Population Size, Growth, Mortality and Movement Patterns of Yellowtail

Snapper (Ocyurus chrysurus) in the U.S. Virgin Islands

CRP Funded Project NMF4540114Funding :

Federal=$132,850CFMC=$20,000

STFA in-kind=$11,200

# STT/STJ Yellowtail Fishing Trips

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

2003-04

2004-05

2005-06

2006-07

0

200

400

600

800

1,000

1,200

1,400

1,600

0

50

100

150

200

250

300

Line Fishing TripsSeine Fishing Trips

Line

Fis

hing

Trip

s

Sein

e Fi

shin

g Tr

ips

Yellowtail lbs/Trip

0

20

40

60

80

100

120

140

160

Seine Fishing Trips

Line Fishing Trips

Yellowtail Snapper Annual STT/STJ Landings# lbs

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

2003-04

2004-05

2005-06

2006-07

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000Trap Fishing lbs.Seine Fishing Lbs.Line Fishing Lbs

Annual Yellowtail Landings # Fish

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

2003-04

2004-05

2005-06

2006-07

0

20,000

40,000

60,000

80,000

100,000

120,000Trap Fishing # Fish

Seine Fishing # Fish

Line Fishing # Fish

Average Monthly Handline & SeineTrips (1997-2008 Average)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec70

75

80

85

90

95

100

8

9

10

11

12

13

14

15

16

Line TripsSeine Trips

# H

andl

ine

Trip

s

# Se

ine

Trip

s

Yellowtail per Trap /Haul

1 2 3 4 5 6 7 8 9 10 11 120.00

0.02

0.04

0.06

0.08

0.10

0.12

f(x) = 0.0000102021 x⁶ − 0.000342536 x⁵ + 0.00422758 x⁴ − 0.0233757 x³ + 0.0566732 x² − 0.0509065 x + 0.0536458R² = 0.831780854529242

Month

Fish

/Tra

p Ha

ul

Pit Tags

Scanner for Port Sampling

Weight Calculations

200 250 300 350 400 450 500 550 6000

500

1,000

1,500

2,000

2,500

3,000

f(x) = 4.07311784274785E-05 x^2.83389025365432R² = 0.92811483610145

Length (mm)

Wt (

gms)

Study StatusTagging Trips # Fish Total Lbs Average

Hand line 27 2023 2431 1.23Traps 10 99 113 1.15Total 36 2122 2544 1.21

Port Sampling 208 15,119 20,103 1.33

Port Sample Locations

Length at First Reproduction (FISHBASE) 188 mm Male, 224 mm Female

CFMC Size Limit 304.8 TL, 244.7 FL

Length at First Capture (FL in mm)

Traps 228 mm

Hand Line 208 mm

Nets 198 mm

Length at Full Recruitment

Traps 270 mm

Hand Line 290 mm

Seine Nets 260 mm

Calculation of Total Mortality Rate (Z)

Where: is the number of fish at time (t) and Z is the rate of total mortality.

An age specific instantaneous rate of Z was calculated by solving the Von Bertalanffy growth equations for t (median age of the size class in the frequency distribution.*

Where: is the length (in mm) at age (t). is the asymptotic length at which growth is zero. t0 is included to adjust the equation for the initial size of the organism and is defined as age at which the organisms would have had zero size.

Solving equation for t (age) allows for calculation of the age (in years) of each size class.

2005=0.1742011-12=0.249

*Manooch, C.S. III. and C.L. Drennon, 1987. Age and growth of yellowtail snapper and queen triggerfish collected from the U.S. Virgin Islands and Puerto Rico. Fish. Res. 6:53-68. Otolith analysis.

Hand line Size Frequency

220240

260280

300320

340360

380400

420440

460480

500520

540560

580600

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

Fork Length (mm)

#

220240

260280

300320

340360

380400

420440

460480

500520

540560

580600

0.0%2.0%4.0%

6.0%8.0%

10.0%12.0%14.0%

16.0%

Project Yellowtail Snapper

Fork Length (mm)

#Age 4 5 6 7 8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 190

50100150200250300350400450500

Age (yrs)

Fork

Len

gth

(mm

)

𝒍_((𝒕))=𝑳_∞ (𝟏−𝒆^(−𝒌(𝒕−𝒕_𝟎 ) ) )𝑳_∞=510𝒌=0.139𝒕_𝟎=-.96

Manooch, C.S. III. and C.L. Drennon, 1987. Age and growth of yellowtail snapper and queen triggerfish collected from the U.S. Virgin Islands and Puerto Rico. Fish. Res. 6:53-68.

Fish Trap Size Frequency

200230

260290

320350

380410

440470

500530

560590

620650

6800%

5%

10%

15%

20%

25%%

of T

otal

Tagging/Port Sampling Summary

Sep-11

Oct-11

Nov-11

Dec-11

Jan-12

Feb-12

Mar-12

Apr-12

May-12

Jun-12Jul-1

2

Aug-120

500

1000

1500

2000

2500

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Total Tags

Survivors

Port Samples/Tag

# Ta

gs/S

urvi

vors

Port

Sam

ples

/Tag

Summary of Mortality• 2005 Size/Frequency Distribution=0.174 (0.0154/month)• 2011-12 Size/Frequency Distribution=0.249

(0.0208/Month)• Coral World

– Initial “Fishing/Transport” Mortality=9.6%Heavy stress from transport to tanks analogous to additional mortality from predators.

– Tag Loss= 1.6%– Pre “Catastrophic” Mortality=2.1% (matches 2011-2012 rate)

Gear Selectivity

Where:S is Selectivity and and are calculated iteratively via nonlinear regression. From the non-linear model (Proc NLIN in SAS) with known values of size class and percent of the sampled population for that size class. The output was estimates of both parameters, which were then used within the selectivity equation to estimate size selectivity for each size class and particularly the size class at which selectivity peaked.

Selectivity Analysis: Fish TrapsYellowtail snapper (Ocyurus chrysurus) [Traps]

Size Class

220 230 240 250 260 270 280 290 300

Sel

ectiv

ity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

ObservedPredicted

Selectivity Analysis: Hand LineYellowtail snapper (Ocyurus chrysurus) [Handline]

Size Class

200 220 240 260 280 300 320

Sel

ectiv

ity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

ObservedPredicted

• Assess rate of tag loss (1.7%)• Assess mortality

– 9.6% initial “fishing/transport” mortality– Mortality following initial mortality almost exactly

that indicated from size/frequency analysis.– Catastrophic mortality after 3 weeks.– Necropsy revealed that 60% had small livers when

compared to fish from market and 69% had liver fluke infestation.

Coral World Studies

Survivorship at Coral World

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 300%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

"3/18 All Tagged"

"5/27 Tagged"

"5/27 No Tag"

"7/27 No Tag, Octogon"

"7/27 No Tag, Quarantine"

Days

% S

urvi

vors

hip

Recaptures• None so far• Comparison with Rick Niemeth’s tagging. All tagging

done on aggregation site. To date Niemeth has tagged – 751 Nassau (2004-2010) and have recaptured 187 back on

the aggregation site. In addition 3 have been captured by fishermen and reported to UVI by STFA members (0.5/year).

– 661 yellowfin grouper and recaptured 25. All tags and recaps were on the aggregation site.

– 3644 red hind (1999-2006) and recaptured 99. 47 Red hind were recaptured off the aggregation site (6.7/year).

Next Steps• Finish Coral World Studies• Double Tagging with Floy and Pit tags.

Started 8/15)• Floy Tagging of remainder• Continue Port Sampling.• Data from DFW.