Francisco Arreguín-Sánchez

Flows of biomass and structure in an exploited benthic ecosystem in the gulf of California, Mexico

Abstract We constructed a mass-balanced model of a benthic ecosystem exploited by shrimp trawlers in the Gulf of California, Mexico. The model is based on the software ecopath with ecosim Version 4a, which takes into account the contribution of functional groups to bycatch. The model represents the state of the ecosystem in 1978–79, and reflects the exploitation rate of shrimp at that time. We included 27 groups in the model: aquatic birds, marine mammals, shark/rays, 11 groups of teleost fish, five macrocrustaceans, two macromolluscs, polychaetes, meiobenthos, zooplankton, phytoplankton, detritus and dead fish. With respect to the bycatch, it was assumed that fish died on-board the trawlers while macroinvertebrates were returned to the sea alive. The macroinvertebrates would become more vulnerable to predation as a result of this practice but we assumed that this effect would be reflected in diets. The most important families of fish in the bycatch were Haemulidae, Serranidae, Paralichthydae, accounting for 75% of the total fish catch. These families include important shrimp predators, suggesting that fish mortality in the bycatch could have a positive impact on the shrimp stock. Total system throughput was up 4000 t km-2 year-1; total consumption 52%; flows to respiration 40%; and flows to detritus 7%. The total system production was almost equal to its consumption as was net primaty production to respiration. It is suggested that ecosystem efficiency was relatively low. Ecosystem overhead was 2.4 times the Ascendency, indicating that the shrimp-trawl ecosystem was in a develope stage, probably as a result of fishing. Because a decrease in biomass causes a loss of Ascendency, it is hypothesized that the previous state of the ecosystem (unexploited or with low exploitation rate) was more developed, and probably had a higher production.

An inverse relationship between stability and maturity in models of aquatic ecosystems

The relationships among stability, maturity and complexity of ecosystems have been studied for many years. These ecosystem attributes are important in ecological theory and also for the appropriate management of resources. In a previous work, we proposed the U index, which accounts for complexity and recycling of detritus, and measures maturity in ecosystems according to attributes of E. P. Odums theory of ecosystem development. Here we compare the behaviour of the U index and its ability to measure stability. Using models of ecosystems, we simulated disturbances and measured stability through resistance, persistence, resilience and recovery time. We found that the index is correlated with these attributes, but in an inverse way to that expected; that is, immature ecosystems were more stable and stability decreased when the systems matured.

Trophic structure and flows of energy in the Huizache-Caimanero lagoon complex on the Pacific coast of Mexico

Abstract The Huizache–Caimanero coastal lagoon complex on the Pacific coast of Mexico supports an important shrimp fishery and is one of the most productive systems in catch per unit area of this resource. Four other less important fish groups are also exploited. In this study, we integrated the available information of the system into a mass-balance trophic model to describe the ecosystem structure and flows of energy using the E copath approach. The model includes 26 functional groups consisting of 15 fish groups, seven invertebrate groups, macrophytes, phytoplankton, and a detritus group. The resulting model was consistent as indicated by the output parameters. According to the overall pedigree index (0.75), which measures the quality of the input data on a scale from 0 to 1, it is a high quality model. Results indicate that zooplankton, microcrustaceans, and polychaetes are the principal link between trophic level (TL) one (primary producers and detritus) and consumers of higher TLs. Most production from macrophytes flows to detritus, and phytoplankton production is incorporated into the food web by zooplankton. Half of the flow from TL one to the next level come from detritus, which is an important energy source not only for several groups in the ecosystem but also for fisheries, as shown by mixed trophic impacts. The Huizache–Caimanero complex has the typical structure of tropical coastal lagoons and estuaries. The TL of consumers ranges from 2.0 to 3.6 because most groups are composed of juveniles, which use the lagoons as a nursery or protection area. Most energy flows were found in the lower part of the trophic web.

A measure of ecosystem maturity

A measure to quantify maturity in ecosystems is proposed. The index is based on the analysis of flows of biomass. A measure of the uncertainty of the determination of the route of a given particle of matter will follow through a system and the ability of the system to recycle matter from detritus were used as estimators of maturity. The index was tested by comparing the index values against those of 17 maturity attributes in each ecosystem. We found a significant correlation in 16 of them. With the index, we can determine the maturity and stability of any ecosystem.

Interannual variation of growth of the brown shrimp Farfantepenaeus californiensis and its relation to temperature

Abstract We evaluated the interannual variation in the growth of brown shrimp Farfantepenaeus californiensis and the relation of this variation with sea surface temperature in the Gulf of California, Mexico. We used daily samplings of commercial captures at the packing plant at Guaymas, Sonora, Mexico from 1978 to 1994, samplings of commercial captures on board trawlers of the commercial fleet that operated along the coast of Sonora during the fishing seasons 1989–1995, and the monthly average of the sea surface temperature recorded by the oceanographic station of the Institute of Geophysics of the National University of Mexico, in Guaymas, Sonora from 1978 to 1995. The growth in the brown shrimp showed clear interannual variations. The relation between the temperature and the φ′and temperature and the growth coefficient K could be represented by a gaussian function that was significant (P

Life history stage duration and natural mortality for the pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) in the southern Gulf of Mexico, using the gnomonic model for time division

The gnomonic model proposed by Caddy [Aquat. Living Resour. 9 (1996) 197] to estimate life history stage duration and natural mortality values (M) is applied to the pink shrimp Farfantepenaeus duorarum of the southern Gulf of Mexico. Estimates of life history stage duration and M were consistent with other estimates in the literature. Evidence from the literature suggests that M declines with age, which is also reflected by results through the gnomonic model. If the product of natural mortality and duration for gnomonic intervals is close to constant, as assumed by the model, then age specific natural mortality rates estimated in this study may be useful in modeling and managing the fishery for pink shrimp.

Climate Change Effects on Aquatic Ecosystems and the Challenge for Fishery Management: Pink Shrimp of the Southern Gulf of Mexico

Ecosystems that change through time impose new scientific challenges for fisheries management advice. We present a case study to illustrate our view on how to face such challenges. The Pink Shrimp fishery in the Southern Gulf of Mexico has collapsed. Annual yields were about 24,000 metric tons during the mid-1950s to early 1970s; currently, they are about 1,200 metric tons. Overfishing was assumed as the main cause, but single-species models failed to provide the advice necessary for recovery. An inverse relationship between stock abundance and temperature was demonstrated, and a decline in recruitment and primary production (since 1970s) was observed. We constructed a trophic model for the ecosystem using Ecopath with Ecosim, incorporating the annual mean anomaly of the Atlantic Multidecadal Oscillation as a climate change index to force primary production. Signals were propagated throughout the food web, and biomasses were simulated for the period of 1956 to 2011. Ecosystem changes were estimated with t...

Fishing power, efficiency and selection of gillnets for the shortfin grunt (Microlepidotus brevipinnis Steindachner, 1869), in the southern coast of Jalisco, Mexico

Con el fin de determinar la selectividad, poder de pesca y eficiencia de las redes de enmalle para la sarangola Microlepidotus brevipinnis (Steindachner, 1869) en la zona de Bahia de Navidad, Jalisco, se efectuaron muestreos mensuales de la captura obtenida con redes de 7,62 y 8,89 cm de luz de malla, de abril de 1994 a marzo de 1995. Los resultados indican que la red de 8,89 cm de tamano de malla captura organismos en promedio 3 cm mas grandes y 110 g mas pesados que los capturados por la red de 7,62 cm. La red de 7,62 cm obtiene 1,9 veces mas organismos por lance y 1,3 veces mas biomasa por lance que la obtenida por la red de 8,89. En el analisis de selectividad, se obtuvo una longitud optima (100% de probabilidad de retencion) de 27,7 y 32,2 cm de longitud total para las redes de 7,62 y 8,89 cm de luz de malla, respectivamente. La eficiencia de una red con respecto a la otra cambia en una proporcion entre 25 y 39% conforme aumenta la talla de los peces.

Nota sobre la distribución geográfica de Chione cortezi (Carpenter, 1864) (Mollusca Pelecypoda: Veneridae)

Con el fin de determinar la selectividad de redes de enmalle para los pargos Lutjanus guttatus y L argentiventris en la zona de Bahia de Navidad, Jalisco (Mexico), se analizo la captura obtenida con redes de 7.62 y 8.89 cm de luz de malla. Se capturaron 475 organismos de L. guttatus y 134 organismos de L. argentiventris. Los resultados muestran que la red de 8.89 cm de tamano de malla captura organismos que en promedio son 4 cm mas grandes y 110 g mas pesados que los capturados por la red de 7.62 cm. Para L. guttatus, se obtuvo una longitud optima de 29.1 cm de longitud total para la red de 7.62 cm y de 33.9 cm para la red de 8.89 cm. Para L. argentiventris, la longitud optima calculada fue de 28.9 y 33.7 cm para las redes de 8.89 y 7.62 cm, respectivamente. Si bien la red de 7.62 cm obtuvo una mayor captura, tanto en numero como en biomasa, la red de 8.89 cm asegura que los organismos ya se hayan reproducido al menos una vez al momento de ser capturados. Gillnet selectivity for Lutjanus guttatus and L. argentiventris in Navidad Bay, Jalisco (Mexico), was estimated using monthly samples. Gillnets of 7.62- and 8.89-cm mesh size were used for the experimental design; 475 organisms of L. guttatus and 134 organisms of L. argentiventris were caught. The results show that the organisms caught with the 8.89-cm mesh were on average 4 cm larger and 100 g heavier than those caught with the 7.62-cm mesh. For L. guttatus, the optimum length (100% retention probability) was 29.1 cm for the 7.62-cm mesh and 33.9 cm for the 8.89-cm mesh; for L. argentiventris, the optimum length for the 7.62-cm mesh was 28.9 cm and for the 8.89-cm mesh, 33.7 cm. In both cases the catch mode corresponds to the calculated optimum length. The gillnet of 7.62-cm mesh caught the largest abundance in terms of number of individuals and biomass; however, the 8.89-cm mesh assures the catch of organisms that have reached first maturity length.

Analysis of the spatial and seasonal variation in catchability of red grouper, Epinephelus morio (Valenciennes, 1828), in the Campeche Bank before overfishing (1973-1977)

La pesqueria de mero Epinephelus morio en el Banco de Campeche, frente a la costa norte de la Peninsula de Yucatan, esta sobreexplotada. Las principales causas son la elevada presion de pesca en zonas de agregacion reproductiva y en zonas de crianza de juveniles. Se realizo un analisis de la variacion espacio-temporal de la capturabilidad, usando datos de 1973 a 1977, con el objetivo de detectar las zonas de mayor vulnerabilidad del mero segun su estado de desarrollo (juveniles, preadultos y adultos). Los resultados mostraron que durante la epoca de reproduccion (enero-marzo) la capturabilidad de los adultos fue mayor en la parte oriental del Banco de Campeche. Se encontraron centros de alta capturabilidad en juveniles durante todas las estaciones del ano en las regiones cercanas a Celestun, Dzilam de Bravo, Rio Lagartos y el Cuyo. Se recomienda la creacion de zonas de restriccion de pesca en dichas areas con el objetivo de reducir la mortalidad por pesca para permitir la recuperacion de la poblacion.