Ecology and fate of butterflyfishes, Chaetodon spp., in the temperate, western North Atlantic

Three of seven Chaetodon species in the western North Atlantic are reported from temperate waters, quite unlike most other chaetodontids which are onl y found at tropical and subtropical latitudes. This study describes the eco logy of these species at temperate latitudes and tests the hypothesis that these individuals are expatriates that die from hypothermal conditions at t he onset of winter. We collected fish with dip nets and bottom traps during 4 yrs, 1990-1993, in a New Jersey estuary. The most abundant species, C. o cellatus, arrived as pelagic juveniles (or tholichthys stage) as early as J uly and at sizes of 17-22 mm total length. It settled as small as 18 mm, gr ew about 0.1-0.2 mm d(-1), and reached a maximum size of 77 mm (n = 388). A ll sizes appeared to be young-of-the-year fish, based on modal progression of lengths from July to November. Eighteen of 52 (35%) marked C. ocellatus were recaptured, generally within 10 m of their release point, indicating g ood short-term survival and high site fidelity. Individuals were collected during early November in four consecutive years, at temperatures as low as 12 degrees C, but not in winter months. In the laboratory, C. ocellatus sto pped feeding at about 12 degrees C and did not survive temperatures of abou t 10 degrees C or less. Chaetodon capistratus was present in 3 of 4 yrs, bu t the total number collected (n = 28) precluded detailed examination. Despi te earlier reports of C. striatus in this region, we did not observe this s pecies. Overall, Chaetodon species in our study area were much more abundan t than previously reported, and they grew and survived well for several mon ths in estuarine conditions. Nonetheless, the evidence did not suggest they were capable of emigrating during autumn nor surviving the ambient winter temperatures, so they become expatriates that will not survive through thei r first winter.