During 8 of the past 14 days, I have been fishing and freediving 18 to 55 miles offshore from San Diego, and on every one of those days I have had multiple hammerhead sightings.
In addition to hammerhead sharks, our local offshore waters currently have populations of yellowfin and bluefin tuna that far exceed “normal” historical numbers. Most unusual is that there are bluefin tuna that have been caught by anglers and by spearfishermen that have been in excess of 200 lbs., which is also extremely rare for our waters. With the exception of what I will call a freak occurrence of some really giant bluefin (fish in excess of 600 pounds) for two summers circa 1987-88, large bluefin were pretty much absent since the 1920’s from our local Southern California waters.
Also currently present in our waters is a large population of striped marlin that are swimming in the waters west of Catalina Island, as evidenced by the catch reports from Thursday and Friday’s Annual Tuna Club Marlin Tournament, where the number of strikes was astonishing.
Yesterday the surface water temperature on the 9 mile bank was as high as 79.2 degrees; most of the surface ocean temperature offshore of San Diego is about 73 degrees. Yesterday two short-billed spearfish were caught in our local waters, again an oddity, but generally associated with more tropical conditions.
There are indeed many unusual things happening in our offshore waters.
Hammerheads Among Us
The numbers of hammerhead shark sighting that I have had recently could only be compared to those that I had seen back in the early 1980’s. Since the 1980’s I have been very concerned that the lack of hammerheads in our waters was an indication of overfishing by shark fin fishermen somewhere along the migratory path of the sharks. Today I feel encouraged that, at least off of Southern California, the hammerhead populations have returned, or rebounded, or recovered or some words that describe them as being more abundant than they have been in many years.
The behavior of the sharks that I have seen has varied substantially, however by far the most frequent behavior that I have witnessed is their almost manic behavior to feed. This puzzles me since there is so much that they have available to feed upon. Both the bluefin and yellowfin tuna that we have examined have been absolutely stuffed with primarily tuna crabs followed by sardines, mackerel, what I believe to be lantern fish, and flying fish. It is inconceivable to me that the hammerheads are not also feeding on the abundant prey species, but it appears that they have dietary demands for larger prey, the tunas for example.
I should point out that also in abundance are schools of small skipjack tuna, and while skipjack tuna is not unusual for San Diego’s water the abundance of the school of small skipjack is an oddity.
Back to the hammerhead’s behavior… They arrive at a stopped boat whether the boat is actively catching fish or not very quickly and when they arrive they demonstrate an active interest in feeding. Additionally their agitation level is quite high. These hammerheads are not swimming in and swimming away like blue sharks, and they are not darting in and dashing off like Mako sharks, but rather they hurry in and go on an active aggressive patrol and leave only when satisfied that there is absolutely no sign of food around.
As strange as this may sound, it would seem that the sharks recognize that people are fishing, then patrol under the boat until a fish is brought near to the boat. Then the hammerheads strike in a near frenzied behavior. I believe that the sharks have been conditioned to “boat stops, people fish, hooked fish come to the boat, shark feeding begins”.
Why the Hammerhead’s behavior is so much more blatant and aggressive than it is with Blue or Mako Sharks, I cannot say. Could it be that the reason that the diver back in August was bitten by a hammerhead was that the hammerhead thought that the boat above it was a fishing boat and that it had been conditioned to expect to find food? Only the Hammerhead knows for sure. One thing is for sure, there are many more fishing boats than dive boats especially offshore so you might want to consider that when you go blue water diving in areas known to have large tuna populations.
Respecting the Hammerheads
While we all enjoy diving and diving with a large variety of fish and mammals in the ocean and can even feel comfortable diving around apex predators, I think it wise to respect the hammerheads that have arrived off of our coast this summer. These are not six gills, they are not topes, they are in my opinion not even Blues or Makos in terms of their approachability, and they are not behaving like the docile mating hammerheads that arrive around the pinnacles in the Sea of Cortes. To me it appears that the hammerhead populations in our waters is far greater than the great white shark population, so the chances of encounters are greater with these seasonal hammerheads than with white sharks, again especially offshore, but not exclusively offshore.
The fact that there have been hammerhead sightings close to shore is no surprise given the abundance of them that I have seen offshore. Evolutionarily, they have been provided a special electro-sensory system that enables them to operate in water with limited visibility so seeing them in coastal water should not be considered unusual. Some hammerheads pup in Kaneohe Bay on the island of Oahu and those waters are often quite turbid. The young hammerheads thrive in those turbid waters and in order for there to be small hammerheads in those water there had to have been large hammerheads first.
Hammerheads will not keep me out of the water, but I will be diving with an elevated sense of awareness and upon sighting a hammerhead I might pause for a picture or two, but I will likely make my way back to the boat smoothly and cautiously.
Having an elevated sense of awareness even when coastal diving is a good thing.
Special thanks to Carl Robbins for this story.