At this time of year, the waters of Whyalla are normally home to tens of thousands of giant Australian cuttlefish, but so far this winter, they haven't arrived in even close to those numbers.Marine experts fear the harmful algal bloom has had a devastating impact on the species, which annually breeds in the Upper Spencer Gulf.Owner of the Whyalla Dive Shop and Eyre Lab director Manny Katz said those thousands of cuttlefish "should" have arrived, with waters now within the temperature range for the species' breeding conditions, yet they're almost nowhere in sight."We've seen maybe a couple dozen spread out across all of the different sites that we go to, across the 8 kilometres of coast," Mr Katz said."There's been maybe 25 to 30 that we've been able to spot However, the population's migratory patterns take the species out of that protected area during warmer seasons.Mr Katz said they will not fully know how the tourism season will fare until temperatures drop further, but his business had thus far been postponing tours."If the cuttlefish don't rock up, there's not going to be a season."Tony Bramley has been a scuba diver, environmentalist and tourism operator in the Upper Spencer Gulf for almost four decades, and previously owned the Whyalla Dive Shop.He said there have been a number of times the species has had a sharp decline in its numbers since he arrived in the town in the 1980s.He pointed to when commercial fishing decimated the species in 1997 and 1998