Causal studies in SEAPOP

SEAPOP’s monitoring data are needed to analyse which environmental variables cause observed population trends, and to make reliable predictions for the further development of the seabird populations. To understand why populations change over time, more data than just the variations in numbers are needed.

The whole life cycle is studied

Population counts are of course important, and they give good indications as to whether a population is increasing, declining, or stable, but they will seldom reveal which demographic mechanisms or environmental conditions are the driving forces behind these changes. To shed light on this, it is completely necessary to study the whole life cycle of the birds and measure the effect of environmental changes on vital life history traits. Important data for such analyses include the birds’ migrations outside the breeding season, as well as measures of the variation in their diet, breeding success, and survival. This encompasses the data that are collected at SEAPOP’s selected key sites.

The effect of climate

Climate-driven processes can have direct and indirect effects on the population dynamics of seabirds. Indirect effects often operate through the food chain, are complex and involve production and predation conditions at several trophic levels. Reduction in food availability is a sizable threat for many seabird populations and influences both survival and breeding success, e.g., by the timing of breeding not matching the occurrence and availability of the most important prey for the seabirds. Illustration: Tycho Anker-Nilssen

Climate is an important component in these analyses. Climate conditions have explained much of the variation in the seabirds’ breeding success and survival, and there are large concerns as to how the future climate changes will influence the seabird populations that Norway has an extra management responsibility for. Climate effects can be both direct and indirect. Persistent changes in weather conditions or higher frequencies of extreme weather can influence both adult survival and breeding success directly, while the indirect effects often operate through the climate’s effect on the quantity and availability of food.

The probability of extinction

An important tool in the quantification of future effects of environmental variation (including pollution) on population development is the use of prognostic models or viability models. These are mathematical models developed to predict future population developments over time, and are based on past trends and variations in population size and demography. The models calculate a probability distribution for possible trends in population size and thereby suggest how viable or vulnerable to extinction the populations will be in the future. This gives important indications as to which populations have the greatest need for special management measures, if such exist.


Below is a list with examples of the work conducted in SEAPOP, or in close collaboration with the programme; analyses have been conducted as to which environmental factors are important for variation in different life history traits and population trends. Follow the links to view the full publication list:

Dissemination of knowledge 2005-2014 (Norwegian only, PDF, 0.6 MB)

SEAPOP Prosjektkatalog 2005-2014 (Norwegian only, PDF, 0.4 MB)




Selected publications:

Barrett, R.T. 2007. Food web interactions in the southwestern Barents Sea: black-legged kittiwakes Rissa tridactyla respond negatively to an increase in herring Clupea harengus. Marine Ecology Progress Series 349: 269-276.

Barrett, R.T., Erikstad, K.E., Sandvik, H., Myksvoll, M., Jenni-Eiermann, S., Lyngbo-Kristensen, D., Moum, T., Reiertsen, T. and Vikebø, F. 2015. The stress hormone corticosterone in a marine top predator reflects short-term changes in food availability. Ecology and Evolution 5:1306-1317.

Bustnes, J.O., Anker-Nilssen, T., Erikstad, K.E., Lorentsen, S.-H. & Systad, G.H. 2013. Changes in the Norwegian breeding population of European shag correlate with forage fish and climate. Marine Ecology Progress Series 489: 235-244.

Bustnes, J.O., Erikstad, K. E., Hanssen, S.A., Tveraa, T., Folstad, I. & Skaare, J.U. 2006. Anti-parasite treatment removes negative effects of environmental pollutants on reproduction in an arctic seabird. Proceedings of the Royal Society London Series B 273: 3117-3122.

Cury, P.M., Boyd, I.L., Bonhommeau, S., Anker-Nilssen, T., Crawford, R.J.M., Furness, R.W., Mills, J.A., Murphy, E.J., Österblom, H., Paleczny, M., Piatt, P.F., Roux, J.-P., Shannon, L. & Sydeman, W.J. 2011. Global seabird response to forage fish depletion – one-third for the birds. Science 334: 1703-1706.

Descamps, S., Yoccoz, N., Gaillard, J.-M., Gilchrist, H.G., Erikstad, K.E., Hanssen, S.A., Cazelles, B., Forbes, M.R. & Bêty, J. 2010. Detecting population heterogeneity in effects of North Atlantic Oscillations on seabird body condition: get into the rhythm. Oikos 119: 1526-1536.

Descamps, S., Strøm, H. & Steen, H. 2013. Decline of an arctic top predator: synchrony in colony size fluctuations, risk of extinction and the subpolar gyre. Oecologia 173(4): 1271-1282.

Durant, J.M., Hjermann, D.Ø., Anker-Nilssen, T., Beaugrand, G., Mysterud, A., Pettorelli, N. & Stenseth, N.C. 2005. Timing and abundance as key mechanisms affecting trophic interactions in variable environments. Ecology Letters 8: 952-958.

Erikstad, K.E., Reiertsen, T.K., Barrett, R.T., Vikebø, F. & Sandvik, H. 2013. Seabird–fish interactions: the fall and rise of a common guillemot Uria aalge population. Marine Ecology Progress Series 475: 267-276.

Erikstad, K.E., Sandvik, H., Reiertsen, T.K., Bustnes, J.O. & Strøm, H. 2013. Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival. Proceedings of the Royal Society B 280: 2013.1483.

Fauchald, P. 2009. Spatial interaction between seabirds and prey: review and synthesis. Marine Ecology Progress Series 391: 139-151.

Fauchald, P. 2010. Predator-prey reversal: A possible mechanism for ecosystem hysteresis in the North Sea? Ecology 91: 2191-2197.

Frederiksen, M., Anker-Nilssen, T., Beaugrand, G. & Wanless, S. 2013. Climate, copepods and seabirds in the boreal Northeast Atlantic – current state and future outlook. Global Change Biology 19: 364-372.

Irons, D., Anker-Nilssen, T., Gaston, A.J., Byrd, G.V., Falk, K., Gilchrist, G., Hario, M., Hjernquist, M., Krasnov, Y.V., Mosbech, A., Olsen, B., Petersen, A., Reid, J., Robertson, G., Strøm, H. & Wohl, K.D. 2008. Fluctuations in circumpolar seabird populations linked to climate oscillations. Global Change Biology 14: 1455-1463.

Letcher, R.J., Bustnes, J.O., Dietz, R., Jenssen, B.M., Jørgensen, E.H., Sonne, C., Verreault, J., Vijayan, M.M. & Gabrielsen, G.W. 2010. Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish. Science of the Total Environment 408: 2995–3043.

Lorentsen, S.-H., Anker-Nilssen, T., Erikstad, K.E. & Røv, N. 2015. Forage fish abundance is a predictor of timing of breeding and hatching brood size in a coastal seabird. Marine Ecology Progress Series 519: 209-220.

Myksvoll, M.S., Erikstad, K.E., Barrett, R.T., Sandvik, H. & Vikebø, F. 2013. Climate-driven ichthyoplankton drift model predicts growth of top predator young. PLoS ONE 8(11).

Reiertsen, T.K., Erikstad, K.E., Barrett, R.T., Sandvik, H. & Yoccoz, N.G. 2012. Climate fluctuations and differential survival of bridled and non-bridled common guillemots (Uria aalge). Ecosphere 3(6): article 52.

Reiertsen, T.K., Erikstad, K.E., Anker-Nilssen, T., Barrett, R.T., Boulinier, T., Frederiksen, M., González-Solís, J., Grémillet, D., Johns, D., Moe, B., Ponchon, A., Skern-Mauritzen, M., Sandvik, H. & Yoccoz, N.G. 2014. Prey density in non-breeding areas affects adult survival of Black-legged Kittiwakes Rissa tridactyla. Marine Ecology Progress Series 509: 289-302.

Sandvik, H., Reiertsen, T.K., Erikstad, K.E., Anker-Nilssen, T., Barrett, R.T., Lorentsen, S.-H., Systad, G.H. & Myksvoll, M.S. 2014. The decline of Norwegian kittiwake populations: modelling the role of ocean warming. Climate Research 60: 91-102.

Sandvik, H., Erikstad, K.E., Barrett, R.T. & Yoccoz, N.G. 2005. The effect of climate on adult survival in five species of North Atlantic seabirds. Journal of Animal Ecology 74: 817-831.

Sandvik, H., Erikstad, K.E. & Sæther, B.E. 2012. Climate affects seabird population dynamics both via reproduction and adult survival. Marine Ecology Progress Series 454: 273-284.