150
ANTON F. BRUUN
‘‘ I1 est en outre trhs net que, si les courant qui entrent portent
aouvent des civelles en grand nombre, il est exceptionnel d’en trouper en
quantitb notable, aux abords du lac, par courant sortant.” On several
occasions Heldt and Heldt caught from 2000 to 4000 elvers in 2 to 3 hr,
and once 10000 in 14 hr, but with an outgoing current they most often
caught none at all, arid only on two occasions more than 60, namely
300 and 400.
I have rcpcntcdly visited lake ‘Cunis and been shown the elvers by
Or. Hcldt and Madame Dr. Heldt, who also demonstrated how
literally every single silver eel was caught when the elvers had grown
up. Heldt (1931, p. 23) describes the departure: “ Dans les lacs cbtiers,
commes aux esbuaires, l”appe1 du large’ est nhcessaire pour decider
les reproducteurs i i prendre la mer. I1 faut que l’eau de l’O&an les
vienne baigner, les sollicite, les dirige. I1 faut du gros temps, une nuit
obscure et un courant de flot. Si ces conditions se produisent au
moment favorable, la passe sera bonne. Des lacs se vident ainsi en
quelques nuits de toutes leurs anguilles matures. C’est par centaines
de tonnes qu’on lea capture alors dans nos lacs de 1’Afrique du
Nord.”
If for nothing else these observations, together with the well-known
fact that the majority of males grow up only in waters of a salinity
higher than about 10 parts per thousand, should have made Tucker
hesitate writing (1959a, p. 498) : “ The evidence shows that the debility
of the (European) eel which is obliged to drift passively downstream in
the current is due to demineralization of the starving body a t the
inception of gonadial and other ho~montt activity, and that ro-mineralizatiori arid rcsumed livalincn~ occiir whon tho eel reaches tho ma.”
I havo Reen thousandn arid hnntllcd hundrcdn of nilver ueln, from
fresh water, brackish water tlnd sea water aa well, and can fully
confirm the statement of D’Ancona (1959, p. 1405) and J. W. Jones
(1959, p. 1281) that the European silver eel is “ vigorous, extremely
energetic and in good condition.” But Tucker (1959, p. 1282) is not
“ subdued by Dr. Jones’s expericnco with thousands of eels. The groat
curse of the voluminous work upon eels, upon tho Salmonidno and upon
sundry other animals, has been that too much of it ha^ been mochanical
and repetitive, replete with experiments unintelligcntly planned and
mountains of data inadequately pondered, parochial alike in the range
of its geographical experience and in it8 isolation from relevant literature
from alien countries and related disciplines.”
This is just after citing Keys (1 933) whose experimental results are
used as a support for Tucker’s ideas, but Krogh (1939, p. 160) has
called attention to the fact that Keys unfortunately did not pay any
ANTON F. BRUUN
‘‘ I1 est en outre trhs net que, si les courant qui entrent portent
aouvent des civelles en grand nombre, il est exceptionnel d’en trouper en
quantitb notable, aux abords du lac, par courant sortant.” On several
occasions Heldt and Heldt caught from 2000 to 4000 elvers in 2 to 3 hr,
and once 10000 in 14 hr, but with an outgoing current they most often
caught none at all, arid only on two occasions more than 60, namely
300 and 400.
I have rcpcntcdly visited lake ‘Cunis and been shown the elvers by
Or. Hcldt and Madame Dr. Heldt, who also demonstrated how
literally every single silver eel was caught when the elvers had grown
up. Heldt (1931, p. 23) describes the departure: “ Dans les lacs cbtiers,
commes aux esbuaires, l”appe1 du large’ est nhcessaire pour decider
les reproducteurs i i prendre la mer. I1 faut que l’eau de l’O&an les
vienne baigner, les sollicite, les dirige. I1 faut du gros temps, une nuit
obscure et un courant de flot. Si ces conditions se produisent au
moment favorable, la passe sera bonne. Des lacs se vident ainsi en
quelques nuits de toutes leurs anguilles matures. C’est par centaines
de tonnes qu’on lea capture alors dans nos lacs de 1’Afrique du
Nord.”
If for nothing else these observations, together with the well-known
fact that the majority of males grow up only in waters of a salinity
higher than about 10 parts per thousand, should have made Tucker
hesitate writing (1959a, p. 498) : “ The evidence shows that the debility
of the (European) eel which is obliged to drift passively downstream in
the current is due to demineralization of the starving body a t the
inception of gonadial and other ho~montt activity, and that ro-mineralizatiori arid rcsumed livalincn~ occiir whon tho eel reaches tho ma.”
I havo Reen thousandn arid hnntllcd hundrcdn of nilver ueln, from
fresh water, brackish water tlnd sea water aa well, and can fully
confirm the statement of D’Ancona (1959, p. 1405) and J. W. Jones
(1959, p. 1281) that the European silver eel is “ vigorous, extremely
energetic and in good condition.” But Tucker (1959, p. 1282) is not
“ subdued by Dr. Jones’s expericnco with thousands of eels. The groat
curse of the voluminous work upon eels, upon tho Salmonidno and upon
sundry other animals, has been that too much of it ha^ been mochanical
and repetitive, replete with experiments unintelligcntly planned and
mountains of data inadequately pondered, parochial alike in the range
of its geographical experience and in it8 isolation from relevant literature
from alien countries and related disciplines.”
This is just after citing Keys (1 933) whose experimental results are
used as a support for Tucker’s ideas, but Krogh (1939, p. 160) has
called attention to the fact that Keys unfortunately did not pay any