Frequency Of Empty Stomachs Research Articles

Ecological Observations on Hybrid Populations of European Plethodontid Salamanders, Genus Speleomantes

Speleomantes are the only plethodontid salamanders present in Europe. Multiple studies have been performed to investigate the trophic niche of the eight Speleomantes species, but none of these studies included hybrid populations. For the first time, we studied the trophic niche of five Speleomantes hybrid populations. Each population was surveyed twice in 2020, and stomach flushing was performed on each captured salamander; stomach flushing is a harmless technique that allows stomach contents to be inspected. We also assessed the potential divergence in size and body condition between natural and introduced hybrids, and their parental species. Previously collected data on Speleomantes were included to increase the robustness of these analyses. In only 33 out of 134 sampled hybrid Speleomantes we recognized 81 items belonging to 11 prey categories. The frequency of empty stomachs was higher in females and individuals from natural hybrid populations, whereas the largest number of prey was consumed by males. We compared the total length and body condition of 685 adult salamanders belonging to three types of hybrids and three parental (sub)species. Three group of salamanders (one hybrid and two parental species) showed significantly larger size, whereas no difference in body condition was observed. This study provided novel ecological information on Speleomantes hybrid populations. We also provided insights into the potential divergence between hybrids and parental species in terms of size and body condition. We discuss our findings, and formulate several hypotheses that should be tested in the future.

Fine-scale spatiotemporal variation in juvenile Chinook Salmon distribution, diet and growth in an oceanographically heterogeneous region

The existence of fine-scale structure in the abiotic and biotic characteristics of pelagic habitats is widely recognized, but the ecological significance of that structure is understudied. Logistical considerations have meant that research on the ecology of commercially and ecologically important marine species generally occurs at relatively coarse spatial and temporal scales. Many populations of Chinook Salmon (Oncorhynchus tshawytscha) in the Northeast Pacific are currently experiencing low productivity. The hypothesis that survival, and hence recruitment, of Chinook Salmon is related to growth early in marine residence has led to intensive research on the trophic ecology of this species during the first year at sea. We employed a small vessel-based methodology to simultaneously characterize fine-scale spatial and temporal variation in physical and biological oceanography, and juvenile Chinook Salmon distribution, size, diet, temperature exposure, and growth from July through October at five sites within the Southern Gulf Islands of the Salish Sea. Densities of zooplankton prey of Chinook Salmon declined to very low levels by the end of the study period. Juvenile Chinook Salmon stomach fullness and growth also declined by early fall while frequency of empty stomachs and importance of fish in diets increased. We found that both oceanographic conditions and trophic ecology of juvenile Chinook Salmon varied among sites only a few (2–23) kilometers apart. Juvenile Chinook Salmon were larger and faster growing at sites where fish (generally Pacific Herring Clupea pallasii) constituted a larger proportion of the diet. Overall, the most important prey of juvenile Chinook Salmon by mass proportion (25.6%) was Pacific Herring; however, only 8.4% of individuals contained C. pallasii. Analysis of co-occurrence of diet items suggested alternate foraging strategies, with some individuals specializing on Pacific Herring while others targeted a variety of small crustacean zooplankton. Juvenile Chinook Salmon which had consumed Pacific Herring had greater mean stomach fullness than those which had not. Predation on Pacific Herring was strongly related to juvenile salmon length, suggesting that age-0 Pacific Herring may have been too large to be consumed by smaller Chinook Salmon. Our results reinforce the importance of the transition to piscivory in the trophic ecology of juvenile Chinook Salmon. Further research is necessary to determine if fine-scale distribution of larger, piscivorous juvenile salmon is linked to the distribution of their forage fish prey and to understand the role of prey to predator size ratios in limiting the ability of juvenile salmon to transition to piscivory.

Which processes are behind the relationship between species abundance and environmental suitability? Monte Albo cave salamander as model species

Species can show a strong variation of local abundance across their ranges. Recent analyses suggested that variation in abundance can be related to environmental suitability, as the highest abundances are often observed in populations living in the most suitable areas. However, there is limited information on the mechanisms through which variation in environmental suitability determines abundance. We analyzed populations of the microendemic Monte Albo cave salamander Hydromantes (Speleomantes) flavus Stefani, 1969 (Plethodontidae), and tested several hypotheses on potential relationships linking environmental suitability to population parameters. For multiple populations across the whole species range, we assessed suitability using species distribution models and measured density, activity level, food intake, and body condition index. In high-suitability sites, the density of salamanders was up to 30 times higher than in the least suitable ones. Variation in activity levels and population performance can explain such variation of abundance. In high-suitability sites, salamanders were active close to the surface and showed a low frequency of empty stomachs. Furthermore, when taking into account seasonal variation, body condition was better in the most suitable sites. Our results show that the strong relationship between environmental suitability and population abundance can be mediated by the variation of parameters strongly linked to individual performance and fitness. Furthermore, we highlighted the potential use of cave animals as model species to answer macroecological questions.

Do drifting and anchored Fish Aggregating Devices (FADs) similarly influence tuna feeding habits? A case study from the western Indian Ocean

Anchored and drifting Fish Aggregating Devices (FADs) are intensively used in tropical tuna fisheries. In both small-scale and industrial fisheries, skipjack ( Katsuwonus pelamis) and yellowfin tuna ( Thunnus albacares) are the main targets. The increasing development of this fishing practice by industrial purse seiners has raised the question of the impact of FADs on tuna communities, as they might act as an ecological trap. This study investigated the feeding habits of skipjack and yellowfin tuna associated with anchored and drifting FADs in the western Indian Ocean. The diet of 352 tunas was analysed taking into account the type of FAD, ontogenetic variations, and the resources richness of the area. Poor-food and rich-food areas were defined according to the abundance of stomatopod Natosquilla investigatoris, the main prey of tunas, on the fishing sites. Diet composition was expressed through functional groups of prey. Significant dietary differences were found between both FAD types, as well as an effect of individual size. Around anchored FADs tuna preyed on diverse assemblages of coastal fish and crustacean larvae and juveniles, whereas a low diversity of epipelagic prey dominated the tuna diet associated with drifting FAD. Compared to anchored FADs, the frequency of empty stomachs was significantly higher and the stomach content mass significantly lower among skipjack and small yellowfin tunas caught around drifting FADs. This was magnified in poor-food areas, where drifting FADs often evolved, suggesting that these FADs could negatively impact the growth of skipjack and small yellowfin tuna. Larger yellowfin tuna exhibited differences in their dietary habits between anchored and drifting FADs, and between poor-food and rich-food areas. However, drifting FADs did not impact them as strongly as juveniles of yellowfin or skipjack tunas. Our study gives new highlights on possible detrimental effects of FAD on tunas, and this has to be considered in future sustainable management strategies of tuna fisheries.

Effects of Striped Bass Stocking on Largemouth Bass and Spotted Bass in Lewis Smith Lake, Alabama

AbstractIntroductions of striped bass Morone saxatilis into U.S. reservoirs have caused concern among anglers that target other species owing to the perception that this predator reduces the number of other sport fish and can limit available prey supplies. Recently, this controversy arose in Lewis Smith Lake (8,583 ha), Alabama, prompting this study to examine the effects of stocking striped bass on the resident population of black bass Micropterus spp. From October 2006 to August 2007, the diets of striped bass, largemouth bass M. salmoides, and spotted bass M. punctulatus were examined in this reservoir. The density and biomass of striped bass and black bass were computed from estimates of age‐0 black bass abundance, striped bass stocking rates, growth, and survival. Bioenergetics models were used to estimate striped bass and black bass consumptive food demands. Striped bass diets (by weight) were dominated by shad Dorosoma spp. (64%), followed by crayfish Oronectes spp. (12%), while black bass and sunfish Lepomis and crappies Pomoxis spp. comprised 5% and 6% of the diet, respectively. Numerically, sunfish–crappies and black bass only comprised 0.28% and 0.16% of the diets of striped bass. The diets of largemouth bass and spotted bass (by weight) were dominated by crayfish (72% and 75%, respectively) and sunfish–crappies (21% and 9%, respectively), while shad comprised 6% and 14% of the diets, respectively. Diet overlap values between striped bass and black bass were generally low but varied seasonally among species. The highest overlap between the diets of striped bass and black bass was observed in April and June. However, the relative weights of black bass did not decline or the frequency of empty stomachs among these species did not increase during or after this time. Overall, consumptive prey demand was similar between striped bass and black bass. Bioenergetics modeling estimated striped bass consumption of shad, bass–sunfish–crappies, and crayfish averaging 14, 3, and 5 kg/ha, respectively, compared with 3, 6, and 16 kg/ha, respectively, for black bass. Shad consumption by striped bass and black bass (relative to the total annual supply) was within acceptable levels. Striped bass consumption of black bass was low, striped bass and black bass partitioned prey resources, and the temporal differences in maximum consumptive demand varied between black bass and striped bass. Thus, we found that the impact of striped bass stocking on the black bass population was minimal.

Temporal and size‐related changes in the frequency of empty stomachs in smelt

The frequency of empty stomachs (FES) of 3290 smelt Osmerus eperlanus was analysed during winter and two growing seasons. Variations in FES showed that smelt is a daytime feeder and feeding activity is low during the hours of darkness and also during the winter under ice cover. The results suggested further that the diet shifts of smelt are not permanent until the onset of piscivory.

Recent changes in the winter diet of murres (Uria spp.) in coastal Newfoundland waters

We investigated the winter diet of murres (Uria spp.) in coastal Newfoundland waters in relation to environmental and ecological changes that have occurred in the Northwest Atlantic since the 1980s. We analyzed the contents of 371 stomachs (311 from Thick-billed Murres, Uria lomvia, and 60 from Common Murres, Uria aalge) of birds shot by hunters around the Newfoundland coast during the winters of 1996-1998. We observed that the frequency of empty stomachs was greater in our study than in a similar study conducted during 1984-1986. We found no difference in the proportion of fish in the diet between the 1980s and the 1990s, however, Arctic cod (Boreogadus saida; from 55 to 12%) and capelin (Mallotus villosus; from 28 to 6%) decreased in frequency of occurrence. The proportion of stomachs containing crustaceans and squid did not change between the 1980s and 1990s, but hyperiid amphipods (Parathemisto spp.) replaced euphausiids (Thysanoessa spp.) as the predominant crustacean. Changes in murre winter diet off the coast of Newfoundland corroborate other sources of information indicating that major changes in the distribution and biology of marine organisms occurred in the Northwest Atlantic during the 1990s.

Diel Feeding Habits of Sockeye and Chum Salmon in the Bering Sea during the Summer.

Diel feeding habits of sockeye salmon Oncorhynchus nerka and chum salmon O. keta in the Bering Sea during the summer were investigated by four parameters: the frequency of empty stomachs, stomach content weight, digestion stage, and pH of the inner wall of the blind sac in the stomach. Stomach samples were obtained at various times of day from gillnet surveys. Sockeye and chum salmon exhibited similar diel feeding patterns, although each of the four parameters of sockeye salmon fluctuated more distinctly than in chum salmon. Based on the present results together with previous knowledge, it is hypothesized that the two species obtain metabolic energy in different ways; sockeye salmon feed on more nutritious food organisms than chum salmon, but are inferior to chum salmon in digestion abilities. Chum salmon can utilize peculiar or poorly nutritious food organisms such as jellyfish, on which other salmonid fish seldom feed, with the help of physiologically and morphologically greater digestion abilities.

The Food of the Pike, Esox lucius, in Heming Lake, Manitoba

The stomach contents of 29,477 northern pike (Esox lucius) captured mainly in gill nets at Heming Lake, Manitoba, between 1950 and 1962 were examined. The food consisted almost exclusively of fish: trout-perch (Percopsis omiscomaycus) and yellow perch (Perca flavescens). Other fish included common suckers (Catostomus commersoni), spottail shiners (Notropis hudsonius), sticklebacks (Eucalia inconstans and Pungitius pungitius), pike, burbot (Lota lota), whitefish (Coregonus clupeaformis), tullibee (Leucichthys sp.), yellow walleye (Stizostedion vitreum), cottid (Cottus cognatus), and darters (Etheostoma nigrum). Among invertebrates were crayfish, mayflies, dragonflies, caddisflies, and leeches. Ducks, small mammals, and frogs formed an insignificant part of the diet. Seasonal variation in food content and annual variation in the degree of feeding were evident. Trout-perch were important as food items in May and June, the spottail shiner in July, the yellow perch in August and September, and stickleback between October and March. Coregonine fishes, important in the life-cycle of Triaenophorus crassus but of minor importance as pike food, occurred in higher concentrations in October. There appeared to be annual differences in the degree of feeding, possibly related to differences in temperature. The frequency of empty stomachs from pike caught by angling and in gill nets was approximately the same. No obvious differences were noted in feeding habits of male and female pike, but there were some minor differences in the food of pike from shallow and deeper water habitats. Over an 11-year period of intensive fishing, there did not appear to be any unusual changes in the food habits of pike. The size of the prey is related to the size of the pike. There is a marked increase in the number of small perch, trout-perch, and spottail shiners consumed by pike of increasing size. The possible effects of the predator (pike) on other prey species is discussed. Relative abundance and seasonal availability appeared to determine the incidence of prey consumed. The reduction in the average size of the pike appears to have had some effect on the survival of other species of fish.