Browsing by Author "Isaksson, Simon"

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Evaluation of photo-ID technique to estimate harbour seal numbers in Gullmarsfjorden, Sweden
(2022-10-26) Isaksson, Simon; University of Gothenburg / Department of Biological and Environmental Sciences; Göteborgs universitet / Instiutionen för biologi och miljövetenskap
To be able to preserve areas in nature in a careful way a good understanding of the biodiversity living there is needed. The harbour seals are a top predator that affect and is affected by the whole food chain and plays a vital role in the ecosystem. Some seals migrate long distances and some are relatively stationary, it is therefore very important that we can get to know the population on an individual level. Earlier, the way to identify an individual has been through physically tag them, this thesis explored both the possibility to use the natural patterns in the fur to identify individual harbour seals by Photo-ID. The images were processed using the software Wild-ID, the population sizes were estimated in two different locations in Gullmarsfjorden, Sweden. The software worked well, 58 potentially unique individuals were managed to be identified during the project, 22 of these with both their left and right side of their face. The similarity scores the software gave the matched images were to 99% scored beneath 0.3 (0 = no similarity, 1 = exact copies) which is a relatively low score. Still, the software ranked about 75% of the matches as the best suggestion and 95% as one of the top 10 suggestions. This shows that even though the scores were very low, the software could still usually pick out the correct match. With the information gathered and capture-recapture statistics, population sizes of two different locations in the fjord was estimated, 26 (12 – 60) individuals on one site and to 73 (47 – 129) on the other. This is the first time identification of harbour seal individuals in Sweden has been done with the help of photo-ID and it’s a important step for better understand migration and spatial structures by the harbour seal population. This information can lead to better management and conservation of our marine ecosystems.
Movement patterns and social dynamics of male African Savannah elephants (Loxodonta africana). Following the steps of giants.
(2024-11-29) Isaksson, Simon; University of Gothenburg / Department of Biological and Environmental Sciences; Göteborgs universitet / Institutionen för biologi och miljövetenskap
Wildlife populations are decreasing all over the globe. Conflicts with humans increase as the wild landscapes shrink. The African savannah elephant (Loxodonta africana) used to roam in most parts of Africa but only a fraction of the historical numbers remains today. Botswana is home to 130,000 elephants, about 1/3 of the elephants remaining in Africa. Savannah elephants have traditionally made large seasonal migrations for resources, but landscape fragmentation has made these movements much harder. The savannah elephant is an endangered species and even if the social lives of matriarchal families are well-studied, the groups that the bulls may form have been less so. This study aimed to fill some of these gaps and contribute with knowledge about movement patterns and social dynamics of males to better conserve the species and decrease human-wildlife conflicts. Photo identification was used to track individuals in the Makgadikgadi and Nxai Pan National Park in Botswana to estimate how many days the bulls stayed inside and outside the park, and how it differed between different age groups and seasons of the year. I also investigated the social dynamics of male associations to increase the knowledge about bull groups. I found that a bull on average stayed for 37 (CI 31-48) days inside the park before leaving the park for 108 (CI 87-138) days. My findings also suggest that the youngest males stayed and left for shorter periods under both the wet and dry seasons compared to the oldest bulls. Both age groups stayed and left for longer periods during the dry season compared to the wet. The research also showed that bull association isn’t random even though most relationships will be short-term. My results indicated that elephant movement generally increased during the wet season and that young bulls in general moved more in and out of the park, increasing their risk of conflict with people living in the surroundings. It also indicated that elephants do have preferred companions, and all these findings should be taken into consideration for the conservation of the species.