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Fishermen's Journal

A Brief Synopsis of Study

Shark Feeding Study

by Chris Huff

The Friday night San Pedro-to-Avalon boat was passing the pilot station headed toward the breakwater when I noticed the little boy seated in front of me, nose pressed to the window, straining to see into the darkness outside. Intrigued by his curiosity, I watched as his mother asked if he was looking for sharks. He nodded that he was. I smiled in anticipation of the conservation lesson I knew Mom was about to deliver to her inquisitive six year old, when she leaned over and said, “Don’t fall in or the sharks will eat you up for a snack.” So much for the conservation lesson.


The irony of her statement came back to me when our chum line brought the first Blue shark to the boat after an hour and forty-two minutes of sloshing mackerel blood and guts off the swim step into the slow-drifting current. I began to think about the number of people who believe that all you have to do to find sharks is fall overboard.


My colleagues (Ron Moore & Rob Fazio) and I are working on a prey capture behavior study of Blue sharks (Prionace glauca) off the coast of Catalina. The premise is relatively simple: sharks come to the boat, we put food into the water, the sharks eat the food, we videotape the feeding sequences and then use a frame-by-frame VCR to analyze how the shark uses its jaws. Actually, it’s a bit more complicated than that. To be technically correct, we are looking at food capture kinematics (how the shark uses its jaws without consideration for the force applied by the biting movement, which would be mechanics) rather than behavior in an ethological sense, in other words, how the shark uses its jaws rather than how does it behave while feeding, although there is a behavioral aspect to what we’re doing.


Unlike you and me, the shark has an upper jaw that is separate from, but is attached to, its cranium. In a sense, the upper and lower jaws “float” in the shark’s mouth. Think of pictures of a great white opening its mouth to bite a bait and the jaw moving forward looking as if it’s about to leave the shark’s mouth. The farther a shark can extend its jaws, the wider gape it can produce, theoretically resulting in a larger selection of variably-sized prey items, resulting in a more effective cutting angle for the teeth, and increasing the likelihood of capturing the intended prey. In addition, some shark species have a tissue hinge in the front (symphysis) of both jaws that may add to the utility of the jaw design. Evolution at work.


Our study is multi-faceted. We hope to find out if the Blue shark modulates or changes how it uses its jaws in response to a variety of scenarios, i.e., large pieces of food items compared to small pieces, taking food items high or low in the water column, taking food items above, below, or to the side of its head, etc. We’ll use different prey items (squid) as well as examine what feeding method or combinations of methods (suction, ram, or bite) are used by blues. You can see how quickly a simple premise becomes complicated.


Of the four days we spent on the water, we found sharks two of those days, both at Avalon Banks, an occurrence that makes good sense if you think like a shark. They tend to be opportunistic feeders and will likely be found near food sources. Anglers go to where the fish are, why wouldn’t sharks?


            Once we had a shark at the boat, we continued to chum, waiting to see if it was going to stay. If it stayed, it was time to get in. The sharks wouldn’t tolerate scuba. We tried a couple of times, but they left each time a diver got in with tanks. So the tanks stayed on the boat, and we used weights, masks and snorkels. I could touch the blues from the swim step without having any apparent effect on their behavior, but scuba drove them away. Once the videographer was in place in the water, we put pieces of mackerel in and filmed the feeding sequences for later analysis. Since the sharks won’t take cues from us as to where and how to take the food items, it’s difficult to get all the specific shots you want in one or two sessions in the water. The scarcity of sharks also slows down the process. Quality science, however, is generally not done in a hurry.


We had a juvenile Shortfin Mako (Isurus oxyrinchus) at the boat each of the two days we found sharks, and it was interesting to observe the differences between the two species, aside from size and shape. Where the blue is a slow, graceful, deliberate swimmer, the mako appears agitated or in a hurry. Although the mako was smaller (3-4 ft), the larger blue (5-6 ft) swam away as the mako followed the chum line to the boat. The blue returned once the mako left. We were fortunate that one blue had rake marks on its head and the other, a slice in its right pectoral fin, which allowed us to identify positively each of the blues.


As expected, the sharks bumped the video camera, responding to its electronics. For the most part, the sharks seemed to tolerate us being in the water. They circled around the swim step where their sensory organs indicated the scent trail ended, swimming past us as need be. One blue violated my comfort zone, and a poke on the snout sent him away, only to return to the boat a few minutes later. Keeping our attention focused on the sharks, we spent thirty minutes or so in the water with these most amazing of predators.


The only time we felt it best to get out of the water was when one of the blues began acting in what appeared to be an agitated manner. Side-to-side head snapping and aggressive bites on the swim ladder suggested it was time to dry off. My experience with sharks in the water leads me to believe discretion is always the better part of valor. No ego here.


Reading the shark-related postings to this site, I’m encouraged to see a conservation thread running through them. No need here for me to wade into the abysmal statistics regarding sharks. Attention is being focused on diminishing shark populations. Progress is being made. There is reason to be encouraged.  For those of you who have seen sharks in their habitat doing what they have done for millions of years, consider yourself fortunate. Very few people get the chance. Let’s be sure we’re doing what we can to ensure the shark’s place in a healthy, vibrant ocean ecosystem.


Comments, questions, suggestions? Email me at chuff8@sbcglobal.net

I met Chris via this site a couple years back when he was working on his masters degree.  He found the website searching out info on sharks, his marine animal of interest.  We swapped tales, offered a few tee shirts for an event he was involved in.  He got a hold of me about a year later and let me know about his study, and of course I asked for some info to pass along.  Along with the info, his cohort Rob Fazio supplied some super photos of the sharks they were studying. 


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Last modified: 06/09/13.