Bark if you love today’s featured creature, the Spiny Dogfish! At MSI, we like to bring attention to distant and exotic species, but also to creatures that we deal with on a daily basis, whether in our Discovery Aquarium or on board our ship. However, despite being a common resident of the San Francisco Bay, Spiny Dogfish can be tough to catch! In my 9 years of working at the Marine Science Institute, I have only caught the spiny Dogfish (Squalus acanthias) once when the R/V Robert G. Brownlee left port from the Richmond Marina. These are very small sharks and can grow to 3-4 feet.
You might think that this shark has a funny name, but let me break it down for you. Spiny may not be a word that springs to mind when you think of sharks, but it describes these ones pretty accurately. Spiny Dogfish get their name from the venomous barbs that stick out from the front part of their dorsal fins (Watch out for those! Ouch!). As for being a dogfish, that is more of a reflection of their behavior. Like dogs or wolves, dogfish feed in packs and can roam the waters in groups of over one hundred, eating anything that they can fit into their mouths. In addition to hunting in the buddy system, dogfish have tremendous endurance. The geographic range of this species is truly amazing! One Spiny Dogfish was recorded making the journey from Washington State to Japan – a trip of approximately 5000 miles! And I thought my commute was long!
Like the sharks highlighted in our previous posts, Spiny Dogfish are ovoviviparous, which means that the embryos are contained in a placenta yolk sac. They receive their nutrition this way, instead of directly from the mother as is normal with mammals. Ovoviviparous mothers still do their part to keep their babies healthy by helping with gas exchange. A gas exchange is when gases, like oxygen, are transferred in opposite directions. The gestation period (which is the time between fertilization and birth) for the Spiny Dogfish is one of the longest in the animal kingdom – 22 months! Once the young are born they will continue to feed on the yolk sac until it is depleted and falls away. Though some of the sharks we’ve discussed in previous posts only have a life expectancy of 15-20 years, the Spiny Dogfish matures at age 20 and can live up to 100 years.
Due to the long lifespan, later maturity, and the rate of fishing of this species Spiny Dogfish are regarded as “Vulnerable” in the Black Sea, “Endangered” in the Mediterranean, and “Vulnerable” and “Critically Endangered” in the Northeast Atlantic on the IUCN Red List of Threatened Species. Throughout history the regulations that have been made for the protection of dogfish have not been highly enforced throughout the world. Check out http://www.iucnredlist.org/details/39326/0 for more information on the status of dogfish and other creatures.
Tune in next week while we head to the West Coast South America territory to learn about the top four dangerous sharks.
Edited by KC O’Shea