The basking shark, Cetorhinus maximus, is the second largest fish in the world and the largest shark that lives and feeds in the waters off New England. Basking sharks are sighting in New England waters during the spring, summer, and fall, yet little is known about their distribution and movements offshore. The basking shark is that largest fish that is often seen traveling or feeding near the water's surface. This behavior is why their common name in the United States is the "basking" shark. Basking sharks are widely distributed throughout the world's oceans, in temperate and tropical waters. Other common names for this species include boneshark, elephant shark, and sail fish. Although a massive and powerful fish, basking sharks are harmless and are considered a gentle giant of the ocean.
Classification
- Kingdom - Animalia
- Phylum - Chordata
- Class - Chondrichthyes
- Order - Lamniformes
- Family - Cetorhinidae
- Genus - Cetorhinus
- Species - maximus
The scientific name of the basking shark is Cetorhinus maximus which translates to "big-nosed sea monster." Basking sharks belong to a group of cartilaginous fish called the elasmobranchs for their skeleton is made up of cartilage instead of bone. Basking sharks have a nose that is quite large, especially for the adults. When feeding at the water's surface, a basking shark's nose often protrudes out of the water, as well as its large, sail-like first dorsal fin. Often, the tip of the tail fin (caudal fin) will be visible just behind the dorsal fin. Don't mistake the tip of the tail fin for the dorsal fin of another basking shark. Unlike a dorsal fin, the tail fin sweeps slowly in a side-to-side motion.
Biology
Basking sharks that are observed in our New England waters are typically 20 to 28 feet in length and weigh close to several tons. However, adults have been recorded at lengths of over 40 feet, weighing close to 19 tons. The only shark larger than a basking shark is the whale shark, a more tropical species that also filters plankton from the water.
Basking sharks are a coastal pelagic species for they feed in cold temperate waters during the spring, summer and fall and then migrate to warmer, more tropical waters each winter. Although a slow swimmer, basking sharks are constantly on the move and therefore, can cover large distances in a short period of time. When disturbed, basking sharks have been known to jump out of the water, a behavior called breaching.
Feeding
Basking sharks filter their food out of the water using bristle-like structures called gill rakers located near the gill structure in the back of their throat. Gill rakers strain copepods and other types of zooplankton out of the water as water move over the gills and out the 5 large gill slits near the back of the head. Basking sharks are passive filter feeders that must keep moving to ensure that a constant flow of water passes over the gills. This is called ram filter-feeding.
Basking sharks are very selective about what they eat and focus their diet on small-sized species of zooplankton that include: copepods, fish eggs, and fish larvae. To consume large quantities of these tiny organisms, basking sharks keep their mouths wide open as they swim slowly through a plankton patch. When feeding, the opening of the mouth is approximately 1 meter wide and this creates a funnel-like opening for water flow. Inside the mouth, the gill supports are white, but when viewed under the water, they appear greenish in color due to the microscopic phytoplankton suspended in the water column. Look for a greenish patch near the mouth of a basking shark and you can often tell if that animal is feeding or just traveling near the surface. As water passes over the gills, bristle-like structures called gill rakers trap the zooplankton as the water flows over the gills and out of the body through a series of 5 gill slits.
When filter feeding, a basking shark passes 1.5 million liters of salt water over the gill structures per hour. As the shark slowly swims through the plankton with its mouth wide open, this animal creates a set-up similar to that of a plankton net that a scientist or biologist would use. Both the shark and the plankton net have a wide opening that tapers down to a smaller collection area. Both have some type of mesh-like structure that traps small organisms out of the water. Although we can see the similarities, it is still hard to understand how a fish of this size can survive on such tiny food or prey. However, zooplankton are close to the base of the marine food chain, and therefore, are packed with energy making them quite nutritious.
Ecology
Although the basking shark is found in temperate and tropical waters worldwide, the biology and ecology of this species is not well understood. What we do know is that this pelagic species travels great distances from high latitude waters in the spring and summer to low latitude waters in the fall and winter. These types of seasonal movements are similar to other big fish and many big whales, who utilize different geographical areas over the course of the year.
In the spring, basking Sharks in the northern hemisphere migrate to high latitude areas to feed in cold productive waters throughout the spring and summer. As fall approaches, they being their migration south to warmer, more tropical waters. There basking sharks spend little time on the surface as they potentially feed over the course of the fall and winter. Crossing international borders means that any meaningful research or conservation activities for basking sharks must be done in a collaborative manner and on an international basis.
Photo-Identification of Basking Sharks
Photographs taken of basking sharks can be used to identify individuals within a population. The collection of pictures and their analysis can help researchers better understand the migration patterns and behaviors of basking sharks in general and individual animals as well.
Basking sharks can be identified by observing individual characteristics, which include:
- markings on the body, including scratches, scars, and white patches
- size and shape of the dorsal fin
- cuts and notches on the dorsal fin, pectoral fin, and caudal fin
- natural pigmentation patterns along the length of the body.
Tips when Photographing Basking Sharks for Photo-ID
- Set your camera to the highest resolution and fastest shutter speed.
- Ensure that the sun is not in the background of the picture.
- Take photos of the dorsal fin from both sides, if possible.
- Take photos of the tail and snout of the shark.
- Take photos of the animal's mouth to see if it is open (feeding).
Basking Shark or Ocean Sunfish?
In our New England waters, the two large fish that are typically seen at the water's surface are the basking shark and the ocean sunfish (Mola mola). For both species, what attracts your attention is often a large dorsal fin visible above the surface of the water. It is helpful to get a good look at the size, shape, and movement of this fin to help you determine whether you are looking at a basking shark or an ocean sunfish. Don't forget that basking sharks have two dorsal fins and the first dorsal fin is quite large and triangular in shape. Ocean sunfish only have one dorsal fin that is more pointed and elongated.
The first dorsal fin on a basking shark is located in the middle of the body, past the insertion of the pectoral fins. This fin is typically erect and for adults, can be 1 meter tall. The second dorsal fin is much smaller in size and is positioned behind the first dorsal fin and forward of the caudal or tail fin. For some reason that is not understood, a small number of individuals have a first dorsal fin is not erect, but instead, flops over onto one side of the animal's body.
Ocean sunfish also have a tall dorsal fin, but the shape is not as triangular as that of the basking shark. When swimming at the surface, an ocean sunfish will often swim on its side as it repeatedly lifts the dorsal fin in and out of the water. This behavior is called skulling and is quite unique to this species. By examining the movement of the dorsal fin and the overall swimming pattern of the animal, you can distinguish between these two species. If you see the dorsal fin cutting smoothly through the water in a forward motion, then you are looking at a basking shark. If on the other hand, you see that the dorsal fin is being skulled above the water's surface, then you are looking at an ocean sunfish.
The video below illustrates the different swimming patterns between a basking shark and an ocean sunfish swimming at the water's surface.
.Conservation
The basking shark is listed as Protected in the waters of the United States. This means that if you catch a basking shark on a fishing line or in a net, you must immediately release it back into the water. Internationally, the basking shark is currently listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). They are also listed as Vulnerable on the IUCN (International Union for the Conservation of Nature) Red List of Threatened Species. The basking shark has specific life history characteristics that puts this species at risk when faced with a changing environment. These biological characteristics include a long lifespan, a slow growth rate, and a low birth rate. One major threat for basking sharks and all marine organisms is climate change and the impacts and consequences of warming oceans. It is unclear how copepods and other zooplankton species will respond to warmer waters in terms of impacts on their abundance and distribution. If there are significant changes in prey abundance, it is not clear how this will impact the survivability of basking sharks and their distribution in New England waters and waters worldwide.
Fisheries on Basking Sharks
The life history characteristics mentioned above also played a key role in the decline of basking sharks due to directed and non-directed fisheries. In New England, as in other parts of their worldwide distribution, basking sharks were fished for their oil, meat, and skin. The large liver of the basking shark contains a fine oil that was valued for lighting and in the tanning process. The meat was eaten in many areas and their skin was used in the shark leather industry. By the 1950’s, many of these fisheries had collapsed due to significant declines in population numbers. It was clear that this species could not withstand any type of directed fishery conducted over a prolonged period of time.
Although there has been a falling demand for basking shark products since the 1980's, a new market for their fins has brought life back into this fishery. Filling the demand of shark fins for shark fin soup, a delicacy in East Asia, is once again putting pressure on many basking shark populations.
One way you can help to protect basking sharks on a worldwide basis is not to support any type of basking shark fishery. Do not purchase anything that contains basking shark tissue or material. Be a choosy consumer and know that what you choose to spend your money on, has great impact on many population of wild animals around the world.
