Cusk (Brosme brosme) COSEWIC assessment and status report 2012: chapter 4
Brosme brosme
Cusk Brosme
Range of Occurrence in Canada: Atlantic Ocean (Scotian Shelf – Gulf of Maine, Northwest Atlantic Ocean)
Demographic Information
| Generation time (% age of maturity +1/Natural Mortality) | 12.1 yrs (could be as high as 21 years) |
| Is there an observed continuing decline in number of mature individuals? | Yes |
| Estimated percent of continuing decline in total number of mature individuals within 2 generations (24 years) | 72% decline |
| Estimated percent reduction in total number of mature individuals over the last 3 generations (36 years) | 85% decline |
| Suspected percent reduction in total number of mature individuals over the next 3 generations. | Forward projections were not carried out |
| Estimated percent reduction in total number of mature individuals over any 3 generation period, over a time period including both the past and the future. | Forward projections were not carried out |
| Are the causes of the decline clearly reversible and understood and ceased? | No. Overfishing is the main cause of the decline but it has not ceased nor is it clearly reversible. |
| Are there extreme fluctuations in number of mature individuals? | No |
Extent and Occupancy Information
| Estimated extent of occurrence | 302,311 km2 |
| Index of area of occupancy (IAO) | 3,616 km2 |
| Is the total population severely fragmented? | No |
| Number of locations. Does not apply | NA |
| Is there an observed continuing decline in extent of occurrence? | Yes |
| Is there an observed continuing decline in index of area of occupancy? | Yes |
| Is there an observed continuing decline in number of populations? | Unknown |
| Is there an observed continuing decline in number of locations? | NA |
| Is there an observed continuing decline in area, extent and quality of habitat? | No |
| Are there extreme fluctuations in number of populations? | No |
| Are there extreme fluctuations in number of locations? | No |
| Are there extreme fluctuations in extent of occurrence? | No |
| Are there extreme fluctuations in index of area of occupancy? | No |
Number of Mature Individuals (in each population)
| Population | N Mature Individuals (2002-2010 avg); see note below |
|---|---|
| Canadian portion | 217,000 |
Note: these numbers are based on the DFO summer bottom trawl surveys. For reasons outlined in this report, they are considered biased low and are a minimum estimate. The true number is considerably higher.
Quantitative Analysis
Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]. Not done
Threats (actual or imminent, to populations or habitats)
Overfishing as bycatch to Cod, Haddock, Pollock, Halibut and Lobster fisheries
Rescue Effect (immigration from outside Canada)
Status of outside population(s)?
US portion of population in similar state to that in Canada
Is immigration known or possible?
Likely limited due to both limited mobility and poor status in the USA
Would immigrants be adapted to survive in Canada?
Yes
Is there sufficient habitat for immigrants in Canada?
Yes
Is rescue from outside populations likely?
No
Status History
COSEWIC: Designated Threatened in May 2003. Status re-examined and designated Endangered in November 2012.
Status and Reasons for Designation
Status:
Endangered
Alpha-numeric code:
A2b
Reasons for designation:
This species is a large, slow-growing, bottom-living fish that resides in the Gulf of Maine and Scotian Shelf, and which has been declining continuously since 1970. The mature portion of the population has declined by approximately 85% over three generations. There is also strong evidence that its area of occupancy has declined considerably. Average fish size has also declined, consistent with a decline in abundance. Limited management efforts have not been effective in halting the decline.
Applicability of Criteria
Criterion A
(Decline in Total Number of Mature Individuals): Meets criteria A2b. Abundance indices appropriate for the species indicate a decline in mature individuals of 85% over the past 3 generations and the decline has not ceased.
Criterion B
(Small Distribution Range and Decline or Fluctuation): Does not apply. The population distribution exceeds criteria.
Criterion C
(Small and Declining Number of Mature Individuals): Does not apply. The number of mature individuals exceeds criteria
Criterion D
(Very Small or Restricted Total Population): Does not apply
Criterion E
(Quantitative Analysis): Not done.
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