Southwest Nova Scotia Research Articles

Thinking big starting small: identifying considerations for small-scale tidal energy in southwest Nova Scotia

Nova Scotia’s marine renewable energy (MRE) sector can contribute to provincial goals for carbon neutrality. With this, tidal energy has been an interest to industry stakeholders for over two decades, yet general momentum for the industry has shifted. Previous tidal energy projects and recent studies suggest there needs to be a shift in focus towards scalable tidal energy (i.e., small-scale) development in the province. This research explores the considerations of developing tidal energy in Southwest Nova Scotia with an emphasis on small-scale tidal devices. Using a comprehensive literature review and in-depth semi-structured interviews with stakeholders from different sectors of Nova Scotia’s MRE energy industry, key issues and challenges were explored. Results underline four main themes that affect industry potential, which include cost and financing, technology, policy, and energy distribution. These results support a discussion around the value of small-scale technology, regulatory pathways, industry collaboration, and using global best practices to accelerate tidal energy industry goals in Nova Scotia.

Tracking pollution from fur farms using forensic paleolimnology

Eutrophication, which remains one of the greatest threats to water quality worldwide, is particularly acute in agricultural areas. Here we assessed long-term drivers of potential pollution inputs to lakes in southwest Nova Scotia (Canada), a region marked by fur farming (mainly mink) and other agricultural activities. We used a BACI (before-after-control-impact) study design with sediment cores collected from 14 lakes selected based on their proximity to mink farms. We combined economic data, mink faecal samples, and a series of geochemical markers in dated sediment cores, including sterols, δ15N, visible reflectance spectroscopy (VRS)-inferred chlorophyll-a, and heavy metals, to relate changes in sediment geochemistry to the growth of mink farms in the region. Sterol biomarkers (cholesterol and β-sitosterol) measured in a range of samples (i.e. mink faeces and feed, aquaculture feed), were elevated where mink farms were located close to each study lake. Mink-related sterols (cholesterol, β-sitoserol), δ15N measurements, VRS chlorophyll-a, and heavy metals As, Cu, Sr increased in the 1980s coeval with a ∼400% increase of mink farms in the region, especially near Nowlans Lake. Agricultural impacts were subtler in other lakes. Our study expands on prior applications of geochemical fingerprinting in forensic paleolimnology when direct monitoring data are incomplete. This multi-proxy approach has promising applications for environmental pollution assessments in other lake ecosystems experiencing water quality issues.

Seasonal and circadian patterns of herring gull (Larus smithsoniansus) movements reveal temporal shifts in industry and coastal island interaction

AbstractAnthropogenic food subsidies attract opportunistic generalists like gulls in high densities, which may lead to negative impacts on human communities and local ecosystems. Managing impacts requires understanding why gulls use particular natural or industrial sites at different times of day or phases of the breeding cycle. Use of natural and human‐influenced habitats likely varies temporally as gulls alter schedules and site selection to match the predictability of different resources as they vary through space and time relative to patterns in human activities (seasonal industries, the work week, working hours) and natural rhythms (daylight, tide cycles), while gull resource requirements and restrictions to movement also shift with changing reproductive demands.We quantified seasonal and circadian patterns in American herring gull (Larus smithsoniansus) interactions with anthropogenic and natural sites throughout breeding using GPS data from 15 gulls tracked over 3 years from two colonies. We examined the weekly probability of gull occurrence at distinct destinations (e.g. breeding colony, islands, offshore, fish processing plants), and how occurrence varied with time of day, weekday/weekend, tide phase and colony, using GLMMs with a binomial response for destination‐specific occurrence.Probability at the colony varied predictably through the breeding season (highest attendance from dusk to dawn, during incubation and early chick rearing), providing confidence in the modelling approach for detecting temporal patterns in behaviour. Gulls visited other islands mostly outside incubation and early chick rearing, and from dusk through the night, likely roosting. Occurrence offshore where interaction with fishing vessels is possible was highest from dusk to dawn, and differed among colonies, but was the most likely destination during incubation and early chick rearing. Occurrence at fish plants gradually increased until after fledging when attendance was highest from Aug‐Oct coincident with the peak of Atlantic herring (Clupea harengus) processing and was more likely during the weekdays, during working hours, and during low and flood tide.Gulls in southwest Nova Scotia, Canada, have the behavioural flexibility to adapt to both natural rhythms and human schedules when beneficial, enabling them to thrive in a region where industry and natural resources are abundant. These findings can provide information to guide when and where to test different subsidy management strategies locally, while also considering potential increased pressures on island ecosystems. We emphasise that management outcomes of reductions of food subsidies for opportunistic species depend on multiple factors, including availability of alternative food sources and timing of use.

Environmental and economic impacts of retrieved abandoned, lost, and discarded fishing gear in Southwest Nova Scotia, Canada

Abandoned, lost, and discarded fishing gear (ALDFG), negatively impacts marine environments. Managing ALDFG in Atlantic Canada is challenging due to knowledge gaps on loss rates, locations, data availability/accuracy, impacts, and regulatory barriers for retrieval. This study removed ALDFG in Southwest Nova Scotia in collaboration with local fishers (with local knowledge and practical ALDFG removal expertise), government, non-profit organizations, and academia. A total of 29,298 kg of ALDFG was retrieved, including 24,630 kg using towed grapples covering ~3986 km of seafloor and 4668 kg from shorelines (comprising, 68 % lobster traps and 12 % dragger cable by weight). Traps ranged from <1 to 37 years old (median, 10 years). Traps continued to catch target and non-target species with 25 species released, including 652 individual lobsters (82 % were market-sized) and 57 fish (42 were species-at-risk). Based on estimated 2 % trap losses, annual commercial losses from ALDFG were $155,836 CAD in Lobster Fishing Area 34.

Temporal and spatial variability in hydrography and dissolved oxygen along southwest Nova Scotia using glider observations

Dissolved oxygen (DO) in the global ocean is on the decline, resulting in the degradation of coastal habitats. As aquaculture production occurs in these regions, proper understanding of coastal DO dynamics is important for improved farm management (e.g. site selection). The main objective of this study was to quantify along-shore and cross-shore variability in DO dynamics, as well as onshore advection of offshore waters to the bays that could contain aquaculture farms. For that purpose, a Slocum underwater glider was deployed between September 25 and October 12, 2020 to collect high-resolution data of temperature, salinity and DO along a transect between Shelburne Bay and St. Margarets Bay, Nova Scotia, Canada, with an average distance of about 15 km from shore. The observations revealed the variable nature of cross-shore water properties. Shoreward bottom currents transport offshore waters to the coast, and combined with longer residence times, mixing of these waters with those present created a mosaic of differing water properties, with warmer, fresher, and less oxygenated shoreward waters. The glider intercepted an upwelling event due to strong and persistent southwesterly winds, which cooled the upper water layers by 6 °C and increased DO by 1.4 mg L−1. This strong upwelling event detected at 10 km from the coast was also captured 30 h later within St. Margarets Bay, depicting a potential offshore-inshore interaction. Therefore, bay-wide ecosystems and aquaculture production could be affected by intrusions of offshore waters.

An examination of mercury concentrations in eggshells of the common snapping turtle (Chelydra serpentina) in Nova Scotia, Canada

Mercury (Hg) is a potentially toxic metal that has bioaccumulating and biomagnifying properties. In egg laying animals, it can be transferred from an adult female to offspring. However, in turtles, the inter-and-intra-nest variation of Hg concentrations remains unknown. We investigated the concentration of Hg in preyed-upon Common Snapping Turtles (Chelydra serpentina) eggshells. The variability in Hg contamination between and within each nest was assessed. In June 2021, 368 eggshells left behind by predators were sampled from 14 nests, from three different sites in southwest Nova Scotia. Ten eggshells were randomly selected from each nest for analysis. We found no correlation between estimated number of eggs in a nest and average nest Hg concentration. Significant inter-nest variation (Hg ranging from 12.0 ± 3.85 to 172.3 ± 43.9 µg/kg) and intra-nest variability may indicate maternal transfer. The collection of the shells of freshly preyed- upon eggs is a useful non-destructive sampling technique to maintain sustainable turtle populations. Our results demonstrate the need for further investigation into the impact of Hg on temperate, freshwater turtle reproduction. Keywords: mercury concentration, maternal transfer, common snapping turtle, eggshells

Kejimkujik calibrated catchments: A benchmark dataset for long‐term impacts of terrestrial and freshwater acidification

AbstractDelays in forest recovery from terrestrial acidification combined with climate change are leading Acadian Forest ecosystems into new territory. The Kejimkujik Calibrated Catchments (KCC) Study Program was established in and adjacent to Kejimkujik National Park and Historic Site (KNP) in Southwest Nova Scotia (SWNS), Canada, in the late 1970s to study the impacts of acid precipitation on pristine and vulnerable ecosystems. The KCC now have one of the longest continuously monitored water chemistry records in North America, with data collection beginning in 1980. Its infrastructure includes three gauged streams with regular water chemistry sampling, 12 forest inventory plots, and an atmospheric deposition monitoring station. Recently, LiDAR data coverage was acquired for the study basins. Data collected at the KCC form part of the lake monitoring program of Environment and Climate Change Canada used in acidification, climate change, and mercury studies. Important characteristics of the KCC watersheds are their high sensitivity to acid deposition, high and increasing dissolved organic carbon (DOC) levels and lowland topography causing extensive wetlands. The KCC are also emerging as an important location for the study and protection of terrestrial and aquatic species‐at‐risk.

Parasitism of Brook Trout (Salvelinus fontinalis) during the first month post-emergence in streams in southwest Nova Scotia

Parasite recruitment of recently emerged fry of brook trout (Salvelinus fontinalis) in three streams in southwestern Nova Scotia was documented. In early April, fry appeared to leave the protective gravel redds parasite free but began acquiring parasites within the next 2-4 weeks, with prevalence of infections of any given species reaching 21 to 46% by mid-May. The initial infections involved 1) directly transmitted ectoparasites Gyrodactylus colemanensis and Salmincola edwardsii and 2) food-borne endoparasites (Echinorhynchus lateralis and Crepidostomum sp.). Colonizing parasites found in the first month post-emergence varied by locality: at Bangor Creek, it involved G. colemanensis, E. lateralis, and Crepidostomum sp., while at Germaine East, it involved only G. colemanensis and at Germaine North, only S. edwardsii. In each case, the initial colonizers reflected what was abundant locally and within a regional pool of 10 parasite species. Localized skin thickening and sometimes tissue erosion were evident at sites of attachment of S. edwardsii. Minor disruption of fin margins was seen with G. colemanensis. No pathology was associated with E. lateralis nor Crepidostomum sp. The predictable timing of emergence and ease of sampling fry of S. fontinalis near redds represents a convenient system with which to assess impact of initial parasitism on fish recruitment at the local level. Keywords: Echinorhynchus, Gyrodactylus, initial parasite colonization, regional parasite pool, Salmincola

Incorporating intra-annual variability in fisheries abundance data to better capture population dynamics

To reduce the risk of overexploitation and the ensuing conservation and socio-economic consequences, fisheries management relies on receiving accurate scientific advice from stock assessments. Biomass dynamics models used in stock assessment tend to rely primarily on indices of abundance and commercial landings data. Standard practice for calculating the indices used in these models typically involves taking averages of survey tow data over large, diverse spatial domains. There is a lot of variability in the choice of methodologies used to propagate index uncertainty into the assessment model, many of which require specifying it through expert knowledge or prior distributions. Here we propose an alternative approach that treats each individual survey tow as an independent estimate of the true underlying biomass in the stock assessment model itself. This reduces information loss and propagates uncertainties into the model directly. A simulation study demonstrates that this approach accurately captures underlying population dynamics and reliably estimates variance parameters. We further demonstrate its utility with data from the Inshore Scallop Fishery of south-west Nova Scotia. Results show significant improvements in parameter estimation over previous models while providing similar predictions of biomass with less uncertainty. This reduced uncertainty can improve the resulting scientific advice and lead to improved decision-making by fisheries managers.

Retrieval of abandoned, lost, and discarded fishing gear in Southwest Nova Scotia, Canada: Preliminary environmental and economic impacts to the commercial lobster industry

Southwest Nova Scotia (SWNS) is Canada's most productive lobster (Homarus americanus) fishing region. Abandoned, lost, and discarded fishing gear (ALDFG) is widespread. This baseline study provides the first preliminary assessment of environmental and economic impacts of ALDFG on the commercial lobster industry in SWNS. Fishers conducted 60 retrieval trips, searched ~1523 km2 of the seafloor and removed 7064 kg of ALDFG (comprising 66% lobster traps and 22% dragger cable). Results showed that lost traps continued to capture target and non-target species until gear degraded. A total of 15 different species were released from retrieved ALDFG, including 239 lobsters (67% were market-sized) and seven groundfish (including five species-at-risk). The present findings, combined with information on regional fishing effort and market prices, estimate that commercial losses from ALDFG can exceed $175,000 CAD annually. This baseline assessment provides useful data for government and commercial fishing stakeholders to improve ALDFG management.

Contrasting trends in gray seal (Halichoerus grypus) pup production throughout the increasing northwest Atlantic metapopulation

AbstractThe northwest Atlantic subspecies of gray seal (Halicheorus grypus grypus) has been increasing for more than a half century and has reestablished breeding colonies in Canadian and US waters. In 2016, visual, oblique, and vertical large‐format digital photographic surveys were conducted at all known breeding colonies in the northwest Atlantic. Total pup production in the northwest Atlantic was estimated to be 109,000 (SE = 17,500) pups. At 87,500 (SE = 15,100) pups, Sable Island accounts for 80% of total pup production. Regional differences in pup production trends are evident. Pup production in the Gulf of St. Lawrence and along the eastern shore of Nova Scotia has been relatively stable. Since 2004, the rate of increase in pup production at Sable Island has slowed to about 5%–7% per year, while the newer colonies in southwest Nova Scotia and the northeastern United States are increasing rapidly. In 2016, the Muskeget Island (MA) breeding colony produced 3,900 (SE = 200) pups, making it the third largest breeding colony in the northwest Atlantic. This southward shift in production may reflect climate‐mediated changes in population growth as well as reestablishment of colonies throughout the former range associated with increased protection.

Meguma terrane orocline: U–Pb age and paleomagnetism of the Silurian Mavillette gabbro, Nova Scotia, Canada

Paleomagnetic results and a U–Pb baddeleyite age from the Silurian Mavillette gabbroic sill in southwest Nova Scotia, Canada, provide new evidence about the Paleozoic tectonic evolution of the Meguma terrane. The Mavillette gabbro sill intruded ca. 440–430 Myr old bimodal rift-related metavolcanic and metasedimentary rocks of the White Rock Formation in the Silurian–Devonian Rockville Notch Group. The 426.4 ± 2.0 Ma Mavillette gabbro age is notably younger than the ca. 440 Ma magmatism, but is part of a geochemically defined suite of within-plate sills and volcanic rocks of the Rockville Notch Group with ages as young as Early Devonian. Paleomagnetic investigation of 13 sites distributed along the Neoacadian (ca. 390 Ma) synclinal limbs of the Mavillette sill reveal magnetization directions that fail a fold test and therefore postdate Silurian emplacement of the gabbro. The post-folding remanence has a mean direction of D = 153.4, I = 17.1°; α 95 = 6.5° (n = 12 sites), with corresponding paleopole 31.9 °S, 325.2 E; dp = 3.5°, dm = 6.7° that resembles a pervasive late Carboniferous Kiaman overprint magnetization in North America, but is rotated significantly 22.2° ± 8.1° counter-clockwise (CCW). Mavillette remanence acquisition likely occurred in concert with fluid mobilization related to Alleghanian deformation, recorded locally by ca. 320 Ma muscovite 40Ar–39Ar ages. Previously published paleomagnetic results from the Meguma terrane also have Carboniferous remanence directions with similar ∼24° CCW discordance. The regional CCW rotation of the southwest Meguma terrane post-dates this ca. 320 Ma tectonothermal remanence acquisition event, likely recording the development of an oroclinal bend of the Meguma terrane during the Alleghanian orogeny.

Coastal Upwelling Off Southwest Nova Scotia Simulated With a High‐Resolution Baroclinic Ocean Model

AbstractA high‐resolution baroclinic coastal ocean model is applied to study seasonal circulation and upwelling off South West Nova Scotia (SWNS) based on 1 year simulations for 2010. The model reasonably reproduces tidal currents, seasonal hydrography, and circulation from multiyear observations, in consistence with the observed strong seasonal variations of these properties in the study area. The main physical processes affecting circulation are analyzed using numerical experiments, with focus on the effect of tidal and density induced currents on topographic upwelling. It is confirmed that the shoreward near‐bottom currents and associated upwelling are tidally induced and persistent throughout the year. It is revealed that these currents have seasonal variability, with cross‐isobath component being strong in summer throughout a large area, but weaker and confined to deeper regions in winter. The seasonal variability of Scotian Current is the dominant forcing affecting the variability of onshore bottom currents. Lagrangian particle tracking identifies two major pathways of source waters arriving at the SWNS upwelling region. A large proportion of particles come from the east with the Scotian Current, mostly from the surface layer; and a small portion of water parcels come from a mean depth exceeding 100 m from the Gulf of Maine and Northeast Channel.

Regional differences and linkage between canopy structure and community composition of rockweed habitats in Atlantic Canada

Ascophyllum nodosum (rockweed) is a dominant, habitat-forming seaweed on intertidal rocky shores in the North Atlantic and commercially harvested in Canada, Maine and Europe. Rockweed plant structure varies regionally, and several morphotypes have been identified in Atlantic Canada alone. Yet the regionality of canopy structure, associated species communities and the link between the two have not been well understood. Using large-scale field surveys and multivariate statistical approaches, we report distinct canopy structures between sites in southwest Nova Scotia and southwest New Brunswick, the two major rockweed harvesting areas in Atlantic Canada, as well as distinct associated community composition. We then demonstrate significant links between canopy and community structure. Importantly, plant and canopy structure, including length, circumference and density, were much better predictors of associated community structure than rockweed biomass, which is often used for single-species monitoring. Adding region or site as predictors further improved model fits. Therefore, measuring plant or canopy structure would strongly improve insight regarding ecosystem changes. Moreover, incorporating information about regional differences in canopy structure and the dependence of associated communities on those canopies is critical for spatially refined, ecosystem-based management of the rockweed harvest.

Laying the foundation for a digital Nova Scotia

In 2013, the Province of Nova Scotia began an effort to modernize its coordinate referencing infrastructure known as the Nova Scotia Coordinate Referencing System (NSCRS). At that time, 8, active GPS stations were installed in southwest Nova Scotia to evaluate the technology's ability to address the Province's coordinate referencing needs. The success of the test phase helped build a business case to implement the technology across the entire Province. It is anticipated that by the end of 2015, 40 active GPS stations will be in place across Nova Scotia. This infrastructure, known as the Nova Scotia Active Control Stations (NSACS) network, will allow for instantaneous, centimetre level positioning across the Province. Originally designed to address the needs of the surveying community, the technology has also proven to have applications in mapping, machine automation, agriculture, navigation, emergency response, earthquake detection and other areas. In the foreseeable future, all spatial data sets captured in Nova Scotia will be either directly or indirectly derived from the NSACS network. The technology will promote high accuracy and homogenous spatial data sets across the Province. The technology behind the NSACS and the development of the system are described. Examples of how the technology is contributing to a digital Nova Scotia are presented. Future applications of the technology are also considered.

Enacting and contesting neoliberalism in fisheries: The tragedy of commodifying lobster access rights in Southwest Nova Scotia

Atlantic Canadian fisheries policy exhibits a tension between competing objectives of economic efficiency, and of well-being and equity within coastal communities and small-scale fisheries. The struggle between different actors over these objectives has generated distinct forms of neoliberalism in different regions and fishing fleets. In the lobster fishery, the right to fish has been concentrated since limited-entry licensing policy was introduced in the 1980s. This paper examines actors and events at two scales, including Lobster Fishing Area (LFA) 34 Advisory Committee meetings involving fishermen, representatives of Fisheries and Oceans Canada (DFO), and other stakeholders, and broader scale strategies of the Canadian Independent Fish Harvesters Federation (CIFHF). A Foucauldian perspective aids in understanding how fisheries governance is the product of struggles between the power and agency of individual fishermen, fishing organizations, processing companies, the DFO, the Minister of Fisheries and the courts. While many theorists view fisheries through the lens of the “tragedy of the commons”, alternative tragedies are developing in Atlantic Canadian fisheries. These include rising levels of debt, reduced earnings, vulnerability to financial volatility, loss of fishing rights within communities, and too much processor control.

Movements of the Eastern Ribbonsnake (&lt;em&gt;Thamnophis sauritus&lt;/em&gt;) in Nova Scotia

The disjunct Eastern Ribbonsnake (Thamnophis sauritus) population in southwest Nova Scotia is listed as “threatened” by the committee on the Status of Endangered Wildlife in Canada. A study of the movements of the species at two lakeshore locations known to support a high density of Eastern Ribbonsnakes was undertaken in 2007 and 2008. Average seasonal movements at both sites ranged from 17 m to 84 m for juvenile snakes and 21 m to 130 m for adults; one neonate was recaptured during the study after travelling 32 m. The maximum distance travelled by an individual snake was 391 m in one season. The best-fit model to explain differences in daily movement patterns included year (P = 0.041), indicating that there is annual variation in the movements of this species. Low recapture rates precluded accurate estimates of home-range size, which varied roughly from 0.16 ha to 0.78 ha. Both movements and home ranges were larger than previously documented in Nova Scotia, but maximum distances travelled were consistent with a previous study in Michigan. Most documented movements were along the lakeshore within contiguous, suitable habitat. More work is needed to understand the frequency of large movements and triggers that initiate movements, e.g., changes in water levels, habitat suitability, or prey availability.

Life cycle assessment of the Maine and southwest Nova Scotia lobster industries

Commercial fisheries contribute to a number of non-localized environmental and resource depletion problems, such as climate change, through the provision and use of fossil fuels, vessels, gear, refrigeration, and bait, and during post-capture processes. Here, we investigate the degree to which different management regimes may affect two fisheries’ contributions to a suite of non-localized environmental concerns. Life cycle assessment (LCA) is used to quantify the contributions made by the 2006 Maine and 2005–2006 southwest Nova Scotia fisheries for American lobster (Homarus americanus) to a suite of global environmental problems. The lobster fishery phase was the primary driver of resource and environmental impacts as characterized in the selected impact categories. Direct diesel use by the lobster boat was the primary source of impacts at the fishery phase, but the provision and use of bait was also a substantial contributor, particularly in the Maine fishery. Post-capture transportation of live lobster by air was a major contributor in the LFA 34 model. Lobstermen in both fisheries reported using approximately one liter of fuel per kilogram of lobster landings, but Maine lobstermen reported using three kilograms of bait per kilogram of lobster landings, while LFA 34 lobstermen reported using only one kilogram of bait per kilogram landings. The difference in bait use per unit landings resulted in the Maine lobster fishery having slightly higher global environmental impacts, when measured by the chosen impact categories, than the Nova Scotia fishery. However, the two fisheries’ contributions to the selected environmental impact categories were broadly similar, despite their different management regimes, and an obvious influence of management was not identified. The findings for the lobster fisheries are placed into context with other food production systems.

Seismic stratigraphic framework and depositional history of a large Upper Cretaceous and Cenozoic depocenter off southwest Nova Scotia, Canada

Interpretations of the Late Cretaceous to Quaternary geological history of the North American Basin rely on a seismic and lithostratigraphic framework developed predominantly from data along the northeastern United States margin. Prior to this study, attempts to extend this framework northward to the Nova Scotia margin were hindered by correlation issues across seamounts, limitations in data coverage, and significant complications caused by widespread canyon erosion and shallow salt structures. These challenges are overcome using modern seismic reflection data along the southwestern Nova Scotia margin, in the Shelburne sub-basin, where Upper Cretaceous through Quaternary sequences manifest four distinct phases in the interplay between down-slope and along-slope depositional and erosional processes. The first phase, spanning the Late Cretaceous to Late Eocene, is characterized by widespread periods of gully erosion interspersed with periods of pelagic and hemipelagic, carbonate-rich sedimentation. Extensive failure of upper slope regions related to the Montagnais meteorite impact also occurred during this time. The second phase, spanning the Oligocene to Late Miocene, is dominated by widespread erosion, deposition by gravity flow processes, and sediment re-working by bottom currents. Marked erosion and/or non-deposition along the mid-to lower slope is attributed both to down-slope and along-slope processes. The third phase, spanning the Late Miocene to Late Pliocene, is dominated by bottom current deposition including stacked sequences of giant sediment waves and large contourite drifts along the slope. The final phase, from the Late Pliocene to present, exhibits a return to predominance of down-slope gravity flows with deposition focused below the upper slope. This four phase history of depositional and erosional processes is similar to that documented south of the study area along the U.S. margin.

Patterns and correlates of songbird movements at an ecological barrier during autumn migration assessed using landscape‐ and regional‐scale automated radiotelemetry

Departure decisions of songbirds at ecological barriers they encounter en route can strongly influence time, energy and survival costs of migration. To date, most field studies of departure decisions and their correlates have used indirect methods and followed migrants at a single stopover site, with limited information on what happens to individuals after they depart from the site. We used an automated radiotelemetry array extending 350 km from southwest Nova Scotia to southern Maine to study the migratory and stopover movements of Northern Waterthrushes Parkesia noveboracensis, Red‐eyed Vireos Vireo olivaceus and Yellow‐rumped Warblers Setophaga coronata in relation to fuel load and weather at the northeastern edge of the Gulf of Maine. From the 105 radio‐transmitters we deployed in southwest Nova Scotia, we recorded 42 landscape‐scale stopover flights and 47 migratory flights by 75 individuals. Of the migratory flights, 57% were orientated southwest, a trajectory that, if held, would require individuals to complete a 350–440 km overwater flight. The remaining 43% of migratory flights were orientated northwest, away from the Gulf of Maine, and 15 individuals were confirmed to have detoured around all or a portion of the barrier, as evidenced by their being re‐detected over the Bay of Fundy and/or along the coast of Maine between 4 h and 15 days later. Across all individuals, initial fat score had a positive effect on departure probability, especially for individuals that made stopover flights. Among weather variables, tailwind assistance was the best predictor of migratory departures but did not appear to be the main factor determining whether individuals orientated towards or away from the Gulf of Maine. Weather had little effect on departure decisions of individuals that made stopover flights. These differences in the correlates of migratory departures and stopover flights would probably not have been distinguishable had our study been restricted to a local scale. Therefore, our findings highlight the importance of expanding the scale at which departure decisions and the ecology of stopover in general are studied.