Bottom trawl fishing footprints on the world’s continental shelves

Bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high-resolution satellite vessel monitoring system (VMS) and logbook data on 24 continental shelves and slopes to 1,000-m depth over at least 2 years. Trawling footprint varied markedly among regions: from 50% in some European seas. Overall, 14% of the 7.8 million-km2 study area was trawled, and 86% was not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept area ratio (SAR; ratio of total swept area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing an approach to estimate regional trawling footprints when high-resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller and SAR was ≤0.25 in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing

Horizontal distribution of dominant pelagic fish eggs in West African waters

Early life stages of dominant West African pelagic fishes, most of which are commercially important, are rarely studied especially in Senegalese and Mauritanian coastal waters. The aim of the present study was to examine the horizontal distribution of pelagic fish eggs of European sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), round sardinella (Sardinella aurita) and horse mackerel (Trachurus trachurus) in winter-spring and summer. The two seasons revealed two contrasting environmental conditions. While in late winter strong upwelling shaped the environmental conditions, in summer a warm tropical influx of surface water from Senegal towards Mauritania was observed. Fish eggs occurred in both seasons along the shelf coasts of Mauritania and Senegal. The distribution of fish eggs was related to temperature, salinity and chlorophyll data obtained at each sampling position. Eggs of most species were concentrated in coastal waters off the Banc d'Arguin, in Saint-Louis and along the Senegalese sub-region. Spawning occurs mainly during winter and would be linked to environmental changes in particular temperature that significantly vary eggs distribution as notified with Sardina pilchardus and Sardinella aurita during late winter. Moreover, results have shown a significant role of other habitat factors such as chlorophyll, depth and also the continental shelf-break, as a mechanism of retention of fish eggs

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

Early life stages of dominant West African pelagic fishes, most of which are commercially important, are rarely studied especially in Senegalese and Mauritanian coastal waters. The aim of the present study is to examine the horizontal distribution of pelagic fish eggs of Atlantic sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), sardinella (Sardinella aurita) and horse mackerels (Trachurus trachurus.) in late winter and summer. The two seasons revealed two contrasting environmental conditions. While in late winter a permanent upwelling shaped the environmental conditions, in summer a warm tropical influx of surface water towards Mauritania was observed. We collected fish eggs in both seasons along the shelf coasts of Mauritania and Senegal. These data were then related to the sea surface temperature obtained at each sampling position from a conductivity-temperature-depth (CTD) instrument. This study showed that eggs of most species are concentrated in the coastal waters in front the Banc d'Arguin, in Saint-Louis and along the Petite-côte of Senegal. Moreover, it has been shown that spatial distribution of fish eggs is controlled by several factors such as temperature and also by the role of the continental shelf-break, as a mechanism of retention of fish eggs and larvae

PREFACE MS45 report : pelagic fish and prey field dynamics in their habitat

This milestone report contains an update on the analysis of Yellowfin tuna (YFT) bioclimatic modelling as well as the synthesis based on D12.2 and MS42. Local Yellowfin tuna (Thunnus albacares, YFT) catch rates covering the area 10-20°N latitude and 10-30°W longitude were analysed to indicate catch opportunities in Cape Verde waters. Local catch-per-unit-effort (CPUEl) is treated as a function of stock size, Ns, and environmental factors, Vi, the latter at local scale or at stock scale in terms of climate indices. Of the two indices applied to indicate stock size, i.e. the Japanese long line stock index (LLindex) and the so-called Index4 series, the LLindex

Rapport PREFACE MS45 : dynamique des poissons pélagiques et des champs de proies dans leur habitat

This milestone report contains an update on the analysis of Yellowfin tuna (YFT) bioclimatic modelling as well as the synthesis based on D12.2 and MS42. Local Yellowfin tuna (Thunnus albacares, YFT) catch rates covering the area 10-20°N latitude and 10-30°W longitude were analysed to indicate catch opportunities in Cape Verde waters. Local catch-per-unit-effort (CPUEl) is treated as a function of stock size, Ns, and environmental factors, Vi, the latter at local scale or at stock scale in terms of climate indices. Of the two indices applied to indicate stock size, i.e. the Japanese long line stock index (LLindex) and the so-called Index4 series, the LLindex.Ce rapport d'étape contient une mise à jour de l'analyse de la modélisation bioclimatique du thon à nageoires jaunes (YFT) ainsi que la synthèse basée sur D12.2 et MS42. Les taux de capture locaux de l'albacore (Thunnus albacares, YFT) couvrant la zone de 10-20° de latitude nord et de 10-30° de longitude ouest ont été analysés pour indiquer les possibilités de capture dans les eaux du Cap-Vert. La capture locale par unité d'effort (CPUEl) est traitée en fonction de la taille du stock, Ns, et des facteurs environnementaux, Vi, ces derniers à l'échelle locale ou à l'échelle du stock en termes d'indices climatiques. Parmi les deux indices appliqués pour indiquer la taille des stocks, à savoir l'indice japonais des stocks de poissons à long terme (LLindex) et la série dite "Index4", le LLindex

Species richness in North Atlantic fish: Process concealed by pattern.

Aim: Previous analyses of marine fish species richness based on presence-absence data have shown changes with latitude and average species size, but little is known about the underlying processes. To elucidate these processes we use metabolic, neutral and descriptive statistical models to analyse how richness responds to maximum species length, fish abundance, temperature, primary production, depth, latitude and longitude, while accounting for differences in species catchability, sampling effort and mesh size. Data: Results from 53,382 bottom trawl hauls representing 50 fish assemblages. Location: The northern Atlantic from Nova Scotia to Guinea. Time period: 1977–2013. Methods: A descriptive generalized additive model was used to identify functional relationships between species richness and potential drivers, after which nonlinear estimation techniques were used to parameterize: (a) a ‘best’ fitting model of species richness built on the functional relationships, (b) an environmental model based on latitude, longitude and depth, and mechanistic models based on (c) metabolic and (d) neutral theory. Results: In the ‘best’ model the number of species observed is a lognormal function of maximum species length. It increases significantly with temperature, primary production, sampling effort, and abundance, and declines with depth and, for small species, with the mesh size in the trawl. The ‘best’ model explains close to 90% of the deviance and the neutral, metabolic and environmental models 89%. In all four models, maximum species length and either temperature or latitude account for more than half of the deviance explained. Main conclusions: The two mechanistic models explain the patterns in demersal fish species richness in the northern Atlantic almost equally well. A better understanding of the underlying drivers is likely to require development of dynamic mechanistic models of richness and size evolution, fit not only to extant distributions, but also to historical environmental conditions and to past speciation and extinction rate