US Waters Research Articles

The hidden risk of keystone invaders in Canada: a case study using nonindigenous crayfish

Invasive species have long been recognized as a serious threat to freshwater ecosystems. This is especially true for invasive species in keystone positions in food webs that can cause major disruption and can lead to unexpected outcomes. Crayfish occupy a central trophic position and nonindigenous crayfish have been shown to substantially disrupt ecosystems they invade. Here, we assess eight nonindigenous crayfish to 21 freshwater ecoregions in Canada using a screening-level risk assessment. We found that ecoregions in Canada that were warmer and contained high native freshwater diversity were most at risk from crayfish invasions, particularly: the Laurentian Great Lakes, St. Lawrence, English–Winnipeg lakes, and Coastal British Columbia ecoregions. Four crayfish species consistently had higher-risk scores: rusty ( Faxonius rusticus), virile ( Faxonius virilis), signal ( Pacifastacus leniusculus), and red swamp ( Procambarus clarkii). Of these high-risk crayfish, only the red swamp crayfish is not yet established in Canada but is present in US waters of the transboundary Great Lakes ecoregion. Our study is the first to evaluate the relative risks that nonindigenous crayfish pose to freshwater ecosystems in Canada.

Emissions from fossil fuels produced on US federal lands and waters present opportunities for climate mitigation

Between 2005 and 2019, a quarter of US fossil fuel production came from federal lands and waters. We estimate that the extraction, transportation and combustion of these fuels resulted in emissions equivalent to roughly 1.4 billion metric tons of carbon dioxide equivalent per year. To better understand their future role in the US emissions profile, we use publicly available data and machine learning to model coal, oil and natural gas production on federal lands and waters to 2030, and calculate associated life cycle climate emissions. We estimate that total emissions from fossil fuels produced on federal lands and waters decline 6% below 2019 levels by 2030; and note that absent additional policy, further reductions may be challenging as some of the cheapest fossil fuels occur on federally owned lands and many are effectively subsidized.

The next generation of conservation research and policy priorities for threatened and exploited chondrichthyan fishes in the United States: An expert solicitation approach

AbstractChondrichthyan fishes are ecologically and economically important, yet many are overfished or at elevated risk of extinction. Researchers report a desire to perform policy‐relevant science that can generate data in support of effective conservation and management plans, but also report a lack of clarity about how to most effectively to do that. To address this gap, we created a list of research and policy priorities for chondrichthyan species of conservation concern in US waters using a modified expert solicitation horizon scan approach. Thirty‐five policy‐relevant research priorities and twenty‐seven policy priorities are presented here, a list which can help to guide scientists and conservationists to maximize the effectiveness of their research and policy advocacy.

Environmental DNA evidence of the Critically Endangered smalltooth sawfish, Pristis pectinata, in historically occupied US waters

Abstract Formerly common in tropical and subtropical waters of the Atlantic Ocean, the Critically Endangered smalltooth sawfish, Pristis pectinata, underwent severe declines over the past century, restricting population(s) to south and south‐west Florida in the US, and Bahamian waters. Anecdotal evidence (e.g. encounter reports from the public) suggests that P. pectinata have recently been observed in historically occupied US waters; however, no directed surveys have been conducted to verify their extent of occupancy. Here, environmental DNA (eDNA) surveys were used to investigate the occurrence of P. pectinata in three formerly occupied estuaries in US waters. Water samples were collected in the summer from the Indian River Lagoon and Tampa Bay, Florida, in 2018 and 2019, and from Mississippi Sound, Mississippi, in 2018, and screened for target DNA using a highly sensitive Droplet Digital™ polymerase chain reaction assay. Target DNA was detected at four sites in the Indian River Lagoon in 2018 and at one site in 2019 (average concentration: 0.086 copies μl−1; SE = 0.004), but was not detected in either year in Tampa Bay. Target DNA was also detected at three sites near Deer Island in Mississippi Sound in 2018 (average concentration: 0.090 copies μl−1; SE = 0.005). These surveys provide additional lines of evidence that P. pectinata is re‐occurring within two historically occupied estuaries in US waters. More comprehensive eDNA surveys in historically occupied regions, combined with clearly defined post‐survey management actions, can direct additional research and outreach initiatives in emerging priority areas, fostering recovery of this Critically Endangered species.

Meta-analysis of salt marsh vegetation impacts and recovery: a synthesis following the Deepwater Horizon oil spill.

Marine oil spills continue to be a global issue, heightened by spill events such as the 2010 Deepwater Horizon spill in the Gulf of Mexico, the largest marine oil spill in US waters and among the largest worldwide, affecting over 1,000 km of sensitive wetland shorelines, primarily salt marshes supporting numerous ecosystem functions. To synthesize the effects of the oil spill on foundational vegetation species in the salt marsh ecosystem, Spartina alterniflora and Juncus roemerianus, we performed a meta‐analysis using data from 10 studies and 255 sampling sites over seven years post‐spill. We examined the hypotheses that the oil spill reduced plant cover, stem density, vegetation height, aboveground biomass, and belowground biomass, and tracked the degree of effects temporally to estimate recovery time frames. All plant metrics indicated impacts from oiling, with 20–100% maximum reductions depending on oiling level and marsh zone. Peak reductions of ~70–90% in total plant cover, total aboveground biomass, and belowground biomass were observed for heavily oiled sites at the marsh edge. Both Spartina and Juncus were impacted, with Juncus affected to a greater degree. Most plant metrics had recovery time frames of three years or longer, including multiple metrics with incomplete recovery over the duration of our data, at least seven years post‐spill. Belowground biomass was particularly concerning, because it declined over time in contrast with recovery trends in most aboveground metrics, serving as a strong indicator of ongoing impact, limited recovery, and impaired resilience. We conclude that the Deepwater Horizon spill had multiyear impacts on salt marsh vegetation, with full recovery likely to exceed 10 years, particularly in heavily oiled marshes, where erosion may preclude full recovery. Vegetation impacts and delayed recovery is likely to have exerted substantial influences on ecosystem processes and associated species, especially along heavily oiled shorelines. Our synthesis affords a greater understanding of ecosystem impacts and recovery following the Deepwater Horizon oil spill, and informs environmental impact analysis, contingency planning, emergency response, damage assessment, and restoration efforts related to oil spills.

Estimating catch curve mortality based on relative return rates of coded wire tagged lake trout in US waters of Lake Huron

We estimated total mortality using catch curves based on relative return rates (RRs) of coded wire tagged lake trout (Salvelinus namaycush) in US waters of Lake Huron. RR was calculated as age-specific CPUE per million of fish stocked. Annual mortality for the late 1990s through early 2000s was estimated as 38% from the 1991–1995 year classes, with an effective age range of 5–10 years, and then was estimated as 24% for the post-2000 period from the 1996–2009 year classes. The two estimates from simple catch curve regressions based on average RR at age values were the same as from a mixed model with individual RR values from all stocking events. These two estimates were also comparable to the findings from statistical catch-at-age assessments with fundamentally different assumptions. Our approach is not constrained by the assumption that the expected recruitment is a constant over time and thus has the advantage to use multiple observations on each age from multiple cohorts. Our approach has broad applicability to aquatic ecosystems in which multiple mark-and-release events of fish stocking have been implemented.

Cruise Ship Travel in the Era of Coronavirus Disease 2019 (COVID-19): A Summary of Outbreaks and a Model of Public Health Interventions.

BackgroundCruise travel contributed to SARS-CoV-2 transmission when there were relatively few cases in the United States. By March 14, 2020, the Centers for Disease Control and Prevention (CDC) issued a No Sail Order suspending U.S. cruise operations; the last U.S. passenger ship docked on April 16.MethodsWe analyzed SARS-CoV-2 outbreaks on cruises in U.S. waters or carrying U.S. citizens and used regression models to compare voyage characteristics. We used compartmental models to simulate the potential impact of four interventions (screening for COVID-19 symptoms; viral testing on two days and isolation of positive persons; reduction of passengers by 40%, crew by 20%, and port visits to one) for 7-day and 14-day voyages.ResultsDuring January 19–April 16, 2020, 89 voyages on 70 ships had known SARS-CoV-2 outbreaks; 16 ships had recurrent outbreaks. There were 1,669 RT-PCR-confirmed SARS-CoV-2 infections and 29 confirmed deaths. Longer voyages were associated with more cases (adjusted incidence rate ratio, 1.10, 95% CI: 1.03-1.17, p < 0.0001). Mathematical models showed that 7-day voyages had about 70% fewer cases than 14-day voyages. On 7-day voyages, the most effective interventions were reducing the number of individuals onboard (43-49% reduction in total infections) and testing passengers and crew (42-43% reduction in total infections). All four interventions reduced transmission by 80%, but no single intervention or combination eliminated transmission. Results were similar for 14-day voyages.ConclusionsSARS-CoV-2 outbreaks on cruises were common during January-April 2020. Despite all interventions modeled, cruise travel still poses a significant SARS-CoV-2 transmission risk.

Recent Development on Herder Commercialization

Abstract Herders (also known as surface collecting agents) are made of surface active compounds (surfactants). They reduce the surface tension of water and thereby change the spreading behavior of immiscible liquids, such as an oil slick, floating on the surface. Oil slicks that have spread too thin to burn can be re-thickened if herders are sprayed on the water surface around a slick. Once the slick is thickened, it is amenable to in situ burning without the need for fire-resistant boom. Herders are listed as surface collecting agents on the National Contingency Product Schedule administered by the US Environmental Protection Agency (USEPA, 2019) for use in US waters. Herders are commercially available and oil spill response organizations have the capability to utilize herders. A new joint industry / government agency project was recently initiated to develop a novel herder delivery and ignition system. The initial plan is to develop a remotely operated surface vehicle (RSV) that will deliver herder from an onboard reservoir and a system to ignite herded slicks. The RSV we are developing has 10–12 hours of operation time, a range of 500 miles and can travel at speeds of up to 65 miles/hour. The RSV can be deployed from a helicopter that has a cargo hook, a boat, and potentially a fixed-wing aircraft that has an appropriately sized hatch. The vision is rapid deployed to a remote spill location using a helicopter (or a fixed-wing aircraft) and operated from this platform until a response vessel arrives on the scene. The response vessel can then take over RSV control freeing the aircraft for other duties. This paper will describe the planned development and testing of the RSV and other progress toward herder commercialization.

Multi-decadal trends in contingent mixing of Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic from otolith stable isotopes

The Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic is comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in US fished regions. Thus, assessment and management of this population can be sensitive to levels of mixing between contingents, which remain unknown. Multi-decadal trends in contingent mixing levels within the US fisheries region were assessed, and the contingent composition across seasons, locations, ages, and size classes were characterized using archived otoliths and developing a classification baseline based on juvenile otolith carbon and oxygen stable isotopes (δ13C/δ18O values). Classification of age ≥ 2 adults demonstrated that northern contingent mixing was prevalent within the US continental shelf waters during the past 2 decades (2000–2019), providing an important seasonal subsidy to the US winter fishery despite substantial depletion in spawning stock biomass of the dominant northern contingent. While the majority of older fish were of the northern contingent during the early 2000s, the southern contingent contribution increased with age/size class during the recent period (2013–2019). Spatial mixing was most prevalent during February and March when the northern contingent occurred as far south as the Delmarva Peninsula, but were mostly absent from US waters in May. A positive relationship (albeit not significant; r = 0.60, p = 0.07) occurred between northern contingent mixing and US fisheries landings, which could imply that higher contingent mixing levels might be associated with greater landings for the US winter mackerel fishery. The yield of the Northwest Atlantic mackerel depends upon the status of the northern contingent, with the southern contingent possibly more prone to depletion. Spatially explicit stock assessment models are recommended to conserve both productivity and stability in this two-component population.

Yellowfin tuna (Thunnus albacares) foraging habitat and trophic position in the Gulf of Mexico based on intrinsic isotope tracers.

Yellowfin tuna (YFT, Thunnus albacares) is a commercially important species targeted by fisheries in the Gulf of Mexico (GM). Previous studies suggest a high degree of residency in the northern GM, although part of the population performs movements to southern Mexican waters. Whether YFT caught in southern waters also exhibit residency or migrate to the northern gulf is currently uncertain, and little is known regarding their trophic ecology. The isotopic composition (bulk & amino acids) of YFT muscle and liver tissues were compared to a zooplankton-based synoptic isoscape from the entire GM to infer feeding areas and estimate Trophic Position (TP). The spatial distribution of δ15Nbulk and δ15NPhe values of zooplankton indicated two distinct isotopic baselines: one with higher values in the northern GM likely driven by denitrification over the continental shelf, and another in the central-southern gulf, where nitrogen fixation predominates. Based on the contribution of the two regional isotopic baselines to YFT tissues, broad feeding areas were inferred, with a greater contribution of the northern GM (over a one-year time scale by muscle), and to a lesser extent in the central-southern GM (over the ca. 6-month scale by liver). This was corroborated by similarities in δ15NPhe values between YFT and the northern GM. TP estimates were calculated based on stable isotope analysis of bulk (SIA) and compound-specific isotope analysis (CSIA-AA) of the canonical source and trophic amino acids. Mean TP based on SIA was 4.9 ± 1.0 and mean TP based on CSIA-A was 3.9 ± 0.2. YFT caught within the Mexican region seem to feed in northern and in central and southern GM, while feeding in the northern GM has a temporal component. Thus, management strategies need to consider that YFT caught in US and Mexican waters are a shared binational resource that exhibit feeding migrations within the GM.

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.

Saws and the city: smalltooth sawfish Pristis pectinata encounters, recovery potential, and research priorities in urbanized coastal waters off Miami, Florida, USA

As coastal urbanization increases globally, the subsequent effects on marine animals, especially endangered species, inhabiting nearshore waters have become a research priority. The smalltooth sawfish Pristis pectinata, once abundant in US waters, now only persists in a few parts of its former range, including South Florida. Many areas utilized by smalltooth sawfish are estuarine systems or other shallow coastal habitats, making this species particularly vulnerable to threats associated with coastal development. To date, P. pectinata has been understudied in the waters in and around Biscayne Bay, Florida, a coastal waterway subjected to the urbanization of adjacent Miami-Dade County. Here, we summarize data from reported smalltooth sawfish encounters dating as far back as 1895 (N = 90) and detail opportune recordings (incidental catches, acoustic detections, and baited remote underwater videos) of sub-adults and adults (N = 14 individuals) in Biscayne Bay and the adjacent reef tract. These data demonstrate historical and increased contemporary use of the study area by this imperiled species, suggesting potential local and regional recovery. Most documented sawfish occurrences were near the urban center, indicating a need to understand the effects of coastal urbanization on sawfish and on the species' recovery potential. We suggest priorities for future research on P. pectinata in the study area that will assist in addressing regional management goals and contribute to understanding the ecology of smalltooth sawfish under environmental change.

Environmental impacts on walleye pollock (Gadus chalcogrammus) distribution across the Bering Sea shelf

Adult and juvenile (age-1) walleye pollock (Gadus chalcogrammus) were sampled by the US NOAA Alaska Fisheries Science Center summer bottom trawl survey in 2010, 2017, 2018, and 2019 in the northeastern and southeastern Bering Sea, with profiles of temperature collected concurrently. Similarly, the Russian Research Institute of Fisheries and Oceanography, Pacific branch, collected adult and juvenile pollock and temperature profiles on summer bottom trawl surveys in the northwestern Bering Sea. Results from these surveys show that adult pollock abundance in recent years (2017, 2018, 2019) has increased in northern regions of the Bering Sea shelf in both the US and Russian sectors. Lower abundances, compared to historic means, were observed in southern regions of the shelf, suggesting the pollock moved directionally from the south to the north. We relate changes in pollock distribution in recent intermediate (2017) and warm, low-ice years (2018–2019) to a prior cold, high-ice year (2010) and describe how these observations relate to our longer time series. We link temperature data from bottom trawl surveys (US and Russian), sea-ice indices (retreat timing and extent), as well as model-based estimates of ocean circulation to changes in pollock distribution and examine potential environmental factors driving the observed changes. Changes in sea-ice and bottom temperature (e.g., reductions in ice extent and shrinking of the cold pool), and changes in circulation (stronger northward currents over the northeastern shelf in warmer years, particularly in 2018) led to changes in distributions of adult and age-1 pollock. Adult pollock were concentrated north of St. Lawrence Island and had larger longitudinal distributions in warm years, 2017–2019; whereas they had a more southerly and narrow distribution over the outer shelf in the cold year, 2010. Age-1 pollock had higher densities over the inner eastern shelf in 2017–2019 compared to 2010. Northward flow around St. Lawrence Island (particularly in the spring) alternated between stronger flow on the west side of the island in 2010 and 2017 and stronger flow on the east side of the island in 2018 and 2019; variations in flow may have impacted the location of prey and movement of feeding pollock to the Chukchi Sea. Size structure comparisons between NW, NE and SE sections of the Bering Sea shelf suggest that movement of fish between US and Russian waters may have been highest in 2019, one of the two warmest years, and lowest in 2010, the coldest year. Spatial comparisons of distributions and size structure across the Bering Sea help provide a comprehensive view of factors affecting the movement of this highly important commercial fish species.

Recreational boaters’ preferences for boating trips associated with offshore wind farms in US waters

This study used a stated preference approach to assess potential impacts of offshore wind farms on recreational boaters in and around Rhode Island (US) waters. To develop the stated preference survey, seven focus groups were conducted with recreational boaters in Rhode Island (RI) in 2017. A combined mail and on-line choice experiment survey was administered in the spring and summer 2018 to 2500 owners of US Coast Guard-documented recreational vessels with a hailing port in Rhode Island. The survey instrument elicited recreational boaters’ preferences for particular attributes of a recreational boating trip (location, proximity to a wind farm, amount of nearby boating activity, main activity during trip, trip costs). Data were analyzed using the mixed logit model to understand how changes in individual attributes affect the acceptability of a boating trip. Findings indicate that the value of a recreational boating experience is considerably reduced in areas with offshore wind farms. Findings from this study provide valuable insights into the potential impacts of the growing offshore wind industry on one group of marine resource users and potential management strategies for addressing these impacts in the US.

Inconspicuous, recovering, or northward shift: status and management of the white shark (Carcharodon carcharias) in Atlantic Canada

Although white sharks (Carcharodon carcharias) have been considered rare in Atlantic Canada waters, recent sighting records indicate a potentially increasing presence. We combine historical to present sighting data with satellite telemetry tracks of large juvenile and adult white sharks tagged in US (n = 9) and Atlantic Canada waters (n = 17) to show seasonal white shark presence and distribution in Atlantic Canada, returns by individuals over multiple years, and high site fidelity to the region. Telemetry data indicate that white sharks are a more common and consistent occurrence in Canadian waters than previously thought, presenting two potential scenarios: (i) tagging technology is revealing white shark presence that was historically cryptic and (or) (ii) a northward range expansion of white sharks in the Northwest Atlantic, potentially due to climate change, population recovery, and (or) increasing pinniped prey. Given combined sighting and telemetry data indicate a current need for proactive management of white sharks in Atlantic Canada waters, we propose the basis for a management action plan, addressing conservation priorities, management goals, and research incentives while considering the potential for human–shark interactions.

The Complexity of Spills: The Fate of the Deepwater Horizon Oil.

The Deepwater Horizon oil spill was the largest, longest-lasting, and deepest oil accident to date in US waters. As oil and natural gas jetted from release points at 1,500-m depth in the northern Gulf of Mexico, entrainment of the surrounding ocean water into a buoyant plume, rich in soluble hydrocarbons and dispersed microdroplets of oil, created a deep (1,000-m) intrusion layer. Larger droplets of liquid oil rose to the surface, forming a slick of mostly insoluble, hydrocarbon-type compounds. A variety of physical, chemical, and biological mechanisms helped to transform, remove, and redisperse the oil and gas that was released. Biodegradation removed up to 60% of the oil in the intrusion layer but was less efficient in the surface slick, due to nutrient limitation. Photochemical processes altered up to 50% (by mass) of the floating oil. The surface oil expression changed daily due to wind and currents, whereas the intrusion layer flowed southwestward. A portion of the weathered surface oil stranded along shorelines. Oil from both surface and intrusion layers were deposited onto the seafloor via sinking marine oil snow. The biodegradation rates of stranded or sedimented oil were low, with resuspension and redistribution transiently increasing biodegradation. The subsequent research efforts increased our understanding of the fate of spilled oil immensely, with novel insights focusing on the importance of photooxidation, the microbial communities driving biodegradation, and the formation of marine oil snow that transports oil to the seafloor.

Urban manta rays: potential manta ray nursery habitat along a highly developed Florida coastline

The giant oceanic manta rayMobula birostriswas listed in the US Endangered Species Act as a threatened species in 2018, yet insufficient data exist on manta populations throughout US waters to designate critical habitat. Taxonomic and genetic evidence suggests that manta rays in the Western Atlantic are a separate species (M.cf.birostris) and little is understood about the ecology and life history of this putative species. The juvenile life stage of bothM. birostrisandM.cf.birostrisis particularly understudied. Here, we are the first to describe the characteristics of a manta ray population along a highly developed coastline in southeastern Florida using boat-based surveys and photo identification of individuals. Fifty-nine manta individuals were identified between 2016 and 2019. All males were sexually immature based on clasper development, and 96% of females were classified as immature based on size and absence of mating scars or visible pregnancies. Twenty-five (42%) individuals were observed more than once during the study period and 8 individuals were sighted over multiple years. The occurrence of juveniles, high site fidelity and extended use of the study area by juvenile manta rays suggest that southeastern Florida may serve as a nursery habitat. High occurrence of fishing line entanglement (27% of individuals) and vessel strike injury were documented, and rapid wound healing was observed. Future research and conservation efforts will focus on identifying the physical and biological features of the potential nursery habitat and on mitigation of anthropogenic impacts.

A 50-year conundrum is conclusively solved: nudibranchs Dendronotus albus (= D. diversicolor) and Dendronotus robilliardi are valid species with compelling evidence from type materials, bibliographic sources, and molecular data

A persistent confusion in the identification of two similar species of nudibranch molluscs of the genus Dendronotus Alder and Hancock, 1845, which inhabit shallow Canadian, Russian, and US waters of the northern Pacific Ocean, has caused a considerable taxonomic conundrum for over 50 years. In this study, we present compelling evidence for the first time, including morphological and molecular data as well as a study of type materials, to definitively conclude that Dendronotus albus MacFarland, 1966 was misidentified in the publication of G.A. Robilliard (1970; Veliger, 12: 433–479). This caused the long-term incorrect application of the characters of the real D. albus sensu F.M. MacFarland (1966; Mem. Calif. Acad. Sci. 6: 1–546) (which is still circulated in the literature) to a completely different, though externally similar, species incorrectly named “D. albus” in G.A. Robilliard (1970; Veliger, 12: 433–479). This species was properly described only 3 years ago as Dendronotus robilliardi Korshunova, Sanamyan, Zimina, Fletcher and Martynov, 2016. Using multiple evidence in this study, we firmly conclude that D. robilliardi is a well-supported valid species, whereas “Dendronotus diversicolor” Robilliard, 1970 is a junior synonym of D. albus. We also present rare bibliographic materials that shed light on the source of the misidentification of these species and also confirm the designation of the lectotype for D. albus. Biogeographical data, which are important for conservation and ecological studies, are also presented for D. albus and D. robilliardi in the Canadian and American Pacific Ocean.

Effect of wind directionality on fatigue life of monopile support structures for offshore wind turbines

The U.S. offshore wind industry can expect higher costs due to the lack of domestic experience with offshore wind technology. A key factor of the capital expenditure related to offshore wind farms is the cost of the support structures of offshore wind turbines. Therefore, improvements to the reliability of support structures under ultimate and fatigue loading conditions will help reduce the levelized cost of energy of offshore wind. This study presents a framework that accounts for the wind directionality by assuming a distinct and independent wind speed distribution per each wind direction and investigates its effect on the fatigue life of offshore wind turbine support structures. A monopile support structure in a potential wind site close to a National Oceanic and Atmospheric Administration buoy in the north-eastern US waters is used in this study. Fatigue damage assessment is performed for the normal operational condition of wind turbine, and the results are presented considering both cathodic protection and free corrosion conditions at the mudline level of the monopile. The location and extent of the predicted fatigue damages are found to vary due to accounting for the wind directionality.

Northwest Atlantic mackerel population structure evaluated using otolith δ18O composition

Abstract The Northwest Atlantic mackerel (Scomber scombrus) population is comprised of northern and southern contingents, each with distinct natal regions in the United States and Canada. We tested hypotheses on natal origin and contingent mixing by analysing natal otolith δ18O values, evaluating the approach through an out-group comparison with the Northeast Atlantic population. Otolith δ18O values varied according to expectations between the Northeast (higher) and the Northwest (lower) Atlantic basins, and between contingents within the Northwest Atlantic stock, although contingent differences varied between years. Most adults (age-3+ years) sampled from US waters (1999–2003) represented the northern contingent (Canadian spawning site). The confirmation of the seasonal mixing of older and larger fish between the two contingents provides support and justification for the development of bi-national (United States–Canada) assessment and management of Northwest Atlantic mackerel.