Referential conversion table LD1 to LF

Source: R/data.R

During the sampling process, fishes length can be collected and expressed in different standards.
For example, regarding field constraints and more precisely the length of the different species, sampling data covered in T3 can by express in first dorsal length (LD1) or curved fork length (LF).
Generally, length of small individuals are provided in LF because it’s logistically possible and easier to measure the entire fish, while length of bigger individuals are provided in LD1, for the same reciprocal reasons.
To standardize this standard among sampling data and at the end have only length sampling data expressed in LF, the process use this referential conversion table LD1 to LF.

data(length_step, package="t3")

Format

length_step: data frame with 3951 rows and 6 columns:

ocean_code

Ocean code, type integer. For example ocean_code=1 for the Atlantic Ocean and ocean_code=2 the Indian Ocean

species_code

Species code, type integer.

species_fao_code

Species FAO code, type character.

ld1_class

First dorsal length (LD1) class (cm), type double.

lf_class

Curved fork length (LF) class (cm), type integer.

ratio

Percentage (%) of samples to be allocated to the corresponding lf_class, type double. For example, for the samples from the Atlantic Ocean (1), of the species YFT (*Thunnus albacares*), with a first dorsal length class (LD1) measured at ld1_class=8 (cm), a percentage of ratio=50 % will be assigned to the curved fork length class: lf_class=32 (cm) and 50% of these samples will obtain a lf_class=34 (cm).

Details

This table are expressed and used through a stratification by ocean and specie.
For one LD1 length class measured we can have several LF length classes associated, according to the distribution ratio. That mean that in our data processed the number of sampling item could rise.
Furthermore, tunas regional fisheries management organisations, like International Commission for the Conservation of Atlantic Tunas (ICCAT) or the Indian Ocean Tuna Commission (IOTC), have validated conversion factors for types of size measurements. One of our next update will be to modify the process according theses formula.