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COSEWIC Assessment and Status Report on the Basking Shark (Pacific population) in Canada

Technical Summary

Cetorhinus maximus

Basking Shark
Pacific population

Range of Occurrence in Canada: Pacific Ocean

Extent and Area Information

Extent of occurrence (EO) (km2)
Pacific: no basis to estimate current area

Specify trend in EO


Are there extreme fluctuations in EO?


Area of occupancy (AO) (km2)
Pacific: no basis to estimate current area


Specify trend in AO

Large reduction

Are there extreme fluctuations in AO?


Number of known or inferred current locations

Continuous distribution

Specify trend in #

Not applicable

Are there extreme fluctuations in number of locations?
Some indication of interannual variability.

Not applicable

Specify trend in area, extent or quality of habitat

Pacific population no longer present in areas of historical importance

Population Information

Generation time (average age of parents in the population)
Probably 22-33 years

Number of mature individuals


Total population trend:


% decline over the last/next 10 years or 3 generations.

 >90% (inferred)

Are there extreme fluctuations in number of mature individuals?


Is the total population severely fragmented?

Continuous distribution

Specify trend in number of populations

Not applicable

Are there extreme fluctuations in number of populations?
Possible extremes in locations but not actual populations.

Not applicable

List populations with number of mature individuals in each:

Threats (actual or imminent threats to populations or habitats)

Historical fisheries and directed eradication program are the most likely cause for the low abundance of basking sharks observed today. Interaction with fishing gears is currently the single greatest known threat to this species in Canada. Basking sharks are vulnerable to being caught/entangled in nearly all forms of fishing gear (seines, gillnets, troll, traps, longlines, salmon net pens and trawls). Occasional bycatch is reported on Pacific coast. Collisions with vessels are not often reported but may also cause mortality. The biology and population history of this species suggests that they are especially vulnerable to long term human-induced mortality.

Rescue Effect (immigration from an outside source)

Status of outside population(s)?
probably same population as in Canada. Numbers severely depleted in primary US site, California.

Is immigration known or possible?

Would immigrants be adapted to survive in Canada?


Is there sufficient habitat for immigrants in Canada?


Is rescue from outside populations likely?
Abundance in US waters is similarly depleted.


Quantitative Analysis

[provide details on calculation, source(s) of data, models, etc.]
Not undertaken

Current Status

COSEWIC: Endangered (2007)
IUCN (2000): Globally-vulnerable, NE Atlantic-Endangered, North Pacific endangered
CITES: Appendix II

Status and Reasons for Designation

Status: Endangered
Alpha-numeric code: A2a; C1

Reasons for Designation: This shark species is the only extant species in the family Cetorhinidae. It occurs circumglobally in temperate coastal shelf waters, and exists in Canada as two geographically isolated designatable units – Atlantic and Pacific. The species is vulnerable to incidental fishing mortality because of its low intrinsic productivity. Females do not mature until 16 to 20 years old, gestate between 2.6 and 3.5 years (the longest known gestation period for any vertebrate), and produce litters of only about 6 “pups”. These sharks are especially susceptible to entanglement in fishing gear and collision with boats because of their large size, surface behaviour and fearlessness around boats, and because their coastal distribution overlaps fishing and boating areas. Prior to 1970, large aggregations of these sharks were seasonally common in Pacific Canada, but only 6 sightings have been confirmed since 1996. This dramatic reduction in abundance is attributed to directed fisheries for liver oil (1941-1947) and an eradication program (until 1970) that killed hundreds, perhaps thousands of individuals between 1945 and 1970. The minimum historical population reconstructed from documented kills was at least 750 individuals, whereas the current population is virtually nil, implying a rate of decline exceeding 90% within < 2 generations. The species is believed to migrate seasonally between Canada and California, where regional aggregations were also severely depleted by historic fisheries. Rescue from outside Canada is unlikely.

Applicability of Criteria

Criterion A (Declining Total Population):
Meets Endangered A2a (Population decline >50% over the past 3 generations, based on direct observation, where the reduction or its causes may not have ceased, may not be understood, or may not be reversible).

Criterion B (Small Distribution, and Decline or Fluctuation):
Not available. No overall decline figures and range too large and not severely fragmented

Criterion C (Small Total Population Size and Decline):
Meets Endangered C1 (Number of mature individuals <2500 and an estimated continuing decline rate of at least 20% in 2 generations (44-66 years); only 6 confirmed sightings since 1996 of which 4 were encountered as bycatch and likely died.

Criterion D (Very Small Population or Restricted Distribution):
May apply since remaining population is suspected to be less than 250 individuals, but current estimates are not sufficiently precise to defend this conclusion.

Criterion E (Quantitative Analysis):
Not applicable.