new insights on reproductive strategy of swordfish ( xiphias gladius )
DESCRIPTION
F.Poisson. Fauvel C. New insights on Reproductive strategy of swordfish ( Xiphias gladius ) In the Southwestern Indian OCean. Part 2: Fecundity and spawning pattern. Close to over-exploitation (IOTC). 35,000 Tonnes. 1990. Aims of this study. - PowerPoint PPT PresentationTRANSCRIPT
New insights on Reproductive strategy of swordfish (Xiphias
gladius) In the Southwestern Indian
OCean
F.Poisson. Fauvel C.
Part 2: Fecundity and spawning pattern
Close to over-exploitation (IOTC)
35,000 Tonnes
1990
Monitor the gonadal development of individuals around Reunion Island,
Review all information available in the Indian and western Pacific Oceans.
Aims of this study
Sampling program
Over 32 CONSECUTIVE MONTHS
52 trips onboard domestic longlinersonboard domestic longliners 294 days at sea, 235 longline sets 1727 gonads sampled
Spawning occurs from October to April
Threshold value1.375
Gonadal Index (Hinton et al. 1996)
Spawning
Spawning season is longer for bigger (older)
females
The Big individuals arrived at the beginning of the Spawning season
Sex ratio fluctuated seasonaly according to SST
Batch fecundity increases with the fish weight (age)
0
5
10
0 150 300
fish weight (kg)
Millions of oocytes
Big Old Fat Fecund Female Fish (BOFFFF) hypothesis
(Longhurst 2002, Berkeley et al. 2004)
Diameter of eggs
offsprings Viability
BOFFFF more biologically valuable
Growth
☺
☺
☺
Spawning activity is localized in discrete
areas
Spawning activity localised in discrete areas
Synchronised movements between spawning ground and neighboring regions
Major role of the BOFFF in the reproductive capacity
Conclusion
PROSPECTS
Confirm migration pattern (homing pattern)
Consider the protection of BOFFFF
How to preserve the population age structure
Fishing closure ? Protected marine areas? Gear selectivity ?
Acknowledgements
This project was an financed by the European Union (FEDER), and the Conseil Régional and Conseil Général de La Réunion.
The authors would like to express their gratitude to the skippers who volunteered to allow scientific observers on board their vessels and to all people involved in the sampling. We thank the fishery industry of Reunion Island for their outstanding support of the “Programme Palangre Réunion” (PPR) project.
THANKS FOR YOUR ATTENTION
DO SWORDFISH ♂ PREFER THE BOFFFF ?
Spawning occurs in the vicinity of Reunion Island
Histologicalanalyses
Transverse section of a an early developing ovary stage
Transverse section of a a ripe ovary in
hydratation
Stages
1 Immature
2
3
4
5
6
developing
maturing
ripening
Spawning
Spent or resting
Maturity scale for females
0 undeveloped
Ovocyte diametersDistribution
0
0,05
0,1
0,15
0,2
0,25
0,3
0,350
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35