CIAC, Hobart, 2006

Statolith and gladius aging of the Southern

Arrow Squid (Nototodarus sloanii)

Jean F. McKinnonDepartment of Marine Science, University of

OtagoGeorge D. Jackson

Institute of Antarctic and Southern Ocean Studies, University of Tasmania.

Photo by Kerry Perkins

CIAC, Hobart, 2006

Introduction

• The statolith is the most commonly used structure for ageing, life history reconstruction and growth studies. However, the gladius has been investigated more recently as a tool for age and growth studies.

Photo by Kerry Perkins

CIAC, Hobart, 2006

Aims

• To age N. sloanii using the statoliths.

• To develop a technique to read the increments in the gladius.

• To create individual growth curves from the gladius data.

CIAC, Hobart, 2006

Capture locations for squid• Squid were collected from south-eastern NZ during

commercial jigging operations

North Island

South Island

A

PN

MHEG

COJ

F

QBLD

IK

R

West Coast

CanterburyOtago

Catlins

South Snares

CIAC, Hobart, 2006

Statolith aging

• Stage of maturity was noted for each squid

• Statoliths were removed from the statocyst

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Statolith aging

• The right statolith was used as a matter of convention

• The statolith was mounted on a microscope slide, ground on wet carborundum paper and polished with 0.05µm Alumina on felt

• 281 statoliths were polished (139 male and 142 female) Photomicrograph by Jean McKinnon

CIAC, Hobart, 2006

Statolith aging

• The increments in the dorsal dome of the polished statolith were counted using a camera lucida

• To ensure accuracy the increments were counted three times for each statolith with a month between each count. Each count had to be within 10% of the average to be considered precise.

Typical Camera Lucida drawing of a statolith (scale bar = 0.1mm)

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Statolith aging results

• Squid ranged in age from 29 days to 206 days old.

• There was increase in size, (both mantle length and weight) with increasing age, but there was low correlation between age and either mantle length or weight

• The log transformed slopes of the regressions for log age versus log mantle length were significantly different (p<0.05) for male and female squid.

CIAC, Hobart, 2006

Statolith aging

0

50

100

150

200

250

300

350

400

0 50 100 150 200 250

Age (days)

Dors

al m

antle

length

(m

m)

050100150200250300350400

0 50 100 150 200 250

Age (days)

Dors

al m

antle

le

ngth

(mm

)

0

200

400

600

800

1000

1200

0 50 100 150 200 250

Age (days)

Tot

al b

ody

mas

s (g

)

020040060080010001200

0 50 100 150 200 250

Age (days)

Tot

al b

ody

mas

s (g

)

Female

Male

r2= 0.491 r2= 0.377

r2= 0.2566 r2= 0.2565

CIAC, Hobart, 2006

Statolith aging

• There was considerable overlap when the range of ages was compared to stage of maturity (Table one). On average, however, the more mature the squid was the older it was.

Maturity Stage

Age Range Days

Mean Age days

Std Error

1 29-116 76.71 2.67

2 57-152 97.89 1.44

3 86-163 119.17 1.71

4 97-180 144.52 5.02

5 110-206 169.00 7.99

Table one. Maturity stage and age range for Nototodarus sloanii (Males and females combined

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Age at maturity

0

10

20

30

40

50

60

70

80

90

100

0-30 31-60 61-90 91-120 121-150 151-180 181-210

Age interval (days)

Per

cen

tag

e o

f m

ale

mat

uri

ty s

tag

es in

eac

h a

ge

inte

rval

0

10

20

30

40

50

60

70

80

90

100

0-30 31-60 61-90 91-120 121-150 151-180 181-210

Age interval (days)

Per

cen

t o

f fe

mal

e m

atu

rity

sta

ges

in e

ach

ag

e in

terv

al

Mature

Maturing

Preparatory

Juvenile

Immature

Female

Male

5 25 25 25 25 25 12

25 25 25 25 20 19

CIAC, Hobart, 2006

Increment Validation

• Seven juvenile Nototodarus sloanii were caught in a light trap off the Portobello Marine Laboratory Jetty.

• They were held in a 65L glass tank with flow through seawater and were fed live zooplankton. They were left to recover for twenty-four hours.

• The squid were transferred to a 10L bucket containing calcein at a concentration of 0.5gcalcein/L seawater. They were left in the bucket for two hours.

• After two hours, the animals were returned to the 65L holding tank.

• The squid were checked several times a day and were fed zooplankton in excess once a day.

Photograph by Kerry Perkins

CIAC, Hobart, 2006

Validation

• Calcein was present in the statoliths of five of the seven squid stained.

• The calcein band was indistinct and incomplete.

Photomicrograph by Jean McKinnon

CIAC, Hobart, 2006

Modal Analysis

• A Modal analysis (Uozumi, 1998) was run on the data collected from three of the Catlins sites; Haldane 1, Haldane 2 and Haldane 3.

Validation

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Location of samples used for modal analysis

North Island

South Island

DIK

Validation

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Validation

• A length composition graph was created for each sampling date where length-frequency interval was taken for every 10mm dorsal mantle length.

• The age of the squid from this sub sample was regressed against sample date.

CIAC, Hobart, 2006

• There was a gradual progression in the modes from 160mm DML to 220 mm DML between 22nd of January and 30th of January 1999. This suggests

that the squid are from the same cohort.

0

5

10

15

20

25

30

121-

130

131-

140

141-

150

151-

160

161-

170

171-

180

181-

190

191-

200

201-

210

211-

220

221-

230

231-

240

241-

250

251-

260

261-

270

271-

280

281-

290

Dorsal mantle length (mm)

Fre

qu

en

cy

22-Jan N= 90

25-Jan N=41

30-Jan N=32

Validation

CIAC, Hobart, 2006

• The relationship between the number of increments and sampling date was linear The equation for the regression was

y = 1.0503 x + 4.0206

(r2 = 0.08, n = 56)

• The relationship was significant at the 5% level (ANOVA) The estimated value of the slope is very close to one, suggesting that the periodicity of the increments is daily

0

20

40

60

80

100

120

140

21-Jan 22-Jan 23-Jan 24-Jan 25-Jan 26-Jan 27-Jan 28-Jan 29-Jan 30-Jan 31-Jan

Sampling date

Nu

mb

er

of

inc

rem

en

ts

Validation

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Gladius aging

• The gladii were removed, dried under weight and stored in labeled tissue paper in tall glass jars.

• 293 gladii were prepared for aging, by wiping the surface with mineral oil.

• The increments were counted using a dissection microscope with an adjustable fibre optic light source.

• Counting criteria were the same as for the statoliths.

CIAC, Hobart, 2006

Gladius aging

• The measurements from the gladius were used to reconstruct growth curves from the oldest and youngest individual found at each sample location.

• Only the increments from two individuals from each location were measured as it is an extremely time consuming procedure

• Because growth was extremely variable, the curves were smoothed by calculating the running mean

CIAC, Hobart, 2006

Gladius aging

• Gladius increments could be seen on the central rib and lateral plate.

Lateral rib

Increments

Photomicrograph by Jean McKinnon

Central rib

Lateral plate

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Gladius aging

• The counts were very similar to those of the statolith from the same animal.

0

50

100

150

200

Gla

diu

s age (

days

)

0 50 100 150 200 250

Statolith age (days)

0

50

100

150

200

Gla

diu

s age (

days

)

0 50 100 150 200 250

Statolith age (days)

female male

Statolith versus gladius increment counts

r2=0.980 r2=0.997

CIAC, Hobart, 2006

Gladius aging

• The growth curves showed a period of slow growth ranging from 20 to 70 days long then there may or may not be a period of faster growth followed by a period of rapid growth.

• There was variation in this pattern which could not be attributed to location or hatch season.

• Gender appears to be an important factor in the growth rate of the squid.

• Female squid show growth curves with only a short period of slow growth, male squid have a longer period of slow growth.

CIAC, Hobart, 2006

Gladius aging

0

20

40

60

80

100

120

140

160

180

1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161

A

0

20

40

60

80

100

120

140

160

1 11 21 31 41 51 61 71 81 91 101 111

C

Gladius increment number

Gla

diu

s in

crem

ent

gro

wth

(m

m)

Female growth curve

Male growth curve

•Curves are from squid from the same location, with similar hatch seasons and caught at the same time.

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Discussion• Previous research has found N. sloanii aged

up to 270 days, this study 206 days old (mature at 6 months?).

• May have an ontogenetic migration • Restricted sample period=> older animals not

present?• Tropical squid often have life spans of less

than one year and mature earlier than temperate species.

• Jackson et al (2000), found that N. sloanii predominantly occur in warmer waters.

• Southland current has subtropical characteristics.

CIAC, Hobart, 2006

Discussion

• The direct validation of the periodicity of the squid statoliths using calcein was not a success, however modal analysis suggests daily periodicity of the growth increments.

• The juvenile squid in this study did not survive longer than 48 hours.

• The individual growth curves show that most squid have rapid growth, but that the degree of that growth is extremely plastic.

• The growth curves reconstructed for N. sloanii are different to those reconstructed for most other squid species. Gender differences not seen.

• This period of slow growth may be an example of the squid showing “cool” strategies with a slow growing period which eventually leads to a large size.

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Discussion

• Gladius growth increments have the potential to provide information on the growth of individual squid.

• May be used as an environmental indicator? Squid growth may be readily influenced by both biological and environmental parameters.

CIAC, Hobart, 2006

AcknowledgementsSupervisors/Thesis readers!

Dr George Jackson,Dr Philip Mladenov

Assoc. Prof. Mike BarkerSquid Collectors

Sea Resources Ltd., WellingtonMaster and Crew F. V. Fuji Maru 63

Dr Steve O’Shea , AUT Master and Crew R.V. Kaharoa

Sandford South Island LtdOtakou Fisheries Ltd

Mr Peter Fullerton, Sea Lord Co. LtdMaster and Crew F.V. Meridien

GeneralStaff and Students of the

Department of Marine Science and Portobello Marine Laboratory,

Especially, Kerry Perkins, Bev Dickson, Karen Bonney and Daryl

CoupTravel Funding

New Zealand Marine Science Society; First overseas conference travel

fund