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Bitetto, I., Romagnoni, G., Adamidou, A., Certain, G., Di Lorenzo, M., Donnaloia, M., et al. (2019). Modelling spatio-temporal patterns of fish community size structure across the northern Mediterranean Sea: an analysis combining MEDITS survey data with environmental and anthropogenic drivers. Sci. Mar., 83, 141–151.
Résumé: The state of marine systems subject to natural or anthropogenic impacts can be generally summarized by suites of ecological indicators carefully selected to avoid redundancy. Length-based indicators capture the status of fish community structure, fulfilling the Marine Strategy Framework Directive (MSFD) requirement for Descriptor 3 (status of commercial fish species). Although the MSFD recommends the development of regional indicators, a comparison among alternative length-based indicators is so far missing for the Mediterranean Sea. Using principal component analysis and dynamic factor analysis, we identified the most effective subset of length-based indicators, whether or not based on maximum length. Indicator trends and lime series of fishing effort and environmental variables are also compared in order to highlight the individual and combined capability of indicators to track system changes across geographical sub-areas. Two indicators, typical length and mean maximum length, constitute the smallest set of non-redundant indicators, capturing together 87.45% of variability. Only in combination can these indicators disentangle changes in the fish community composition from modifications of size structure. Our study supports the inclusion of typical length among the regional MSFD Descriptor 3 indicators for the Mediterranean Sea. Finally, we show dissimilarity between the western and eastern-central Mediterranean, suggesting that there are sub-regional differences in stressors and community responses.
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Ho, H. - C., Séret, B., & Shao, K. - T. (2011). Records of anglerfishes (Lophiiformes: Lophiidae) from the western South Pacific Ocean, with descriptions of two new species. Journal of Fish Biology, 79(7), 1722–1745.
Résumé: Species of Lophiidae collected from the western South Pacific Ocean are examined. Nine nominal species are recognized, all but one species with their distributions extended eastwards and southwards from the western Pacific Ocean. Two new species are described from Polynesia. Lophiodes iwamotoi n. sp. is described from five specimens collected from Savannah Seamount. It is characterized by a relatively long third dorsal-fin spine (56.9-70.8% standard length, L(S)) that extends (when retracted) to between the end of the soft dorsal fin and caudal-fin base; a relatively short fifth dorsal-fin spine (10.5-13.1% L(S)); a relatively short and narrow head; 19-20 pectoral-fin rays. Lophiodes maculatus n. sp. is described from 20 specimens collected from Marquesas Islands. It is characterized by an extremely long third dorsal-fin spine (71.9-87.2% L(S)), extending well beyond the caudal-fin base; a relatively short fifth dorsal-fin spine (11.4-16.5% L(S)); 17-18 pectoral-fin rays. A key to the lophiids in the western South Pacific Ocean is provided.
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Meynard, C. N., & Kaplan, D. (2013). Using virtual species to study species distributions and model performance. Journal of Biogeography, 40(1), 1–8.
Résumé: Simulations of virtual species (i.e. species for which the environmentoccupancy relationships are known) are increasingly being used to test the effects of different aspects of modelling and sampling strategy on performance of species distribution models (SDMs). Here we discuss an important step of the simulation process: the translation of simulated probabilities of occurrence into patterns of presence and absence. Often a threshold strategy is used to generate virtual occurrences, where presence always occurs above a specific simulated probability value and never below. This procedure effectively translates any shape of simulated species response into a threshold one and eliminates any stochasticity from the species occupancy pattern. We argue that a probabilistic approach should be preferred instead because the threshold response can be treated as a particular case within this framework. This also allows one to address questions relating to the shape of functional responses and avoids convergence issues with some of the most common SDMs. Furthermore, threshold-based virtual species studies generate over-optimistic performance measures that lack classification error or incorporate error from a mixture of sampling and modelling choices. Incorrect use of a threshold approach can have significant consequences for the practising biogeographer. For example, low model performance may be interpreted as due to sample bias or poor model choice, rather than being related to fundamental biological responses to environmental gradients. We exemplify these shortcomings with a case study where we compare results from threshold and probabilistic simulation approaches.
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Ortega-Cisneros, K., Shannon, L., Cochrane, K., Fulton, E. A., & Shin, Y. - J. (2018). Evaluating the specificity of ecosystem indicators to fishing in a changing environment: A model comparison study for the southern Benguela ecosystem. Ecological Indicators, 95, 85–98.
Résumé: Ecological indicators used to monitor fishing effects in the context of climate change and variability need to be informative to enable effective ecosystem-based fisheries management. We evaluated the specificity of the response of ecosystem indicators to different fishing and environmental pressure levels using Ecosim and Atlantis ecosystem models for the southern Benguela ecosystem. Three fishing strategies were modelled to represent a variety of ways of targeting fishing within an ecosystem: one focused on low trophic levels (i.e. forage species), another on higher trophic levels (i.e. predatory fish) and a third tested fishing pressure across the full range of potentially exploitable species. Two types of environmental change were simulated for each fishing mortality scenario – random environmental variability and directional climate change. The specificity of selected ecological indicators (mean trophic level of the community, proportion of predatory fish, biomass/landings, mean intrinsic vulnerability and marine trophic index) was evaluated for different combinations of fishing strategy, fishing mortality and both types of environmental change. While there were mostly large differences in indicator values computed from the Atlantis and Ecosim models, the specificity of the ecological indicators considered under changing climate generally corresponded between the two models. Certain indicators (i.e. mean trophic level of the community) were less specific in detecting effects of fishing in the southern Benguela for some of the three fishing strategies modelled (i.e. high trophic level fishing strategy) under climate change. This helped refine the most appropriate indicator set for our system, reflecting the focus of a particular fishing strategy, and improved confidence in the suitability of these indicators for monitoring fishing effects in the Southern Benguela.
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