Science Advisory Report  2011/030

Recovery Potential Assessment of American Plaice (Hippoglossoides platessoides) in Newfoundland and Labrador

Summary

• Abundance of American Plaice has declined over its entire range. In some parts of its range the decline was over 90% compared to historic population. American Plaice populations have shown some improvement but are still at low levels.
• The greatest threat to the recovery of American Plaice over most of the area is continued fishing mortality. Fishing mortality occurs exclusively as by-catch in other commercial fisheries. In the SA2+Div.3K population productivity remains very low, probably as a result of high natural mortality.
• The results of this RPA are mainly based on projections of stock size over 48 years (3 generations). Long term projections are dominated by process error (uncertainty in recruitment rates, mortality rates, etc.) so that their utility is not in providing probabilities of specific outcomes but rather in defining the uncertainty. The entire range of uncertainty, particularly the lower limits need to be considered in any conclusion.
• Given the results of these projections, there is scope for management action to facilitate recovery through a reduction in fishing mortality.
• For the Newfoundland and Labrador designatable unit (DU) as a whole, results of projections of population biomass over 48 years at current fishing mortality (F) range from an increase of more than 7 times to a decrease in biomass to reach less than 50% of the biomass in 2009. Most of the range encompassed by approximately 95% of the results is above the level of biomass at the beginning of the projection period.
• For Div. 3LNO at current F (0.172), projections of population biomass show that biomass could be from 6.5 times to only 45% of 2009 biomass by the end of the 48 year projection. It should be noted that at current F by the end of the projection period a substantial proportion of the projected spawning stock biomasses (SSB) remain below Blim.
• For SA 2+Div. 3K at current F (<0.001), projections of population biomass show that biomass could increase from 10 to 2400% compared to the biomass in 2009.
• In Subdiv. 3Ps at current F (0.025), projections of population biomass show that biomass could increase from 4 to 9 times the biomass in 2009.
• For the DU as a whole there is a substantial increase in biomass over 48 years with an F=0. All populations in the DU have an increase under the scenario of no fishing.However, for SA 2+Div. 3K there is some possibility of only a small increase in this population even with no fishing. For Div. 3LNO American Plaice the management target of exceeding Blim is also projected to be reached under an F=0 fishing scenario.
• For Div. 3LNO the maximum F for allowable harm is less than F=0.15.  At this level of F, most of the range encompassed by 95% confidence intervals shows an increase in biomass and in spawning stock numbers relative to 2009. However, a substantial number of the results do not reach Blim.
• For SA2+Div.3K the maximum F for allowable harm is near F=0.06. At this level of F, most of the range encompassed by the 95% confidence intervals shows increase in biomass relative to the biomass in 2009. However, some of the projection results showed a more than 30% decline in biomass relative to 2009.
• For Subdiv. 3Ps the maximum F for allowable harm is less than F=0.137. At this level of F, most of the range encompassed by the 95% credible intervals shows increase in biomass relative to the biomass in 2009. However, some of the projection results showed a more than 30% decline in biomass relative to 2009.
• Habitat availability is not considered to be a limiting factor in the recovery of the Newfoundland and Labrador DU of American Plaice.

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Regional Advisory Meeting of January 24-26^th, 2011 on Recovery Potential Assessment (RPA) of American Plaice, Newfoundland and Labrador DU. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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