HARDWICKE'S SCIENCE-GOSSIP. 



217 



THE POLLAN, OR FRESHWATER HERRING 



OF LOUGH NEAGH (COREGONUS POLLAN, Thompson). 



By W. MACILWAINE, D.D. 



N reading the highly 

 interesting and 

 suggestive paper 

 by his Grace the 

 Duke of Argyll 

 ("A few Weeks on 

 the Continent"), 

 in the " Contem- 

 porary Review " 

 for July, I was 

 particularly struck 

 with what ap- 

 peared to me a 

 coincidence be- 

 tween a portion 

 of the fauna of 

 Italy and that of a 

 well-known Irish 

 locality, and, on a 

 more attentive 

 consideration, this 

 coincidence has appeared to me sufficiently remarkable 

 to warrant my drawing the attention thereto of the 

 readers of Science-Gossip. 



The Duke's attention, when visiting Venice, was 

 attracted to a remarkable species of gigantic prawn, 

 {Nephrops Norzvegicits), there exposed for sale, and 

 on inquiry, its habitat was traced to the northern 

 extremity of the Adriatic. On further pursuing his 

 investigation respecting the occurrence of this 

 crustacean in so unexpected a locality, his Grace goes 

 on to observe, "Is it possible that the Adriatic may 

 be a portion of the Mediterranean Basin, which at 

 one time had a communication with the northern 

 seas, and that this species is a survivor of a northern 

 fauna which has been destroyed in the warmer waters 

 of the rest of the basin ? " 



The distinguished writer of the paper proceeds to 



give his own belief, " That this survival of an extinct 



fauna may be referred to a time when the waters of 



the North Sea found entrance into the Adriatic over 



No. 190. 



what are now the lower passes of the Alps, and this 

 time belongs to the period of the glacial epoch, 

 when we know from other evidence that there was a 

 submergence of the land in our own islands to the 

 extent of at least 2000 feet." 



Further on a fact is mentioned in connection with 

 the fauna of the Italian lakes, namely, the occurrence 

 of " a small freshwater herring (Algoni), larger than 

 the sardine, but a good deal smaller than the pilchard, 

 which, according to Dr. Giinther, of the British 

 Museum, is identical with the twaite-shad {Clitpea 

 pinta)." 



The following is the inference drawn by the Duke : 

 "The Algoni is, therefore, a survivor of the Italian 

 lakes, from the time when these lakes were actually 

 arms of the Adriatic Sea which occupied the Lombard 

 plain, and were at least accessible from that sea by 

 rivers which presented no obstacle to the migration 

 of that fish." 



These remarks at once recalled to my recollection 

 a half-formed theory, in which, during years long 

 past, I had ventured to indulge respecting Lough 

 Neagh and its well-known Pollan. The striking 

 resemblance, both in its outward appearance and 

 structure as well as in its habits, have, as all know, 

 conspired to give it the name of freshwater herring. 

 These coincidences, recorded by W. Thompson in 

 his "Natural History of Ireland," vol. iv. page 168, 

 are so many and so apparent, that they must occur to 

 the most ordinary observer. The gregarious habits 

 of this species, its appearance at stated seasons in 

 certain parts of the lake in enormous shoals, the 

 parts of the lough frequented by it, and other 

 herring-like peculiarities, which afford to the fishers 

 of Lough Neagh their ready means of capture, all 

 conspire to remind us of the genuine herring of the 

 sea (Chpca karengus). Thompson refers, though 

 not without hesitation, to the occurrence of the 

 Pollan in other Irish lakes, Loughs Erne and Derg, 

 and probably in Lough Corrib. This is, however, 

 doubtful, and the dissimilarity which that acute 



