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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.

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.

Los cambios en la estructura demográfica del mero rojo Epinephelus morio en el sureste del Golfo de México fueron evaluados para períodos durante los cuales se observaron: una disminución en las capturas totales, la CPUE y el rendimiento anual de la especie. Las muestras (n = 1887) fueron obtenidas a partir de las capturas comerciales realizadas entre agosto de 1989 y febrero del 2004 y la distribución de frecuencia de talla por sexos, la proporción por sexos, las tallas de primera madurez sexual y de inversión sexual, fueron comparadas entre tres períodos: P11989-1992 (n = 886); P21996-1998 (n = 413) y P32003-2004 (n = 588). La estabilidad temporal de las distribuciones de frecuencia de talla por sexos con los machos siempre de tamaño superior al de las hembras, y los valores de proporción sexual siempre sesgados a favor de las hembras fueron congruentes con el tipo de sexualidad presentada por la especie. La disminución del tamaño de las hembras y de los machos, así como de las tallas de primera madurez sexual y de inversión sexual de la especie entre el período de estudio más lejano hasta el más reciente, podrían ser una consecuencia de la intensidad pesquera ejercida sobre este stock. Las disminuciones de talla de las hembras y de los machos, asociadas a la relativa estabilidad de la proporción sexual y a la ausencia de una reducción drástica de la proporción de macho, pueden ser explicadas por la ecología reproductiva de la especie. Los resultados obtenidos son discutidos en relación con la capacidad de resiliencia reproductiva del mero rojo a la presión por pesca sufrida actualmente por el stock del Banco de Campeche. Changes in the demographic structure of red grouper Epinephelus morio from the southern part of the Gulf of Mexico, were evaluated during periods when total catches, CPUE and annual yields of the specie decreased. Fishery-dependent samples (n = 1887) were obtained between August 1989 and February 2004 from the Campeche Bank, and size-frequency distributions by sex, sex ratios and sizes of sexual maturation and sex change were compared between three periods: P11989-1992 (n = 886); P21996-1998 (n = 413); and P32003-2004 (n = 588). The temporal stability of size-frequency distribution by sex, with males always being larger than females, and the sex ratios always biased towards females, were consistent with this species’ type of sexuality. Size for females and males, as well as sizes at first sexual maturity and at sex reversal all decreased from the oldest period to the more recent one and could be a consequence of the fishing intensity applied to this stock. The reductions in size of females and males associated with a relatively stable sex ratio and the lack of any drastic decrease in the number of males can be explained by this species’ reproductive ecology. Results are discussed regarding the capacity for reproductive resilience of red grouper in response to fishing pressure like that currently experienced by the Campeche Bank stock. As mudanças na estrutura demográfica da garoupa São Tomé, Epinephelus morio, no sudeste do Golfo do México foram avaliadas em períodos durante os quais se observaram: uma redução nas capturas totais, a CPUE e o rendimento anual da espécie. As amostras (n = 1887) foram obtidas a partir das capturas comerciais realizadas entre agosto de 1989 e fevereiro de 2004 e a distribuição de frequência de tamanho por sexos, a proporção por sexos, os tamanhos de primeira maturidade sexual e de inversão sexual, foram comparadas entre três períodos: P11989-1992 (n = 886); P21996-1998 (n = 413) e P32003-2004 (n = 588). A estabilidade temporária das distribuições de frequência de tamanho por sexos com os machos sempre de tamanho superior ao das fêmeas, e os valores de proporção sexual sempre inclinado a favor das fêmeas foram congruentes com o tipo de sexualidade apresentada pela espécie. A diminuição do tamanho das fêmeas e dos machos, assim como dos tamanhos de primeira maturidade sexual e de inversão sexual da espécie entre o período de estudo mais distante até o mais recente, poderiam ser uma consequência da intensidade pesqueira exercida sobre este estoque. As diminuições de tamanho das fêmeas e dos machos, associadas à relativa estabilidade da proporção sexual e à ausência de uma redução drástica da proporção de macho, podem ser explicadas pela ecologia reprodutiva da espécie. Os resultados obtidos são discutidos com relação à capacidade de resiliência reprodutiva da garoupa São Tomé à pressão por pesca sofrida atualmente pelo estoque do Banco de Campeche.&nbsp

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.