This work investigated the feeding ecology and behaviour of gray whales in Bahı´a Magdalena. Underwater observations of bottom feeding were made (n ¼ 4). Skin biopsies of the gray whale had a carbon isotope value of )16.5 ± 0.1& (range from )16.4 to )16.7, n ¼ 7). Prey in Bahı´a Magdalena had a carbon isotope value of )18.4&. Dietary enrichment from prey in Bahı´a Magdalena would correspond to 2 ± 0.1&, whereas previously published results for prey in Alaska would result in an enrichment of 3&, which suggests that whales were more likely feeding on prey from Bahı´a Magdalena. Carbon isotopic oscillation along the baleen plate of a stranded 1-year-old whale showed a variation in diet during the year, which suggests continual feeding during this time and corresponding to dietary sample measurements from Bahı´a Magdalena in winter and Alaska in summer.

Stable-carbon and nitrogen isotopic compositions (d 13 C, d 15 N) of baleen plates of two juvenile and four adult gray whales (Eschrichtius robustus) were examined. High variance in isotopic composition of baleen plates was detected among individuals and, unlike other migratory species of baleen whales examined isotopically, d 13 C and d 15 N values of most whales showed no regular oscillations. Only one baleen plate reflected the assumed principal Arctic prey (ampeliscid amphipods) during growth on the summer grounds. The rate of baleen growth inferred for one of the juveniles in the last 5 months of life (4.7 mm/week) was similar to the rate calculated previously for a rehabilitating gray whale calf. Autumn corresponded to the timing of the formation of lowest d 15 N values measured along plates. We estimate that the baleen length in all adult gray whales recorded around a year of information (1.3 ± 0.3; Mean ± SD). This short period of dietary integration precludes long time series analyses in this species and reflects the extensive wear on baleen plates due to benthic foraging.

The isotopic composition of baleen whales’ epidermis structural layers can give information about dietary change over time. This study investigated if epidermis layers integrated isotopic values that record physiological changes from gestation to lactation. Epidermis tissues (n = 43) were collected from free ranging lactating female gray whale and calves during the beginning of three breeding seasons. Modelling of δ 13 C and δ 15 N values show intra- and inter-individual differences based on epidermal layers, age class and year of sampling. The isotopic composition of mother-calf pairs is correlated, and the estimates of the maximum mother-to-calf isotopic difference was ~1.4‰ for δ 13 C and between 1 and 1.5‰ for δ 15 N values. Change in δ 15 N values among epidermal layers in calves was associated with the transition from fetus to consumption of maternal milk. It is here proposed when lactation influences calf epidermis, δ 15 N values decrease consistently from the outermost to the innermost layer. However, if a calf was born only few days before collection, epidermis integrates more variable δ 15 N patterns because gestation still affects the isotopic composition of the layers. The possibility of calculating mother-to-calf nitrogen isotope fractionation, and the regularity of changes between calf layer δ 15 N values, allowed results of an isotopic clock model to predict the age of each calf when sampled with its mother. This model has the potential to be a straightforward method to estimate the beginning of lactation, therefore calf birth date when direct observations are not feasible. The non-lethal remote collection of epidermis appears to be an effective tool for the study of the physiology of reproduction of baleen whales. The parallel study of the three epidermal structural layers highlighted the importance of considering the unique mother-calf pair physiological status at the time of sampling time when stable isotope results are interpreted.

ABSTRACT. Fish assemblages of lakes from central México have been altered as a result of water overexploitation, pollution, habitat fragmentation, and introduction of exotic species. Patterns and the extent of change in most of these systems are poorly documented. This paper presents a long-term study of changes in the fish fauna of Lago de Pátzcuaro (State of Michoacán, México). Long-term information (years 1900-2010) of fish communities was used to explore trends in the composition of the fish community and their ecological attributes. Trends across time for each fish guild were evaluated through a multivariate analysis of variance. Native species dominated total species richness over the entire study period, but exotic fish comprised 46% of the community in the 2010s. During the last 110 years, there has been a decline in the number of carnivore species and an increase of omnivore species in the Lago de Pátzcuaro fish community. Sensitive species have disappeared from the lake and species tolerant to environmental degradation have increased from 13 to 61%. The data suggest that anthropic effects on the environmental condition of Lago de Pátzcuaro are associated with the loss of ecosystem elements (fish species) and ecosystem processes (species interactions). Ecological restoration and conservation programs must include information of these long term studies to be more effective in their efforts. Keywords: shallow lake, environmental degradation, ecological guilds, historical analysis, exotic species, México.Cambios a largo plazo en la fauna de peces del Lago de Pátzcuaro en México central RESUMEN. El ensamble de las comunidades de peces en los lagos de México Central ha sido alterado como resultado de la sobre-explotación del agua, contaminación, fragmentación de hábitat y la introducción de especies exóticas. Los patrones y la extensión de los cambios en la mayoría de estos ecosistemas están escasamente documentados. Este artículo presenta un estudio a largo plazo de los cambios en la fauna de peces del Lago de Pátzcuaro (Estado de Michoacán, México). La información a largo plazo (años 1900-2010) de las comunidades de peces fue usada para explorar las tendencias en la composición específica y los atributos ecológicos de las especies en la comunidad. Las tendencias a través del tiempo para cada gremio de peces fueron evaluadas mediante análisis de varianza multivariado. Las especies nativas dominaron a través de todo el periodo de estudio, pero las especies exóticas alcanzaron 46% de la comunidad en la década del 2010. Durante los últimos 110 años, ha habido disminución en el número de especies carnívoras e incremento de las especies omnívoras en este ecosistema. Las especies intolerantes han desaparecido del lago y las especies tolerantes a la degradación ambiental han incrementado de 13 a 61%. Los datos sugieren que los efectos antrópicos sobre la condición ambiental del Lago de Pátzcuaro se asocian con la pérdida de elementos (especies de peces) y procesos (interacciones entre las especies) del ecosistema....

Ecología trófica del pez exótico Guatapote del Lerma Poeciliopsis infans (Cyprinodontiformes: Poeciliidae) en el Lago de Pátzcuaro, Región Central de México. Exotic fish species has caused several impacts on aquatic biodiversity. The Lago de Pátzcuaro has some well-studied exotic species, except the Lerma livebearer Poeciliopsis infans. This fish species was introduced into the Lago de Pátzcuaro before 1997 and the aspects of its biology are still unknown. In this study we assessed aspects of the trophic ecology of this exotic fish, P. infans, using gut content and stable isotope analysis to understand its capacity to tolerate anthropogenic environmental degradation in the Lago de Pátzcuaro. We also determined its trophic guild position (TP) using the TrophLab Program and stable isotope. Niche breadth was calculated by standardized Levins' Index (Bi). Fish was captured with a seine during wet and dry seasons at six environmentally different sites and gut contents were obtained. We analyzed a total of 239 gut contents of P. infans. The contribution of each food item in the diet was quantified using frequency of occurrence and area percentage. The importance of each prey item was determined according to the index of relative importance (IRI), and the omnivory index (OI) was used to assess the feeding behavior. Fish were categorized by size and the diet was compared between fish sizes and sites. Dorsal muscle tissue and water hyacinth tissue was obtained for nitrogen isotope signature (δ 15 N) analysis. Additionally, we measured water and habitat quality to evaluate environmental conditions at each site. We concluded that P. infans is an omnivore (OI=0.28) that consumes mainly detritus (44%), epiphytic diatoms (37%), and secondary on terrestrial insects (6%) and zooplankton (10%). The fish can behave as a specialist (Bi=0.39) or generalist (Bi=0.68) and as a primary consumer (TROPH=2.2; TP=2.3) with a feeding strategy that was the same at different sizes, seasons and sites. None of the evaluated sites showed good environmental quality. We argue that P. infans can tolerate changes in water quality and feeding items availability, because it can exploit resources in multiple trophic webs. However, this species could be dependent on habitat complexity, especially in the aquatic vegetation cover.