Shark Habitat Studies

Biologists with the Fisheries Resources Division determine Essential Fish Habitat (EFH) for pelagic sharks along the U.S. West Coast in order to support the Pacific Fishery Management Council's efforts in developing a Fishery Management Plan (FMP)The previous link is a link to Non-Federal government web site. Click to review NOAA Fisheries disclaimer for highly migratory species.The species listed under this FMP are blue shark (Prionace glauca), shortfin mako shark (Isurus oxyrinchus), thresher shark (Alopias vulpinus), pelagic thresher (Alopias pelagicus), and bigeye thresher (Alopias superciliosus), and researchers also opportunistically monitor the white shark (Carcharodon carcharias). These studies help determine the areas within the U.S. Exclusive Economic Zone (EEZ) that are occupied by our migratory pelagic sharks and how best to manage them.

 Sea surface temperature (SST) off the Pacific West Coast. Cooler temperatures are seen north of Point Conception and warmer temperatures are seen in the Southern California Bight. Image credit NOAA.  Various currents and upwelling domains influence the oceanic habitat off the Pacific West Coast. Image credit NOAA.


Essential Fish Habitat


EFH is defined as "waters and substrate necessary to fish for spawning, breeding, feeding, or growth to maturity" and determining these areas involves assessing environmental, biological, and anthropogenic variables. The Pacific West Coast is a complex oceanic system with the south-flowing California Current, the inshore countercurrent, shifting subarctic and subtropical frontal zones, and coastal upwelling areas all changing position and intensity over time. Diverse bathymetric features such as basins, ridges, seamounts, canyons, and wide continental shelves affect the distribution of shark species. Additionally, sea surface temperatures (SST) are generally cooler north of Point Conception and warmer south, creating a natural barrier for species that tolerate only a certain range of temperatures. All these oceanic features affect the pattern and distribution of pelagic rays and sharks throughout the entire west coast region.  

Researchers determine shark habitat range by analyzing observed catch from fishery observer records, skipper bridge logs, and recreational fishing boat log data. Movement data from tagging efforts are also important to consider, as many of these species are highly migratory and will spend only certain life stages in these habitats. Three life stages of observed catch were considered in habitat utilization:

  1. Neonates and small juveniles: post-partum and young pups (less than 2 years old). Occurrence indicates possible pupping grounds and early juvenile feeding areas.
  2. Large juveniles and sub-adults: Immature fish (older than 2 years). Occurrence may show increased mobility patterns and more migratory behavior.
  3. Adults: Sexually mature fish. Occurrence may show mating grounds or parturition grounds.

Although migratory, most of these sharks regularly occupy EFH within the US Pacific Coast EEZ (pelagic thresher in warm water years). The area is variously important as nursery, feeding, and pupping grounds for these species and most show distinctly different distribution patterns with sex and life stage.   



 Blue Shark Habitat

 Essential Fish Habitat (EFH) of the blue shark (Prionace glauca).


Blue shark (Prionace glauca). Image credit Walter Heim.


Neonate and juveniles: less abundant than adults and they are distributed in epipelagic, oceanic waters throughout the US West Coast EEZ from the Mexico border north to the Canada. Pupping seems to occur offshore, then fish move to inshore waters where they generally occur beyond the continental shelf (seaward of the 100 fm isobath).

Large juveniles and adults: occur throughout EEZ from 100 and 1000 fathoms (fm) isobath out to and beyond boundaries. Most blues are juveniles (avg 110 cm FL), unlike in Hawaii where most are adult fish (avg 180 cm FL). Sex ratio near 1:1 in very young fish until about 100 cm FL, then males begin to dominate and females decline in catch with a ratio of about 1.8 males to each female. Adult females are more often found north of Monterey and adult males south of Monterey.


  


Mako Shark Habitat

Essential Fish Habitat (EFH) of the shortfin mako shark (Isurus oxyrinchus).



Shortfin mako shark (Isurus oxyrinchus).


Oceanic and epipelagic from the US-Mexico border northward to Washington, but most common off California. Mako sharks occur from the surface to at least 150 m depth, with catches associated with sea surface temperatures ranging from 15°C to 25°C.


Neonates and juveniles: usually less than 101 cm FL and mainly occur south of Eureka, CA. Inhabit mainly inshore (100-2000 fm and 100 fm) waters and then extend further offshore when north of Monterey, CA. The sex ratio of juveniles appears to be 1:1 and nursery habitat utilization appears to be concentrated in the Southern California Bight south of Los Angeles.

Large juveniles and adults: Males mature at a much smaller size than females (>170 cm FL males; >248 cm FL females), however 99% of the mako sharks encountered off the west coast are males; adult females and large males seldom occur in the EZZ except occasionally around the California Channel Islands and outer banks of the Southern California Bight in late summer and early fall.

 


 Thresher Shark Habitat

Essential Fish Habitat (EFH) of the thresher shark (Alopias vulpinus).



Thresher shark (Alopias vulpinus).


Threshers prefer areas associated with high biological productivity and an abundance of the small schooling fish upon which it feeds within the epipelagic zone above 200 meters, often near or at the surface. Habitat occurs entire length of the EEZ from about 6-1900 fathoms; out to about 127°W north of Mendocino Escarpment. Preferred SST is 56°-72°F.

Neonates and juveniles: Young pups occur primarily inshore along beaches and shallow bays (6-400 fm. deep) from the US-Mexico border to off Santa Cruz, CA (37°N latitude). They occur primarily in water less than 100 fathoms.  

Large juveniles and adults: Occurs the entire length of the EEZ, however adults occur especially off Oregon and Washington, with sub adults south of San Francisco. Mean observed size is 165 cm FL, Juveniles occur in open coast, bays, and offshore, ranger further north to off Pigeon Point, CA and sometimes to San Francisco Bay during warm water years. Adult threshers also occur off beaches but tend to occur in deeper water and further north seasonally to Cape Flattery, WA. but then to occur in deeper water and further north seasonally.  



Pelagic Thresher Shark Habitat

Essential Fish Habitat (EFH) of the pelagic thresher shark (Alopias pelagicus).



Pelagic thresher shark (Alopias pelagicus).

The more tropical pelagic thresher shark generally moves into California waters during periodic warm water episodes relating to El Nino conditions, being more abundant to the south off the Pacific coast of northern Mexico. When it occupies epipelagic habitat within the US West Coast EEZ, it usually does not range north of southern California waters. Associated with sea surface temperatures 21°C and warmer.

Neonates and juveniles: Only a single neonate was observed in the Southern California Bight, near the Mexican border, according to the time period analyzed.

Large juveniles and adults: Occur primarily south of Point Conception in warm water years, east of Santa Rosa-Cortes Ridge where water is warmest. Half are adults and half are large juveniles. Females outnumber males 5:1 and 41% of females were found to be pregnant. No discernible difference in distribution among stages. 




Bigeye Thresher Habitat

Essential Fish Habitat (EFH) of the bigeye thresher shark (Alopias superciliosus).



Bigeye thresher shark (Alopias superciliosus).

An epipelagic and mesopelagic species occurring off the US West Coast from the Mexico border north to off Cascade Head, Oregon. Ranges deeper than the other thresher species, at depth down to 723 meters and can reportedly stay in cooler water for longer periods of time than other pelagic sharks.

Neonates and juveniles: Juveniles occur mostly south of 37°N latitude but there is no evidence of nursery habitat within the US West Coast EEZ and pupping probably occurs elsewhere. Females dominate the juvenile population by 4:1.

Large juveniles and adults: The population off California are predominantly adult males (71% of the observed catch) and are distributed offshore in north, inshore in the south, though could be due to effort pattern. Adults extend farthest north to 45°N latitude, males dominate 9:1.  




White Shark Habitat

Essential Fish Habitat (EFH) of the white shark (Carcharodon carcharias).




White shark (Carcharodon carcharias).


Neonates and juveniles: White sharks are born at a total length of 110-160 cm total (TL) and the Southern California Bight appears to be a nursery area for the species, between Point Conception and the US-Mexico border. 

Large juveniles and adults: Larger juveniles and adults occur more frequently north of Point Conception. Along the US West Coast, they are distributed sparsely along the coast with small groups of individuals observed near major pinniped rookeries, especially around colonies of the northern elephant seal. Most white shark interactions with seals and sea lions at the Farallon Islands rookery off central California occur in shallow water from 4-12 m (2-6.6 fm) deep. The majority of white shark capture records off the U.S. West Coast have been over bottom depths less than 80 m (44 fm) with the median depth 20.6 m (11.3 fm), though some were taken in water as shallow as 5.5 m (3 fm) and as deep as 366 m (200 fm). Documented white shark attacks on humans (1926-1983) are primarily close to shore, occurring from San Miguel Island, southern California, north to off Cannon Beach, Oregon. 

Until recently, white sharks off the US West Coast were thought to be restricted only to relatively shallow waters over the continental shelf as described. But recent satellite archival tagging by Boustany et al. (Nature, Vol. 415, 3 Jan 2002), has revealed another oceanic pelagic and deeper water existence as well. Four white sharks tracked for 4-6 months experienced a near-shore phase, then moved offshore where they remained exclusively pelagic, one traveling 3,800 km to waters off Hawaii, and others southwestward to a region of the subtropical eastern Pacific off Mexico.


Last modified: 12/8/2015