Shark Food Habits Studies


 
  
Collection locations for bigeye thresher shark (Alopias superciliosus) stomach samples (left) and the subsequent results of geometric index of importance (GII) analyses for the 20 prey taxa (right). 


Shark biologists at the SWFSC investigate the feeding habits of various sharks off the US west coast by analyzing stomach contents of samples as they become available from natural mortality or fishery interactions. Species include the shortfin mako shark (Isurus oxyrinchus), blue shark (Prionace glauca), thresher shark (Alopias vulpinus), bigeye thresher shark (Alopias superciliosus), white shark (Carcharodon carcharias), and others. While sharks are known and feared for their occasional attacks on humans, the majority of species prefer a diet of small fishes and invertebrates. A few (like the adult white shark) appear to prefer larger prey such as marine mammals, large fishes and other species of sharks. Some, like the tiger shark and blue shark, even include seabirds in their diets.



Watch SWFSC biologist Antonella Preti at work investigating shark food habits:

 NOAA Video: A Mako Shark's Last Meal The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries disclaimer

SWFSC shark biologist, Antonella Preti, studies shark food habits by looking at stomach contents of sharks in the Southern California Bight.



Thresher Shark Food Habits

Analysis of 185 thresher shark stomach samples collected from the California/Oregon (CA/OR) drift net fishery revealed the following prey items: Northern anchovy, Pacific sardine, Pacific mackerel, California barracuda, Pacific hake, pelagic red crab, louvar, grunion, jack mackerel, shortbelly rockfish, market squid, and euphausiids.

By sampling stomach contents of bigeye threshers caught from Cape Mendocino down to San Diego, researchers found that teleosts of the family barracudinas (Paralepididea) were the most important prey item in number, frequency, and weight. Other dominant teleost prey included Pacific hake (Merluccius productus), Pacific saury (Cololabis saira), Pacific mackerel (Scomber japonicus), and northern anchovy (Engraulis mordax). They concluded that the bigeye thresher shark appears to be more of a generalist and opportunist than the other sharks of the Southern California Bight (SCB), with the possible exception of the blue shark. A broad range of prey from mesopelagic, epipelagic, and epi-benthic habitats was observed in the stomachs of only 23 individuals.

Read more here.


Mako Shark Food Habits

The prey of the shortfin mako is known to include a variety of pelagic fishes including mackerels, bonito, anchovies, herrings, grunts, lancetfishes, cod, salmon, dorado, small sharks and squid. Looking at fishing catches from commercial operations, it appears the species feeds predominantly during the day. The stomach of an 11-ft (3.4 m), 986 lb female taken near Santa Barbara Island contained remains of a young harbor seal, a small common dolphin, and vertebrae of one or more unidentified small sharks. The stomach of a 9 ft (2.7 m TL), 402-lb male caught near Santa Monica Bay, CA, was found to contain remains of a billfish, tentatively identified as striped marlin, plus another unidentified teleost.

Watch this research in a NOAA Video: A Mako Shark's Last Meal The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries disclaimer



Blue Shark Food Habits

In coastal waters off the U.S. West Coast, blue sharks reportedly feed on anchovy, mackerel, hake, dogfish, squid and pelagic crustaceans including euphausiids (Tricas 1979; Harvey 1989; Brodeur et al. 1987). Elsewhere also known to feed also on small sharks and seabirds (Compagno 1984). Sciarrotta and Nelson (1977) noted that species seemed to feed around the clock but was more active at night, with highest activity in the early evening. These authors observed a twilight movement from offshore to shallower waters around Santa Catalina Island, California, during March and June, but a shift to offshore waters during late June to October, suggesting a response to a change in prey availability.


White Shark Food Habits

White shark (Carcharodon carcharias).

According to Compagno (1984), large white sharks above 3 meters long tend to prey heavily on marine mammals, while smaller sharks below 2 meters long generally feed on bony fishes and small sharks. In-between sizes evidently feed on a mix of both (e.g., Fitch 1949). McCosker (1985) and Tricas and McCosker (1984) have pointed out that the tooth shape of juveniles and sub adults (less than 3-4 m TL ) is longer and narrower than that of adults, which allows them to grasp small bony fishes and elasmobranchs, but lacks the cutting ability of the broader tooth of the adult. The smaller young are also considered more agile with better turning abilities with which to better capture quickly moving fish prey. Juvenile northern California white sharks are known to feed on California bat ray, spiny dogfish, leopard shark, soupfin shark, smoothhound sharks, lingcod, Pacific sardine, king salmon, Pacific hake, white seabass, rockfishes, and cabezon, while the adults feed heavily on northern elephant seals, also harbor seals and California sea lions and occasionally some fishes and crab, including Pacific hake and sharks (including the basking shark) and Cancer spp. crabs.

White sharks are also known to attack northern fur seals, Steller sea lions (Eumetopias jubatus), sea otters (Enhydrya lutris) and leatherback sea turtles (Dermochelys coriacea), but these are not considered regular diet items (Bonnot 1928; Orr 1959; Ames and Morejohn 1980; Long 1985). They occasionally prey on small odontocetes along the U.S. West Coast and scavenge on carcasses of large cetaceans, but in general predation on cetaceans is uncommon (Long and Jones 1985). Because of the apparent reliance of U.S. West Coast white sharks on pinnipeds, especially the northern elephant seal, major rookeries are considered vital fish habitat sites for this species. The two largest colonies (for both elephant seals and sea lions) are located on the Southeast Farallon Islands and Aсo Nuevo Island (Long et al 1985; Stewart et al 1994, Mark Lowry, NMFS, pers. comm. 5/00) These and other northern elephant seal rookeries represent a massive expansion of the population over the last century, which was presumed extinct by 1892 owing mainly to commercial harvesting for blubber oil that began in the early 1800s. A small residual breeding colony survived at Isla de Guadalupe off central Baja California Mexico, and with legal protection, rebounded rapidly through the early 1900s, with immigration to other sites in California and Baja from which additional colonies were also established as far north as the Point Reyes Headlands, California (Stewart et al 1994). The population is thought to be still expanding with haul-out locations now extending as far north as Cape Arago, Oregon and Vancouver Island, British Columbia --possible locations of future breeding colonies (ibid). While this expansion has likely contributed to an increase in U.S. West Coast white sharks, even the largest rookeries support relatively small white shark populations that have the capability of being swiftly reduced by very little fishing effort (Ainley et al 1981).


Selected publications:


Last modified: 12/8/2015