Last week I left you with a young sea lion hovering over me as I filmed mating squid off Hen Rock. I said I'd continue that story this week, which is a good thing because I haven't been in the water since. My friend Jenny Yee from Singapore flew in this weekend to dive with me, but the weather was not to our liking so we watched underwater videos instead. She is an active diver in regions like her native Malaysia, Indonesia, the Philippines and the Maldives so she was less than impressed with the rather drab fish species that dominate the kelp forests of our temperate waters! In the future we may dive her region's waters or even try the Red Sea.
On to this week's subject. First, let's get a few facts down about our market squid. This species is found from Alaska to the tip of Baja, but it is common from southern British Columbia to central Baja including offshore Guadalupe Island where I filmed the great white sharks a year ago. Adults are found to depths of 1,600 ft or more, while the juveniles generally live above 300 ft. The adults do move towards the surface to feed at night.
Our understanding of the squid's natural history and population is surprisingly limited since it is the number one fishery in our state. Their bodies are like tapered cylinders with an internal horny or chitinous shell unlike that of other molluscs. Market squid reach lengths of about a foot with the male generally larger than the female. The mantle or body is not fused with the head, so they have a fair degree of movement possible. Squid have eight short tentacles or arms surrounding the mouth, and two longer tentacles which are used for capturing food. These tentacles have a club-like ending with may sucker discs.
Squid have a highly developed nervous system, just like their octopus relatives (and me). They are even raised by scientists for nerve fiber and genetic studies. Their nerve axons are 100 times longer (about 2mm or less than 0.1") than a human's so they are easier to conduct experiments with. Their bodies are generally white in color, but can change rapidly due to nerve impulses triggering color cells called chromatophores. These rapid color changes may be used to communicate with other squid, or for camouflage against predators.
Squid generally swim forward using two fleshy fins at either side of the tail. Recent studies have shown that their swimming speeds are about 50% faster than previously thought, and they are capable of long-distance migrations along the California coast. They may also "jet" backwards to escape predators. They do so by taking water into their body or mantle cavity and ejecting it through a funnel like structure that can be directed by the animal.
Squid are voracious predators just like me. They feed on shrimp-like animals, fish, other molluscs, bottom-dwelling worms and even their own young (unlike me). In waters where plankton is abundant due to upwelling, they feed on the same krill that whales love. These food chains can be quite simple: sunlight to phytoplankton to krill to squid, which also makes them vulnerable to changes in the environment. In general the adults are fast swimming hunters who capture their prey in midwater using their good eyesight (unlike me). They have a sharp beak that cuts their prey into pieces which are held by the smaller tentacles. A structure inside the mouth known as the radula grinds up the food so it can be easily digested. One study found they may grow at a rate of 1.7% per day. At that rate, I could add more than 30 pounds in one week! In turn squid are eaten by fish including salmon and their relatives, flatfish, and sharks as well as marine mammals like sea lions and sea birds. They may use their camouflage for protection, or release an inky substance just like an octopus to confuse predators. They are also known to mingle with schools of fish for protection. Predators eat the fish instead of the squid.
Both males and females eat less while spawning. Perhaps this is because their mating behavior is very elaborate, involving movements and changes in body color! At this time they come inshore to spawn... hence the many squid fishing boats in our waters. It is believed that water temperature affects the timing of mating by determining when the male gonads mature. Although some reports state they are sexually mature at 1-2 years and mate at 3 years, it appears that squid live only about one year and therefore complete their entire life cycle in that relatively brief time. This makes reproductive success each year very important in continuing the species, since the adults all die after mating.
Squid generally spawn over sandy or mud bottoms at depths down to about 130 ft. The male grabs the female from below with his tentacles and holds her. Of course he usually has to fight off other males (as I do). One of his tentacles, the hectocotylus, is adapted to transfer packets of sperm into the female's mantle or body cavity. They are then moved to a sperm receptacle for fertilization. Each female will lay 20-30 egg capsules, each with 160-300 eggs in it. The egg capsules, commonly referred to as candles because they look like one, are made of many layers of proteins. They are inserted into the sand and have a sticky substance that helps anchor them. Females continue to lay eggs in the same masses for up to about a week. The older egg capsules in the center turn brown while the newer ones at the edges are white. One study estimated there were about 6.5 million eggs in an area about 100 ft by 100 ft. Although it is said the squid die shortly after laying, they may actually live for several weeks or possibly months as spawning continues before dying.
The eggs need to be bathed in oxygen which is accomplished by surge and currents since they are not actively tended by the adults. While doing research for this column, I discovered the eggs are indeed eaten by bat stars, Kellet whelks and brown cowries in addition to the blacksmith mentioned last week. A scientist at Stanford University's Hopkin's Marine Station in the Monterey area noticed the eggs don't rot or get infected by bacteria or fungi. He assumed they had natural antibiotics in them, but discovered that the female squid actually deposit layers of bacteria within the capsules. These bacteria are believed to release their own antibiotics to prevent other bacteria from competing with them.
The eggs hatch into miniature "adults" since development is "direct" with the young looking like the adults. It may take 15 to 90 days for the eggs to hatch depending on the water temperature (61 to 46 degrees for that time range). The tiny hatchling larvae (about 2-3mm or 0.1") feed on crustaceans known as copepods in the plankton. They migrate from depths of about 100 ft during day up to 50 ft at night to feed. The young begin schooling at about two months in age (just over a half inch in length).
The squid fishery, which began in the 1850's, is the most important in our state in terms of economic value and weight. It was worth $41 million in the year 2000 and the catch is used for bait, food, and fish meal. Squid are fished at different times in different parts of the state. Near Monterey the fishery is from April to November while it is October to March in our waters. Lights are used to attract the spawning squid at night and they are netted. In some types of nets there is the danger of incidental take of marine mammals including Risso's dolphin. The recent designation of marine reserves in the northern Channel Islands, especially Anacapa, may have increased squid fishing pressure in our waters since 7 to 10% of the catch was previously taken from those now protected waters.
Due to their short life history, the squid fishery is easier to manage. However, it also means their populations are closely tied to changes in conditions each year. El Nino events can seriously affect squid because the increased water temperatures decrease plankton productivity and therefore decrease their food supply. Landings had increased 400% from 1990 to 1997, but an El Nino the following year caused the fishery to collapse temporarily.
© 2006 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Look for my new DVD on the giant sea bass to be released in January.
Group of mating squid at Hen Rock, males competing
for one of the young lovelies;
a male holding a female in his tentacles over previously laid egg capsules and
a male and female mating in the open.
This document maintained by
Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia