Atlantic bluefin tuna

Transcription

1 Atlantic bluefin tuna An overview Jean-Marc Fromentin

2 Complex population dynamics Spatial distribution over the whole North Atlantic and Mediterranean Population structure still unknown Spawning in a small spatial and temporal window : Homing (May / June in areas of Mediterranean & Gulf of Mexico) Highly migratory fish with complex and variable migration patterns (7700 km within 50 days, mean speed ~ 6 km/h up to 30 km/h)

3 Complex population dynamics Pelagic (mainly in surface but performing deep dives) Top predator (opportunistic feeder) Thermoregulation (environment: 3 C to 30 C; body T ~20-25 C) Maximum size > 3m and up to 700kg Longevity > 20 years Maturity East ~4 years (~120cm, 30kg) ; West ~8 years (~190cm, 130kg) Fecundity related to weight (up to 45,000,000 eggs for a large female) Is recruitment success related to the age of the spawners (parental effects)? Long live species: more fragile to exploitation (low population growth rate)

4 Complex population dynamics Intriguing events What s happen to the Nordic BFT fisheries? Changes in migration patterns? Changes in population size? Eradication of a sub-population? What s happen offshore the Brazilian coasts? No satisfying hypothesis 40 years later Landings (tonnes) Skagen 1950 Nordic area Brazilian area Bergen

5 Complex population dynamics European programme STROMBOLI Collection of 110 series of trap catches Dominant secular cycles ( yr) Synchronous long-term fluctuations all around the West Med. and Gibraltar Straits: variations in stock size or migrations? Number of Tuna caught Favignana - Formica (Sicilia-Italy) South Sardinia (Italy) Medo das Casas (Portugal) Sidi - Daoud (Tunisia) BFT long-term fluctuations are strongly and negatively related to those in temperature: Changes in migration patterns is the most likely hypothesis Quantité de thon rouge

6 Complex population dynamics Need research for better understanding: (1) Spatial and temporal variations in migration patterns (2) Reproductive biology (site fidelity/homing, parental effect) (3) Population structure: A panmictic population (1 stock)? Two stocks with homing, but with mixing on the feeding grounds? A meta-population or a puzzle of independent sub-populations? A good quantification of these biological and ecological processes is crucial for management and conservation, e.g. to preserve genetic diversity and thus the ability of the population to face environmental changes: Need for more research in E.U.

7 Resource shared by many countries others Japan 7% 9% USA Spain 3% 16% Canada 1% Turkey 8% France 20% Tunisia 5% Marocco 5% Libya Malta 3% 1% Croatia Algeria 3% 3% Greeçe Italy 1% 14% Portugal 1%

8 Resource shared by many countries In a context of high value Rather low value until the development of deep freezing (canning) Since the 1980s BFT mostly exported to Japan (sushi and sashimi market) Steep increase in price and then in fishing effort/capacity BFT farming: 1997 : 200 tonnes 2004 : tonnes Spectacular increase of farming since 1997 This high value is a major threat for BFT as it allows fishing even at low catch rates and generates strong conflicts of interest between fisheries/countries

9 Resource shared by many countries Along its migration routes, bluefin tuna can be caught by: 1. Canada, Japan and USA 2. Japan, Marocco, Portugal, Spain 3. France, Italy, Japan, Spain, Tunisia (Marocco, Algeria) Croatia, France, Greeçe, Italy, Lybia, Malta, Turkey Need for an international assessment and management

10 INTERNATIONAL COMMISSION FOR THE CONSERVATION OF ATLANTIC TUNA (ICCAT) Born in starting with 28 contracting parties - 42 currently (European Union since 1997) COMMISSION Decision of Management Recommandations on the basis of scientific advice Political body Advice SCRS Standing Committee for Reasearch and Statistics Scientific body Species Groups Sub-committee on Statistics Sub-committee on by-catch Sub-committee on Ecosystem ad hoc WG Methods WG Precautionary Approach WG

11 The scientific diagnostic ICCAT stated BFT overfished in 1996 and implemented TAC in Since then, strong deterioration of the official (ICCAT) catch database Poor reporting of non-iccat members Illegal fishing (under-sized and flag of convenience) Important under-reporting of ICCAT members in relation to the implementation of the TAC Great loss of information in recent years due to farming Strong uncertainties regarding the current total catch level as well as the size composition, area and flag origin of the catch since 10 years: Preclude the use of some models (but not the diagnostic)

12 The scientific diagnostic The 1998, 2002 and 2006 ICCAT stock assessment sessions lead to the same conclusion of overfishing and overexploition Large overcapacity of the fishing fleet: 1700 boats in the Mediterranean (250 large & powerful boats targeting BFT, 1350 artisanal / multipecies boats) Highest catch ever met: about tonnes/year since Mediterranean East Atlantic West Atlantic Current catch are two times higher than the productivity of the stock, estimated at tonnes/year

13 The scientific diagnostic Rapid expansion of the fishing areas: no more refuge for spawning BFT is more fragile to exploitation: long live species and concentration during spawning Stable recruitment, but strong decline in spawning stock biomass (impact on trap and recreational fisheries?) The current exploitation of bluefin tuna gathers most of the biological and economic traits that have led several fish stocks in the past to depletion With a high risk of weak recovery (as the southern bluefin tuna or Canadian cod)

14 Conclusion: Two priorities Urgent need for a real and efficient management Current exploitation levels are NOT sustainable Protection of both juveniles & adults are needed The key problem remains the overcapacity: The tragedy of the Commons Need for better expertise & research To get satisfactory fisheries statistics and access to fish into cages To develop scientific surveys and operating management models To increase research effort (population structure, spatial and temporal dynamics and reproductive biology)