Science Advisory Report 2011/037
Recovery potential assessment for the Newfoundland and Labrador Designatable Unit (NAFO Divs. 2GHJ, 3KLNO) of Atlantic Cod (Gadus morhua)
- The Newfoundland and Labrador (NL) DU of Atlantic Cod comprises three stocks or management units: Labrador cod (NAFO Divs. 2GH), Northern cod (Divs. 2J+3KL) off southern Labrador and eastern Newfoundland both managed by Canada, and southern Grand Banks cod (Divs. 3NO) managed by the Northwest Atlantic Fisheries Organization (NAFO). The Northern cod population was by far the largest in the NL DU, and was historically the largest cod population in the northwest Atlantic.
- Long-term projections were undertaken for the 2J+3KL and 3NO stocks and at the DU level based on a combination of results from these stocks. Future productivity conditions are very uncertain. Thus, these projections should not be interpreted as forecasts of future stock status as they depend on assumptions about future productivity and fishing mortality. The probability of current conditions continuing for a long period of time is unknown. These projections are explorations of the consequences of particular productivity assumptions.
- Projections are illustrated using the median and the 2.5th and 97.5th percentiles. The full range of uncertainty should be considered when interpreting these projections.
- The demersal juvenile stage (4 - 35 cm long) is the most habitat-dependant period in the life-cycle of Atlantic Cod. Physical disturbance of structural components of habitat can reduce its value and increase mortality of juvenile cod. Existing data lack the spatial resolution required to evaluate the amount of suitable habitat available to demersal juveniles and whether it has changed in the past three generations, especially in the offshore. However, there is no indication that the amount of suitable habitat is currently limiting recovery of cod in this DU.
Labrador cod (2GH)
- Information on the Labrador cod stock is sparse and there is no survey time series from which to evaluate trends. Reported landings of cod from this stock declined in the late 1960s and there have been no reported landings since the late 1980s. This stock has shown no sign of recovery since a moratorium on directed fishing was imposed in 1993.
Northern cod (2J+3KL)
- The Northern cod stock declined by over 99% since the peak in the late 1960s, and by over 90% compared to the 1980’s. The population remained very low for several years after the moratorium, but has shown slight improvement during 2005-08.
- A conservation limit reference point (LRP) has been established for Northern cod. Estimated SSB has been well below the LRP since the early 1990s, but SSB increased during 2005-08 and is currently 90% below the LRP.
- Total mortality rates of Northern cod based on a cohort analysis of survey catches have been high through much of the 1983-2009 period, with two peaks, one in the early 1990’s and a second during the early 2000s when directed inshore fisheries were reopened. Total mortality rates declined during 2003-05 when inshore fishing was more restricted; total mortality rates remained low during 2005-08.
- There are no direct estimates of natural mortality for Northern cod. However, total mortality remained low during 2005-08 in spite of a reopening of inshore fisheries, suggesting that natural mortality rates declined substantially. Estimates of fishing mortality based on tagging have been low for cod tagged inshore (<0.1 since 2007) and offshore (0.06 in 2008) and spawning stock biomass (SSB) has improved.
- Recruitment has remained low since the early 1990s. Other components of productivity such as length-at-age, weight-at-age and condition have improved since the low values of the early 1990s and were close to (Div. 2J) or above average (Divs. 3K and 3L) for several years, but declined in 2009. Age at 50% maturity for female cod declined in cohorts produced during the 1980s and remains low (~5.0) compared to earlier decades (>6.0).
- For the 2J+3KL stock, using 1983-2009 as the period to infer future productivity conditions and under the current fishing mortality rate (F=0.06), projections indicate an initial increase in SSB until 2016 followed by a decline and stabilization at a level lower than current SSB. In 2016 there is a low probability (approx. 10%) of reaching the LRP. At F=0 the probability of reaching the LRP is about 30% in 2016.
- Additional sensitivity analyses were conducted using conditions observed during various portions of the 1983-2009 period. The most optimistic of these analyses assumed that low natural mortality rates, similar to those estimated for 2005-09, would prevail over the next 36 years. For F=0, 65% of the projection results indicated the LRP will be exceeded in the next 36 years. For F=0.06, 40% of the results indicated the LRP will be exceeded. However, it is less likely that conditions in the recent period will persist the further the projection proceeds into the future.
Southern Grand Banks cod (3NO)
- The 3NO cod stock peaked in the 1960s but decline to < 20% of 1960s values by the mid-1970s. The population increased rapidly during the late 1970s but declined again steeply during the late 1980s and remained low throughout the 1990s to about 2005. In recent years the stock has increased and the average number of spawners in the last 3 yrs (2008-10) is 25% of the 1980-89 average.
- A conservation limit reference point (Blim) was established for the 3NO cod stock in 1999 at 60,000 t. Estimated SSB has been well below the LRP since the early 1990s, but SSB increased recently and is currently 79% below Blim.
- Trends in total mortality rate of 3NO cod show two peaks, with higher values during 1965-75 and during the late 1980s. During the late 1970s and early 1980s, total mortality rates were much lower. Total mortality rate has been low since the moratorium, except during 2003.
- Although F in the post-moratorium period is generally low, recent bycatch fisheries generated high levels of F in some years, coincident with pulses of improved recruitment. Fishing mortality from bycatch has contributed significantly to the lack of recovery since the moratorium.
- Recruitment for 3NO cod has generally remained low for several years since the early 1990s. However, the 2005 and 2006 year classes are stronger and these have not been heavily fished and are now contributing significantly to the recent improvements in SSB.
- For the 3NO stock, using 1974-2009 as the period to infer future productivity conditions and under the current fishing mortality rate (F=0.07), there is a sustained rapid increase in SSB and all projection results suggest that Blim is surpassed by 2016. For the F=0 scenario, the trends are similar but increases are larger and all projections results suggest Blim is surpassed by 2015.
NL DU (2GHJ3KLNO)
- Projected status of the DU was inferred by combining the stock-specific projections of spawning stock numbers. Under the current levels of fishing, spawning stock numbers increase and peak in 2026. Under F=0 overall trends are similar, but reach a higher peak. Although the historic 2J+3KL stock was much larger than the 3NO stock, these results at the DU level are dominated by the much more optimistic trajectory in 3NO.
- For both 3NO and 2J+3KL, age at maturity has declined and remained low and increased mortality associated with spawning at these younger ages may be expected.
- The greatest threats to the recovery of the NL DU cod are high level of natural mortality (in 2J+3KL) and fishing mortality (in 2J+3KL and 3NO). Fishing mortality occurs primarily through directed stewardship and recreational fisheries in 2J+3KL and as bycatch in 3NO.
- In consideration that both populations have recently shown increases, there appears to be scope for allowable harm permitting, if current levels of productivity continue. Catches that have resulted in current levels of fishing mortality, (estimated as F=0.06 for 2J+3KL cod, F=0.07 for 3NO cod), would not appear to be sufficient to jeopardize survival or recovery of the species in the short term (3-years). This should allow sufficient time for recovery plans to be developed.
This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Zonal Advisory Meeting of February 21-25th, 2011 on the Recovery Potential Assessment (RPA) for Atlantic Cod (Newfoundland and Labrador, Laurentian North, Laurentian South, Southern Designatable Units). Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.
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