Science Advisory Report  2012/035

Reference points consistent with the precautionary approach for a variety of stocks in the Maritimes Region

Summary

General

• The scientific basis for Limit Reference Points (LRPs), Upper Stock References (USRs), and Removal References (RRs) was proposed or presented for a variety of fish and invertebrate stocks in the Maritimes Region. It is expected that these reference points (particularly the USRs and RRs) will be reviewed with the fishing industry and other advisory committee members prior to their adoption and implementation, with a particular focus on incorporating socio-economic considerations where appropriate to do so. 
• The approaches proposed for the selection of reference points for modelled, empirically assessed, and data deficient stocks in the Maritimes Region used different methods depending on the information available for each stock, and were reviewed with respect to consistency with DFO’s precautionary approach (PA) framework.
• It was assumed that surveys and other data sources used to establish reference points would continue to be available, in some form, to enable monitoring of stock status relative to these points. 

Modelled

3NOPs4VWX+5 Atlantic Halibut

• PA reference points for 3NOPs4VWX+5 Atlantic halibut, based on a modified Sissenwine-Shepard production model using the full time series, were presented for information only.
• Forty percent of spawning stock biomass at maximum sustainable yield (SSB_MSY) was presented as the LRP (1,960 t), and 80% of SSB_MSY was presented as the USR (3,920 t).
• Fishing mortality at MSY (F_MSY=0.36) was presented as a limit RR. 
• A target RR of 0.2 has been proposed based on an examination of the data (natural mortality and a rate at which there is scope for growth) and discussions with industry.

4Y5Y Atlantic Cod

• An LRP and limit RR for 4X5Y Atlantic cod were presented for information only. A USR was proposed.
• The LRP (24,000 t) was based on a Beverton-Holt stock-recruitment model using the full time series. The limit RR (0.2) was calculated as F_0.1 in the 1990s. The USR (48,000 t) is double the LRP.   

5Zjm Atlantic Cod

• An LRP for 5Zjm Atlantic cod was presented for information only.
• The LRP (21,000 t) was based on a Beverton-Holt stock-recruitment model using the full time series.  

4VsW Atlantic Cod

• An LRP for 4VsW Atlantic cod was presented for information only. A USR was proposed.
• The LRP (50,000 t) was based on 40% of SSB_MSY during the productive period before 1990.
• The USR (100,000 t) was based on 80% of SSB_MSY during the productive period before 1990.

5Zjm Haddock

• Biomass at MSY (B_MSY) and an LRP for 5Zjm haddock were presented for review.   
• B_MSY (78,000 t) was calculated using a Sissenwine-Shepherd production model for the full time series. The LRP (10,340 t) was based on B_recover.   

4X5Y Haddock

• PA reference points for 4X5Y haddock, based on a Sissenwine-Shepard production model using the full time series, were presented for information only.
• Forty percent of SSB_MSY was presented as the LRP (20,800 t), and 80% of SSB_MSY was presented as the USR (41,600 t).

4VWX Snow Crab

• PA reference points for 4VWX snow crab, based on a modified biomass dynamics model using the full time series, were presented for review.  
• The LRP was proposed as 25% of the carrying capacity of fishable biomass, and the USR was proposed as 50% of the carrying capacity.
• F_MSY was proposed as a limit RR. A target RR of 10-30% of the fishable biomass was proposed based upon an examination of the biology of the species, past stock behavior, and discussions with industry.
• The actual values associated with the biomass reference points would be expected to vary over time due to the relative brevity of the current time series. 

4VWX American Plaice

• PA reference points for 4VWX American plaice, using a stage-based population model for the full time series to estimate MSY, were presented for review. 
• An LRP (12,952 t) of 40% of female-only SSB _MSY and a USR (25,905 t) of 80% female-only SSB _MSY were proposed.
• F_MSY (0.16) was proposed as a limit RR. 

Western Component (4Xopqrs5) Pollock

• A Management Strategy Evaluation (MSE) approach has been applied to manage western component (4Xopqrs5) pollock. The MSE approach and Harvest Control Rule (HCR) were presented for information only. How this might be translated into PA reference points was the subject of some discussion.
• The LRP could be defined as the Survey Index Ratio (J_y)=0.2, i.e., when the 3-year geometric mean survey biomass index falls to 20% of the geometric mean survey biomass index for 1984-1994. However, J_y=1.0, i.e., when the 3-year geometric mean survey biomass index reaches the same value as the geometric mean survey biomass index for 1984-1994, was not considered to reflect the definition of a USR. The Survey Index Ratio curve is not used directly to set catch limits, so it was not considered to be reflective of an RR.  

Empirical

Eastern Component (4VWXmn) Pollock

• An LRP and USR for eastern component (4VWXmn) pollock were presented for review, based on a proxy for B_MSY using data from DFO’s summer Research Vessel (RV) survey time series (1970-2011).   
• The proposed LRP (40% B_MSY proxy) was calculated to be 20,100 t, and the proposed USR (80% B_MSY proxy) was calculated to be 40,100 t.

Unit 3 Redfish

• Biological reference points for Unit 3 redfish were presented for information only, based on a proxy for B_MSY from DFO’s summer RV survey mean (1970-2011). An RR was presented for review.
• Forty percent of the B_MSY proxy was presented as the LRP (29,000 t), and 80% of the B_MSY proxy was presented as the USR (58,000 t).
• A target RR (0.068) was proposed based on the maximum relative fishing mortality rate (F) that would not result in a reduction in population biomass. 

Cusk in the Maritimes Region

• An LRP and USR for cusk in the Maritimes Region were presented for review.
• The proposed LRP (13.3 kg/1000 hooks) and USR (26.6 kg/1000 hooks) were calculated as 40% and 80% of the MSY proxy (commercial longline catch per unit effort from period of high catches, 1986-1992). 
• The 3-year geometric mean of the catch per unit effort (2009-2011) from the halibut industry longline survey was 18.2 kg/1000 hooks, which suggests that the stock is in the cautious zone.

Southwest Nova Scotia (SWNS) / Bay of Fundy (BoF) Herring

• An LRP for SWNS/BoF herring was presented for review. 
• With the evidence of the decline in spawning grounds, targeting of juveniles in the fishery, declines in catches, as well as the science advice indicating the need for rebuilding, it was proposed that the average of the 2005 to 2010 acoustic survey values be identified as the LRP for SWNS/BoF herring (German Bank and Scots Bay). 
• The stability at the 2005-2010 level was support for this as the LRP, and it provided data from which to select a point below which the risk of serious harm would be unacceptable.  Other considerations that lead to the selection of this point related to the objective of avoiding negative impacts to the ecosystem and long-term loss of fishing opportunities.

Banquereau and Grand Bank Arctic Surfclam

• PA reference points for Banquereau and Grand Bank Arctic surfclam were presented for review.
• A target RR of F = 0.33M (0.0264) had been recommended previously for Banquereau Arctic surfclam, with a similar approach recommended for Grand Bank Arctic surfclam.  
• Using fishable biomass per recruit and estimated average recruitment, the B_MSY proxy for Banquereau Arctic surfclam was proposed as 1,015,059 t.  Using the default 80% and 40% of the B_MSY proxy, the USR for Banquereau was proposed as 812,047 t and the LRP as 406,024 t.  
• Using fishable biomass per recruit and estimated average recruitment, the B_MSY proxy for Grand Bank Arctic surfclam was proposed as 703,065 t.  Using the default 80% and 40% of the B_MSY proxy, the USR was proposed as 562,452 t and the LRP as 281,226 t.  
• Currently both stocks are in the healthy zone, above their target biomasses.    

Inshore and Offshore Scallop in the Maritimes Region

• The offshore scallop industry developed an LRP, USR, and a target RR for the scallop fishery on Georges Bank to meet requirements for Marine Stewardship Council certification; these were presented for information only. The biological reference points were established as 30% (LRP = 3,000 t) and 80% (USR = 8,000 t) of the mean biomass from the stock assessment population model from 1981-2009 as a proxy for B_MSY (10,000 t). The target exploitation rate (0.25) corresponds to the mean exploitation rate since 1999, a period over which population biomass had remained above average. A similar approach was proposed for scallops on Brown's Bank. 
• For the inshore scallop fishery, the currently used target RR of 0.15 was proposed for areas where population models are used. For these areas, LRPs based on the lowest biomass that the stocks have recovered from were proposed. For areas where models are not used, the possibility of using commercial catch rate and/or survey catch rates as biomass proxies, and effort as an exploitation proxy, will be investigated.
• For Scallop Fishing Area 29, current research has been directed towards defining reference points based on a habitat suitability model, which has been shown to match the distribution of the fishery.

Scotian Shelf (4VWX) Shrimp

• PA reference points for Scotian Shelf shrimp were presented for review.
• An LRP and USR of 30% (5,459 t) and 80% (14,558 t) of the average SSB maintained during the modern fishery (2000-2010) were proposed.
• Secondary indicators, which were also proposed for review, have been used to inform management responses (i.e., the total allowable catch).   
• A target RR of 20% of the SSB (female exploitation) was proposed.
• These reference points had been set for a productive period and may have to be revisited if natural mortality were to increase significantly.

Inshore Lobster (Lobster Fishing Areas [LFAs] 27-36, 38)

• LRPs and USRs for inshore (LFAs 27-36, 38) lobster were presented for review.An approach to establishing a limit RR was also proposed.
• For inshore lobster, PA reference points were provided on an LFA basis, with a B_MSY proxy estimated as the median of the landings over a productive period.  For the USR and LRP, the values of 80% and 40% of the B_MSY proxy were proposed. Where there were observations of lower landings from 1985-2009 from which the fishery recovered, the lowest point of a 3-year running average was proposed as the LRP.
• Secondary indicators for lobster may change the perception of stock status and inform management responses to changes in stock condition. LFAs are not biological units, and connectivity among them should be recognized at the level of secondary indicators.
• Under current conditions, lobsters appear to be resilient to high exploitation. If an RR were to be adopted, it was proposed that it be at the high end (e.g., 90^th percentile) of estimates from 1999-2010.

Offshore Lobster (LFA 41)

• PA reference points are being developed as part of the Marine Stewardship Council conditions for the offshore (LFA 41) lobster fishery. Progress to date was presented for information and comment.
• It was proposed that the mean number per tow from DFO’s summer (4X) and winter (5Z) RV trawl surveys be assessed as a biomass proxy (B_MSY) for the 4X and 5Z portions of the offshore lobster stock.
• Exploitation rates cannot be estimated directly but are inferred to be low based on stability in size structure since the start of the fishery in 1972. Without a direct estimate of exploitation rates, it was proposed that the median size be used as a proxy or index of the exploitation rate.
• Secondary indicators were proposed to assess the stock health, in combination with the primary indicators, and aid in determining the management responses to changes in stock condition.    

Atlantic Salmon in the Maritimes Region

• LRPs for Atlantic salmon in the Maritimes Region (Areas 19, 20, 21 and 23) were presented for review.
• The empirical work defining 2.4 eggs/m² of fluvial rearing habitat as the Atlantic salmon conservation requirement, its adoption by the Canadian Atlantic Fisheries Scientific Advisory Committee, and recent population dynamics research supporting the Beverton-Holt relationship indicate that, in the Maritimes Region, the conservation requirement is consistent with an LRP in the PA framework.
• Individual river values based on 2.4 eggs/m² of fluvial rearing habitat had been estimated using methods that were consistent with the framework advice on dealing with changes in productivity.  It was proposed that these estimated values be used as individual river LRPs for the Maritimes Region.
• It was proposed that additional research on refinement of reference points and HCR for fishery removals in this region is not warranted given the current stock status and level of fish removals.  Rather, it was proposed that research guiding recovery action plans to appropriately limit mortality from all sources, or to increase productivity would be required.  

American Eel in the Maritimes Region 

• An LRP and RR for American eel in the Maritimes Region were presented for information only.   
• Spawner per Recruit (SPR) modelling was used to define mortality reference points, with the mortality rate that results in 30% of SPR (F_30%SPR) proposed as the limit RR, and the mortality rate that results in 50% of SPR (F_50%SPR) proposed as the target RR. 

Data Deficient

Sea Cucumber in the Maritimes Region

• Two approaches to the setting of reference points for sea cucumber in the Maritimes Region were proposed: one based on split weight and one based on spatial habitat information.

This Science Advisory Report is from a Regional Science Advisory meeting of 6-9 February 2012; review of the Precautionary Approach Reference Points for a Variety of Fisheries Resources in the Maritimes Region. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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