Anne F. Sell

A reliable DNA barcode reference library for the identification of the North European shelf fish fauna.

Valid fish species identification is an essential step both for fundamental science and fisheries management. The traditional identification is mainly based on external morphological diagnostic characters, leading to inconsistent results in many cases. Here, we provide a sequence reference library based on mitochondrial cytochrome c oxidase subunit I (COI) for a valid identification of 93 North Atlantic fish species originating from the North Sea and adjacent waters, including many commercially exploited species. Neighbour‐joining analysis based on K2P genetic distances formed nonoverlapping clusters for all species with a ≥99% bootstrap support each. Identification was successful for 100% of the species as the minimum genetic distance to the nearest neighbour always exceeded the maximum intraspecific distance. A barcoding gap was apparent for the whole data set. Within‐species distances ranged from 0 to 2.35%, while interspecific distances varied between 3.15 and 28.09%. Distances between congeners were on average 51‐fold higher than those within species. The validation of the sequence library by applying BOLDs barcode index number (BIN) analysis tool and a ranking system demonstrated high taxonomic reliability of the DNA barcodes for 85% of the investigated fish species. Thus, the sequence library presented here can be confidently used as a benchmark for identification of at least two‐thirds of the typical fish species recorded for the North Sea.

20 years of the German Small-Scale Bottom Trawl Survey (GSBTS): A review

AbstractThe German Small-scale Bottom Trawl Survey (GSBTS) was initiated in 1987 in order to provide complementary investigations to the International Bottom Trawl Survey (IBTS) in the North Sea, using the same methodology but focussing high-intensity sampling on selected survey areas. Over the last 20 years, the initial number of 4 survey areas (10 × 10 nautical miles; “Boxes”) has been increased to 12, which are distributed over the entire North Sea. This paper describes the survey methods of the GSBTS, summarizes the scientific outcome of the first 20 years, and suggests that international fisheries research institutions would join the GSBTS.The major outcomes of the survey include to date:— Documentation changes in the distribution of fish species and in species assemblages (e.g. changes in species richness, shifts in the southern species component).— Geostatistical evaluation of GSBTS data.— Analysis of spatial scale effects: the relevance of GSBTS survey results for interpreting large-scaled abundance and distribution data from the IBTS.— Description of benthic habitats, composition of invertebrate fauna and its variability.— Process studies, especially investigation of predator-prey interactions between fish through analyses of stomach contents.— Characterization of the typical hydrographic conditions in the survey areas and their variability, and description of the nutrient supply.— Observations of seabirds and their feeding habits.— Analysis of the effects of different parameters on catch rates for bottom fish and on the estimates of abundance indices (e.g. vessel and gear effects, towing time, hydrographic conditions, time of day, number of hauls per area). In continuing this interdisciplinary survey with simultaneous sampling of all faunal and environmental compartments and especially in making it an international effort, we see the possibility of contributing data for the implementation of the ecosystems approach to fisheries management. Particularly, the following aspects can be addressed and would further increase the scientific value of the GSBTS:— Combining the survey data with highly resolved data from the commercial fishery to separate the effects of fishing from natural variability.— Further interdisciplinary analyses of the entire data set. Main aspects include benthos-fish-bird-community changes over time and their relation to historic fisheries impacts, and the coupling of biological and physical habitat characterisation.— Collection of accompanying data (phyto-, zoo- and ichthyoplankton data) in order to make the GSBTS a true ecosystem survey in detecting temporal changes in nearly all major levels of the food web.

Solutions for ecosystem-level protection of ocean systems under climate change.

The Paris Conference of Parties (COP21) agreement renewed momentum for action against climate change, creating the space for solutions for conservation of the ocean addressing two of its largest threats: climate change and ocean acidification (CCOA). Recent arguments that ocean policies disregard a mature conservation research field and that protected areas cannot address climate change may be oversimplistic at this time when dynamic solutions for the management of changing oceans are needed. We propose a novel approach, based on spatial meta-analysis of climate impact models, to improve the positioning of marine protected areas to limit CCOA impacts. We do this by estimating the vulnerability of ocean ecosystems to CCOA in a spatially explicit manner and then co-mapping human activities such as the placement of renewable energy developments and the distribution of marine protected areas. We test this approach in the NE Atlantic considering also how CCOA impacts the base of the food web which supports protected species, an aspect often neglected in conservation studies. We found that, in this case, current regional conservation plans protect areas with low ecosystem-level vulnerability to CCOA, but disregard how species may redistribute to new, suitable and productive habitats. Under current plans, these areas remain open to commercial extraction and other uses. Here, and worldwide, ocean conservation strategies under CCOA must recognize the long-term importance of these habitat refuges, and studies such as this one are needed to identify them. Protecting these areas creates adaptive, climate-ready and ecosystem-level policy options for conservation, suitable for changing oceans.

Benthos and demersal fish habitats in the German Exclusive Economic Zone (EEZ) of the North Sea

We compiled data from different monitoring surveys to analyse and compare community and diversity patterns of fish, epi- and infauna in the German Exclusive Economic Zone (EEZ) of the North Sea in order to identify benthic habitats common to all faunal components. We found congruent community patterns of fish, epi- and infauna for the coastal waters, the Oysterground and the area called “Duck’s Bill”, which coincided with specific abiotic characteristics of these regions. The three regions were defined as special habitats for fish, epi- and infauna species in the German EEZ. The differences in the seasonal variability of abiotic factors seem to be the most important discriminating abiotic characteristic for the three habitats. The spatial distribution of fish, epifauna and infauna communities remained stable over time although habitat characteristics such as sea surface temperature increased due to climate change. However, it is expected that the coastal habitat will be more sensitive to future climate change effects in contrast to the Oysterground and Duck’s Bill habitat.

Cross-realm assessment of climate change impacts on species’ abundance trends

Climate change, land-use change, pollution and exploitation are among the main drivers of species’ population trends; however, their relative importance is much debated. We used a unique collection of over 1,000 local population time series in 22 communities across terrestrial, freshwater and marine realms within central Europe to compare the impacts of long-term temperature change and other environmental drivers from 1980 onwards. To disentangle different drivers, we related species’ population trends to species- and driver-specific attributes, such as temperature and habitat preference or pollution tolerance. We found a consistent impact of temperature change on the local abundances of terrestrial species. Populations of warm-dwelling species increased more than those of cold-dwelling species. In contrast, impacts of temperature change on aquatic species’ abundances were variable. Effects of temperature preference were more consistent in terrestrial communities than effects of habitat preference, suggesting that the impacts of temperature change have become widespread for recent changes in abundance within many terrestrial communities of central Europe.

A trophic cascade with Chaoborus : population dynamics of ex-ephippial generations of Daphnia

Changes in population dynamics and competitive outcome between Daphnia pulex and D. rosea in response to severe predation by Chaoborus larvae were investigated in a field experiment. In a nearly fishless lake with unusually high densities of Chaoborus flavicans and C. obscuripes, the two coexisting Daphnia species developed morphological defense structures to a different degree. An enclosure-exclosure setup was applied to investigate the population dynamics of both species in presence and absence of the predators. The field study followed the population growth of freshly hatched juveniles of D. pulex and D. rosea as they naturally emerged from ephippia in the lakes sediment during spring. Both Daphnia species have a large body size and, in enclosures with Chaoborus only, developed neckteeth and elongated tail spines as inducible defenses. Nevertheless, Chaoborus accounted for high mortality rates in ephippial neonates and strongly reduced the chance of individuals to reach maturity, especially in D. rosea, the dominant species in enclosures without Chaoborus. It is concluded that, in the first generation, when otherwise large and morphologically defended Daphnia are synchronized by ephippial origin to a population of only juveniles, a trophic cascade with Chaoborus may become highly effective.

Pelagic habitat: exploring the concept of good environmental status

Acknowledgements This food for thought contribution was initiated by theme session J “What is a good pelagic habitat?” at the 2016 ICES annual science conference http://www.ices.dk/news-and-events/asc/ASC2016/Pages/Theme-session-J.aspx. All who took part in the session are thanked for their contributions. All participants were welcome to contribute to this article. Funding J. F. Tweddle was supported by the Natural Environment Research Council [NERC grant reference number NE/P005756/1]. E. Bresnan was supported by the Scottish Government’s schedules of service ST02a and ST03r. A. McQuatters-Gollop was supported by the Natural Environment Research Council [NERC grant reference number NE/L002663/1].

Forage fish control population dynamics of North Sea whiting Merlangius merlangus

Predator populations are often affected by the abundance of their prey, but pronounced effects on predatory fish have mainly been demonstrated in ecosystems where a key predator depends largely on one key prey species. The North Sea food web has a comparatively high level of complexity with a high diversity of forage fish, and hence strong effects are less likely to occur. However, in the early 2000s within large parts of the North Sea, several forage fish stocks simultaneously suffered from successive years of recruitment failure together with decreasing stock abundances. Whiting Merlangius merlangus is a major fish predator in the North Sea ecosystem and is known to be almost exclusively piscivorous. We hypothesised that shortages in forage fish should lead to negative effects on growth or condition of a predator that relies on a few dominant prey fish species. In our study, we combined 6 different North Sea data sets on abundance of forage fish and length-at-age, condition and stomach contents of M. merlangus to analyse contrasting periods with high and low forage fish availability. We found a simultaneous decrease in forage fish availability and M. merlangus length-at-age in the period from 2000-2007 and a subsequent parallel increase in prey abundance and length-at-age after 2007. In the period of low forage fish availability, mean stomach content mass was on average 60% less than in the reference periods. Additionally, a bioenergetics calculation revealed that even smaller differences in the stomach contents than those observed would have been sufficient to explain the observed differences in length-at-age. Our findings emphasize the need to incorporate predator-prey interactions in assessment models and management strategies.