Reference Points Flashcards
What is a reference point?
a conventional value, derived from technical analysis, which represents a state of the fishery or population, and whose characteristics are believed to be useful for the management of the unit stock
What are reference points typically based on?
fishing mortality rates (F), biomass levels (B), or recruitment indices
What are reference points used for?
used to determine allowable effort and harvest
-important that reference points are agreed upon by managers and fishery stakeholders.
What are the three reference points used?
Target Reference Point (TRP)
Limit Reference Point (LRP)
Trigger (or Threshold) Reference Point
Target Reference Point (TRP)
indicates a state of a fishery and/or a resource that is considered desirable and at which management action should aim
include economic or social considerations (ideal state of fishery) in addition to biological criteria
Limit Reference Point (LRP)
indicates a state of a fishery and/or a resource that is considered undesirable and which management action should avoid
Includes on only biological based
Trigger (or Threshold) Reference Point
set between TRP and LRP to promptadditional management response to help ensure fishery remains close to target and/or avoidsbreaching limit
MSY stand for
Maximum sustainable yield
Maximum sustainable yield
largest amount of resource that can be taken continuously without causing a population decline
What are some reference points based around MSY
BMSY or X%BMSY
FMSY or X%FMSY
BMSY or X%BMSY
biomass at MSY or X% MSY
FMSY or X%FMSY
fishing mortality rate that leads to BMSY or X% fishing mortality rate that leads to BMSY
How can MSY reference points be produced?
from a variety of population models (surplus production, age-structured) and are considered more data-intensive as compared to alternatives
MSY in fisheries management
now more often used as a limit
Pretty Good Yield
Considerable uncertainty both in stock size and harvest rate that achieve MSY as well as in ability to manage for MSY
Pretty good yield → 80% of MSY
PGY occur
Occurs over broad range of stock sizes and harvest rates
What does PGY depend on?
steepness of S/R curve (productivity of stock when fished to low level)
Fmax and F0.1
Based on yield per recruit (YPR) curve → how changes in exploitation rate affect lifetime expected yield of an individual recruit or cohort
Fmax
fishing mortality rate that maximizes YPR
F 0.1
fishing mortality rate where slope of YPR curve is 10% slope at origin
F 0.1
is more conservative and may be a target or limit reference point
Fmax
(when used) is typically a limit
YPR curve depends on
growth, natural mortality, and age-specific fishery selectivity (relatively low data requirements)
Fmax , F0.1 used where
growth overfishing is a concern
What is the downside to Fmax , F0.1
does not consider recruitment overfishing and may lead to fishing mortality rates that are too high
Fmax , F0.1 can be > FMSY
Recruitment based reference points
FX%
Fmed
Used as reference points for recruitment overfishing
FX%
fishing mortality rate that reduces stock to X% of maximum spawning potential
Can be target or limit (for target, X typically 40-50%, whereas limit is lower)
Fmed
fishing mortality rate that corresponds to median value of stock-recruit ratio
What are the data requirements for both recruitment-based reference points?
Minimal data requirements (natural mortality, age-specific fishery selectivity and fecundity); possible to use life history correlates
FMEY
fishing mortality rate that produces maximum economic yield
Index or empirical reference points
points such as historical CPUE values (e.g., median) are occasionally used; often easier to understand though more error-prone
Multispecies Biological Reference Points
Single species reference points
Multispecies Maximum Sustainable Yield (MMSY)
Single species reference points
can be fit into multispecies framework using models that incorporate multispecies interactions, e.g., include predation mortality (often referred to as “M2”) in determining FMSY or FX%
MMSY
incorporates predation and trophic relationships (bioenergetics) in estimating MSY across species/system → often (but not always) found to be less than sum of single species MSYs
Examples of reference points based on environmental conditions:
Pacific sardine effort targets depend on sea-surface temperature
Atlantic menhaden example with an environmental reference point - why?
Atlantic menhaden supports an important commercial reduction fishery as well as a growing bait fishery
Menhaden are also an important prey item for several species (e.g., striped bass, bluefish)
Single species reference points based on fecundity had been used until 2020; menhaden above threshold since 1991
2021/2022 TAC based on ecological reference points
Atlantic menhaden example with environmental reference point - resolution
Ecological reference points (ERPs) evaluated using the Northwest Atlantic Coastal Shelf Model of Intermediate Complexity for Ecosystems (NWACS-MICE)
Menhaden target and threshold fishing mortality rates are a function of striped bass biomass and fishing mortality target
Northwest Atlantic Coastal Shelf Model of Intermediate Complexity for Ecosystems (NWACS-MICE)
Includes four key predators (striped bass, bluefish, weakfish and spiny dogfish) and three key prey (menhaden, Atlantic herring, and bay anchovy)
Harvest control rules (HRCs)
Guidelines for allowable catch, effort, or fishing mortality based on fishery reference points
Pre-agreed upon management response thought to increase efficiency and transparency of management process
How are HCRs assessed?
compared through management strategy evaluations (MSEs)
MSE is what type of approach?
simulation
can be used to evaluate assessment models in comparison to “true” stock abundances as well as to determine what decision rules are most effective in meeting target reference points
What do MSEs generally allow for?
“implementation error” → HCRs/management measures not perfectly implemented
