Caracterización del forzamiento ambiental sobre la dinámica del intervalo de plastocrono en Zostera marina L. en el estuario de Punta Banda B.C. México: una aproximación de modelado empírico

This paper presents a characterisation of the most significant environmental influences on plastochrone interval variation for Zostera marina L. in Punta Banda estuary B.C. Mexico. Data were collected from April 1998 to December 2001. Using correlation and principal component analysis, we found that the combination of sea surface temperature, light radiation and dissolved nutrients explains the observed variability consistently. Sea surface temperature was found to be the dominant environmental influence (r=0.89, pEn este artículo se presenta una caracterización de las influencias ambientales mas importantes sobre la variación del intervalo de plastocrono para Zostera marina L. en el estuario de Punta Banda B. C. México. Los datos fueron recogidos de abril de 1998 a diciembre de 2001. Utilizando análisis de correlación y análisis de componentes principales se encontró que una combinación de luminosidad, temperatura superficial del mar y nutrientes disueltos explica la variabilidad observada de una manera consistente. La temperatura superficial del mar es el factor dominante (r=0.89,

An Evaluation of Leaf Biomass : Length Ratio as a Tool for Nondestructive Assessment in Eelgrass (Zostera marina L.)

The characterization of biomass and its dynamics provides valuable information for the assessment of natural and transplanted eelgrass populations. The need for simple, nondestructive assessments has led to the use of the leaf biomass-to-length ratio for converting leaf-length measurements, which can be easily obtained, to leaf growth rates through the plastochrone method. Using data on leaf biomass and length collected in three natural eelgrass populations and a mesocosm, we evaluated the suitability of a leaf weight-to-length ratio for nondestructive assessments. For the data sets considered, the isometric scaling that sustains the weight-to-length proxy always produced inconsistent fittings, and for leaf-lengths greater than a threshold value, the conversion of leaf length to biomass generated biased estimations. In contrast, an allometric scaling of leaf biomass and length was highly consistent in all the cases considered. And these nondestructive assessments generated reliable levels of reproducibility in leaf biomass for all the ranges of variability in leaf lengths. We argue that the use of allometric scaling for the representation of leaf biomass in terms of length provides a more reliable approach for estimating eelgrass biomass

Utilización de métodos cuantitativos para el estudio de la dinámica de los pastos marinos: una revisión crítica

Se presenta una revisión sobre el tema: aplicación de métodos cuantitativos al estudio de aspectos dinámicos en poblaciones de pastos marinos. Se incluyen los modelos más importantes utilizados para describir crecimiento, edad, demografía y densidad. En algunos casos se proponen modificaciones a los modelos existentes o bien se sugieren ideas para la realización de futuras investigaciones

Comparative statistical analysis of incidental dolphin mortality, during fishing trips of the Mexican purse seine tuna fishery in the Eastern Pacific Ocean recorded by two scientific observer programs

Scientific observer programs in fisheries are being deployed worldwide in order to obtain robust data for fishery studies, and in relation to its interaction with target and bycatch species. A comparison between two observer programs in Mexican purse seine tuna fishery in the Eastern Pacific ocean is performed considering the incidental mortality per trip as a metric recorded by both observers programs from 1999 to 2016. A Bayesian t-test approximation was used for the comparison between the two methods since, due to its probabilistic nature reduces uncertainty. The analysis showed a very low probability of differences for the estimated bycatch rate between both programs

Mortality rate estimation for eelgrass Zostera marina (Potamogetonaceae) using projections from Leslie matrices

The main goal of this study is to provide estimations of mean mortality rate of vegetative shoots of the seagrass Zostera marina in a meadow near Ensenada Baja California, using a technique that minimizes destructive sampling. Using cohorts and Leslie matrices, three life tables were constructed, each representing a season within the period of monthly sampling (April 1999 to April 2000). Ages for the cohorts were established in terms of Plastochrone Interval (PI). The matrices were projected through time to estimate the mean total number of individuals at time t, n(t) as well as mortality. We found no statistical differences between observed and predicted mean values for these variables (t=-0.11, p=0.92 for n(t) and t=0.69, p=0.5 for mean rate of mortality). We found high correlation coefficient values between observed and projected values for monthly number of individuals (r=0.70, p=0.007) and monthly mortality rates (r=0.81, p=0.001). If at a certain time t a sudden environmental change occurs, and as long as the perturbation does not provoke the killing of all the individuals of a given age i for 0 = i = x - 1, there will be a prevailing number of individuals of age or stage x at a time t+1. This nondestructive technique reduces the number of field visits and samples needed for the demographic analysis of Z. marina, and therefore decreases the disturbance caused by researches to the ecosystem

Estimación del descarte por exceso de captura en la pesquería industrial de cerco del stock Norte-Centro de la anchoveta peruana Engraulis ringens a partir de un programa de observación a bordo

En este trabajo se presenta la estimación del descarte por exceso de captura en la pesquería industrial de cerco del stock Norte-Centro de anchoveta peruana. Se define el descarte por exceso de captura, como la porción de captura que se arroja al mar cuando se ha capturado más de lo que la capacidad de bodega de la embarcación puede almacenar. El análisis de estimación para el periodo 2005 - 2014, se realizó a partir del “Programa de observadores a bordo de la flota de cerco” que ejecuta el Instituto del Mar del Perú (IMARPE), en donde 5 837 viajes, que representan el 1.6% de los viajes totales, fueron muestreados. Las metodologías utilizadas en la estimación fueron: Modelo Lineal Generalizado (GLM) y el Modelo Delta. Las estimaciones por el Modelo Delta y el GLM fueron diferentes en magnitudes pero similares en tendencias, sin embargo la evaluación del funcionamiento del Modelo Delta, indica que este modelo se ajusta mejor a los datos. El Modelo Delta estimó que la pesquería descarta por exceso de captura entre 2 954 y 199 164 toneladas, con un promedio de 121 312 toneladas para el periodo de estudio, el cual representó una tasa del 2.6% en relación a los desembarques. Se sugiere la incorporación de variables espaciales (p. ej. distancia a la costa, latitud, longitud), físicas (TSM) y del comportamiento del cardumen (p.e. agregación), para mejorar el análisis y comprender mejor el comportamiento de este tipo de descarte

Micromollusk families in 2 contrasting seasons in Bahia de los Angeles, Gulf of California, Mexico

Marine mollusks provide important ecosystem services. They create habitats for benthic organisms, filter water, biodeposit organic carbon in the seafloor, and serve as food sources for other organisms. Studies of mollusk diversity require time-consuming methods to process samples and identify species. Thus, it is not surprising that most studies have focused on macromollusks that can be collected and processed easily, ignoring micromollusk species. Without understanding the ecology and distributions of micromollusks properly, it is impossible to assess their populations and implement adequate conservation measures. Here we present microgastropods collected in Bahia de los Angeles at the family level for September 2013 (summer) and February 2014 (winter). During each season, we sampled 6 coastal sediment stations, and analyzed depth, salinity, temperature, granulometry, and organic matter. A total of 20,353 specimens were collected: 15,310 in summer and 5,043 in winter. Seven micromollusk families were identified: Barleeidae, Caecidae, Cerithiidae, Eulimidae, Pyramidellidae, Rissoidae, and Tornidae. Caecidae and Barleeidae exhibited the highest densities among all families in summer and winter, respectively (278,044 ind·m–2, 142,222 ind·m–2). The lowest densities for summer and winter were observed for the Tornidae family (~1,867 ind·m–2, ~1,411 ind·m–2). Barleeidae, Caecidae, Cerithiidae, Rissoidae, and Tornidae were classified as herbivorous and detritivorous; Eulimidae and Pyramidellidae, as carnivorous and ectoparasitic. Tornidae and Eulimidae showed symbiotic relationships with various invertebrate species. The Bayesian analysis of variance indicated a high probability of differences only in summer (BF > 3). When comparing the stations in both periods, all stations, except station 6, showed differences between periods (BF > 3). The canonical correlation analysis indicated some associations between family abundances and temperature. This study provides valuable information that expands the knowledge of micromollusk biodiversity in the coastal area of Bahia de los Angeles, an important site for conservation in Mexico

The effect of parameter variability in the allometric projection of leaf growth rates for eelgrass (Zostera marina L.)

Restoration of eelgrass Zostera marina meadows from harmful anthropogenic influences has made it essential to evaluate these efforts by using non-destructive assessments. Allometric methods provide a convenient framework for the derivation of reliable indirect assessments of leaf biomass and leaf growth of eelgrass. Invariance of the involved parameters could grant truly nondestructive assessments because previously fitted values could be used to produce consistent estimations. In order to explore this property we analyzed data from two natural eelgrass populations in the East Pacific (México), as well as populations in the West Pacific (two natural in Korea and one mesocosm in Japan). When we compared observed leaf growth rates with those projected allometrically by using parameter values fitted at different sites, we found that only parameter values fitted at sites within the same geographical region can produce consistent results. Therefore if this restriction holds previously fitted parameters can indeed be used to produce reliable non-destructive assessments of eelgrass leaf growth rates