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Snappers are opportunistic carnivores with a leading role in energy flows between trophic interactions within tropical ecosystems. In the southern Gulf of Mexico, the few reported trophic-structure models are based on snapper stomach content data from other geographic regions (e.g. Atlantic coast of United States, northern Gulf of Mexico, Caribbean Sea and Brazil). To optimise the reliability of these models, we present new information on the diet composition of two commercially important species: lane snapper Lutjanus synagris and yellowtail snapper Ocyurus chrysurus. From January 2008 to 2009, the stomach contents of 1,074 L. synagris and 1,516 O. chrysurus were collected from three fishing sites off the northern coast of Yucatan, Mexico. Contents were analysed using frequency, number and weight of the identified prey species. A three-level, nested PERMANOVA analysis was used to assess differences between the potential prey and their biomass using the factors of snapper species, fishing site and climate season. Multidimensional scale (MDS) and SIMPER analyses were run to establish dissimilarity within the discriminating factors. The main food items found in the L. synagris diet were Brachyura, Penaeioidea and unidentified shrimps. Penaeioidea were the most abundant items in the O. chrysurus diet. Prey biomass analysis revealed a dissimilarity in diet composition between the two snapper species, as well as between fishing sites and climate seasons. The principal discriminatory prey categories were Brachyura, Penaeioidea, Osteichthyes, with Caridea and unidentified shrimps accounting for slightly smaller proportions. The results confirm the trophic position of these two sympatric snappers, showing that each plays a different trophic role in the ecosystem of the northern coast of the Yucatan Peninsula.

The grey snapper Lutjanus griseus is one of the main snapper species exploited by Mexican artisanal fishers in the southern Gulf of Mexico. An analysis was done of oocyte growth dynamic in the gonads of female L. griseus from the continental shelf of the Yucatan Peninsula, Mexico. Oocytes were found to develop homogeneously within the ovaries of this snapper. Lutjanus griseus exhibits an asynchronous ovarian organization and is a batch spawner. Oocyte diameter frequency distributions in ovaries suggest that L. griseus fecundity may be indeterminate.

Growth stanzas or abrupt changes in growth rates are present throughout the life span of fish. Identifying growth stanzas will help to adequately described growth taking into account that fishes are indeterminate growers. In this study, we used length-weight (L-W) relationships to analyze the growth stanzas in the Grouper-Snapper complex of Southern Gulf of Mexico. For this, the type of sexuality, sex and different sexual maturity phase were considered in the analyses of three species of gonochoric Snappers (Lutjanidae) and six species of protogynous hermaphrodite Groupers (Epinephelidae). Welch ANOVA tests were carried out to determine the existence of differences in length and weight between juveniles and adults per sex. According to the observed differences, L-W relationship parameters (a and b), standard error (SE b) and coefficients of determination (R2) were calculated for all species separately by sex and sexual maturity phase. Snappers’ juvenile-females b-value ranged from 2.44-2.77, juvenile-males from 2.16-2.94, adult-females from 2.63-2.80 and adult-males from 2.63-2.98. Groupers’ b-value ranged for juvenile-females 2.66-3.20, adult-females from 2.73-3.31 and for adult-males 2.93-3.29. For each relationship b-value was t-tested (t-Student) to explore differences from the allometric coefficient (b=3), which indicated changes in body form. Hypothesis test, for regression slopes (b) between Snappers’ juvenile-females vs. adult-females and juvenile-males vs. adult-males and Groupers’ juvenile-females vs. adult-females and adult-females vs. adult-males, indicated different growth stanzas related to gonadal development for Snappers, and to gonadal development and sex change in Groupers. The identification of growth stanzas is crucial to avoid an overestimation or misleading growth rate which is used in fisheries management to establish some target reference points, such as maximum sustainable yield or yield-per-recruit. Distintos estados o estanzas de crecimiento descritos por cambios en el ritmo de crecimiento, se pueden observar en peces a lo largo de su vida ya que presentan crecimiento indeterminado. A través del análisis de relaciones longitud-peso (L-P), se identificaron distintas estanzas de crecimiento considerando el tipo de sexualidad, sexo y madurez sexual de individuos de tres especies de pargos (Lutjanidae) gonocóricos y seis de meros (Epinephelidae) hermafroditas protóginos. Pruebas independientes de ANOVA de Welch se aplicaron para conocer si existían diferencias estadísticas significativas en la media de la longitud y peso de juveniles, adultos, hembras y machos de pargos y en juveniles hembras, hembras y machos de meros. De acuerdo a las diferencias observadas, se procedió al cálculo de la relación L-P, parámetros a y b, error estándar (SE b) y coeficiente de determinación (R2) por separado (juveniles, adultos, hembras y machos) para cada especie. Los valores del parámetro b para todas las especies se encontraron dentro del rango esperado de 2.5 a 3.5 para pendientes de la relación L-P en peces. Los pargos tuvieron valores de b: juveniles de hembras de 2.44-2.77, juveniles de machos 2.16-2.94, hembras adultas 2.63-2.80 y machos adultos 2.63-2.98. Los meros tuvieron un valor de b para juveniles de hembras: 2.66-3.20, adultos hembras: 2.73-3.31 y adultos de machos: 2.93-3.29. Para cada relación, el valor de b fue probado a través de una prueba de t-Student para explorar diferencias significativas del coeficiente alométrico (b=3), lo cual indicaría cambios en la forma del cuerpo de los individuos. Finalmente pruebas de hipótesis sobre las diferencias entre pendientes obtenidas de las relaciones L-P mostraron distintas estanzas de crecimiento relacionadas en pargos con el desarrollo gonadal y en meros con el desarrollo gonadal pero también con el cambio de sexo. A través de este estudio se pudo observar la existencia de distintas estanzas de crecimiento en especies de alta importancia comercial para el Sur del Golfo de México. Por lo tanto se recomienda la obtención de las relaciones L-P por separado según el sexo y desarrollo gonadal de cada especie, para evitar una sobre estimación o un cálculo erróneo de la tasa de crecimiento poblacional la cual se utiliza en manejo de las pesquerías para determinar algunos puntos de referencia como el criterio de máximo rendimiento sostenible o bien el criterio de rendimiento por recluta.

Accuracy of the muscle bundle criterion is analysed to distinguish regenerating ovaries from immature ones in three commercially important hermaphroditic grouper species from the southern Gulf of Mexico: red grouper Epinephelus morio (Valenciennes, 1828); black grouper Mycteroperca bonaci (Poey, 1860); and gag Mycteroperca microlepis (Goode & Bean, 1880). The presence of muscle bundles in ovaries is a generally accurate criterion for distinguishing between regenerating and immature females in these species. However, reproductively inactive specimens could not be exactly identified as regenerating or immature females in 22% of E. morio, 4% of M. bonaci and 9% of M. microlepis, and are classified as being of uncertain maturity. Median size and size-frequency distributions analysis among females in different reproductive phases indicate that uncertain maturity E. morio females are probably immature, while uncertain maturity M. bonaci females are probably regenerating. The reproductive status of uncertain maturity M. microlepis females could not be clarified. Maturity ogive and size at maturity estimates for females of the studied species exhibit variable bias in response to the percentage of uncertain maturity females.

An analysis was made of sexual pattern, spawning season, sizes at sexual maturation, and sex change in black grouper (Mycteroperca bonaci) from the southern Gulf of Mexico. Samples were taken between 1996 and 2000, from industrial and small-craft commercial fi sheries, in offshore and inshore waters of the continental shelf of the Yucatan Peninsula (Campeche Bank), including the shallow waters of National Marine Park Alacranes Reef. For all collected specimens (n=1229), sex and maturation condition were determined by histological analysis of the gonads. The offshore sample consisted of 75.1% females, 24.3% males, and 0.6% transitional-stage fish. All individuals collected from inshore waters were females. Gonadal structure and population structure characteristics for Campeche Bank black grouper were consistent with the characteristics of monandric protogynous hermaphrodism for a serranid fish. Sexually active males and females were observed year-round, although ripening females, with stage-III, -IV, and -V vitellogenic oocytes in the ovaries, dominated in samples taken between December and March. In addition, peak occurrence of ripe-running females with hyaline oocytes or postovulatory follicles (or both) in the ovaries was recorded in January and February. A few precocious females began spawning in October and November, and others were still in spawning condition in May and June. Fifty percent maturity of females was attained at 72.1 cm fork length (FL). Median size at sexual inversion was 103.3 cm FL, and 50% of the females measuring 111.4 cm FL had transformed into males. The southern Gulf of Mexico grouper fishery was considered deteriorated and lacked a well-defined management strategy. Results of the present study provide helpful information on black grouper reproduction in this area and could help Mexican authorities choose appropriate management strategies for this fishery, such as minimum size limit, closed fishing season, and protection of spawning aggregations.