For those of my readers who were "with" me last week, I'm sure you've been chafing at the bit to read the second part of my recent shark diving experience. Well, sit down in your easy chair, grab your favorite beverage, and "Dive Dry with Dr. Bill" once again. I promised I'd tell you more about the biology, behavior and ecology of the sharks I observed on my dive. And in doing so, I'll undoubtedly reveal some of the same information about myself. Are you sure you're ready for that? No, this column will be rated PG so it's safe to continue.
Blue sharks in our waters are very sleek with slender, somewhat elongated bodies. They may be a dark blue on their upper (dorsal) surface, transitioning to a silver blue on the sides and white on the lower (ventral) surface. They have a long, pointed snout and the mouth is under slung. Along our coast, this species is found occasionally as far north as Oregon or even the Gulf of Alaska, and south down to Chile. Worldwide they are known throughout temperate and tropical seas. Although they usually are 3-6 feet in length here, in other areas they may reach a maximum length of over 12 feet. A 6-7 foot individual is about seven years old and they may live 20 years.
I mentioned last week that I used to see them frequently in the near shore waters off Catalina's leeward coast in the 1960's and 1970's, as well as in the San Pedro Channel. However, they are generally considered a pelagic or open ocean species usually residing near the surface but also to depths of 900 feet or more. Although blues will frequently approach divers closely, they are not considered very aggressive. You think Dr. Bill is going to risk his own skin just for the few bucks this column pays? Hey, I went to Harvard... hopefully I'm smarter than that. Blues are in the requiem shark family along with great whites and tiger sharks. They are known to mistakenly bite divers when chum or blood is in the water. Fortunately their sense of smell is sufficient to distinguish between these substances and yours truly!
According to Dr. Milton Love, blues prefer waters in the 52-63 degree range. During summer when waters warm, they may be found further north. Their numbers apparently increase in our waters during this period. Interestingly, I think sharks began to decline here in the late 1970's. That coincides with a period of warmer ocean temperatures that has extended to the present. Even though it contradicts the previous information, perhaps this long-term change has influenced their decline here. Love states that most of the individuals seen in our waters are immature or early reproductive adults. They are known to migrate over significant distances. They also exhibit a diurnal (24-hour) pattern, living out in open waters during the day and entering shallower waters at night to feed.
Like many shark species, male blue sharks are quite aggressive in their mating rituals. They often bite their females on the back. I usually bite mine on the neck, but only during full moons. Female sharks like blues have much thicker skin on their backs, and are rarely seriously hurt by the male during mating. Female humans have thin, soft skin on their necks and... ah, wishful thinking! Studies indicate mated females may store the male's sperm in their bodies for months before allowing fertilization to occur. The young sharks develop within the mother for 9-12 months and are about 1 1/2 feet long at birth. A single female may give birth to 135 pups in a year! Good thing they don't have to bear the child care expenses.
Fortunately for us, blues prefer prey much smaller than the average human swimmer or diver. They relish a wide variety of fish including anchovies, dogfish, slender soles, sanddabs, blacksmith and even pipefish! Their favorite invertebrates include squid and the pelagic red crabs that occasionally enter our waters. They will also eat dead animals including seals, sea lions and whales. Since most species in "the mutual eating society" not only eat, but are eaten, blues fall prey to mako sharks, living sea lions and northern elephant seals.
Although the Native Americans apparently ate them, I mentioned last week that I did not find them worthy of preparation in my own kitchen! Dr. Love states that there have been attempts to develop a commercial fishery for them off California. However there is a rapid build up of urea in their bodies after death, making the flesh taste like ammonia and rendering it essentially inedible. Since fish caught on long lines often sit unharvested for "long" periods of time, this usually "effective" fishing technique doesn't work well with blues. However, Dr. Love says they make very good jerky. In my opinion, only a real jerk would jerk sharks. I'll stick to beef... or bison or turkey! When I was teaching at Toyon, I did tan several blue shark hides. I tried to use them to make shark skin moccasins in those "back to the Earth" days. Suffice it to say my shoe making skills are even poorer than my culinary ones.
© 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. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles" or "Gentle Giants: Giant Sea Bass" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!
Blue shark turning on a dime... or a hub cap, blue's
dorsal surface from above;
a close but harmless approach, the fishing hook embedded in the shark's jaw.
This document maintained by
Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia