Science Advisory Report  2011/064

Assessment of Lobster off the Atlantic Coast of Nova Scotia (LFAs 27-33)

Summary

General

• Three stock assessment units were defined based on cluster analysis of historical landings of Statistical Districts (smaller than LFAs): LFA 27, LFAs 28-32 and LFA 33.  Recent trends (last 10-12 years) within the assessment units have not been identical, and where appropriate, analysis at subunit levels is provided.
• Landings are the only available proxy for lobster abundance that has a time series greater than 20 years.
• In more recent years, the main abundance trends for all assessment units come from catch per unit effort (CPUE) expressed in numbers per trap haul (N/TH) or weight per trap haul (kg/TH).  CPUE is related to abundance but is affected by a variety of factors. 
• Where CPUE has been standardized with a model, it is referred to as an index or indices.  Unstandardized CPUEs are annual means.
• Unstandardized CPUE from mandatory logs corresponds well with unstandardized CPUE from voluntary logs (longer time series, fewer participants) where the two data types overlap.
• An index of exploitation rate (ER) has been stable or declined slightly in all assessment units.  It is concluded that the current levels of exploitation do not threaten sustainability in any of the assessment units under current environmental conditions. 
• Size at onset of maturity (SOM) was estimated for 3 locations in Cape Breton from 2006-2008.  SOM estimates varied annually, spatially and seasonally.  The percent mature at the minimum legal size (MLS) ranged from 77-100%.
• SOM estimates are not yet available for sites in LFA 31A, 32 and 33, but evidence suggests a spatial trend of increasing SOM going from LFA 31A to LFA 33.
• Preliminary estimates of bycatch and discards for the lobster fishery in LFAs 27-33 are available for the first time.  The proportion of the non-targeted bycatch varies from 0.1% in LFA 32 to 7.5% in LFA 33.  There were low occurrences of species listed under the Species at Risk Act (SARA).  Sublegal lobsters represent the majority of discards.  

LFA 27

• Indicators of stock health for lobsters in LFA 27 overall are positive.
• Landings in 2010 in LFA 27 (2,568 t) and the mean for the last 3 years (2,532 t) were above the median for 1985-2004 (1996).
• Effort as indicated by days fished (2002-2010) and total trap hauls (2004-2010) was stable or without trend. 
• Unstandardized commercial CPUE from available logs in LFA 27 has trended upwards since 2002.  
• LFA 27 abundance indicators for sublegals and legal sizes based on standard traps deployed by the Fishermen and Scientists Research Society (FSRS) are positive overall.  A CPUE index for sublegals increased from 1999 to 2010 and the mean of the last 3 years is above the median for 1999-2007.  A CPUE index for legal sizes fluctuated without trend but the mean for 2008-2010 is above the median for 1999-2007.
• Unstandardized CPUE for ovigerous females in FSRS traps is up from 1999, as is the unstandardized CPUE of ovigerous females in voluntary fishing logs and the unstandardized CPUE from at-sea samples in a port in the northern portion of LFA 27.
• The increase in unstandardized CPUE of ovigerous females and sublegals is consistent with the expectations from the increase in Minimum Legal Size (MLS) in LFA 27 from 70 to 76 mm Carapace Length (CL) (1998-2002) and from 76 to 81 mm CL (2007-2009).
• The exploitation rate index (0.77, mean of last 3 years) is close to the median for the 1999-2007 period (0.76).  An index of ER that accounts for the increases in MLS from 2007 to 2009 indicates that ER in LFA 27 was approximately 30% lower once the current MLS was reached.   

LFAs 28-32

• Indicators of stock health for lobsters in LFAs 28-32 overall are mainly positive. 
• Landings in 2010 in LFAs 28-32 (3,866 t) and the mean for the last 3 years (4,224 t) were well above the median for 1985-2004 (822 t).
• In the LFA 28-32 assessment unit, reported effort increased from 2005 to 2009 and decreased in 2010.  Within individual LFAs, the pattern varied.
• Unstandardized commercial CPUE from available logs in LFAs 28-32 has trended upwards since the 1990s.  This trend was strongest from 2004 to 2009. 
• LFA 28-32 abundance indicators for sublegals and legal sizes based on standard traps deployed by the FSRS are positive and well above levels seen in earlier periods.  A CPUE index for sublegals increased substantially from 2002-2007 and declined recently, but the mean of the last 3 years is still above the median for 2000-2007. 
• A CPUE index for legal sizes followed the sublegal index trend, increasing from 2004 to 2009, with the mean of the last 3 years 1.7 times the median for 2000-2007. 
• An egg index for LFA 31A based on at-sea samples and the length-fecundity relationship was substantially higher in more recent years (2008-2010) compared to 2002-2003.
• The ER index for LFAs 29-32 has fluctuated with no consistent trend.  Mean ER for the last 3 years (0.61) is below the median for 2000-2007 (0.70).

LFA 33

• Indicators of stock health for lobsters in LFA 33 overall are positive.
• Landings in LFA 33 for the 2009-2010 season (3,377 t) and the mean for the last 3 years (3,126 t) were above the median for 1984-1985 to 2003-2004 (2,071 t).
• Reported effort increased by 10-15% from 2001-2002 to 2007-2008, with no apparent change in the last 3 fishing seasons.  The changes occurred in total days fished, mean days fished and in estimated trap hauls from mandatory logs.
• Unstandardized commercial CPUE from available logs in LFA 33 CPUE has trended upwards since the 1990s.
• LFA 33 abundance indicators for sublegals and legal sizes based on standard traps deployed by the FSRS are positive or neutral.  A temperature-corrected abundance index for sublegals (76-80 mm CL) increased from 1999-2000 to 2008-2009 and the mean for the two seasons ending in spring 2009 was 1.3 times the median of the period 1999-2000 to 2006-2007.  Unstandardized CPUE of sublegals in FSRS traps increased from the 2000-2001 season to the 2009-2010 season.  Unstandardized CPUE of legal sizes in FSRS traps fluctuated without trend.
• Mean ER for the last 3 years (0.67) is below the median for 1999-2000 to 2006-2007 (0.76).  

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Advisory meeting of July 21-22, 2011, on the assessment of lobster off the Atlantic coast of Nova Scotia.  A meeting to develop the framework for this assessment was held February 1-3, 2011. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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