Nonlethal Sex Determination of the Greater Amberjack, with Direct Application to Sex Ratio Analysis of the Gulf of Mexico Stock

Abstract

Stock assessments for the Gulf of Mexico (Gulf) Greater Amberjack Seriola dumerili continue to designate the stock as overfished and undergoing overfishing, despite increasing regulatory measures. Knowledge of sex‐specific spatial distribution and fishing mortality may contribute to our understanding of the stock's overexploitation, especially since Greater Amberjacks may be subject to sex‐specific mortality resulting from minimum size regulations. Currently, the sex ratio of the stock is assumed to be 1:1. An average and range of sex ratios were estimated for the Gulf stock based on sampling of fish landed in the recreational and commercial fisheries and based on released fish that were nonlethally sexed during a tagging study of sex‐specific movement patterns and release mortality. The nonlethal method of sex determination was developed based on external features of the urogenital region; urogenital catheterization was used to validate the external sexing and to collect oocyte samples for determining maturity stages of females during the spawning season. Of the 238 fish (108 males and 130 females) for which sex was verified, only one smaller female was incorrectly sexed. Urogenital catheterization identified females that were spawning or that would likely spawn in the upcoming spawning season, but no differentiation could be made between immature and resting females. Analysis of published data sets suggested that the Gulf stock has an overall female‐skewed sex ratio, with estimates ranging from 1:1.7 to 1:2.5 (male : female), while the nonlethal sexing data from the current study suggest that the overall sex ratio is slightly male skewed (1:0.8) in some regions. All studies report a female‐skewed sex ratio of 1:2.3, on average, for 1,000‐mm FL and larger fish in the Gulf. Sex ratios that deviate from the assumed 1:1 ratio should be incorporated into future assessments of the Gulf Greater Amberjack stock to investigate potential consequences for stock status and management. Received December 30, 2013; accepted May 8, 2014

Identifications, distributions, and life history of four species of Seriola (Carangiformes: Carangidae) in the western North Atlantic based on contemporary and historical data

“…They indicated that spawning was concentrated off south Florida and the Florida Keys in April and May. A similar spawning period (March-May) was reported for S. dumerili in the Gulf of Mexico (Smith et al, 2014). Larval collections in the Mid-Atlantic Bight (Fahay, 2007) suggest that: S. dumerili spawn through winter into spring; S. fasciata spawning possibly peaks in summer; and S. rivoliana probably spawn spring through fall.…”

“…Fixed samples were dehydrated in EtOH, embedded in paraffin, thin sectioned, and stained with periodic acid Schiff-Mallory trichrome (Massachusetts Histology Services, Worcester, MA). Gonad histology (oocyte stages and the presence and stage of post ovulatory follicles in females; spermatogonia, spermatocysts, spermatozoa, and spermatids in males) was evaluated following Brown-Peterson et al (2011) and Smith et al (2014) to differentiate immature, resting, and spawning-capable individuals.…”

Histological evaluation of sex differentiation and early sex identification in hatchery-produced greater amberjack (Seriola dumerili) reared in sea cages

“…408 Sex identification in fish is a rather complicated process, as fish do not possess sexspecific external characteristics; identifying fish sex, however, is very useful for aquaculture 410 purposes and different methods for sex recognition have been suggested, with the 11-KT/E2 ratio being the most common (Baroiller et al 1999). In the greater amberjack, observation of 412 external urogenital pore characteristics (Smith et al 2014) and11-KT concentration (Aoki et al 2019) have been suggested as non-invasive methods for sex identification. However, the 414 first method is more applicable in fish larger than 50 cm fork length (FL), whereas the latter was conducted in sexually differentiated fish older than 412 dph and larger than 39 cm FL.…”

Sex differentiation and early sex identification in hatchery produced greater amberjack (Seriola dumerili) reared in sea cages

“…Sex identi cation in sh is a rather complicated process, as sh do not possess sex-speci c external characteristics; identifying sh sex, however, is very useful for aquaculture purposes and different methods for sex recognition have been suggested, with the 11-KT/E 2 ratio being the most common (Baroiller et al 1999). In the greater amberjack, observation of external urogenital pore characteristics (Smith et al 2014) and 11-KT concentration (Aoki et al 2019) have been suggested as non-invasive methods for sex identi cation. However, the rst method is more applicable in sh larger than 50 cm fork length (FL), whereas the latter was conducted in sh older than 412 dph and larger than 39 cm FL.…”