GEOGRAPHIC DIFFERENCES IN RECRUITMENT AND POPULATION-STRUCTURE OF A TEMPERATE REEF FISH

The purpose of this study, was to assess the importance of pre-and pos t-settlement processes in the temperate reef fish Tautogolabrus adsper sus at multiple spatial scales and in 2 distinct regions, Newfoundland , Canada, and the Gulf of Maine, USA. We examined a total of 20 sites (separated by 100 to 1000 m) nested within 10 locations (separated by ca 10 km). Greater numbers of adult fish were observed in Newfoundland than in the Gulf of Maine; however, higher abundances of newly recrui ted fish occurred in the Gulf of Maine. An experiment in which we prov ided standardized habitats in both regions also revealed that recruitm ent was higher in the Gulf of Maine than Newfoundland. In the Gulf of Maine, variation in the densities of adults and newly recruited fish w as most pronounced among sites, but in Newfoundland we detected pronou nced variability at both the site and location scales. Algal height wa s not associated with among-site variability in the abundances of recr uits or adults. Algal coverage, however, was an important predictor of variability of fish abundance in the Gulf of Maine but not in Newfoun dland. The age structure of Newfoundland populations suggests that str ong recruitment years are rare, while in the Gulf of Maine the age str ucture is consistent with the expectation of declining abundance with age. Our data suggest that pre-settlement processes are not of primary importance to cunner populations in the Gulf of Maine. Rather, we hyp othesize that habitat-related differences in post-settlement processes are the most significant factors affecting these populations. However , in Newfoundland the evidence gathered thus far supports the hypothes is that episodic settlement is responsible for much of the variation i n population size in this region.