Interactions between adult migratory striped bass (Morone saxatilis) and their prey during winter off the Virginia and North Carolina Atlantic coast from 1994 through 2007

The migratory population of striped bass (Morone saxatilis) (>400 mm total length[TL]) spends winter in the Atlantic Ocean off the Virginia and North Carolina coasts of the United States. Information on trophic dynamics for these large adults during winter is limited. Feeding habits and prey were described from stomach contents of 1154 striped bass ranging from 373 to 1250 mm TL, collected from trawls during winters of 1994-96, 2000, and 2002-03, and from the recreational fishery during 2005-07. Nineteen prey species were present in the diet. Overall, Atlantic menhaden (Brevoortia tyrannus) and bay anchovy (Anchoa mitchilli) dominated the diet by boimass (67.9%) and numerically (68.6%). The percent biomass of Atlantic menhaden during 1994-2003 to 87.0% during 2005-07. Demersal fish species such as Atlantic croaker (Micropogonias undulatus) and spot (Leiostomus xanthurus) represented <15% of the diet biomass, whereas alosines (Alosa spp.) were rarely observed. Invertebrates were least important, contributing <1.0% by biomass and numerically. Striped bass are capable of feeding on a wide range of prey sizes (2% to 43% of their total length). This study outlines the importance of clupeoid fishes to striped bass winter production and also shows that predation may be exerting pressure on one of their dominant prey, the Atlantic menhaden.

The feeding ecology of some zooplankters that are important prey items of larval fish

Diets of 76 species of fish larvae from most oceans of the world were inventoried on the basis of information in 40 published studies. Although certaln geographlc, size- and taxon-specific patterns were apparent, certain zooplankton taxa appeared in the diets of larvae of a variety of fish species in numerous localities. Included were six genera of calanoid copepods (Acartia, Calanus, Centropages, Paracalanus, Pseudocaianus, Temora), three genera of cyclopoid copepods (Corycaeus, Oilhona, Oncata), harpacticoid copepods, copepod nauplii, tintinoids, cladocerans of the genera Evadne and Podon, barnacle nauplii, gastropod larvae, pteropods of the genus Limacina, and appendicularians. Literature on feeding habits of these zooplankters reveals that most of the copepods are omnivorous, feeding upon both phytoplankton and other zooplankton. Some taxa, such as Calanus, Paracalanus, Pseudocalanus, and copepod nauplii appear to be primarily herbivorous, while others, such as Acartia, Centropages, Temora, and cyclopoids exhibit broad omnivory or carnivory. The noncopepod zooplankters are primarily filter-feeders upon pbytoplankton and/or bacterioplankton. Despite the importance of zooplankters in larval fish food webs, spectic knowledge of the feeding ecology of many taxa is poor. Further, much present knowledge comes only from laboratory investigations that may not accurately portray feeding habits of zooplankters in nature. Lack of knowledge of the feeding ecology of many abundant zooplankters, which are also important in larval fish food webs, precludes realistic understanding of pelagic ecosystem dynamics. (PDF file contains 34 pages.)

The choice of a suitable sampler for benthic macroinvertebrates in deep rivers

Both chemical and biological methods are used to assess the water quality of rivers. Many standard physical and chemical methods are now established, but biological procedures of comparable accuracy and versatility are still lacking. This is unfortunate because the biological assessment of water quality has several advantages over physical and chemical analyses. Several groups of organisms have been used to assess water quality in rivers and these include Bacteria, Protozoa, Algae, macrophytes, macroinvertebrates and fish. Hellawell (1978) provides an excellent review of the advantages and disadvantages of these groups, and concludes that macroinvertebrates are the most useful for monitoring water quality. Although macroinvertebrates are relatively easy to sample in shallow water (depth < 1m), quantitative sampling poses more problems than qualitative sampling because a large number of replicate sampling units are usually required for accurate estimates of numbers or biomass per unit area. Both qualitative and quantitative sampling are difficult in deep water (depth > 1m). The present paper first considers different types of samplers with emphasis on immediate samplers, and then discusses some problems in choosing a suitable sampler for benthic macroinvertebrates in deep rivers.

Prey preference of lingcod (Ophiodon elongatus), a top marine predator: implications for ecosystem-based fisheries management

Many highly exploited ecosystems are managed on the basis of single-species demographic information. This management approach can exacerbate tensions among stakeholders with competing interests who in turn rely on data with notoriously high variance. In this case study, an application of diet and dive survey data was used to describe the prey preference of lingcod (Ophiodon elongatus) in a predictive framework on nearshore reefs off Oregon. The lingcod is a large, fast-growing generalist predator of invertebrates and fishes. In response to concerns that lingcod may significantly reduce diminished populations of rockfishes (Sebastes spp.), the diets of 375 lingcod on nearshore reefs along the Oregon Coast were compared with estimates of relative prey availability from dive surveys. In contrast to the transient pelagic fishes that comprised 46% of lingcod diet by number, rockfishes comprised at most 4.7% of prey items. Rockfishes were the most abundant potential prey observed in dive surveys, yet they were the least preferred. Ecosystem-based fisheries management (EBFM) requires information about primary trophic relationships, as well as relative abundance and distribution data for multiple species. This study shows that, at a minimum, predation relative to prey availability must be considered before predator effects can be understood in a management context.

Feeding ecology of juvenile Pacific salmon (Oncorhynchus spp.) in a northeast Pacific fjord: diet, availability of zooplankton, selectivity for prey, and potential competition for prey resources

We investigated the feeding ecology of juvenile salmon during the critical early life-history stage of transition from shallow to deep marine waters by sampling two stations (190 m and 60 m deep) in a northeast Pacific fjord (Dabob Bay, WA) between May 1985 and October 1987. Four species of Pacific salmon—Oncorhynchus keta (chum) , O. tshawytscha (Chinook), O. gorbuscha (pink), and O. kisutch (coho)—were examined for stomach contents. Diets of these fishes varied temporally, spatially, and between species, but were dominated by insects, euphausiids, and decapod larvae. Zooplankton assemblages and dry weights differed between stations, and less so between years. Salmon often demonstrated strongly positive or negative selection for specific prey types: copepods were far more abundant in the zooplankton than in the diet, whereas Insecta, Araneae, Cephalapoda, Teleostei, and Ctenophora were more abundant in the diet than in the plankton. Overall diet overlap was highest for Chinook and coho salmon (mean=77.9%)—species that seldom were found together. Chum and Chinook salmon were found together the most frequently, but diet overlap was lower (38.8%) and zooplankton biomass was not correlated with their gut fullness (%body weight). Thus, despite occasional occurrences of significant diet overlap between salmon species, our results indicate that interspecific competition among juvenile salmon does not occur in Dabob Bay.

Diet composition and prey selection of the introduced grouper species peacock hind (Cephalopholis argus) in Hawaii

The introduced grouper species peacock hind (Cephalopholis argus), was the dominant large-body piscivore on the Main Hawaiian Island (MHI) reefs assessed by underwater visual surveys in this study. However, published data on C. argus feeding ecology are scarce, and the role of this species in Hawaiian reef ecosystems is presently not well understood. Here we provide the first comprehensive assessment of the diet composition, prey electivity (dietary importance of prey taxa compared to their availability on reefs), and size selectivity (prey sizes in the diet compared to sizes on reefs) of this important predator in the MHI. Diet consisted 97.7% of fishes and was characterized by a wide taxonomic breadth. Surprisingly, feeding was not opportunistic, as indicated by a strongly divergent electivity for different prey fishes. In addition, whereas some families of large-body species were represented in the diet exclusively by recruit-size individuals (e.g., Aulostomidae), several families of smaller-body species were also represented by juveniles or adults (e.g., Chaetodontidae). Both the strength and mechanisms of the effects of C. argus predation are therefore likely to differ among prey families. This study provides the basis for a quantitative estimate of prey consumption by C. argus, which would further increase understanding of impacts of this species on native fishes in Hawaii.

Spatial and seasonal relationships between Pacific harbor seals (Phoca vitulina richardii) and their prey, at multiple scales

Knowing where pinnipeds forage is vital to managing and protecting their populations, and for assessing potential interactions with fisheries. We assessed the spatial relationship between the seasonal distribution of Pacific harbor seals (Phoca vitulina richardii) outfitted with satellite transmitters and the seasonal distributions of potential harbor seal prey species in San Francisco Bay, California. Pearson’s correlation coefficients were calculated between the number of harbor seal locations in an area of the San Francisco Bay and the abundance of specific prey species in the same area. The influence of scale on the analyses was assessed by varying the scale of analysis from 1 to 10 km. There was consistency in the prey species targeted by harbor seals year-round, although there were seasonal differences between the most important prey species. The highest correlations between harbor seals and their prey were found for seasonally abundant benthic species, located within about 10 km of the primary haul-out site. Probable foraging habitat for harbor seals was identified, based on areas with high abundances of prey species that were strongly correlated with harbor seal distribution. With comparable local data inputs, this approach has potential application to pinniped management in other areas, and to decisions about the location of marine reserves designed to protect these species.

Age- or length-based methods of growth estimation. What drives the choice?

Based upon a global comparison of over 400 fisheries, the Principal Components Analysis (PCA) methodology was used to identify factors affecting the choice of growth estimation methods. Of the six factors examined, the growth rate (K) and asymptotic length (L8) explained most of the variations. Financial resources, i.e., Gross National Product (GNP), and latitude were also important factors.

Use of enriched live prey in promoting growth and maturation of tiger shrimp (Penaeus monodon)

This study was undertaken to determine the effect of nutritional management of broodstock of Penaeus monodon on growth and maturation. Test specimens were obtained from a grow-out pond before attainment of maturity and were reared in hatchery tanks. Four types of dietary treatments (M1–M4) were given to separate batches that were run in duplicate. Feeding trials continued for five months. A diet with live bloodworm, bioencapsulated to contain tricalcic phosphate as its major component, was found to be the most efficient. Specimens of this particular batch assimilated food more efficiently, grew at a faster rate and attained maturity earlier than other groups. Bloodworm provided the lipid fractions for which there is no de novo synthesis in shrimp. The enrichment product acted by promoting somatic growth and increasing transfer of biochemical constituents needed by the ovary for develop

Factors influencing choice of fishing location in Nankumba Peninsula: A case of study of gillnet and chilimira fisheries

This study was carried out to identify factors that influence choice of fishing location and carry out profitability analysis of Chilimira and Gillnet in different fishing locations. A survey using semi-structured questionnaire was administered to 99 Gillnet and 101 Chilimira fishers in Nankumba Peninsula in Mangochi District. The logit model was used to determine the factors influencing choice of fishing location among the fishers. The study showed that 92.1% of Chilimira fishers are operating in offshore areas while 69.7% Gillnet fishers are operating in inshore areas. Chilimira offshore fishers have higher daily average gross margins than their inshore counterparts and Gillnet fishers. However, they incurred more operating costs than the inshore Chilimira and Gillnet fishers. Furthermore, they find their fishing occupation more rewarding as evidenced by the higher returns to labour. The factors that influenced fisher’s choice of fishing location were Age of the fisher, type of fishing vessel and gear, possession of motor sail engine and access to information about previous day’s catch rates. Finally the study concluded that artisanal fishers in Malawi use different criteria in deciding where to fish. The criterion involves a complex interaction of biological, technological, personal and economical factors and time. However, the resource constrained artisanal fisher will need support to enable him exploit offshore fishery resources. Consequently the study recommends that appropriate fishery development interventions by the government and other stakeholders must adapt to the economics and lifestyles driving the artisanal fishers to fish in particular locations and therefore, build on this foundation to improve the existing fishing technologies.