A mismatch between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition and reduced paternity. Here, spawning behaviour of free-living Arctic charr (Salvelinus alpinus) was video recorded, and their reproductive behaviour was analysed. From evaluating 157 spawning events we observed that females mainly spawned with a guarding male and the female and the guarding male synchronized timing of gamete releaseunder sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single male spawning events, the average sneaker released his milt 0.6 seconds after the spawning female under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioural sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes the spawning couple vibrates their bodies in close contact and it seems likely that vibrational communication between the spawning couple reveals time of gamete release to surrounding sneaker males. This might explain the relative high level of synchrony in gamete release between the female and the males from both reproductive tactics under sperm competition. Thus, vibrational communication between the guarding male and the female comes with the cost of higher detectability from surrounding males and may represent a “double-edged sword” for the guarding male.