Little is known about the costs of relocating a territory into an established neighbourhood. In this study we investigated short-term costs of relocation in the longfin damselfish, Stegastes diencaeus, on a fringing reef in Barbados. Experimental removals of residents created vacancies, and focal observations over two days examined the intensity and duration of behavioural changes in the newcomers. Newcomers used smaller territories than original residents, and exhibited increased movement, increased agonistic behaviour and decreased foraging. The behavioural changes suggest that energetics are a major cost to relocation, but that opportunity costs, predation risk and injuries are also important. Differences between strangers and expanding neighbours support the concept of 'dear enemy' recognition, but familiarity does not influence the agonistic behaviour initiated by these newcomers. The costs reported here represent important limitations to the mobility of individuals and provide insights into the stability of fish territories.

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