Population Monitoring
Monitoring survival and reproduction
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​Our marked bear population allows us to monitor reproduction as well as survival across age and sex within the population. We assess reproduction and cub survival by monitoring bears via helicopter or drone several times throughout the year: when they emerge from their dens in April/May, during summer in June, and during fall in September. We monitor all collared bears to track survival and work with the local county boards to determine if marked bears have been taken during the fall hunt.
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Current DNA-based population monitoring
Genetic tagging, or the identification of single individuals using their unique DNA-profile, e.g., noninvasively from feces, hair, or tissue or other biological material from recovered dead animals, has been used to monitor bear populations in Sweden and Norway since 2001 and 2005, respectively. In short, each piece of genetic material collected points to a unique individual at a unique time and location on the landscape, providing a minimum number of individuals detected each year. Determining the number of identified individuals using the DNA, i.e., the minimum number of individuals as well as the estimated number of individuals, is crucial to the wildlife management to evaluate whether national population management goals are met.
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Data collection for Norway started in 2005 and from 2009, this data collection has been annually conducted nationwide. Efforts involve both managers and the public, mainly hunters. This data is used in a model to estimate the number of annual reproductions in Norway. Rovdata (www.rovdata.no) is responsible for the monitoring of bears in Norway. In Sweden, the first regional survey was conducted in 2001. At first these were performed at irregular intervals in different regions but later a rotating schedule was introduced so that every region would have a population survey every 5th year. The survey, starting the 21st of August and continuing until the end of October, is mainly conducted by hunters via opportunistic sampling of scats. These are sent to a genetic lab for registration and analysis (currently The Swedish Museum of Natural History). The individual detection data are then fed into a closed capture-mark-recapture model in Program MARK to estimate population size. The most commonly used models include mixture models to account for individual heterogeneity. These models are robust estimators of wildlife populations as they can account for variation in individual detection, time, and imperfect detection (not all animals are detected). Data for both countries are maintained in RovBase, a joint database for monitoring large carnivores in Scandinavia. An updated method, Open Population Spatial Capture Recapture Model developed by the RovQuant research group in collaboration with the SBBRP, uses individual-based DNA detections to estimate brown bear population size, density, survival, and reproduction.
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Numerous studies and tests of new methods have been conducted in or on the Scandinavian brown bear population since these methods were developed and are used and constantly improved for more effective monitoring and management. Such methods are also routinely updated to implement the latest technological advancements based on next-generation sequencing, and to compare data from Scandinavian population monitoring to neighboring population. The SBBRP has also utilized and evaluated a variety of other population monitoring methods. Other methods for monitoring population parameters and trends include:
Large Carnivore Observation Index (LCOI)
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The Swedish Association for Hunting and Wildlife Management has been collecting data on observations of bears made by Swedish moose hunters since 1998. Observations are collected during the first 7 days (within the first 30 days) of each year’s moose hunt. Hunters also report the time they spent in the field, which can then be used to correct for effort. The LCOI observational data are closely correlated with relative bear density, and these data have been previously used to estimate population size and growth at the national and county level.
Hunting data
Hunters in Sweden are required by law to report all shot bears and submit them for a compulsory inspection on the day the kill is made. Although such hunting data can sometimes be a reliable proxy for population parameters and trends, our research suggests bear hunting data in Sweden represent a biased sample of the population and should thus be used cautiously within a management context. All hunting data is stored in Rovbase.