In the second part of this story, the causes and beginning consequences of the Humboldt squid expansion are revealed.
They go anywhere, eat everything, and do anything. They are the biker gang of the Eastern Pacific.” So said Ken Cooke, fisheries biologist from Canada, of Dosidicus gigas, the Humboldt squid, a recent resident of our coast. In 2002, these squid famously invaded and stranded themselves by the thousands at La Jolla Cove and other San Diego beaches. Though they used to be found only in the Pacific Ocean’s warmest stretches near the equator, this squid species has been a frequent visitor to our waters since the 1997-’98 El Nião. However, increased water temperatures are not the sole reason for their foray into our latitude, as cold water from a subsequent La Niãa didn’t send them packing. Since 2003, these large, subtropical predators have taken up fulltime residence, with multiple generations now able to call themselves California natives. At a recent CalCOFI (California Cooperative Oceanic Fisheries Investigations) conference, scientists compared data collected on these squid to better understand the causes and consequences of their range expansion.
As quick-growing predators with soaring metabolisms and high population turnover rates, Humboldt squid swiftly respond to changes in their environment. For example, they typically prey on various fish and invertebrate stocks of commercial and ecological importance, including those favored by their predators and competitors ” such as tuna, swordfish and sharks. But overfishing of these game fish has drastically depleted their numbers to allow the squid a foot in the door to expand their range. Scientists have noted a corresponding drop in the local Pacific hake population (a whitefish often used in fish sticks and popular squid prey) that has remained low ever since.
Mako sharks (Isuraus oxyrinchus), whose population is in serious trouble, are managing by eating squid, the predators of their preferred prey. According to Russ Vetter, NOAA fisheries biologist, over the last few years, the mako diet has averaged 32 percent squid. Yet this new food comes at a price in the form of sucker scars and tooth tracks that mar the sharks’ bodies, demonstrating the squids’ killer instincts. Vetter, who briefly captures makos for tagging purposes said, “By 2007, all mako sharks look like they’ve been in a bar fight.”
Humboldt squid are so flexible that there are even two sizes of mature adult populations. Big squid mature at 2.5 feet and grow to 4 feet long. Small squid mature at 1.25 feet long and grow to 2 feet long. It is hypothesized that temperature and food abundance may dictate what size and age they mature. If so, this implies that small squid, which mature early, migrate a shorter distance under warmer conditions, and big squid, which mature later, migrate longer distances under colder conditions. But what could be the benefit of having two different adult-sized populations? Maybe because the smaller mature adults reproduce faster, they better ensure continuation of the species. The bigger mature squid reproduce more slowly but in doing so may select out for the fittest individuals.
On a daily basis, Humboldt squid tolerate oxygen and depth extremes as large as what can be found in the ocean. In deeper waters, there are areas where the oxygen concentration is so low it will not support most life. Squid can withstand these zones, which not only expands their feeding territory but also provides a safety zone of sorts to escape predators incapable of accessing this zone. They may be found from the surface to more than 4,500 feet deep. More typically, squid spend time in shallower waters at night and deeper waters during the day, yet data show that they make forays into the deep at night and venture to the shallows during the day.
It seems that whenever one tries to find a pattern in the behavior of these environmental chameleons, there are exceptions. However, it is clear that wherever they put down roots, Humboldt squid play a major role in what the ecosystem looks like. Changing climate conditions will likely lead to further alterations in their numbers and where they are found, and to their relationships with fish, seabirds, marine mammals and us.
” Judith Lea Garfield, biologist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. www.judith.garfield.org. Questions, comments or suggestions? Email [email protected].