Papers by Tycho Anker-Nilssen
Mitochondrial control region sequences for all Leach's storm-petrels used in our study (inclu... more Mitochondrial control region sequences for all Leach's storm-petrels used in our study (including from Hydrobates leucorhoa leucorhoa, H. l. chapmani, H. socorroensis, H. cheimomnestes, and outgroup sequences from H. castro)
In this first study of full-grown Black Guillemot Cepphus grylle diet in the Norwegian mainland, ... more In this first study of full-grown Black Guillemot Cepphus grylle diet in the Norwegian mainland, 62 of 63 birds caught incidentally in Lumpfish Cyclopterus lumpus gillnets in the north of the country in April-June 2012 and 2013 contained food remains in their stomachs. Fourteen prey taxa were identified and crustaceans were present in 90% of the stomachs containing food, with squat lobsters (sub-order Anamura) being most common (in 79%). Rock Gunnel Pholis gunnellus was present in 17 (27%) of the samples. The only other prey types found in more than 20% of the samples were sculpins (Cottoidei, probably Cottidae and Agonidae, in 13 samples = 21%) and remains of caridean shrimps (in 13 samples). There were no differences in the frequencies of taxa in the diets of immature and adult birds or between males and females.
ICES Journal of Marine Science
Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the contine... more Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (Phalacrocorax carbo sinensis) in the Baltic and North Sea increase, while local cod (Gadus morhua) stocks decline. In contrast, numbers of the Atlantic subspecies (Phalacrocorax carbo carbo), breeding along the Norwegian and Barents Seas, have been relatively stable. We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated the biomass of fish consumed annually by great cormorants in Norwegian waters. The birds’ consumption was compared with estimated fish stock sizes and fishery catches. Cod and saithe (Pollachius virens) dominated the diet in the Norwegian Sea and wrasses in the North Sea and Skagerrak. Estimated total fish consumption of cod and saithe by great cormorants was <1.7% of estimated fish stocks and <9% of that of human catches and therefore considered minor. ...
Ices Journal of Marine Science, Feb 11, 2021
Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the contine... more Piscivorous wildlife is often perceived as competitors by humans. Great cormorants of the continental subspecies (Phalacrocorax carbo sinensis) in the Baltic and North Sea increase, while local cod (Gadus morhua) stocks decline. In contrast, numbers of the Atlantic subspecies (Phalacrocorax carbo carbo), breeding along the Norwegian and Barents Seas, have been relatively stable. We investigated the diet of both great cormorant subspecies in breeding colonies along the Norwegian Coast from Lofoten to the Skagerrak and estimated the biomass of fish consumed annually by great cormorants in Norwegian waters. The birds' consumption was compared with estimated fish stock sizes and fishery catches. Cod and saithe (Pollachius virens) dominated the diet in the Norwegian Sea and wrasses in the North Sea and Skagerrak. Estimated total fish consumption of cod and saithe by great cormorants was <1.7% of estimated fish stocks and <9% of that of human catches and therefore considered minor. Cormorant consumption of wrasses amounted to 110% of human catches. The practice of using wrasses as cleaner fish in the salmon farming industry leads to a conflict with cormorants, and we urge for a better understanding and management of wrasse populations, taking ecosystem functioning and natural predation into account.
Journal of Applied Ecology
Bottom‐up control is an important regulator of marine mesopredators such as seabirds. The prevale... more Bottom‐up control is an important regulator of marine mesopredators such as seabirds. The prevalence of top‐down control on these species is however less well understood. In particular, how native predators affect seabird populations has rarely been quantified. Here, we investigate how an increase in white‐tailed eagles in northern Norway, a stronghold for the species, affected a local population of 25,000 pairs of black‐legged kittiwakes, a red‐listed seabird, during a 42‐year period ending with colony extinction. We use a natural experiment of two neighbouring colonies with/without eagle predation to disentangle the effects of eagles from local kittiwake foraging conditions (using size of young herring as a proxy). At the colony where eagle predation occurred, and in contrast to the eagle‐free colony, kittiwake breeding success and population size declined with increased eagle abundance, the latter more strongly under poor foraging conditions. Breeding success increased with impro...
Ardea
Two subspecies of the Great Cormorant breed in Norway; the continental Phalacrocorax carbo sinens... more Two subspecies of the Great Cormorant breed in Norway; the continental Phalacrocorax carbo sinensis in the south, along the Skagerrak coast, and the marine P. c. carbo from Central Norway and northwards. Here we review the existing information on population status and trends, breeding performance and diet of these two subspecies in Norway. The most recent national population estimates are approximately 2500 (in 2012) and 19,000 (in 2012−2014) breeding pairs of sinensis and carbo, respectively. The sinensis population established itself in 1996 in Rogaland at the southwestern tip of Norway, and in 1997 in Østfold close to the Swedish border, and increased for about ten years. Since then the numbers have stabilised. For carbo, the population increased from 21,000 pairs in the early 1980s to 27,000 in 1995, and then decreased to the current number of 19,000 pairs. Significant annual variations in clutch size and reproductive output have been observed, but the drivers of these changes have not been identified. Unidentified gadoids and Atlantic Cod Gadus morhua were the most common prey of carbo, whereas inshore species such as Corkwing Wrasse Symphodus melops, Rockcook Centrolabrus exoletus, Goldsinny Wrasse Ctenolabrus rupestris and Black Goby Gobius niger were the most common caught in the eastern Skagerrak by sinensis. Carbo take very large numbers of 1-3 yr old gadoids during the year, and we cannot exclude the possibility this can have local effects on fish mortality rates.
Marine Biology
The intensification of coastal development poses potential threats for coastal seabirds, and unde... more The intensification of coastal development poses potential threats for coastal seabirds, and understanding their habitat use is a key factor to guide conservation and management. In sub-arctic areas, black guillemots (Cepphus grylle) use coastal habitats year-round, which makes them vulnerable to the increasing human activities in these areas. In mainland Norway, one of the species’ strongholds, black guillemots are red-listed after substantial population declines. However, their fine-scale foraging behaviour has received little attention to date. We collected and analysed GPS tracking data from adult black guillemots at three sites located over a latitudinal gradient of 250 km in central/northern Norway. Maximum foraging ranges of 33 km at Sklinna (65°12′N) for incubating birds, and 18 km at both Vega (65°34′N) and Sklinna for chick-rearing birds, are among the longest reported for this species. At all three sites, foraging probability was highest in shallow waters (< 50 m depth...
Marine Biology, May 25, 2023
The intensification of coastal development poses potential threats for coastal seabirds, and unde... more The intensification of coastal development poses potential threats for coastal seabirds, and understanding their habitat use is a key factor to guide conservation and management. In sub-arctic areas, black guillemots (Cepphus grylle) use coastal habitats year-round, which makes them vulnerable to the increasing human activities in these areas. In mainland Norway, one of the species' strongholds, black guillemots are red-listed after substantial population declines. However, their finescale foraging behaviour has received little attention to date. We collected and analysed GPS tracking data from adult black guillemots at three sites located over a latitudinal gradient of 250 km in central/northern Norway. Maximum foraging ranges of 33 km at Sklinna (65°12′N) for incubating birds, and 18 km at both Vega (65°34′N) and Sklinna for chick-rearing birds, are among the longest reported for this species. At all three sites, foraging probability was highest in shallow waters (< 50 m depth) close to the colony and declined with increasing water depth and distance from colony. However, birds from Vega also foraged over deeper waters. Kelp presence was of high importance at Sklinna, but apparently less important at Røst (67°26'N) and Vega. We also found distinct differences in foraging activity across the day and with tidal height among the sites. Inter-site differences in habitat use and foraging activity may be explained by differences in the availability of habitats and suitable prey. Our study highlights the importance of shallow marine areas for black guillemots and shows that habitat use can vary substantially between sites.
Ardea, Jul 1, 2022
Two subspecies of the Great Cormorant breed in Norway; the continental Phalacrocorax carbo sinens... more Two subspecies of the Great Cormorant breed in Norway; the continental Phalacrocorax carbo sinensis in the south, along the Skagerrak coast, and the marine P. c. carbo from Central Norway and northwards. Here we review the existing information on population status and trends, breeding performance and diet of these two subspecies in Norway. The most recent national population estimates are approximately 2500 (in 2012) and 19,000 (in 2012−2014) breeding pairs of sinensis and carbo, respectively. The sinensis population established itself in 1996 in Rogaland at the southwestern tip of Norway, and in 1997 in Østfold close to the Swedish border, and increased for about ten years. Since then the numbers have stabilised. For carbo, the population increased from 21,000 pairs in the early 1980s to 27,000 in 1995, and then decreased to the current number of 19,000 pairs. Significant annual variations in clutch size and reproductive output have been observed, but the drivers of these changes have not been identified. Unidentified gadoids and Atlantic Cod Gadus morhua were the most common prey of carbo, whereas inshore species such as Corkwing Wrasse Symphodus melops, Rockcook Centrolabrus exoletus, Goldsinny Wrasse Ctenolabrus rupestris and Black Goby Gobius niger were the most common caught in the eastern Skagerrak by sinensis. Carbo take very large numbers of 1-3 yr old gadoids during the year, and we cannot exclude the possibility this can have local effects on fish mortality rates.
Frontiers in Marine Science
Human activity in the coastal zone is increasing worldwide, putting a number of seabird species u... more Human activity in the coastal zone is increasing worldwide, putting a number of seabird species under pressure. Norway is no exception to this development, and with > 35% of the NE Atlantic population of the currently declining European shag (Gulosus aristotelis) population, Norway has an international responsibility for the conservation of this species, and its important foraging habitats during breeding. We analysed tracking data from shags breeding in five colonies along the Norwegian coast spread over a latitudinal gradient of > 1700 km. We identified foraging locations and associated environmental characteristics. Using model cross-validation, we assessed the transferability of habitat models, both spatially (across colonies) and temporally (within colonies and across years), based on three modelling approaches: Training datasets consisted either of the data from one year at one colony, all years at one colony, or all years from all colonies except the testing colony. Acr...
Journal of Animal Ecology
Seabird Journal
An abnormal movement of auks occurred in the eastern Skagerrak in the third week of September 200... more An abnormal movement of auks occurred in the eastern Skagerrak in the third week of September 2007. Large numbers of Razorbills Alca torda were reported along the coasts of southeast Norway and western Sweden, many thousands entered Oslofjorden (Norway), and their migration past the northern tip of Denmark into the Kattegat began a month earlier than normal. This preceded heavy mortality of the species that lasted several weeks, and numbered thousands of individuals. Unusually for the time of year, Razorbills greatly outnumbered Common Guillemots Uria aalge in reports of live and dead birds. Of 376 Razorbills collected in Oslofjorden, 87% were adults, 9% immatures, and 4% juveniles. Among 326 adults, females (71%) outnumbered males, and 18% showed two white inner bill grooves instead of the normal one. All birds were extremely emaciated and had presumably starved to death. Virtually all adults and older immatures were still regrowing their outer primaries after the post-breeding mou...
... Contributors Tycho Anker-Nilssen Maria de Fátima Borges Keith Brander Daniel Duplisea M... more ... Contributors Tycho Anker-Nilssen Maria de Fátima Borges Keith Brander Daniel Duplisea Morten Frederiksen Alejandro Gallego Astthor Gislason Ralf ... 3). The two longest instrumentally recorded time-series of temperature data in the Northeast Atlantic (Kola section and ...
Marine Ecology Progress Series, 2021
Migratory seabirds are exposed to various pollutants throughout their annual cycle. Among them, m... more Migratory seabirds are exposed to various pollutants throughout their annual cycle. Among them, mercury (Hg) is of particular concern given its large impact on animal health. Recent studies suggest that winter is a critical period for seabirds when contamination by Hg can be higher than at other times of year. However, individuals within and between species can have different migration strategies and winter distributions that could affect their exposure. Here, we combined multi-year individual tracking data and Hg measurements from 6 Arctic seabird species. We investigated whether inter-annual variations in individual winter contamination with Hg was related to seabird fidelity to a wintering site over years. First, our results show that Hg concentrations above the toxicity threshold (i.e. 5 µg g-1dry weight in feathers) were observed in variable proportions according to species (from 2% of northern fulmars to 37% of Brünnich’s guillemots). Second, individuals with high fidelity to ...
Fisheries Research, 2017
Worldwide, in recent years capture fisheries targeting lower-trophic level forage fish and euphau... more Worldwide, in recent years capture fisheries targeting lower-trophic level forage fish and euphausiid crustaceans have been substantial (∼20 million metric tons [MT] annually). Landings of forage species are projected to increase in the future, and this harvest may affect marine ecosystems and predator-prey interactions by removal or redistribution of biomass central to pelagic food webs. In particular, fisheries targeting forage fish and euphausiids may be in competition with seabirds, likely the most sensitive of marine vertebrates given limitations in their foraging abilities (ambit and gape size) and high metabolic rate, for food resources. Lately, apparent competition between fisheries and seabirds has led to numerous high-profile conflicts over interpretations, as well as the approaches that could and should be used to assess the magnitude and consequences of fisheriesseabird resource competition. In this paper, we review the methods used to date to study fisheries competition with seabirds, and present "best practices" for future resource competition assessments. Documenting current fisheries competition with seabirds generally involves addressing two major issues: 1) are fisheries causing localized prey depletion that is sufficient to affect the birds? (i.e., are fisheries limiting food resources?), and 2) how are fisheries-induced changes to forage stocks affecting seabird populations given the associated functional or numerical response relationships? Previous studies have been hampered by mismatches in the scale of fisheries, fish, and seabird data, and a lack of causal understanding due to confounding by climatic and other
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Papers by Tycho Anker-Nilssen