Trophodynamics of the Fish Valenciennellus tripunctulatus. II. Selectivity, Grazlng Rates and Resource Utilization

The feeding ecology of 2 vertically migrating midwater fishes -Hygophum benoiti and Myctophum punctaturn -found stranded along the shores of the Straits of Messina was studied in order to reconstruct the ecological mechanisms involved in their stranding processes. Diet analyses revealed that both fishes fed mostly on copepods and euphausiids but also on a variety of other food items. Ontogenetic changes in the diet indicated that size selection determined prey choice in all stages in the life cycle of H. benoiti. M. punctatum, on the other hand, became opportunistic with age, adding new components to the diet without excluding prey items eaten by smaller individuals. At the species level, prey choice involved selective feeding on more visible prey items such as bioluminescent copepods. The prey population primarily included surface and migrating sub-surface species. Knowledge of prey vertical distribution patterns in the Mediterranean Sea suggests active feeding by both predators in surface waters at night. The absence of deep water non-migrating elements in the diet implies that the current hypothesis of passive transport of species due to surfacing deep water masses in the Straits may not hold true for all stranded organisms. Alternative stranding mechanisms involving active trophic migrations are proposed for midwater species known to undergo strong diel vertical movements.

Section: Diet Analysis Of Stranded Hygophum Benoiti Andmentioning

confidence: 78%

Feeding Ecology and Stranding Mechanisms in Two Lanternfishes, Hygophum benoiti and Myctophum punctatum

Carlo¹,

Costanzo²,

Fresi³

et al. 1982

“…Other studies have attempted to measure prey size selection by comparing the size composition of zooplankton in a predator's diet to the size composition of prey in the surrounding water (Baird & Hopkins 1981, Scott & Murdoch 1983, Mikheev 1984, Magnhagen 1985, Main 1985, Grover & Olla 1986, Khadka & Ramakrishna 1986, Schmitt 1986, Collie 1987, Confer et al 1990, Forrester et al 1994. Size distribution of prey, as perceived by the predator, may differ from that measured with field sampling approaches that integrate across relatively large volumes of water.…”

Section: Introductionmentioning

confidence: 99%

Virtual reality of planktivores:a fish's perspective of prey size selection

Luo¹,

Sb²,

Mj³

1996

Tradit~onally, field studies of size selective predation by visual-feeding planktivorous fish compare the size distribution of prey in stomachs to that of zooplankton measured in the field However, the size frequency of prey perceived by a fish may differ from that measured by researchers using integrative plankton nets. In this study, a mechanistic spatial foraging model was developed to test the hypothesis that size-selective predation by visual-feeding planktivorous fish can arise simply by random encounters with prey. Our model was based on movement of a single predator and a size structured prey population distributed in 3-dimensional space. The model assumed that a predator's encounters with prey was a function of prey size and predatol-swimming speed. Upon encounter, the predator either selected prey by random choice or the largest apparent size. The size frequency and distance distribution of prey encountered, selected, and captured were estimated using Monte Carlo techniques. The model performance was initially evaluated wlth hypothetical prey slze frequencies, and different light attenuation coefficients, capture efflciencies, visual distances and predator swimming speeds. Simulation results showed that the size frequency of prey encountered randomly by a predator is very different from the size frequency of the a i n b~e n t prey In the environment The s l r c frequency of prey selected by random c h o~c c only differed from that selected by appal-ent size choice when visual distance was greater than reactive distance. Prey distance distribution, which was defined as frequency of prey encountered a t different distances, showed that as prey density increased predators sclected prey at closer distances by the largest apparent size choice than by random choice. We also tested the model specifically for the bay anchovy Anchoa mitchilli. Ambient zooplankton size frequencies found in m~d-Chesapeake Bay were used to predict the size frequencies of zooplankton consumed by fish. Predicted prey size frequency in the diet matched the size frequency of zooplankton found in bay anchovy stomachs. We conclude that prey slze selection by fish can be described mechanistically by differentlal random encounter from a flsh's perspective, and that behavioral choice plays a minor role In prey size selection.

“…1.5 mm for size class 1-2 mm) was assigned to every individual in that size class. Prey density was taken from data presented by Baird and Hopkins (1981). Information on prey utilization and encounter rates were obtained from the same source and estimates of the caloric contribution of each prey size class to the diet and to total prey available in the expected search volume were made.…”

Section: Energetics Food Availability and Resource Utilizationmentioning

confidence: 99%

Trophodynamics of the Fish Valenciennellus tripunctulatus. Ill. Energetics, Resources and Feeding Strategy

Baird¹,

Hopkins²

1981

Self Cite

A model was constructed which relates energy in diet to metabolic requirements for the mesopelagic zooplanktivore fish Valenciennellus tripunctulatus. Linear and Von Bertalanffy growth models were used to explore the energetic consequences of a number of feasible age/growth strategies. Maxlmum efficiencies were obtained with linear growth to about 30 mm in 1 y. Efficiencies declined rapidly for slower growth strategies. It was hypothesized that a n 'annual' life history strategy was optimum based on energetic considerations. Copepod prey in the 1-2 mm size class were an order of magnitude more abundant and over 4 tlmes higher in caloric content than larger size classes. V. tripunctulatus, however, is highly efficient in obtaining calories from larger prey size classes ( 2 4 mm) which contain a high caloric content per individual. The resource field places severe constraints on predator growth and at 38 mm no surplus energy is estimated available from daily ration over and above metabolic requirements. V tripunctulatus should be sensitive to 'nearfield' competitors as well a s 'remote' predators grazing zooplankton populations in different space/time.