Known slave voyages directly from Scottish Ports were small, records show only seven from Port Glasgow over the period 1717-30, and 14 from Greenock, mainly in the 1760s, and even smaller numbers from other ports, with a recorded total of 4,500 slaves (Devine, 2011, page 44, or 6 in the pdf).

Scottish merchants based in English cities (Liverpool, London, etc) also had involvement in the slave trade, but the slave trade overall was fairly unimportant to British shipping. Eltis and Engerman (2000) note that in 1792, the busiest single year of the British slave trade, about 204 vessels with a total capacity of 38,099 tons left Britain to carry slaves from Africa to the Americas, this was out of 14,334 vessels registered in Britain, totalling 1.44 million tons, so the slave trade was less than 1.5 percent of British ships and 3 percent of shipping tonnage (page 129).

Devine (2011) argues that the slave trade was important to Scottish economic development indirectly: Glasgowian merchants dominated the tobacco trade, Scottish merchants were heavily involved in sugar, and the slave plantations were a large source of demand for linen and cotton textiles spun and wove in Scotland. Devine notes the irony of this involvement despite Scottish intellectuals leading the moral assault against slavery.

On top of the relatively small slavery ships, the slave trade was a triangular trade, where ships sailed from Europe to Africa, bringing manufactured goods, which were exchanged from slaves. The slaves were then shipped across the Atlantic to the Americas, where they were traded for agricultural commodities and other raw materials, which was then shipped back to Europe, to start the exchange again - and also ships sailed directly between Europe and the Americas (well as direct as you get with prevailing winds and currents), as the Americans had demands for European manufactured goods in their own right. Slaves weren't shipped to Europe in large quantities, though up until 1778 reportedly it was fashionable for Scottish wealthy families to have a young 'black boy' or 'black girl' attending them and Scottish newspapers would openly carry ads offering slaves for sale. But I've never seen any estimate that this was a significant number relative to the scale of the Scottish population at the time, of over 1 million people.

In summary, known slave voyages sailing from Scottish ports were very small in number, the influence of slavery on the Scottish economy was more indirect, through the imports of slave products and the plantation-based markets for Scottish textile production.

Sources

Devine, T 2011, 'Did Slavery make Scotia great?', Britain and the World, vol. 4, no. 1, 2, pp. 40-64. https://doi.org/10.3366/brw.2011.0004 https://www.research.ed.ac.uk/portal/files/8206494/Did_slavery_make_Scotia_great.pdf

National Library of Scotland, Scotland and the slave trade, https://www.nls.uk/collections/topics/slavery

Eltis, D., & Engerman, S. (2000). The Importance of Slavery and the Slave Trade to Industrializing Britain. The Journal of Economic History, 60(1), 123-144. Retrieved from http://www.jstor.org/stable/2566799, https://www.researchgate.net/profile/David_Eltis/publication/23565372_The_Importance_of_Slavery_and_the_Slave_Trade_to_Industrializing_Britain/links/588e2abb92851cef1362c973/The-Importance-of-Slavery-and-the-Slave-Trade-to-Industrializing-Britain.pdf