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Population Size, Growth, Mortality and Movement Patterns of Yellowtail Snapper (Ocyurus chrysurus) in the U.S. Virgin Islands CRP Funded Project NMF4540114.

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Presentation on theme: "Population Size, Growth, Mortality and Movement Patterns of Yellowtail Snapper (Ocyurus chrysurus) in the U.S. Virgin Islands CRP Funded Project NMF4540114."— Presentation transcript:

1 Population Size, Growth, Mortality and Movement Patterns of Yellowtail Snapper (Ocyurus chrysurus) in the U.S. Virgin Islands CRP Funded Project NMF Funding : Federal=$132,850 CFMC=$20,000 STFA in-kind=$11,200

2 Pit Tags

3 Scanner for Port Sampling

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13 Study Results TaggingTrips

14 # days at large Grew from 320 to 386 mm

15 Length at First Reproduction (FISHBASE) We have a photo of a 135 mm with ripe eggs. 188 mm Male, 224 mm Female CFMC Size Limit304.8 TL, FL Length at First Capture (FL in mm) Traps228 mm Hand Line208 mm Nets198 mm Length at Full Recruitment Traps270 mm Hand Line290 mm Seine Nets260 mm

16 Calculation of Total Mortality Rate (Z)

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18 Gear Selectivity

19 Selectivity Analysis: Fish Traps

20 Selectivity Analysis: Hand Line

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23 Survivorship at Coral World

24 What Happened to the Tagged Fish? 1 Recapture 12/4/2013 one year after end of tagging. Was 35 mm larger than predicted from Manooch and Drennan growth curve. Tag Loss- Only one out of 82 fish at Coral World lost a tag and that was improperly inserted. Tagging Mortality-There was little immediate mortality at Coral World Delayed Stress-The difference between what the coral world fish encountered (catching, transport, transport from the boat to the pond and life in the pond itself differed from on-board tagging in which the fish were seldom out of the water for more than 2 minutes.

25 What Happened to the Tagged Fish? Predatory Mortality-During 59 tagging trips predation (of hooked fish) only occurred on six occasions. Migration-Although Randall (1964) recaptured 13 (out of 397 tagged) his fish were all trap captured in shallow water. All of the project fish were caught off-shore. The one recapture was exactly where it was tagged 555 days earlier. Port sampling- In the course of the project, we port sampled about 36% of the probable landings. Project fishermen and non-project fishermen continued to “sample” fish with tails that appeared to have been cut (for genetic sampling). In summary, we don’t have any idea what happened to the tagged fish.

26 Calculation of Estimated Yellowtail Landings Data Sources – CCR Landings by method – TIP Data (Length data and Species Composition)

27 Finfish Landings by Method

28 St. Thomas Species Groups

29 St. Croix Species Groups

30 Estimated Snapper Landings

31 St. Thomas Snapper Species (% of Total TIP Samples ) Line Caught Snapper

32 St. Croix Snapper Species

33 Estimated Yellowtail Landings Hugo

34 Average FL (mm)

35 Total Mortality (Z)

36 Average Size and Years of Reproduction St. Thomas

37 Average Size and Years of Reproduction: St. Croix

38 Conclusions Fishing pressure and landings on St. Thomas are nearly 10 times higher than on St. Croix. Currently the average size yellowtail being harvested in St. Croix is larger than on St. Thomas. Total mortality (Z) as determined from catch curves is significantly higher on St. Croix. There are no particular trends on CPUE on either island. There do not appear to be signs of overfishing on either island. Average size on both islands is close to the age at which 50% of the population become reproductive. This should be monitored in order to insure the continued health of the fishery. There should be more study of this species given its importance. Particularly: – Size at first reproduction – Age and Growth


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