Food habits and consumption rates of common dolphinfish (Coryphaena hippurus) in the eastern Pacific Ocean

An ecosystem approach to fisheries management requires an understanding of the impact of predatory fishes on the underlying prey resources. Defining trophic connections and measuring rates of food consumption by apex predators lays the groundwork for gaining insight into the role of predators and commercial fisheries in influencing food web structure and ecosystem dynamics.We analyzed the stomach contents of 545 common dolphinfish (Coryphaena hippurus) sampled from 74 sets of tuna purse-seine vessels fishing in the eastern Pacific Ocean (EPO) over a 22-month period. Stomach fullness of these dolphinfish and digestion state of the prey indicated that diel feeding periodicity varied by area and may be related to the digestibility and energy content of the prey. Common dolphinfish in the EPO appear to feed at night, as well as during the daytime. We analyzed prey importance by weight, numbers, and frequency of occurrence for five regions of the EPO. Prey importance varied by area. Flyingfishes, epipelagic cephalopods, tetraodontiform fishes, several mesopelagic fishes, Auxis spp., and gempylid fishes predominated in the diet. Ratios of prey length to predator length ranged from 0.014 to 0.720. Consumption-rate estimates averaged 5.6% of body weight per day. Stratified by sex, area, and length class, daily rations ranged up to 9.6% for large males and up to 19.8% for small dolphinfish in the east area (0–15°N, 111°W–coastline). Because common dolphinfish exert substantial predation pressure on several important prey groups, we concluded that their feeding ecology provides important clues to the pelagic food web and ecosystem structure in the EPO.

The state and known impacts of fish species transferred to or within continental Africa

Fish introductions have been made from small fish ponds to the largest lakes in Africa. The primary intent of these introductions has been to sustain or increase fish production, although some introductions have been made to develop sport fisheries and to control unwanted organisms. Some of these introductions have fulfilled their objective in the short term, but several of these "successful" introductions have created uncertainties about their long term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into lakes Victoria and Kyoga in 1950s and early 1960s. By the 1980s O. niloticus and O. niloticus dominated the fisheries of these lakes, virtually eliminating a number of endemic fish species. The loss of genetic diversity of the fish in the worlds second largest lake has also been accompanied by a loss of trophic diversity. The transformation of the fish community has, in Lake Victoria coincided with a profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. In contrast, the introduction of a planktivore, Limnothrissa miodon into Lake Kivu and the Kariba reservoir has established highly successful fisheries with little documented effect on the pre-existing fish community or trophic ecology of the lakes. The highly endemised species-rich African Great lakes may be particularly sensitive to species introductions and require special consideration and caution when introductions are contemplated because species extinctions, introgressive hybridization and ecosystem alterations may occur following fish introductions.

Sobre el ecosistema de las aguas litorales de Mar del Plata. Niveles tróficos y cadenas alimentarias pelágicos demersales y bentónicos-demersales

The present paper deals with the trophic relationships of the communities of the coastal fishing area of Mar del Plata (Argentine). Different trophic levels of two main food chains (pelagic-demersal and benthic-demersal)were established. There are connections between both chains through certain species of invertebrates and fishes. This first try to establish the trophic relationships of our most important littoral communities, aims to set the preliminary bases for future energetic flow studies through the trophic web that gives a real economic importance to this productive area. (Document contains 45 pages)

Diet composition and food habits of demersal and pelagic marine fishes from Terengganu waters, east coast of Peninsular Malaysia

Fish stomachs from 18 demersal and pelagic fishes from the coast of Terengganu in Malaysia were examined. The components of the fishes’ diets varied in number, weight, and their frequency of occurrence. The major food items in the stomachs of each species were determined using an Index of Relative Importance. A conceptual food web structure indicates that fish species in the study area can be classified into three predatory groups: (1) predators on largely planktivorous or pelagic species; (2) predators on largely benthophagous or demersal species; and (3) mixed feeders that consume both pelagic and demersal species.

PICES-GLOBEC International Program on Climate Change and Carrying Capacity: Report of the 1999 MONITOR and REX Workshops, and the 2000 MODEL Workshop on Lower Trophic Level Modelling

Table of Contents [pdf, 0.11 Mb] Executive Summary [pdf, 0.07 Mb] MODEL Task Team Workshop Report Final Report of the International Workshop to Develop a Prototype Lower Trophic Level Ecosystem Model for Comparison of Different Marine Ecosystems in the North Pacific [pdf, 11.64 Mb] Report of the 1999 MONITOR Task Team Workshop [pdf, 0.32 Mb] Report of the 1999 REX Task Team Workshop Herring and Euphausiid population dynamics Douglas E. Hay and Bruce McCarter Spatial, temporal and life-stage variation in herring diets in British Columbia [pdf, 0.10 Mb] Augustus J. Paul and J. M. Paul Over winter changes in herring from Prince William Sound, Alaska [pdf, 0.08 Mb] N. G. Chupisheva Qualitative texture characteristic of herring (Clupea pallasi pallasi) pre-larvae developed from the natural and artificial spawning-grounds in Severnaya Bay (Peter the Great Bay) [pdf, 0.07 Mb] Gordon A. McFarlane, Richard J. Beamish and Jake SchweigertPacific herring: Common factors have opposite impacts in adjacent ecosystems [pdf, 0.15 Mb] Tokimasa Kobayashi, Keizou Yabuki, Masayoshi Sasaki and Jun-Ichi Kodama Long-term fluctuation of the catch of Pacific herring in Northern Japan [pdf, 0.39 Mb] Jacqueline M. O’Connell Holocene fish remains from Saanich Inlet, British Columbia, Canada [pdf, 0.40 Mb] Elsa R. Ivshina and Irina Y. Bragina On relationship between crustacean zooplankton (Euphausiidae and Copepods) and Sakhalin-Hokkaido herring (Tatar Strait, Sea of Japan) [pdf, 0.14 Mb] Stein Kaartvbeedt Fish predation on krill and krill antipredator behaviour [pdf, 0.08 Mb] Nikolai I. Naumenko Euphausiids and western Bering Sea herring feeding [pdf, 0.07 Mb] David M. Checkley, Jr. Interactions Between Fish and Euphausiids and Potential Relations to Climate and Recruitment [pdf, 0.08 Mb] Vladimir I. Radchenko and Elena P. Dulepova Shall we expect the Korf-Karaginsky herring migrations into the offshore western Bering Sea? [pdf, 0.75 Mb] Young Shil Kang Euphausiids in the Korean waters and its relationship with major fish resources [pdf, 0.29 Mb] William T. Peterson, Leah Feinberg and Julie Keister Ecological Zonation of euphausiids off central Oregon [pdf, 0.11 Mb] Scott M. Rumsey Environmentally forced variability in larval development and stage-structure: Implications for the recruitment of Euphausia pacifica (Hansen) in the Southern California Bight [pdf, 3.26 Mb] Scott M. Rumsey Inverse modelling of developmental parameters in Euphausia pacifica: The relative importance of spawning history and environmental forcing to larval stage-frequency distributions [pdf, 98.79 Mb] Michio J. Kishi, Hitoshi Motono & Kohji Asahi An ecosystem model with zooplankton vertical migration focused on Oyashio region [pdf, 33.32 Mb] PICES-GLOBEC Implementation Panel on Climate Change and Carrying Capacity Program Executive Committee and Task Team List [pdf, 0.05 Mb] (Document pdf contains 142 pages)

Ichthyoplankton community structure and comparative trophodynamics in an estuarine transition zone

Surveys were conducted to evaluate and compare assemblage structure and trophodynamics of ichthyoplankton, and their variability, in an estuarine transition zone. Environmental gradients in the saltfront region of the Patuxent River subestuary, Chesapeake Bay, were hypothesized to define spatiotemporal distributions and assemblages of ichthyoplankton. Larval fishes, zooplankton, and hydrographic data were collected during spring through early summer 2000 and 2001. Larvae of 28 fish species were collected and species richness was similar each year. Total larval abundance was highest in the oligohaline region down-estuary of the salt front in 2000, but highest at the salt front in 2001. Larvae of anadromous fishes were most abundant at or up-estuary of the salt front in both years. Two ichthyoplankton assemblages were distinguished: 1) riverine—characterized predominantly by anadromous species (Moronidae and Alosinae); and 2) estuarine—characterized predominantly by naked goby (Gobiosoma bosc) (Gobiidae). Temperature, dissolved oxygen, salinity-associated variables (e.g., salt-front location), and concentrations of larval prey, specifically the calanoid copepod Eurytemora affinis and the cladoceran Bosmina longirostris, were important indicators of larval fish abundance. In the tidal freshwater region up-estuary of the salt front, there was substantial diet overlap between congeneric striped bass (Morone saxatilis) and white perch (M. americana) larvae, and also larvae of alewife (Alosa pseudoharengus) (overlap= 0.71–0.93). Larval abundance, taxonomic diversity, and dietary overlap were highest within and up-estuary of the salt front, which serves to both structure the ichthyoplankton community and control trophic relationships in the estuarine transition zone.

Diets of and trophic relationships among dominant marine nekton within the northern California Current ecosystem

In this study we analyzed the diets of 26 nekton species collected from two years (2000 and 2002) off Oregon and northern California to describe dominant nekton trophic groups of the northern California Current (NCC) pelagic ecosystem. We also examined interannual variation in the diets of three nekton species. Cluster analysis of predator diets resulted in nekton trophic groups based on the consumption of copepods, euphausiids, brachyuran larvae, larval juvenile fishes, and adult nekton. However, many fish within trophic groups consumed prey from multiple trophic levels—euphausiids being the most widely consumed. Comparison of diets between years showed that most variation occurred with changes in the contribution of euphausiids and brachyuran larvae to nekton diets. The importance of euphausiids and other crustacean prey to nekton indicates that omnivory is an important characteristic of the NCC food web; however it may change during periods of lower or higher upwelling and ecosystem production.

Domoic acid contamination within eight representative species from the benthic food web of Monterey Bay, California, USA

Benthic food webs often derive a significant fraction of their nutrient inputs from phytoplankton in the overlying waters. If the phytoplankton include harmful algal species like Pseudo-nitzschia australis, a diatom capable of producing the neurotoxin domoic acid (DA), the benthic food web can become a depository for phycotoxins. We tested the general hypothesis that DA contaminates benthic organisms during local blooms of P. australis, a widespread toxin producer along the US west coast. To test for trophic transfer and uptake of DA into the benthic food web, we sampled 8 benthic species comprising 4 feeding groups: filter feeders (Emerita analoga and Urechis caupo); a predator (Citharichthys sordidus); scavengers (Nassarius fossatus and Pagurus samuelis) and deposit feeders (Neotrypaea californiensis, Dendraster excentricus and Olivella biplicata). Sampling occurred before, during and after blooms of P. australis in Monterey Bay, CA, USA during 2000 and 2001. DA was detected in all 8 species, with contamination persisting over variable time scales. Maximum DA levels in N. fossatus (674 ppm), E. analoga (278 ppm), C. sordidus (515 ppm), N. californiensis (145 ppm), P. samuelis (56 ppm), D. excentricus (15 ppm) and O. biplicata (3 ppm) coincided with P. australis blooms, while DA levels in U. caupo remained above 200 ppm (max. = 751 ppm) throughout the study period. DA in 6 species exceeded levels thought to be safe for higher level consumers (i.e. ≥20 ppm) and thus is likely to have deleterious effects on marine birds, sea lions and the endangered California sea otter, known to prey upon these benthic species.

Impact of plankton structure on primary productivity in two beels of West Bengal, India

Planktonic community in floodplain wetlands embodies the energy transfer through this phase and indicates trophic status of lake. Originally rich bottom coupled with a conducive physicochemical environment encourages fast colonization of the plankton population. Present investigation was carried out in two floodplain wetlands having characteristics of open (Amda beel) and closed (Suguna beel) system. The physicochemical parameters of water and soil of the investigated heels were by and large conducive for planktonic growth. The density of plankton population varied between 1,346 and 2,170 u/l in Suguna bed whereas in Amda beel it ranged from 1,030 to 1,802 u/l. Seasonal fluctuations in water column were conspicuous and mostly dependent on the replenished resources and volume, A mixed and balanced population of diversified fauna constituted the plankton population of the investigated ecosystems. Mostly the diversity was observed to be maximum during winter seasons with coincidence of favorable temperature, dissolved oxygen and other physico-chemical parameters of water besides optimum solar penetration. Richness of planktonic structure in closed system (Suguna) resulted in higher fish production (1,570,05 kg/ha/yr) than that of open system (Amda) (384.4 kg/ha/yr).

Implications of changes in trophic diversity and food webs on fisheries and the environment

Most of the earth's ecosystems are experiencing slight to catastrophic losses of biodiversity, caused by habitat destruction, alien species introduction, climate change and pollution (Wilcove et al., 1998). These human effects have led to the extinction of native fish species, the collapse of their populations and the loss of ecological integrity and ecosystem functioning (Ogutu-Ohwayo & Hecky, 1991; Witte et al. , 1992a; Mills et al., 1994; Vitousek et al., 1996). Food webs are macro-descriptors of community feeding interactions that can be used to map the flow of materials and nutrients in ecosystems (Jepsen & Winemiller, 2002). Comparative food web studies have been used to address theoretical questions such as 'does greater trophic connectivity increase stability?' (Cohen et al., 1990), and 'does the number of trophic levels increase with productivity?' (Briand & Cohen, 1987). Answers to such questions have obvious applications for natural resources management. From a multi-species fisheries standpoint, there is a need to understand consumer-resource dynamics within complex trophic networks.