46 



Fishery Bulletin 94|l). 1996 



ing of these species occurs in winter-spring when 

 nearshore sea surface temperatures off southern 

 California usually are 13-17°C (Petersen et al., 1986). 



Although seasonal spawning peaks of the four spe- 

 cies coincide with their temperature tolerance ranges, 

 all species, except sand bass, spawn to some degree 

 thoughout the year. Moser and Watson ( 1990) exam- 

 ined abundances of California halibut and fantail sole 

 larvae using a 30-year (1951-81) data set with sta- 

 tions from central California to southern Baja Cali- 

 fornia. Densities of sole larvae during the nonpeak 

 winter-spring season were very low; spawning oc- 

 curred primarily off Baja California where mean sea 

 temperatures were somewhat warmer than off south- 

 ern California (Moser and Watson, 1990). Halibut 

 displayed a more complex spawning pattern, which 

 varied with location. Halibut were reported to spawn 

 off southern California primarily when water tem- 

 peratures were lowest (February-March) and to 

 spawn secondarily in July-October (Moser and 

 Watson, 1990). In contrast, off central and southern 

 Baja California, a second spawning stock of Califor- 

 nia halibut occurred with peak spawning in June- 

 August when temperatures are highest. Since we con- 

 ducted our experiments with halibut collected off south- 

 ern California and acclimated to 16°C, it is possible 

 that experiments with eggs from fish collected in other 

 localities or acclimated to other temperatures could 

 result in a different range of survival temperatures. 



Like the spawning patterns of California halibut, 

 temporal spawning patterns of white croaker varied 

 with location in a study conducted during 1978-81 

 by Love et al. (1984). Off southern California, most 

 spawning occurred from November to April, with a 

 peak in February-March; whereas off central Cali- 

 fornia spawning occurred throughout the year, with 

 greatest activity from July through February. Be- 

 cause croaker spawn off southern California during 

 winter when temperatures are lowest. Love et al. 

 (1984) suggested that the colder waters off central 



California allowed for a longer spawning season. Off 

 Monterey, mean temperatures during June-October 

 (the warmest months) are only 13-14°C; thus, the 

 lower temperature tolerance range observed for 

 croaker eggs probably reflects seasonal spawning con- 

 ditions in both southern and central California. 



Although the absolute temperature ranges that 

 were tolerated differed between species, rates of egg 

 development at a specific temperature did not sig- 

 nificantly differ between species (Table 3). However, 

 temperature strongly affected rates of development 

 when data were pooled across species. Hatching 

 times for all four species were inversely proportional 

 to temperature, and the relationship was best fitted 

 by an exponential function. This result is consistent 

 with previous work on eggs of fishes such as Dover 

 sole, Microstomias pacificus, cod, Gadus morhua, and 

 walleye pollock, Theragra chalcogramma (Fonds, 

 1979; Thompson and Riley, 1981; Haynes and Ignell, 

 1983). Although these and many studies present re- 

 sults of single species experiments, reviews by Pauly 

 and Pullin (1988) and Pepin (1991) pooled 84 and 

 124 species, respectively, and they similarly found 

 an exponential relationship between incubation time 

 and temperature. Both reviews also found develop- 

 mental time to be significantly related to egg dia- 

 meter. Although in our study mean chorion diameter 

 differed significantly between species, these differ- 

 ences were not great (0.1 mm between the smallest 

 and largest mean chorion diameters; Table 1 ) and 

 evidently were not large enough to result in signifi- 

 cant differences in developmental rate between spe- 

 cies. The two reviews had somewhat conflicting con- 

 clusions concerning the importance of species-spe- 

 cific differences in developmental rates. Pauly and 

 Pullin ( 1988) felt that after considering differences 

 in developmental rate due to egg diameter and tem- 

 perature, taxonomic differences were not important, 

 whereas Pepin ( 1991) found some evidence for rate 

 differences between groups of similar species. 



