Morus Bassanus Research Articles

Hide and seek in the Bay of Biscay—a functional investigation of marine megafauna and small pelagic fish interactions

AbstractPrey and predator distributions influence one another. Understanding the scale and the orientation of predator–prey spatial correlations is crucial in foraging ecology. Growing evidence suggests that predator–prey interactions are more constrained by functional characteristics of both the predator and the prey. Unfortunately, in marine pelagic systems, the scale and orientation of spatial correlations between predators and prey have been only little explored from a functional point of view. We tested the existence of fine-scale association between predators and fish functional groups. Visual predator sightings and acoustic fish records were collected synchronously during oceanographic surveys from 2004 to 2014. Prey biomass was integrated by nautical miles and split into four size classes (<10 cm; 10–20 cm; 20–30 cm; >30 cm) and two depth layers (surface, deep). We computed the relative biomass by prey size and depth category from 0 to 12 nm around predator sightings to determine the predators’ proximity to local prey biomass. Two cetaceans (common, bottlenose dolphins) and three seabirds (northern gannets, auks, northern fulmars) were studied. No association was found in fulmars, indicating they probably do not feed on considered fishes in the area. Gannets and auks were positively correlated with local prey biomass for sizes <20 cm at both depth layers. Significant negative relationships were found between common dolphins and prey size classes <20 cm at both depth layers, and between bottlenose dolphins and all size ranges at the deeper layer. Our results suggest that the fine-scale spatial overlap of predator and prey is influenced by their functional traits, and that prey exhibit predator avoidance behaviour in presence of swimming predators but not of flying ones.

Frequency and consequences of individual dietary specialisation in a wide-ranging marine predator, the northern gannet

Individual specialisations in animals are important contributors to a wide range of ecological and evolutionary processes, and have been particularly documented in relation to multiple aspects of foraging behaviours. Central-place foragers, such as seabirds, frequently exhibit pronounced specialisations and individual differences in a variety of foraging traits. In particular, the availability of fisheries discards alongside natural prey resources provides additional potential for differentiation and specialisation for opportunistically scavenging seabird species. However, the consequences of such specialisations for at-sea distributions and intraspecific interactions are not well known. Here, we investigated the links between the degree of dietary specialisation on natural or discarded prey and the foraging movements and spatial occupancy of northern gannets Morus bassanus in relation to differing intraspecific competition at 6 colonies of differing sizes. We found that, at most colonies, individuals with different dietary strategies concentrated foraging at differing levels of intraspecific competition. In addition, individuals pursuing different strategies were frequently, but not consistently, spatially separated, distinctions that were most acutely seen in females. However, this variation in individual strategy had no significant impact on current body condition. These analyses demonstrate how foraging-associated metrics need not covary within an unconstrained system. They also reveal that specialisation can have important consequences for the competitive regimes individuals experience, highlighting the complexity of examining interacting consequences at large spatial scales.

Nocturnal flight activity of northern gannets Morus bassanus and implications for modelling collision risk at offshore wind farms

Assessing the potential impacts of proposed offshore wind farm developments on seabird populations requires estimation of nocturnal flight activity of seabirds for input into collision risk models. One of the seabirds considered most at risk from collision with offshore wind turbines is the northern gannet Morus bassanus. The recommended correction for gannet nocturnal flight activity is currently a highly precautionary value. Here we use data from tracking studies to derive evidence-based correction factors for nocturnal flight activity of adult gannets during the breeding and nonbreeding seasons, and of immature gannets during the summer prospecting phase. Flight and diving activity of gannets was minimal during the night, astronomical and nautical twilight, for adults during the breeding season and nonbreeding season, and for immatures. Some flight activity occurred during the short period of civil twilight, but on average at about half the level seen during the day. Based on evidence from numerous tracking studies, we recommend that precautionary values of the nocturnal (sunset to sunrise) flight activity factor for estimating collision risk should be 8% of daytime flight activity during the breeding season and 3% of daytime flight activity during the nonbreeding season. Use of these evidence-based correction factors will improve the accuracy, and reduce the uncertainty of collision risk models, providing a more reliable assessment of the impacts of offshore wind farms on gannets.

Weather effect on widely distributed seabirds through migration flyways: a case study with the Northern Gannet Morus bassanus in the Bay of Biscay

ABSTRACTCapsule: Northern Gannet Morus bassanus counts obtained from a coastal monitoring network in northern Spain were highly determined by wind conditions.Aims: To determine how external factors including weather conditions affect seabird counts in a land-based seabird monitoring project (Red de observación de Aves y Mamíferos marinos, RAM project; Seabird & Marine Mammal Observation Network).Methods: Seabird counts were obtained from four study capes situated in the southeastern part of the Bay of Biscay in northern Spain. Counts were conducted on a monthly-basis for a period of 3 hours starting at dawn on each sampling day. Data used here were compiled over a 10-year period (2006–15).Results: Northern Gannet numbers were chiefly influenced by meteorological conditions at a local spatial scale. Northwesterly winds were found to positively influence gannet abundance, whereas high relative humidity caused a decrease in abundance. Moreover, gannets were more abundant during the non-breeding period as compared to breeding period.Conclusion: We recommend considering the effect of the wind and relative humidity on land-based seabird counts in the Bay of Biscay when handling data from the RAM protocol in order to avoid biases and misinterpretation of data. Since seabirds approach the coast during harsh weather conditions, the RAM protocol should be improved in order to better account for the distance at which the birds are seen.

Decadal stability in top predator habitat preferences in the Bay of Biscay

Most oceanographic systems, especially shelf ecosystems, are characterised by interannual variability in the timing, extent and intensity of their seasonal patterns. Such interannual variations have important consequences on top predator habitat preferences. Capitalising on oceanographic surveys performed every spring since 2004 in the Bay of Biscay (BoB), this study explored interannual variations in habitat preferences exhibited by five mobile top predator species: bottlenose and common dolphins, auks, fulmars and northern gannets. We expected to find species with similar habitat preferences every year or species exhibiting important variability in their habitat preferences. First, we identified with a Principal Component Analysis (PCA) three different habitats of varying extent depending on year: river plumes, central shelf waters and shelf edge. Second, the Principal Components were used to explore the habitat preferences of predators through Generalized Additive Models. We fitted two kinds of models, using and not using the year as an interaction term, to test whether habitat preferences changed across years. Our results showed a range of habitat strategies based on the specificity and stability of species preferences. Species exhibiting narrower habitat preferences also exhibited stronger stability in their preferences among years while the species with wider habitat preferences exhibited higher variability among years. The target habitats differed across studied species, with bottlenose dolphins targeting the shelf edge exclusively, auks preferring river plumes, fulmars exhibiting a gradual preference from the shelf edge to river plumes and gannets being present in any of the three habitats. In contrast, the habitat preferences of common dolphins, the most sighted cetacean species in the BoB, could not be reliably inferred.

Adult Gannet migrations frequently loop clockwise around Britain and Ireland

ABSTRACTThe Gannet Morus bassanus is one of the seabirds considered most at risk from collision mortality at offshore wind farms in UK waters, so a better understanding of migration routes informs assessments of risk for different populations. Deployment of geolocators on breeding adults at the Bass Rock, Scotland, and Skrúður, Iceland, showed that the timing of migrations differed between populations, birds from Bass Rock passing south through UK waters mostly in October and back in February while birds from Skrúður passed south through UK waters mostly later, in November, but returned north earlier, in January. Many birds from both colonies made a clockwise loop migration around Britain and Ireland. Only a minority of birds from the Bass Rock returned northwards to the colony through the southern North Sea. A counter-intuitive consequence is that many Gannets moving northwards through waters to the west of Britain and Ireland in spring may be birds from North Sea colonies. Although Gannets normally remain over the sea, one tracked bird appears to have made a short overland passage in spring from the west of Scotland through central Scotland to the Bass Rock, whereas most returned around the north of Scotland.

Rare birds in Slovenia in 2016 – Slovenian Rarities Committee Report

Summary This report by the Slovenian Rarities Committee presents records of rare bird species in Slovenia in 2016, with some addenda for previous years. The numbers in brackets refer to the number of records (first number) and individuals (second number) recorded between 1 Jan 1950 and 31 Dec 2015. Since 1 Jan 2013, submission to the Committee has been required for 37 additional species, 17 of which are regional rarities. Records of these species are not numbered, since records from previous years were not collected by the Committee. Two new species, Scopoli’s Shearwater Calonectris diomedea and Arctic Tern Sterna paradisaea, were added to Category A. Other notable observations were the second record of Lesser Yellowlegs Tringa flavipes, third and fourth records of Pallid Swift Apus pallidus, fifth to seventh records of Long-legged Buzzard Buteo rufinus and the sixth and seventh records of Gannet Morus bassanus. Twelve records of Pallid Harrier Circus macrourus are an all-time annual high. Among Category E species, the Hooded Merganser Lophodytes cucullatus was recorded for the second time. The list of birds recorded in Slovenia (as of 31 Dec 2016) contains 388 species (373 in Category A, 6 in Category B, 9 exclusively in Category C; 4 species are both in Categories A and C). Category D contains 6 species, while Category E contains 38, two of which are classified into Subcategory E*. These two categories are not part of the list.

Search and foraging behaviors from movement data: A comparison of methods.

Search behavior is often used as a proxy for foraging effort within studies of animal movement, despite it being only one part of the foraging process, which also includes prey capture. While methods for validating prey capture exist, many studies rely solely on behavioral annotation of animal movement data to identify search and infer prey capture attempts. However, the degree to which search correlates with prey capture is largely untested. This study applied seven behavioral annotation methods to identify search behavior from GPS tracks of northern gannets (Morus bassanus), and compared outputs to the occurrence of dives recorded by simultaneously deployed time–depth recorders. We tested how behavioral annotation methods vary in their ability to identify search behavior leading to dive events. There was considerable variation in the number of dives occurring within search areas across methods. Hidden Markov models proved to be the most successful, with 81% of all dives occurring within areas identified as search. k‐Means clustering and first passage time had the highest rates of dives occurring outside identified search behavior. First passage time and hidden Markov models had the lowest rates of false positives, identifying fewer search areas with no dives. All behavioral annotation methods had advantages and drawbacks in terms of the complexity of analysis and ability to reflect prey capture events while minimizing the number of false positives and false negatives. We used these results, with consideration of analytical difficulty, to provide advice on the most appropriate methods for use where prey capture behavior is not available. This study highlights a need to critically assess and carefully choose a behavioral annotation method suitable for the research question being addressed, or resulting species management frameworks established.

Predicting the impacts of wind farms on seabirds: An individual‐based model

Abstract Individual‐based models (IBMs) are a powerful tool in predicting the consequences of environmental change on animal populations and supporting evidence‐based decision making for conservation planning. There are increasing proposals for wind farms in UK waters and seabirds are a vulnerable group, which may be at risk from these developments. We developed a spatially explicit IBM to investigate the potential impacts of the installation of wind farms in the English Channel and North Sea on body mass, productivity and mortality of a breeding population of Northern gannets for which we have tracking data. A baseline model with no wind farms accurately represented the status of a sample of tracked gannets at the end of the 90‐day chick‐rearing period, and the behaviour‐time budget was similar to that of tracked gannets. Model simulations in the presence of wind farms indicated that installations should have little impact on the gannet population, when either avoidance behaviour or collision risk scenarios were simulated. Furthermore, wind farms would need to be ten times larger or in more highly used areas in order to have population‐level impacts on Alderney's gannets. Synthesis and applications. Our spatially explicit individual‐based models (IBM) highlight that it is vital to know the colony‐specific foraging grounds of seabirds that may be impacted, when identifying potential wind farm sites, in order to account for cumulative impacts from multiple sites. Avoiding areas highly used for foraging and commuting, and avoiding large‐scale developments should be effective in limiting gannet mortality as a result of collision, competition and energy expenditure. Our IBM provides a robust approach which can be adapted for other seabird populations or to predict the impacts from other types of spatial change in the marine environment.

Bayesian joint models with INLA exploring marine mobile predator-prey and competitor species habitat overlap.

Understanding spatial physical habitat selection driven by competition and/or predator–prey interactions of mobile marine species is a fundamental goal of spatial ecology. However, spatial counts or density data for highly mobile animals often (1) include excess zeros, (2) have spatial correlation, and (3) have highly nonlinear relationships with physical habitat variables, which results in the need for complex joint spatial models. In this paper, we test the use of Bayesian hierarchical hurdle and zero‐inflated joint models with integrated nested Laplace approximation (INLA), to fit complex joint models to spatial patterns of eight mobile marine species (grey seal, harbor seal, harbor porpoise, common guillemot, black‐legged kittiwake, northern gannet, herring, and sandeels). For each joint model, we specified nonlinear smoothed effect of physical habitat covariates and selected either competing species or predator–prey interactions. Out of a range of six ecologically important physical and biologic variables that are predicted to change with climate change and large‐scale energy extraction, we identified the most important habitat variables for each species and present the relationships between these bio/physical variables and species distributions. In particular, we found that net primary production played a significant role in determining habitat preferences of all the selected mobile marine species. We have shown that the INLA method is well‐suited for modeling spatially correlated data with excessive zeros and is an efficient approach to fit complex joint spatial models with nonlinear effects of covariates. Our approach has demonstrated its ability to define joint habitat selection for both competing and prey–predator species that can be relevant to numerous issues in the management and conservation of mobile marine species.

Seabirds as samplers of the marine environment – a case study of northern gannets

Abstract. Understanding distribution patterns, activities, and foraging behaviours of seabirds requires interdisciplinary approaches. In this paper, we provide examples of the data and analytical procedures from a new study in the German Bight (North Sea) tracking northern gannets (Morus bassanus) at their breeding colony on the island of Heligoland. Individual adult northern gannets were equipped with different types of data loggers for several weeks, measuring geographic positions and other parameters mostly at 3–5 min intervals. Birds flew in all directions from the island to search for food, but most flights targeted areas to the (N)NW (north–northwest) of Heligoland. Foraging trips were remarkably variable in duration and distance; most trips lasted 1–15 h and extended from 3 to 80 km from the breeding colony on Heligoland. Dives of gannets were generally shallow, with more than half of the dives only reaching depths of 1–3 m. The maximum dive depth was 11.4 m. Gannets showed a clear diurnal rhythm in their diving activity, with dives being almost completely restricted to the daylight period. Most flight activity at sea occurred at an altitude between the sea surface and 40 m. Gannets mostly stayed away from the wind farms and passed around them much more frequently than flying through them. Detailed information on individual animals may provide important insights into processes that are not detectable at a community level.

Feather corticosterone during non-breeding correlates with multiple measures of physiology during subsequent breeding in a migratory seabird

Carry-over effects in migratory birds are likely mediated by physiological processes that are activated in response to environmental variation. Such processes affect body condition and/or reproductive success, and can include corticosterone (CORT) because this hormone responds to environmental stressors and influences energy balance. Few studies have considered how CORT levels during non-breeding relate to a broader physiological profile during subsequent breeding, and fewer still have considered measures other than body condition. To explore CORT's potential role in carry-over effects, we investigated the relationship between CORT and foraging ecology of northern gannets (Morus bassanus) during the non-breeding period, and tested for associations between these factors and variation in a suite of physiological and biochemical metrics during subsequent breeding. Northern gannets are the largest seabird top predator in the North Atlantic and were among the hardest hit by the Deepwater Horizon oil blowout in the Gulf of Mexico in 2010. We used light-level geolocators to confirm winter origins of individuals in our study. No interrelationships were found among levels of CORT from feathers grown during non-breeding (CORTf) and variation in foraging ecology, measured by stable isotopes of carbon (δ13C) and nitrogen (δ15N) from the same feathers. CORTf was correlated negatively with hematocrit and positively with triglyceride measured during subsequent incubation, and explained more variation in these variables than did body mass during incubation. These findings provide support for the hypothesis that energy management, measured using CORTf, during non-breeding carries over to influence physiological measures other than body condition. Gannets that previously wintered within the Gulf of Mexico in the years following the Deepwater Horizon oil blowout had higher levels of CORTf compared to birds that wintered along the Atlantic coast, suggesting an increased energetic cost associated with visiting the Gulf of Mexico. Our results indicate that CORT during non-breeding is associated with a broader physiological profile during subsequent breeding than previously reported in birds.

The late-Holocene avifaunal assemblage from the island of Palagruža (Croatia): The earliest record of the Northern Gannet in the Adriatic Sea

The late-Holocene bird remains retrieved during archaeological excavations on pelagic island of Palagruža, Croatia, were analysed. The results of the analysis revealed presence of representatives of nine families: Procellariidae, Sulidae, Ardeidae, Accipitridae, Phasianidae, Rallidae, Laridae, Strigidae and Corvidae. Among the bird remains, the most numerous were remains of the Northern Gannet, Morus bassanus, which were widely distributed in the Mediterranean during the late Pleistocene. The finding of the Northern Gannet bones on Palagruža represents the first fossil record of this species in the Adriatic Sea and indicates a possible breeding site on the island. The direct Accelerator Mass Spectrometry (AMS) radiocarbon dating on two gannet bones revealed the age of 2878 ± 34 and 2694 ± 45 yr BP. Gannet bones from Palagruža were some 6000 years younger than other fossil records of that species from the Mediterranean. It is possible that during the gannet’s northward distributional shift, probably caused by centennial climatic variability and human pressure, gannet colony on that remote island in the Adriatic lasted longer than in the rest of the Mediterranean and existed until the late-Holocene. Lower sea-surface temperatures compared with the eastern Mediterranean, higher nutritive productivity and remoteness of Palagruža provided adequate breeding opportunities during that period.

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and flame retardants in northern gannet (Morus bassanus) eggs from Bonaventure Island, Gulf of St. Lawrence, 1994–2014

Northern gannet (Morus bassanus) eggs from Bonaventure Island, Québec, Canada, were collected to monitor concentrations of contaminants. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) and non-ortho polychlorinated biphenyls (PCBs) were measured in eggs from 2004 and 2009, and several brominated and nonbrominated flame retardants (FRs) were measured every 2–5 years in eggs from 1994 to 2014. The sum (Σ) concentrations of PCDDs/Fs were significantly lower in 2009 relative to 2004, but the total toxic equivalent concentrations for PCDDs, PCDFs, and PCBs showed no significant differences (196 ng/kg wet weight (ww) in 2004 and 220 ng/kg ww in 2009). The mean ΣFR concentrations decreased significantly between 1994 and 2014, from 58 ng/g ww to 19 ng/g ww. Hexabromocyclododecane (HBCDD) was the principal nonbrominated FR detected in gannet eggs and ranged from <1.0 ng/g ww to 6.9 ng/g ww. The PCDD/F and nonortho PCB profiles were dominated by 2,3,7,8- tetrachloro-dibenzofuran (2,3,7,8-TCDF; from 26.2 ng/g ww to 34.8 ng/kg ww) and PCB-77 (from 1580 ng/g ww to 2650 ng/kg ww), respectively. Although the values of both ecological tracer stable isotopes of carbon (δ13C) and nitrogen (δ15N) showed differences among the years, no temporal trends were observed, which indicates relatively stable adults' diet and foraging area over this time period. The trends over time in concentrations of the studied contaminants likely reflect a decrease in environmental contamination. The mean 2012 eggshell thickness was 10% lower than the pre-DDT value and corresponded to a year of poor reproductive success.

On the polar edge: the status of the northern gannet (Morus bassanus) in the Barents Sea in 2015-16

ABSTRACTDuring its population recovery in the North Atlantic in the early 1900s, the northern gannet (Morus bassanus) established its first colony in Norway at Runde in 1946. Since the 1960s, gannets have established (and later abandoned) several small colonies in the north of the country. These colonies have been regularly monitored, and in 2015–16 ca. 3300 apparently occupied nests (AON) were counted in seven colonies in northern Norway. Two colonies that existed in 2008 had been abandoned and four new ones established. Two of the latter were again abandoned before 2015. In 1995, one pair established a colony at Kharlov on the Kola Peninsula, Russia, where numbers increased to 200–250 AON in 2016. The newest and world’s northernmost colony was established at Bjornoya (Bear Island) in 2011, extending the species’ breeding range well into the Arctic. These recent establishments are thought to be associated with a warming of the Barents Sea and the northward spread of common prey of the gannet such as herr...

Diet of Northern Gannet &lt;i&gt;Morus bassanus&lt;/i&gt; chicks in North Norway

Northern Gannets Morus bassanus established colonies in North Norway in the 1960s, since when the breeding population has increased and spread north- and eastwards. Diet data collected at several colonies in North Norway confirm the Gannet’s opportunistic foraging behaviour with Atlantic herring Clupea harengus , Atlantic mackerel Scomber scombrus , sandeels Ammodytidae and saithe Pollachius virens being the main prey brought to chicks. As such, climate change is unlikely to have a negative effect on the Gannet population in the region.

A middle Pleistocene bird community from Saint Lucie County, Florida

Dickerson Coquina Pit (DCP) is a sand and coquina mine located in Saint Lucie County, Florida, 16 km inland from the Atlantic Ocean. Collections were made from a middle Pleistocene (late Irvingtonian Land Mammal Age) vertebrate fossil bed in the Okeechobee Formation at DCP from 2002 until the pit was flooded in 2008. Vertebrate fossils from DCP also were discovered in fill material used in beach replenishment on North Hutchinson Island, St. Lucie County. The avifauna of DCP is based on 65 fossil elements representing 12 orders, 16 families, and 26 species, with habitat preferences ranging from woodlands and prairies to fresh water and estuarine wetlands to the open ocean. Extinct or extralocal species include a transitional Wild Turkey Meleagris cf. M. gallopavo, transitional Short-tailed Albatross Phoebastria cf. P. albatrus, a large stork Ciconia maltha, a large crane Grus sp., Great Auk Pinguinus impennis, and Carolina Parakeet Conuropsis carolinensis. The taphonomy and paleoecology of the Dickerson Coquina Pit generally resemble those of other shell beds in Central and South Florida, such as the Irvingtonian Leisey Shell Pit of Hillsborough County. The avifauna from DCP is distinctive, however, in featuring Florida’s first Pleistocene records of four marine species (Short-tailed Albatross, Northern Gannet Morus bassanus, Great Cormorant Phalacrocorax carbo, and Great Auk) and the Carolina Parakeet.

Possible impacts of offshore wind farms on seabirds: a pilot study in Northern Gannets in the southern North Sea

We studied the impact of offshore wind farms on the distribution of Northern Gannets in the southern North Sea. Distributions were derived from ship-based and aerial-transect counts, and from global positioning system (GPS) tracking of chick-rearing adults from the colony on Helgoland. Foraging trips of tagged Gannets lasted from 0.4 to 53.5 h, with a total distance flown per trip of 4.7–937.9 km, and range of 2.0–320.8 km. Gannets largely avoided the wind farm area north of Helgoland. This avoidance behaviour implies that, although Northern Gannets may not be killed by rotor blades, they may experience substantial habitat loss. GPS tracking is well suited to the study of wind farm effects on birds and possible habituation processes at the individual level.

Seabird diving behaviour reveals the functional significance of shelf-sea fronts as foraging hotspots.

Oceanic fronts are key habitats for a diverse range of marine predators, yet how they influence fine-scale foraging behaviour is poorly understood. Here, we investigated the dive behaviour of northern gannets Morus bassanus in relation to shelf-sea fronts. We GPS (global positioning system) tracked 53 breeding birds and examined the relationship between 1901 foraging dives (from time-depth recorders) and thermal fronts (identified via Earth Observation composite front mapping) in the Celtic Sea, Northeast Atlantic. We (i) used a habitat-use availability analysis to determine whether gannets preferentially dived at fronts, and (ii) compared dive characteristics in relation to fronts to investigate the functional significance of these oceanographic features. We found that relationships between gannet dive probabilities and fronts varied by frontal metric and sex. While both sexes were more likely to dive in the presence of seasonally persistent fronts, links to more ephemeral features were less clear. Here, males were positively correlated with distance to front and cross-front gradient strength, with the reverse for females. Both sexes performed two dive strategies: shallow V-shaped plunge dives with little or no active swim phase (92% of dives) and deeper U-shaped dives with an active pursuit phase of at least 3 s (8% of dives). When foraging around fronts, gannets were half as likely to engage in U-shaped dives compared with V-shaped dives, independent of sex. Moreover, V-shaped dive durations were significantly shortened around fronts. These behavioural responses support the assertion that fronts are important foraging habitats for marine predators, and suggest a possible mechanistic link between the two in terms of dive behaviour. This research also emphasizes the importance of cross-disciplinary research when attempting to understand marine ecosystems.

Survival estimates of Northern Gannets Morus bassanus in Alderney: big data but low confidence

ABSTRACTCapsule: There has been a linear increase in the survival rates for both adult and juvenile Northern Gannets Morus bassanus breeding on Alderney in the English Channel. However, given large confidence intervals, improved monitoring is required to better evaluate threats to this population.Aims: To estimate the age-specific survival and reporting rate from an internationally important population of Northern Gannets M. bassanus breeding at one of the southernmost colonies for this species.Methods: We use 28 years of ringing and recovery data in order to estimate age-specific survival and reporting rates.Results: Adult and juvenile survival rates differ, and both survival and reporting rates are considerably lower in first-year birds than older birds. Additionally there is an increasing linear trend in survival rates over time, and a decreasing trend in reporting rates.Conclusion: Threats to Gannets from anthropogenic disturbance are likely to be age and population specific. While these rates point towards continued growth of this population, the confidence intervals around our estimates are large, highlighting the need for improved resighting efforts in long-term studies of this nature.