Description
Length frequency is defined by UN ESCWA as the number of individuals of a catch or catch sample in each length interval. The modal size is the length group with the higher number of individuals.
Length frequency refers to individual body lengths (or weights) of species per fleet, fishery, year, gear, type of school, month and spatial areas
This form supports the reporting of annual submission of estimates of sample size taken by number (or weight) measures of individual sizes of fish for the IOTC species, common sharks, and other bycatch species. Straight length measurements made with a calliper or measuring board are recommended over fish weights and vary according to fish groups: (i) lower-jaw fork length for billfish, (ii) upper-jaw fork length for tunas, mackerels, sharks, and all other bycatch fish species with forked or lunate tails, (iii) standard length for bycatch fish species with rounded or truncate tails, and (iv) disc width for rays. The Secretariat further recommends the use of length intervals for the IOTC species and most commonly caught sharks along with maximum length intervals and ranges of valid values which are used to filter and consolidate the size-frequency datasets made available to support the IOTC process (see Recommended measurements).
Sampling coverage shall be set to at least one (1) fish measured by tonne caught by fishery and species, with samples being representative of all the periods and areas fished. For each stratum, the data coverage – i.e., the percentage (%) of catch/effort sampled – derived from the coverage type must be reported to assess the representativeness and quality of the estimates. In addition, raised estimates of the size samples must be reported to the Secretariat to account for bias due to unrepresentative sampling. Documents covering sampling and raising procedures must be provided for each fishery and species.
Resources
Length frequency data could be reported:
- by individual fishery and species through the single form 4-SF;
- or for multiple fisheries and species using the form 4-SF multiple.
Contrary to single 4-SF form, where data specifications are to be defined in the metadata worksheet, in the 4-SF multiple these are listed in the data worksheet to align the data with specifications for each fisheries and species.
return back to the list of all IOTC statistical data reporting forms.
Supported resolutions
- 15/02 - Mandatory statistical reporting requirements for IOTC Contracting Parties and Cooperating Non-contracting Parties (CPCs)
- 17/05 - On the conservation of sharks caught in association with fisheries managed by IOTC
- 19/03 - On the conservation of mobulid rays caught in association with fisheries in the IOTC area of competence
- 12/04 - On the conservation of marine turtles
- 12/06 - On reducing the incidental bycatch of seabirds in longline fisheries
- 23/06 - On the conservation of cetaceans
- 13/05 - On the conservation of whale sharks (Rhincodon typus)
Reporting deadlines
- Longline fisheries: 30 June (preliminary), 30 December (final)
- Surface fisheries: 30 June (final)
- Coastal fisheries: 30 June (final)
Stratification
Data elements
Main data elements
Month |
M |
The month of the fishing activities reported through the dataset |
Integer |
Fisheries |
M |
Type of fishing practices based on several factors |
Fisheries |
Grid |
M |
the seven digits grid square of the fishing area in Indian Ocean |
Grid codes |
Species |
M |
Species caught and discarded |
Species |
Sex |
M |
The sex of species sampled |
Sex |
Type of fate |
M |
Fate of fish caught (retained or discarded) |
Types of fate |
Fate |
M |
Reason for retained or discarded of the catch |
Fate |
Sample data
Size class (lo) |
M |
The lowest size recorded for the sample |
integer |
Size class (hi) |
M |
The highest size recorded for the sample |
integer |
Number of samples |
M |
The sample size of strata |
integer |
Number of fish |
M |
The number of fish measured |
integer |
Referenced codelists
Administrative and geospatial domains
Countries (ADM.COU)
Reference codes modeling the flag / reporting country submitting a dataset to the IOTC Secretariat.
IOTC regular grids (GIS.IOTC.CESF)
Codes for all 1°x1° and 5°x5° grids that overlap - at least partially - with the IOTC convention area.
Due to to the large size of the dataset, this is not included for filtering / browsing, but can be directly downloaded as a CSV from here: IOTC_GRIDS_CE_SF.
Fisheries and fishing technologies domains
Fisheries (FIS)
An ad-hoc classification derived from a combination of several factors (purpose, area of operation, vessel size category, gear, gear configuration, fishing mode and target species) that uniquely describe fishing practices for groups of vessels.
An interactive wizard to help CPCs identify the IOTC code for their fisheries (among those currently considered of relevance in the Indian Ocean).
Biological and morphometrics domains
Measurement type (MOR.MTY)
Reference codes that model the measurement types as lengths or weights collected as the size frequency.
Measurement types (MOR.MES))
Reference codes that model the measurement types, combining those specific for individual lengths and weights used to measure individual species.
Type of fate (SPC.FTT)
Reference codes used to identify fate as indicating that the fish has been retained or discarded.
Fates (SPC.FTE.*)
Reference codes used to identify fate combined the reasons for retain and those for discard.
Sex (MOR.SX)
Reference codes used to identify fate combined the reasons for retain and those for discard.
All species (SPC.ALL)
Reference codes modeling the species interacting with the fisheries as:
- target species (retained or discarded)
- bycatch species (retained or discarded)
- sampled individuals
- etc.
These codelists are subsets of the entries in the ASFIS list of species for fishery statistics purposes, from which they inherit the alphabetic codes, English, French and scientific names, as well as the family and order, and add the species category (in the IOTC sense), the IUCN status (retrieved from the IUCN red list of endangered species) and other characteristics of each entry such as their status of single species / species aggregate, bait species, SSI species, IOTC species.
Data and metadata domains
Data types (DTA.TY)
Reference codes modeling the type of statistics provided through a specific form, and in particular if these are:
- preliminary if the statistics were estimated by using some information from the fishery and year concerned, and the data reported are likely to change in the future as more information become available; or
- final if the statistics were estimated by using the complete set of data from the fishery and year concerned, and the data reported are unlikely to change in the future.
Data raising (DTA.RA)
Reference codes modeling the level of raising applied to the data (raised to totals / not raised to totals / unknown).
Size-frequency data sources (DTA.SRC.SF)
Reference codes modeling the source of the data provided through the size-frequency data form
Size-frequency data processings (DTA.PRO.SF)
Reference codes modeling the processing applied to the data provided through the size-frequency data form.
Coverage types (DTA.COV.TY)
Reference codes modeling the type of coverage for the raw information used to obtain the data provided through a specific form.
Estimations (DTA.ES)
Reference codes indicating if the data estimated for a stratum was actually recorded in the stratum or derived from comparable strata through a substitution scheme.