Importancia de la variabilidad climática en las pesquerías y biología de la merluza europea Merluccius merluccius (Linnaeus, 1758) de la costa noroccidental africana

Tesis doctoral[Summary] Fish population and fisheries fluctuations are closely linked to climate dynamics through environmental variability that determines the distribution, migration and abundance of fish. Fishery science were largely focused on the great northern hemisphere fisheries, which some of them fluctuate at decadal time scales and show patterns of synchrony with low frequency signals, as reflected by climatic indices such as the North Atlantic Oscillation (NAO). However, there is scarce information about these patterns at lower latitudes like NW African coast, in spite of this area supports large international fisheries. The aim of this work was to analyze how climate variability described by NAO and the physical environment influences the productivity of European hake abundance, growth and recruitment variability. The European hake is widely distributed in the North Atlantic and their southern distribution limit is located in NW Africa. Historically it has been carried out an important multinational fishery in this area. In order to understand why it is important to test the climatic hypothesis over European hake stock, I presented the background elements in three main discussion lines. In Chapter 1, I compared the biology and population dynamics between European hake of NW Africa and populations from North Atlantic and Mediterranean Sea. In Chapter 2, it is described and analyzed the structure and evolution of European hake fisheries in NW Africa, focused on unexplained variability of stock assessment procedures carried out until now. In Chapter 3, the main climatic and environmental features of NW African coast are described, emphasizing the potential deterministic influence that variability of these features might exert on the biology, population dynamics and fisheries of European hake in this area. In Chapter 4, catch-based abundance indices of Moroccan and Spanish fisheries were used as the dependent variables in correlation analysis with NAO index. Time series analysis techniques were applied to ICOADS data and satellite data of wind stress and phytoplankton biomass as upwelling proxies to assess their dependence with NAO index. It was found a positive relationship between the NAO and hake abundance. NAO explained 35-45% variability of juveniles with 1-year lag and 45- 60% of small and large adults with 2-3-years lag. The NAO index is a proper tool to trace the annual growth of European hake, at least during the first three years of life. Based on this, it is suggested that the growth rate is greater than previous calculus in the area, and it supports the fast growing hypothesis proposed for North Atlantic and Western Mediterranean. The wind stress explained 83% of phytoplankton biomass variability and both of them were positively correlated with NAO index (41- 58% explained variability respectively). The hake abundance was positively related with favorable oceanographic and productive regime associated with positive NAO conditions. The increasing of upwelling events appear to promote increased abundance of hakes mainly during early life stages, probably throughout enhanced productivity conditions. In Chapter 5, it was tasted the relative importance of climate variability on recruitment dynamics estimated from fishery data and scientific Moroccan surveys. The recruitment to the fishery took place during all year with peaks in spring and summer, but the seasonal component was weak. The time series were in synchrony with NAO index of the previous year and showed strong positive correlation. The recruitment success variability explained by NAO was 25 to 82 % depending on time series size. The main NAO effect in recruitment dynamics was the widening-contraction of Recruitment Window. During NAO+ phase several success cohorts were recruited by year, while in NAO- the success cohorts were scarce and weak. The climate signal in recruitment dynamics of European hake was robust, recurrent and persistent independently of fishing effort. Finally, in Chapter 6, the NAO index was included as a state variable in a Ricker Stock-recruitment-environment model, to contrast it with classical Ricker and Beverton & Holt models. The NAO factor enhanced the fitting model and determined the dispersion degree of recruitment at certain stock level, just before of overcompensation effect of Ricker curve. This exercise represents a step forward in order to include the environmental variability induced by climatic system in stock assessment of demersal resources of NW Africa.[Resumen] El impacto de los cambios de escala climática sobre la producción pesquera mundial es una cuestión relevante científica y económicamente, ya que algunas de las principales pesquerías marinas muestran variaciones temporales en sincronía con oscilaciones climáticas. Por esta razón, en años reciente se ha puesto mayor atención en investigar de qué forma responden los ecosistemas marinos a la variabilidad climática natural, y cómo este conocimiento puede ser incorporado en la gestión de los recursos pesqueros. Sin embargo, dilucidar el impacto del clima sobre las pesquerías no es una tarea sencilla, porque se trata de un proceso holístico de gran escala que interactúa con multiplicidad de factores locales que determinan en última instancia el impacto sobre las poblaciones explotadas. Por lo tanto, el objetivo principal de este trabajo de tesis fue analizar de forma amplia la importancia relativa de la variabilidad del clima descrita por la Oscilación del Atlántico Norte (NAO) en la evolución de las pesquerías y la dinámica de población de la merluza europea en la costa Noroccidental Africana. Para entender la necesidad de explorar la hipótesis climática como fuente de variación principal, primero se proporcionan elementos de discusión acerca de los conceptos de referencia que sustentan tal posibilidad, en tres líneas principales. En el CAPÍTULO 1, se analiza comparativamente la biología y dinámica poblacional entre la merluza europea de la costa Noroccidental Africana y las poblaciones de la especie que se distribuyen en el Atlántico norte y Mediterráneo. En el CAPÍTULO 2, se describe y analiza la estructura y evolución de las pesquerías dirigidas a esta especie en el área de estudio, haciendo énfasis en la variabilidad no explicada por las evaluaciones del stock llevadas a caobo hasta el momento. En el CAPÍTULO 3, se presenta una descripción del entorno climático y ambiental de la costa Noroccidental Africana, y se discute acerca del potencial de influencia que la variabilidad de este entorno pudiera tener en la biología, dinámica poblacional y las pesquerías de la merluza europea en esta área geográfica en particular. Posteriormente, en el CAPÍTULO 4 se estableció que la abundancia de merluza europea está correlacionada significativa y positivamente con el índice NAO. La variabilidad de la abundancia de juveniles es explicada por la NAO en un 35-45% con un año de desfase y entre 45 y 60% la de adultos tempranos y adultos grandes, con 2 y 3 años de desfase respectivamente. El desfase del impacto, permite utilizar el índice NAO como trazador del crecimiento anual de la merluza europea, cuya magnitud fue el doble de la estimada en trabajos anteriores en el área. El proceso que presumiblemente vincula la variabilidad climática descrita por la NAO y la abundancia por grupos de talla de la merluza europea, es la extensión espacial y temporal de los afloramientos inducidos por viento. El estrés de viento explica el 83% de la variabilidad de la biomasa de fitoplancton y ambos parámetros se correlacionaron positivamente con el índice NAO del mismo año. Es decir, que la abundancia de juveniles está directamente relacionada con un régimen oceanográfico y productivo favorable asociado con fases positivas de la NAO. Como consecuencia de lo anterior, en el CAPÍTULO 5 se exploró la contribución relativa de la señal climática a la dinámica del reclutamiento de la especie a través de índices derivados de las pesquerías y de campañas científicas. Se determinó que el reclutamiento a la pesquería sucede a lo largo de todo el año, con máximos en primavera y verano, pero con estacionalidad débil. El reclutamiento varía en fase con la NAO del año previo (25-82% de la variabilidad explicada). El mecanismo de respuesta ecológico a las variaciones de la NAO, fue la ampliación-contracción de la Ventana de Reclutamiento (VR). Durante una fase positiva de la NAO, se reclutan varias cohortes en un mismo año, en tanto que durante una fase negativa, el número e intensidad de cohortes reclutadas disminuye sensiblemente. La señal climática en el reclutamiento es robusta, recurrente y persistente independientemente del nivel de esfuerzo de pesca. Finalmente, en el CAPÍTULO 6 se incorporó el índice NAO como un parámetro ambiental en un modelo stock-reclutamiento, que mejora el ajuste de los datos con respecto a los modelos clásicos. El factor NAO determina la dispersión del reclutamiento a un mismo nivel del stock reproductor, previo a la sobre-compensación de la curva de reclutamiento. Esto representa un paso muy importante hacia la incorporación de la variabilidad ambiental inducida por el sistema climático en la evaluación de los stocks demersales de la costa Noroccidental Africana.Instituo Español de Oceanografía; Consejo Nacional de Ciencia y Tecnología (Conacyt) del Gobierno Mexicano; Fundación Meiners-Mandujan

Time-space reproductive differences of black hakes, M. polli and M. senegalensis off the NW African Coast

PosterThe named black hake in the Northwest Africa, M. polli and M. senegalensis, are distributed in Saharan, Mauritanian and Senegalese waters, where they are target species of Spanish trawling fleet and by some longliners. The separation of both species is quite difficult in practice, hence they are usually considered as black hake (mixed) in commercial catch statistics. This fact and the considerable deep distribution range of M. polli, results in a marked scarcity of comparative detailed studies about these species. The aim of this work was to analyze detailed biological data, collected during research trawl surveys and scientific observations onboard of commercial trawlers and longilenrs in Mauritanian and Senegalese waters during 2003-2006. By macroscopic analysis of the gonadic stages and the seasonal evolution of gonadosomatic indices (GSI), it has been determined the spawning season of both species. In order to determine the size at first sexual maturity, a logistic model was fitted to the mature fraction by length separated by species, considering different time periods. In other hand, the monthly time series of commercial gonad yields between 1986 and 2006 were split up in the trend and the seasonal components using a X-12 ARIMA routine. The spawning took place during the cold season, from November to February with the strongest signal during December-January for both species, but it occurs quite early in M. senegalensis. Males consistently maturing earlier than females, but there was a little length difference of sexual maturity for the two species. M. senegalensis reached the first maturity (35,4 cm) at slightly lower length than M. polli (37,0 cm) for combined sexes model. The sex ratio was skewed to females in both species. Because these species inhabits into a highly dynamic oceanographic area, and taking in account that recently it has been suggested a strong dependence between the climate-environment proxy NAO and the black hakes adult abundance dynamics, we explored possible deterministic relationships between reproduction features and sexual maturity of both species in phase with NAO index. It was not possible to determine if the difference in length-maturity values with some previous analyses were related with changes in abundance, the environmental forcing, or due to calculus procedures. However there was synchrony between the pronounced negative NAO phase and decreasing amplitude of seasonal peak of gonad yields for both species. Finally, despite of there was a slightly asynchrony in spawning timing among both species, we believe that in general terms it is justified to consider one set of maturity parameter values to perform the assessment procedures.Instituto Español de Oceanografía (IEO

Dinámica poblacional del pez invasor del género Pterygoplichthys en la cuenca de Chacalapa (cuenca de Coatzacoalcos) Veracruz, México

La presencia reciente del Pterygoplichthys, comúnmente conocidos como plecos, pez diablo o limpia peceras, en las aguas epicontinentales de la zona de Chinameca, Veracruz, se ha convertido en un problema ecológico y ambiental, debido a que por su enorme plasticidad adaptativa y a la ausencia de depredadores naturales, provoca desplazamiento de especies nativas. Actualmente en el estado de Veracruz no se cuenta con trabajos de investigación que permitan sustentar medidas de control y/o erradicación del Pterygoplichthys. Con el objetivo de obtener datos básicos del Pterygoplichthys, se llevaron a cabo muestreos biológicos bimestrales, sobre la parte baja del río Chacalapa y la represa artesanal adyacente denominada “La Chinampita”. Los muestreos iniciaron en el mes de julio de 2012 y culminaron en mayo de 2013, se realizaron con artes de pesca poco selectivos. Se determinó la presencia de la especie P. pardalis, con individuos de 420 mm de longitud total (LT) y un peso de 620 g en los machos, en las hembras fue de 390 mm LT y 650 g. Los registros de captura que mayor abundancia de plecos presentaron, fueron en el mes de mayo con el 43%. A partir del mes de marzo se registró el inicio de la actividad reproductiva, con máximo desarrollo gonadal en mayo

Reproductive biology of little tunny Euthynnus alletteratus (Rafinesque, 1810) in the southwest Gulf of Mexico

The aim of this study was to describe the reproductive dynamic of Euthynnus alletteratus in the southwest Gulf of Mexico. The annual variation of the volume fraction occupied by gametes and tissues in gonads were related with main body indexes, such as the gonadosomatic index (IG), the hepatosomatic index (IH), and the nutrition index (IN), and compared with the sea surface temperature. A total of 951 E. alletteratus individuals were sampled, where a sex ratio of 1:1 and a size interval strongly skewed towards organisms with a fork length (LF) of 36–40 cm were observed. The IG showed an increase from March to September with maximum values in April and July. Two clearly defined peaks were observed, and they were consistent with the histological analysis, where the percentage of ripe gametes predominated from April to September. The optimum thermal window for reproductive activity was from 24 to 28 C. The size of first sex maturity was 34.35 cm of LF for males and 34.60 (LF) for females, without significant difference between sexes

Reproductive biology of little tunny Euthynnus alletteratus (Rafinesque, 1810) in the southwest Gulf of Mexico

The aim of this study was to describe the reproductive dynamic of Euthynnus alletteratus in the southwest Gulf of Mexico. The annual variation of the volume fraction occupied by gametes and tissues in gonads were related with main body indexes, such as the gonadosomatic index (IG), the hepatosomatic index (IH), and the nutrition index (IN), and compared with the sea surface temperature. A total of 951 E. alletteratus individuals were sampled, where a sex ratio of 1:1 and a size interval strongly skewed towards organisms with a fork length (LF) of 36–40 cm were observed. The IG showed an increase from March to September with maximum values in April and July. Two clearly defined peaks were observed, and they were consistent with the histological analysis, where the percentage of ripe gametes predominated from April to September. The optimum thermal window for reproductive activity was from 24 to 28 C. The size of first sex maturity was 34.35 cm of LF for males and 34.60 (LF) for females, without significant difference between sexes

Oocyte dynamics for Atlantic bluefin tuna (Thunnus thynnus) in the southern Gulf of Mexico: A comparative assessment of Mediterranean spawners using two stereological methods

Although most research focused on the northern Gulf of Mexico for western Atlantic bluefin tuna, the histological records of reproductive activity of this species in the southern Gulf of Mexico (Mexican waters) have been presented for the first time. This work is the first to study oocyte dynamics in Atlantic bluefin tuna caught in the southern Gulf of Mexico by assessing and comparing them with Mediterranean stock (BFT-E) through stereology using two different methods. Regardless of Atlantic bluefin tuna females returning to their respective spawning grounds at different months in the southern Gulf of Mexico and the Mediterranean, both stocks arrived reproductively inactive and remained in these zones during periods of similar length; they were reproductively active until March for the southern Gulf of Mexico and May for the Mediterranean females. The comparison of the size structure between the two stocks examined using kernel density estimators demonstrated a quite remarkable difference in mean fork lengths between stocks. The ovarian oocyte density, that is, the number of oocytes per gram of ovary, for each gonad stage predicted using the Weibel and Gomez and oocyte packing density (OPD) methods did not significantly differ between stocks and showed that advanced vitellogenic oocytes from spawning-capable females are an appropriate indicator to estimate potential fecundity, presenting values of c. 1273 and ~1355 eggs per gram for the southern Gulf of Mexico and Mediterranean females, respectively. Females caught in Mexican waters (southern Gulf of Mexico) were larger than those caught in the Mediterranean; however, it was demonstrated that the length and weight of females did not affect ovarian oocyte density production. In addition, densities estimated for each gonad stage using W&G and OPD methods did not differ between stocks and presented equal patterns in their oocyte dynamics. These findings contribute to a better understanding of the reproductive biology of Atlantic bluefin tuna, especially in the southern Gulf of Mexico, due to the lack of information regarding this zone, and may allow to support strategies for proper assessment, management, and conservation