Fisheries Technologist flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Target strength formula

For swimbladder fish, TS ≈ 19.1 log10(L) − 0.9 log10(f) − 62, with L in cm and f in kHz; doubling fish length raises TS by about 5.7 dB.

Acoustic density conversion

Fish density ρ = sa / σbs, where sa is areal backscattering and σbs = 4π·10^(TS/10); a single large target contributes disproportionately to the estimate.

Sonar equation

SL − 2TL + TS − (NL − DI) = DT; echo detection requires received level to exceed the detection threshold after noise is reduced by the directivity index.

Schaefer MSY

In the Schaefer surplus production model, MSY = rK/4 and occurs at biomass B = K/2, where r is intrinsic growth rate and K carrying capacity.

Catchability coefficient

CPUE = q·N, where q is catchability; CPUE is a valid abundance index only if q stays constant across time, area, and gear.

Hyperstability

A condition where catchability rises as stock abundance falls, so CPUE stays high while the stock declines, masking overfishing in index-based assessments.

Length-weight relationship

W = aL^b; b ≈ 3 indicates isometric growth, b > 3 positive allometry, and parameters are fitted by log-linear regression of ln W on ln L.

Gear selectivity logistic

Retention P(L) = 1/(1 + exp[−S(L − L50)]); L50 is the length at 50% retention and S the steepness of the selection curve.

Unionized ammonia toxicity

The NH3 fraction of total ammonia nitrogen rises with pH and temperature, so toxicity worsens at high pH even when measured total ammonia is unchanged.

Biofilter nitrogen cycle

Ammonia-oxidizing bacteria convert NH4+ to NO2−, then nitrite-oxidizing bacteria convert NO2− to NO3−; nitrite peaks during biofilter startup.

Feed conversion ratio

FCR = feed offered / wet weight gain; an apparent FCR near or below 1.0 usually signals measurement error or unaccounted natural food.

Tilapia sex reversal

Feeding 17α-methyltestosterone during the undifferentiated fry stage, roughly the first 21–28 days post-hatch, yields predominantly male tilapia populations.

Dissolved oxygen limitation

Dissolved oxygen is the first limiting factor in intensive aquaculture; warm water holds less oxygen, so safe thresholds fall as temperature rises.

RAS water reuse

Recirculating systems require solids removal, biofiltration, and gas exchange, with water exchange typically a few percent per day and salinity and alkalinity monitored.

Dietary protein and ammonia

Excess dietary protein is catabolized and excreted as ammonia, raising biofilter load; protein requirement falls with fish size and rises with temperature up to the optimum.

Pond carrying capacity

Carrying capacity is set by natural productivity plus aeration and feed; aeration raises standing crop but cannot exceed the oxygen transfer capacity of the installed aerators.

Total mortality equation

Z = F + M; total mortality is estimated as the descending slope of ln(catch) versus age in a catch curve, separating fishing from natural mortality.

Virtual population analysis

VPA back-calculates cohort size from catch-at-age and natural mortality; terminal F assumptions strongly influence estimates for recent years.

Gillnet selectivity shape

Gillnet retention is bell-shaped because it depends on fish girth relative to mesh size, unlike the logistic curve typical of trawl codend selection.

Longline soak-time saturation

CPUE plateaus as soak time lengthens because hooks become occupied or bait is lost, so effort must be standardized to a fixed soak duration.

CPUE standardization

Generalized linear models such as log-link delta-lognormal remove effects of vessel, area, season, and gear from catch rates before CPUE is used as an abundance index.

Yield per recruit

The Beverton–Holt yield-per-recruit model depends on fishing mortality and age at first capture; larger mesh raises yield per recruit when growth overfishing exists.

Bycatch reduction devices

BRDs such as turtle excluder devices and square-mesh panels reduce non-target catch while retaining marketable size classes of the target species.

FAD management

Fish aggregating device sets on purse seiners raise catch of small tunas and bycatch, so closures are used to protect juvenile stocks.

Rigor mortis handling

Fish pass through pre-rigor, rigor, and resolution phases; handling during rigor causes gaping and texture damage, so processing occurs pre-rigor or post-resolution.

Spoilage temperature coefficient

Q10 ≈ 2 for bacterial spoilage means every 10 °C rise roughly doubles spoilage rate, so rapid chilling to 0 °C extends shelf life.

TVB-N spoilage indicator

Total volatile basic nitrogen and trimethylamine indicate spoilage; TVB-N limits around 25–35 mg/100 g are used as rejection thresholds in many standards.

Histamine formation

Scombroid fish held above about 4 °C form histamine by bacterial decarboxylation of histidine; the toxin is heat-stable and survives cooking.

Freezing quality

Freezing at −18 °C or below preserves quality; slow freezing forms large extracellular ice crystals that rupture cells and cause drip loss on thawing.

Water activity in curing

Drying to water activity below about 0.75 inhibits most spoilage bacteria but not all xerophilic molds, so cured fish still requires careful storage.

Fillet yield

Fillet yield = fillet weight / whole fish weight; species with high yield and low processing waste give better economic returns in value-added products.

HACCP cold chain

Critical control points are set at chilling and storage steps; time–temperature integrators and data loggers document abuse from harvest through retail.