Fisheries Ecology: Hunger for Shark Fin Soup Drives Clam Chowder off the Menu

Removal by fishing of large sharks has reduced predation-pressure on shark prey and, via a trophic cascade, caused clam populations to crash. This indirect response illustrates why fisheries should be managed in a whole-ecosystem context

Moonlight drives ocean-scale mass vertical migration of zooplankton during the Arctic winter

The creation of the pan-Arctic archive of ADCP data was supported by the UK Natural Environment Research Council (NERC) (Panarchive: NE/H012524/1 and SOFI: NE/F012381/1) as was mooring work in Svalbard (Oceans 2025 and Northern Sea Program). Moorings were also supported by the Research Council of Norway (NFR) projects: Circa (214271), Cleopatra (178766), Cleopatra II (216537), and Marine Night (226471).In extreme high-latitude marine environments that are without solar illumination in winter, light-mediated patterns of biological migration have historically been considered non-existent [1]. However, diel vertical migration (DVM) of zooplankton has been shown to occur even during the darkest part of the polar night, when illumination levels are exceptionally low [2 and 3]. This paradox is, as yet, unexplained. Here, we present evidence of an unexpected uniform behavior across the entire Arctic, in fjord, shelf, slope and open sea, where vertical migrations of zooplankton are driven by lunar illumination. A shift from solar-day (24-hr period) to lunar-day (24.8-hr period) vertical migration takes place in winter when the moon rises above the horizon. Further, mass sinking of zooplankton from the surface waters and accumulation at a depth of ∼50 m occurs every 29.5 days in winter, coincident with the periods of full moon. Moonlight may enable predation of zooplankton by carnivorous zooplankters, fish, and birds now known to feed during the polar night [4]. Although primary production is almost nil at this time, lunar vertical migration (LVM) may facilitate monthly pulses of carbon remineralization, as they occur continuously in illuminated mesopelagic systems [5], due to community respiration of carnivorous and detritivorous zooplankton. The extent of LVM during the winter suggests that the behavior is highly conserved and adaptive and therefore needs to be considered as “baseline” zooplankton activity in a changing Arctic ocean [6, 7, 8 and 9].Publisher PDFPeer reviewe

Effects of temperature and salinity on four species of northeastern Atlantic scyphistomae (Cnidaria Scyphozoa)

This work was funded by the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland), and we gratefully acknowledge that support. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. C.L.W. is also grateful to the US/UK Fulbright Commission and the University of St Andrews for their financial support.Laboratory incubation experiments were conducted to examine the effects of different temperatures (4, 9, 14, 19, 23°C) and salinities (21, 27, 34) on survival and asexual reproduction of scyphistomae of Cyanea capillata, C. lamarckii, Chrysaora hysoscella, and Aurelia aurita in order to better understand how climate variability may affect the timing and magnitude of jellyfish blooms. Significant mortality was observed only for C. capillata and Ch. hysoscella at the highest and lowest temperatures, respectively, but temperature and salinity significantly affected the asexual reproductive output for all species. As temperature increased, production rates of podocysts increased and, if produced, progeny scyphistomae by side budding also increased. However, strobilation rates, and therefore the mean number of ephyrae produced, decreased when scyphistomae were exposed to elevated temperatures. These results provide a mechanistic explanation for why ephyrae of these species tend to be produced during colder periods of the year whilst summer and early autumn are probably important periods for increasing the numbers of scyphistomae in natural populations.PostprintPeer reviewe

The distribution of pelagic sound scattering layers across the southwest Indian Ocean

Ship of Opportunity Data were sourced from the Integrated Marine Observing System (IMOS)—an initiative of the Australian Government being conducted as part of the National Collaborative Research Infrastructure Strategy and the Super Science Initiative. Other acoustic data were collected as part of the Southwest Indian Ocean Seamounts Project (http://www.iucn.org/marine/seamounts) which was supported supported by the EAF Nansen Project, the Food and Agriculture Organization of the United Nations, the Global Environment Facility, the International Union for the Conservation of Nature, the Natural Environment Research Council (Grant NE/F005504/1), the Leverhulme Trust (Grant F00390C) and the Total Foundation. We thank the Masters, officers, crews and science parties of cruises DFN 2009-410 and JCO66/67 for their assistance during echosounder calibration and data acquisition, and two anonymous reviewers for their comments. PHBS was supported by the German National Academic Foundation, a Cusanuswerk doctoral fellowship, and a Lesley & Charles Hilton-Brown Scholarship.Shallow and deep scattering layers (SLs) were surveyed with split-beam echosounders across the southwest Indian Ocean (SWIO) to investigate their vertical and geographical distribution. Cluster analysis was employed to objectively classify vertical backscatter profiles. Correlations between backscatter and environmental covariates were modelled using generalized additive mixed models (GAMMs) with spatial error structures. Structurally distinct SL regimes were found across the Subantarctic Front. GAMMs indicated a close relationship between sea surface temperature and mean volume backscatter, with significantly elevated backscatter in the subtropical convergence zone. The heterogeneous distribution of scattering layer biota reflects the biogeographic zonation of the survey area and is likely to have implications for predator foraging and carbon cycling in the Indian Ocean.PostprintPeer reviewe

Cryptic hydrozoan blooms pose risks to gill health in farmed North Atlantic salmon (Salmo salar)

This study was made possible through a Marine Alliance for Science and Technology Scotland Prize PhD Studentship awarded to Anna Kintner in 2011, and was further supported with contributions from the School of Biology, University of St Andrews.Sampling at four salmon aquaculture sites along the west coast of Scotland has identified short-lived aggregations of planktonic hydrozoans (>280 individuals m−3), here termed blooms. Several such blooms were linked with increases in gill pathology and mortality in caged fish. Two types, Obelia sp. and Lizzia blondina, were found to cause blooms regularly and often concurrently. Species composition of hydrozoan populations and fluctuations in population sizes were spatially and temporally heterogeneous, with adjacent sites (within 30 km of one another and with similar oceanic exposure) experiencing no correlation between species composition and population density. Blooms appeared temperature-mediated, with all identified blooms by Obelia sp. and L. blondina taking place in water above 12 °C; however, temperature alone was not found to be predictive. Blooms were not significantly associated with change in salinity, water clarity, or photoperiod. Due to the apparent lack of broadly applicable predictors, we suggest that localized, targeted sampling and examination of planktonic hydrozoan populations is required to discern the presence or absence of a bloom. It is likely that many blooms have historically caused harm in salmon aquaculture while remaining unrecognized as the root cause.PostprintPeer reviewe

Impacts of jellyfish on marine cage aquaculture : an overview of existing knowledge and the challenges to finfish health

BBSRC Eastbio funded studentship (lead author).Gelatinous plankton present a challenge to marine fish aquaculture that remains to be addressed. Shifting plankton distributions, suggested by some to be a result of factors such as climate change and overfishing, appear to be exacerbated by anthropogenic factors linked directly to aquaculture. Fish health can be negatively influenced by exposure to the cnidarian hydrozoan and scyphozoan life stages commonly referred to as “jellyfish”. Impact is particularly pronounced in gill tissue, where three key outcomes of exposure are described; direct traumatic damage, impaired function, and initiation of secondary disease. Cnidarian jellyfish demonstrated to negatively impact fish include Cyanea capillata, Aurelia aurita, and Pelagia noctiluca. Further coelenterates have also been associated with harm to fish, including sessile polyps of species such as Ectopleura larynx. An accurate picture of inshore planktic exposure densities within the coastal environments of aquaculture would aid in understanding cnidarian species of concern, and their impact upon fish health, particularly in gill disease. This information is however presently lacking. This review summarises the available literature regarding the impact of gelatinous plankton on finfish aquaculture, with a focus on cnidarian impact on fish health. Present strategies in monitoring and mitigation are presented, alongside identified critical knowledge gaps.PostprintPeer reviewe

Sampling the fish gill microbiome : a comparison of tissue biopsies and swabs

Funding Information: The research costs of this work were supported by the BBSRC EASTBIO DTP and Marine Alliance for Science and Technology Scotland (MASTS) small grants funding scheme. Acknowledgements The authors would like to thank Scottish Sea Farms (SSF) for the kind facilitation of fieldwork that provided material in this project, particularly the staff at the Loch Spelve facility, and the health team at SSF, particularly Dr. Ralph Bickerdike. Thanks are due as well to Professor Matt Holden and Kerry Pettigrew of the Infection Group within the Biomedical Sciences Research Complex, School of Medicine, University of St Andrews, for assistance within the laboratory, as well as Dr. David Bass at the Centre for Environment Fisheries and Aquaculture Science for helpful proofreading.Peer reviewedPublisher PD

Biogeography of the global ocean's mesopelagic zone

The work has arisen from a PhD studentship funded by Australian Antarctic Division, University of Tasmania, and School of Biology. This study has received support from the European H2020 International Cooperation project MESOPP (Mesopelagic Southern Ocean Prey and Predators; http://www.mesopp.eu/).The global ocean’s near-surface can be partitioned into distinct provinces on the basis of regional primary productivity and oceanography [1]. This ecological geography provides a valuable framework for understanding spatial variability in ecosystem function, but has relevance only part way into the epipelagic zone (the top 200 m). The mesopelagic (200-1,000 m) makes up c. 20% of the global ocean volume, plays important roles in biogeochemical cycling [2], and holds potentially huge fish resources [3–5]. It is however hidden from satellite observation, and a lack of globally-consistent data has prevented development of a global-scale understanding. Acoustic Deep Scattering Layers (DSLs) are prominent features of the mesopelagic. These vertically-narrow (10s-100s of m) but horizontally-extensive (continuous for 10s-1,000s of km) layers comprise fish and zooplankton, and are readily detectable using echosounders. We have compiled a database of DSL characteristics globally. We show here that DSL depth and acoustic backscattering intensity (a measure of biomass) can be modelled accurately using just surface primary productivity, temperature and wind-stress. Spatial variability in these environmental factors leads to a natural partition of the mesopelagic into 10 distinct classes. These classes demark a more complex biogeography than the latitudinally-banded schemes proposed before [6,7]. Knowledge of how environmental factors influence the mesopelagic enables future change to be explored: we predict that by 2100 there will be widespread homogenisation of mesopelagic communities, and that mesopelagic biomass could increase by c. 17%. The biomass increase requires increased trophic efficiency, which could arise because of ocean warming and DSL shallowing.PostprintPeer reviewe

Variability in prey field structure drives inter-annual differences in prey encounter by a marine predator, the little penguin

This study was funded by Australian Research Council Linkage Grants (grant nos. LP110200603 and LP160100162), with contributions from the Taronga Conservation Society Australia.Understanding how marine predators encounter prey across patchy landscapes remains challenging due to difficulties in measuring the three-dimensional structure of pelagic prey fields at scales relevant to animal movement. We measured at-sea behaviour of a central-place forager, the little penguin (Eudyptula minor), over 5 years (2015–2019) using GPS and dive loggers. We made contemporaneous measurements of the prey field within the penguins' foraging range via boat-based acoustic surveys. We developed a prey encounter index by comparing estimates of acoustic prey density encountered along actual penguin tracks to those encountered along simulated penguin tracks with the same characteristics as real tracks but that moved randomly through the prey field. In most years, penguin tracks encountered prey better than simulated random movements greater than 99% of the time, and penguin dive depths matched peaks in the vertical distribution of prey. However, when prey was unusually sparse and/or deep, penguins had worse than random prey encounter indices, exhibited dives that mismatched depth of maximum prey density, and females had abnormally low body mass (5.3% lower than average). Reductions in prey encounters owing to decreases in the density or accessibility of prey may ultimately lead to reduced fitness and population declines in central-place foraging marine predators.Publisher PDFPeer reviewe

Ecosystem approach to harvesting in the Arctic : walking the tightrope between exploitation and conservation in the Barents Sea

Funidng: This study was supported by the Changing Arctic Ocean project MiMeMo (NE/R012679/1) jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF/03F0801A). Brierley was also supported by ArcticPRIZE (NE/P005721/1).Projecting the consequences of warming and sea-ice loss for Arctic marine food web and fisheries is challenging due to the intricate relationships between biology and ice. We used StrathE2EPolar, an end-to-end (microbes-to-megafauna) food web model incorporating ice-dependencies to simulate climate-fisheries interactions in the Barents Sea. The model was driven by output from the NEMO-MEDUSA earth system model, assuming RCP 8.5 atmospheric forcing. The Barents Sea was projected to be > 95% ice-free all year-round by the 2040s compared to > 50% in the 2010s, and approximately 2 °C warmer. Fisheries management reference points (FMSY and BMSY) for demersal fish (cod, haddock) were projected to increase by around 6%, indicating higher productivity. However, planktivorous fish (capelin, herring) reference points were projected to decrease by 15%, and upper trophic levels (birds, mammals) were strongly sensitive to planktivorous fish harvesting. The results indicate difficult trade-offs ahead, between harvesting and conservation of ecosystem structure and function.Publisher PDFPeer reviewe