October 29, 2009

Reef Check Swims with Sevengill Sharks in San Diego

By Reef Check California’s Southern California Regional Manager Colleen Wisniewski    

I’ve been diving and snorkeling in Southern California waters since 1997 and I pretty much expect to see the usual fish species on my dives, including kelp bass, garibaldi, blacksmith and various rockfish. However, over the last six months here in San Diego, I’ve been lucky enough to have several encounters with the broadnose sevengill shark (Notorynchus cepedianus). All of these sightings have occurred during Reef Check California training or survey dives. The first sevengill I saw was in La Jolla Cove in March of this year. I was a bit perplexed when I saw it – we rarely see such large fish on our surveys and I’d never seen a sevengill shark before. It was very exciting to observe something completely new to me, especially such a large animal. On several other dives in La Jolla Cove throughout the spring and summer months, I had the opportunity to swim with sevengill sharks and they seem to display similar behavior every time I see them – they swim towards me at a slow pace, will come within 3-6 feet and then continue on their way. Most seem to be approximately 5-7 feet in length.

Since March, I’d heard of other local divers seeing this species a bit further south in Point Loma. On October 11, we had a survey team of about 10 Reef Checkers surveying one of our sites in that area. It was a beautiful day with about 20 feet of visibility. At the start of the second dive, my buddy and I were the first divers in the water. Our goal was to complete a fish survey and to count and measure some urchins. About 2 minutes into my fish count, I saw something just out of my vision to the right. I was intent on correctly counting the fish on my transect line but I turned my head slightly and saw a 6 foot sevengill shark swimming at a slow speed, coming right through my fish transect. This shark was exhibiting the same behavior I’d witnessed in the past and I was able to snap two quick photos of this large fish before I got back to completing my fish survey. It was quite exciting to finally observe one of these on an actual fish survey.

As expected, the divers on the boat were excited about my sighting. Most of them have never seen this species in the wild and were excited to see my photos. A couple of these Reef Check divers have developed a keen interest in the recent observations of sevengill sharks and have developed a photo database to try to track the sightings in the San Diego area. This is another reason why the Reef Check California program is so exciting – not only do we collect data on all of our indicator species and invasive species, which are so important for informing marine management, but we can track rarely seen species and also potentially notice trends in species ranges- all that from teams of volunteer divers! I’m excited to see what these well-trained Reef Check California divers will observe next year!

\"\"About the Sevengill Shark Notarynchus cepedianus

According to FishBase (www.fishbase.org) the sevengill shark is found throughout the world in subtropical and temperate waters. The sevengill was named in 1807. It reaches a maximum size of about 3 meters and is carnivorous, eating other sharks, rays, bony fish, dolphins, porpoises and seals. Like many sharks, they are ovoviviparous, meaning that the fertilized eggs develop inside the mother but are not attached to the mother.  There are 82 to 95 young in a litter. Adults can be aggressive when provoked, and are regarded as potentially dangerous to people in open waters with attacks recorded in captivity and possibly off California and South Africa.

The Florida Museum of Natural History states that, “During the 1930s and 1940s, the sevengill shark was quite common in the shark fisheries along the coast of California. Although the commercial fishery soon collapsed, recreational shark fishing for this species became popular. However, this fishery declined in the late 1980s and 1990s with recreational fishers targeting other species. Today the sevengill shark is caught primarily by anglers as well as incidental bycatch in commercial fisheries targeting other species.

Currently, the California population of sevengill sharks appears to be concentrated in the Humboldt and San Francisco Bays. These two areas provide nursery areas and safe havens for juveniles. The future of the sevengill shark in this region is highly dependent upon the conservation of these habitats.”