Research Document - 2005/048
Management Framework for Strait of Georgia Lingcod
By Logan, G., W. de la Mare, J. King, D. Haggarty
Lingcod populations in the Strait of Georgia have been severely depressed for several decades and a commercial fishery closure was implemented in 1990 followed by a recreational fishery closure implemented in 2002. A Stock Assessment Framework for lingcod suggested that a management framework be developed in consultation with stakeholders that would identify benchmark abundance levels as reference points to measure recovery in abundance and identify management action associated with those benchmarks. In response to that recommendation, the Lingcod Mangement Framework Committee was formed in 2004 and included federal and provincial fisheries agencies’ staff along with representatives of the recreational fishery sector, the commercial fishery sector and conservation groups. The committee identified criteria to be used as reference points in classifying the status of Strait of Georgia lingcod and to be used as decision rules for fishery management. Estimates of historic high levels of biomass are used in lieu of biomass estimates for the unfished Strait of Georgia lingcod population. Proportions of historic high biomass of 40% (B40%), 25% (B25%) and 10% (B10%) were selected as reference points for defining the status of lingcod populations and as decision rules for management actions. The B40% level was identified as a desirable, long-term recovery target for Strait of Georgia lingcod abundance. Between B25% and B10%, the population would be considered to be overfished. B25% was identified as a desirable, short-term recovery target for Strait of Georgia lingcod if the current biomass levels fell below this reference point. The recommended timeframe for assessing forecasted biomass trajectories is 10 years. At B25% the acceptable level of probability associated with identifying potential harvest levels should be at least 90%. At B10% this probability level should be between 99-100%, and as such no harvest would be permitted for population estimates at or below B10%.
A Ricker stock-recruitment age structured model was selected by the committee to estimate historic and current biomass levels. The Strait of Georgia was modelled as a single unit (Statistical Areas 13-19; 28 and 29); as four geographic areas (Southeast: Statistical Areas 28 and 29, excluding 29-5; Northeast: Statistical Areas 15 and 16; Northwest: Statistical Areas 13 and 14; Southwest: Statistical Areas 17, 18, 19 and 29-5); and as a modified geographic area that excluded the Southeast area since catch and effort data for this area were unreliable and its current biomass estimates were less than 1% of historic biomass estimates. Current biomass estimates for the Northeast, Northwest and Southwest geographic areas were 12%, 7% and 20% respectively of historic biomass estimates.
The population model selected by the committee combined these three geographic areas and estimated the lowest level of depletion to have occurred in 1990 (2% of historic biomass) and the current biomass of lingcod is estimated to be 15% of historic biomass levels. Using the outlined management framework, this population is classified as overfished and any harvest level selected should be associated with a 95% probability of maintaining an increase in biomass for 10 years.
The mean annual estimate of recreational landings prior to the closure in 2002 (1991-2001) was 4,880 pieces, ranging from 2,912 pieces in 1999 to 8,219 pieces in 2001. Based on these historic recreational fishery harvest levels, the committee recommended an annual harvest between 5,000 – 7,000 pieces. Stock projections for 5,000 and 7,000 pieces annually for the next 10 years suggests that there is a 50% probability that the stock will be at 44% and 43% respectively of historic biomass in the year 2013.
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