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COSEWIC assessment and update status report on the Atlantic Cod in Canada

Appendix 1: St. Pierre Bank

St. Pierre Bank (NAFO Division 3Ps):

 

The average age among individuals in the current cohort is 7.3 years, based on the survey catch rate data (Brattey et al. 2001a).  Based on data from the 1960s and 1970s, age at 50% maturity is about 6years for St. Pierre Bank cod (Brattey et al. 2001a).  Thus, in an unfished state, generation time is estimated to be 11years, yielding a three-generation time period of 33 years.  The survey data are those reported by Brattey et al. (2001).  Abundance data for the mature part of the population, as estimated by VPA, are also available from Brattey et al. (2001a).  The earliest year for which survey data are available is 1983.  VPA estimates of abundance extend back to 1959.

The 3-generation rate of decline experienced by St. Pierre Bank cod was 47-48% (Figure 14).

Age (yr) at maturityGeneration
time (yr)

Data Source

Data type

Time period

Rate of change
611surveycatch rate
(# per tow)
1983-2001−47%
  VPAnumbers of spawners1968-2001−46%

Area of occupancy:

Between 1983 and 2001 (the range of the reported data), area of occupancy appears to have increased slightly from approximately 38,000 km2 to approximately 45,000 km2, a rate of increase of roughly 16% (Smedbol et al. 2002).

Threats to recovery posed by fishing and marine mammal predation:

In 2000 and 2001, exploitation rates were estimated to be approximately 20% (Smedbol et al. 2002) (prior to the cod collapses in the early 1990s, it was estimated that cod populations could increase in abundance at exploitation rates less than 18%).  Marine

Figure 14.  Temporal variation in the estimated number of mature individuals in the St.


Figure 14.  Temporal variation in the estimated number of mature individuals in the St. Pierre Bank cod stock (NAFO Divisions 3Ps).

mammal predation does not appear to pose a threat to recovery of St. Pierre Bank cod (McLaren et al. 2001).

Northern Gulf of St. Lawrence (NAFO Divisions 3Pn4RS):

The average age among individuals in the current cohort is 5.6 years, based on the survey catch rate data (Alain Fréchet, DFO, Mont-Joli, personal communication).  Based on maturity-at-age data for the 1970s and 1980s, as estimated by Yvon Lambert (DFO, Mont-Joli), age at 50% maturity is about 4 years for northern Gulf cod.  Thus, in an unfished state, generation time is estimated to be 9 years, yielding a three-generation time period of 27 years.  The survey data are those estimated from the Alfred Needler surveys and communicated to me by Alain Fréchet, who also provided me with VPA-based abundance data for the mature part of the population.  The earliest year for which survey data are available is 1990.  VPA estimates of abundance extend back to 1974.

Rates of decline of Northern Gulf cod depended on the source of abundance data.  Importantly, the VPA estimates were the only data that encompassed the 3-generation time frame for each of the age at maturity estimates.  Rate of decline based on the VPA data is 93% (Figure 15).

Age (yr) at maturityGeneration
time (yr)

Data Source

Data type

Time period

Rate of change
49Surveynumber of individuals1990-2002−64%
  VPAnumbers of spawners1975-2002−93%

Area of occupancy:

Between 1991 and 2001 (the range of the reported data), area of occupancy declined from approximately 58,000 km2 to approximately 44,000 km2, a rate of decline of roughly 24% (Smedbol et al. 2002).

Threats to recovery posed by fishing and marine mammal predation:

In the past 5 years, exploitation rates have been steadily increasing to an estimated 30% in 2001 (Smedbol et al. 2002) (prior to the cod collapses in the early 1990s, it was estimated that cod populations could increase in abundance at exploitation rates less than 18%).  In addition to fishing, marine mammal predation appears to pose a threat to recovery for northern Gulf cod, as revealed by McLaren et al.'s (2001) statement: "The conclusion that seals are important predators on cod in this area appears to be inescapable".


Figure 15.  Temporal variation in the estimated number of mature individuals in the Northern Gulf of St.


Figure 15.  Temporal variation in the estimated number of mature individuals in the Northern Gulf of St. Lawrence cod stock (NAFO Divisions 3Pn4RS).

Southern Gulf of St. Lawrence(NAFO Division 4T):

The average age among individuals in the current cohort is 6.5 years, based on the survey catch rate data for 2001 (Smedbol et al. 2002).  Based on data from the 1990s, age at 50% maturity is about 4.5 years for southern Gulf cod (Trippel et al. 1997; Doug Swain, DFO, Moncton, personal communication).  Thus, in an unfished state, generation time is estimated to be 9.5 years, yielding a three-generation time period of 28.5 years.  The survey data are those reported by Chouinard et al. (2001) and communicated to me by Doug Swain.  Abundance data for the mature part of the population, as estimated by VPA, are available from Chouinard et al. (2001).  The earliest year for which survey data are available is 1971.  VPA estimates of abundance extend back to 1950.

Estimated rates of change for Southern Gulf cod differed with the type of abundance data, ranging from a 23% decline to a 27% increase over the past three generations.  Based on the full time series of data (Figure 16), which extend back to 1950, it is clear that the current population size of Southern Gulf cod is similar to that experienced from the mid-1960s through the mid-1970s, and perhaps lower than that experienced in the 1950s.

Age (yr) at maturityGeneration
time (yr)

Data Source

Data type

Time period

Rate of change
4.59.5Survey

catch rate

(# per tow)

1972-2001+27%
  VPAnumbers of spawners1973-2002−23%

Area of occupancy:

Between 1971 and 2001 (the range of the reported data), area of occupancy increased from approximately 58,000 km2 in the early 1970s to 65,000 km2 in the 1980s before returning to approximately 58,000 km2 in 2001 (Smedbol et al. 2002).

Threats to recovery posed by fishing and marine mammal predation:

Since 1999, exploitation rates have been approximately 10% (Smedbol et al. 2002) (prior to the cod collapses in the early 1990s, it was estimated that cod populations could increase in abundance at exploitation rates less than 18%).  Estimates of cod consumption by seals do not seem to implicate seals in the present high adult mortality rate and lack of recovery of cod in the southern Gulf (McLaren et al. 2001).