18.2 Material and Methods
The fundamental source of information scrutinized in this chapter was collected in
the context of the activities of the data collection framework (DCF), carried out from
2002 to the present in the Spanish Mediterranean, both from the commercial fishery
and through an experimental survey carried out in spring, from 1994, to evaluate the
demersal resources (MEDITS, Mediterranean International Trawl Survey).
18.2.1 Sampling of Commercial Fishery
Sampling staff are dispersed at several locations around the coast to reduce traveling
time. In general the different fisheries (otter trawls, purse seines, artisanal fleet, etc.)
are widely distributed along the coast. There is a complete vessel registry and census
data for landings, effort, gear, etc. as required by EU logbooks and sales notes.
The sampling design in the area is done at the metier level, for those metiers
selected by the ranking system, as stated in the GFCM-DCRF Regulation (GFCM
2018a). The design has been done taking into account the representativeness of the
data to collect with relation to the population (catches from the commercial fleet),
considering that these data should be obtained cost-effectively, and the information
obtained can be used to estimate the population characteristics of interest precisely
(low variability) and accurately (unbiased). For the proposed sampling schemes, it is
possible to calculate estimates of the precision of the estimators of the population
parameters.
Both, for at-sea sampling and on-shore sampling, four different strata areas are
considered: GSA, metier, selected ports, and time frame. For each GSA, metiers are
non-probabilistic selected based on the rules of the regional RFMO (GFCM). For
each combination of GSA-metier, the ports to sample have previously been selected
according to previous knowledge which include their importance for each metier
(both in terms of biomass landed and effort as the number of vessels) as well as their
availability to carry out the sampling (both predisposition and adequate facilities).
Finally, the time frame (quarter or month) is set to force the sampling to cover the
entire year.
For the collection of individual information in order to estimate age, maturity, sex
ratio, and weight of the main species, a number of individuals by length class every
period (month, quarter, or year) will be selected.
The estimation of the biological parameters and their uncertainties will be carried
out using the tool INBIO 2.0 (“Estimation of biological parameters and their
uncertainties through simulation techniques”), developed in R environment by the
IEO. INBIO makes it possible to fit the most usual models and to estimate the
coefficient of variation for parameters by using the nonparametric bootstrap
methodology.
592
M. González Aguilar et al.
The fundamental source of information scrutinized in this chapter was collected in
the context of the activities of the data collection framework (DCF), carried out from
2002 to the present in the Spanish Mediterranean, both from the commercial fishery
and through an experimental survey carried out in spring, from 1994, to evaluate the
demersal resources (MEDITS, Mediterranean International Trawl Survey).
18.2.1 Sampling of Commercial Fishery
Sampling staff are dispersed at several locations around the coast to reduce traveling
time. In general the different fisheries (otter trawls, purse seines, artisanal fleet, etc.)
are widely distributed along the coast. There is a complete vessel registry and census
data for landings, effort, gear, etc. as required by EU logbooks and sales notes.
The sampling design in the area is done at the metier level, for those metiers
selected by the ranking system, as stated in the GFCM-DCRF Regulation (GFCM
2018a). The design has been done taking into account the representativeness of the
data to collect with relation to the population (catches from the commercial fleet),
considering that these data should be obtained cost-effectively, and the information
obtained can be used to estimate the population characteristics of interest precisely
(low variability) and accurately (unbiased). For the proposed sampling schemes, it is
possible to calculate estimates of the precision of the estimators of the population
parameters.
Both, for at-sea sampling and on-shore sampling, four different strata areas are
considered: GSA, metier, selected ports, and time frame. For each GSA, metiers are
non-probabilistic selected based on the rules of the regional RFMO (GFCM). For
each combination of GSA-metier, the ports to sample have previously been selected
according to previous knowledge which include their importance for each metier
(both in terms of biomass landed and effort as the number of vessels) as well as their
availability to carry out the sampling (both predisposition and adequate facilities).
Finally, the time frame (quarter or month) is set to force the sampling to cover the
entire year.
For the collection of individual information in order to estimate age, maturity, sex
ratio, and weight of the main species, a number of individuals by length class every
period (month, quarter, or year) will be selected.
The estimation of the biological parameters and their uncertainties will be carried
out using the tool INBIO 2.0 (“Estimation of biological parameters and their
uncertainties through simulation techniques”), developed in R environment by the
IEO. INBIO makes it possible to fit the most usual models and to estimate the
coefficient of variation for parameters by using the nonparametric bootstrap
methodology.
592
M. González Aguilar et al.