Total Stomach Contents Research Articles

Summer feeding habits of the Pacific pomfret Brama japonica in the transitional and subarctic waters of the central North Pacific

Feeding habits of the Pacific pomfret Brama japonica, ranging from 30 to 40 cm in standard length, were quantitatively evaluated using the index of relative importance and were compared between the transitional domain and subarctic region in the central North Pacific. In the transitional domain (between the subarctic boundary and the subarctic front), this species fed mainly on subarctic and transitional‐water gonatid squids such as Berryteuthis anonychus, Gonatus middendorffi and Gonatopsis borealis, the transitional‐water squid Onychoteuthis borealijaponica, and a subtropical and transitional‐water amphipod, Phronima sedentaria. These prey items accounted for 52·8% by wet mass of total stomach contents. In the subarctic region (north of the subarctic front), Pacific pomfrets preyed primarily on subarctic and transitional‐water squids, such as B. anonychus and G. middendorffi, and secondarily on subarctic amphipods such as Hyperia medusarum and Hyperia glaba. These four prey items comprised 71·6% by mass of total stomach contents. Major transitional domain prey items, such as G. borealis, O. borealijaponica and P. sedentaria, were almost non‐existent in stomachs of fish from the subarctic region. The mean wet stomach content mass expressed as a percentage of body mass was significantly higher in the subarctic region (2·35%) than in the transitional domain (0·75%), suggesting that, for this fish, prey items are more readily available in the subarctic region during summer and their northward migration is a feeding migration. Feeding strategy of the Pacific pomfret was discussed in relation to their seasonal south‐north migration.

Diets of herring, mackerel, and blue whiting in the Norwegian Sea in relation to Calanus finmarchicus distribution and temperature conditions

Abstract Diets of Norwegian spring-spawning herring, mackerel, and blue whiting in the Norwegian Sea are investigated in relation to the distribution of plankton and hydrographic conditions. Fish stomachs and zooplankton samples were collected during summer (June and July) cruises in 2001 and 2002. Calanus finmarchicus was the principal prey of mackerel, accounting for 53–98% of total stomach content by weight. The diet composition of herring varied depending on feeding area and availability of food under various environmental conditions. C. finmarchicus was important prey for herring only in July 2001 (about 77% by weight) in the central part of the sea and in June 2002 (about 82% by weight) near the Lofotens. In July 2002 appendicularians (Oikopleura spp.), amphipods (mainly Parathemisto abissorum), and euphausiids were important in the diet of herring, and at some stations cannibalism was observed. The main prey of blue whiting were amphipods (10–34% by weight), appendicularians (11–34%), and euphausiids (8–47%), as they usually feed deep in the water column, though C. finmarchicus was important, particularly in June 2002, when blue whiting were caught in the upper layers of the sea. Higher water temperatures indirectly affect pelagic fish through accelerated development of their prey and favourable conditions for migration farther north.

Mechanistic modelling of gastric evacuation in predatory gadoids applying the square root model to describe surface‐dependent evacuation

A new model approach to gastric evacuation in predatory fishes was shown to give accurate and reliable estimates of evacuation. It is believed that such a model would prove particularly useful in understanding predator‐prey interactions in natural systems. The model is a simple, geometric abstraction of the square root model predicting that evacuation time is proportional to the square root of meal size in accordance with extensive empirical evidence. Digestive processes are assumed to be restricted to an outer surface of total stomach content that is represented by the curved side of a cylinder. This way, total stomach content is considered a cylinder of constant length the mass of which is gradually reduced by successive peeling off its side leaving the ends unaffected. The fundamental rate δ describes mean thickness of the layer that is peeled off the cylinder per time unit. In the model, δ is constant independent of cylinder thickness but inversely proportional to the square root of cylinder length. Anatomical and dynamic characteristics of the stomach render this formulation of δ plausible. Using mean evacuation rate over time during evacuation of a meal, the model disregards prey heterogeneities that influence instantaneous evacuation rate. Relationships between prey heterogeneities and evacuation patterns were indicated by application of a general power model to evacuation data, and it was suggested how the effects of prey characteristics might be incorporated into the square root model to produce a generic model of gastric evacuation.

Comparative Ecology Of The African Bony Tongue Fish <i>Heterotis Niloticus</i> And The Catfish, <i>Clarias Gariepinus</i> In The Lower Oluwa River And Adjacent Floodplains

The ecology of sympatric African bony tongue fish, Heterotis niloticus and the catfish, Clarias gariepinus were compared during the dry and rainy conditions in the lower Oluwa River and its adjacent floodplains. Both species are common economic fish in Nigeria. There was no significant difference in the mean sizes of H. niloticus and C.gariepinus from the samples collected during the rainy season and the dry season. The river channels had the least number of the sampled species for both fish under study. Approximately 65% of the H. niloticus that were collected inhabited the Mahin floodplains while 74% of C. gariepinus were found in the same habitat. During the rainy season, most of the Heterotis caught were juveniles in the middle floodplains while juveniles of Clarias were caught in the upper floodplains. Phytoplankton accounted for over 62.53% of the total stomach contents of H.niloticus using the frequency of occurrence method, while fish parts constituted the highest percentage of components of C.gariepinus (16.62%). By volumetric method, plant materials formed the bulk of the 29.55% of food items observed in H.niloticus while fish parts also formed the highest portion of the diets (25.56%) in C.gariepinus. Fish population of both species were high in all the locations of the study area, however analysis of the preponderance of male to female during the two seasons of the year shows that there were more females to males during the rainy season for both species. Key words: ecology, Heterotis niloticus, Clarias gariepinus, Oluwa River, floodplains Ife Journal of Science Vol. 7(1) 2005: 15-20

Feeding habits of albacore Thunnus alalunga in the transition region of the central North Pacific

The feeding habits of albacore Thunnus alalunga (fork length: 48.9-76.2 cm, n=132) were examined from late spring to early autumn in relation to its northward migration in the transition region between the subtropical and subarctic fronts in the central North Pacific. Samples were collected at night using surface gill nets or during daytime pole-and-line surveys in 2001 and 2002. During May and June, albacore fed mainly on Japanese anchovy Engraulis japonicus, which accounted for 27.2%, 67.0%, and 45.5% of the total stomach contents by number (Cn), wet weight (WW), and frequency of occurrence (F), respectively, and secondarily on the subarctic gonatid squid Gonatopsis borealis (Cn, 15.8%; WW, 10.8%; F, 28.8%). From July to September, albacore continued to depend on Japanese anchovy (Cn, 48.2-52.8%; WW, 79.9-95.2%; F, 27.8-85.4%). These results corresponded well with the remarkable rebound of the Japanese anchovy stock since the 1990s. Gonatopsis borealis, the main squid prey from May to June, almost disappeared from the stomachs of albacore from July to September, probably due to the northward migration of this squid to subarctic waters in summer. The feeding impact of albacore on the Japanese anchovy stock in the transition region was conservatively estimated to be from 1400 to 2100 tons per day from late spring to early autumn.

Digestive enzyme activity and food ingesta in juvenile shrimpLitopenaeus vannamei(Boone, 1931) as a function of body weight

A study was conducted to evaluate variations of digestive enzyme activities in Litopenaeus vannamei (Boone) reared in commercial ponds under semi-intensive conditions. Shrimp were collected at each body weight increase of 2 g. As the shrimp grew (2–12 g), significant increases in the activities of lipase and chymotrypsin were observed. The total protease activity decreased from 6 g onwards. Trypsin activity showed a peak at 6 g and amylase activity increased two-fold after 2 g. Additionally, the stomach contents were analysed microscopically for shrimp between 2 and 10 g. Plant matter contributed above 30% of the total stomach content in 6-, 8- and 10-g shrimp. Detritus represented 58% and 62% of the total stomach content in 2- and 4-g shrimp, respectively, decreasing to 33–43% at greater shrimp weights. Artificial feed showed a maximum contribution of 20% in 6-g shrimp. The present results show changes in the enzyme activity after the shrimp reach 6 g in body weight, evidenced by a decrease in total protease and an increase in lipase and amylase activities. The amylase/protease ratio was 2.6 in 2-g shrimp and increased steadily to 9.6 in 12-g shrimp. These findings suggest an adaptation of the enzymatic activity to diets with lower protein content as body weight increases, and may be related to the variation of the different items found in the stomach.

Comparison of stomach contents of haddock (Melanogrammus aeglefinus) from the 1981 and 1991 North Sea International Stomach Sampling Projects

This study analyses data from over 20 000 haddock stomachs collected during the 1981 and 1991 Stomach Sampling Projects of the North Sea. Sampling was within the framework of the Multispecies Virtual Population Analysis (MSVPA) for fisheries stock assessment. In 1981 stomachs were collected to calculate input feeding parameters from main predators. During 1991 the sampling exercise was repeated to test stability of the parameters in the region. We investigate stability of haddock stomach content weight between years accounting for ontogenic, spatial and temporal variations within the scope of the survey resolution. Analysis using generalized linear and additive models is performed for weight of the stomach content including and excluding empty stomachs and also for proportion of stomachs without food. Results indicate that haddock stomach contents varied significantly between years, quarters and North Sea roundfish areas. Content weights were overall higher in 1981 than in 1991. In 1981 levels were high from spring to fall and in 1991 mostly in spring. During both years levels were lowest in the central North Sea and in winter. Most of the deviance in modelling the stomach weight is explained by the length of the predator. Stomachs sampled in 1981 were most frequently empty in spring and those sampled in 1991 in winter. In both years, proportions decreased with fish length except in winter when levels increased. Proportion of empty stomachs was highest in the central region of the North Sea. Most of the proportion variation is explained by quarterly fluctuation. Variation of content weight can be related to prey composition found in the stomachs. High stomach contents are generally associated with high contribution of fish prey to the total stomach content, mainly sandeels. We propose that sandeels were more vulnerable to predation in 1981 than in 1991 due to colder temperatures.

Changes in piscivory associated with fishing induced changes to the finfish community on Georges Bank

There are many ecologically and commercially important piscivores in the Georges Bank fish community. There has been a noticeable shift in the abundance of these predators during the last four decades which is generally attributed to fishing pressure. Although many fish persist as piscivores in this system, not only has their relative abundance changed but their size composition has also changed. Both factors influence the total magnitude of piscivory by these fish. To ascertain the cascading effects of fishing on fish predation, we examined relative abundance, total stomach contents, diet composition, consumption rates, and total food consumption of fish for several species across the time period. The proportion of the diet comprised by fish for piscivores on Georges Bank has remained remarkably consistent. However, the composition of specific fish prey has changed across the time series. Total fish consumption generally tracked predator abundance, but two species demonstrated compensating consumption rates as larger size classes declined. Contrary to our initial hypothesis, total fish consumption by six major predators has remained generally constant despite changes in predator size, structure and abundance. One reason for constant systemic piscivory is the dominant piscivore in this ecosystem has shifted from cod to spiny dogfish. We assert that a major effect of intense fishing pressure is a shift in energy flow for marine ecosystems.

Weighting and smoothing of stomach content data as input for MSVPA with particular reference to the Barents Sea

Multispecies Virtual Population Analysis (MSVPA) is based on parameterization of the average relative food compositions for all possible prey-age predator-age combinations in the model by year and quarter. This sets high demands on stomach sampling programmes in terms of spatial coverage of the predator population and of sampling intensity for individual cohorts. In practice, there are many sources of error in the input data and large variances, which call for a smoothing procedure to avoid outliers in the MSVPA output. We investigate the potential of geostatistics (specifically kriging) in improving (1) estimates of total and partial stomach content weights from spatially non-uniformly distributed samples and (2) smoothing of the average stomach content weights over the two-dimensional input array of predator age and years. The examples shown indicate that kriging provides an efficient method to deal with geographical variability in food composition and predator abundance as well as to fill gaps and make extrapolations within a two-dimensional array in temporal space characterized by many empty cells or cells not sufficiently well sampled.

The role of iceberg scours in niche separation within the Antarctic fish genus Trematomus

Species of the Antarctic fish genus Trematomus occupy different trophic niches. It is not clear, however, whether small-scale variability in benthic community structure affects niche separation. Therefore abundance and biomass of fish were determined and stomach content and food composition were compared in areas affected by iceberg scours and unaffected areas in the Weddell Sea. Trematomus eulepidotus, T. lepidorhinus and T. scotti dominate undisturbed areas, whereas T. nicolai and especially T. pennellii dominate disturbed areas. Total stomach content and number of prey taxa per fish are higher in preferred than in non-preferred areas. These findings indicate that small-scale horizontal patterns caused by iceberg scours play a distinct role in Trematomus niche separation.

Diet of blue marlin Makaira mazara off the coast of Cabo San Lucas, Baja California Sur, Mexico

Analysis of the stomach contents of 204 blue marlin ( Makaira mazara) caught by the sport-fishing fleet of Cabo San Lucas in the southern Gulf of California is presented. The specimens sampled were caught during the summer and fall of 1987, 1988, and 1989 when the sea is warm (28–30°C). Blue marlin were found to feed on 35 prey species, 3 of which represented 90% of the total stomach contents by frequency of occurrence. The main prey were epipelagic organisms from the oceanic zone and demersal fishes from the neritic zone. The most important prey were bullet mackerel Auxis spp., young finescale triggerfish Balistes polylepis, and the giant squid Dosidicus gigas.

Food Habits of the Chinese Stripe-Necked Turtle, Ocadia sinensis, in the Keelung River, Northern Taiwan

-Stomach contents from 186 Ocadia sinensis collected from the Keelung River, northern Taiwan, between July 1995 and April 1997 were examined. Diet composition varied by sex. Females shifted from an omnivorous to a herbivorous diet as they grew, and they consumed more plant material compared to males. Volumetrically, plant matter represented 87.7% of the total stomach contents in females, whereas it only constituted 39.5% in males. Seasonal differences in diets were also found. Animal matter contributed more to cool season diets. Females, especially, tended to take plants in much greater proportion in the warm season (94.8% in volume) compared to the cool season (50.9%). In males, animal matter occupied 54.4% and 71.1% of the total volume of stomach contents both in the warm and cool season, respectively. The percentage of empty stomachs was greater in the cool season (41.2%) than in the warm season (13.3%). The Chinese stripe-necked turtle (Ocadia sinensis) is reported to be largely herbivorous, feeding mainly on plant material both in nature and in captivity (Smith, 1923; Horikawa, 1934; Ernst and Barbour, 1989). Although 0. sinensis is abundant and widespread in rivers, ponds, and lakes of Taiwan (Pope, 1935; Mao, 1971), its life history is poorly known. Until recently, little has been published dealing with its taxonomy and ecology (McCord and Iverson, 1992; 1994; Chen and Lue, 1998). Knowledge of the food habits of a given species may provide insights into the links between animals and their environments. Many studies on turtles have described resource partitioning in terms of food, space, time, or their interaction (see Toft [1985] for review). Morphometrics and growth rates often are associated with feeding niches (Berry, 1975), and dietary shifts with body size have been documented for several turtles (Clark and Gibbons, 1969; Moll, 1976; Georges, 1982; Hart, 1983). As ectothermic organisms, the foraging behavior and diet composition of turtles may also be affected by seasonal changes of ambient temperature and food availability (Parmenter and Avery, 1990; Lagueuex et al., 1995). In this study, we provide data on the dietary habits of 0. sinensis, and examine intersexual, ontogenetic, and seasonal variation in the composition of the food consumed. MATERIALS AND METHODS Study Area-We collected turtles from a 3.5km stretch of the midstream of the Keelung Riv2 Present Address: National Museum of Marine Science and Technology-Preparatory Office, P.O. Box 7202, Keelung 202, Taiwan, Republic of China. er (121?41'E, 2506'N), at 4-6 m elevation. The river in the study area is narrow, meandering, and sluggish, with a width of about 25 m and depth of approximately 1.5 m (Fig. 1). The river bottom mainly consists of silt and sand. The water is usually turbid. Both banks of the river are covered mostly with cultivated bamboo shrubs. Riparian vegetation consists primarily of exotic perennial grasses (including Brachiaria mutica and Pennisetum purpureum). Some non-grass herbaceous plants, including Murdannia keisak (Commelinaceae), Ludwigia octovalvis (Onagraceae), Seigesbeckia orientalis, Elipta prostrata (Compositae), and some species of Polygonaceae, occasionally grow on both banks. Few typically aquatic plants exist in this area. Only some filamentous algae and Lemna aequinoctialis (Lemnaceae) appear in early summer. The average monthly temperature in the warm season (May-November) was 25.4 C (range: 20.5-28.5 C) and 17.1 C (15.2-20.6 C) in the cool season (December-April). According to data collected by the Environmental Protection Administration, average water temperature also changes seasonally, from 20.0-31.4 C in the warm months to 14.5-18.9 C in the cool months. Precipitation is distinctly seasonal, with an average of 218 mm of rain per month during April-August, although typhoons may bring heavy rain in the course of a few days. A total of 320 mm of rain falls per month during the rest of the year (Fig. 2). Discharge in this area was highly variable, with 7.71-20.16 m3/sec during April-August and 25.34-46.76 m3/sec during September-March. In the cool season, changes in water level often result in the inundation of bank vegetation. The water quality in the midstream of the Keelung River was graded This content downloaded from 207.46.13.93 on Tue, 02 Aug 2016 05:30:31 UTC All use subject to http://about.jstor.org/terms T.-H. CHEN AND K.-Y. LUE FIG. 1. Representative view of the study site of Ocadia sinensis in the Keelung River, northern Taiwan. as medium-polluted by organic sewage discharged from the nearby area. Methods-Our study was conducted during both the warm and cool seasons, July-December 1995, February-May 1996, and March-April 1997. Turtles were collected with funnel traps baited with canned cat food, with a long-handled dipnet, or by hand while patrolling along the banks. The bait was enclosed in a wire cage

Stochastic stomach theory of fish: an introduction

Fish stomach dynamics is discussed and introduced analytically by a simple individually-based stomach model for total stomach content. The predator encounters food (meals) in a Poisson process, starting to search for a new meal when the stomach is empty. Basic equations for the frequency distributions of stomach content are derived for general classes of meal-size distributions and rate models of gastric evacuation. Probability characteristics in steady-state of empty and non-empty stomachs are evaluated from first principles with particular attention to the square root rate model of gastric evacuation. The average rate of food consumption and the functional response are derived from simple renewal theory and from obtaining the average of the gastric evacuation rates. Effects of meal size biased stomach sampling are introduced. As a primer on modelling the stomach content of piscivorous fish, the model is discussed in relation to the empirical distribution of the individual stomach content for more than 4000 North Sea whiting in the length range 20–30 cm. Implications of identical meals and variable meal sizes, exemplified by the log-normal distribution, are considered. Estimated average meal searching time and meal size as well as the average rate of food consumption decrease considerably in the more realistic case of variable meal sizes. The model is able to account for the high frequency of empty stomachs, which occurs simultaneously with a relatively high observed mean stomach content. Need and direction for further developments of fish stomach theory are discussed.

A technique using sequential feedings of different coloured foods to determine food intake by individual rainbow trout, Oncorhynchus mykiss: effect of feeding level

Sequential meals do not mix to any extent in the stomach of rainbow trout. This observation was used to develop a technique to measure food intake by individual fish based on the consumption of sequential meals consisting of different coloured foods [brown (natural coloured food), red (carmine added) or green (chromic oxide added)]. The method was evaluated by examining the effect of underfeeding, feeding to satiety or overfeeding on food intake by individual rainbow trout, Oncorhynchus mykiss, raised in groups. Fish were fasted overnight and fed the test meal at 50, 75, 100 or 133% of predicted satiety for the group as a whole. Following feeding, fish were killed and stomach contents were separated by colour and quantitated by weighing. In fish fasted for 16 h prior to consuming the test meal, almost 1 3 of the total stomach contents were residual contents. Increasing the amount of food provided in the test meal increased the level of consumption, but did not alter the variability between fish within the tank. There was no apparent relationship between body weight and food consumption. This method provides an easy and objective means to quantitate intake of several sequential meals by individual fish.

Somatostatin, Gastrin-Releasing Peptide and Gastrin in the Stomach of Rats with Streptozotocin-Induced Diabetes and Insulinoma

Somatostatin, gastrin-releasing peptide (GRP) and gastrin were measured in the stomach of rats with streptozotocin-induced diabetes, insulinoma-bearing rats and their respective controls. Rats injected with streptozotocin exhibited hyperphagia, insulinopenia and severe hyperglycemia. Stomach weights, and the concentrations and total amounts of GRP and gastrin in the stomach, were similar to nondiabetic control rats. The concentration of somatostatin in the stomach of diabetic rats was 25% greater, but the total stomach content of somatostatin was similar to that of control rats. Insulinoma-bearing rats exhibited hyperphagia, hyperinsulinemia and hypoglycemia. Concentrations of GRP and gastrin in the stomach were 72% and 19% lower, respectively, than in control rats. Despite 45% greater stomach weight, the total stomach content of GRP was 61% lower. Stomach concentrations of somatostatin, and total stomach contents of somatostatin and gastrin, were similar in insulinoma-bearing and control rats. The results demonstrate abnormalities in the stomach concentrations of regulatory peptides in rats with diabetes and insulinoma. These abnormalities are not attributable to changes in food intake alone, suggesting specific effects of these metabolic diseases on gastric regulatory peptides and gastric function.

Notes: A Multiple-Regression Technique for Analyzing Stomach Contents in Fish

We developed a multiple-regression model for estimating the weight contribution of prey taxa in fish diets. In this method, the counts of prey items are regressed against the total stomach content weight for individual fish in order to estimate the mean weight per individual prey item. Estimates obtained by this method were comparable to those obtained by direct measurement of the weights of individual prey items within each stomach. The multiple-regression method substantially reduced processing time by eliminating the need to sort and weigh individual prey items. Reductions in the labor required to process each stomach allow the investigator to examine a fixed number of fish at lower cost or to examine more fish during a fixed time.

Stomach evacuation rate in the planktivorous Antarctic fish Pagothenia borchgrevinki

Specimens of the Antarctic fish Pagothenia borchgrevinki were collected from just below the sea-ice in McMurdo Sound over the period 5–16 November 1987. The stomach contents of 54 freshly captured fish were analysed and showed very strong similarities with an earlier, more extensive, dietary analysis conducted at the same location (Foster et al. 1987). There was as much variation in stomach contents from fish within a school, as there was between schools, contrary to the expectation that fish within a school would have shared a more common feeding history. Fish were maintained in holding tanks for up to 48 h after capture; groups were sacrificed at 6 h intervals and the stomach contents analysed to determine evacuation rates. Evacuation rates of total stomach contents and individual prey species were fitted with an exponential model of decay. The exponential time constant for decay of stomach contents was 32 h (Table 2), while time constants for individual prey species ranged from 12 h for small prey species to 49 h for the larger crustacea. The feeding rate of P. borchgrevinki on important prey species was calculated from the above data (Table 2). Low feeding rates, and the low numbers of P. borchgrevinki argue against removal by predation as being the explanation for the observed reduction in plankton numbers seen in shallow waters (Foster 1989).

The diet of the King Penguin Aptenodytes patagonicus at Macquarie Island

The diet of King Penguins Aptenodytes patagonicus at Macquarie Island was studied between November 1984 and November 1985 based on stomach flushed samples (obtaining 93% of the total stomach content) from ten birds each month. The mean stomach content mass of the 118 samples was 923 0 g. Percentage by number, percentage by weight and dietary coefficient analysis all showed the main prey of the penguins to be myctophid lantern fish of the species Electrona carlsbergi and Krefftichthys anderssoni. Juvenile fish of both species were eaten from December to July, and adults in August and September. Cephalopods were relatively unimportant in contrast to previous indications. The amount of food brought ashore and the composition of the diet varied over the year, with K. anderssoni the dominant food in all but the winter months when E. carlsbergi replaced it as the principal food item.

Contamination of Stream Fishes with Chlorinated Hydrocarbons from Eggs of Great Lakes Salmon

Abstract Pacific salmon Oncorhynchus spp. have been stocked in the Great Lakes where they accumulate body burdens of chlorinated hydrocarbons. The transport of these contaminants to resident communities in spawning streams was studied in two tributaries of Lake Michigan accessible to anadromous spawners and one control tributary blocked to them. No polychlorinated biphenyls (PCBs), DDT, or dieldrin were detected in the sediments or biota of the control stream, or in sediments of the test streams. However, trout Salmo spp. and, to a lesser extent, sculpins Cottus spp. accumulated PCBs and DDT as a result of eating contaminated salmon eggs. Eggs constituted as much as 87% (by weight) of the total stomach contents of trout collected during the salmon spawning season early October to early January. Salmon eggs contained 0.46–9.50 mg PCBs/kg, and 0.14–1.80 mg DDT/kg. Consumption of eggs varied greatly among individual trout, and there was a strong correlation between numbers of eggs in the stomachs and PCB and...

A field study of predation of the hyperiid amphipod Parathemisto japonica on larvae of the Japanese sand eel Ammodytes personatus.

A field study was carried out from January to April in 1981 and 1982 to estimate the effects of predation of the hyperiid amphipod Parathemisto japonica on larvae of the Japanese sand eel Ammodytes personatus in waters off the northeastern coast of the main island of Japan. The degree of vertical co-occurrence was similar during the day and at night and P. japonica fed on the larvae throughout the day. Overlap of the horizontal distributions of the two species increased from January to April. The proportion of sand eel larvae in the total stomach contents of P. japonica varied monthly in the range of 0-8.2% on a dry weight basis. The density of sand eel larvae decreased more markedly in the area where P. japonica occurred in greater abundance. Preliminary estimates of the rate of daily loss of sand eel larvae caused by the predation yielded figures of 0.1% for January, 3.3% for February, 2.8% for March, and 45.2% for April, closely associated with changes in the size and degree of overlap of distribution of the two organisms.