Science Advisory Report  2014/003

Stock assessment and Management Advice for British Columbia Pacific Herring: 2013 Status and 2014 Forecast

Summary

• Commercial fishing for British Columbia (BC) Pacific Herring is managed as five major stock management areas: Haida Gwaii (HG), Prince Rupert District (PRD), Central Coast (CC), Strait of Georgia (SOG), and West Coast of Vancouver Island (WCVI), and two minor herring stock management areas: Haida Gwaii Area 2W, and WCVI Area 27 (Figure 1).
• Recruitment forecasting methodologies were reviewed to assess how uncertainty is represented in the forecasts, and to assess compliance with DFO’s Fisheries Decision-making Framework Incorporating the Precautionary Approach.
• The previous forecasting approach of using trawl survey data to forecast recruitment in two stocks (WCVI, SOG) and the categorization of model-reconstructed recruits (as poor/ average/good categories) applied to all stocks could produce an incorrect perception of forecast stock size and uncertainty.
• It was concluded that the previous approach is not scientifically defensible and that it does not capture the uncertainty in recruitment forecasts and subsequent risks to BC Pacific Herring stocks.
• Consequently, it is recommended that the assessment model be used to estimate the probability of breaching thresholds or achieving desirable outcomes for BC Pacific Herring stocks and fisheries.
• The 2013 spawning biomass and forecast of the 2014 spawning biomass were assessed using an integrated statistical catch-at-age model (“the assessment model”).  Advice for each Pacific Herring stock is presented in probabilistic decision tables showing predicted status in 2014 given a range of constant catches relative to target harvest rates and performance metrics relating directly to the existing herring harvest control rule.
• The assessment results and advice are summarized by management area below.  All herring biomass results are reported in metric tonnes (t).  SB denotes spawning biomass. Stock status is measured relative to equilibrium unfished spawning biomass (SB0).
• Recommendations for future work include evaluating current and proposed alternative Pacific Herring management approaches, including the use of alternative reference levels, via simulation testing.  Additional recommendations for future work include evaluating the drivers of recruitment forecasts produced by the assessment model, incorporating sources of fishing mortality not currently captured (e.g., spawn-on-kelp), and the development of biologically-based limit reference points.
• All quantities in the summaries below are reported as the 5 – 95% credible interval with the median value in parentheses – the quantity has a 90% probability of lying in the credible interval.

Haida Gwaii (HG)

• 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 from 2005 through 2013.
• The estimated spawning biomass in 2013 (SB2013) is 14,357 – 54,537 t (median: 28,294 t). SB2013 is estimated to be 0.42 – 1.49 (median: 0.80) of SB0.
• Median spawning biomass has increased since 2008, in part due to increases in the spawn index from 2011 to 2013, above average recruitment in 2010 to 2013, and possibly decreases in natural mortality.
• The projected spawning stock biomass in 2014, assuming no catch, is 12,270 – 58,540 t (median: 26,260 t), consisting of 9 – 74% (median: 36%) age-3 fish and 19 – 83% (53%) age-4 and older fish.  There is high uncertainty in the estimates of the number of age-3 fish in 2014.

Prince Rupert District (PRD)

• All herring spawning in Statistical Areas 3 to 5 are assumed to belong to the Prince Rupert District stock.
• Commercial seine roe and gillnet roe fisheries caught 743 t and 1,284 t, respectively, in 2013.  Commercial spawn on kelp operations also occurred (five licenses).
• SB2013 is estimated to be 16,762 – 60,283 t (median: 32,568 t) and is estimated to be 0.25 - 0.90 (median: 0.49) of SB0.
• Median spawning biomass has increased since 2012 as a result of increases in the spawning index (since 2010), above average recruitment in 2013 and possibly decreases in natural mortality.
• The projected spawning stock biomass in 2014, assuming no catch, is 19,750 – 109,500 t (median: 44,840 t), consisting of 11 – 82% (median: 49%) age-3 fish and 15 – 82% (median: 45%) age-4 and older fish.  There is high uncertainty in the estimates of the number of age-3 fish in 2014.  The estimated recruitment of age-2 fish in 2013 was similar to historical values from the early 1960s and the highest estimate since this period.

Central Coast (CC)

• 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 from 2008 through 2013.
• SB2013 is estimated to be 17,844 – 48,974 t (median: 29,597 t) and is estimated to be 0.29 - 0.78 (median: 0.48) of SB0.
• Median spawning biomass increased from 2011 through 2013 in part due to above average recruitment in 2008, 2010, and 2012, a high spawn index in 2013 (although this was preceded by seven years with low index values), and apparent decreases in natural mortality.
• The projected spawning stock biomass in 2014, assuming no catch, is 13,230 – 41,210 t (median: 23,370 t), consisting of 13 – 29% (median: 20%) age-3 fish and 53 – 78% (median: 68%) age-4 and older fish.

Strait of Georgia (SOG)

• 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.
• 2013 catch in the winter seine fishery (food and bait, special use) was 4,530 t, in the seine roe fishery was 6,099 t, and in the gillnet roe fishery was 5,937 t.
• SB2013 is estimated to be 83,196 – 220,752 t (median: 136,258 t) and is estimated to be 0.62 – 1.48 (median: 0.97) of SB0.
• Median spawning biomass has increased since 2010 due in part to above average recruitment in 2010 and 2011 and apparent decreases in natural mortality.
• The projected spawning stock biomass in 2014, assuming no catch, is 73,260 – 206,000 t (median: 123,300 t), consisting of 27 – 43% (median: 35%) age-3 fish and 42 – 60% (median: 52%) age-4 and older fish. 

West Coast Vancouver Island (WCVI)

• All herring spawning in Statistical Areas 23 to 25 are assumed to belong to the west coast of Vancouver Island herring stock.
• The WCVI stock has been closed to commercial fisheries from 2006 to 2011 and in 2013.  A commercial harvest option was available in 2012 but was not pursued.
• SB2013 is estimated to be 12,782 – 38,799 t (median: 22,464 t) and is estimated to be 0.23 – 0.66 (median: 0.40) of SB0.
• Median spawning biomass has increased since 2008 from historically low levels due in part to above average recruitment in 2010 and apparent decreases in natural mortality.
• The projected spawning stock biomass in 2014, assuming no catch, is 11,880 – 39,360 t (median: 21,770 t), consisting of 19 – 38% (median: 28%) age-3 fish and 37 – 64% (median: 52%) age-4 and older fish. 

Area 2W

• All herring spawning in Statistical Area 2W (except Herring Section 006) are assumed to belong to this Haida Gwaii minor stock.
• A commercial spawn-on-kelp fishery occurred in this area in 2013 (two licenses).
• SB2013 is estimated to be 1,557 – 9,171 t (median: 3,938 t) and is estimated to be 0.45 – 2.23 (median: 1.10) of SB0.
• Median spawning biomass has declined since 2011 in part due to a decrease in the spawn index since 2010 and possibly increases in natural mortality.  Above average recruitment occurred in 2013.
• The projected spawning stock biomass in 2014, assuming no catch, is 1,520 – 11,761 t (median: 4,427 t), consisting of 8 – 56% (median: 33%) age-3 fish and 41 – 89% (median: 64%) age-4 and older fish.  There is high uncertainty in the estimates of the number of age-3 fish in 2014.

Area 27

• All herring spawning in Statistical Area 27 are assumed to belong to this West Coast of Vancouver Island minor stock.
• A commercial spawn-on-kelp fishery occurred in this area in 2013 (two licenses).
• SB2013 is estimated to be 645 – 2,239 t (median: 1,185 t) and is estimated to be 0.31 – 0.98 (median: 0.55) of SB0.
• Median spawning biomass has remained relatively constant over the past decade while natural mortality may have decreased over the same period.  Below average recruitment occurred in 2011-2013.
• The projected spawning stock biomass in 2014, assuming no catch, is 533 – 2,090 t (median: 1,020 t), consisting of 8 – 28% (median: 16%) age-3 fish and 52 – 84% (median: 71%) age-4 and older fish.

This Science Advisory Report is from the Regional Peer Review meeting on ‘Stock Assessment and Management Advice for BC Pacific Herring: 2013 Status and 2014 Forecast’, held on September 4-6, 2013. Additional publications from this process will be posted the on Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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