Report of the NAMMCO-ICES Workshop on Seal Modelling (WKSEALS 2020)

To support sustainable management of apex predator populations, it is important to estimate population size and understand the drivers of population trends to anticipate the consequences of human decisions. Robust population models are needed, which must be based on realistic biological principles and validated with the best available data. A team of international experts reviewed age-structured models of North Atlantic pinniped populations, including Grey seal (Halichoerus grypus), Harp seal (Pagophilus groenlandicus), and Hooded seal (Cystophora cristata). Statistical methods used to fit such models to data were compared and contrasted. Differences in biological assumptions and model equations were driven by the data available from separate studies, including observation methodology and pre-processing. Counts of pups during the breeding season were used in all models, with additional counts of adults and juveniles available in some. The regularity and frequency of data collection, including survey counts and vital rate estimates, varied. Important differences between the models concerned the nature and causes of variation in vital rates (age-dependent survival and fecundity). Parameterisation of age at maturity was detailed and time-dependent in some models and simplified in others. Methods for estimation of model parameters were reviewed and compared. They included Bayesian and maximum likelihood (ML) approaches, implemented via bespoke coding in C, C++, TMB or JAGS. Comparative model runs suggested that as expected, ML-based implementations were rapid and computationally efficient, while Bayesian approaches, which used MCMC or sequential importance sampling, required longer for inference. For grey seal populations in the Netherlands, where preliminary ML-based TMB results were compared with the outputs of a Bayesian JAGS implementation, some differences in parameter estimates were apparent. For these seal populations, further investigations are recommended to explore differences that might result from the modelling framework and model-fitting methodology, and their importance for inference and management advice. The group recommended building on the success of this workshop via continued collaboration with ICES and NAMMCO assessment groups, as well as other experts in the marine mammal modelling community. Specifically, for Northeast Atlantic harp and hooded seal populations, the workshop represents the initial step towards a full ICES benchmark process aimed at revising and evaluating new assessment models.Publisher PDFPeer reviewe

Ishavssel: fangst, bestandssituasjon, og forskning. 2012

Spørsmål knyttet til forvaltning og fangst av ishavsselene grønlandssel og klappmyss blir tradisjonelt drøftet i en felles arbeidsgruppe nedsatt innafor rammen av Den Blandete Norsk-Russiske Fiskerikommisjonen. Arbeidsgruppas mandat har omfattet gjensidig rapportering om fangst og forskning siste år, vurdering av selbestandene, utarbeidelse av forslag til fangstkvoter og andre reguleringsbestemmelser for kommende sesong, samt gjensidig informasjon og avtale om forskningsarbeid for påfølgende år. I tillegg til norske og russiske forskningsresultater har arbeidsgruppas arbeid i stor grad også bygget på behandlingen av foreliggende materiale i arbeidsgruppa for grønlandssel og klappmyss (Joint ICES/NAFO Working Group on Harp and Hooded Seals, heretter kalt WGHARP). Det er rapportene fra WGHARP som danner grunnlag for ICES sin rådgivning på ishavsselene

The Multivariate Normal Inverse Gaussian distribution: EM-estimation and analysis of synthetic aperture sonar data

The heavy-tailed Multivariate Normal Inverse Gaussian (MNIG) distribution is a recent variance-mean mixture of a multivariate Gaussian with a univariate inverse Gaussian distribution. Due to the complexity of the likelihood function, parameter estimation by direct maximization is exceedingly difficult. To overcome this problem, we propose a fast and accurate multivariate ExpectationMaximization (EM) algorithm for maximum likelihood estimation of the scalar, vector, and matrix parameters of the MNIG distribution. Important fundamental and attractive properties of the MNIG as a modeling tool for multivariate heavy-tailed processes are discussed. The modeling strength of the MNIG, and the feasibility of the proposed EM parameter estimation algorithm, are demonstrated by fitting the MNIG to real world wideband synthetic aperture sonar data

Estimation of Pup Production of Hooded and Harp Seals in the Greenland Sea in 2007: Reducing Uncertainty Using Generalized Additive Models

The pup production of the Greenland Sea populations of hooded and harp seals were assessed in aerial surveys using two aircrafts for reconnaissance flights and photographic surveys along transects over the whelping areas from 14 March to 3 April 2007. One helicopter, operated from the applied expedition vessel, flew reconnaissance flights, monitored the distribution of seal patches and performed age-staging of the pups. The total estimate of hooded seal pup production was 16 140 (SE = 2 140, CV = 13.3%), which is similar to an estimate obtained for comparable surveys in 2005. The total pup production estimate obtained for harp seals was 110 530 (SE = 27 680, CV = 25.0%), which is slightly higher than an estimate obtained for a similar survey in 2002. The pup production and the uncertainty of the pup production estimate were estimated using a standard method for analyzing this type of survey data and a recently developed method that utilized Generalized Additive Models (GAMs). Using the two estimation methods on data from all three surveys (2002, 2005, 2007), comparable estimates of pup production were obtained. In scenarios where pups were clustered, the estimated uncertainty of the pup production estimate was much lower for the GAM method than for the conventional method. This resulted in a considerable reduction of the estimated coefficient of variation. In scenarios where pups were uniformly distributed, both methods performed the same

Recent Harp and Hooded Seal Pup Production Estimates in the Greenland Sea Suggest Ecology-Driven Declines

Pup production of the Greenland Sea populations of harp (Pagophilus groenlandicus) and hooded (Cystophora cristata) seals were estimated based upon aerial surveys in March 2018. One fixed-wing aircraft was used for large-area reconnaissance flights to identify the whelping concentrations and to carry out photographic surveys along systematic transects over the whelping areas. A helicopter, operated from an ice-going vessel, flew more localised reconnaissance flights, deployed GPS beacons within the detected whelping concentrations to monitor ice movements, and determined the proportion of pups in specific age-related developmental stages. While the entire estimated pupping region should ideally be covered during one day, photographic surveys in 2018 were carried out on two consecutive days, March 27 and 28, with slightly different survey designs between the two days to account for potential gaps in coverage caused by changes in visibility and cloud cover. Surveys on the two days were partially overlapping, and pup production estimates were consistent when using different combinations of transects from the two days, suggesting that these photographic counts give a relatively robust estimate of pup production in 2018. The combination of surveys that was deemed most appropriate (in terms of maximum coverage with minimum risk of double coverage) yielded an estimated harp seal pup production of 54,181 (SE=9,236, CV=0.17), which is significantly lower than estimates obtained in similar surveys in 2002, 2007, and 2012. Estimated hooded seal pup production was 12,977 (SE=1,823, CV=0.14), which is lower than estimates obtained from surveys in 2005 and 2007, but similar to estimates from the most recent survey in 2012. The reasons for these declines are unknown, but similar declines in theBarents Sea and White Sea harp seals in the mid-2000s suggest that large-scale environmental or ecological changes affecting the Barents Sea and the Norwegian Sea may be important factors.publishedVersio

Beskrivelse av miljø og levende marine ressurser i havområdene ved Jan Mayen

Resultatene fra et tokt med ”G.O. Sars” på Jan Mayenryggen i oktober 2011 blir sammenstilt med våre andre overvåkingsdata og info fra litteraturen. Hensikten med prosjektet er å beskrive miljø og marine ressurser på sokkelen sør for Jan Mayen. Dette er et område preget av store sesongmessige variasjoner med rike forekomster av plankton, pelagisk fisk, sjøfugl og sjøpattedyr i sommerhalvåret. Bunnfaunaen er preget av fjærestjerner, lærkoraler, ålebrosmer og ringbuk. Det ble funnet en ny fiskeart for norske farvann, glattpaddeulke

Marine indikatorer

The Nature Index (NI) is established to get an overview of the state and development of biodiversity within the major ecosystems of Norway. It includes marine, limnic and terrestrial ecosystems. The aim of the index is to measure if Norway manage to halt the loss of biodiversity by the end of 2010. A number of indicators are chosen to represent the state of biodiversity. 125 scientists from various disciplines of research have contributed with data, expert judgements or modeled data for 310 indicators representing different aspects of biological diversity, such as trophic levels, key species and threatened and common species. In order to assemble all the data to an index, a reference value has been estimated for each indicator. The reference value reflects an ecological sustainable value for the indicator, and the indicator values displays eventual divergence from this state. This report describes how data on reference values, uncertainty and values for 1950, 1990, 2000 and 2010 has been set for each indicator. Furthermore this report documents the data sources for each of the indicators that are included in the data set