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- Objectives
- Develop sampling designs for estimating well-level and trip-level catch composition to be used in the IVL enhanced port-sampling program in 2023-2024.
- Background
- At the 98th Meeting of the IATTC, the Commission established an IVL program for bigeye tuna catches (Resolution C-21-04), which is to include a special portsampling program (“IVL enhanced port-sampling program”) for trips considered to have caught a significant amount of bigeye tuna.
- To implement the IVL enhanced port-sampling program, the sampling protocol of this program needs to be tailored to estimation of well-level and trip-level catch composition.
- The sampling protocol of the current IATTC port-sampling program is not appropriate for this task because it was designed for estimation of fleet-level catch composition and was based on results of studies conducted prior to the expansion of the fishery on fish-aggregating devices in the 1990s.
- Given this, as outlined in SAC-13 INF-E, an IVL pilot study is planned for the second half of 2022 to: 1) collect extensive well sampling data for a simulation study to test sampling designs for well-level and trip-level catch composition estimation; and, 2) field-test the best sampling designs from (1) to identify and mitigate any logistical issues in advance of the initiation of the IVL enhance port-sampling program in 2023.
- Relevance for management
- Development of sampling designs for estimation of catch composition for individual vessel trips is essential to the success of the IVL enhanced port-sampling program and to the IVL Program, more generally.
- Duration
- 6 months
- Workplan and status
- September – December 2022: collect extensive well sampling data and conduct a simulation study to test sampling designs.
- January – February 2023: Field-test sampling designs developed in the simulation study, to identify and mitigate any logistical issues.
- External collaborators
- Government of Ecuador
National observer programs
Purse-seine fleet - Deliverables
- Reports for the SAC and the Commission; publications in peer-reviewed journals.
- Updated date: 01 Mar 2023
- Progress summary for the reporting period
- The pilot study concluded in February 2023. The main results of the pilot study can be summarized as follows:
a) A simulation study using the sample data determined that a systematic sampling protocol with 3.33% coverage of “units” (containers or virtual containers; see SAC-14-10, SAC-14 INF-I) of fish unloaded from a well should be a reasonable compromise between low error and practicality. In actual implementation, this within-well sampling protocol is as follows: sample one out of every 30 units of fish unloaded from a well, from the beginning to the end of the unloading of the well, starting at a randomly selected unit in the first 30 units unloaded.
b) Taking into consideration results from a second simulation study, which was used to determine the number of wells to sample per trip, the following two-stage sampling protocol will be used by the EMP: 1) at least 6 wells will be sampled per trip, selected at random for the primary catch stratum (or strata) of interest; and, 2) one systematic sample will be collected per well, using the protocol described above, where for each unit of fish sampled, the species identification of every fish, and length or weight for every tropical tuna, in the unit will be obtained.
c) This preliminary EMP protocol, which was tested during the latter part of the pilot study, produced reasonably reliable estimates of trip-level BET catch for the primary catch strata of interest, with coefficients of variation largely between 0.22 and 0.39
d) The data collected during the pilot project will be useful for other scientific investigations in support of tuna management, including studies on possible improvements to the sampling protocol of the Commission’s regular port-sampling program for estimation of fleet-level catch composition
- Challenges and key lessons learnt
- The use of “chinguillos” (large cargo nets) for unloading fish from inside individual wells represented a challenge during the sampling. It will be necessary to look for alternatives to the current EMP protocol to sample these types of unloadings, which will surely require additional collaboration from the fleet representatives and delays in the unloading process.
Good communication with fleet representatives is key for proper coordination and collaboration during the sampling.
The use of tools such as voice recorders and scales can improve the sampling process and make it more cost-efficient.
- SAC-14-10
SAC-14 INF-I
Publication currently submitted to the peer-reviewed journal Fisheries Research titled “Within-well patterns in bigeye tuna catch composition and implications for purse-seine port-sampling and catch estimation for the Eastern Pacific Ocean”, with co-authors Lennert-Cody, De La Cadena, McCracken, Chompoy, Vogel, Maunder, Wiley, Altamirano Nieto, and Aires-da-Silva.
Other publications for peer-reviewed journals are in preparation.