MEPS 237:247-256 (2002)  -  doi:10.3354/meps237247

Settlement, movement and early juvenile mortality of the yellowtail snapper Ocyurus chrysurus

M. Watson, J. L. Munro*, F. R. Gell

ICLARM Caribbean/Eastern Pacific Office, 158 Inland Messenger, Road Town, Tortola, British Virgin Islands
*Corresponding author. E-mail:

ABSTRACT: Visual censuses of recently settled yellowtail snapper Ocyurus chrysurus were made within a grid measuring 50 x 25 m established in a <1 m deep seagrass (Thalassia testudinum) bed in the British Virgin Islands, eastern Caribbean, between September 1999 and July 2000. A peak of 92 newly settled O. chrysurus was observed around the new moon in September 1999, followed by a decline of more than 75% over 3 wk. Light trapping near adjacent fringing reefs documented a concurrent pulse of late pelagic stage O. chrysurus. Observations in April-May and June-July 2000 recorded much smaller supply events and lower settlement densities. The effects of post-settlement movement, as opposed to early mortality, were assessed and concluded to be negligible. Firstly, fish <8 cm total length were consistently observed in the seagrass but were never recorded in censuses of adjacent rocky habitat, where older juveniles occurred. Thus, settlement-stage fish were assumed to reside in seagrass for several weeks. Second, average home ranges for fish of 2 to 2.5 cm and 3 to 3.5 cm total length were estimated to be 2.3 m2 and 6.3 m2, respectively, indicating that movement of newly settled O. chrysurus was negligible compared to the size of the census area (1250 m2). Third, late pelagic-stage O. chrysurus caught with light traps in adjacent waters were tagged with fluorescent elastomer and released at the center of the seagrass grid the evening after their capture. Ninety-six individuals were released over 3 evenings in September 1999. Concurrent aquarium studies showed tagging mortality was 13%. Over the following 8 d, 32 re-sightings were made. Only 1 fish was seen more than 2 to 3 m distant from where it was sighted on the first census after releases were completed, providing convincing evidence of site fidelity after settlement. Using a simple model, we conservatively estimated the coefficient of daily mortality, M, at settlement to be about 0.28 (equivalent to 76% survival d-1) and to reduce by 0.042 thereafter.

KEY WORDS: Caribbean · Coral reefs · Fisheries · Elastomer · Recruitment

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