How to calculate BECCA indicators

Catch per unit effort

The basic BECCA calculation is catch-per-unit-effort. In the simplest case:

Catch per hour = catch amount / hours fished or harvested

If a fisher caught 40 fish in five hours, the catch rate is eight fish per hour. If a gleaner collected three baskets in six hours, the catch rate is 0.5 baskets per hour. If an angler had 18 hookups in four hours, the hookup rate is 4.5 hookups per hour.

Standardising to a fishing day

It is often easier to communicate results as catch per standard fishing day. This is calculated by dividing catch by reported hours and multiplying by a locally defined standard day.

Catch per standard day = (catch amount / hours fished) × standard day length

In the bonefish BECCA, sightings were standardised by dividing reported sightings by each respondent’s reported hours per trip and multiplying by the average fishing day length across all respondents. This produced sightings per standardised fishing day. The same logic can be used for eats per day, hookups per day, fish per day, baskets per day, or kilograms per day.

The length of a standard day should be chosen locally and reported clearly. It might be six hours, 7.5 hours, eight hours, or another locally meaningful value.

Person-hours and group catch

Many fisheries involve group effort. If four people collect eight buckets in four hours, the catch should not be treated as one person collecting eight buckets. Total effort is four people multiplied by four hours, or 16 person-hours. The catch rate is therefore 0.5 buckets per person-hour.

This is especially important for gleaning, seining, netting, crew-based fishing, fish fences, and household harvesting. Every BECCA should ask whether the reported catch was for one person, one boat, one crew, one household, or a larger group.

Gear-specific effort

In some fisheries, hours alone may not be enough. A trap fisher using 100 traps is not comparable to a trap fisher using 10 traps. A net fisher using a 500 m net is not comparable to one using a 50 m net. A fisher using 20 hooks is not comparable to one using two hooks.

Where gear strongly affects catch, BECCA should record gear effort. The analysis may then use catch per trap per day, catch per hook per hour, catch per metre of net per soak, catch per haul, catch per tide cycle, or catch per diver-hour. This does not mean every BECCA needs complex effort metrics. It means the field team should understand the fishery well enough to choose the effort measure that makes comparisons fair.

Size indicators

Size is usually not divided by effort. Instead, size is plotted by year, decade, region, or respondent cohort. Size metrics can include largest fish weight, largest fish length, shell size, carapace width, or market grade. In the bonefish and tarpon BECCAs, maximum size was treated separately from encounter metrics because the largest fish reported by a respondent could occur in a different year from their best encounter day.

Aggregating responses

After effort-standardising individual responses, the data can be grouped by year, decade, region, species, gear type, fishing area, respondent group, or management zone. For each group, the analysis should report the number of respondents contributing to the estimate. Means, medians, confidence intervals, and uncertainty ranges can then be calculated depending on the sample size and technical capacity of the team.

For community-facing reports, simple visualisations are often more useful than complex statistical outputs. A line showing catch per standard day through time, with the number of respondents contributing to each decade, can be more powerful than a technical model that communities cannot interpret.