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Om dypvannsreken ved Spitsbergen

Rasmussen, Birger
Research report
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sh_vol07_04_1942.pdf (1.756Mb)
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http://hdl.handle.net/11250/114714
Utgivelsesdato
1942
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  • Fiskeridirektoratets skrifter, Serie Havundersøkelser (1900-1990) [314]
Sammendrag
The life history of the deep sea prawn, Pandalus borealis, in Spitsbergen

waters is traced on the basis af samples collected mainly in

1938 and 1939. In measuring the prawn a different method than that

used by previous authors has been employed, as instead of the total

length, the length of the carapace without the rostrum has been measured

(see fig. 2). The measurement is taken in millimeters from the base

of the eye to the posterior edge of the carapace. For comparison of

the measurements thus obtained with the results of previous authors

stating the total length of the prawn, the length of the carapace is

multiplied by the factor 5,3 which is the average of nunmerous control

measurements.

The adult females carrying eggs are fouild as early as in July, but

the main spawning of the Spitsbergen prawn takes place in August-

September. The females with hatching eggs are found during the

following May-June, and the egg-bearing period is estimated to last

about 9 months.

The smallest bottom stages of the prawn have been caught in the

shrimp trawl at the end of June and beginning of July, and they measured

averagely about 39 mm. These small individuals cannot have been

hatched the same summer, and they are therefore considered to be

1 year old. Next summer, when the prawn is 2 years old, it has reached

an average total length of about 62 mm. When the prawn is 3 years

old it is on the average about 85 mm long in the summer and it matures

as a functioning male the same autumn. The Spitsbergen prawn thus

reaches maturity as male at the same size as the prawn in southern

Norwegian waters, but this latter is by then only 1 year old. When

the Spitshergen prawn is 4 years old it has reached an average total

length of about 103 mm and it participates in the spawning as male

for the second time.

The following spring and summer the male prawn goes through

the transitional stages, and in autumn they reach the maturity of females

and become ovigerous. The Spitsbergen prawn can also spawn

before all the transitional stages are completed. Thus ovigerous females

in transitional stage C and D (fig. 4) are not infrequent in the catches.

The Spitsbergen prawns are 5 years old when they spawn for the first

time, and they have then reached an average total length of about

117 mm, i. e. the same size as prawns in the corresponding stage of

maturity in southern Norwegian waters, but the Spitsbergen prawn is

by then 3 years older than the southern prawn. In the Spitsbergen

prawn there is no apparent difference in size between the transition

individuals and the first time spawners. In fig. 6 are represented the

size of the various age grtiops of the prawn up to first time spawners.

The female prawns carry their eggs all winter, and at the end of

May and beginning of June the ovigerous prawns can still be found

with hatching eggs, or the hatching is just completed. The major part

of these females does not seem to become ovigerous again the same

autumn, but enters apparantly a period of sexual rest. During the

summer, after moulting, they can be sorted out in the catches as females

with undeveloped ovaries. These prawns are by then 6 years old, and

have an average total length of about 123 mm. These old female prawns

apparently become sexually mature again during the following winter

and spring, and they are in the summer found as large females with

ripening ovaries. They should thus spawn for the second time when

they are 7 years old after 1 year of sexual rest. These older prawns

also seem to become ovigerous later in the autumn than do the first

time spawners (fig. 7 C).

The rate of growth of the Spitsbergen prawn compared with the

growth of the prawn in southern Norwegian waters is illustrated in

fig. 9.
Utgiver
[Fiskeridirektoratets havforskningsinstitutt]
Serie
Fiskeridirektoratets skrifter, serie havundersøkelser
vol 7 no 4

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