Friend Feature: Pacific Spiny Dogfish
Dogfish swimming in the Puget Sound. Image by Florian Graner
Pacific Spiny Dogfish Squalus suckeyi
One of the most common questions about what lurks in the Salish Sea is, “Are there any sharks here?” And the answer is, yes! There are sixgill sharks, salmon sharks, and even the rare basking shark in the Salish Sea, but there’s one shark that stands out from the rest. Why? Venomous. Spines. This month’s creature feature spotlight is on the Pacific spiny dogfish (Squalus suckleyi). Spoiler alert: though cute and smart, they don’t look anything like dogs.
Spines aren’t just for looks
A Steller sea lion satisfies its appetite with an oil-rich dogfish, who has had better days than this one. Image by Traci Walter
The Pacific spiny dogfish has two spines in front of its two dorsal fins on its back that it uses for defense against predators, such as sixgill sharks, seals, and sea lions. These spines inject a mild venom when they come in contact with an object, like when a rattlesnake’s fangs pierce its prey. Predators must be skilled at avoiding these spines. These spines give the dogfish its other nickname of “spiked dogfish.”
Speaking of looks, the dogfish also has super scales! In fact, all sharks have a rough skin that is covered in tooth-like scales called “placoid denticles.” The root dent means tooth in Latin (dentist, dental, dentures…), so yep, you got it, their scales are like little teeth. Sharp teeth! These scales are so rough that dogfish skin has been dried and used as sandpaper. Have you pet a dogfish today? Do it if you get a chance.
Baaa-byy shark do doo do doo do dooo
Some sharks lay eggs in cases, called “purses.” Their pups are nourished by yolk sacs in the egg. Other sharks grow their babies in a uterus, nourished by an umbilical cord, just like people and other mammals. But still other sharks, like our dogfish friends, do a combination of these things. Dogfish females grow their pups inside of eggs inside of their bodies until they are ready to fend for themselves. Evidence suggests that female dogfish can’t have pups until they are around 35 years old and males around 19 years old (Pacific spiny dogfish are believed to live to be more than 80 years old!).
After internal fertilization, little teams of fertilized eggs are surrounded in thin shells, called candles. Then they are pregnant for nearly two whole years, the longest gestation period of any animal on Earth. When they’re ready, they just swim right out of mom and are ready to take on the Pacific Ocean. You can see this process in a surprising location: a tank in a sushi restaurant, in the video. It has a very happy ending.
Females can have around 4-22 babies at a time. When the pups are born, they are about 10 inches long and filled with feisty attitude. Immediately, the young are able to hunt for live prey and sometimes even go after fish two or three times their size. Pacific spiny dogfish can grow to about four feet in length and 20 pounds (Great white sharks can grow to over 20 feet long and 7,000 pounds!). Goes to show that it’s not the size of the dog(fish) in the fight, it’s the size of the fight in the dog(fish).
Natural born travelers
Pacific spiny dofish swimming amongst soft corals in the deep sea of Olympic Coast National Marine Sanctuary. Image by NOAA's 'Arc' remotely operated vehicle (ROV).
Sometimes ya just gotta travel. The Pacific spiny dogfish regularly travels long distances. A dogfish that was once tagged in Washington State was tracked and seen to have travelled over 5,000 miles… to Japan! Still not impressed? They can live in shallow waters, but they also live in waters that reach depths of 3,000 feet. How deep can you dive? It is believed that the dogfish will hang out in deep depths during the winter months, and they will return to shallower depths in the summer months to feed and give birth in warmer waters.
Humans are not on the menu
While humans don’t have much to worry about with dogfish, the dogfish actually have some concerns with humans. People catch and consume dogfish regularly!
What do they eat? Dogfish eat a variety of foods, including fish, octopus, jellyfish, crabs, squid, shrimp, krill, and more. They are not picky, but they are persistent and feisty when they hunt. Their name of “dogfish” comes from their behavior of hunting in packs that can sometimes reach hundreds or thousands of others. Though they are small and don’t bother humans, that could still be pretty intimidating for even the bravest of creatures!
Relationship status
Humans and Pacific spiny dogfish could get along better. Well, humans could treat them better, and the sharks can keep doing their sharky thing. In the last 75 years, Pacific spiny dogfish populations have declined more than 30 percent, primarily due to human-related causes. This means we can fix it! Dogfish are oftentimes caught as bycatch, which are the unwanted species accidentally caught in commercial fishing practices. Some places in the world, including the US, purposefully target the sharks for their fins and meat.
Because we don’t understand much about their lifecycles, it is a challenge to plan a sustainable fisheries program to ensure that we don’t take too many or damage their habitats. With the little knowledge we have, it appears that spiny dogfish are not currently being overfished on the West Coast of the U.S., but we still have a lot to learn. These sharks are considered keystone predators, which means that they greatly influence the entire food web within their ecosystems. This makes it super important to know how to manage them and track their populations.
Anyone want to be a shark scientist?
Maybe someday, someone like you could be involved in the science and biology that it takes to make sure that these special creatures are managed properly for future generations to come! And if science isn’t your jam, maybe you can consider advocating for the sharks in another way, like limiting use of plastics and cleaning up our oceans. Fight like a dogfish for a healthy Salish Sea!