Generalizing the first-difference correlated random walk for marine animal movement data

Animal telemetry data are often analysed with discrete time movement models assuming rotation in the movement. These models are defined with equidistant distant time steps. However, telemetry data from marine animals are observed irregularly. To account for irregular data, a time-irregularised first-difference correlated random walk model with drift is introduced. The model generalizes the commonly used first-difference correlated random walk with regular time steps by allowing irregular time steps, including a drift term, and by allowing different autocorrelation in the two coordinates. The model is applied to data from a ringed seal collected through the Argos satellite system, and is compared to related movement models through simulations. Accounting for irregular data in the movement model results in accurate parameter estimates and reconstruction of movement paths. Measured by distance, the introduced model can provide more accurate movement paths than the regular time counterpart. Extracting accurate movement paths from uncertain telemetry data is important for evaluating space use patterns for marine animals, which in turn is crucial for management. Further, handling irregular data directly in the movement model allows efficient simultaneous analysis of several animals

Choosing the observational likelihood in state-space stock assessment models

Data used in stock assessment models result from combinations of biological, ecological, fishery, and sampling processes. Since different types of errors propagate through these processes it can be difficult to identify a particular family of distributions for modelling errors on observations a priori. By implementing several observational likelihoods, modelling both numbers- and proportions-at-age, in an age based state-space stock assessment model, we compare the model fit for each choice of likelihood along with the implications for spawning stock biomass and average fishing mortality. We propose using AIC intervals based on fitting the full observational model for comparing different observational likelihoods. Using data from four stocks, we show that the model fit is improved by modelling the correlation of observations within years. However, the best choice of observational likelihood differs for different stocks, and the choice is important for the short-term conclusions drawn from the assessment model; in particular, the choice can influence total allowable catch advise based on reference points.Comment: To be published in Canadian Journal of Fisheries and Aquatic Science

Elina Screen: Sylloge of Coins of the British Isles, vols. 65 & 66: Nor- wegian Collections, Part I: Anglo-Saxon Coins to 1016 & Part II: Anglo-Saxon and later British Coins 1016–1279.

These two substantial volumes publish an impressive 4230 coins struck at the British Isles prior to 1279 and kept in Norwegian Museums. They are volumes 65 and 66 in the Sylloge of Coins of the British Isles (SCBI). Since the publication of volume 1 in 1958 (Fitzwilliam Museum, Cambridge) this series has under the auspices of the British Academy made thousands of coins kept in public or private collections easily available and thus largely stimulated research into British coins

Defining a National Web Sphere over time from the Perspectives of Collection Technology and Scholarship

This paper describes a framework supporting definition of how to automatically identify national webpages outside a country’s top level domain. The framework aims at a definition that can be put into operation in order to make automatic detection of national web pages. At the same time the framework aims at a definition that can be reused independent of changed behaviours on the net, changes in jurisdiction and changes in technology. A crucial point in this framework is that the perspectives of collection, technology and Scholarship are present in decision making.The framework origins from a study that aimed at evaluation of different two different strategies for automatic identification of national webpages outside a country’s top level domain; one strategy was based on data from Internet Archives wide_005 world wide webcrawl, and the other was based on a local web crawl based on bulk harvests from the Danish national web archive, Netarkivet. However in both cases a definition of national webpages was needed. Thus the creation of the framework was a prerequisite for the rest of this study.Motivation of the study and framework is based on the fact that human communication activities are moving more and more onto the internet. This means that a lot of present and future research in the 20th century information flow depends on optimised collection and archiving of such information in web archives. Web archives often reside within national cultural heritage institutions, regularly having a collection scope outlined within some form of legal deposit legislation. The challenge to define “national webpages” showed out to be is far from trivial, and in creation of the framework it quickly became obvious that such a definition requires that three important perspectives in order to make qualified decisions. In this paper this definition is based on input from three important fields represented by each of the authors, representing the perspectives of scholarship, the Danish web Archive, and computer science. This represents the perspectives of collection, technology and scholarship, which are all very different but also crucial perspectives when formulating definition of national webpages that is basis for actual collection and thus consequently form a web archive. Besides the non-trivial need for formal, the study also found reason for arguing that it is necessary to repeatedly adjust web collection strategies within a web archive. The conditions for web collection is constantly changing. Even over a five year period we see: change in technology that can assist in collection, change in human behavior moving away from countries top levels domains and out on .com, .org etc., and changes in jurisdiction influencing the way that the web can be collected technology, thus regularly adjustments of what is national web pages may likely be needed. Therefore the presented framework consists of a list of general criteria as basis for adjustment of web collection strategies which can be made operational in a specific context taking into account the three perspectives.<br/