Changes in the spatial patchiness of 

 Pacific mackerel. Scomber japonicus, 

 larvae with increasing age and size 



Yasunobu Matsuura 



Instituto Oceanografico da Universidade de Sao Paulo 

 Cidade Universitaria, Butantan, Sao Paulo 05508, Brasil 



Roger Hewitt 



Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 RO. Box 271, La Jolla, California 92038 



terpreted in terms of species-spe- 

 cific differences in life history traits 

 such as adult reproductive behav- 

 ior and larval feeding ecology, size, 

 growth, and mortality (Smith, 1973; 

 Hewitt, 1981; Koslow et al., 1985; 

 McGurk, 1987). Insight into the 

 function of patchiness may be im- 

 proved by comparing how patchi- 

 ness changes with age and size for 

 species with different life histories. 

 In this note, we present patchi- 

 ness-at-age and patchiness-at-size 

 curves for Pacific mackerel, Scom- 

 ber japonicus, larvae and compare 

 them with similar curves for other 

 pelagic fish larvae. 



Several investigators have sug- 

 gested that the spatial patchiness 

 of fish eggs and larvae may be an 

 important factor in the recruitment 

 process (Smith, 1973; Lasker, 1978; 

 Hewitt, 1981; Houde and Lovdal, 

 1985; McGurk, 1986). Patchiness 

 has been linked to success in for- 

 aging (Hewitt, 1981), ontogeny of 

 schooling behavior (Hewitt, 1981), 

 and predation mortality (McGurk, 

 1986, 1987). Contagion in the dis- 

 persion of ichthyoplankton has 

 been described for Pacific sardine, 

 Sardinops sagax, eggs (Smith, 1973); 

 northern anchovy, Engraulis mor- 

 dax, and jack mackerel, Trachurus 

 symmetricus, larvae (Hewitt, 1981); 

 haddock, Melanogrammus aegle- 

 finus, eggs (Koslow et al., 1985); sev- 

 eral taxa found in Biscayne Bay 

 including bay anchovy, Anchoa 

 mitchilli, eggs and larvae (Houde 

 and Lovdal, 1985); Atlantic herring, 

 Clupea harengus harengus, larvae 

 (Henri et al., 1985); Pacific herring, 

 Clupea harengus pallasi, larvae 

 (McGurk, 1987); bluefin tuna, Thun- 

 nus maccoyii, larvae (Davis et al., 

 1990); Brazilian sardine, Sardinella 

 brasiliensis, larvae; and scaled sar- 

 dine, Harengula jaguana, larvae 

 (Spach, 1990). 



The patchy distribution of fish 

 eggs and larvae is initially intro- 

 duced by the spawning behavior of 



adult fish. In order to guarantee 

 successful fertilization in a pelagic 

 environment, eggs must be laid 

 when the adults are highly aggre- 

 gated, and spawning and fertiliza- 

 tion must occur almost simulta- 

 neously (Hewitt, 1981). Alternately, 

 demersal spawners may deposit 

 their eggs in batches that incubate 

 on a substrate before releasing a 

 cohort of larvae into the pelagic 

 environment (McGurk, 1987). 

 Thereafter, eggs or hatching larvae, 

 or both, disperse, principally in 

 horizontal directions; distribution 

 patterns during this period are pri- 

 marily influenced by dispersal, dif- 

 fusion, and transport (Smith, 

 1973). After a few days or weeks, 

 larvae begin to reaggregate, an ac- 

 tivity that becomes more evident in 

 the juvenile stages of most school- 

 ing pelagic fishes. 



Patchiness-at-age curves for sev- 

 eral species of pelagic schooling 

 fishes have been shown to exhibit 

 a characteristic "U" shape: high 

 initial patchiness, followed by a 

 rapid decline as the eggs or newly 

 hatched embryos, or both, passively 

 disperse, followed by an increase in 

 patchiness as the developing fish 

 begin to aggregate in schools 

 (Hewitt, 1981; McGurk, 1987; Spach, 

 1990). Patchiness-at-age curves for 

 fish eggs and larvae have been in- 



Material and methods 



Data base 



The data used in this work came 

 from the California Cooperative 

 Oceanic Fisheries Investigations 

 (CalCOFI) ichthyoplankton data 

 base. These data are available from 

 the CalCOFI on-line data system 

 (Anon., 1988). Details of station and 

 ichthyoplankton data were published 

 in a series of CalCOFI ichthy- 

 oplankton data reports (NOAA Tech. 

 Memo., NMFS, SWFSC, numbers 

 70-88, 92-100, and 102-105). Size- 

 specific catches of Pacific mackerel 

 larvae, collected from 1953 through 

 1981, were extracted and summa- 

 rized for the analyses reported here. 

 Pacific mackerel larvae were col- 

 lected with 1-m ring nets from 1953 

 through 1975 and with bongo nets 

 thereafter. Sampling methods and 

 laboratory procedures were de- 

 scribed by Kramer et al. (1972). Out 

 of 23,963 CalCOFI stations sam- 

 pled from 1953 to 1981, plankton 

 samples from 1,011 stations con- 

 tained at least one Pacific mackerel 

 larva. The 1,011 stations where 

 larva were collected were assumed 

 to define the Pacific mackerel's 



Manuscript accepted 15 June 1994. 

 Fishery Bulletin 93:172-178 (1995). 



172 



