對馬 / 韓國海峽 - 長體蛇鯔的年齡與成長
DESCRIPTION
對馬 / 韓國海峽 - 長體蛇鯔的年齡與成長. 邱惠君. Introduction. 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. Saurida elongata. LOW. Per unit effort 9℅. 2006. 1982. Total landing. - PowerPoint PPT PresentationTRANSCRIPT
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