composition of their products is reflected by alterations in their chemical profile, making them suitable bioindicators.

Factors affecting site selection by beavers colonizing streams in the upper Midwest region of the United States

Beaver management requires understanding beaver habitat preferences. Despite the American beaver ( Castor canadensis Kuhl, 1820) being relatively common in the upper Midwest region of the United States, there are no beaver habitat relationship models based on this area. We used 1735 colonization events from long-term monitoring data generated by the Chequamegon-Nicolet National Forest in northern Wisconsin, USA, to determine what geomorphological and biological factors were selected by beavers colonizing new sites. We developed and evaluated prediction performance for three colonization models: geomorphology factors only, geomorphology and vegetation factors, and a full colonization model based on geomorphology, vegetation, and availability of dispersing beavers. Overall, the geomorphology–vegetation–colonizer model was the best model, predicting actual colony locations better than the other two models. Spatially, the landscape open to beaver colonization was a mosaic of streams with suitable and unsuitable habitat. These models improve our understanding of how beaver site selection factors in the upper Midwest region differ from factors identified in the literature for the western and eastern United States. This information may be useful for land managers in this region seeking to spatially target resources for restoring northern forest landscapes such as the Chequamegon-Nicolet National Forest.

DESTRUCTION OF GUILLEMOT COLONIES IN THE SOUTHERN BARENTS SEA AND THE FACTORS THAT DETERMINE IT

Features of Common guillemot (Uria aalge) and Brünnich’s guillemot (U. lomvia) numbers dynamics have been analyzed based on long-term monitoring data obtained from colonies from the southern Barents Sea coast. Since the 2000s, the numbers of guillemots in colonies have been shown to gradually decrease. In 2019–2021, most of the guillemot colonies of the southern Barents Sea coast disappeared. Two factors have been found to affect the guillemot colonies’ dynamics in the last decades: fishing industry and change in oceanographic conditions. These two factors indirectly influence the guillemot populations in the winter-spring area, changing the availability of the birds’ food resources. The former affects only the birds from southwestern Barents Sea colonies, but the second is relevant within the whole winter-spring area from the Barents Sea to the western areas of the North Atlantic. They affect the guillemots’ living conditions in the most critical periods of their life. In future this may cause significant changes in the location of guillemot colonies in the southern Barents Sea.

Estimating Cause‐Specific Mortality and Survival of Juvenile Fall Chinook Salmon: An Investigation of Avian Predation across Large Spatial Scales

AbstractTo investigate the effects of piscivorous colonial waterbird predation on juvenile salmonids (smolts) and to determine what proportion of all sources of smolt mortality was due to predation, we analyzed a data set describing fall Chinook Salmon Oncorhynchus tshawytscha that were marked with PIT tags in the Columbia River, USA. We used a state‐space Bayesian model that incorporated live detections of tagged fish and recoveries of tags from dead fish to jointly estimate predation and survival over multiple river reaches and years (2008–2019). By incorporating recoveries of tags on bird colonies, the model was also able to increase the precision and spatial extent of survival estimates compared with a more traditional capture–recapture model. Results indicated that the avian predation probability (proportion of available fish consumed) varied depending on the predator species, colony location, and the fish's rearing type. Estimates of cumulative predation probability ranged annually from 0.066 (95% credible interval = 0.049–0.089) to 0.283 (0.210–0.419), and predation accounted for 7.3% (4.3–11.9%) to 29.1% (19.7–40.2%) of all sources of smolt mortality during out‐migration to Bonneville Dam. Probabilities of predation on wild smolts were significantly higher than those for hatchery smolts in most river reaches and years. Predation probabilities were the highest for colonies of American white pelicans Pelecanus erythrorhynchos and double‐crested cormorants Nannopterum auritum, which were located near where wild smolts rear and congregate. Estimates of predation by Caspian terns Hydroprogne caspia, California gulls Larus californicus, and ring‐billed gulls L. delawarensis were often &lt;0.03 of available smolts annually. Collectively, results indicated that the cumulative effects of predation on Chinook Salmon smolts were substantial in some but not all river reaches and years. Future models that consider biological and environmental factors influencing smolt susceptibility to avian predation may provide a more holistic understanding of the degree to which predation limits fish survival.