Total Stomach Contents Research Articles

Diets of invasive channel catfish are subsidized by invasive riparian trees

AbstractRussian olive (Elaeagnus angustifolia) is an invasive, fruit‐bearing riparian tree that dominates riparian zones of the San Juan River in the southwestern United States. Previous research in this river suggests olive fruit is common in diets of invasive channel catfish (Ictalurus punctatus), but its energetic importance is unknown (i.e. critical for catfish fitness vs. incidental consumption). We assessed Russian olive consumption in channel catfish diets bimonthly for 1 year, hypothesizing that olive consumption would be greatest during periods of high olive availability and low benthic aquatic invertebrate availability. We found that catfish consumed olive fruit throughout the year and that olive comprised up to 44% of total stomach contents by mass, with peaks in spring and fall. Regression models revealed the presence and mass of olive fruit in catfish stomachs were positively associated with catfish total length, with a significant interaction between water temperature and river discharge. Catfish were more likely to consume olive fruit during higher flows, regardless of temperature and at low discharge with higher temperature. Contrary to our hypothesis, neither olive nor benthic invertebrate availability were associated with olive presence in channel catfish diets. Nutrition analysis indicated that olive alone was a low‐quality diet item but has the potential to provide a reliable energy source. We used seasonal data to estimate the energetic contribution of olive fruit to catfish populations using a bioenergetic model, which estimated that olive fruit accounted for 35.6% of energy (Joules) consumed by catfish populations and satisfied 38% of their metabolic demand. Our results suggest that Russian olive fruit is a significant subsidy to channel catfish in the San Juan River. However, more research is needed to determine the indirect effects of this interaction on native fishes and ecosystem function.

Mangroves and the Sustainability of Longtail Shad Fish (Tenualosa macroura) in Riau Province Water, Indonesia

Mangroves are crucial to fisheries as nurseries; they can be used as spawning and feeding grounds for fish, including Longtail Shad fish (Tenualosa macroura). The objective of the study was to analyze the mangrove vegetation used as Longtail Shad fish spawning ground. It was carried out from January to May 2021, using a checkered line method with six sampling stations. Each station was placed in three transects with three plots for each transect. Density, relative density, frequency, relative frequency, dominance, relative dominance, and importance value index were included in the vegetation analysis. There were 13 true mangrove types and 1 mangrove associate type at the study locations. The highest mangrove density was found at Station 3 with 3300.48 Ind/Ha, categorized as good. The highest mangrove coverage was found at Station 2, with an exceptionally dense category (76.34%). The regression analysis revealed a substantial relationship between density and mangrove and the water salinity at a 0.002 significance value (<0.05). Based on the gut content analysis in establishing the fish's eating habits, the type of food consumed by the Longtail Shad fish was mostly mangrove litter, representing 44.66% of the total stomach contents. The result of the study clearly shows that mangroves are crucial for Longtail Shad fish. A good mangrove ecosystem will provide good water quality for the migration process of longtail shad fish and produce mangrove litter as fish food. Mangrove ecosystem management can support the management of Terubuk fisheries.

Diet and stomach characteristics of feral piglets (Sus scrofa): Implications for farmed piglets.

Evaluation of the diet of the pig (Sus scrofa) in natural settings may provide new views on diet optimization for growth and development of commercially raised piglets under farm conditions. A field study was conducted to gain insight in the diet and stomach characteristics of feral piglets. Forty animals (body weight: 4.6 ± 1.37 kg) were collected from the Bahía Samborombón (Buenos Aires, Argentina). Stomachs were weighed after storage in formalin and the particle size distribution of their contents was determined by wet sieving. Diet items present in their stomachs were classified and their proportional weight and relative abundance was calculated. Based on their dentition, 5, 16 and 19 piglets were approximately 1, 3-6and 6-16 weeks of agerespectively. Vegetable matter (mainly 'leaves and stems') was predominantly present in 39 animals. It represented on average 83 ± 36.4% of total stomach contents by weight. The stomachs of 12 piglets contained curd and represented on average 16 ± 35.1% by weight. Other diet items were less abundant or absent. The proportion of stomach particles retained were 24%, 13%, 22%, 13% and 28% for sieves with mesh sizes of 2000, 1000, 420, 210 and <210 µmrespectively. For comparison, we used data of farmed piglets of similar age and fed a nutrient-dense, finely ground diet. Feral piglets' relative empty stomach weights increased with age (p < 0.050), whereas this was not the case for farmed piglets. Relative stomach contents weight increased significantly with age only for farmed piglets (p < 0.050). We infer from our data that feral suckling piglets consumed a variety of non-milk items, mainly consisting of vegetable material with a coarse particle size from their first week in life onwards. Their diet is associated with an enhanced stomach development compared to those of farmed piglets.

Çardak Lagünü (Türk Boğazlar Sistemi)’nde bulunan portunid yengeç, Carcinus aestuarii Nardo,1847’nin beslenme ekolojisi

The aim of the present study was to determine the feeding ecology of portunid crab, Carcinus aestuarii in Çardak Lagoon. For this purpose, a total of 533 crab stomachs were analyzed. Stomach contents were examined under a binocular stereomicroscope and 240 (45%) of the stomach samples were recorded as full (containing at least one food item) and 293 (55%) were recorded as empty. The occupancy rates were 25% in 127 stomachs, 50% in 69, and 100% of 44. The main diet of crab individuals was composed of fragments of fish species. Diatoms were the least consumed food by crabs. A total of 8494 diet fragments were found in the stomachs. Total stomach content was 26.39 g of fish vertebrates having the highest weight (3.58 g).

Competition between Invasive Ruffe (Gymnocephalus cernua) and Native Yellow Perch (Perca flavescens) in Experimental Mesocosms

Ruffe (Gymnocephalus cernua) were introduced to North America from Europe in the mid-1980s and based on similar diets and habit use may compete with yellow perch (Perca flavescens). To examine competitive interactions between invasive ruffe and native yellow perch, individually marked perch and ruffe were placed in mesocosms in a small lake. Mesocosms allowed fish to interact and feed on the natural prey populations enclosed. In the first experiment, four treatments were assessed: 28 perch, 14 perch + 14 ruffe, 14 perch, and 7 perch + 7 ruffe. Yellow perch growth was significantly lower in the presence of ruffe (ANOVA, p = 0.005) than in treatments containing only perch. In a second experiment, an increasing density of one species was superimposed upon a constant density of the other in parallel treatment series. Growth rates of both ruffe and perch declined when ruffe density was increased (t test, p = 0.006). However, neither ruffe nor perch growth was affected by increasing perch density. Total stomach content mass of perch was significantly decreased by ruffe in both years (p &lt; 0.02), but no effects of ruffe on the composition of perch diets were observed. Ruffe growth and food consumption was greater than that of perch for both experiments. Ruffe can outcompete yellow perch when both species depend on a limited benthic food resource. Thus there is reason for concern for the ecological effects of ruffe if they expand their range into Lake Erie or North American inland lakes that contain yellow perch.

Acute Effects of Lixisenatide on Energy Intake in Healthy Subjects and Patients with Type 2 Diabetes: Relationship to Gastric Emptying and Intragastric Distribution.

Glucagon-like peptide-1 receptor agonists induce weight loss, which has been suggested to relate to the slowing of gastric emptying (GE). In health, energy intake (EI) is more strongly related to the content of the distal, than the total, stomach. We evaluated the effects of lixisenatide on GE, intragastric distribution, and subsequent EI in 15 healthy participants and 15 patients with type 2 diabetes (T2D). Participants ingested a 75-g glucose drink on two separate occasions, 30 min after lixisenatide (10 mcg) or placebo subcutaneously, in a randomised, double-blind, crossover design. GE and intragastric distribution were measured for 180 min followed by a buffet-style meal, where EI was quantified. Relationships of EI with total, proximal, and distal stomach content were assessed. In both groups, lixisenatide slowed GE markedly, with increased retention in both the proximal (p < 0.001) and distal (p < 0.001) stomach and decreased EI (p < 0.001). EI was not related to the content of the total or proximal stomach but inversely related to the distal stomach at 180 min in health on placebo (r = −0.58, p = 0.03) but not in T2D nor after lixisenatide in either group. In healthy and T2D participants, the reduction in EI by lixisenatide is unrelated to changes in GE/intragastric distribution, consistent with a centrally mediated effect.

Relationships between mercury concentrations in fur and stomach contents of river otter (Lontra canadensis) and mink (Neovison vison) in Northern Alberta Canada and their applications as proxies for environmental factors determining mercury bioavailability

The fur of piscivorous animals such as river otter (Lontra canadensis) and mink (Neovison vison) has been proposed to be used as a biomarker medium to assess mercury (Hg) exposure, but the relationship with dietary and environmental Hg exposure has not been fully characterized. The objective of this study was to investigate the relationship between fur total mercury (THg) and stomach content THg in river otter and mink, and their relationships with environmental factors. THg concentrations were measured in fur and stomach contents of river otter (n = 35) and mink (n = 30) collected from northern Alberta, Canada between 2014 and 2017. The fur THg concentration (mean ± standard deviation) was 6.36 ± 4.12 μg/g fur weight and 5.25 ± 3.50 μg/g fur weight and the average stomach content THg was 0.95 ± 0.56 μg/g dry weight and 0.71 ± 0.54 μg/g dry weight in river otter and mink respectively. There was a positive relationship between the log fur THg and log stomach contents THg for both species (p < 0.05). There was a positive relationship between the log THg of stomach contents and the percent of deciduous forest and a negative relationship with soil pH. There was a positive relationship between the log THg of fur and the total area burned by forest fire and a negative relationship with the percentage of wetlands. These results provide field evidence that fur can be used to reflect dietary Hg exposure and to identify sources and environmental factors that affect the bioavailable Hg in the habitats of these wildlife species.

Gastric evacuation rates in farmed brook trout subjected to a range of feeding conditions fed commercial pellets

A previously parameterized gastric evacuation rate (GER) model of brook trout dStdt=−ρLL1.31St, where St is current stomach mass (g), L is total fish length (cm), t is time (h), and ρL is the rate parameter constant (g0.5 h−1), was extended to describe the effects of dietary energy density E (kJ g−1), temperature T (°C), feed storage conditions (frozen and non-frozen), and the arrival of an additional meal on GER of total stomach contents. The resulting data revealed a considerable effect of E and T while feed storage conditions and the arrival of an additional meal have no effect on GER of brook trout. The GER tends to increase as the energy contents of the diet were reduced. The relationship between GER and the energy contents of diet was described by a power function of E. The GER increased exponentially as the temperature increases to a maximum value at the optimum temperature (c. 18.9 °C) and then declines rapidly. The optimum temperature model adequately described this temperature dependency of the GER at both low and high temperatures. The estimated parameters of E and T were then added to the GER model of brook trout as dStdt=−0.000860L1.31E−0.41e0.08T1−e1.82T−20.6St (g h−1). The model was tested to predict the stomach fullness in brook trout fed for three consecutive days. The predicted values were closely in line with the actual values of stomach fullness (r2 = 0.987). This parameterized model can be used to predict levels of stomach fullness independent of meal size and timing, and should have useful applications in the development of feeding regimes for brook trout.

Influence of Aquatic Macrophytes on Age‐0 Largemouth Bass Growth and Diets

AbstractMacrophyte removal by lakefront property owners occurs on glacial lakes throughout the range of Largemouth Bass Micropterus salmoides, yet little information exists on how it affects recruitment of these fish populations. We hypothesized that with greater prey availability in macrophytes, age‐0 Largemouth Bass consumption and growth would increase. To test this hypothesis, we conducted an in‐lake experiment with age‐0 Largemouth Bass in twelve 9.29‐m2 littoral mesocosms in glacial Chancellor Lake, Michigan, during summer and fall 2014. We removed macrophytes from mesocosm substrates to produce low‐coverage, high‐coverage, and vegetation edge treatments and determined treatment effects on consumption and growth at differing age‐0 Largemouth Bass stocking densities (0.86–2.15 fish/m2). When macrophytes were present, age‐0 Largemouth Bass stomachs contained fewer zooplankton, contained terrestrial invertebrates more often, and contained aquatic macroinvertebrates less often than when macrophytes were absent. Age‐0 Largemouth Bass consumed more fish prey in macrophyte edge and high macrophyte coverage enclosures stocked at moderate densities, resulting in total stomach content biomass increases that increased growth and, potentially, recruitment. Age‐0 Largemouth Bass from enclosures with macrophyte edge and high macrophyte coverage grew 9.7 ± 2.2% (mean ± SD) and 8.3 ± 1.9% longer, respectively, than their counterparts in low macrophyte coverage enclosures; fish in macrophyte edge or high macrophyte coverage treatments at moderate stocking density gained 109.3 ± 45.1% and 110.7 ± 45.0% more weight, respectively, than those in low‐coverage enclosures. These results demonstrate a causal linkage between macrophytes and age‐0 Largemouth Bass consumption and growth in lakes. We recommend that fisheries managers seeking to increase consumption and growth rates in age‐0 Largemouth Bass consider protecting and restoring macrophytes in littoral habitats up to 60% coverage to potentially decrease mortality and improve recruitment.

Mammal predation by an ariid catfish in a dryland river of Western Australia

The presence of the spinifex hopping mouse Notomys alexis in the diet of lesser salmon catfish Neoarius graeffei from the Ashburton River, Western Australia, is reported for the first time. The consumption of terrestrial mammals by Australian freshwater fishes is widely considered to be an infrequent occurrence, of limited importance to aquatic food webs. However, remains of N. alexis were present within the stomachs of 44% of N. graeffei sampled, constituting approximately 95% of the total stomach contents. These findings suggest that N. graeffei will consume large quantities of terrestrial vertebrates when available, and may represent a valuable energy source for this ecologically important species in dryland rivers.

Aquatic pollution increases use of terrestrial prey subsidies by stream fish

Summary Stream food webs are connected with their riparian zones through cross‐ecosystem movements of energy and nutrients. The use and impact of terrestrial subsidies on aquatic consumers is determined in part by in situ biomass of aquatic prey. Thus, stressors such as aquatic pollutants that greatly reduce aquatic secondary production could increase the need for and reliance of stream consumers on terrestrial resource subsidies. To test this hypothesis, we surveyed stream fish, their diets and resource availability in 16 subalpine streams over a regional gradient of trace metals known to strongly impact aquatic insect communities (i.e. fish prey) in the Colorado Rocky Mountains, USA. Fish increased their reliance on terrestrial insect prey as stream metals increased. Relative biomass of terrestrial insects in stomach contents of Brook and Brown Trout increased with respect to aquatic insect biomass and total stomach contents. Drifting insect biomass showed a declining trend for aquatic, but not terrestrial insects, over the metal gradient. Trout densities were unrelated to metal concentrations in streams where we found fish. Synthesis and applications. Our results indicate that diets of aquatic consumers can become more terrestrial as aquatic stressors that limit in situ food production increase and that these subsidies may compensate for loss of aquatic resources. This work implies an important connection between preserving aquatic–terrestrial linkages and management of fish populations in stressed watersheds. Specifically, intact riparian zones and aquatic–terrestrial linkages are likely to be important for maintaining trout production in streams with moderate metal contamination.

Rediscovery of bonnethead shark Sphyrna tiburo after more than two decades of non-record on central coast of Brazil

We report the sighting of bonnethead shark Sphyrna tiburo juveniles <60 cm total length (L T ) after more than two decades of apparent absence in Todos os Santos Bay (Brazilian eastern coast). A total of 8 specimens were collected on the Paraguacu estuary during a Long Term Fish Monitoring Programme. The L T , total body mass and stomach contents are reported. Relevance for nursery areas to this threatened species is also discussed.

Winter diet shift of long-beaked common dolphins (Delphinus capensis) feeding in the sardine run off KwaZulu-Natal, South Africa

Unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run (Sardinops sagax) have been documented in recent years along the coastline of KwaZulu-Natal, South Africa. This study aimed to determine whether variations in the availability of sardine were reflected in the diet and condition of common dolphins (Delphinus capensis) over the past three decades. Stomach contents from 95 common dolphins incidentally caught between 2000 and 2009 were analysed and compared to historical data collected between 1972 and 1992. A shift in the principal prey species consumed by the dolphins was observed over the past 30 years. Prior to 1992, sardine comprised up to 49 % of the total stomach contents by mass, whilst chub mackerel (Scomber japonicus) was the dominant prey recorded in the stomach contents between 2000 and 2009 (66 %). As common dolphins prey on locally abundant fish species, this dietary shift may indicate changes in the availability of the most abundant fish prey. Stable isotope analyses of tooth tissue revealed no significant changes in the δ15N and δ13C isotopic ratios over the past three decades (P = 0.283 for N and P = 0.922 for C). Blubber thickness as a percentage of body length and blubber weight as a percentage of total body weight were assessed as indicators of animal condition. No significant changes in proportional blubber weight or blubber thickness were seen over the last 40 years (1970–2009) for all age cohorts. This species appears to be well adapted to cope with changes in prey species availability, without impacting on body condition.

Temporal feeding habits of the whitemouth croaker Micropogonias furnieri in a shallow coastal lagoon (southwestern Atlantic Ocean, Uruguay)

We analyzed the stomach contents of 2915 individuals of the whitemouth croaker, Micropogonias furnieri, ranging from 15.6 to 42.0 cm total length, collected from a coastal lagoon in Rocha, Uruguay, during 1997–1999. A total of 56% (n = 1646) of individuals were found with content in their stomachs. Six food items were identified and classified as crustaceans (49%), polychaetes (26%), vegetal debris (15%), molluscs, juvenile fishes, and unidentified contents, the latter three representing less than 5% of the total stomach contents. Fishes displayed a higher proportion of stomachs with food between February and August 1998, simultaneous with a low gonadosomatic index and a decrease in water temperature. Crustaceans were the dominant food item from November 1997 to March 1998 and from November to December 1998 (austral summer), whereas polychaetes were predominant from April to October 1998 and from January to February 1999. Availability of polychaetes and their higher frequency of occurrence in the stomachs before the reproductive period could play an important role in the reproduction of the species. Feeding frequency was correlated with length classes. Smaller fishes (&lt;25 cm) preyed on polychaetes and vegetal debris, whereas larger fishes fed mainly on crustaceans and fishes. The temporal feeding habits of M. furnieri in this coastal lagoon showed selective and opportune utilization of prey items according to annual variability in reproductive status and water temperature.

Does the cylinder model of gastric evacuation predict observed evacuation of mixed meals of prey of contrasting geometries in a piscivorous fish?

The simple surface abstraction of the cylinder model (each prey as well as the total stomach contents is considered a cylinder that is gradually reduced by successive peeling off its curved side) was challenged by data on evacuation of a meal composed of three sandeels Ammodytes tobianus and a dab Limanda limanda fed to Atlantic cod Gadus morhua. While the body shape of A. tobianus comes close to that of a cylinder, the flatfish L. limanda takes a discoid form. As opposed to a modified form of the cylinder model, where the contrasting geometries of the fish prey were implemented, the simple, original cylinder model held the potential to predict evacuation of the individual prey types as well as the total stomach contents. Thus, the present study adds significantly to the increasing evidence that points to the generic nature of the model and its implicit square root function. Also, the present study corroborated a basic assumption that the variability of evacuation data not accounted for by the cylinder model primarily can be ascribed to the intraspecific variation in gastric performance of the predator.

Vomit or Flush? Diet analysis using samples from spontaneous regurgitates or the water-off-load technique

Several methods, each with specific advantages and disadvantages, are frequently used to obtain diet samples from seabirds. The collection of regurgitates (REG) as well as samples from the stomach water-off-load (WOL) or flushing technique are some of the most commonly used approaches. During the Austral breeding season of 2005/06 diet samples from Cape Petrel Daption capense and Snow Petrel Pagodroma nivea were collected at Signy Island, South Orkney Islands, Antarctica. Primarily, diet samples were obtained by stomach flushing but occasionally (8 Snow Petrels and 12 Cape Petrels) birds spontaneously regurgitated their stomach contents before flushing. These regurgitates were sampled completely and stored separately. Afterwards the remainder of the bird’s stomach contents was flushed. By doing so, a comparison could then be made between the REG samples and the total stomach contents (REG+WOL). In the REG samples of both species the fraction of fish was underestimated and the fraction of crustaceans overestimated compared to the REG+WOL samples. This study shows that methodology-specific outcomes are potentially to be expected when doing dietary research. Using REG samples is shown not to be suitable for quantitative assessments of the diets of petrels. The WOL technique, which collects the entire stomach content, suits this purpose better.

Natural Food Selectivity Changes with Weights of Nile Tilapia, Oreochromis niloticus (Linnaeus), Reared in Fertilized Earthen Ponds

This work was carried out to study the relationship between fish weight and natural food selectivity of Nile tilapia, Oreochromis niloticus (Linnaeus) reared in earthen ponds without supplementary diet and to guide the adaptation of feeding and fertilization strategies. Fish were stocked (1.5 fish/m2) in four fertilized earthen ponds (0.1 ha) for 6 months. Fifty fish were sampled monthly to estimate individual total weight and length and evaluate stomach contents. Fish specimens were categorized into different weight classes: <25 g, 25–50 g, 50–75 g, 75–100 g, and 100–125 g. Overall, the 50–75 g weight class had the highest degree of stomach fullness. The intestinal length-fish length ratio was similar across all fish weights, ranging from 2.9–3.4. Likewise, the composition of food items found in fish stomach was ranked as phytoplankton > detritus > zooplankton. Phytoplankton contribution to gut content increased with increasing fish weight, while detritus and zooplankton contribution decreased. Zooplankton never exceeded 1% of total stomach contents. Cyanobacteria, Chlorophyceae, Bacillariophyceae and Euglenophyceae mostly represented the phytoplankton. Bacillariophyceae dominated the phytoplanktonic portion of stomach contents at small fish size (<75 g/fish), while Chlorophyceae is the dominant group at large fish size (> 75 g/fish). Fish could select Cyanobacteria and Euglenophyceae at all fish weights, meanwhile Chlorophyceae and Bacillariophyceae were eaten with slight selectivity at larger weights..

A spatial analysis of trophic composition: a case study of hairtail (Trichiurus japonicus) in the East China Sea

The spatial distribution of fish on feeding grounds is an important factor in determining their prey composition. Of the factors that may influence the spatial distribution on the feeding ground and subsequent diet composition is the fish maturation stage. Using hairtail (Trichiurus japonicus) as an example, we evaluated the impacts of gonad development stage on diet composition. Hairtail supports one of the most valuable and largest fisheries in the East China Sea. As one of the top predators, it plays an important role in the ecosystem. We analyzed hairtail stomach samples collected on their feeding grounds from a fisheries-independent survey program in September 2005. Our analyses suggest that females in their third maturity stage tended to feed more intensively. Fish were the most important preys for hairtail, accounting for 72.6% of the total stomach contents in weight. The four most important fish species were juvenile hairtail (25.2%), Japanese scad (11.4%), Japanese jack mackerel (7.7%), and small yellow croaker (5.9%), suggesting strong cannibalism. A cluster analysis suggests that hairtail could be divided into three groups in their spatial distribution based on their diets: one group with similar percentages of fish and crustacean preys mainly distributed in the south of East China Sea far from the coast; one group mainly consuming fish and distributed over the north of East China Sea near the coast; and the third group consuming mainly crustacean species mainly distributed in the open sea. We hypothesize that gonadal development stage of hairtail may determine their movement from spawning ground to feeding ground, and subsequently spatial distribution on the feeding ground, which in turn results in different feeding intensities and prey compositions.

Biological and ecological characterization of the catfish Cathorops melanopus off the west coast of Campeche, Mexico

Cathorops melanopus is the most abundant fish on the west coast of Campeche, Mexico. Its distribution is influenced by water temperature, salinity, and transparency, and it is frequently found in river outlets. To analyze the main biological and ecological patterns of this species, from February 2003 to February 2004 a total of 19,048 specimens were collected using a trawl net at 37 sampling stations along the west coast of Campeche. A subsample was formed of 14,446 randomly selected specimens, and each one was measured and weighed (length range = 35–302 mm, mode = 90 mm; weight range = 0.1–224 g, mode = 6 g). The highest mean abundance values were recorded in May (1.24 ind m–2, 15.31 g m–2, and 12.26 g ind–1), and the lowest in April (0.25 ind m–2, 2.5 g m–2, and 9.9 g ind–1). The parameters of the weight/length model were a = 1 × 10–5 and b = 2.96, with a correlation coefficient of 0.95. The relative condition factor showed a major pulse in July (2.1 × 10–5). The female:male ratio was 1:0.69. Of the 159 females collected, 111 had gonads at maturity stages II and III, and only one was in stage IV. The most common food item was unidentified organic matter, which represented 79% of the total stomach content weight and 92.1% of the encountered food types; the second most abundant food item was crustacean remains (4.8% of the total weight and 10% of the encountered contents). Growth parameters were: L∞ = 317.5 mm, K = 0.45, C = 0.7, WP = 0.16, and t0 = 7.5 × 10–12. Total mortality was 1.22, while natural mortality was 0.65. Recruitment patterns showed a significant pulse between July and August, which together contributed 47.65% of the total number of specimens collected.

Trophic ecology of Greenland halibut (Reinhardtius hippoglossoides) on the Icelandic continental shelf and slope

The feeding habits of Greenland halibut (Reinhardtius hippoglossoides) in Icelandic waters were investigated. In total, 1595 Greenland halibut were collected during the period from May 1991 to March 1992. The main prey species were capelin (Mallotus villosus), eelpouts (Lycodes spp.), northern ambereye (Hymenodora glacialis) and northern shrimp (Pandalus borealis), comprising two-thirds of the total stomach contents by weight. Small crustaceans, mainly euphausiids, were the main prey of the smallest (<20 cm) Greenland halibut, whereas capelin and shrimps dominated the diet of fish 20–59 cm in length. The largest individuals (>80 cm) mainly consumed eelpouts and other relatively large fish. This ontogenetic shift in diet was confirmed by multivariate canonical correspondence analysis (CCA), which explained 6% of the total variation in the diet composition. The CCA further revealed spatial and seasonal effects on the variation in diet. This study indicates that small and medium-sized Greenland halibut (<60 cm) off Iceland are mainly pelagic or semi-pelagic feeders, whereas the largest individuals (>80 cm) seem to feed mainly on or near the bottom.