對馬 / 韓國海峽 - 長體蛇鯔的年齡與成長

對馬 /韓國海峽 -長體蛇鯔的年齡與成長

邱惠君

Introduction

Saurida elongata

•Inhabits sandy-mud bottoms.

•Depths less than 100m.

•Japanese trawl fisheries.

•High meat yield and high gel-foeming ability → surimi and fish cakes in Japan.

Stock levels of lizardfish in the East China Sea。。 Similar to those of other demersal

fishes LOW

Japanese large pair-trawl fishery catch of lizardfish in the East China Sea

Per unit effort 9℅20061982

Total landing 1982 2006

23 t8585 t

Lizardfish landings by Japanese offshore trawl fishing in the

Tsushima/Korea Strait Decreased about 30℅1973 2006

overfishing

Biological characteristics: growth and sexual maturation rates

Sardinops melanostictus Gadus morhua

Little information: temporal variations in growth and reproductive traits for other lizardfish of this genus.

Annual growth marks on scales → previous studies (age and growth of lizardfishes) ↓May underestimate lizardfish age

Materials and Methods

Offshore pair trawlers

Small trawlers

N= 695 specimens

Fork length (FL) → nearest 1mm

Body weight (BW) → nearest 1g

Gonad weight (GW) → nearest 0.1g

Sex → determined by visual examination of the gonads

Otoliths → preserved in 70% ethanol

GSI = 100 × GW /BW

Prepared from 20 species

Embedding the otoliths in epoxy resin

Microcutter

Polishing with a grinder

Mounting on glass slides

Transverse section

Embedding the otoliths in epoxy resin on a glass slide

Grinding them down with rotary whetstones

The core became clearly visible

Sagittal section

Preliminary examination

Counted twice

N = number of fish aged

T = number of times each fish was aged

Xij = the ring count from the Ith reading of the jth fish

Xj = the average age of the jth fish

Arrowheads outer margin of each translucent zone

Observe the Sagittal section

Reflected-light projector at 20x magnification

Examined twice → number must the same →used

the frequency of occurrence of a translucent zone on the outer otolith margin → the season when the translucent zone formed

Determine the age of each fish

Assigned an age in years to each individual equal to the number of translucent zones observed

The time elapsed From 1 June to the day of sampling

was then added to yield an age estimate for each fish specimen

Assumed a birth date of 1 June

The growth of males and females

FLt = fork length (mm) at age t (years)

FL∞ = asymptotic fork length

K = growth coefficient

t0 = hypothetical age at which FL = 0 mm

Results

Comparison of transverse and sagittal sections

75%

85%

>

≒

Length-frequency distribution

Range 280~360 mm~ 75%

~ 75%

Range 340 ~ 440 mm

Body weight and fork length

Monthly change in GSI

Spawning occurs

Translucent zone formation period

All 695Two readings did not agree for 32 (4.6%)Nine otoliths were broken (1.3%)IAPE of 686 individuals was 0.49%654 otoliths showed distinct ring marks (94.1%) → used for growth analysis

Age-frequency distribution

2-11 translucent zone

2-12 translucent zone

Minimum ages of specimens from small trawlers and offshore pair trawlers were 1 and 2 years old, respectively.

Female

male

Greater

Female growth faster than male

Discussion

Lizardfish

from Tsushima/Korea Strait

Offshore pair trawlers

Small trawlers

Lager mesh cod end

1. Youngest specimens were 2 years old

1. Youngest specimens were 1 years old

Pagrus major

Younger fish occupying shallower waters

Adult fish tending to migrate into offshore waters

Autumn and Winter

Alternating periods of rapid and slow growth

Seasonal growth cycle → physiological changes

Temperature

Feeding regime

Reproductive cycle

Opaque zone → during spring and summer

Spawning season

Spawning occurs

S. Undosquanmis and S. tumbil → ring makesPhysiological cjanges related to the reproductive cycle

Female

male Females reach a greater maximum length than males

similar

S. umeyoshii

Females grow faster

live longerSaurida species

FL∞

Previous estimates of the maximum age of S. elongata in Japanese → using scale for age determination

Male 4 years or 7 years

Female 4 years or 7 years

Otolith method

Male 10 years

Female 11 years

Underestimates

Suitable

S. Elongata populationPopulation biomass

Standing stock

Accurate age determination

Use otoliths to determine the age and growth

of S. elongata

First

S. elongata slower growth and a longer life span

THE END

THANKS