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Facts & hypothesis upon Indian Ocean billfishes, by Alain Fonteneau

Facts & hypothesis upon Indian Ocean billfishes, by Alain Fonteneau. SWO is a deep species (at least during the day), when all other BILL are shallow species : BILL more vulnerable in the traditional LL than for deep LL (the opposite for SWO)…

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Facts & hypothesis upon Indian Ocean billfishes, by Alain Fonteneau

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  1. Facts & hypothesis upon Indian Ocean billfishes,by Alain Fonteneau • SWO is adeep species (at least during the day), when all other BILL are shallow species: BILL more vulnerable in the traditional LL than for deep LL (the opposite for SWO)… • BILL are most often by-catch species in all the LL fisheries (but not white Marlin?), then (1) their local concentrations may be heavily overfished (as they are not well protected by the IFD rules (Fonteneau and Richard 2004), and (2) their spawning & feeding concentration have not been targeted by LL fleets, unless they are identical to tuna concentrations (then these area of concentration are much less visible in the fishery data, unless they spawn or feed in the sale strata as tunas…) • BILL species are showing relatively low levels of total biomass (biomass of each species, well < 50.000 tons for black and white marlin?), biomass widely scattered in the entire IO (in all warm and temperate SST); such species must have peculiar “spawning hot spots” and showing a homing behavior: never a random spawning, as it would not allow to produce enough recruits. • Potential interaction between industrial LL oceanic fisheries and sport fisheries • Marlin & Sailfish stocks can be of major social and economic interest for many coastal countries in the Indian Ocean, developing sport fisheries and associated tourism. These valuable sport fisheries are perfectly sustainable if they target catch & release of tagged fishes!

  2. Trends of yearly catches: widely different for SWO vs BILL 5000t Black M SWO 10000t 5000t Blue M Striped M > Trend of BUM & BLM billfish catches not showing visible overfishing symptoms > Trend of MLS catches indicative of severe overfishing? (Very pessimistic diagnosis in the Atlantic based on similar catch and CPUE trends)

  3. Billfish nominal CPUEs in the Indian Ocean (North of 40°S): • Major decline of nominal BILL CPUEs (as in the Atlantic): recent nominal CPUEs being at only 1%, 4% and 2.5% of their initial levels (Black M, Blue M, and striped M) (similar declines observed in the Atlantic ocean) • A 3 steps decline: first 10 years, intermediate period 1960-89, and after 1990 • On the opposite, SWO CPU being quite stable, & dome-shaped, during the 55 years, much lower than marllns in the early period, and much lower during recent years

  4. All marlin species are predominantly caught associated to warm SST over 25°C (only 6.5% of billfish catches / LL taken at SST <25°C)

  5. Nominal CPUEs of istiophorids, Japanese LL, average of all 5°-month fished strata with effort >10000 hooks, & calculated only in the 5°-quarter strata with average statistical SSTs >25°C (NOAA Levitu atlas 1995) Black marlin Blue marlin White marlin Istiophorids nominal cpues in warm water strata Declines of CPUEs for Blue and Black M. are similar; quite different for Striped M.

  6. Peculiar case of sailfish • An important species in the Western Indian Ocean: catches larger than SWO? • serious species composition uncertainties? Short & long bill? • Very fast swimming >70km/h, but scale of movement patterns still highly questionable: high viscosity? (W Atl and Iranian sea tagging) or large/fast movements?(Taiwanese tagging: 1150 km in 30 days)? • A billfish showing some kind of schooling, and always a clear shallow behavior…. • Present large catches: widely increasing since 1980, reaching 30000t, probably much more (large coastal artisanal catches widely undeclared?) • A lack of potential analysis, due to the strange lack of SFA C/E data in the historical file of Japanese LL C/E data: when these sailfish C/E data have been well reported by Japan in the Atlantic (and Pacific?) since the early fisheries. Total SFA Japanese catches: an average catch of only 290 t/year, possibly underreported?. Active SAI fisheries in Africa, but never reporting SAI transatlantic migration

  7. EEZ? Marlin catches 1953-1960, period of very high CPUEs

  8. Marlin CPUEs 1953-1960, period of very high CPUEs

  9. Effort 1953-1960, period of very high CPUEs

  10. Marlin Catches /Japan LL, 1990-2007, period of very low CPUEs

  11. Marlin Catches /Japan LL,1990-2007, period of very low CPUEs, but scale *10

  12. Marlin CPUEs of Japan LL, 1990-2007, period of very low CPUEs

  13. Marlin CPUEs / Japan LL, 1990-2007, period of very low CPUEs, scale *10

  14. Marlin Efforts 1990-2007, period of very low CPUEs

  15. Why the major declines of BILL cpues? YEAR • LL Deepening since 1975 shown by HBF • But major CPUE declines observed well before 1975; • And real depth of the recent HBF >20, are still widely questionable: YFT being the dominant species would tend to indicate a shallow fishing, typical of BILL (effect of monofilament and gear handling? Bach and Fonteneau 2006). HBF • Changes in fished zones: more temperate zones, then less marlins available • Effect of technological changes in the LL targeting an increase q on tunas, and having a potential <0 impact on billfish catches (P.Ward WCPFC) • Other potential factors explaining the early declines of YFT early CPUEs: billfish behavior, learning, changes in fisheries, local effects, genetic erosion, etc…

  16. Conclusion upon billfishes sensu largo • Bery little can be said on sailfish due to the lack of data • SWO stock status can be well assessed by traditional SA methods, global and analytical ones (based on CAS, effort and CPUEs) • Marlins: status of all marlin stocks remain entirely questionable • Billfish, marlin+sailfish, species are not important for their market value, but they are of great scientific and ecosystem interest due to their extreme characteristics, and also for sport fisheries in coastal countries tourism and (cf Rosenthal movie). • Billfishes may be “key stone” species? • CPUE of these by-catch species are theoretically often “better” than for targeted species (more representative of local densities), but the marlin LL CPUE trends do not appear to be representative of their stock densities and biomass • The major decline of marlin CPUEs observed in all the areas, may be excessive, but they should be a source of worry for scientists and managers:

  17. Recommendation • A much more active research should be developed upon these species, for instance targeting: • Much better statistics, on industrial fleets, sport (historical CPUEs and sizes) and artisanal fisheries (catches / species: Iran, Sri Lanka, Indonesia, et al…), • Active data mining targeting billfish sport fisheries in the IO. • Recovery & better analysis of existing historical C/E data, including from sport fisheries • Much more biological investigation: on growth, movements, spawning, behavior, etc (cf investigations in the Pacific ocean) • Tentative stock assessment of Marlin stocks: taking into account the limited amount of data available on these stocks, should be attempted, using ad hoc methods.

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