This document describes the operating model for the narrownose smooth-hound (Mustelus schmitti), commonly known in Argentina as gatuzo, and the rationale for the choice of values used for each parameter.
The following documents were provided and were used to populate the operating model:
Anon., (2017) Grupo de Trabajo Condictios, Reunion 02/2017, Buenos Aires, 28 al 31 de marzo de 2017.
Hozbor, Natalia, M, Saez, M, and Massa, A.M., (2010). Eday y crecimiento de Mustelus schmitti (gatuzo), en la region costera bonaerense y uruguaya.
Cortes, Federico, Hozbor, Natalia, Marcelo y Massa, Perez (2016) Aplicacion de un modelo de dinamica de biomasa al gatuzo (Mustelus schmitti) en el area del tratado del rio de la plata y su frente maritimo (1983-2016). Instituto Nacional de Investigación y Desarrollo Pesquero.
Other published scientific literature were also used to decide the values for some operating model parameters, and are included in the reference list at the end of the document.
For this initial base-case analysis we are running 100 simulations. The other parameters of the operating model have been kept at the default values. We may wish to increase the number of simulations, or modify the other operating model control parameters, once the operating model has been revised and accepted as the best description of the fishery.
This operating model was constructed based on the available information and for the purpose of demonstrating MSE of a data-limited fishery using DLMtool. There are several parameters in the operating model that could be improved after discussion with the Gatuzo experts. We may also wish to do robustness testing by developing alternative operating models with different hypotheses about the current or future stock and fishery dynamics.
Here we have outlined several OM parameters that could be modified to better reflect the fishery dynamics or explored in a set of alternative OMs to evaluate the robustness of the MP performance to different hypotheses.
For this base case OM we have assumed that there is no fishing mortality on animals that are discarded by the fishing fleet. This may be an inappropriate assumption for this stock and the values in the Fdisc slot could be modified to account for the expected discard mortality for this species.
The steepness of the stock-recruitment relationship and the expected inter-annual variability in recruitment were not known for this species and we have used wide ranges to reflect this uncertainty. The Gatuzo species experts may have additional data or knowledge on suitable ranges for these parameters (h, Perr, and AC).
For this OM we have assumed that the fishery commenced in the 1950. We have assumed a linear increase in fishing effort from 1950 till the first year when effort data is available. The historical exploitation pattern can be modified by changing the values in Effyears, EffUpper, and EffLowerslots.
The values for the selectivity parameters were based on a study of the artisinal gillnet fleet. This selectivity pattern may not be representative of the exploitation of the species because the main fleet that catches this species uses trawl gear. The L5, LFS and Vmaxlen slots could be updated based on knowledge of the selectivity pattern of the main fleet.
The DR slot refers to the discard ratio - the fraction of catch that is typically discarded. In this base case OM we have assumed that there is no general discarding of gatuzo. However, after discussions with the gatuzo scientists we have learned that gatuzo is not targeted and some fraction of the catch may be discarded at sea. We can explore the impacts of this discarding by modifying the values of the DR parameter.
The Obs (Observation) parameters have been based on a generic values from other OMs in DLMtool. However it is highly likely that they do not reflect the likely uncertainty in the data collection and analysis for Gatuzo.
For example, the beta parameter is used to account for a hyper-stable or hyper-deplete index of abundance. The current values for this parameter have been set very wide. Information on the methods used to construct the index of abundance may be used to reduce the range of this value to better reflect the properties of this fishery. For example, if the index is based on a stratified survey we may expect it to be a fair representation of the stock abundance. On the other hand, if commerical CPUE data is used for the index of abundance we may expect that the index is hyper-stable and does not decrease as quickly as the true abundance.
Another example is the error (Cobs) and potential bias (Cbiascv) in the catch data.
We have assumed that there is some error and variability in implementing a TAC or TAE. These assumptions could be updated based on knowledge of the likely implementation error in the different management approaches for this fishery.
The OM rdata file can be downloaded from here
Download and import into R using myOM <- readRDS('OM.rdata')
Species: Mustelus schmitti
Common Name: *Narrownose smooth-hound