https://septentrio.uit.no/index.php/NAMMCOSP/issue/feed NAMMCO Scientific Publications 2021-08-25T11:16:17+02:00 Heleen Middel heleen@nammco.org Open Journal Systems <p>The NAMMCO Scientific Publications series makes available in published, peer-reviewed form, scientific knowledge that is important for decision-making on the conservation and management of marine mammals.</p> https://septentrio.uit.no/index.php/NAMMCOSP/article/view/5821 Recent Harp and Hooded Seal Pup Production Estimates in the Greenland Sea Suggest Ecology-Driven Declines 2021-08-25T11:16:17+02:00 Martin Biuw martin.biuw@hi.no Tor Arne Øigård tor.arne.oigard@nr.no Kjell Tormod Nilssen kjell.tormod.nilssen@hi.no Garry Stenson Garry.Stenson@dfo-mpo.gc.ca Lotta Lindblom lotta.lindblom@hi.no Michael Poltermann michaelp@hi.no Martin Kristiansen martin.kristiansen@hi.no Tore Haug tore.haug@hi.no <p>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 the Barents 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.</p> 2022-01-19T00:00:00+01:00 Copyright (c) 2022 Martin Biuw, Tor Arne Øigård, Kjell Tormod Nilssen, Garry Stenson, Lotta Lindblom, Michael Poltermann, Martin Kristiansen, Tore Haug https://septentrio.uit.no/index.php/NAMMCOSP/article/view/5794 Report of the NAMMCO-ICES Workshop on Seal Modelling (WKSEALS 2020) 2021-05-18T21:25:58+02:00 Sophie Smout scs10@st-andrews.ac.uk Kimberly Murray kimberly.murray@noaa.gov Geert Aarts geert.aarts@wur.nl Martin Biuw martin.biuw@hi.no Sophie Brasseur sophie.brasseur@wur.nl Alejandro Buren aburen@mun.ca Fanny Empacher fe21@st-andrews.ac.uk Anne Kirstine Frie anne.kirstine@hi.no James Grecian wjg5@st-andrews.ac.uk Mike Hammill Mike.Hammill@dfo-mpo.gc.ca Bjarni Mikkelsen bjarnim@hav.fo Arnaud Mosnier arnaud.mosnier@dfo-mpo.gc.ca Aqqalu Rosing-Asvid aqqalu@natur.gl Debbie Russell dr60@st-andrews.ac.uk Hans Skaug Hans.Skaug@uib.no Garry Stenson Garry.Stenson@dfo-mpo.gc.ca Len Thomas len.thomas@st-andrews.ac.uk Jay ver Hoef jay.verhoef@noaa.gov Lars Witting larsw@natur.gl Vladimir Zabavnikov ltei@pinro.ru Tor Arne Øigård oigard@nr.no Ruth Fernandez ruth.fernandez@ices.dk Fern Wickson fern@nammco.org <p>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.</p> 2021-05-18T00:00:00+02:00 Copyright (c) 2021 Sophie Smout, Kimberly Murray, Geert Aarts, Martin Biuw, Sophie Brasseur, Alejandro Buren, Fanny Empacher, Anne Kirstine Frie, James Grecian, Mike Hammill, Bjarni Mikkelsen, Arnaud Mosnier, Aqqalu Rosing-Asvid, Debbie Russell, Hans Skaug, Garry Stenson, Len Thomas, Jay ver Hoef, Lars Witting, Vladimir Zabavnikov, Tor Arne Øigård, Ruth Fernandez, Fern Wickson