In a certain population of the blue-ringed octopus (Hapalochlaena maculosa), a rare "melanistic" morph occurs where individuals display solid black rings instead of iridescent blue. This melanistic phenotype is caused by a recessive allele resulting from a mutation in the MOB gene. In this population, one in 625 individuals is observed to have this melanistic phenotype. According to the Hardy-Weinberg principle, the following equations can be used to estimate allele and genotype frequencies within a population:

$$p^2+2pq+q^2=1$$ $$p+q=1$$

Use the Hardy-Weinberg equations to calculate the percentage of individuals in this octopus population that are heterozygous (carriers) for the MOB gene. Give your answer to one significant figure. Show your working.