A LABORATORY STUDY OF PARTICULATE AND FILTER FEEDING 

 OF THE PACIFIC MACKEREL, SCOMBER JAPONICUS 



Charles P. O'Connell and James R. Zweifel^ 



ABSTRACT 



In laboratory feeding trials Pacific mackerel, Scomber japonicns, averaging 147 g in 

 weight did not respond to Artemia nauplii, but did capture Artemia adults by biting 

 (particulate feeding) when density was 1 or 2/liter and by filtering when density was 

 22 to 112/liter. Particulate feeding is described by Np = 60.3f/?, where N is the number 

 of Artemia ingested in t minutes at D numbers per liter. Filter feeding is described 

 by Nf- = 23,788 (1 — e-o.ooastvD)^ where 23,788 is an asymptotic estimate of the number 

 of Artemia in the digestive tract at full capacity. 



The results suggest that the mackerel utilizes only the larger of the planktonic crusta- 

 ceans, such as euphausiids, in the sea. For the relatively low average densities of such 

 organisms the derived equations indicate that the mackerel could not obtain its daily 

 nutritional requirement, estimated to be 8% of body weight, in less than 24 hr of feeding. 

 Though the daily requirement could be obtained in much shorter periods, perhaps by 

 filter feeding, if such crustaceans are encountered in aggregations of considerably higher 

 density than reflected by area averages, it is probable that the mackerel must often de- 

 pend in part on such larger organisms as fish to fulfill its needs. 



Comparison of the mackerel ingestion rates to those for the smaller northern anchovy 

 indicates that while the individual mackerel may generally capture a greater proportion 

 of the large crustaceans encountered than the anchovy, the proportion captured would 

 have a relatively lower nutritional value for the mackerel. 



The Pacific mackerel, Scomber japonicus, is one 

 of several pelagic schooling fishes of the eastern 

 temperate Pacific which feed on zooplankton, but 

 it does not depend entirely on zooplankton. Fitch 

 (1956) reported that stomach contents contained 

 about 30*;/ larval and juvenile fish by volume, 

 with the remainder composed largely of such 

 crustaceans as mysids, copepods, and euphau- 

 siids. Frey (1971) commented that larval and 

 juvenile fish appear to be the most important 

 food, but that the mackerel relies heavily on 

 euphausiids at times. Hatanaka et al. (1957) 

 showed that S. japonicus in coastal regions of 

 Japan consume mainly small anchovies in the 

 late summer and autumn and euphausiids in 

 other seasons. The biomass of euphausiids con- 



' National Oceanic and Atmospheric Administration, 

 National Marine Fisheries Service, Southwest Fisheries 

 Center, La Jolla, CA 92037. 



sumed annually was estimated to be three or 

 four times that of anchovies. 



In addition to being the dominant element in 

 the diet of S. japonicus, the larger crustaceans 

 are an important class of food for a number of 

 other pelagic schooling fishes. The jack mack- 

 erel {Trachurus syynynetricus) is known to feed 

 heavily on small fish and squid at times (Fitch, 

 1965), but about 10 ''/c of stomach contents by 

 volume is euphausiids (Carlisle, 1971) . The Pa- 

 cific sardine (Sardinops caerulea) feeds largely 

 on copepods smaller than those consumed by the 

 jack mackerel but is occasionally gorged on 

 euphausiids, and these average about 5% of 

 stomach contents by volume (Carlisle, 1971). 

 The northern anchovy {Engraulis mordax) con- 

 sumes phytoplankters and small zooplankters, 

 but large copepods and euphausiids appear to be 

 the most important food items (Loukashkin, 

 1970). Thus while all of these species prey on 



Manuscript accepted April 1972. 



FISHERY BULLETIN: VOL. 70, NO. 3, 1972. 



973 



