Feeding habits of the fishes Lutjanus peru and Lutjanus guttatus (Pisces: Lutjanidae) of Guerrero, México

Diet composition of the Pacific snapper (Lutjanus peru) 130-684 mm fork length (FL) and the spotted snapper (Lugjanus guttatus) 120-550 mm FL, was analyzed. Monthly samples were obtained from commercial landings in three regions off the coast of Guerrero, Mexico. Percentage by number (%N), percentage by weight (%W), and percentage of occurrence (%O) were calculated for each prey and summarized as the index of relative importance. Both species are polyphagous predators feeding on a variety of prey: Sixty-eight prey items, mainly fish (%W = 50.9), crustaceans (%W = 35.6), and mollusks (%W = 7.2), were found in the stomach contents of L. peru, while 88 components were identified in the diet of L. guttatus, the most important prey being fish (%W = 50.8) and crustaceans (%W = 43.4). Diet overlap between species is not significant (p<0.05), indicating that competition for food is unlikely. Based on published values of the relative importance index, the diets of these Lutjanidae were analyzed considering different regions of the Pacific coast of Mexico and Costa Rica, and similarities among sites and species were discussed. The cluster analysis showed that similarities among species inhabiting in the same area are more important than within organisms of the same species living in different zones. Results suggest that prey availability rather than food selectivity, conditions the feeding behavior of these fish species.     

Coexistence of Lutjanus peru and Lutjanus guttatus (Pisces: Lutjanidae) in the coast of Guerrero, México: association with the temporal variation of recruitment

Monthly volumes of capture of Lutjanus peru and Lutjanus guttatus from the coast of Guerrero, Mexico, were analyzed considering eight annual cycles. Time-series, auto correlation, and cross-correlation analysis showed that monthly abundance of populations display unsystematic variations. The FiSAT software was used to obtain the recruitment patterns of both species, using length-frequency data. Our results support the hypothesis that temporal phase-shifts in reproductive events, hence recruitment, explain the coexistence of these species. The outcome of this mechanism is a temporal succession of specific recruit abundance off the coasts of Guerrero, Mexico. The uncoupling of the recruitment events between these species, induces a separation of recruits: therefore, the intake of a particular set of preys could take place at different times.     

Host selection by the cleaner shrimp Ancylomenes pedersoni: Do anemone host species,prior experience or the presence of conspecific shrimp matter?

In the symbiotic association that exists between cleaner shrimp Ancylomenes pedersoni (=Periclimenes pedersoni) and host sea anemones, specificity varies among populations, and shrimp are believed to search among different individual hosts for favourable positions from which to attract client fish. Four laboratory-based experiments were conducted to test host selection of A. pedersoni between the following: i) Bartholomea annulata (corkscrew anemone) and Condylactis gigantea (condy anemone), ii) B. annulata, with or without a conspecific resident, iii) a previously known or unknown B. annulata, and iv) a previously known or unknown C. gigantea. Preference (active selection) was distinguished from mere passive association by comparing shrimp acclimation to anemones offered in choice and no-choice (control) situations. The results were analysed using asymmetrical χ² contingency tables (in each experiment, n = 60) where expected frequencies were obtained with maximum likelihood estimators. Shrimp acclimated more frequently to B. annulata than to C. gigantea, but they acclimated similarly to anemones with or without another resident and to those B. annulata and C. gigantea anemones that were familiar rather than unfamiliar. However, none of the χ² values were statistically significant (χ²_df = 1 = 0.48, 0.19, 0.42, 0.42; overall p > 0.45), suggesting that preference may not be responsible for the association between adult A. pedersoni and its host anemones observed in the field. Differences in the frequency of association may be due to factors other than the active decisions made by shrimp when presented with more than one alternative host.     

Ichthyoplankton distribution as an indicator of hydrodynamic conditions of a lagoon system in the Mexican Caribbean

The salt-water intrusion into a lagoon system of the Sian Ka’anBiosphere Reserve was assessed during 1 year and related tothe marine component of the larval fish assemblage. This systemis environmentally complex because of the penetration of marinewater, and the discharge of surface and subterranean water.Biological samples were collected during four field expeditionsfrom October 1996 to August 1997. Surface circular tows with500-µm-mesh conical plankton nets with a flowmeter weremade during the day. Position, depth, temperature and salinitywere recorded at each sampling station. All fish larvae wereremoved from the samples and identified to the lowest possibletaxon. Ichthyoplankton abundance was normalized to 100 m³ ofwater. The distribution patterns of the carangiid Oligoplitessaurus, the herring Opisthonema oglinum, the dragonet Diplogrammuspauciradiatus and members of the Tetraodontidae were relatedto the wind-driven circulation pattern of the lagoons obtainedusing a numerical model. The analysis of the distribution ofichthyoplankton showed that these species are good indicatorsof the spatial salinity variations controlled by the hydrodynamiccharacteristics of the system. The spatial use of these estuariesas a habitat for fish larvae is therefore strongly influencedby salinity distribution, itself modulated by annual variationof wind stress.     

Feeding ecology of the waterbirds in a tropical mangrove in the southeast Gulf of Mexico

ABSTRACT

Species that exploit the same type of environmental resources are defined as a guild, which have similar needs in the use of food or habitat. It was analyzed the diet of five waterbirds’ offsprings species (Neotropic Cormorant (Nannopterum brasilianus), Reddish Egret (Egretta rufescens), Boat-billed Heron (Cochlearius cochlearius), Snowy Egret (Egretta thula) and Great Egret (Ardea alba)), by prey identification and calculated the relative importance, overlap and breadth diet. The general diet of the piscivorous guild consisted of 17 fish species from 13 genera and eight families. The highest overlap was between the Reddish Egret and Boat-billed Heron. Fish species dominated the diets of all studied waterbirds, Poecilia velifera was the most abundant prey species in each of the birds, suggesting that they are abundant in the wetlands system of northern Yucatan. Diet overlap in waterbirds species depends on the use of resources and feeding habitat. Since reproductive success largely depends on the availability of food resources, mainly of resident or estuarine fishes. The information about diet is important for the conservation of waterbirds.     

Size-selective foraging behaviour of blue crabs,Callinectes sapidus (Rathbun), when feeding on mobile prey: Active and passive components of predation

Size-selective predation by small (30-50 mm carapace width) and large (90-110 mm) Callinectes sapidus when feeding on three different size classes of Litopenaeus setiferus was investigated. Laboratory experiments using no-choice and multiple-choice designs were carried out. Active and passive components of predation were evaluated by comparing the probability of attacking (active) and capturing (passive) shrimp. Small C. sapidus consumed shrimp of all size classes in similar frequencies during multiple and no-choice experiments, and the probability of attacking and capturing shrimp of all size classes was similar. Large crabs consumed large shrimp with a significantly higher frequency during multiple than during no-choice experiments, and the probability of capturing large shrimp was significantly higher than medium and small ones. Results in the present study suggest that size-specific consumption rates of C. sapidus are mainly the result of a passive mechanism associated with the salience of shrimp to predation. However, an active component of foraging behaviour related to the decision to attack an alternative prey whilst consuming one that has already been captured, helps to explain the differences in shrimp consumption between multiple and no-choice experiments. The complex interaction between active, passive components and satiation is discussed.