Göteborgs ocîi Bohusläns

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Göteborgs ocîi Bohusläns

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riANTlKF.STIDNINOKNS IIOl.AOR TKTCKKKI.

1808.

Skarptillen är deremoti

uti siora massor om hösten uti fjordarne. Den träffas alla ude- af året nti den djupa rännan emellan Kostcrskären och fastlandet och uppstiger vid lektiden mot norr uti den fjord, som inskjuter emellan Svenska och Norska landet, fiskas vid Spånviken, i Säcken och ända in i Svinesund samt fiera af de smärre fjor­

darne i vår nordligaste skärgård; mot söder intränger den mellan öarne i Fjellbaeka-trakten och utgör der föremål för ett lönande fiske.

Fisket i Spånviken och i Säcken bedrifves med notar af såväl svenskar som norrmän, ömsom vid ena, ömsom vid andra rikets kuster, och har sedan år 18ö0, synnerligen vid först­

nämnde ställe, uppgått till enorma qvautiteter samt skatta»

1867 till icke mindre än 100,000 tunnor. Skarpsillen har hittills alltid afiåtits färsk till uppköpare, oftast för en ringa penning, då någon gång fångsten varit så stor, att den till och med måst säljas såsom gödningsämne till jordbrukare i Smaa- ieriene. Först för tvenne år sedan företog en norsk köp­

man, Carl Andersen, insaltning i större skala och lyckades temmeligen bra, enligt de intyg professor ltaseh afgifvit, men någon beredning af denna »ill, annat än till anjovis, har bos oss ännu icke förekommit. Den uppköpta .Skarpsfilen transporteras af uppköparebåtar, synnerligast Irån södra skärgårdens fisk­

lägen, till Uddevalla, Oxevik, Göteborg och flera andra ställen, hvarifrån den genom andra mellanhandlare utminuteras inåt landet och lemnar en lönande behållning.

. skärgården årvisa och intränger

Af den Skarpsill, som uppfångas i Fjellbaeka-trakten, be­

rede» genom dervarande köpmäns företagsamhet anjovis i större skala, så att för närvarande insaltas der årligen iner än 3,000 tunnor. Det är icke tvifvel, att detta fiske är förtjent af största uppmärksamhet och att insaltning i stort skalle vara en lönande handtering.

Åfven i södra skärgården visar Skarpsillen sig i mängd, men dess förekommande är icke der så årviss som i norra skärgården. Fisket bedrifves med vadar och fångsten afyttras

Göteborg till rätt höga priser.

å

MEDDELANDE från

HAVSFISKELABORATORIET • LYSEKIL nr

146

GROWTH AND ENVIRONMENT OF SPRAT by

Armin Lindquist

August, 1973

GROWTH AND ENVIRONMENT OF SPRAT by

Armin Lindquist

Introduction

In two preliminary contributions the author (1972 a, b) presented the results of his investigations on the changes in the mean length of sprat in the Kat­

tegatt and Skagerak since the end of the 1920ies. The view was expressed that there may be many factors causing the variations, presumably some of them are independent from another. The changes are so marked that one has to look for corresponding long term changes in the marine environment.

- The material has now been completed until the season 1972/73 and new in­

formation on environmental factors is added, l) Materials and Methods

The sprat is mostly taken from commercial samples. Two areas are compared:

the open sea of the Kattegatt and the archipelago consisting of the Gullmars- fjord and some neighbouring fjords, Fig. 1. In the open sea sprat is fished with bottom trawls, since the 1950ies also with pelagic trawls. In the Gull- marsfjord sprat is fished with purse seines, earlier to" a less extent also beach with seines. Surface lights were introduced into the purse seine fishery in the 1960ies. The samples are taken from mid-September one year to March next year, i.e. during the main fishing season. The figures presen­

ted here are based on individually measured and agedetermined fish. The length figures - with exception of L, - are thus not backcalculated. Figu­

res on the catch are from the statistics of this laboratory; observations on precipitation, radiation, temperature are from published Swedish records.

Results

Fig. 3 shows the mean length of sprat with S.D. in the second and third pe­

riod of growth. The years are fishing seasons. It is evident that in both areas studied there are considerable changes, showing Fhe same trend: at the end of the 1930ies and in the beginning of the 1940ies~the length decreased.

During the 1960ies it increased very strongly.

In Fig. 3 A & B the background material for Fig. 3 is given. Each dot rep­

resents the mean of at least 10 fish from one sample. The fish are indivi­

dually agedetermined and measured; lower half sprat caught in the second pe­

riod of growth, upper part sprat in the third period of growth.

Fig. :2 shows the mean age of sprat from both areas. Despite a wide scat­

tering a decrease in mean age of the Kattegatt sprat can be discerned; this coincides in time with the introduction of pelagic trawls.

Fig. 4 shows backcalculated L,-values from fish in the second period of growth. Both areas studied snow a considerable increase.

Fig. 5 shows catch per unit effort figures for the whole west coast - kg/lan­

ding - for purse seine (archipelago only), pelagic and bottom trawls (open sea only). Some "good" years are distinguished (e.g. I960) but no general trend, (it should be remembered that the fishermen's effort is limited by catch restrictions.)

l) A somewhat shorter version of this contribution is given at the ICES- meeting 1973, document "C.M. 1973/H:3".

2

The year can be divided into a warm season, from April to August, and a cold one, from September to March, when the main fishery for sprat is carried out in the waters studied.

Fig. 6 shows the air temperature of Göteborg. There is a decrease in tempe­

rature during both halfyears since the 1930ies. The cold winters in the early 1940ies are well revealed in the curve.

The number of sunshine hours/incoming radiation (partly extrapolated) has been observed in the coastal area close to Göteborg (at Vinga) since the beginning of the 1950ies. There is no clear trend during the warm half year but there is a very pronounced decrease during the cold season (cf. running means over five years shown in the figure). It can be expected that the de­

crease in sunshine hours is related to precipitation.

Fig. 7 shows precipitation figures for Göteborg. During the cold season there is a pronounced increase. When analysed according to month it becomes clear that this increase in rain and snow is mainly due the months of Novem­

ber, December and January. (A corresponding decrease in surface salinities is the Kattegatt is seen from the figures given by SVANSSON (1972 a and b)„) Discussion

MOLANDER (1940, 1943, 1947) has commented on variations in the mean length of year classes of sprat: strong winters give a bad growth, cf. the strong winters 1940 to 1943. However, the trend to a weaker growth existed already before those heavy winters. Increases in length are known from other marine fish (herring, haddock, plaice). Considerable fluctuations in the mean length are known from pelagic fish in closed water systems, as lakes (Core- gonidae). These fluctuations are related to changes in food supply, compe­

tition, strength of year classes and hydrological factors.

The sprat is a plankton feeder. An increased output of organic matter is likely to have occured in the whole Kattegatt and coastal area. Unfortunate­

ly, there are no long time observations regarding nutrients, primary produc­

tion or biomass.

The increase of precipitation during the early winter occured at the same time as the increase in length of sprat. When temperatures are extremely low the fish is small. There seem to be two separate mechanisms and tempe­

rature is of importance only in extreme situations.

How increasing precipitation acts is not clear. One easy explanation may be through fertilization of coastal waters from land: precipitation carries nut­

rients to the sea where they are needed this time of the year when production normally is low. The prolonged production during early winter results in a prolonged growth.

The increase between and (and L^/L^) has hardly changed significantly during the course of time. has increased, as seen in Fig. 4. Observa­

tions exist only since the early 1960ies and figures are backcalculated.

It seems nevertheless reasonable to assume that the increase in length of the adult sprat mainly is due to an increase in .

The hypothesis is now that high precipitation at the end of the season of growth, i.e. early winter, prolonges production, increases food supply for the young sprat of the year and results in their better growth and later greater individual length when fished.

Literature

LINDQUIST, ARMIN, 1972 a: Långtidsförändringar på västkusten. Ett prelimi­

närt meddelande. - Fauna och Flora 67(2):61-64.

- " - 1972 b: Growth changes of sprat in the Skagerak-Kattegatt. ICES C.M. 1972/H:27, 2 pp~:-+ figs.

MOLANDER, ARVID R., 1940: A research upon the sprat at the west coast of Sweden. - Svenska Hydrogr,-Biol.Komm.skr. N.S., Biologi 2 (4):l-63.

- " - 1943: Sprat and milieu conditions. - Ann. Biol. 1: 165-174.

- " - 1947: The growth of the sprat at the west coast of Sweden during the coaid winters 1940-42 and some notes on the great coastal fishery for sprat during February-March 1943, - ibidem. 2:

113-129.

SVANSSON, ARTUR, 1972 a: Canal models of sea level and salinity in the Bal­

tic and adjacent waters. - Fishery Board of Sweden, Ser.Hydrogr., Rep. No. 26, 72 pp.

- " - 1972 b: Några svenska hydrografiska problem under det senaste de­

cenniet. - Fauna och Flora 67(2):67-72.

Yearbooks of the Swedish Meteorological Service.

SAMPLING AREAS

FIG. 1

îTEBORG

GULLMARFJORD ETC.

(SURROUNDING FJORDS) PURSE SEINES

KATTEGATT

BOTTOM AND PELAGIC TRAWLS

FIG. 2

•

MEAN AGE • KATTEGATT

YEARS A GULLMARFJORD ETC.

3-0I-

• à

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FISHERY SEASON

c m

FIG. 3

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19601961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972

SEASON

61 62 63 64 65 66 67 68 69 70 71 72 73

* 1959 60 61 62 63 64 65 66 67 68 69 70 71

FIG. 5

CATCH PER LANDING

1700 h

PELAGIC TRAWL

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