Acoustic tracking of adult white grunt, Haemulon plumieri, in Puerto Rico and Florida

Abstract

Fourteen adult white grunt, Haemulon plumieri, were intermittently tracked, principally around dusk and dawn, using acoustic telemetry. Nine fish were tracked on coral reef habitats off La Parguera, Puerto Rico, April–May 1989. Combined distances traversed and acoustic contact time for all nine were 3.6 km and 117.5 h, respectively. Total contact times ranged from 8–20 h per individual; two fish exhibited behaviours considered to be dusk/dawn migrations in three episodes for distances of 100–530 m; two episodes were probably associated with nocturnal foraging. One fish transferred 1 km from one reef to another and did not return across deep water to its home reef. Five fish were tracked on patch reef habitats surrounded by seagrass meadows in the Key Largo National Marine Sanctuary, Florida, May–June 1990. Combined distances and contact time were 2.8 km and 71.5 h, respectively. Total contact times ranged from 6.5 to 17.5 h per individual; three fish exhibited behaviours considered to be dusk/dawn migrations in seven episodes for distances of 130–560 m; five of these episodes were probably related to nocturnal foraging and two were between patch reefs. One individual displaced to seagrass meadow 290 m from its daytime resting patch reef, ‘homed’ directly back to its capture site within 30 min of release. In Puerto Rico and Florida the majority of contacts were categorized as sedentary or roaming, the latter being meandering movements usually within 100 m of the animal's apparent home within each reef complex. Movements of adult white grunt differed from published accounts of juveniles with respect to timing and frequency; off-reef migrations were initiated at irregular times and did not occur as regularly as those in younger fish, yet the essential character of nocturnal or crepuscular migration was maintained, suggesting that a significant behavioural change takes place with increasing size or maturity. The scales and swimming speeds of nocturnal foraging migrations were of the same orders of magnitude as in juveniles. Implications for fishery stock assessments are discussed.