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Fish and fishing in the Baltic Sea during the Middle Ages is partly known through research on historical records and zooarchaeological materials, and combinations of them. Due to the uneven distribution of written records and research focus, much is known about the large-scale cod and herring fisheries in the southern parts of the Baltic Sea. However, in the northern parts of the Baltic Sea, both large-scale and small local fisheries are less researched. This article considers the species richness, resource availability, and human selection identifiable in these sources. Zooarchaeological material from the Franciscan friary on the island of Kökar in the Åland archipelago will be discussed in relation to zooarchaeological and written sources from the Castle of Kastelholm (Åland). Historical records identify the friary as having taxation rights to large-scale seasonal catches of cod in the outer archipelago; how the friary collected this toll is unclear. It has been assumed, based on the historical records, that cod was the most consumed fish at the site. This study revealed that the zooarchaeological assemblage does not support the interpretation of cod as the most important fish for consumption at the friary during the Medieval Period (AD 1450–1530).

Understanding fishing practices through the zooarchaeological record offers crucial insights into past human-environment interactions, subsistence strategies, and the development of the modern fishery practices. Past fishing practices varied widely depending on geographical location, environmental factors, and cultural contexts. In this thesis, I explore fish and fisheries in the Baltic Sea from different time frames. Evidence from archaeological fishbones and teeth provides a direct link to fishing practices in the past. Species diversity and anatomical distribution patterns are used to explore fishing methods. Isotope analysis on fish teeth offers further refinement of ecological patterns, including fish migration and mobility. Using zooarchaeological materials from Gotland and Åland, this thesis identifies and discusses patterns in relation to climate change and cultural shifts from the Mesolithic until the Early Modern Period. By applying the theoretical framework of negative space and values the formation of past assemblages and the remains excavated in the present are evaluated. Using strontium isotope analysis, the likely origin, fresh or brackish water, of euryhaline fish on Gotland is explored. The results indicate that fluctuations in aquatic habitat utilisation are tied to environmental shifts and influenced by cultural preferences and values.  To understand how fish are transformed from living creatures to products for human consumption, Medieval zooarchaeological material from Åland was used to investigate shifting patterns in the transportation of cod from a local fishery.  A possible difference in fish products was identified related to the Gotlandic sources. This has implications on how the written record might be interpreted. The aspects above are discussed in a diachronic way and modern concepts such as fishing down the food web are used to examine the sustainability of past fisheries. The findings contribute to broader discussion on past aquatic resource utilisation and fish's value and identities at different time frames in the Baltic Sea context. Highlighting the significance of fishbone analyses and the potential to incorporate archaeological data in contemporary sustainability discourse. 

The importance of marine resources for the Neolithic hunter-fisher-gathers of the Pitted Ware Culture of Gotland, Sweden, is well documented through zooarchaeological analyses and diet studies of human remains. Terrestrial areas were important for living and supplementing the diet but the extent of the terrestrial territories and regions of land use for different groups is largely unknown. The presence of euryhaline species in recovered zooarchaeological assemblages indicates that freshwater fishing or fishing in the brackish estuaries of the Baltic Sea was part of the subsistence practises. To explore if the inland freshwaters of Gotland were used and, if exploited, where they were located, 18 teeth from euryhaline fish from the Pitted Ware Culture site Ajvide on Gotland were selected. The Sr-87/Sr-86 isotope ratios in the fish teeth were analysed using laser ablation-multi collector-inductively coupled plasma-mass spectrometry and correlated with an updated bioavailable baseline of Gotlandic water sources. Through this approach, the habitational origin of the fish was shown to primarily stem from at least six freshwater sources located in the west-central area of Gotland, in close relation to the site, with a few individuals originating from within the Baltic Sea. The study highlights the significance of ichthyoarchaeological analysis in understanding the territorial practice of past foraging societies and recommends further studies on euryhaline species to expand our knowledge of fish habitat, human resource utilization and land use.

In April and May 2022, Uppsala University, Campus Gotland conducted seminar excavations at Västergarn, 25 kilometers southwest of Visby. Five trenches and two trial trenches were investigated covering an area of 208 sqm. At Snauvalds 1:2 four early medieval house structures have been exposed out of which two had been excavated. According to 14C the the two houses investigated date between c. 1040-1180/1230s. House 11 c. 4.5x7 meters is a one-room cabin with an oven places in the south-west corner. The building shows evidence of various crafts, including blacksmithing, textiles and the production of beads. House 12, a post two room cabin, c. 5x8 meters also with a hearth was probably used as a residence. The open space between house 11 and 11 was interpreted as a yard with evidence of processing cat furs and other activities. The purpose of the investigation at Hamngården 1:2 was to locate the harbor area of medieval Västergarn west of Klintehamnvägen. A geomagnetic survey conducted on the property in 2022 indicated anomalies in the beach meadow. For this purpose, a search trench was opened in an east-west direction between Klintehamnvägen and Västergarnsån. Coin and pottery finds indicate activities between 16th and 18th centuries. The find material has probably a connection with Hamngården, the residence of the port bailiff mentioned in the hictorical sources.

In April and May 2021, Uppsala University Campus Gotland performed an archaeological investigation at Västergarn, 25 kilometres southwest of Visby, as part of an advanced field course in archaeology. Two trenches were investigated, covering an area of 90 m2. The purpose was to reinvestigate post-holes, remains of a wooden floor and a water hole unearthed in 2013. Further to understand how these remains relate to a number of Late Viking Age artefacts discovered in the same area. As a result it could be established that the wooden floor belongs to a medieval house foundation with corner-hearth and a partly preserved stone-lined sill. The foundation is mainly dated by shards of Baltic ware to the period 1100/1125-1230. Find concentrations of iron tools adjacent to the hearth, iron armory plates and glass beads may indicate a small workshop. The Viking Age artefacts relate to a separate post-hole building probably dated to the 11th century. The date and the function of the water hole remain inconclusive. The large amount of animal bones deposited in the stone paved water hole, among them a high proportion of horse bones indicates a function as a well for grazing cattle in the area during the dry season. A coin-like copper pendant with pseudo-Islamic glyphs found adjacent to the water hole underlines Viking Age activity in the area. The results show that the house remains in the area investigated probably belong to the outer precinct of the harbour settlement in Västergarn. This particular area within the Västergarn rampart was settled presumably between AD 1000/1050-1200/1230. Findings such as cultural layers, strengthens indications of a complex and active settlement in the late Viking and early medieval period.