Doctoral Programme on Marine Ecosystem Health and Conservation
 The MARES Researchers and their Research
Assessing and modelling population recruitment dynamics in the mediterranean and eastern atlantic bluefin tuna under a fishery-independent research framework
PhD Code: MARES_18_2010:
Mobility
  • Host institute 1: P3 - University of Bologna
  • Host institute 2: P18 - AZTI-Tecnalia
  • Host institute 3: P1 - Ghent University
Research fields:
  • T4 - Natural resources : overexploitation, fisheries and aquaculture
Promotor(s):
  • Fausto Tinti
  • Haritz Arrizabalaga
  • Magda Vincx
Contact Person and email: Fausto Tinti - fausto.tinti@unibo.it

Subject description
The assessment of population dynamics, environmentally-driven changes and levels of exploitation in large pelagic fish (e.g. tunas, billfishes and sharks) is crucial for both stock management and conservation of marine ecosystems where top predators exert a top down control [1-3]. Significant biomass declines of top predator stocks have documented by several high-profile research papers by analysing aggregated fisheries data [4-7] and feeding the public perception that fisheries are in crisis [8]. Stock depletion may indeed result from poor management, but several recent studies raised doubts on the quality of the scientific data analysed, hitting back at this crisis’ scenario (e.g. [9-12]) and whenever possible, fishery data should be compared with those of fishery-independent approaches, such as genetic experiments and electronic tagging programmes [13, 15] in order to get more robust and integrated scenarios.
The Atlantic bluefin tuna (ABFT) is one of the most exploited species of tunas [8,16]. Even though it has been continually exploited in the Mediterranean Sea for thousands of years by tuna traps, only in these last decades the exploitation rate is far beyond the sustainable level, with a quite high risk of fisheries’ decline and stock collapse [17]. The International Commission for the Conservation of Atlantic Tunas (ICCAT)started a new 15-years plan for the recovery of the stock (EC N. 644/2007, 11th June 2007). The concern for conservation and sustainable management of ABFT has enforced scientists to constantly monitor stocks with a multidisciplinary approach whose results have largely contributed to increase knowledge on ABFT bio-ecological traits. ABFTs of the eastern population migrate to spawn in the Mediterranean Sea, and then come back to the Western and Eastern Atlantic foraging grounds [18]. Three spawning grounds are known in the Mediterranean sea: south to the Balearic Islands, in the southern Tyrrhenian Sea [19] and in the eastern Mediterranean [20]. In recent years, pop-up satellite data indicated that some individuals are permanently resident in the Mediterranean Sea [21]. The existence of a separate Mediterranean population was already proposed in the past by several Authors [22,23]; this "native hypothesis" is still supported by fishermen that claim to be able to distinguish tunas of Atlantic origin from those that are resident in the Mediterranean by their morphological appearance. Recent comparative genetic analyses have revealed that a low but significant population genetic structuring persists temporally in the Eastern Atlantic and Mediterranean stock [24-26]. The heterogeneity of spatial genetic patterns detected within the Mediterranean ABFTs leads to suspect that the basin is inhabited by somewhat distinct geographical populations showing more or less pronounced independent demographic dynamics and histories. However, this critical new knowledge is not considered in ABFT management, which is based on the assumption that all the Eastern and Mediterranean ABFT belongs to a single panmictic population.
Objectives and R&T activity plan
The PhD proposal subject aims at 1) assessing the self-recruitment rate in the Mediterranean populations and the immigration rate of native Mediterranean individuals in the feeding ABFT stock aggregates in the Bay of Biscay using fishery-independent approaches (genetic assignment analyses coupled with microchemical tagging); 2) Providing more robust management options with regard to uncertainties in recruitment dynamics by developing a general simulation modelling framework for Eastern Atlantic and Mediterranean ABFT populations.
Research objective 1 will be addressed by
1a) the genetic and microchemical-based assignment analysis of ABFT individuals of three age classes (young-of-the-year, juveniles, adults) collected in the spawning areas Western of the Mediterranean (i.e. Balearic Islands and Southern Tyrrhenian Sea) together with the assessment of self-recruitment rate in the populations based on a comparative composition analysis of individuals of different age classes; 1b) the genetic and microchemical-based assignment analysis of ABFT individuals composing the feeding aggregates in the Bay of Biscay together with the assessment of immigration rates of native Mediterranean individuals based on a comparative composition analysis against the Mediterranean populations.
To reach this objective, R&T support and expertise will be provided by both promoting partners which are involved in ongoing national (PRIN2008; ATM2009Hegalabur) and EU (FishPopTrace,) research projects on ABFT and other fishery resources in the target areas. Genetic and microchemical markers at the population level (i.e. panels of SNP and microsatellite species-specific loci and rare elements-signatures, respectively) are available within an ongoing joint research collaborative project from partners 1 and 2 (26, 27)
Research objective 2 will be addressed by
2a) developing a general simulation modelling framework where to test alternative management strategies. This will include (i) an operational model to reflect alternative plausible recruitment dynamics (based on new knowledge generated under objective 1) as well as additional population and fishery dynamics (based on the literature), an (ii) observation model that describes how pseudo- data are generated from the operating model, and (iii) an stock assessment and management model to derive estimates of stock status [28]. 2b) analysing how stock status varies depending on the recruitment dynamics assumed [e.g. 29], as well as its management implications [30], allowing to choose the most robust management strategy to the uncertainty on recruitment dynamics.
To reach this objective, R&T support and expertise will be provided by both partners and within the framework of scientific collaborations that promoting partners have within national (ATM2010MSE) and EU (SESAME, FEMS) ongoing and already finalized research projects. Also , the strong involvement of the partners in the scientific committee of the International Commission for the Conservation of Atlantic Tunas (ICCAT) guarantees the access to available data and further modelling expertise.

References (citations on the proposal subject from the pormoting partners are in full)
1  Jennings S Kaiser M 1998 Adv Mar Biol 34 201–352
2  Perry A et al 2005 Science 308 1912–1915
3  Council National Research 2006 Natl Acad Press Washington DC
4  Pauly D et al 1998 Science 279 860-863
5  Pauly D et al 2000 Am Sci 88 46–51
6  Myers RA Worm B 2003 Nature 423 280-283
7  Safina C Klinger DH 2008 Cons Biol 22 243-246
8  WWF 2006 Available at wwwpandaorg/about_wwf/where_we_work/europe/publications/indexcfm?uNewsID=75040 
9  Beddington JR et al 2007 Science 316 1713-1716
10  Walters C 2003  Can J Fish Aquat Sci 60 1433–1436
11  Hampton J et al 2005 Nature 434 E1-2
12  Sibert J et al 2006 Science 314 1773-1776
13  Rouyer T et al 2008 PNAS USA 105 5420-5425
14  de Mutsert K et al 2008 PNAS USA 105 2740-2744
15  ICCAT 2008 ICCAT Santander Spain
16  Rooker JR et al 2007 Rev Fish Sci 15 265-310 6
17  ICCAT 2007 PART I 2006 Vol 2
18  Rooker JR et al 2008 Science 322 742-744
19  Medina A et al 2002 J Fish Biol 60 203-217
20  Oray IK Karakulak F S 2005 J Appl Ichthyol 21  236-240
21  De Metrio G et al 2004 ICCAT 54 415-424
22  Cetti F 1777 Piattoli Sassari
23  Pavesi P 1889 Ministero di Agricultura Industria e Commercio Roma, Italia 
24  Carlsson J et al 2007 Journal of Heredity 98(1)23-28
25  Carlsson J et al 2004 Mol Ecol 133345-3356
26  G Riccioni, M Landi, G Ferrara, I Milano, A Cariani, L Zane, M Sella†, G Barbujani, F Tinti (2010) Spatio-temporal population structuring and genetic diversity retention in depleted Atlantic bluefin tuna of the Mediterranean. PNAS USA, 107 2102-2107
27  G Ferrara, L Zane, JKJ Van Houdt, I Milano, A Cariani, GE Maes, F Tinti (2010) Isolation, characterization and multiplex genotyping of 16 EST-SSR loci for the Atlantic bluefin tuna, Thunnus thynnus Mol Ecol Res 10 576-579
28  Kell et al 2007 ICES J Mar Sci 64 640-646
29  H Arrizabalaga, V López-Rodas, E Costas, and A González-Garcés Use of genetic data to assess the uncertainty in stock assessments due to the assumed stock structure: the case of albacore (Thunnus alalunga) from the Atlantic Ocean  Fish Bull 105 140-146
30  Kell et al 2004 J Sea Res 51 287– 299


Expected outcomes
Scientific publications

- a peer-reviewed paper reporting the assessment of self- recruitment rate in the Western Mediterranean populations and of the immigration rates in the feeding aggregates of the Bay of Biscay based on the genetic assignment of ABFT individuals

- a peer-reviewed paper on the assessment of self-recruitment rate in the Western Mediterranean populations and of the immigration rates in the feeding aggregates of the Bay of Biscay based on the microchemical assignment of ABFT individuals

- a peer-reviewed paper on the modelling of dynamics of Mediterranean populations

Socioeconomic impact

- to ocusing one of the most endangered fish stock and species

- to develop population dynamic models based on data independent from fishery

- to achieve data useful for predicting short and long-term changes of the Mediterranean ABFT stock under different exploitation scenarios

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