Science Advisory Report  2011/061

Stock Assessment Report on Pacific Herring in British Columbia in 2011

Summary

• The five major BC herring stocks are Haida Gwaii (Area 2E), Prince Rupert District, Central Coast, Strait of Georgia, and West Coast of Vancouver Island, while the two minor herring stocks are Area 2W and Area 27 (Figure 1). 
• The Fishery Management Framework establishes harvest control rules setting the  maximum available commercial harvest for each of the major stock areas at 20% of the forecast of mature stock biomass (males and females combined) when the forecast of mature stock biomass is above the commercial fishery threshold or “cutoff.”  The cutoff is established as 25% of estimated unfished biomass (0.25 B₀). If a forecast exceeds a cutoff, but a 20% harvest rate would result in spawning biomass that is less than the cutoff, the maximum available harvest is determined as the difference between the forecast and cutoff.
• A new integrated statistical catch age model (ISCAM) was used to assess the 2011 herring spawning stock biomass and forecast of the 2012 pre-fishery mature stock biomass.  Key differences between ISCAM and the HCAM model used previously relate to the scaling of the spawn abundance index, parameterization of fishing gear selectivity, and the likelihood assumption for the age composition data.  The time series of abundance trends from ISCAM and HCAM are comparable, but ISCAM resulted in biomass estimates that are larger.
• Given that a number of alternative assumptions were implemented in developing the new ISCAM model, and insufficient evaluation of the effects of these changes on existing harvest control rules occurred, it is recommended that a more comprehensive evaluation of the ISCAM model and its impact on the decision rules for the herring assessment be conducted.
• The following is a summary of the assessment results and advice by management area. Abundances are reported in metric tons (tonnes).

Haida Gwaii (Area 2E)

• All herring spawning from Cumshewa Inlet in the north to Louscoone Inlet in the south are assumed to be part of the Haida Gwaii stock.   
• No commercial herring fishery occurred in this area in 2011 (or 2003-2010).
• The median estimate of the 2011 spawning stock biomass (and 95% confidence interval) is 16,579 (7,700-33,630) tonnes.
• The forecast of mature stock biomass for 2012 is 9,618 tonnes (assuming poor recruitment), which is below the fishing threshold of 0.25B₀ (10,436 tonnes).
• Stock abundance has remained at relatively low levels and there is uncertainty about the cause of its current low productivity.  Given that there has been limited stock recovery, even in the absence of commercial fisheries, an assessment to determine appropriate rebuilding and harvest strategies is recommended prior to reopening fisheries in this area.

Prince Rupert District

• All herring spawning in Statistical Areas 3 to 5 are assumed to belong to the Prince Rupert District stock.   
• In 2011, the total roe herring seine fishery validated catch was 883 tonnes (approximately 14% of the total coast-wide catch) and the total roe herring gillnet fishery validated catch was 1,264 tonnes (approximately 19% of the total coast-wide catch).
• The median estimate of the 2011 post fishery spawning biomass (and 95% confidence interval) is 27,046 (14,340-50,590) tonnes.
• The forecast of mature stock biomass for 2012 is 27,492 tonnes (assuming average recruitment), which is above the fishing threshold of 0.25B₀ (19,641 tonnes).
• Retrospective analysis of abundance estimates for this stock suggests that the forecast biomass has been biased high in recent years.  The tendency to overforecast stock abundance is not evident in the other areas and warrants caution in fishery management decisions around harvest levels due to the increased level of uncertainty.

Central Coast

• All herring spawning in Kitasu Bay (a portion of Statistical Area 6), in Statistical Area 7, and in part of Statistical Area 8 (Kwakshua Channel and Fitzhugh Sound) are assumed to be part of the Central Coast stock.
• No commercial herring fishery occurred in this area in 2011 (or 2008-2010).
• The median estimate of the 2011 spawning biomass (and 95% confidence interval) is 14,666 (7,280-27,280) tonnes. 
• The forecast of mature stock biomass for 2012 is 11,357 tonnes (assuming poor recruitment), which is below the fishing threshold of 0.25B₀ (15,600 tonnes).
• Stock abundance has remained at relatively low levels and there is uncertainty regarding the reason for the current low productivity.  Given that there has been limited stock recovery, even in the absence of commercial fisheries, an assessment to determine appropriate rebuilding and harvest strategies is recommended prior to reopening fisheries in this area.

Strait of Georgia

• All herring spawning in Statistical Areas 14 to 19, 28 and 29 (excluding Section 293), and part of 13 (Herring Sections 132 and 135, Deepwater Bay area south) are assumed to belong to the Strait of Georgia herring stock.  
• In 2011, the roe herring seine fishery total allowable catch was 6,999 tonnes; however the fishery was not opened due to a large recruitment of small fish and roe size. The total roe herring gillnet fishery validated catch was 4,415 tonnes (approximately 67% of the total coast-wide catch).
• The median estimate of the 2011 spawning biomass (and 95% confidence interval) is 125,261 (70,430-217,950) tonnes.
• The forecast of mature stock biomass for 2012 is 138,448 tonnes (assuming good recruitment), which is above the fishing threshold of 0.25B₀ (35,013 tonnes).

West Coast Vancouver Island

• All herring spawning in Statistical Areas 23 to 25 are assumed to belong to the West Coast of Vancouver Island herring stock.
• No commercial fishery occurred on the west coast of Vancouver Island in 2011 (or 2006-2010).
• The median estimate of the 2011 spawning biomass (and 95% confidence interval) is 14,679 (6,990-27,630) tonnes.
• The forecast of mature stock biomass for 2012 is 15,321 tonnes (assuming poor recruitment), which is above the fishing threshold of 0.25B₀ (14,894 tonnes).
• Stock abundance has remained at relatively low levels and there is uncertainty about the cause of its current low productivity. Given that there has been limited stock recovery, even in the absence of commercial fisheries, an assessment to determine appropriate rebuilding and harvest strategies is recommended prior to reopening fisheries in this area.

Area 2W

• All herring spawning in Statistical Area 2W (except Herring Section 006) are assumed to belong to this Haida Gwaii minor stock.
• No commercial spawn-on-kelp fishery occurred in this area in 2011.
• The median estimate of the 2011 spawning biomass (and 95% confidence interval) is 5,448 (1,920-13,610) tonnes.
• The forecast of mature stock biomass for 2012 is 5,398 tonnes (assuming average recruitment).

Area 27

• All herring spawning in Statistical Area 27 are assumed to belong to this West Coast of Vancouver Island minor stock.
• A small commercial spawn-on-kelp fishery occurred in this area in 2011.
• The median estimate of the 2011 post fishing spawning biomass (and 95% confidence interval) is 1,077 (500-2,370) tonnes)
• The forecast of mature stock biomass for 2012 is 1,124 tonnes (assuming average recruitment).

This Science Advisory Report has resulted from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat Pacific Regional Advisory Meeting of September 7-9, 2011 on Pacific Herring Stock Assessment.  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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