Ireland's sea fisheries addresses the historical problem of determining the population of fish in the north Atlantic and the number of fish caught in the period 1400–1600. While more recent science and advanced technology has begun to record current numbers, establishing the ‘baseline’ in the Renaissance is indeed a difficult task. Only recently has there been a collaborative effort to develop the means to begin to count fish through a diverse set of criteria. Patrick Hayes has been part of the advanced work done at Trinity College, Dublin under the leadership of Dr Poul Holm through several projects: Marine Animals Population (2000–10), NorFish (2016–20) and, most recently, 4-Oceans (2021–6).

One of the best studies until recently was L. A. Clarkson and Margaret Crawford's Feast and famine: a history of food and nutrition in Ireland, 1500–1920 Oxford (2001), which claimed that fisheries in Ireland did not develop until the sixteenth and seventeenth centuries when English settlers organised them. By contrast, Hayes has argued that fisheries were already thriving in Ireland by the fourteenth and fifteenth centuries. However, by 1600, there was a near total collapse. By 1500, Irish vessels carried fish to markets in England: ‘53 per cent across the whole century, with a further 28 per cent carried in English vessels and 14 per cent in Welsh. In 1516–17 alone, Irish boats carried 83 per cent of the salmon’ (pp 107–8). However, by 1594, Irish vessels were involved in only 2.4 per cent of the trade (p. 122). Thus, a new question arises: why did these earlier fisheries collapse?

Hayes acknowledges there is very little quantitative evidence, as well as scant qualitative sources available; however, trade data from the English High Court of the Admiralty and some other qualitative sources ‘strongly suggest that from 1480 to 1540, fisheries were booming’ (p. 224). Hayes has also used the more recent Atlantic Multidecadal Variability (A.M.V.) record of temperature variations to show the relationship between temperature and herring abundance in the North Sea. Lower temperatures led to higher plankton abundance, which in turn led to greater herring catches. It is well-acknowledged that Christian Europe prescribed fish as protein during the Lenten season (forty days) rather than meat, hence the demand was high. The fact that huge shoals of herring migrated to nearby fishing grounds meant an abundant catch in the winter when other fish, such as eel, cod, hake and salmon, were not present, making herring a very noble fish.

Until the Desmond Rebellions (1569–73, 1579–83) and Nine Years War (1593–1603), Gaelic lords in the south-west of Ireland exploited the rivers and sea for their wealth, unlike the east coast where agriculture was strong. Berehaven and Baltimore were the most prominent ports in the southwest. While maritime technology was limited for Gaelic lords, they had lively relations with the French, Basque and Spanish who brought salt, wine and luxury items to Ireland and who were granted the right to fish in local waters. In turn, salt, naturally available in Ireland, was used to preserve fish, meats, and hides. Hides became one of the largest exported products. Once many of the Gaelic lords left Ireland after the rebellions (Flight of the Earls, 1607), English fishers dominated Irish waters. William Barbazon, then treasurer of war, reported that ‘600 English fishing boats were taking part in the herring fisheries’ (p. 28). Ireland's most important exports by the seventeenth century were timber, hides, wool and tallow, but no longer fish.

One of the strengths of Hayes's study is the consideration of many factors in the change in Irish fishing, thus the appropriate sub-title, ‘Economics, environment, and ecology’. In addition to his analysis of the Irish rebellions and their effect on fishing, Hayes demonstrates a thorough study of other factors that led to change. While the Basque, Spanish and Portuguese fishermen exploited Irish waters until 1500, the discovery of an unlimited supply of cod in Newfoundland meant that it became the largest supplier of protein in Europe, and the need to fish in Irish waters greatly diminished. By 1558, ‘the duties for most commodities roughly doubled to align with the rising market prices’ (p. 91). The war in Europe between England and Spain (1585–1604) also disrupted trade between Ireland and the continent, followed by the rise of piracy around the southwest coast of Ireland from the 1650s to the 1730s. As Britain further colonised Ireland, many Irish fishermen were pressed into service in the English navy. Hereafter, English vessels caught most of the fish and Ireland's abundant fish became exploited by other states.