Higher Trophic Level Fish Research Articles

Regional patterns in mercury and selenium concentrations of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) in the Pacific Ocean

Mercury (Hg) concentrations in high trophic level fish, such as bigeye tuna ( Thunnus obesus ) and yellowfin tuna ( Thunnus albacares ), can often exceed consumption advisories. Here we sampled 444 yellowfin and bigeye tuna to determine whether tuna Hg concentration varies regionally in the eastern and central Pacific Ocean and whether this variation corresponds to environmental characteristics that promote the bioavailability of Hg. Of the five regions sampled, we found significantly higher Hg concentrations in the eastern equatorial region (5°S–5°N; 110°W–120°W) for both species. Hg concentrations in this region were elevated by 0.22 and 0.17 µg·g–1for yellowfin and bigeye tuna, respectively, compared with Hg concentrations in the other regions. Tuna selenium concentrations, which may alter the toxicity of Hg, did not vary by region. Oceanographic data indicated that the eastern equatorial region had elevated chlorophyll a concentrations and shallow minimum oxygen depths, both of which promote Hg methylation. These findings suggest that methylation-promoting mechanisms may translate into regional variation in the Hg concentrations of highly mobile, high trophic level fish.

First Evidence of Elasmobranch Predation by a Waterbird: Stingray Attack and Consumption by the Great Blue Heron (Ardea herodias)

A Great Blue Heron (Ardea herodias) foraging on an Atlantic Stingray (Dasyatis sabina) was observed off coastal Mississippi. Although elasmobranchs have been previously reported in the diets of birds, this observation was the first documenting the attack and consumption behavior by a bird on an elasmobranch. The behaviors in the event mirror previous observations of A. herodias attacking large and unwieldy prey items. Consumption of a high trophic-level fish by A. herodias further emphasizes its role as a top predator in shallow marine food webs.

Seasonal shift in the foraging niche of Atlantic puffins Fratercula arctica revealed by stable isotope (δ15N and δ13C) analyses

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 9:13-22 (2010) - DOI: https://doi.org/10.3354/ab00225 Seasonal shift in the foraging niche of Atlantic puffins Fratercula arctica revealed by stable isotope (δ15N and δ13C) analyses April Hedd1,*, David A. Fifield1,2, Chantelle M. Burke1, William A. Montevecchi1, Laura McFarlane Tranquilla1, Paul M. Regular1, Alejandro D. Buren1, Gregory J. Robertson3 1Cognitive and Behavioural Ecology, Psychology Department, Memorial University, St. John’s, Newfoundland A1C 3X9, Canada 2Canadian Wildlife Service and 3Science and Technology Section, Environment Canada, 6 Bruce St., Mount Pearl, Newfoundland A1N 4T3, Canada *Email: ahedd@mun.ca ABSTRACT: We measured tissue stable nitrogen (δ15N) and carbon (δ13C) values to investigate the extent of seasonal and age-related variation in the foraging ecology of Atlantic puffins. For adults, there was considerable seasonal variation in the foraging niche. A generalized, lower trophic level (TL) diet during the winter moult was replaced by a highly specialized, higher TL diet during summer when birds were rearing chicks. The seasonal δ15N enrichment of 2.36‰ is consistent with an increase of 0.65 TL. Output from a 2-source single isotope (δ15N) mixing model suggested that adult diets were composed largely of zooplankton during winter with a switch to capelin (or other higher TL prey) in summer. A concurrent decrease in δ15N variability suggests that adult diets are more varied in winter. Trophic position of first-year birds was similar across summer and fall, as they went from being provisioned by parents at the colony to feeding independently. Both isotope mixing model and stomach contents analysis suggested that first-year birds relied largely (>85%) on capelin (or other higher TL fish) in fall. In summer, the trophic position of adults was significantly higher than that of nestlings; however, greater δ15N variability suggested that nestling diet was mixed overall. Shipboard surveys indicated an offshore movement of puffins post-breeding; however, this distributional shift was not reflected in δ13C signatures of adults. The dietary shift and increased TL of adult Atlantic puffins from winter to summer is consistent with reports for puffin species in the Pacific, suggesting that puffins may undergo the most extensive seasonal trophic shift among the auk species. KEY WORDS: Seasonal diet shift · Winter diet · Stable isotope analysis · δ15N · δ13C · Trophic level · Fratercula arctica Full text in pdf format PreviousNextCite this article as: Hedd A, Fifield DA, Burke CM, Montevecchi WA and others (2010) Seasonal shift in the foraging niche of Atlantic puffins Fratercula arctica revealed by stable isotope (δ15N and δ13C) analyses. Aquat Biol 9:13-22. https://doi.org/10.3354/ab00225 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 9, No. 1. Online publication date: March 25, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Stable isotopic evidence for diet at the Imperial Roman coastal site of Velia (1st and 2nd Centuries AD) in Southern Italy

Here we report on a stable isotope palaeodietary study of a Imperial Roman population interred near the port of Velia in Southern Italy during the 1st and 2nd centuries AD. Carbon and nitrogen stable isotope analyses were performed on collagen extracted from 117 adult humans as well as a range of fauna to reconstruct individual dietary histories. For the majority of individuals, we found that stable isotope data were consistent with a diet high in cereals, with relatively modest contributions of meat and only minor contributions of marine fish. However, substantial isotopic variation was found within the population, indicating that diets were not uniform. We suggest that a number of individuals, mainly but not exclusively males, had greater access to marine resources, especially high trophic level fish. However, the observed dietary variation did not correlate with burial type, number of grave goods, nor age at death. Also, individuals buried at the necropolis at Velia ate much less fish overall compared with the contemporaneous population from the necropolis of Portus at Isola Sacra, located on the coast close to Rome. Marine and riverine transport and commerce dominated the economy of Portus, and its people were in a position to supplement their own stocks of fish with imported goods in transit to Rome, whereas at Velia marine exploitation existed side-by-side with land-based economic activities.

Trophic transfer of paralytic shellfish toxins from the cladoceran ( Moina mongolica) to larvae of the fish ( Sciaenops ocellatus)

The dynamic transmission and transformation of paralytic shellfish toxins (PSTs) from the toxic dinoflagellate Alexandrium tamarense to the cladoceran Moina mongolica and subsequently to the larvae of the fish Sciaenops ocellatus were investigated under laboratory conditions. The results showed that PSTs could be transferred to S. ocellatus when they preyed on PST-containing M. mongolica. During the experimental period, A. tamarense, M. mongolica and the digestive glands of the fish larvae contained C 1/2 toxins, and the viscera of S. ocellatus contained neoSTX. The proportion of β toxin (C 2) in C 1+2 toxins increased when PSTs were transferred from A. tamarense to M. mongolica, but in the subsequent transfer from M. mongolica to S. ocellatus the proportion of α toxin (C 1) increased. During depuration, the contents of C 1 and C 2 toxins in fish larvae decreased with the duration of depuration, but neoSTX remained relatively constant. The present results indicated that, using a cladoceran as the vector, PSTs can be transferred from toxic algae to a high trophic level fish and metabolized in the fish. Future work should address the metabolic characteristics of PSTs in cladocerans and the end result when they are transferred to fishes.

Environmental management with knowledge of uncertainty: A methylmercury case study

In Oregon's Willamette River Basin, health advisories currently limit consumption of fish that have accumulated methylmercury to levels posing a potential health risk for humans. Under the Clean Water Act, these advisories represent an impairment of the beneficial use of fish consumption and create the requirement for a mercury total maximum daily load. A percent load reduction for total mercury was determined by comparing mercury levels in surface water to a water column guidance value linked to the protection of specified beneficial uses. In this case study, we discuss how probabilistic (Monte Carlo) methods were used to quantify uncertainty in the water column guidance value, how they provided decision makers with knowledge as to the probability of any given water column guidance value affording human health protection for methylmercury, and how this knowledge affected decisions as to a mercury load reduction for the Willamette River Basin. Through consultations with stakeholders, a water column guidance value of 0.92 ng/L (a median for higher trophic level fish) was chosen from among a suite of values of differing probabilities. The selected water column guidance value, when compared with ambient total mercury levels, indicated that a 50% probability of achieving the tissue criterion would require a load reduction of about 26%. Having and working with an explicit knowledge of uncertainty was not easy for many decision makers or stakeholders. However, such knowledge gave them more informed choices, a better understanding of what a specific choice of water column guidance value could mean in terms of achieving protectiveness, and led to a lower load reduction than suggested by a purely deterministic analysis. Nonetheless, more attention must be given to developing management, communication, and regulatory frameworks that can effectively use the greater knowledge of uncertainty afforded by probabilistic methods.

What relative seafood prices can tell us about the status of stocks

AbstractChanges in the distribution of seafood prices can provide useful insights into the availability of different species to fishermen and to fish markets. We propose a log‐relative‐price‐index (LRPI) and demonstrate how such a concept might be useful for exploring long‐term changes in wild fish communities as a result of intensive exploitation. We estimate the LRPI for 26 fish species in the Celtic Sea (UK) and for 33 species on Italian fish markets. In both systems the LRPI changed significantly during recent decades, and in the Celtic Sea this probably resulted from a decline in the availability of high trophic level target species such as cod and hake as well as an increase in the availability of low trophic level pelagic species. By contrast, the LRPI of Italian fishes remained relatively constant from 1972 to 1980, but declined thereafter as a result of widespread expansion in fin‐fish aquaculture, and a consequential increase in the supply, and hence decrease in the price of high trophic level fish such as seabass and seabream.

THE TROPHIC ROLE OF MARINE MAMMALS IN THE NORTHERN GULF OF ST. LAWRENCE

AbstractThe trophic role of apex predators was evaluated in the northern Gulf of St. Lawrence ecosystem. An Ecopath model was developed for the period 1985–1987 prior to the collapse of commercially exploited demersal fish stocks in this area. Marine mammal trophic levels were estimated by the model at 4.1 for cetaceans, 4.4 for harp seals (Pagophilus groenlandicus), 4.7 for hooded seals (Cystophora cristata), 4.5 for gray seals (Halichoerus grypus), and 4.3 for harbor seals (Phoca vitulina). Harp seals were the third most important predator on vertebrate prey following large Atlantic cod (Gadus morhua) and redfish (Sebastesspp.). Different seal species preyed on different levels of the food chain. Harp seals preyed on most trophic groups, whereas larger seals, such as gray seals and hooded seals, mainly consumed higher trophic levels. The model suggested that apex predators had a negative effect on their dominant prey, the higher trophic level fish, but an indirect positive feedback on the prey of their preferred prey, mainly American plaice (Hippoglossoides platessoides), flounders, skates, and benthic invertebrates. Our results suggest that both marine mammals and fisheries had an impact on the trophic structure.

Residues of toxaphene decrease in estuarine fish after removal of contaminated sediments

To determine if toxaphene residues in edible fish tissue decreased after removal of contaminated sediments from an estuarine site in 1999, 51 composite samples representing six finfish species were collected in 2001 and analyzed using gas chromatography with electron capture and negative ion mass spectrometric detection. The grand mean total toxaphene residue concentration on a wet weight basis (ΣTOXwet) was 1,400 ± 3,500 ng g−1 (range: < 18 to 18,000 ng g−1) and was positively correlated with extractable lipid. On a lipid basis, the mean ΣTOXlip was 26 ± 33 μg g1, which decreased with increasing distance from the study site. Although benthically-oriented species, such as spot (Leiostomus xanthurus) and striped mullet (Mugil cephalus), exhibited higher mean ΣTOXwet than those of higher trophic level fish, mean ΣTOXlip were not significantly different among species. The grand mean ΣTOX for 2001 was 3.8 (wet) and 2.6 (lipid) times less than corresponding preremedial action (1997) concentrations, suggesting that bioavailable toxaphene residues in this system have been reduced. Forage species, such as croaker (Micropogonias undulatus), mullet, and spot, preferentially accumulate toxaphene residues in this system and may serve as vectors of organochlorine contaminants in the estuarine and coastal ocean food web.

Congruent shifts in sand eel abundance in western and eastern North Atlantic ecosystems

It has been suggested, on the basis of model simulations and slowly accumulating empirical data, that changes in the structure of marine ecosystems may be caused as much by changes in the trophic levels as by environmental factors1,2. Support for this is found in recently observed shifts in species abundance of North Sea fish stocks, where large catches in the 1970s of small, fast-growing, opportunistic plankton-feeding fishes—sprat, sand eel and Norway pout—have been accounted for as the result of the replacement by these species of depleted herring and mackerel stocks3,4. This suggestion is difficult to confirm, as knowledge of the abundance of these ‘opportunistic’ species since the mid–1960s is largely limited to catch data for the North Sea5. The only sand eel report independent of commercial fisheries catch data is for larvae collected in 1948–68, just before the sharp decline in mackerel and herring stocks6. The area surveyed did not, however, cover all the major population centres in the North Sea. In support of replacement, we describe here evidence from the north–west Atlantic which indicates that population explosions of small, fast–growing sand eel can coincide with depletions of larger tertiary predators, including herring and mackerel in a continental shelf ecosystem. Sand eels serve as an important link in marine food chains, preying on secondary producers and constituting an important food of higher trophic level fish and marine mammals7,8.