Ernesto A. Chávez

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.

POTENTIAL PRODUCTION OF THE CARIBBEAN SPINY LOBSTER (DECAPODA, PALINURA) FISHERIES

[The spiny lobster Panulirus argus (Latreille, 1804) constitutes the most important fishery of the Caribbean: it accounts for nearly 42 000 tonnes. Evidence suggests that high fishing mortality (F) may have been overexploiting most stocks. An assessment was carried out providing the basis for a sustainable exploitation of the nine most important producing countries. Values were assessed and each fishery was simulated; age structure was reconstructed linking biological, economic, and social variables. The results show that advice is required to enhance recruitment and to restore biomass of most stocks. Among the nine fisheries examined in detail, the Bahamas, the main producer, is slightly overexploited, and the overexploitation of four others ranges from moderate to severe. An arbitrary F value, lower than the one producing the Maximum Sustainable Yield, or extreme reference point, is adopted as management target and was proposed for adoption by these fisheries; in order to attain the target, gradual F reductions are required to restore stock biomass in eight fisheries, and a slight increase of F in one case. La langosta Panulirus argus (Latreille, 1804) constituye la pesqueria mas importante del Caribe: se capturan cerca de 42,000 toneladas. La evidencia sugiere que la alta mortalidad por pesca (F) podria haber provocado la sobre explotacion de la mayoria de las poblaciones. Las pesquerias mas importantes fueron evaluadas, proporcionando las bases para una explotacion sustentable en nueve paises que la explotan. Se evaluaron los parametros de las poblaciones y cada pesqueria fue simulada; la estructura por edades fue reconstruida vinculando las variables biologicas, economicas y sociales. Los resultados sugieren que se requiere de un manejo informado para mejorar los niveles de reclutamiento y recuperar la mayoria de las poblaciones. De las nueve pesquerias analizadas en detalle, se encontro que la de las Bahamas el principal productor, esta ligeramente sobreexplotada y otras cuatro se encuentran en un grado de sobreexplotacion que va de moderado a severo. Se identifico un valor arbitrario de F, mas bajo que el requerido para el nivel de Rendimiento Maximo Sostenible que es un punto de referencia extremo y se propone aqui como objetivo de manejo para estas pesquerias; para el logro de ese objetivo, es necesario reducir gradualmente la F en ocho pesquerias para que sus biomasas se restablezcan y en un caso implica un ligero aumento de la F., The spiny lobster Panulirus argus (Latreille, 1804) constitutes the most important fishery of the Caribbean: it accounts for nearly 42 000 tonnes. Evidence suggests that high fishing mortality (F) may have been overexploiting most stocks. An assessment was carried out providing the basis for a sustainable exploitation of the nine most important producing countries. Values were assessed and each fishery was simulated; age structure was reconstructed linking biological, economic, and social variables. The results show that advice is required to enhance recruitment and to restore biomass of most stocks. Among the nine fisheries examined in detail, the Bahamas, the main producer, is slightly overexploited, and the overexploitation of four others ranges from moderate to severe. An arbitrary F value, lower than the one producing the Maximum Sustainable Yield, or extreme reference point, is adopted as management target and was proposed for adoption by these fisheries; in order to attain the target, gradual F reductions are required to restore stock biomass in eight fisheries, and a slight increase of F in one case. La langosta Panulirus argus (Latreille, 1804) constituye la pesqueria mas importante del Caribe: se capturan cerca de 42,000 toneladas. La evidencia sugiere que la alta mortalidad por pesca (F) podria haber provocado la sobre explotacion de la mayoria de las poblaciones. Las pesquerias mas importantes fueron evaluadas, proporcionando las bases para una explotacion sustentable en nueve paises que la explotan. Se evaluaron los parametros de las poblaciones y cada pesqueria fue simulada; la estructura por edades fue reconstruida vinculando las variables biologicas, economicas y sociales. Los resultados sugieren que se requiere de un manejo informado para mejorar los niveles de reclutamiento y recuperar la mayoria de las poblaciones. De las nueve pesquerias analizadas en detalle, se encontro que la de las Bahamas el principal productor, esta ligeramente sobreexplotada y otras cuatro se encuentran en un grado de sobreexplotacion que va de moderado a severo. Se identifico un valor arbitrario de F, mas bajo que el requerido para el nivel de Rendimiento Maximo Sostenible que es un punto de referencia extremo y se propone aqui como objetivo de manejo para estas pesquerias; para el logro de ese objetivo, es necesario reducir gradualmente la F en ocho pesquerias para que sus biomasas se restablezcan y en un caso implica un ligero aumento de la F.]

INTERANNUAL VARIABILITY OF THE REPRODUCTIVE PERIOD OF THE BROWN SHRIMP, FARFANTEPENAEUS CALIFORNIENSIS (HOLMES, 1900) (DECAPODA, NATANTIA)

[Interannual changes in the reproductive pattern of the brown shrimp, Farfantepenaeus californiensis, a commercially important marine crustacean, were analysed as a function of sea water temperature. Daily samples of gravid females from 1979 through 1994 and monthly sea water temperatures were examined. The results show a high interannual variability of the reproductive period with two patterns; one in which spawning occurs throughout the year, the other with two peaks of mass spawning. The first of the two peaks is the more intense, occurring from March to May; the other is in October and November and is less intense. The extended spawning period occurs under warmer conditions and is probably associated with El Nino events. The pattern with two peaks is associated with average sea water temperatures. Occurrence of one pattern or the other may have significant consequences for managing this fishery. Los cambios interanuales en el patron reproductivo del camaron cafe Farfantepenaeus californiensis, un crustaceo escencialmente marino, fueron analizados en funcion de la temperatura del agua de mar. Se analizaron muestreos diarios de hembras ovigeras y temperatura promedio mensual del agua de mar desde 1979 a 1994. Los resultados muestran, una alta variabilidad interanual del periodo reproductivo con dos patrones: uno en el que el desove se efectua a todo lo largo del ano y otro con dos periodos masivos de reproduccion. El primero de ellos siendo el mas intenso y presentandose durante marzo a mayo, el segundo es menos intenso y ocurre de octubre a noviembre. La extension del periodo reproductivo ocurre cuando se presentan condiciones calidas y es probable que este asociado a eventos El Nino. El patron con dos periodos de reproduccion masiva se observo principalmente bajo condiciones promedio. La ocurrencia de uno y otro patron puede tener consecuencias importantes para el manejo de la pesqueria., Interannual changes in the reproductive pattern of the brown shrimp, Farfantepenaeus californiensis, a commercially important marine crustacean, were analysed as a function of sea water temperature. Daily samples of gravid females from 1979 through 1994 and monthly sea water temperatures were examined. The results show a high interannual variability of the reproductive period with two patterns; one in which spawning occurs throughout the year, the other with two peaks of mass spawning. The first of the two peaks is the more intense, occurring from March to May; the other is in October and November and is less intense. The extended spawning period occurs under warmer conditions and is probably associated with El Nino events. The pattern with two peaks is associated with average sea water temperatures. Occurrence of one pattern or the other may have significant consequences for managing this fishery. Los cambios interanuales en el patron reproductivo del camaron cafe Farfantepenaeus californiensis, un crustaceo escencialmente marino, fueron analizados en funcion de la temperatura del agua de mar. Se analizaron muestreos diarios de hembras ovigeras y temperatura promedio mensual del agua de mar desde 1979 a 1994. Los resultados muestran, una alta variabilidad interanual del periodo reproductivo con dos patrones: uno en el que el desove se efectua a todo lo largo del ano y otro con dos periodos masivos de reproduccion. El primero de ellos siendo el mas intenso y presentandose durante marzo a mayo, el segundo es menos intenso y ocurre de octubre a noviembre. La extension del periodo reproductivo ocurre cuando se presentan condiciones calidas y es probable que este asociado a eventos El Nino. El patron con dos periodos de reproduccion masiva se observo principalmente bajo condiciones promedio. La ocurrencia de uno y otro patron puede tener consecuencias importantes para el manejo de la pesqueria.]

Modeling of the Pacific sardine Sardinops caeruleus fishery of the Gulf of California, Mexico

We used a stochastic age-structured model with density-dependent recruitment to study the fishery and population dynamics of the Gulf of California Pacific sardine (Sardinops caeruleus) stock for the period 1972–1973 to 1989–1990. To determine the value of fishing mortality (F) which corresponds to the long-term optimum yield and cost–benefit ratio (C/B), we simulated fished population trajectories over a period of 50 years. Our results indicated a good fit between observed and predicted annual recruitment and catch. Quasiperiodic oscillations of a five year periodicity for an unfished population faded with increasing F. Maximum yield and C/B were obtained with F=0.475 and 0.275, and the simulated population began declining with F≥0.5 and ≥0.3, respectively. It is proposed that F<0.25 would be adequate for this fishery.

POTENTIAL YIELD OF A ROCK SHRIMP STOCK, SICYONIA PENICILLATA IN THE NORTHERN GULF OF CALIFORNIA

A stock of rock shrimp Sicyonia penicillata was assessed in a fishery recently opened at Bahoa Kino, Sonora, Mexico. An age-structured model with stochastic recruitment was developed, which considers growth rate, natural mortality, and fishing mortality by age. Age groups were followed year by year with a stock-recruitment Ricker function where the seasonal recruitment pattern was defined as well. Simulations might be interpreted as showing a stable population with four year cycles, reflecting a density-dependent process. In 1996, fishing intensity had an apparent compensatory effect on the stock, decreasing the amplitude of natural oscillations and maintaining the stock at a biomass level similar to the size observed in a condition of no exploitation. The stock was found currently underexploited. As a result of the seasonal accessibility and the age of first-catch fishing (adult shrimp), the stock might be capable to withstand high fishing pressure without being overexploited. Se evaluo una poblacion de camaron de roca Sicyonia penicillata, de una pesqueroa recientemente abierta en Bahoa Kino, Sonora, Mexico. Se desarrollo un modelo basado en la estructura por edades que considera reclutamiento estocastico, tasa de crecimiento, mortalidad natural y mortalidad por pesca por grupo de edad. Estos grupos de edad fueron determinados ano tras ano mediante la funcion de reclutamiento de Ricker, en los que tambien se definio el patron estacional de reclutamiento. Las simulaciones muestran una poblacion estable con ciclos de cuatro anos, que indican un proceso de densodependencia. En 1996, la intensidad de pesca tuvo un efecto compensatorio sobre la poblacion, reduciendo la amplitud de las oscilaciones naturales y manteniendo al stock en un nivel de biomasa similar al observado en la condicion sin explotacion. Se encontro que el recurso esta subexplotado. Como resultado de la accesibilidad estacional y de que la edad de primera captura corresponde a camaron adulto, el recurso soporta alta presion de pesca sin dar evidencias de sobreexplotacion.