Stock assessment diagnostics for South Atlantic swordfish

Catch and catch per unit effort are used to fit a biomass dynamic stock assessment model. A variety of diagnostics are then used to check for violations of model assumptions and to explore the information in the data. Potential problems are identified and ways to overcome or avoid them discussed.Versión del edito

Kobe II strategy matrices for North Atlantic swordfish based on catch, fishing mortality and harvest control rules.

Scientific stock assessment advice given by the SCRS is presented in the form of the Kobe II Strategy Matrix (K2SM). Traditionally the K2SM shows the probabilities by year for different catches of achieving the management objective of ensuring that the stock biomass is greater than BMSY and fishing mortality less than FMSY. However, a K2SM can also be used, as in this paper, to help guide discussion about choice of reference points for use as part of a Harvest Control Rule.Versión del edito

Stock assessment diagnostics for North Atlantic swordfish

Catch and catch per unit effort are used to fit a biomass dynamic stock assessment model. A variety of diagnostics are then used to check for violations of model assumptions and to explore the information in the data. Potential problems are identified and ways to overcome or avoid them discussed.Versión del edito

Implementation of a harvest control rule for northern Atlantic albacore

A Harvest Control Rule was developed for North Atlantic albacore during the 2013 assessment, this paper documents the procedure used.Versión del edito

Analysis of Turkish swordfish (Xiphias gladius) catch rates in the eastern Mediterranean

Indices of abundance of swordfish (Xiphias gladius) from the Turkish gillnet and longline fisheries operating in the eastern Mediterranean are presented for the period 2008-2013. Annual standardized indices were estimated by means of Generalized Linear Modeling techniques and the predictor variables included the Year and, Month of sampling. Gillnet CPUE data suggested the presence of and increasing abundance trend over the period 2008- 2010, while not any particular trend was identified from the analysis of the longline data set.Versión del edito

ASSESSING THE APPLICABILITY OF ENVIRONMENTAL INDICATORS FOR IMPROVING THE FISHERIES ASSESSMENT OF THE ALBACORE (Thunnus alalunga) UNDER THE A4A APPROACH

In this study we explore the potential for improving the stock assessment of Mediterranean Albacore by integrating environmental indicators. For this purpose we developed a catch at age model within the A4A stock assessment approach. The input data was similar to that used in the official SCRS stock assessment in 2017 but with an updated larval index. The environmental indicator provides information on the interannual variability of the sea surface temperature in the Balearic Sea during the spawning season, and it is included in the “Environmental pressure” component of the Ecosystem Report Card. The indicator is included in the assessment model in different ways, as index of the class age 0, as vector for the Stock/recruitment model, and as productivity value in other stock recruitment models (Ricker, Beverton-Holt). The results showed that incorporating the environmental variability indicators provide a better stock assessment fits (AIC, BIC), and also show the need for more advanced techniques to test stock assessment performance when testing the inclusion of environmental variability

Stereological comparison of oocyte recruitment and batch fecundity estimates from paraffin and resin sections using spawning albacore (Thunnus alalunga) ovaries as a case study.

Traditional histological protocols in marine fi sh reproductive laboratories using paraf fi n as the embedding medium are now increasingly being replaced with protocols using resin instead. These procedures entail differ- ent degrees of tissue shrinkage complicating direct comparisons of measurement results across laboratories or articles. In this work we selected ovaries of spawning Mediterranean albacore ( Thunnus alalunga ) as the subject of our study to address the issue of structural changes, by contrasting values on oocyte recruitment and fi nal batch fecundity given from the same tissue samples in both paraf fi nandresin.Amodernstereologicalmethod, the oocyte packing density (OPD) theory, was used supported by initial studies on ovarian tissue sampling and measurement design. Examples of differences in the volume fraction of oocyte stages, free space and connective tissue were found between the embedding media. Mean oocyte diameters were smaller in paraf fi nthaninresin with differences ranging between 0.5% in primary growth and 24.3% in hydration (HYD) stage oocytes. Fresh oocyte measurements showed that oocytes shrank as a consequence of the embedding process, reaching the maximaldegreeofshrinkageforoocytesintheHYDstage(45.8%inparaf fi nand26.5%inresin).Inordertoassess the effect of oocyte shrinkage on the OPD result, and thereby on relative batch fecundity (F r ), oocyte diameters corrected and uncorrected for shrinkage, were used for estimations. Statistical signi fi cant differences were found ( P b 0.05) between these two approaches in both embedding media. The average F r was numerically smaller in paraf fi n compared to resin (86 ± 61 vs. 106 ± 54 oocytes per gram of body mass (mean ± SD)). For both embedding media statistical signi fi cant differences ( P b 0.05) were seen between F r results based on either oocytes in the germinal vesicle migration stage or HYD stage. As a valuable adjunct, the present use of the OPD theory made it possible to document that the oocyte recruitment of spawning ovaries of Mediterranean albacore followed the typical pattern of an asynchronous oocyte development and indeterminate fecundityPostprint2,444

ASSESSING THE APPLICABILITY OF ENVIRONMENTAL INDICATORS FOR IMPROVING THE FISHERIES ASSESSMENT OF THE ALBACORE (THUNNUS ALALUNGA) UNDER THE A4A APPROACH

In this study we explore the potential for improving the stock assessment of Mediterranean Albacore by integrating environmental indicators. For this purpose we developed a catch at age model within the A4A stock assessment approach. The input data was similar to that used in the official SCRS stock assessment in 2017 but with an updated larval index. The environmental indicator provides information on the interannual variability of the sea surface temperature in the Balearic Sea during the spawning season, and it is included in the “Environmental pressure” component of the Ecosystem Report Card. The indicator is included in the assessment model in different ways, as index of the class age 0, as vector for the Stock/recruitment model, and as productivity value in other stock recruitment models (Ricker, Beverton-Holt). The results showed that incorporating the environmental variability indicators provide a better stock assessment fits (AIC, BIC), and also show the need for more advanced techniques to test stock assessment performance when testing the inclusion of environmental variabilityEn prens

Updated standardized joint CPUE index for bluefin tuna (Thunnus thynnus) caught by Moroccan and Spanish traps for the period 1981- 2012.

Relative abundance indices of bluefin tuna (Thunnus thynnus) caught by the Moroccan and Spanish traps in the area close to the Strait of Gibraltar were estimated for the period 1981- 2013. Standardized CPUEs were estimated through a General Linear Modeling (GLM) approach under a negative binomial error distribution assumption.Versión del edito

UPDATED STANDARDIZED CATCH RATES IN NUMBER FOR SWORDFISH (Xiphias gladius L.) CAUGHT BY THE SPANISH LONGLINE FLEET IN THE MEDITERRANEAN SEA, 1988- 2013

A General Linear Modeling (GLM)approach to analysis of variance was used to analyze swordfish logged catch rates in number of fish from 24 , 239 trips carried out by the Spanish surface longline fleet addressed to this species in the Western Mediterranean f or the period 1988 - 2013.Postprin