Shortfin mako (Isurus oxyrinchus) COSEWIC assessment and status report: chapter 11
Technical Summary
Isurus oxyrinchus
Shortfin mako (Atlantic population) – requin-taupe bleu (Population de l’Atlantique)
Range of Occurrence in Canada:
Atlantic Ocean - Georges and Browns Bank, along the continental shelf of Nova Scotia, the Grand Banks and into the Gulf of St. Lawrence
Extent and Area Information
Extent of occurrence (EO) (km²)
Sum across the annual Canadian distributional range determined from catches: 1,200,000 km²
Specify trend in EO:
Unknown
Are there extreme fluctuations in EO?
Unknown
Area of occupancy (AO) (km²)
Represents Canadian area of frequent and regular sightings (catches). 800,000 km²
Specify trend in AO:
Unknown
Are there extreme fluctuations in AO?
Unknown
Number of known or inferred current locations:
Widespread, non localized.
Specify trend in # :
Not Applicable
Are there extreme fluctuations in number of locations?
Not Applicable
Specify trend in area, extent or quality of habitat:
Habitat not considered to have changed
Population Information
Generation time (average age of parents in the population):
14 years (minimum)
Number of mature individuals:
Unknown
Total population trend:
North Atlantic
- US longline 1986-2000 (Baum): 40% decline
- Japan and US longline 1971-2003 (ICCAT): 50% decline
Canadian North Atlantic
- Canada and Japan longline Scotian shelf 1988-2003 (Campana): No trend
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
No
Specify trend in number of populations:
Considered one North Atlantic population
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each:
Not Applicable
Threats (actual or imminent threats to populations or habitats)
The primary threat is mortality from fishing operations where shortfin makos are taken as bycatch.
Rescue Effect (immigration from an outside source)
Status of outside population(s)?
Shortfin mako throughout the North Atlantic are considered to be a single population. Status in Canada is a reflection of the population as a whole. Indices of abundance indicate a decline in the North Atlantic population.
Is immigration known or possible?
Yes
Would immigrants be adapted to survive in Canada?
Yes (seasonal)
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
Yes, but N. Atlantic source population is apparently in decline
Quantitative Analysis
Not undertaken
Current Status
- COSEWIC: Threatened
- IUCN: lower risk/ near threatened
Status and Reasons for Designation
Status: Threatened
Alpha-numeric code: A2b
Reasons for Designation: As a large (maximum length 4.2 m), relatively late-maturing (7-8 yrs) pelagic shark, the species has life-history characteristics making it particularly susceptible to increased mortality from all sources, including human activities. The species is circumglobal in temperate and tropical waters. Individuals found in Canada are considered part of a larger North Atlantic population. There does not appear to be any reason to assume that the Canadian Atlantic “population” is demographically or genetically independent from the larger Atlantic population, so the status of the species in Atlantic Canada should reflect the status throughout the North Atlantic. Although there is no decline in an indicator of status for the portion of the species that is in Atlantic Canada, two analyses suggest recent declines in the North Atlantic as a whole (40% 1986-2001; 50% 1971-2003). The main causes of the species’ decline (mortality due to bycatch in longline and other fisheries) are understood and potentially reversible, but these sources of mortality have not been adequately reduced.
Applicability of Criteria
Criterion A: (Declining Total Population): CPUE in the US longline fleet declined 41% between 1986 and 2000, while ICCAT analysis of longline data from Japan and US fleets showed a 50% decline from 1971-2003 (meets Threatened A2b). Very preliminary ICCAT estimates suggesting that the current Atlantic population is at approximately 31-33% of virgin biomass was given lower weight than the abundance trends. Analysis of longline CPUE in Canada(1988-2003) shows no trend but this index was given lower weight due to high variability and because it only represents part of the population (animals entering Canada).
Criterion B: (Small Distribution, and Decline or Fluctuation): Not applicable
Criterion C: (Small Total Population Size and Decline): Not applicable
Criterion D: (Very Small Population or Restricted Distribution): Not applicable
Criterion E: (Quantitative Analysis): Not applicable.
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