Analysis and Response
Fishery Managers requested DFO Science provide and organize available data and other information to address the questions outlined below. These responses will facilitate consultation with First Nations, Industry and other stakeholders in the development of additional fishery management measures that may be required to address declines in Chinook Salmon stock productivity.
Q1. Provide information to determine which stocks require a reduction in fishery exploitation.
Criteria that may be used to determine which stocks may require further management measures to adjust fishery impacts include:
· Recent average exploitation rates relative to estimates of sustainable exploitation (EMSY) given current stock productivity (Table 6);
· Level of recent escapement relative to management goals (Table 7);
· Evidence of recent declines in marine survival rate (Figure 2);
· Identification of other fishery related impacts, such as selective fishing practices, that may be contributing to declines in stock productivity.
A significant issue for these preliminary analyses is that most of the data used to estimate these management parameters are from data-rich stocks. In all cases, there are significant sources of uncertainty with the available data and analysis of management parameters. Further work is required to develop and evaluate stock assessment methods that can be applied to more data limited stocks. Science is currently developing these methods and more complete information to inform data limited assessments and risk-appropriate management responses will be available through future work.
Q2. What tools and information can Science provide to inform trade-offs associated with a range of potential reductions in fishery exploitation rates?
Reductions in fishery exploitation rates to achieve stock rebuilding objectives and fishery objectives inherently involve management choices such as rebuilding times and risk tolerance (i.e., the probability of achieving those objectives). Appropriate tools to inform decisions regarding the trade-offs are not currently available; however development of these tools is already underway within DFO Science. For example, simulations or retrospective analyses can identify benefits and costs associated with a range of fishery reductions and management strategies. Retrospective analysis or simulations will require management input in the form of development of target objectives for evaluation, and the identification of potential management strategies to achieve those objectives. Co-management processes, such as the Southern BC
Chinook Initiative, are recommended as appropriate venues to conduct such management strategy evaluations due to their inclusivity and broad representation.
Q3 What information can Science provide to inform development of management measures if it is determined reductions are required?
Declines as described in the Background section may warrant either reduction in exploitation rates and/or measures to reduce fishery related impacts that may contribute to negative demographic changes in populations (e.g. harvest practices that selectively remove older and larger fish). Strategies for reducing fishing impacts on stocks of concern may include implementing measures such as reductions in total allowable catch or fishing effort; area closures in times when stocks of concern are prevalent; bag limits; size limits; and other gear restrictions (e.g., net mesh size). Once the stocks and targets for potential reductions are identified, more specific input can be provided by Science to inform development of specific management measures. Methods used to assess proposed fishery measures on a by-fishery basis will depend on how proposed reductions are implemented. Science can use data including historical fishery impacts, stock distribution and timing, size at catch and fishing effort to model expected reductions in fishery impacts. However, these plenary models are limited by the available data and information. This limitation is particularly important for data-limited stocks or CUs because the scale of reductions that can be modeled is directly related to the quality of the data inputs; the data are generally inadequate to model finer-scale or incremental reductions in fisheries associated with data-limited management units.
Q4 What are the potential metrics/indicators that could be used to assess whether or not objectives have been met? Provide commentary on strengths and weaknesses of proposed assessment methods.
Metrics/indicators that could be used to assess whether or not objectives have been met should be similar to the criteria used to set targets for reduction. That is, for the management units in which management actions are taken, performance metrics could include:
· A reduction in observed exploitation rate to a level consistent with EMSY;
· An increase in escapement of indicator stocks within the management unit (i.e., observe
rebuilding towards a target);
An observed reduction in size-selective fishery impacts.
In all cases, the sources of uncertainty associated with potential metrics and data deficiency should be considered and targets set accordingly. The ability to assess the achievement of specific reduction targets post-season on a by-fishery basis is dependent on catch monitoring and sampling programs conducted during the fishing season. Current sampling programs in many fisheries are inadequate to evaluate incremental reductions in fishery impacts and it may be impractical to increase sampling in order to assess incremental reductions. Therefore, the choice of performance metrics/indicators identified on a by-fishery basis that are inconsistent with current stock assessment and catch monitoring frameworks (or highly sensitive to the uncertainty of the available data) may require additional monitoring and sampling programs. As well, many escapement programs produce relatively imprecise estimates of spawning abundance. Finally, detecting measurable improvements associated with fishery actions on annual basis may not be possible given inter-annual variation in environmental conditions that influence marine survival rate and stock abundance.