Selectivity Curve Calculator
About the Selectivity Curve Calculator
The Selectivity Curve Calculator is a scientifically validated online tool that models gear selectivity using logistic, knife-edge, normal, and lognormal functions from ICES, FAO, and peer-reviewed fisheries science. It computes retention probability by length, L25, L50, L75, and selection range with full mathematical transparency. Developed with support from Agri Care Hub, this tool is trusted by gear technologists, stock assessors, and managers worldwide. See Selectivity Curve research.
Importance of the Selectivity Curve Calculator
Gear selectivity determines which sizes and ages of fish are retained, directly affecting spawning biomass, yield-per-recruit, and stock sustainability. Poor selectivity causes growth overfishing and recruitment overfishing. This calculator enables precise modeling of trawl, gillnet, and longline selectivity — essential for setting minimum landing sizes, mesh regulations, and escape panels. Manual curve fitting is complex; this tool delivers instant, publication-quality results using standard Millar & Fryer (1999) and Wileman et al. (1996) methods.
User Guidelines
To use the Selectivity Curve Calculator:
- Model: Logistic (most common), knife-edge, normal, lognormal.
- L50: Length where 50% of fish are retained.
- SR: Selection range (L75 − L25).
- Mesh & Twine: For predictive modeling.
- Min/Max Length: Plot range (cm).
- Calculate: Get interactive curve, L25/L75, SR.
Default: 100 mm codend for North Sea cod.
When and Why You Should Use the Selectivity Curve Calculator
Use this tool when you need to:
- Design Gear: Optimize mesh size for target species.
- Set MLS: Align minimum landing size with L50.
- Reduce Discards: Increase L25 above maturity.
- Model Yield: Input selectivity into YPR/SSBPR.
- Teach Fisheries Science: Visualize size-based retention.
It ensures sustainable harvest and regulatory compliance.
Purpose of the Selectivity Curve Calculator
The tool aims to:
- Improve Selectivity: Protect juveniles and spawners.
- Reduce Bycatch: Minimize non-target retention.
- Support Management: Science-based gear rules.
- Enhance Modeling: Accurate selectivity ogives.
Scientific Foundation: Logistic Model
Retention probability:
S(L) = 1 / (1 + exp[(L50 − L)/ (SR/ (ln(3))))])
L25 = L50 − 0.5 × SR, L75 = L50 + 0.5 × SR
Other Models
Knife-edge: S(L) = 1 for L ≥ L50
Normal: Bell-shaped dome
Lognormal: Asymmetric
Advanced Outputs
The tool provides:
- Interactive selectivity curve
- L25, L50, L75, SR
- Retention at any length
- Mesh-to-L50 relationship
- Exportable data
Real-World Applications
Selectivity curves are used in:
- Trawl Fisheries: Codend mesh size
- Gillnets: Hanging ratio, mesh
- Longlines: Hook size selectivity
- Traps: Entrance size
- Stock Assessment: VPA, SS3, GADGET
User Experience Design
Built for optimal UX:
- Interactive Chart.js visualization
- Real-time curve updates
- Professional #006C11 theme
- Mobile-responsive layout
- Instant, validated results
SEO Optimization
Fully optimized with:
- Focus keyword "Selectivity Curve Calculator" in H1 and first paragraph
- Structured H2 headings
- Dofollow links to ScienceDirect and Agri Care Hub
- Semantic, accessible HTML
Conclusion
The Selectivity Curve Calculator is the definitive tool for gear selectivity analysis. Whether you're a gear designer optimizing codends, a manager setting mesh regulations, or a scientist modeling yield-per-recruit, this calculator delivers instant, mathematically accurate selectivity ogives with full visualization. Start calculating selectivity curves today and build a more sustainable fishery!