132 



COLIN 



Most of the larger fishes at Enewetak produce plank- 

 tonic eggs. Relatively little has been published about the 

 spawning of larger fishes at Enewetak. What has been writ- 

 ten is limited to the papers by Helfrich and Allen (1975), 

 Thresher (1982), and Bell and Colin (1986). There are 

 considerable unpublished data of Colin and Bell. Spawning 

 habits of about 60 species are known and, although gen- 

 eral patterns are known for these, there are exceptions to 

 every generalization. 



Many planktonic-egged species can spawn at any time 

 during the day in certain locations when tidal conditions 

 are correct. This is generally true for the labrids and parrot 

 fishes, but other families, such as the Pomacanthidae, are 

 believed to spawn only near sunset (Thresher, 1982; Bell 

 and Colin, 1986). In spite of the abundance of large pis- 

 civores, predation on spawning fishes appears to be rare. 

 Predation on eggs immediately after release by particulate 

 plankton-feeding fishes is also uncommon, occurring in only 

 a few percent of spawning releases. 



Planktonic eggs and larvae from both demersal and 

 planktonic eggs are carried by currents during their 

 development. Larvae produced on the windward side of 

 the lagoon, particularly the northern part, would have an 

 excellent chance of undergoing their entire development 

 within the lagoon, since water residence times in that area 

 are above the mean of about 30 days, reaching as much 

 as 4 months. The mid-depth water return mechanisms of 

 the lagoon would ensure return of larvae to the windward 

 side in spite of the westward surface drift. 



There is no distinct seasonality known in spawning of 

 fishes at Enewetak, but relatively small differences cannot 

 be ruled out. Gerber (1981) found approximately a two- 

 fold increase in the mean number of fish eggs in mid- 

 lagoon plankton tows during summer as opposed to winter 

 periods, but considerable variability in individual collections 

 indicated different means were not significant. Given the 

 transitory nature of fish spawning, the observed patchiness 

 of eggs is not surprising. A similar situation existed for fish 

 larvae (Gerber, 1981). Higher concentrations of fish eggs 

 and larvae at significant levels were found at Gerber's 

 (1981) "behind reef" station than in the mid-lagoon during 

 winter and may be the result of distance from sources 

 (reefs and their immediate vicinity) of eggs and larvae. 

 Other larvae are undoubtedly carried out to sea, but their 

 potential fate is not well known. The presence of down- 

 current eddies (in this case to the west) behind islands (and 

 atolls) is well documented and may serve to return larvae 

 to the vicinity of Enewetak after a p)eric)d of days or 

 weeks. More work is needed on this phenomenon. Many 

 larvae are certainly lost into the general westward drift of 

 the North Equatorial Current, but sufficient numbers of lar- 

 vae develop within the lagoon or are returned by eddies to 

 maintain fish populations at the atoll. A limited number of 

 recruits must originate east of Enewetak, from Bikini and 

 other atolls of the northern Marshalls, but in terms of 

 numbers are probably overwhelmed by locally produced 

 offspring. 



Nearly all Enewetak fishes recruit as free-swimming lar- 

 v.Tse. Exceptions would include elasmobranchs (sharks, rays) 

 bearing live young and a limited number of reef fishes 

 which have live young (Brotulidae, Ophidiidae) or a greatly 

 modified larval life (Syngnathidae). Most of the reef fishes 

 have planktonic larvae which must make a transition when 

 becoming juveniles, often moving into a reef environment 

 crowded with others of their species and other species. 



There was no significant evidence for seasonality of 

 reef fish recruitment to artificial reefs in Nolan's (1975) 

 study. Some species, however, did not recruit at all sea- 

 sons. Possibly, this was because of the relative scarcity of 

 those species, but one common species Apogon 'nouae- 

 guinae" (the species identified as nouaeguinea by Lachner, 

 Schultz, and collaborators, 1953, appears to be A. c^iano- 

 soma though seemingly subspccifically different) did not 

 recruit during the summer. Since it did appear in small 

 numbers on natural reefs, Nolan (1975) attributed this, 

 potentially, to reduced recruitment during the summer. 



Year-round spawning activity and reproductive colora- 

 tion were observed in some apogonids and pomacentrids. 

 Female chaetodontids with ripe ovaries were noted at all 

 seasons by E. S. Reese (personal communication). 



The role of predators in limiting the numbers of some 

 small reef fishes on patch reefs has been amply demon- 

 strated by Nolan (1975). He found that when additioijal 

 pomacentrids {Chromis and Dascy//us) were added to reefs 

 already at saturation levels with conspecifics, the new 

 arrivals were readily eaten by cruising piscivores. One 

 artificial reef already at equilibrium had additional damsel- 

 fishes added. Within a day or two almost all additions had 

 perished. Shelter is a factor which limits absolute numbers 

 of such reef fishes; the excess individuals which cannot 

 find a refuge are easily taken by the abundant predators of 

 Enewetak reefs. 



CIGUATERA 



Ciguatera is the most common tropical fish jjoisoning 

 known in the Marshall Islands, including Enewetak. Randall 

 (1980) has reviewed the historical reports of ciguatera in 

 the Marshall Islands. Of relevance was information pro- 

 vided by Iroij Johannes Peter that before 1946, some reef 

 fishes from certain areas of Enewetak were pxDisonous to 

 eat. Randall (1980) described instances of ciguatera poison- 

 ing at Enewetak. The internal organs (which are consider- 

 ably more toxic than the flesh) of 47 species of large reef 

 fishes were tested using a mongoose bioassay for toxicity. 

 At least one individual of five species produced the strong- 

 est reaction (death within 48 hours), whereas 31 species 

 produced at least some response by mongooses to inges- 

 tion. Even in the species producing the most frequent reac- 

 tion, the percentage of individuals producing a response is 

 relatively small. Ciguatoxic fishes at Enewetak were found 

 to fit the recognized pattern of being generally large indi- 

 viduals, mostly roving predators, and largely piscivorous 

 (Randall, 1980). No evidence exists that the occurrence of 



