If we lose an apex predator from the food chain it causes other species to then have population explosions. For example, Sharks and Tuna are the natural predators of the Humboldt squid. If you kill off all the sharks, the squid population (each female can potentially have 20 million "babies") will begin to overpower the part of the food chain below them. They will eat anything and everything. As they swarm for food they exhaust feeding grounds and fisheries as they move.Cassell doesn't have a scientist's reluctance to make absolute statements, a feature that many journalists probably appreciate. But of course I can't resist jumping in with all the caveats . . .
Firstly and obviously, not all shark species eat Humboldt squid. The blue shark, on which Cassell is particularly focused, is one of the sharks that does, but only rarely (see second page of Field et al. 2007). Far more terrifying from the adult squids' point of view are sperm whales, and from the baby squids' point of view--well, anything from chaetognaths to other squid. Those millions of babies are awfully vulnerable! So, while some sharks do eat some squid, I don't think they're a critical check on the population that, if eliminated, will lead to overpowering swarms of squid.
Will Humboldt squid eat "anything and everything"? Of course not, but hey, we should all recognize that as hyperbole! They are capable generalist predators.
Do Humboldt squid "exhaust feeding grounds and fisheries"? Well, despite anxiety from hake fishermen, market squid fishermen, and salmon fishermen, it hasn't happened yet.
All this doesn't mean I'm indifferent to the idea of killing off sharks! There are numerous reasons to be concerned about shark decline, from the aesthetic to the economic, and my love for squid doesn't extend to the extermination of their predators.
Even those terrifying sperm whales.