Documenting the short‐tailed albatross ( Phoebastria albatrus ) clades historically present in British Columbia, Canada, through ancient DNA analysis of archaeological specimens

The short‐tailed albatross (Phoebastria albatrus) is a threatened seabird whose present‐day range encompasses much of the North Pacific. Within this species, there are two genetic clades (Clades 1 and 2) that have distinctive morphologies and foraging ecologies. Due to a global population collapse in the late 19th and early 20th centuries, the frequency of these clades among the short‐tailed albatross population that historically foraged off British Columbia, Canada, is unclear. To document the species' historical genetic structure in British Columbia, we applied ancient DNA (aDNA) analysis to 51 archaeological short‐tailed albatross specimens from the Yuquot site (Borden site number: DjSp‐1) that span the past four millennia. We obtained a 141 bp cytochrome b sequence from 43 of the 51 (84.3%) analyzed specimens. Analyses of these sequences indicate 40 of the specimens belong to Clade 1, while 2 belong to Clade 2. We also identified a single specimen with a novel cytochrome b haplotype. Our results indicate that during the past four millennia most of the short‐tailed albatrosses foraging near Yuquot belonged to Clade 1, while individuals from other lineages made more limited use of the area. Comparisons with the results of previous aDNA analyses of archaeological albatrosses from Japanese sites suggest the distribution of Clades 1 and 2 differed. While both albatross clades foraged extensively in the Northwest Pacific, Clade 1 albatrosses appear to have foraged along the west coast of Vancouver Island to a greater extent. Due to their differing distributions, these clades may be exposed to different threats.

Early evidence for historical overfishing in the Gulf of Mexico

Fisheries encompass complex interplays between social, economic, and environmental factors, but limitations on historical fisheries data can hamper efforts to identify and contextualize the long-term spatiotemporal patterns that shape them. We integrate 2500 years of stable isotope (δ³⁴S, δ¹³C, and δ¹⁵N) and zooarchaeological evidence from Gulf of Mexico fisheries to assess cultural, demographic, and technological changes affecting sheepshead (Archosargus probatocephalus) populations and fishing practices in Louisiana, USA. Concurrent with human population growth, average sizes of sheepshead caught decreased from the 1720s to 1830s. The size of fish caught after the 1830s increased to pre-1720 levels at the same time that isotopic compositions of fish bone collagen show that fish were being caught from a more diverse range of ecosystems, including distant seagrass beds. Our findings provide the first evidence for large-scale depressions of historical sheepshead populations and the processes driving them, including rapid human population growth and sustained harvesting pressure.

Seaweed-eating sheep show that δ34 S evidence for marine diets can be fully masked by sea spray effects

RATIONALE

Stable sulfur isotope compositions (δ³⁴ S values) are a useful marker of terrestrial (lower δ³⁴ S) versus marine (higher δ³⁴ S) diets. In coastal areas, ³⁴ S-enriched sea spray can obscure these marine/terrestrial differences. We sought to establish whether δ³⁴ S values of sea spray-affected terrestrial fauna can be distinguished from those of marine-feeding terrestrial fauna.

METHODS

We measured bone and dentine collagen δ³⁴ S values, as well as stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope compositions via continuous flow elemental analysis/isotope ratio mass spectrometry of 21 sheep (Ovis aries) raised on an island (North Ronaldsay, UK) of <7 km² that had widely divergent access to marine (seaweed) and heavily sea spray-affected terrestrial (grass) food sources. We also analyzed the bone collagen of marine and terrestrial fauna from this island.

RESULTS

Sheep bone collagen showed well-defined trends with highly significant correlations between δ¹³ C and δ¹⁵ N values indicative of feeding along a continuum of fully terrestrial to fully marine diets, consistent with other modern baseline data from marine and terrestrial animals in the same area. In contrast, δ³⁴ S values were generally elevated for all sheep and were not significantly correlated with either δ¹³ C or δ¹⁵ N values.

CONCLUSIONS

Our findings demonstrate that δ³⁴ S values are poorly suited for differentiating marine and terrestrial diets in terrestrial animals in areas with pronounced sea spray effects. Care must be taken to characterize the isotopic compositions of potential food items before δ³⁴ S values are used as a marker for reliance on marine protein in modern and ancient contexts.

Integrating fish scale and bone isotopic compositions for 'deep time' retrospective studies

Isotopic studies of archived fish scales have tremendous potential to develop long-term retrospectives that provide important insights into how humans have altered aquatic ecosystems. However, fish specimens in museum archives and other repositories typically date to time periods when the impacts of industrial societies may have already caused profound environmental changes. Archaeological fish bones offer an opportunity to bridge this key temporal gap by providing samples spanning from the recent past to as far back as the Pleistocene. Collagen is the primary protein component of both fish scale and bone, but the comparability of isotopic compositions from these tissues has not been established experimentally. To lay the framework for integrating isotopic datasets from these tissues, we compare δ¹³C and δ¹⁵N of bone and scale collagen, as well as other tissues, from fish with life-time controlled diets. Results show that while there is no difference in δ¹³C between scale and bone collagen, there may be a very slight but meaningful inter-tissue offset in δ¹⁵N (<0.3‰). We discuss potential sources of δ¹⁵N variation in scale and bone collagen measurements. Because there is no difference in scale and bone δ¹³C, and the observed offset in δ¹⁵N is very small (less than analytical uncertainty in many studies), our findings demonstrate that collagen isotopic compositions from these tissues should be directly comparable when integrating datasets from modern and ancient samples to build more powerful, millennium-scale isotopic times series. In linking isotopic compositions of collagen from modern, historical (scales), and archaeological (bones) fish, our findings open the way for more nuanced contextualization of how ecosystems functioned prior to large-scale exploitation and how they have responded to mounting anthropogenic pressures in the intervening centuries.

Effects of lipid extraction and ultrafiltration on stable carbon and nitrogen isotopic compositions of fish bone collagen

RATIONALE

Fish bone collagen isotopic measurements are increasingly important in palaeodietary and paleoenvironmental studies yet differences in the chemical and physical properties of fish relative to other vertebrate bones are rarely considered. Lipid content in fish bone, which can exceed 50%, may underlie the poor collagen integrity criteria typically observed in archaeological studies.

METHODS

We compare stable carbon and nitrogen isotopic and elemental compositions of bone collagen prepared using four different methods from a wide range of modern fish species to: (1) assess the extent to which lipid content influences bone collagen δ(13) C and δ(15) N values, and (2) evaluate the relative efficacy of chemical (2:1 chloroform/methanol) and physical (30 kDa ultrafilters) methods for removing lipids from bones.

RESULTS

Lower δ(13) C values were observed when the lipid content exceeded 5% of the initial bone mass. The lipid content did not influence the δ(15) N values. 30 kDa ultrafiltration, a common pretreatment for purifying archaeological collagen, removed fewer lipids and was associated with reduced collagen yields (37% loss) as well as altered amino acid compositions. In contrast, collagen prepared using a 2:1 chloroform/methanol lipid extraction step resulted in significantly improved collagen yields, elemental compositions, and isotopic measurements relative to a control treatment.

CONCLUSIONS

The chemical lipid extraction method (2:1 chloroform/methanol) performed significantly better than the physical lipid extraction method (30 kDa ultrafilters). Given the high quantities of lipids in fish bones we recommend the inclusion of a chemical lipid extraction step when isolating collagen from modern and archaeological fish bones. Copyright © 2016 John Wiley & Sons, Ltd.