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

Pit Tags

Scanner for Port Sampling

Study ResultsTagging Trips # Fish Total Lbs Average

Wt. (lbs)Hand line 48 3,959 4,767 1.20

Traps 11 118 134 1.14Total 59 4,077 4,901 1.20

Port Sampling 279 15,119 27,177 1.33Tag TypePit Tags Only 1,989

Pit Tags + Spaghetti Tags

1,346

Spaghetti Tags 742Genetic Samples 2,724

#2080555 days at large

Grew from 320 to 386 mm

Length at First Reproduction (FISHBASE)We have a photo of a 135 mm with ripe eggs.

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.

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

050

100150200250300350400450500

Age (yrs)

Fork

Len

gth

(mm

) 𝒍𝒕=𝑳∞ (𝟏−𝒆(−𝒌(𝒕−𝒕𝟎 ) ))𝑳∞=510 mm𝒌=0.139 (FishBase Length Frequency Analysis gives k=0.29)𝒕𝟎=-0.96Manooch, 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.

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

Se

lectivity

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

Se

lectivity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

ObservedPredicted

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

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.

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.

Calculation of Estimated Yellowtail Landings

• Data Sources– CCR Landings by method 1974-2012– TIP Data 1980-2012 (Length data and Species

Composition)

Finfish Landings by Method

19751978

19811984

19871990

19931996

19992002

20052008

2011

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

900,000

1,000,000St. Croix

Diving Nets Line Fishing

Traps

Tota

l Fin

fish

Land

ings

(lbs

)

19741976

19781980

19821984

19861988

19901992

19941996

19982000

20022004

20062008

20102012

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000St. Thomas

Diving Nets Line Fishing

Traps

Tota

l Fin

fish

Land

ings

(lbs

)

St. Thomas Species Groups GROUPER;

14%

SNAPPER; 15%

TRIGGERFISH; 24%

SHELLFISH; 9%

SQUIRRELFISH; 1%

PORGY; 7%

PARROTFISH; 13%

GRUNT; 12%ANGELFISH, 4%

Trap Catch

GROUPER; 7%

SNAPPER; 57%

TUNA; 10%

JACK; 14%

Line Catch

SNAPPER; 39%

TUNA; 5%

JACK; 52%

Seine Net Catch

GROUPER; 15%

SNAPPER; 25%

TRIGGERFISH; 11%

PARROTFISH; 28%

JACK; 5%

GRUNT; 4% ANGELFISH; 8%

Diving Catch

GROUPER SNAPPER TRIGGERFISH DOLPHIN WAHOO TUNA BARRACUDA SHELLFISH SQUIRRELFISH PORGY PARROTFISH KING MACKEREL JACK HOGFISHGRUNT GOATFISH GAR ANGELFISH

St. Croix Species Groups

GROUPER4%

SNAPPER14%

TRIGGERFISH8%

PARROTFISH43%

GRUNT16%

Traps GROUPER6%

SNAPPER34%

DOLPHIN24%

WAHOO7%

TUNA17%

Line Fishing

SNAPPER4%

LOBSTER25%

CONCH29%

PARROTFISH31%

Diving

SNAPPER2%

PARROTFISH80%

JACK6%Nets GROUPER SNAPPER

LOBSTER CONCH

TRIGGERFISH DOLPHIN

WAHOO TUNA

BARRACUDA SHELLFISH

SQUIRRELFISH PORGY

PARROTFISH JACK

GRUNT GOATFISH

GAR ANGELFISH

Estimated Snapper Landings

0

50,000

100,000

150,000

200,000

250,000 St. Thomas Snapper Landings (Estimated and Reported)

Estimated Snapper Landings

SEFSC ReportedSnapper

R2 (1998-2012)=0.746

19751977

19791981

19831985

19871989

19911993

19951997

19992001

20032005

20072009

2011

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

180,000 St. Croix Snapper Landings (Estimated and Reported)

Calculsted Snapper Landings

SEFSC Reported Landings

R2 (1998-2012)=0.726

St. Thomas Snapper Species(% of Total TIP Samples 1984-2012)

YELLOWTAIL SNAPPER, 98.81%

Net Caught Snapper

YELLOWTAIL SNAPPER; 94.45%

DOG SNAPPER; 2.30%

CARDINAL SNAPPER; 2.2%

YELLOWTAIL SNAPPER14%

VERMILION SNAPPER; 6.1%

MUTTON SNAPPER; 2.8%

CUBERA SNAPPER; 5.8%

SCHOOLMASTER; 4.2%SILK SNAPPER; 8.0%LANE SNAPPER; 5.1%

DOG SNAPPER; 22.7%

MAHOGANY SNAPPER; 4.3%

BLACKFIN SNAPPER; 0.2%

QUEEN SNAPPER; 6.9%

GRAY SNAPPER, 9.5%CARIBBEAN RED SNAPPER; 8.5%

Trap Caught Snapper CARDINAL SNAPPER

YELLOWTAIL SNAPPER

VERMILION SNAPPER

MUTTON SNAPPER

CUBERA SNAPPER

SCHOOLMASTER

SILK SNAPPER

LANE SNAPPER

DOG SNAPPER

MAHOGANY SNAPPER

BLACKFIN SNAPPER

QUEEN SNAPPER

GRAY SNAPPER

CARIBBEAN RED SNAPPER

Line Caught Snapper

St. Croix Snapper Species

MUTTON SNAPPER

15%

YELLOWTAIL SNAPPER

8%

BLACKFIN SNAPPER23%SILK SNAPPER

36%

VERMILION SNAPPER

4%

WENCHMAN12%

St. Croix Line Snapper Landings

MUTTON SNAPPER YELLOWTAIL SNAPPER SCHOOLMASTERDOG SNAPPER LANE SNAPPER MAHOGANY SNAPPERBLACKFIN SNAPPER CUBERA SNAPPER SILK SNAPPERVERMILION SNAPPER WENCHMAN SNAPPERS, LUTJANIDAE

MUTTON SNAPPER

14%

YELLOW-TAIL

SNAPPER43%

SCHOOLMASTER

23%

St. Croix Trap Snapper Landings

Estimated Yellowtail Landings

19741976

19781980

19821984

19861988

19901992

19941996

19982000

20022004

20062008

20102012

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000Estimated St. Thomas Yellowtail LandingsDiving

Traps

Seine Net

Hand Line

19751977

19791981

19831985

19871989

19911993

19951997

19992001

20032005

20072009

2011

0

5,000

10,000

15,000

20,000

25,000

Estimated St. Croix Yellowtail Snapper LandingsTraps

Line Fishing

Hugo

Average FL (mm)

1980 1985 1990 1995 2000 2005 2010 2015200

220

240

260

280

300

320

340

360

380St. Croix Yellowtail FL (mm)

Ave

rage

FL

(mm

)

1980 1985 1990 1995 2000 2005 2010 2015200

220

240

260

280

300

320

340

360

380

St. Thomas Yellowtail FL (mm)

Ave

rage

FL

(mm

)

Total Mortality (Z)

1980 1985 1990 1995 2000 2005 2010 20150.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

St. Thomas Yellowtail Total Mortality (Z)

Tota

l Mor

talit

y (Z

)1980 1985 1990 1995 2000 2005 2010 2015

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

St. Croix Total Mortality (Z)

Tota

l Mor

talit

y (Z

)

Average Size and Years of Reproduction St. Thomas

1970 1975 1980 1985 1990 1995 2000 2005 20100

0.5

1

1.5

2

St Thomas Yellowtail SnapperNetsLine

Year

Stan

dard

ized

CPU

E

1980 1985 1990 1995 2000 2005 2010 20150

100

200

300

400

-1

1

3

5

St Thomas Yellowtail Snapper

Avg FL

Size @ 50% reproduction

Yrs of reproduction

Year

Avg

FL

Yrs

of R

epro

ducti

on

Average Size and Years of Reproduction: St. Croix

1970 1975 1980 1985 1990 1995 2000 2005 20100

0.51

1.52

2.53

Line

Traps

Year

Stan

dard

ized

CPU

E

1980 1985 1990 1995 2000 2005 2010 20150

100

200

300

400

-1

1

3

5

St Croix Yellowtail Snapper

Avg FLSize @ 50% reproductionYrs of reproduction

Year

Avg

FL

Yrs

of R

epro

ducti

on

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