Víctor H. Cruz-Escalona

Changes to Marine Trophic Networks Caused by Fishing

Andres F. Navia1,2, Enric Cortes3, Ferenc Jordan4, Victor H. Cruz-Escalona2 and Paola A. Mejia-Falla1 1Fundacion Colombiana Para la Investigacion y Conservacion de Tiburones y Rayas SQUALUS 2Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional 3NOAA, National Marine Fisheries Service, Panama City Laboratory 4The Microsoft Research – University of Trento COSBI, Trento 1Colombia 2Mexico 3USA 4Italy

Putative extinction of two sawfish species in Mexico and the United States

All species of sawfish are listed by the International Union for the Conservation of Nature (IUCN) as endangered or critically endangered. In fact, the smalltooth sawfish Pristis pectinata, and the largetooth sawfish Pristis pristis, have been declared to be regionally and locally extinct from the US Atlantic coast and the Gulf of California, Mexico, respectively, likely due to overfishing. However, here we dispute these claims by illustrating how lack of existence of a given species within a region can be misconstrued as evidence for extinction. Todas as especies de peixe-serra sao qualificadas pela Uniao Internacional para a Conservacao da Natureza como ameacadas ou criticamente ameacadas de extincao. De fato, o peixe-serra-de-dentes-pequenos, Pristis pectinata, bem como o peixe-serrade-dentes-grandes, Pristis pristis, tem sido declarados como regionalmente e localmente extintos da costa atlântica dos EUA e do Golfo da California e Mexico, respectivamente, provavelmente devido ao excesso da pesca. No entanto, aqui pretendemos questionar estas extincoes ilustrando como a falta de evidencias da existencia de uma especie em uma regiao pode ser mal interpretada como evidencia de extincao.

Feeding ecomorphology of seven demersal marine fish species in the Mexican Pacific Ocean

How fish functional morphology shapes species co-existence and assemblage diversity patterns is a fundamental issue in ecological research. In fishes, much is known about the ecomorphological relationships of feeding morphology in coral reef fishes and in freshwater taxa inhabiting distinct environments. However, little is known about the patterns and processes shaping morphological variation in other oceanic taxa; particularly those inhabiting soft bottom habitats. In this study, we assessed patterns of feeding ecomorphology in seven demersal teleost species associated with soft bottoms of the continental shelf in the central Mexican Pacific Ocean. Feeding analyses indicated that some species groups shared similar diets. Likewise, patterns of morphological variation based on geometric morphometrics demonstrated that some taxa did not differ in body shape, while patterns of variation in other species were seen in body length and height, caudal peduncle height and the anal fin anterior insertion point. A multivariate association between diet composition data and overall body shape indicated significant ecomorphological relationships, describing a continuum between species displaying benthopelagic morphology and specializing on prey with high speed swimming ability (Engraulidae), versus species with benthic morphology and specializing on fast escape prey (crustacea). The clear ecomorphological patterns observed for these seven species at both the individual and species levels imply that environmental conditions and resource availability allow these taxa to differentially inhabit and exploit the soft bottom ecosystem. Fish diversity is principally represented by the benthic morphology, although benthopelagic morphology, also show a high degree of success in this environment.

How many trophic roles can elasmobranchs play in a marine tropical network

The aims of the present study were to identify the trophic roles of shark and batoid species in a tropical marine food web and to examine how ontogenetic dietary changes affect these roles. Elasmobranch species at different stages of maturity (juveniles and adults) are distributed at medium and high trophic levels (3.2–4.2), preying on numerous fish and invertebrates. Nine trophic groups comprising species at different stages of maturity were identified. Considering the maturity stages, elasmobranchs were found in five trophic groups and 37.5% of the regular equivalence nodes in the web. These species had roles as both predator and prey in four trophic levels of the web, participating in most of the roles identified, and are highly redundant in their functions as prey and mesopredators, but not in their role as top predators. The results of the present study suggest that elasmobranchs can be fundamental to the structure and function of marine food webs and highlight the need to include the effect of ontogenetic changes in the diet of these predators in future assessments of their ecological relevance.

Reproductive Strategy of the Giant Electric Ray in the Southern Gulf of California

AbstractThe objective of the present study was to describe and characterize macroscopic and microscopic aspects of the reproductive biology of the Giant Electric Ray Narcine entemedor, a viviparous elasmobranch targeted by commercial fishers in Mexico. A total of 305 individual rays were captured (260 females, 45 males); all males were sexually mature. The median size at maturity for females was estimated to be 58.5 cm TL, the median size at pregnancy was 63.7 cm TL, and the median size at maternity was 66.2 cm TL. The range of ovarian follicles recorded per female was 1–69; the maximum ovarian fecundity of fully grown vitellogenic oocytes was 17, and uterine fecundity ranged from 1 to 24 embryos per female. The lengths of the oblong ovarian follicles varied significantly among months, and the largest ovarian follicles were found in July, August, and September. Median embryo size was largest in August, and the size at birth was between 12.4 and 14.5 cm TL. Histological evidence of secretions from the glan...

Reproductive strategy of the Pacific cownose ray Rhinoptera steindachneri in the southern Gulf of California

Rhinoptera steindachneri is one of the most common batoid species in the artisanal gill net fishery of the Gulf of California. In this study we investigated its reproductive biology based on 317 specimens caught in Bahia de la Paz, Mexico. Females measured up to 94.2-cm disc width (DW) and males reached 82.5cm DW; there were no significant differences in size or weight between sexes. The median size at maturity was estimated at 68.5cm DW for males and 71.8cm DW for females, and the median size at pregnancy was 84.3cm DW. Only the left ovary and uterus were functional; a maximum of six preovulatory vitellogenic follicles per female was recorded, although uterine fecundity was one embryo per female. Ovulation and birth occurred in May, June and July, with birth sizes ranging from 38.1 to 42cm DW. R. steindachneri in Bahia de la Paz exhibited low fecundity, large size at maturity and birth and a continuous and synchronous annual reproductive cycle.