Billfish larvae of the Straits of Florida

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Robert K. Cowen - Committee Chair

Second Committee Member

Joseph E. Serafy - Committee Member


The goal of this dissertation was to examine the role of the Straits of Florida (SOF) as spawning habitat for billfishes (families Istiophoridae and Xiphiidae) by: (1) accurately identifying larval istiophorids; (2) developing an age-length relationship for larval sailfish; and (3) describing the spatial and temporal distribution of billfish larvae by species and age, with first approximations of potential origination points.A molecular technique was used to identify reference larvae of sailfish, blue marlin, and white marlin. Canonical Variates Analysis (CVA) revealed the extent to which the combination of morphometric measurements, lower jaw pigment patterns, and month of capture information was species-diagnostic. An identification key was constructed of characteristic jaw pigment patterns, month of capture, and linear regressions of the snout length:eye orbit diameter ratio against standard length. The key correctly identified 69.6% of 283 (blind sample) larvae used to test it, with one mis-identification. Of the 85 larvae that could not be identified by the key, 75 (88.2%) were correctly identified using CVA.Of the billfishes, larval age-length relationships exist for only blue marlin and swordfish, but larval sailfish were most abundant in the SOF. Growth increments were enumerated on sagittae of sailfish ranging in length from 2.8 to 15.2 mm. Estimated ages of larvae ranged from three to eighteen days. Length and age data were fitted with an exponential model (R2 = 0.85). Estimated size at hatch for sailfish is 1.9 mm, and the daily instantaneous growth rate coefficient is 0.14. As in the other billfishes, rapid early growth is an attribute of the sailfish.Identity was determined and age estimated for all larval billfishes captured in SOF waters. Minimum transport times through the SOF were determined for each site. If this time exceeded the age estimates of pre-flexion larvae caught at that site, it was concluded that those larvae were spawned within the SOF. The SOF is a major sailfish spawning area, with at least 52% of the pre-flexion larvae captured originating there. These results illustrate the importance of the SOF as billfish habitat, and provide a basis for further characterization of billfish spawning and nursery grounds.


Biology, Oceanography; Agriculture, Fisheries and Aquaculture

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