DOI: 10.5061/dryad.c59zw3rg3
title: Regional demography of Icelandic rock ptarmigan and its implications for harvest management

description: The rock ptarmigan is a popular game bird in Iceland, but management of
 hunting has tended to be controversial.  We were interested in
 whether regional differences in ptarmigan demography exist and, if so,
 their implications for harvest management. We fit integrated population
 models (IPMs) to monitoring data from six hunting regions of Iceland
 during 2005 – 2023, and then examined equilibrium and non-equilibrium
 harvests strategies based on an objective to maximize sustainable harvest.
 Survival and reproductive rates tended to be similar among regions, except
 in the demographically important Northeast, where survival was lower and
 productivity was higher.  There was a negative relationship
 between post-breeding age ratio and spring abundance in all regions,
 although the strength of density dependence varied.  Spring
 abundance was stable in all regions, although harvest rates tended to
 decline, and adult survival rates tended to increase.  There was
 a tendency for temporal patterns of demography to be positively correlated
 among regions.  Evidence for cyclical patterns in abundance was
 weak, but this may be an artifact of the relatively short time series.
 Sustainable harvest potential varied among regions and was greatest in the
 East and Northeast.  It appears that harvests during 2005 – 2022
 were somewhat less than the sustainable maximum.  Non-equilibrium
 harvest strategies, in which the allowable harvests depend on spring
 population size and anticipated productivity, are so-called “bang-bang”
 strategies, meaning that no or very little harvest is optimal until the
 population is at or above its maximum level of net production. Synthesis
 and applications:  Regional differences in ptarmigan demography
 warrant different harvest strategies.  Yet the hunting season in
 Iceland historically has been regulated on a country-wide basis, with
 population abundance and dynamics in the Northeast playing a key
 role.  To implement regional harvest management, decision makers
 must first agree on harvest-management objectives that satisfy most
 stakeholders, who tend to hold very diverse values.  Moreover,
 the historical relationship between season length and harvest rate is
 tenuous at best, yet season length is the primary mechanism traditionally
 used to control harvest.  The uncertainty in this relationship
 could be addressed in an adaptive-management framework.
description: We relied on ptarmigan monitoring data collected and compiled by
 the Icelandic Institute of Natural History and made publicly available
 (https://www.ni.is/en/research/monitoring-and-research/voktun-rjupnastofnsins).   We partitioned data into six regions used for setting hunting seasons in Iceland: E – East, NE – Northeast, NW – Northwest, S – South, W – West, and WF - Westfjords (Fig. 1).  For each region, we compiled transect-based estimates of spring abundance, hunting-season age ratios, spring age ratios (where and when available), total harvests, and the number of days afield by hunters.  For each region, we used the same basic structure for population dynamics of the spring breeding population, expressing change in population size as a function of seasonal survival of juveniles and adults, post-breeding age ratio, and harvest rate. To estimate model parameters, we used Markov Chain Monte Carlo simulation, using JAGS 4.3.0 run in the R computing language with the package jagsUI.
description: # Regional demography of Icelandic rock ptarmigan and its implications for
 harvest management
 [https://doi.org/10.5061/dryad.c59zw3rg3](https://doi.org/10.5061/dryad.c59zw3rg3) Data from six hunting regions in Iceland that were used to fit integrated population models for rock ptarmigan. ## Description of the data and file structure Data are stored as [RDS (R Data Serialization) files. An RDS file is a binary serialization format in R that allows you to save R objects to a file while preserving their class, attributes, and structure. ](https://www.geeksforgeeks.org/data-serialization-rds-using-r/)They can be read with the readRDS() command in R. There is one file for each hunting region. The files contain a single R list, with the following variables: nyears - number of years beginning in 2005 (except 2006 in the West region); pop - spring abundance in thousands; H - harvest in thousands; F - the number of birds aged in the fall; yf - number of those that were juveniles; S - number of birds aged in the spring; ys - number of those that were juveniles; lmean.n - prior lognormal mean for initial population size; ltau.n - lognormal precision for initial population size; and days - number of hunter days afield in thousands. ## Sharing/Access information Links to other publicly accessible locations of the data: * [https://www.ni.is/en/research/monitoring-and-research/voktun-rjupnastofnsins](https://www.ni.is/en/research/monitoring-and-research/voktun-rjupnastofnsins)