Fishery Exam 2

Recruitment

The number of fish reaching a defined life stage, such as reaching age 1 or entering the harvested fishery.

Spawning stock biomass (SSB)

The total biomass of mature, reproductive fish within a population.

Stock-recruit relationship

The mathematical or empirical link between spawning biomass and the subsequent number of recruits produced.

Critical period hypothesis (Hjort)

A mechanism proposing that massive larval mortality occurs immediately after yolk-sac absorption if suitable first-feeding food is unavailable.

Match-mismatch hypothesis (Cushing)

A principle stating that larval survival improves when the timing of spawning and first feeding coincides with peak seasonal zooplankton blooms.

Lasker ocean stability hypothesis

The concept that calm, stratified ocean conditions concentrate prey into dense micro-patches essential for larval feeding, whereas storm mixing disperses food.

Effect of moderate turbulence on larvae

Increases encounter rates between feeding larvae and prey without completely dispersing food patches.

Bigger-is-better hypothesis

The idea that larger, faster-growing larvae suffer lower cumulative mortality because they experience lower vulnerability to size-selective predators.

Reynolds number ($Re$)

The dimensionless ratio of inertial forces to viscous forces in a fluid, calculated as $Re = \frac{Ud}{\nu}$.

Low Reynolds number regime

A hydrodynamic condition where viscous forces dominate over inertial forces, characterizing the physical environment of small fish larvae.

Pelagic larval duration (PLD)

The time larvae spend developing in the open water column, dictating their potential dispersal distance and drift trajectories.

Population connectivity

The demographic exchange and movement of individuals between geographically distinct sub-populations or habitats.

Dispersal impact on assessment

Movement across management boundaries complicates stock unit definitions, abundance indexing, and jurisdictional harvest regulations.

Unit stock

A self-contained biological population characterized by uniform vital rates that can be assessed and managed as a discrete harvest unit.

Stock identification methods

Techniques used to distinguish discrete fish stocks, including genetics, electronic or physical tagging, otolith microchemistry, stable isotopes, and parasite tags.

Density dependence

The process whereby per-capita demographic rates such as survival, growth, or reproductive output vary according to population density.

Negative density dependence

The decline in per-capita survival, somatic growth, or fecundity as abundance increases due to crowding and resource competition.

Ideal free distribution (IFD)

A behavioral distribution theory predicting that organisms distribute across habitats until realized per-capita suitability across all patches becomes equal.

Basin model

A spatial pattern where a fish population expands into lower-quality peripheral habitats at high abundance and contracts into core areas at low abundance.

Hyperstable CPUE

A scenario in which catch per unit effort remains high despite severe underlying declines in stock biomass.

Mechanism of hyperstable CPUE

Occurs when schooling fish stay aggregated in preferred areas and commercial fishers deliberately locate and target these dense patches.

Climate-driven range shifts

Shifts in spatial distribution caused by thermal or oceanographic alterations that happen independently of total population abundance.

Bioenergetics

The study and quantitative tracking of energy acquisition, metabolic expenditure, waste losses, and somatic growth in an organism.

Bioenergetics budget equation

Somatic growth equals energy consumed minus energy lost to respiration, digestion, waste excretion, egestion, and gonadal tissue.

Bioenergetic consumption ($C$)

The total energy acquired by an individual through food intake.

Bioenergetic respiration ($R$)

The energy expended on standard basal metabolism, active movement, and cellular maintenance.

Specific dynamic action (SDA)

The metabolic cost and energy required to ingest, digest, absorb, and process food.

Egestion ($F$)

The energetic loss of unassimilated food material through fecal matter.

Excretion ($U$)

The loss of assimilated nitrogenous wastes and metabolic byproducts through urine and gill surfaces.

Gonad growth ($G$)

The fraction of assimilated energy allocated directly to the development of reproductive tissues.

Effect of elevated metabolic costs with fixed consumption

Leaves less net energy available for somatic tissue accumulation, resulting in reduced somatic growth.

Fish condition

The relative health, body chunkiness, or mass-to-length ratio of a fish compared to an expected reference standard.

Stunting

Abnormally small body size at age resulting from prolonged resource deprivation, overcrowding, or poor environmental quality.

Aerobic scope

The physiological difference between an organism's maximum metabolic rate and its standard basal metabolic rate.

Impact of dissolved oxygen reduction

Suppresses aerobic scope and limits maximum feeding capacity, ultimately constraining growth.

Thermal effects on oxygen and metabolic demand

Warm temperatures lower ambient oxygen solubility while simultaneously increasing basal metabolic rates and tissue oxygen requirements.

Seasonal cohort

A distinct pulse of individuals born during a specific spawning window that experiences unique environmental regimes during early life.

Von Bertalanffy growth model equation

The mathematical formulation describing length as an asymptotic function of age: $L(t) = L_\infty \left[1 - e^{-k(t - t_0)}\right]$.

Asymptotic length ($L_\infty$)

The theoretical mean length individuals would reach if they lived indefinitely, rather than the maximum possible length an individual can attain.

Growth curvature parameter ($k$)

The rate constant determining how rapidly an individual's mean length approaches asymptotic length.

Theoretical age at zero length ($t_0$)

The modeled mathematical intercept where calculated length equals zero, representing an equation artifact rather than biological size at hatch.

Consequence of higher von Bertalanffy $k$

A more rapid approach toward asymptotic mean length, assuming all other model parameters remain unchanged.

Consequence of higher $L_\infty$

A larger theoretical average asymptotic size at old ages, assuming other parameters remain fixed.

Size-at-age data

Empirical observations pairing individual measured body lengths or weights with their corresponding estimated ages.

Ogle (2013) interpretation warning

Reminds practitioners that $L_\infty$ is an average asymptotic length rather than an absolute maximum, and $k$ is a curvature coefficient rather than annual length gained.

Stock assessment

The quantitative scientific evaluation of fish population status and the demographic responses expected under alternative harvest strategies.

Stock assessment versus management

Scientists provide quantitative demographic predictions and risk evaluations, whereas managers establish regulatory actions and acceptable risk thresholds.

Population dynamics

The quantitative study of temporal changes in population size, demographic rates, and age or size structure.

Exponential growth

Unconstrained population increase occurring at a constant per-capita rate, expressed as $\frac{dN}{dt} = rN$.

Logistic growth

Density-limited population growth where per-capita rate declines as abundance approaches environmental carrying capacity.

Intrinsic rate of increase ($r$)

The maximum theoretical per-capita population growth rate in the absence of density-dependent limits.

Carrying capacity ($K$)

The maximum equilibrium population abundance or biomass that an environment can support over time.

Logistic growth differential equation

The rate of population change described by $\frac{dN}{dt} = rN\left(1 - \frac{N}{K}\right)$.

Net logistic growth at $N = K$

Zero net production, as recruitment perfectly balances natural mortality at carrying capacity.

Abundance producing maximum logistic surplus production

Occurs at half of environmental carrying capacity: $N = \frac{K}{2}$.

Logistic population trajectory when $N < K$

Positive net population growth directing abundance upward toward carrying capacity.

Logistic population trajectory when $N > K$

Negative net growth causing abundance to decline back toward carrying capacity.

Fisheries catch equation

The formulation relating catch to abundance and fishing activity: $C = qEN$.

Catch per unit effort (CPUE)

Catch divided by fishing effort ($\frac{C}{E}$), functioning as an index of abundance only when catchability is constant.

Catchability ($q$)

The proportion of the total stock biomass or population removed by one standard unit of fishing effort.

State/process model

The assessment component representing true unobserved biological dynamics, survival, and transition rules over time.

Observation model

The assessment component linking true underlying stock states to observed sampling data, such as surveys and commercial catches.

Simulation model

A forward-projecting framework using fixed input parameters to model hypothetical outcomes without fitting to empirical data.

Estimation (assessment) model

A statistical framework that estimates unknown demographic parameters by fitting equations to collected empirical observations.

Least squares estimation

A model-fitting procedure that optimizes parameters by minimizing the sum of squared differences between observed and predicted values.

Maximum likelihood estimation

A statistical parameter optimization method that maximizes the probability of observing the sampled data under the model.

Adaptive management

A structured management framework that accounts for uncertainty, implements actions, monitors outcomes, and adjusts future decisions based on learning.

Shifting baseline syndrome

The gradual shift in human perception of normal ecological abundance as successive generations accept increasingly degraded conditions as baseline.

Age-structured model

A population model that tracks individual age classes, age-specific mortality, maturation, and gear selectivity over time.

Error propagation

The transfer and magnification of observation noise and parameter errors through mathematical models into final forecasts.

Myers et al. (2001) approach

A meta-analytic study evaluating stock-recruit dynamics across hundreds of fish populations to uncover universal reproductive metrics.

Myers et al. maximum reproductive rate finding

Depleted stocks typically generate $1$ to $7$ replacement spawners per spawner per year at low population density.

Drivers of high recruitment variability (Myers et al.)

Low spawner abundance, high fecundity, locations at geographical range margins, and unstable oceanographic regimes.

Beverton-Holt stock-recruit curve

A formulation where recruitment increases toward an asymptotic ceiling as spawner biomass increases, representing post-settlement competition.

Ricker stock-recruit curve

A dome-shaped curve where recruitment increases to an intermediate peak and subsequently declines at high spawner abundance due to cannibalism or crowding.

Compensation

The density-dependent increase in per-capita survival or reproductive success that occurs as spawning abundance drops.

Overcompensation

Severe density dependence at high spawner levels that causes total absolute recruitment to decrease.

Depensation (Allee effect)

A critical drop in per-capita reproductive rate or juvenile survival when a population declines to very low abundance.

Maximum sustainable yield (MSY)

The largest long-term average harvest that can be continuously removed from a stock under prevailing environmental conditions.

Biomass at MSY ($B_{\text{MSY}}$)

The stock biomass level that generates maximum surplus production and sustains maximum sustainable yield.

Fishing mortality at MSY ($F_{\text{MSY}}$)

The instantaneous fishing mortality rate that results in maximum sustainable harvest over the long term.

Schaefer MSY formulation

The maximum sustainable yield derived from the logistic surplus production model: $\text{MSY} = \frac{rK}{4}$.

Schaefer $B_{\text{MSY}}$ formulation

The biomass level supporting peak logistic production: $B_{\text{MSY}} = \frac{K}{2}$.

Schaefer exploitation rate at MSY ($U_{\text{MSY}}$)

The harvest fraction corresponding to maximum surplus production: $U_{\text{MSY}} = \frac{r}{2}$.

Impact on MSY if $r$ doubles

Maximum sustainable harvest doubles, provided that carrying capacity $K$ remains constant in the Schaefer model.

Impact on $B_{\text{MSY}}$ if $K$ doubles

The biomass required for maximum sustainable yield doubles, as $B_{\text{MSY}} = \frac{K}{2}$.

Yield per recruit (YPR)

The expected harvested weight generated from an average individual recruit under specified fishing mortality and gear selectivity.

Growth overfishing

Harvesting fish at an excessively small size or high rate before they have realized their individual growth potential.

Recruitment overfishing

Depleting mature spawning biomass to a level that impairs replacement recruitment.

$F_{\text{max}}$ reference point

The fishing mortality rate that maximizes total yield per recruit on a standard yield-per-recruit curve.

$F_{0.1}$ reference point

A conservative harvest benchmark where the slope of the yield-per-recruit curve is $10\%$ of its initial value near the origin.

Gear selectivity

The size- or age-dependent probability that an individual fish is retained upon encountering fishing gear.

Biomass limit ($B_{\text{lim}}$)

A critical biological threshold below which recruitment is severely threatened and stock collapse risks increase dramatically.

Target reference point

A desirable stock biomass or harvest rate benchmark that fishery managers actively aim to achieve and maintain.

Limit reference point

A dangerous threshold of stock status or fishing mortality that management rules seek to avoid crossing.

Overfishing limit (OFL)

The annual catch limit estimated from stock assessment that corresponds to the maximum rate of fishing mortality before overfishing occurs.

Acceptable biological catch (ABC)

A harvest quota reduced below the overfishing limit to buffer against scientific uncertainty in assessment models.

Total allowable catch (TAC)

A harvest allocation set below the acceptable biological catch to account for operational and management implementation uncertainty.

Hierarchy of harvest limits

The standard risk-averse ordering of annual fishing thresholds: $\text{TAC} < \text{ABC} < \text{OFL}$.

Harvest control rule (HCR)

A predefined operational guideline that systematically adjusts fishing mortality in response to changes in estimated stock biomass.