Spearfishing in Aberdeen

Good questions, surprised nobody responded sooner. In theory, there is no spearfishing season in the UK, although there are some seasonal restrictions around "bass nurseries" (river estuaries usually). Some would have you believe it is a year round activity, at least on the south coast of England - I would disagree (Feb. & March are usually pretty awful weather-wise & fish-wise). My current thinking is that, in practice, it is seasonal - especially if your main interest is bass (there are other species worth spearing of course). There will always be a few fish caught early in the season but in general, in my experience, they seem to like warmer water conditions so the summer & autumn months seem to be the most productive.

In Scotland, it may be that your quarry will be different though, for example, perhaps more cod/lobster/crab and less bass. Dive & see what you find.

Re. wetsuit, I use a 5mm wetsuit year round & would normally recommend that. If you tend to feel the cold (e.g. skinny, from a tropical clime, etc.) you might want to go thicker (e.g. 6-7mm) but then you will need to carry more lead on your weight belt. Check the relative sea temperature on-line for where you plan to dive & the south coast of England (where I dive) - if it is significantly colder you should factor that in to your decision.