Genetic validation of the unexpected presence of a tropical tuna, bigeye tuna (Thunnus obesus), in the Mediterranean

Bigeye tuna (Thunnus obesus, Lowe, 1839) is one of the eight recognized species of the genus Thunnus. It is considered a tropical species distributed in the Atlantic, Pacific and Indian Oceans. To date, no validated presence of this species has been reported inside the Mediterranean Sea. This study, however, confirms, for the first time, the presence of three young individuals of this species within the Mediterranean Sea.Versión del editor1,83

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

Implications for fishery management in small tunas the case of genetic population structure of bullet tuna in the west Mediterranean

Knowledge of population structure of species is needed to establish appropriate management regulations. Of particular concern are those commercial species; these exploited fish populations can undergo loss of genetic variability that ultimately may lead the loss of regional small populations. This situation could occur in the small tuna species, which in some cases are heavily targeted by artisanal fisheries. Here, we focused on the Bullet tuna (Auxis rochei) with an extensive sampling (n = 431) along the north and south coast of the west Mediterranean and one location on the east Atlantic. The analysis of the mtDNA control region revealed that seven (about 1.6%) individuals were not identified as Bullet tuna suggesting a species misidentification with possible implications in stock assessment. Population genetics results showed clear genetic differentiation between the Iberian Peninsula and North African locations. These results have a clear impact on the conservation and management strategies, and if it is confirmed in other small pelagic species, the pattern of population structure in the Mediterranean is more complex than initially expected

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

REPORT OF THE 2019 ICCAT WORKSHOP ON SWORDFISH BIOLOGY STUDIES FOR GROWTH, REPRODUCTION AND GENETICS

This report describes the June, 2019 ICCAT workshop on swordfish biology studies for growth, reproduction and genetics, hosted by the Instituto Português do Mar e da Atmosfera, Olhão, Portugal . The major objectives of the workshop were to 1) refine sampling and biological data collection protocols, 2) develop protocols and start the sample processing and analysis, and 3) plan for the project future steps. The biological sampling program was established by ICCAT’s Swordfish Species Group in 2018, aiming to improve knowledge of the stock distribution, age and gender of the catch, growth rate, age at maturation, maturation rate, spawning season and location and diet. This work will contribute to the next major advance in the assessment of swordfish status, by permitting the development of more spatially and biologically realistic population models used in both Atlantic and Mediterranean populations assessments and within the ICCAT Management Strategy Evaluation (MSE) for North Atlantic swordfish.En prens

Preliminary management strategy evaluation for blue shark in the Indian Ocean using a data-limited approach

In tuna-RFMOs there has been an effort to move to quantitative stock assessments for pelagic sharks, especially for the main species such as blue shark Prionace glauca. In IOTC, blue shark was last assessed in 2017 with the use of an integrated length-based age-structured model (SS3). This paper now presents a preliminary exercise with data-limited Management Strategy Evaluation (MSE) to test options for different potential management procedures (MPs), using the data-limited methods toolkit (DLMtool). Reference points have not yet been adopted for sharks in IOTC, so for this exercise we set some tentative reference points noting that those can be updated in the future as needed. Eighty-nine MPs were evaluated with 9 considered potentially acceptable. Options and tradeoffs between those MPs are shown and described in the paper. We have focused mainly on trade-offs between biomass and yield, but according to the management objectives agreed other performance metrics can be applied. Even thought this is a preliminary exercise at this point, we hope that it provides initial thoughts and opens the discussion for the advancement of the blue shark management and conservation in the Indian Ocean

Environmental variablity in three major Mediterranean tuna spawning grounds.

We propose four different environmental indicators, three related to temperature variability in three major spawning grounds of tuna species in the Mediterranean, and one related to the sea surface salinity variability in the Balearic Sea. These oceanographic indicators show the annual variability of environmental parameters affecting growth and survival of tuna eggs and larval. The indicators are intended to provide quick access to assessment working groups and fisheries scientist to identify potentially anomalous year

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

EFFECTS OF ICCAT Rec [2016-05] SIZE REGULATION ON THE DISCARDS OF THE SPANISH LONGLINE FISHERY TARGETING SWORDFISH (Xiphias gladius Linnaeus, 1758) IN THE WESTERN MEDITERRANEA

The ICCAT Commission, at its meeting on November 2016, approved a multi-annual recovery plan for the Mediterranean swordfish starting in 2017 and continuing through 2031 (ICCAT Rec [2016-05]). Among other provisions, the recovery plan proscribed a minimum landing size (MLS) of 100 cm (lower-jaw fork length- LJFL), which is 10 cm higher than the previously implemented (ICCAT Rec [2013-04]). The aim of this study is to assess the effect of the recently implemented MLS on the swordfish discarding activities by the Spanish surface longline fishery operating in the western Mediterranean for the period 2015-2017. Our results show that: i) as compared to the former MLS (ICCAT Rec [2013-04]), a higher percentage of undersized dead fish is now discarded at sea, with the additional risk that does not be reported and taken into consideration during the assessment of the stock; ii) the amount of fishing effort (number of hooks) for fulfilling the allocated quota has increased; iii) the fishing season must be longer to achieve the allocated quota. Both the increase in fishing effort and the lengthening of the fishing season have an adverse effect on the economic profitability of the surface longline fleet without achieving the intended reduction in the fishing mortality exerted on the juvenile fraction of the Mediterranean swordfish stock