269 Part III. — Twenty-fifth Annual Report 



occur more frequently than the records of them would seem to indicate, 

 for it is quite possible they may sometimes be included under the more 

 general name of Euphausiidae. The use of this less definite name is often 

 rendered necessary owing to the disentegrated condition of the food, 

 which, though perfect enough to show the relationship of the organisms 

 composing it with the family referred to, are too incomplete to permit 

 of the satisfactory identification of the species or even of the genus 

 to which they belong. 



5th — Decapod larvae. In the observations on the food of herrings 

 given under each district, it will be observed that Decapod larvae, though 

 they may occasionally be found in considerable numbers in a few of the 

 stomachs examined, they do not appear to hold a very important place in 

 the herrings' bill of fare. Of the stomachs containing food examined for 

 this paper, Decapod larvae were observed in scarcely 3| per cent, of them, 

 and the percentage of records for these larval forms in Brook and 

 Calderwood's paper was even less. This infrequency of their occurrence 

 in the stomachs of herrings, as compared with Calanus, can hardly be 

 ascribed to the rarity of these organisms, for at times they are present in 

 the sea in considerable numbers, as shown in plankton gatherings. It has 

 to be remembered, however, that many of these larvae are provided with 

 a tough carapace and a spiny armature of a somewhat formidable 

 character, which may tend to make herrings reluctant to attack them if 

 other food of a more harmless kind be within reach. 



Some other forms, i.e., Pseudocalanus, Centropages, Temora, &c, among 

 the Copepoda, Evadne, as representing the Cladocera, Sayitta, and other 

 Annelida, and the eggs and scales of fishes have also been recorded, but 

 they occur so very sparingly as to suggest that their presence with the 

 other organisms in the stomachs may be due to their having been 

 accidentally captured by the fish while in pursuit of other species. 



In dealing with a subject like this, it sometimes happens that a 

 question emerges which, though not bearing directly upon it, is yet of 

 interest because of its negative character. In studying the food of 

 herring it soon becomes evident that Calanus, for some reason, forms an 

 important part of it, and one likely reason, though it may not be the only 

 one, is that this Copepod abounds everywhere throughout the wide area 

 where herring fisheries are carried on. It has also been shown that the 

 herring does not gather its food from the water merely by using its 

 gills as a kind of seive, but hunts for and captures the organisms it lives 

 on, and this seems to indicate that the fish may be able to some extent to 

 discriminate between forms it prefers and those it dislikes. But though 

 it may be able to do so, it is doubtful if it can distinguish differences that 

 seperate closely-allied species, as, for example, between Calanus and 

 Pseudocalanus, or between that species and Temora or Metridia, except 

 that the Calanus is larger than the others. It is not surprising, therefore, 

 to find that while the herring apparently prefers Calanus, other species 

 should occasionally be present amongst its food, especially if they 

 are moderately common. Keeping this in view, it is interesting to 

 note that in the published accounts relating to the food of Clyde ani 

 Loch Fyne herrings there is not, so far as I know, a single record of 

 Euchoeta norvegica having been observed amongst the food contained 

 in their stomachs. This Euchwta is now known to be generally common 

 and at times abundant in Loch Fyne and it is moderately frequent 

 in other portions of the Clyde area, but iri none of the samples of Clyde 

 herrings submitted for examination has Euchaeta been observed as part 

 of their food. No doubt this Calanoid appears to be a true deep-water 

 form, but it is also occasionally obtained amongst plankton collected 



