Mass Stranding of Squid off Vancouver Island
Wednesday, October 21 2009 @ 12:54 AM EDT
Contributed by: jkr
Photograph by: N. Gervais, Canwest News Service
Two mass strandings of Humboldt squid in the last two months on the West Coast have locals asking the question no one seems to be able to answer: why is this happening?
Though no one has the exact answer, scientists aren't short on theories and speculation. Some say perhaps the squid were following their prey and got caught in a current that washed them ashore.
Others think maybe the squid were disoriented by a change in one (or all of) several ocean conditions: temperature, salinity, or oxygen levels. Some have even suggested strandings could be a result of old age in a cephalopod that tends to have a life span of two years at most; the pack simply follows one senile leader and they all end up on the beach at the same time by accident.
More interesting to scientists than why squid strand on beaches is why their range has expanded as far north as Alaska when prior to the 1990s they were never seen further north than Oregon.
Vancouver Island's resident squid and octopus expert, James Cosgrove, says all, one or none of these could be true.
"The strandings are not unusual -- that happens in the Gulf of Mexico as well -- but why [it's] happening, I don't think anyone knows."
Cosgrove spent 20 years of his career managing the natural history section at the Royal BC Museum in Victoria, home to more than half a million specimens, but chose among them squid and octopi as his personal interests.
A scuba diver for more than 45 years, he co-authored Super Suckers: The Giant Pacific Octopus and Other Cephalopods of the Pacific Coast, published in March 2009. The book documented, in part, the Humboldt squid.
Before 1934, the Humboldt squid had not been seen further north than San Francisco. In the early 1990s reports of the species were recorded off the coast of Oregon.
Cosgrove and his team at the museum first recorded the appearance of the newly arrived aliens in B.C. coastal waters in 2003. Every year since the squid have returned.
Because squid strandings happen in the species' home territory in Mexico, Cosgrove says the more interesting question is why the squid have expanded their range as far north now as Alaska.
"Normally when they move out of Mexico, they make a left-hand turn and move down to South America," he says, "so why have they decided to take a right hand turn and come up the coast of North America?"
The answer eludes the few researchers in the field challenged by resources and capacity to properly look into the causes and effects.
But if they could, Cosgrove says they'd likely look at how the squid's food sources are moving, where the squid are in relation to them and what the ocean conditions are around both.
"Whatever they are normally hunting, perhaps it is also affected by the changes in water temperature, salinity, oxygen levels and ocean currents. The squid are merely reacting to the movement of its prey item, rather than to the water conditions that affect them directly."
Cosgrove says the movement of the squid's prey--hake, herring, sardines, pilchards -- could be influenced by ever-increasing ocean temperatures due to climate change. For example, sardines and hake, both species caught commercially in B.C., like warmer water temperatures.
According to Fisheries and Oceans Canada's (DFO) annual State of the Oceans reports, the warmest ocean temperatures in 50 years were recorded in the summer of 2004 off B.C.'s coast and the Gulf of Alaska. Up until 2007 that warming trend continued with temperatures in B.C. waters down to 175 metres deep recorded at 0.5 to five degrees Celsius warmer than in the 1990s.
In 2007, B.C. was recording colder than normal ocean temperatures, even though January that year was the warmest on record globally.
Bill Crawford, a scientist with the Institute of Ocean Sciences, says after the last two colder than usual winters, the West Coast can expect warmer air and water temperatures this winter.
Even though the last couple of years have brought colder water temperatures off the coast, Ian Perry, a research scientist at the Pacific Biological Station in Nanaimo, says water off the West Coast in the near-shore is warmer.
Perry says it could be that the squid and their prey are being squeezed in between the cold water offshore and land, more so than if they were spread out in a larger area of ocean like in previous years when all the areas warmed up.
Many fish orient themselves along temperature gradients, so if the squid are simply following their prey that like warmer water, that could explain why they are close to shore this year than they have been in the past, Cosgrove notes.
When ocean temperature goes up, oxygen content goes down and salinity increases; there is a direct cause and effect relationship among the three. In fact, Cosgrove says ocean oxygen content has been steadily declining for the last 20 years as temperatures have been steadily rising.
"It's down about 30 per cent below its historic norms," he says -- new information soon to be published in his colleague's forthcoming paper on the subject. "That's brand new info; it's not out in the general public yet."
DFO's 2008 State of the Oceans report notes West Coast waters are becoming increasingly hypoxic (lacking oxygen) and Cosgrove says that could be another factor in both the squid and its prey's expanded range.
Although oxygen levels tend to be low in the summer anyway, Crawford says there has been a recent concern that they might drop further, resulting in marine life dying off.
Squid tend to thrive in oxygen-poor water. During the day they live in an oxygen minimum layer about 250 metres or deeper below the ocean surface.
Graham Gillespie, a researcher with the Pacific Biological Station in Nanaimo who has studied Humboldt squid, explains that the squid hunt at night, rising to the surface to feed.
"But even during the night they make regular trips back down into the oxygen-poor water that is a refuge for them," Gillespie says.
But, Gillespie and Cosgrove are careful to say no research has been done to correlate increasingly hypoxic waters with increasing Humboldt squid distribution.
Scientists have also speculated that long-term, large-scale fisheries have eased predation pressure on the Humboldt squid population.