LOVE: ISOLATION OF OLIVE ROCKFISH POPULATIONS 



three oil platforms off Summerland (15.2%), all of 

 which were heavily fished by partyboats. Eighty- 

 one percent of all returns were made by partyboat 

 fishermen. 



Only the fish tagged around the Summerland oil 

 platforms showed any movements; here nine 

 moved from one platform to another (about 0.8 

 km). 



Regarding biological tags, only the incidence of 

 infection of Microcotyle sebastis (Table 3) differed 

 significantly among study sites. Naples Reef and 

 Ellwood Pier differed significantly from the other 

 four sites: a G-test of independence (Sokal and 

 Rohlf 1969) was significant when all six sites were 

 included (G = 186.45, P<0.005), but not sig- 

 nificant when only the oil platforms, 4 Mile Reef, 

 and Horseshoe Reef were included (G = 1.14, 

 0.9>P>0.5). Naples Reef also differed sig- 

 nificantly from Ellwood Pier (G = 16.8,P<0.005). 



There was no seasonality in incidence of infec- 

 tion, as G-tests of independence among four sea- 

 sons were not significant for any site (Table 3). 



To test whether environmental conditions at 

 Ellwood Pier were suitable for the monogenetic 

 trematodes, tagged fish from Horseshoe Reef in- 

 fected with M. sebastis were introduced into the 

 site. Untagged fish were collected 1 and 6 mo later. 

 After 1 mo 2 of 20 untagged fish (10%) were in- 

 fected and after 6 mo 7 of 20 (35%) were infected 

 (not a significant difference, G = 3.6, 

 0.1>P>0.05). The presence of M. sebastis in the 

 population seems to indicate that conditions were 

 suitable for the trematode. 



Fish lengths averaged significantly shorter 

 it = 9.3, P<0.001) at the heavily fished Naples 

 Reef than at the lightly fished Haskels site (Figure 

 2). Most fish taken from Naples Reef were prere- 

 productive, while mature individuals made up 

 about 45% of the Haskels catch. 



DISCUSSION 



Kabata (1963) lists five criteria which should 



ideally be met if a parasite is to be useful as a tag: 

 1) the parasite should be common in one popula- 

 tion and rare or absent in another; 2) the parasite 

 should have a direct life cycle, infecting only one 

 host species during its life; 3) the parasitic infec- 

 tion should be of fairly long duration; 4) the inci- 

 dence of infection should stay relatively stable; 5) 

 environmental conditions throughout the study 

 site(s) must be within the physiological tolerance 

 of the parasite. 



Compared with artificial tags, biological tags 

 have both advantages and disadvantages. Arti- 

 ficial tags may alter the normal behavior of the 

 tagged animal, whereas, in most cases, parasites 

 do not. Moreover, the parasite mix of a population 

 is usually the result of long-term processes, and 

 may be a more accurate indicator of movements 

 than short-term tagging studies. On the other 

 hand, parasite tags will not indicate individual 

 movements. Over the past 20 yr, studies using 

 parasites as tags have delineated nursery grounds 

 (Olson and Pratt 1973), spawning grounds (Mar- 

 golis 1963; Hare and Burt 1976), and discrete or 

 semidiscrete populations (Sindermann 1961; 

 Kabata 1963). 



Results of both artificial and biological tagging 

 indicated that olive rockfish rarely moved be- 

 tween shallow water reefs. A good example of this 

 was the apparent lack of movement between 

 Naples Reef and Ellwood Pier. Though only about 

 2 km apart, no tagged Naples Reef fish were taken 

 at Ellwood Pier or anyplace else, nor were any of 

 the M. sebastis found to be infecting Ellwood Pier 

 fish before I introduced it, though they infect 

 Naples Reef fish. 



Like other monogeneans, M. sebastis has a di- 

 rect (one host) life cycle. The maximum distance 

 the infective oncomiricidium larval stage can 

 travel before finding a host is not known, though it 

 is probably limited to a few meters (Llewellyn 

 1972). Apparently, Ellwood fish were not 

 parasitized because they were sufficiently isolated 



Table 3.— Incidence of parasite Microcotyle sebastis in 80 olive rockfish sampled 20/mo from 

 each of six sites off Santa Barbara, Calif. P values reflect G-teste of independence (Sokal and 

 Rohlf 1969) for incidence of infections among four seasons. 



979 



