Non-lethal age determination for juvenile goliath grouper Epinephelus itajara from southwest Florida

Abstract

Previous studies have developed size-at-age curves for goliath grouper; however, these data were based on relatively few immature individuals, and age estimation was otolith-based, requiring sacrifice of this federally protected fish. In the present study, scales, dorsal fin-rays and dorsal spines were explored as potential non-lethal ageing alternatives for juvenile goliath grouper. Annulus marks were validated using marked-recaptured fish, oxytetracycline injections, and edge analysis. A subset of fish was sacrificed to compare the scale, spine and ray ages to otolith ages. A 40% recapture rate provided a useful time series of in situ age and growth data. Scale and ray ages were unreliable, but dorsal spines demonstrated agreement with corresponding otolith ages. Annuli were best represented by translucent bands in spines, as opposed to opaque bands in otoliths. Spines were positively validated for periodicity of annulus formation. Annuli formed at different times of the year in spines than in otoliths. By correcting for this difference using a biological age method, better agreement between otolith and spine age was achieved. Dorsal spines are recommended as the primary method for ageing goliath grouper between the ages of 0 and 6 yr. This study illustrates the use of a non-lethal method to determine age of a protected species.

Evaluating the effectiveness of teeth and dorsal fin spines for non‐lethal age estimation of a tropical reef fish, coral trout Plectropomus leopardus

“…maculatus (Ferreira & Russ, ), and the close agreement between ages determined from dorsal spines and otoliths indicates that increments observed in dorsal spines are annuli. Furthermore, annuli have been validated in dorsal spines of another serranid species (Brusher & Schull, ).…”

“…Removal of fin spines was also non‐lethal in other marine (Metcalf & Swearer, ) and freshwater fishes (Beamish & Harvey, ; Faragher, ; Collins & Smith, ). Numerous recaptures of another serranid that had a dorsal spine removed (Brusher & Schull, ) are a positive sign that spine removal may have minimal effect on survivorship in wild populations, but further studies are required to confirm this.…”

“…For example, species in the genus Plectropomus are among the most highly valued commercial and recreational target species on coral reefs (Heemstra & Randall, ; Sadovy et al , ; Frisch et al , ) and the majority are listed as Near Threatened or Vulnerable (IUCN, ). The success of dorsal spines and fin rays for estimating age in another serranid, the critically endangered goliath grouper Epinephelus itajara (Lichtenstein 1822) (Brusher & Schull, ; Murie et al , ), indicates that this non‐lethal approach may be effective for a wide range of serranids. Given that serranids (particularly Plectropomus ) are major targets for the live fish trade (Sadovy et al , ), it would be relatively easy and beneficial to monitor age structure of exploited stocks by removing the dorsal spine of live fish during transit.…”

“…Fin rays and spines have been successfully used to age many freshwater and marine species ( Debicella, ; Moltschaniwskyj & Cappo, ); however, in some species, it can be difficult to determine the first annulus (due to occlusion and resorption) and to distinguish annuli on the outer edge of spines of older fish (Beamish & Chilton, ; Graynoth, ; Debicella, ). In the marine environment, fin spines have been used to successfully age pelagic species (Franks et al , ; Kopf et al , ), as well as temperate (Metcalf & Swearer, ) and subtropical reef fishes (Debicella, ; Brusher & Schull, ). The suitability of fin spines to age tropical reef fishes has seldom been evaluated (Manooch & Drennon, ) and may be difficult because increments are often less well defined in scales and otoliths of fishes from low latitudes (Longhurst & Pauly, ; Fowler, ).…”

Fisheries Volume 45 Number 1 January 2020

“…Timing of the spawning season and larval planktonic duration (30-80 d) corresponds to the most favorable times for larval settlement in mangrove leaf litter in South Floridathat is, during the dry season (December-May) when salinity is high and prey resources abundant (Lara et al 2009 ; ). As they grow, juveniles move from leaf litter to red mangrove Rhizophora mangle prop-root systems and undercuts along mangrove shorelines (Koenig et al 2007 ) where they reach total lengths of about 1.0 m over their 5-to 6-year sojourn in that habitat (Koenig et al 2007 ;Brusher and Schull 2008 ).…”