H. de Pontual, A. Jolivet, F. Garren, M. Bertignac & R. Fablet

Ifremer Brest, dpt Sciences et Technologies Halieutiques

First archival tagging on European hake:First archival tagging on European hake:what have we learnt?what have we learnt?

Key featuresKey features

� Widely distributed over the north east Atlantic shelf(Norway to Mauritania)

� Total landings declined 120,000 tons in 1960's to ~ 50,000 tons

� Recent concerns about the stock status: Low SSB,

low recruitment,

Recovery Plans in 2004 (NS) and 2006 (SS)

� Uncertainties on biological parameters Slow growing vs fast growing hypotheses

(Hickling, 1935; Belloc, 1935)

� Uncertainties about the population structure:2 stocks ?

carte

Recent advances from mark-recapture experiments

� Conventional tagging (pilot study 2002)

Growth underestimation …

Age (years)

0 2 4 6 8 10

Tota

l len

gth

(cm

)

0

20

40

60

80

100

120 Lucio et al. (2000a)ICES (1993)de Pontual et al. (2006)

♂ ♀ 301 days at liberty, TL 30 cm −−−−>>>> 49 cm

●●●● Winter ring (blind interpretation)●●●● OTC mark

… due to age overestimation

(de Pontual et al. 2003, 2006)

Fast growth confirmed:- experiments: BoB + off the Iberian Peninsula + Mediterranean Sea (Pineiro et al. 2007; Mellon et al. in prep; de Pontual et al. in prep)

- controlled conditions: growth rate ~ of cod (Jolivet et al. submitted)

� Archival tagging (pilot study in 2006)- Relate opacity complex pattern to temperature history

- Analyze migrations

DST methodologyDST methodology

� Can hake survive to archival tagging ?Controlled conditions: similar survival rate for conventional and DST tagging

(Jolivet et al. in press)

� Methodology:• Star-Oddi « DST micro » surgically implanted in the peritoneal cavity

• Temperature and pressure at 30’ intervals

• 115 tagged fish released (31- 40 cm)

• 4 recoveries / 3 fish returned with DST

• 18 – 80 days at liberty

Effects of conventional and DST tagging on survival and growth of European hake (Merluccius merluccius)

Aurélie Jolivet1, Hélène de Pontual1, François Garren1 and Marie-Laure Bégout2

1Ifremer LASAA, Brest, France 2Ifremer CRELA, L’Houmeau, France e-mail : ajolivet@ifremer.fr

Methods

Results

Conclusion

Fish were all caught in the wild in September 2005 and acclimated during 7 months. The tagging experiment started on February 7, 2006 and ended 128 days later. Two size groups were considered : small fish (average length ±SD, 29.9 cm ±2.17; SF) and larger fish (36.4 cm ± 2.5; LF). All fish were anaesthetized in a solution of benzocaïne (ethyl p-aminobenzoate), measured and weighted prior to subsequent treatment. For each size group, fish were randomly partitioned in 3 treatment groups : control (C), conventional tagging (CT : T-bar tag + oxytetracycline (OTC) injection), DST tagging (dummy tag + T-bar tag + OTC injection).

Anesthesia and sedation experiment

7:19 (±0:21)3b : Anesthesia

13:11(±3:58)3:54 (±0:39)3a : Total loss of equilibrium

11:27 (±8:31)1:48 (±0:44)2 : Deep sedation

Low dose (20 mg l-

1)High dose (100 mg l-

1)Stage

These data give anesthesia and sedation induction time at 9°C for hake (TL: 31.2cm ± 2.3). Benzocaïne was applied at a high concentration of 100 mg l-1 for surgery, and a low concentration of 20 mg l-1 for transport.

Important results are: 1) Conventional tagging impacts the survival probability which questions the use of mark-recapture data for estimations of natural mortality. 2) DST tagging should be feasible in the wild on “small fish” with survival rate and probabilities of recapture similar to that of conventional tagging. European hake is not a farmed species and husbandry conditions need to be improved. This was a limiting factor for this study.

Initial condition factor (CF) w.r.t size group and treatment

Distribution of Specific Growth Rate

- Out of the 60 fish, 21 survived (35%). - Survival probability for tagged fish decreased (CT or DST) particularly during the first 50 days-No significant difference between survival of SF tagged with CT and DST(P = 0.77). - Younger fish better supported stress induced by handling, anesthesia and tagging- Higher survival time for fish with a ratio: Weight DST/Weight Fish < 2% (Mantel-Cox : P = 0.04).

- High individual variability- No significant difference between control and tagged fish SGR (t-test: P>0.05). - Negative SGR for fish with a poor initial CF- 2 periods : recovery step during the first 30 days and a growth step with food intake.-Low survival limited further growth analysis

- Initial CF varying from 71% to 127%. - Homogeneity between treatment and group (KW test : P = 0.906).- Low survival (10%) for fish with initial CF <80%.

Initial condition GrowthSurvival

Introduction

(Mean response time in min:s ± SD)

CF >1

00%

CF 80-10

0%

CF < 8

0%

CF >1

00%

CF 80-

100%

CF < 8

0%

CT

DST

Control0

1

2

3

4

5

6

7

8

9

SF

LF

ControlDSTCT

European hake, Merluccius merluccius, is a major demersal resource in the North East Atlantic which has been heavily exploited. Recent mark-recapture experiments provided evidence of growth underestimation of the species due to bias in the agreed method of age estimation. To fully exploit mark-recapture data, estimations of the effects of tagging on both survival and growth are required. Hake is a little-known species and enriching information can be expected from DSTtagging at sea which requires a feasibility study on this reputed fragile species. The goal of this study were the following: 1) Establishing the conditions of application for surgery (anesthesia protocol);2) Estimation of the effects of conventional tagging on survival and growth; 3) Feasibility of DST tagging in the wild and estimation of effects on survival and growth.

120100806040200

Survival time

1,0

0,8

0,6

0,4

0,2

0,0

Cum

surv

ival

LF_DSTLF_CTLF_CSF_DSTSF_CTSF_C

Group_treatment

Survival function to the average of covariates

Survival time (days)

120100806040200

survival time

2,00

0,00

-2,00

-4,00

-6,00

-8,00

-10,00

spec

ific g

rowt

h ra

te

73,85

75,96

72,25

86,33

77,76

LF_DSTLF_CTSF_DSTSF_CT

Group_treatment

Survival time (days)

Kaplan –Meier survival function

F1 (U90)

Date30/ 06 07/ 07 14/ 07

Dep

th (

m) 0

10

20

30

40

50

60

Tem

pera

ture

(°C)

10

12

14

16

18

20

DST profile (1)DST profile (1)

18 days at liberty

♀♀ , TL 34 cm

LT

HT

Out of Range

62 days at liberty♂, TL 31 cm -> 32.5 cm

F2 (U72)

Date30/06 07/07 14/07 21/07 28/07 04/08 11/08 18/08 25/08

Dep

th (

m) 0

10

20

30

40

50

Tem

pera

ture

(°C

)

10

12

14

16

18

20

22

DST profile (2)DST profile (2)

OOR

80 days at liberty

♀♀, TL 34.5 cm -> 35.1 cm

F3 (U87)

Date 01/07 08/07 15/07 22/07 29/07 05/08 12/08 19/08 26/08 02/09 09/09 16/09

Dep

th (

m) 0

20

40

60

80

100

120

Tem

pera

ture

°C

10

12

14

16

18

20

DST profile (3)DST profile (3)

OOR

� Questions to be addressed:

• Main characteristics of the VM behavior ?

(rhytmicity, amplitude, temperature variation,

tidal effects)

• What about horizontal movements ?

� Proposed method

• Automated analysis of DST signals

• Statistical analysis of extracted features

Quantitative analysis of DST signals: Quantitative analysis of DST signals: separation of vertical movement, seabed and tidal signalsseparation of vertical movement, seabed and tidal signals

Change detection

DST bathymetricsignal

VM signal

VM-removed signal

Low-pass filter

Seabed signal

VM- and seabed-removed signal

0 10 20 30 40 50 60 70 80

0

50

100

Dep

th(m

)

DST signal processingDST signalSeabed

0 10 20 30 40 50 60 70 800

50

100Estimated VM relative to seabed

Am

plitu

de (

m)

0 10 20 30 40 50 60 70 80

-5

0

5

Time (days)

Am

plitu

de (

m) Estimated seabed- & VM- removed signal

TF analysis of the ~ tidal signal

Time (days)

Num

ber

of p

erio

ds p

er d

ay

10 20 30 40 50 600

1

2

3

4

5

Time (days)

Num

ber

of p

erio

ds p

er d

ay

10 20 30 40 50 60 70 800

1

2

3

4

5

6Time (days)

Num

ber

of p

erio

ds p

er d

ay

5 10 150

1

2

3

4

5

Common features:• 1.93 period/day: M2 tidal constituent (period 12.4 hours)

Spring tide

• Higher intensities during spring tides : higher tidal signal and/or change of behavior

F3 (U87)

Date 01/07 08/07 15/07 22/07 29/07 05/08 12/08 19/08 26/08 02/09 09/09 16/09

Dep

th (

m) 0

20

40

60

80

100

120

No correlation between activity duration and night duration (p=0.13)

Rhythm persists even at high depth (>100 m)

20.5 21 21.5 22 22.5

20

21

22

23

Sunset time

VM

sta

rtin

g ho

urVertical movement: rhythmicity

VM activity begins at ~ sunset

Vertical movements: amplitude

45.5 46 46.5 47 47.5

30

40

50

60

70

80

90

100

Time (day)

Dep

th (

m)

0 20 40 60 800

20

40

60

80

Time (days)

Am

plitu

de (

m)

MaxMean

0 10 20 30 40 50 60 70 800

100

200

300

400

500

Date (days)

Cum

ulat

ive

dist

ance

(m

)

Vertical movements: temperature

High temperature High temperature

gradient for gradient for

several hoursseveral hours

Date (days)

Time (hours) at seabed T + DT (°C)

DT=0

0 2 4 6 80

5

10

15

Temperature gradient

Act

ivity

dur

atio

n

R = 0.0551p = 0.6732

No correlation btw activity duration and experienced temperature gradient

VMsVMs: tidal amplitude effect: tidal amplitude effect

20 40 60 80 100 1200

0.2

0.4

0.6

0.8

Tidal coefficient

Nor

mal

ized

div

e am

plitu

deR = - 0.4922p = 0.0001

VM amplitude decreases at spring tides

Horizontal movements

releaserecapture

SummaryFirst behavioral information

� Nocturnal activity characterized by :• high amplitude (cumulative distances)

• persisting at high depth

• depending on tidal amplitude

• high temperature variations

� Horizontal movements:• Homing behavior?

Prospect� More data needed: longer sequences , different areas, different seasons (large scale experiment at the EU level)

� Joint analyses of individual markers (natural & artificial)

Thanks:scientific team (Ifremer STH/Brest and EMH/Nantes)crew of the RV “Gwen Drez”participating fishermen Demostem and Sidepêche programs for funding

Thank youfor

listening

Pho

to F

. Gar

ren

ThankThank youyou for for listeninglistening

Date (days)

Time (hours) atseabedT + DT

‘‘Environmental’ factors: temperatureEnvironmental’ factors: temperature

Date (days)

Time (hours) atseabedT + DT

Date (days)

Time (hours) atseabedT + DT

Vertical behavior: Vertical behavior: rhythmicityrhythmicity (1)(1)

Activityduration(hours)

0 6 12 18 244

6

8

10

0 6 12 18 240

5

10

15

0 6 12 18 240

10

20

Timing of activity start (hour)

Vertical behavior: temperature (2)Vertical behavior: temperature (2)

0 2 4 6 80

10

20

30

40

Temperature gradient

VM

spe

ed

0 2 4 6 80

5

10

15

Temperature gradientA

ctiv

ity d

urat

ion

R = 0.326p = 0.0103

R = 0.0551p = 0.6732

Vertical behavior: temperature (2)Vertical behavior: temperature (2)

0 2 4 6 80

5

10

15

Temperature gradientA

ctiv

ity d

urat

ion

R = 0.326p = 0.0103

R = 0.0551p = 0.6732