Bycatch Rate Calculator
Compute bycatch rate using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
Bycatch Rate = ((Total - Target) / Total) x 100
Proportion of non-target catch in total harvest. Adjusted for gear selectivity. Endangered impact as individuals per metric ton.
Worked Examples
Example 1: Shrimp Trawl
Problem: Total 3000 kg, target 800 kg, 80 hrs, 5 endangered, selectivity 1.0.
Solution: Bycatch=2200 kg\nRate=73.3%\nPer hour=27.5 kg/hr\nEndangered/ton=1.67
Result: 73.3% bycatch (Critical)
Example 2: Trap Fishery
Problem: Total 2000 kg, target 1850 kg, 200 hrs, 0 endangered, selectivity 0.4.
Solution: Bycatch=150 kg\nRate=7.5%\nAdjusted=3.0%\nPer hour=0.75 kg/hr
Result: 7.5% bycatch (Sustainable)
Frequently Asked Questions
What is bycatch and why is it a problem?
Bycatch refers to non-target species unintentionally caught during commercial fishing including wrong species marine mammals sea turtles and sharks. Globally bycatch accounts for 10 to 40 percent of total catch representing 7 to 10 million metric tons of wasted marine life annually. It contributes to population declines of vulnerable species disrupts food webs and undermines fishery sustainability.
How is the bycatch rate calculated?
Basic bycatch rate is the weight of non-target catch divided by total catch as a percentage: (Total - Target) / Total x 100. It can also be expressed as bycatch per unit effort such as kg per fishing hour. Adjusted rates account for gear-specific selectivity since some methods inherently produce more bycatch. These metrics allow comparison between different gear types areas and seasons.
Which fishing gear types produce the most bycatch?
Bottom trawls are the most indiscriminate with rates often exceeding 30 to 60 percent. Shrimp trawls discard 5 to 10 kg of bycatch per kg of shrimp. Gillnets entangle marine mammals and turtles. Longlines attract non-target seabirds and sharks. Purse seines have lower rates but trap entire non-target schools. Trap and pot fisheries generally have the lowest bycatch because non-target species can often escape.
How does bycatch affect endangered species?
Bycatch is the greatest direct threat to many endangered marine species. An estimated 300000 cetaceans 250000 sea turtles and 100000 albatrosses die annually as bycatch. For small populations even a few individuals caught can push species toward extinction. The vaquita porpoise with fewer than 10 remaining has been driven to near-extinction primarily by gillnet bycatch in the Gulf of California.
What technologies reduce bycatch?
Turtle excluder devices in trawl nets reduce turtle bycatch by 97 percent. Circle hooks on longlines reduce turtle hooking 50 to 90 percent versus J-hooks. Acoustic pingers on gillnets deter mammals reducing dolphin bycatch 80 to 90 percent. LED lights help turtles avoid nets. Modified trawl designs with sorting grids and escape panels allow non-target species to exit. These technologies are proven and increasingly mandated.
How do regulations address bycatch?
Regulations include gear restrictions area closures observer programs and catch limits. Many countries require bycatch reduction devices in specific fisheries. Time-area closures protect species during spawning or migration. Observer programs monitor compliance. The EU landing obligation requires all regulated species to be landed creating incentives to avoid bycatch. Some fisheries impose hard caps triggering closure when exceeded.