Birds of a Feather Eat Plastic Together: High Levels of Plastic Ingestion in Great Shearwater Adults and Juveniles Across Their Annual Migratory Cycle

Limited work to date has examined plastic ingestion in highly migratory seabirds like Great Shearwaters (Ardenna gravis) across their entire migratory range. We examined 217 Great Shearwaters obtained from 2008–2019 at multiple locations spanning their yearly migration cycle across the Northwest and South Atlantic to assess accumulation of ingested plastic as well as trends over time and between locations. A total of 2328 plastic fragments were documented in the ventriculus portion of the gastrointestinal tract, with an average of 9 plastic fragments per bird. The mass, count, and frequency of plastic occurrence (FO) varied by location, with higher plastic burdens but lower FO in South Atlantic adults and chicks from the breeding colonies. No fragments of the same size or morphology were found in the primary forage fish prey, the Sand Lance (Ammodytes spp., n = 202) that supports Great Shearwaters in Massachusetts Bay, United States, suggesting the birds directly ingest the bulk of their plastic loads rather than accumulating via trophic transfer. Fourier-transform infrared spectroscopy indicated that low- and high-density polyethylene were the most common polymers ingested, within all years and locations. Individuals from the South Atlantic contained a higher proportion of larger plastic items and fragments compared to analogous life stages in the NW Atlantic, possibly due to increased use of remote, pelagic areas subject to reduced inputs of smaller, more diverse, and potentially less buoyant plastics found adjacent to coastal margins. Different signatures of polymer type, size, and category between similar life stages at different locations suggests rapid turnover of ingested plastics commensurate with migratory stage and location, though more empirical evidence is needed to ground-truth this hypothesis. This work is the first to comprehensively measure the accumulation of ingested plastics by Great Shearwaters over the last decade and across multiple locations spanning their yearly trans-equatorial migration cycle and underscores their utility as sentinels of plastic pollution in Atlantic ecosystems.

Gut content metabarcoding reveals potential importance of fisheries discards consumption in marine fauna

Fisheries discards have become a source of concern for the perennation of marine resources. To reduce discards, the European Union adopted a Landing Obligation under the reform of its Common Fisheries Policy. However, food web consequences of reducing discards remain uncertain since their degree and pathway of reintegration are understudied. We used multi-marker DNA metabarcoding of gut contents and an ecological network approach to quantify marine fauna reliance on discarded fish and functional importance of discard consumers in coastal fishing grounds. We show that potential discard consumption is widespread across fish and invertebrates, but particularly important for decapods which were also pinpointed as functionally important. Potential discard consumption may represent up to 66% of all interactions involving fish prey in the reconstructed network. We highlight that discard reliance may be more important than previously assessed in some fishing areas and support functionally important taxa. While reducing discarding remains a conservation priority, it is crucial to understand discards reintegration in marine food webs to anticipate changes in the context of an ecosystem approach to fisheries management.

The role of the gut microbiota in the dietary niche expansion of fishing bats

Background Due to its central role in animal nutrition, the gut microbiota is likely a relevant factor shaping dietary niche shifts. We analysed both the impact and contribution of the gut microbiota to the dietary niche expansion of the only four bat species that have incorporated fish into their primarily arthropodophage diet. Results We first compared the taxonomic and functional features of the gut microbiota of the four piscivorous bats to that of 11 strictly arthropodophagous species using 16S rRNA targeted amplicon sequencing. Second, we increased the resolution of our analyses for one of the piscivorous bat species, namely Myotis capaccinii, and analysed multiple populations combining targeted approaches with shotgun sequencing. To better understand the origin of gut microorganisms, we also analysed the gut microbiota of their fish prey (Gambusia holbrooki). Our analyses showed that piscivorous bats carry a characteristic gut microbiota that differs from that of their strict arthropodophagous counterparts, in which the most relevant bacteria have been directly acquired from their fish prey. This characteristic microbiota exhibits enrichment of genes involved in vitamin biosynthesis, as well as complex carbohydrate and lipid metabolism, likely providing their hosts with an enhanced capacity to metabolise the glycosphingolipids and long-chain fatty acids that are particularly abundant in fish. Conclusions Our results depict the gut microbiota as a relevant element in facilitating the dietary transition from arthropodophagy to piscivory.

Individual and population dietary specialization decline in fin whales during a period of ecosystem shift

This study sought to estimate the effect of an anthropogenic and climate-driven change in prey availability on the degree of individual and population specialization of a large marine predator, the fin whale (Balaenoptera physalus). We examined skin biopsies from 99 fin whales sampled in the St. Lawrence Estuary (Canada) over a nine year period (1998–2006) during which environmental change was documented. We analyzed stable isotope ratios in skin and fatty acid signatures in blubber samples of whales, as well as in seven potential prey species, and diet was quantitatively assessed using Bayesian isotopic models. An abrupt change in fin whale dietary niche coincided with a decrease in biomass of their predominant prey, Arctic krill (Thysanoessa spp.). This dietary niche widening toward generalist diets occurred in nearly 60% of sampled individuals. The fin whale population, typically composed of specialists of either krill or lipid-rich pelagic fishes, shifted toward one composed either of krill specialists or true generalists feeding on various zooplankton and fish prey. This change likely reduced intraspecific competition. In the context of the current “Atlantification” of northern water masses, our findings emphasize the importance of considering individual-specific foraging tactics and not only population or group average responses when assessing population resilience or when implementing conservation measures.

Spatial and Ontogenetic Patterns in the Trophic Ecology of Juvenile Bull Sharks (Carcharhinus leucas) From the Northwest Gulf of Mexico

A combination of stomach content and stable isotope (δ13C, δ15N, and δ34S) analyses were used to characterize and examine spatiotemporal and ontogenetic trends in the feeding ecology of juvenile bull sharks (Carcharhinus leucas) captured in estuaries throughout the northwest Gulf of Mexico (GoM) between 2013 and 2016. Shark diets were dominated by fish prey taxa [>98% index of relative importance (%IRI)], and of those identified to the family level, two families comprised greater than 50% IRI, Mugilidae (mullets: ∼32%) and Sciaenidae (drums and croakers: 27%). Clupeidae (herrings: 14%) and Ariidae (sea catfishes: 15%) also contributed substantially to the diet of juvenile sharks, though consumption of Ariidae increased as consumption of Clupeidae decreased in juvenile sharks larger than 893 mm Fork Length (FL) (∼1 year old). Values of δ15N increased significantly with shark size, indicating a shift toward larger or higher trophic level prey with increasing shark size. Latitudinal and temporal trends in δ13C and δ34S suggest isotopic variation occurred in correspondence with shifts in primary producer assemblages and environmental drivers of sampled estuaries. These results highlight the importance of teleost prey resources along the freshwater-marine continuum in the diet of juvenile bull sharks, as well as the utility of natural tracers in tracking ontogenetic trends in feeding ecology.

New insight into trophic niche partitioning and diet of mackerel (Scomber scombrus) and herring (Clupea harengus) in Icelandic waters

Understanding the competitive interactions of ecological similar species is essential to determine their role and niche in the ecosystem. Using both conventional dietary methods and stable isotope analysis, we examined the feeding ecology, trophic position and possible niche partitioning of Northeast Atlantic mackerel (Scomber scombrus), Icelandic summer spawning (ISS) herring (Clupea harengus), and Norwegian spring spawning (NSS) herring from Icelandic waters during the spring and summer 2012 and 2014. The stomach analysis showed differences in prey preferences among the species during summer, where mackerel diets were almost exclusively calanoid copepods, while herring ate larger zooplankton, i.e. euphausiids and amphipods. Analysis of isotopic diet contribution of mackerel and herring using Bayesian mixing models, representing mainly the spring consumption, revealed that euphausiids were the main dietary contributor of both mackerel and herring. Fish prey were also an important dietary source for ISS herring, and amphipods were important to the diet of NSS herring. In addition, mackerel encompassed a broad isotopic niche, whereas the two herring stocks had narrower and separated niches from each other. The results from this analysis reveal new and holistic information into the diet of these species, which have various ecological implications.

A tale from the middle Paleocene of Denmark: A tube-dwelling predator documented by the ichnofossil Lepidenteron mortenseni n. isp. and its predominant prey, Bobbitichthys n. gen. rosenkrantzi (Macroridae, Teleostei)

The ichnofossil Lepidenteron provides a unique taphonomic window into the life habits of a tube-dwelling predator, probably an eunicid polychaete, and its fish prey. Here we describe a new tube-like ichnofossil Lepidenteron mortenseni n. isp. from the Kerteminde Marl (100–150 m palaeo-water depth) from the Gundstrup gravel pit near Odense, Fyn, Denmark. 110 individual tubes were examined which contain fish remains, including a variety of disarticulated bones and otoliths, by far dominated by a single gadiform taxon referred herein to as Bobbitichthys n. gen. The isolated otoliths here associated with disarticulated gadiform bones have previously been described, from the time equivalent Lellinge Greensand exposed in the Copen-hagen area, as Hymenocephalus rosenkrantzi, a grenadier fish (family Macrouridae). The abundance of associated bones and otoliths in the examined tubes allowed us to reconstruct part of the cranial configuration of Bobbitichthys rosenkrantzi and to tentatively interpret it as a stem macrourid. Bobbitichthys rosenkrantzi represents the earliest grenadier known in the fossil record. Additional, although considerably less abundant, skeletal remains and otoliths have been tentatively referred to a long-fin bonefish (family Pterothrissidae, Pterothrissus? conchaeformis), a viviparous brotula (family Bythitidae, Bidenichthys? lapierrei), a conger eel (family Congridae, possibly belonging to Rhynchoconger angulosus), and another unidentified gadiform.

The role of the gut microbiota in the dietary niche expansion of fishing bats

BackgroundDue to its central role in animal nutrition, the gut microbiota is likely a relevant factor shaping dietary niche shifts. We analysed both the impact and contribution of the gut microbiota to the dietary niche expansion of the only four bat species that have incorporated fish into their primarily arthropodophage diet.ResultsWe first compared the taxonomic and functional features of the gut microbiota of the four piscivorous bats to that of 11 strictly arthropodophagous species using 16S rRNA targeted amplicon sequencing. Second, we increased the resolution of our analyses for one of the piscivorous bat species, namely Myotis capaccinii , and analysed multiple populations combining targeted approaches with shotgun sequencing. To better understand the origin of gut microorganisms, we also analysed the gut microbiota of their fish prey ( Gambusia holbrooki ). Our analyses showed that piscivorous bats carry a characteristic gut microbiota that differs from that of their strict arthropodophagous counterparts, in which the most relevant bacteria have been directly acquired from their fish prey. This characteristic microbiota exhibits enrichment of genes involved in vitamin biosynthesis, as well as complex carbohydrate and lipid metabolism, likely providing their hosts with an enhanced capacity to metabolise the glycosphingolipids and long-chain fatty acids that are particularly abundant in fish.ConclusionsOur results depict the gut microbiota as a relevant element in facilitating the dietary transition from arthropodophagy to piscivory.