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℅ Total landing t 8585 t Lizardfish landings by Japanese offshore trawl fishing in the Tsushima/Korea Strait Decreased about 30 ℅ 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 X ij = the ring count from the Ith reading of the jth fish X j = 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 FL t = fork length (mm) at age t (years) FL ∞ = asymptotic fork length K = growth coefficient t 0 = hypothetical age at which FL = 0 mm

Results

Comparison of transverse and sagittal sections 75% 85% > ≒

Length-frequency distribution Range 280~360 mm ~ 75% Range 340 ~ 440 mm

Body weight and fork length

Monthly change in GSI Spawning occurs

Translucent zone formation period All 695 Two 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 Spawni ng occurs S. Undosquanmis and S. tumbil → ring makes Physiological cjanges related to the reproductive cycle

Female male Females reach a greater maximum length than males similar S. umeyoshii Females grow faster live longer Saurida 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 population Population 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

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