Winter skate (Leucoraja ocellata) COSEWIC assessment and status report: chapter 14
Leucoraja ocellata
Winter Skate, Southern Gulf population
Raie tachetée
Canadian Range: Southern Gulf of St. Lawrence (Northwest Atlantic Fishery Organization division 4T)
Extent and Area Information
| Extent of occurrence (EO) (km2) | Approx. 15 000 |
| Specify trend in EO | Stable |
| Are there extreme fluctuations in EO? | No |
| Area of occupancy (AO) (km2) | Approx. 3 000 |
| Specify trend in AO | Decline |
| Are there extreme fluctuations in AO? | No |
| Number of known or inferred current locations | Unknown |
| Specify trend in # | Unknown |
| Are there extreme fluctuations in number of locations? | No |
| Specify trend in area, extent or quality of habitat | Unknown |
Population Information
| Generation time (average age of parents in the population) | 22 Years |
| Number of individuals | 100 000 (minimum estimate) |
| Total population trend | Decline |
| % decline | 98.1% |
| Are there extreme fluctuations in number of mature individuals? | No |
| Is the total population severely fragmented? | No |
| Specify trend in number of populations | Unknown |
| Are there extreme fluctuations in number of populations? | No |
Threats (actual or imminent threats to populations or habitats)
Winter skate is subjected to bycatch in fisheries for other groundfish species, perhaps most notably by directed fisheries for flatfish.
Rescue Effect (immigration from an outside source)
| Status of outside population(s)? Eastern Scotian Shelf population is Threatened; the species is rare in the northern Gulf of St. Lawrence and in Newfoundland waters |
|
| Is immigration known or possible? | Unknown |
| Would immigrants be adapted to survive in Canada? | Yes |
| Is there sufficient habitat for immigrants in Canada? | Yes |
| Is rescue from outside populations likely? | Unlikely |
Quantitative Analysis
Not available
Current Status
COSEWIC: Endangered (May 2005)
Status and Reasons for Designation
| Status: Endangered |
Alpha-numeric code: A4b |
| Reasons for Designation: The species possesses life history characteristics that increase vulnerability to exploitation, that reduce rate of recovery, and that increase the risk of extinction. These characteristics include delayed age at maturity, long generation time, low fecundity, and consequently slow population growth rate. Narrow latitudinal ranges and a high degree of endemicity have been documented for the skate family worldwide. This population appears to have a restricted distribution, based on distributional maps of fisheries-independent survey catches. Individuals from this population mature at a significantly smaller size than those found elsewhere in Canadian waters. Abundance of mature individuals in the Southern Gulf of St. Lawrence is estimated to have declined 98% since the early 1970s, and is now at a historically low level. The probable cause of decline is an unsustainable rate at which they were captured as bycatch in fisheries directed at other groundfish species. |
|
Applicability of Criteria
Criterion A (Declining Total Population):
meets criterion for Endangered A4b.
meets criterion for Endangered A4b.
Criterion B (Small Distribution, and Decline or Fluctuation):
extent of occurrence is <20 000 km2 but does not apply because the species occurs at >10 locations, is not fragmented, and extreme fluctuations are unknown.
extent of occurrence is <20 000 km2 but does not apply because the species occurs at >10 locations, is not fragmented, and extreme fluctuations are unknown.
Criterion C (Small Total Population Size and Decline):
does not apply because number of mature individuals is >10 000.
does not apply because number of mature individuals is >10 000.
Criterion D (Very Small Population or Restricted Distribution):
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
Criterion E (Quantitative Analysis):
not done.
not done.
Leucoraja ocellata
Winter Skate, Eastern Scotian Shelf population
Raie tachetée
Canadian Range: Eastern part of the Scotian Shelf off eastern Nova Scotia (Northwest Atlantic Fishery Organization divisions 4VW)
Extent and Area Information
| Extent of occurrence (EO) (km2) | Approx. 230 000 |
| Specify trend in EO | Stable |
| Are there extreme fluctuations in EO? | No |
| Area of occupancy (AO) (km2) | Approx. 35 000 |
| Specify trend in AO | Decline |
| Are there extreme fluctuations in AO? | No |
| Number of known or inferred current locations | Unknown |
| Specify trend in # | Unknown |
| Are there extreme fluctuations in number of locations? | No |
| Specify trend in area, extent or quality of habitat | Unknown |
Population Information
| Generation time (average age of parents in the population) | 17 Years |
| Number of individuals | 750 000 (minimum estimate) |
| Total population trend | Decline |
| % decline | 91.8% (based on Scotian Shelf Summer RV Survey) 96.4% (based on 4VW Cod March RV Survey) |
| Are there extreme fluctuations in number of mature individuals? | No |
| Is the total population severely fragmented? | No |
| Specify trend in number of populations | Unknown |
| Are there extreme fluctuations in number of populations? | No |
Threats (actual or imminent threats to populations or habitats)
Caught as by-catch in fisheries for other groundfish species. The population is also subjected to a small, directed fishery.
Rescue Effect (immigration from an outside source)
| Status of outside population(s)? Southern Gulf population is Endangered; Georges Bank-Western Scotian Shelf-Bay of Fundy population is Special Concern |
|
| Is immigration known or possible? | Yes |
| Would immigrants be adapted to survive in Canada? | Yes |
| Is there sufficient habitat for immigrants in Canada? | Yes |
| Is rescue from outside populations likely? | Possible, but unlikely |
Quantitative Analysis
Not available
Current Status
COSEWIC: Threatened (May 2005)
Status and Reasons for Designation
| Status: Threatened |
Alpha-numeric code: Meets criterion for Endangered, A4b, but assessed Threatened because the population is not considered to be at imminent risk of extinction. |
| Reasons for Designation: The species possesses life history characteristics that increase vulnerability to exploitation, that reduce rate of recovery, and that increase the risk of extinction. These characteristics include delayed age at maturity, long generation time, low fecundity, and consequently slow population growth rate. Narrow latitudinal ranges and a high degree of endemicity have been documented for the skate family worldwide. This population appears to have a restricted distribution, based on distributional maps of fisheries-independent survey catches. Individuals from this population mature at a significantly larger size than those in the Southern Gulf and have been reported to mature at a significantly different age than those inhabiting waters further south. Abundance of mature individuals on the Eastern Scotian Shelf is estimated to have declined by more than 90% since the early 1970s and is now at a historically low level. The area occupied by the population appears to have declined significantly since the mid-1980s. Larger, older individuals have been severely depleted from this population, producing a significant truncation in the length distribution of the population over time. The probable cause of the decline is an unsustainable rate at which they were captured as bycatch in fisheries directed at other groundfish species. They have been caught, and continue to be caught, in a directed fishery for skate, although current reported catches are low. |
|
Applicability of Criteria
Criterion A (Declining Total Population):
meets criterion for Endangered A4b.
meets criterion for Endangered A4b.
Criterion B (Small Distribution, and Decline or Fluctuation):
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
Criterion C (Small Total Population Size and Decline):
does not apply because number of mature individuals is >10 000.
does not apply because number of mature individuals is >10 000.
Criterion D (Very Small Population or Restricted Distribution):
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
Criterion E (Quantitative Analysis):
not done.
not done.
Leucoraja ocellata
Winter Skate, Georges Bank-Western Scotian Shelf-Bay of Fundy population
Raie tachetée
Canadian Range: Canadian portion of Georges Bank, western Scotian Shelf off southern Nova Scotia, Bay of Fundy (Northwest Atlantic Fishery Organization divisions 4X5Ze)
Extent and Area Information
| Extent of occurrence (EO) (km2) | Approx. 110 000 |
| Specify trend in EO | Stable |
| Are there extreme fluctuations in EO? | No |
| Area of occupancy (AO) (km2) | Approx. 40 000 |
| Specify trend in AO | Varies |
| Are there extreme fluctuations in AO? | No |
| Number of known or inferred current locations | Unknown |
| Specify trend in # | Unknown |
| Are there extreme fluctuations in number of locations? | Unknown |
| Specify trend in area, extent or quality of habitat | Unknown |
Population Information
| Generation time (average age of parents in the population) | 22 Years |
| Number of individuals | 1.7 million (minimum estimate) |
| Total population trend | No overall trend |
| % decline | Stable |
| Are there extreme fluctuations in number of mature individuals? | No |
| Is the total population severely fragmented? | No |
| Specify trend in number of populations | Unknown |
| Are there extreme fluctuations in number of populations? | Unknown |
Threats (actual or imminent threats to populations or habitats)
The population is subjected to bycatch in fisheries for shellfish on Georges Bank and for other species of groundfish.
Rescue Effect (immigration from an outside source)
| Status of outside population(s)? Winter skate on the U.S. portion of Georges Bank, although not overfished, are at low levels relative to their abundance from the late 1960s through to the late 1990s; Eastern Scotian Shelf population is Threatened. |
|
| Is immigration known or possible? | Yes |
| Would immigrants be adapted to survive in Canada? | Yes |
| Is there sufficient habitat for immigrants in Canada? | Yes |
| Is rescue from outside populations likely? | Yes |
Quantitative Analysis
Not available
Current Status
COSEWIC: Special Concern (May 2005)
Status and Reasons for Designation
| Status: Special Concern |
Alpha-numeric code: |
| Reasons for Designation: The species possesses life history characteristics that increase vulnerability to exploitation, that reduce rate of recovery, and that increase the risk of extinction. These characteristics include delayed age at maturity, long generation time, low fecundity, and consequently slow population growth rate. The area of occupancy of this species has been stable. Estimates of population status on Georges Bank show no discernible trend over time. Abundance elsewhere appears to have been stable over time. There is a high probability that the population receives immigrants from the species inhabiting the American portion of Georges Bank. The population is subjected to bycatch in fisheries for other groundfish shellfish species. There are directed fisheries for this species in U.S. waters. |
|
Applicability of Criteria
Criterion A (Declining Total Population):
does not apply because the population does not exhibit an overall trend in abundance.
does not apply because the population does not exhibit an overall trend in abundance.
Criterion B (Small Distribution, and Decline or Fluctuation):
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
Criterion C (Small Total Population Size and Decline):
does not apply because number of mature individuals is >10 000.
does not apply because number of mature individuals is >10 000.
Criterion D (Very Small Population or Restricted Distribution):
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
does not apply because number of mature individuals is >1000 and area of occupancy is >20 km2.
Criterion E (Quantitative Analysis):
not done.
not done.
Leucoraja ocellata
Winter Skate, Northern Gulf-Newfoundland population
Raie tachetée
Canadian Range: Northern Gulf of St. Lawrence, southern Newfoundland, southern Grand Bank (Northwest Atlantic Fishery Organization divisions 3NOP4RS)
Extent and Area Information
| Extent of occurrence (EO) (km2) | Approx. 420 000 |
| Specify trend in EO | Unknown |
| Are there extreme fluctuations in EO? | Unlikely |
| Area of occupancy (AO) (km2) | Approx. 200 000 |
| Specify trend in AO | Unknown |
| Are there extreme fluctuations in AO? | Unknown |
| Number of known or inferred current locations | Unknown |
| Specify trend in # | Unknown |
| Are there extreme fluctuations in number of locations? | Unknown |
| Specify trend in area, extent or quality of habitat | Unknown |
Population Information
| Generation time (average age of parents in the population) | Unknown |
| Number of individuals | Unknown |
| Total population trend | Unknown |
| % decline | Unknown |
| Are there extreme fluctuations in number of mature individuals? | Unknown |
| Is the total population severely fragmented? | Unknown |
| Specify trend in number of populations | Unknown |
| Are there extreme fluctuations in number of populations? | Unlikely |
Threats (actual or imminent threats to populations or habitats)
Winter skate is caught as bycatch in fisheries for other groundfish.
Rescue Effect (immigration from an outside source)
| Status of outside population(s)? Southern Gulf population is Endangered |
|
| Is immigration known or possible? | Unknown |
| Would immigrants be adapted to survive in Canada? | Yes |
| Is there sufficient habitat for immigrants in Canada? | Yes |
| Is rescue from outside populations likely? | Unlikely |
Quantitative Analysis
Not available
Current Status
COSEWIC: Data Deficient (May 2005)
Status and Reasons for Designation
| Status: Data Deficient |
Alpha-numeric code: |
| Reasons for Designation: The species exists in low concentrations in the Northern Gulf of St. Lawrence, in the coastal waters off the southern coast of Newfoundland, and on the southern portion of the Grand Bank. A quantitative analysis of spatial and temporal variation in population size is not possible because of the infrequency with which the species is caught. The population is subjected to bycatch. |
|
Applicability of Criteria
Criterion A (Declining Total Population):
insufficient data to quantify temporal changes in abundance because of the rarity of the species in this area.
insufficient data to quantify temporal changes in abundance because of the rarity of the species in this area.
Criterion B (Small Distribution, and Decline or Fluctuation):
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
does not apply because extent of occurrence is >20 000 km2 and area of occupancy is >2 000 km2
Criterion C (Small Total Population Size and Decline):
an estimate of the number of mature individuals is not available.
an estimate of the number of mature individuals is not available.
Criterion D (Very Small Population or Restricted Distribution):
an estimate of the number of mature individuals is not available; area of occupancy is >20 km2.
an estimate of the number of mature individuals is not available; area of occupancy is >20 km2.
Criterion E (Quantitative Analysis):
not done.
not done.
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