Pascal Lorance

Does Presence of a Mid-Ocean Ridge Enhance Biomass and Biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007–2010. The MAR, 3,704,404 km2 in area, accounts for 44.7% lower bathyal habitat (800–3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Variation in locomotion behaviour in northern cutthroat eel (Synaphobranchus kaupi) on the Bay of Biscay continental slope

Based on the analysis of video sequences recorded during four dives with a manned submersible in the Bay of Biscay, NE Atlantic, evidence is provided that the northern cutthroat eel Synaphobranchus kaupi shows marked variations in abundance and in the adoption of three locomotion behaviours—forward movement, station holding, and drifting—among six ecologically different habitats. Furthermore, significant variations in association with the bottom and disturbance responses to the submersible were found. Two swimming velocity measures taken from eels during forward movement were significantly correlated with both depth and temperature. The behavioural variations observed partly occurred also between adjacent habitats that were crossed during the same dive. These results and additional observations of instantaneous fluctuations in hydrological conditions suggest that these deep-sea eels are able to adjust to ecological variability at small spatial and temporal scales in a flexible and adaptive way.

CPUE abundance indices of the main target species of the French deep-water fishery in ICES sub-areas V-VII

Abstract Three major fleets of high sea trawlers practising deep-water fishing are defined. Altogether, these fleets catch more than 90% of the French landings of deep-water species. A multiplicative model has been adjusted to monthly catch per unit effort (CPUE) weighted by effort to estimate annual abundance indices for the main deep-water species exploited since the late 1980s (Coryphaenoides rupestris, Hoplostethus atlanticus, Aphanopus carbo, Centroscymnus coelolepis and Centrophorus squamosus) and for the main other species caught by these fleets (Pollachius virens, Molva dipterygia and Molva molva). For the deep-water species, the CPUE trends are not consistent between fleets. The differences are interpreted to be due to technical changes and the indices from the fleet of larger specialised deep-water trawlers is considered to be the most representative of the actual fish abundance. For saithe and blue ling the declining trend in CPUE previously documented are observed again with slight differences in slopes probably due to method. The CPUE of deep-water species show strong declining trends suggesting severe impact of the fishery. However, declining CPUE is a normal feature of any new fishery. The possible effect of the fishing strategy on the amount of effort counted as species directed effort cannot be excluded because the catch and effort data available is detailed by statistical rectangles while the proper scale would be the trawl haul.

Habitat, behaviour and colour patterns of orange roughy Hoplostethus atlanticus (Pisces: Trachichthyidae) in the Bay of Biscay

Analyses of 13 submersible dives on the continental slope of the Bay of Biscay (north-east Atlantic) showed that: (i) orange roughy formed dense aggregation of more than 4000 individuals per ha close to the bottom of a small underwater canyon. In all other study areas only a few individuals were observed. Orange roughy aggregations are probably associated with areas of high water mass movements and mixing; (ii) most individuals observed within this aggregation or in its peripheral areas were behaviourally inactive and could be approached with the submersible at close distance; (iii) a large number of these orange roughy showed a completely pigmentless white, or weak red coloration, never observed from specimens caught in trawls. Two individuals which were disturbed by the submarine changed from white to the ‘typical’ red coloration. These observations suggest fine tuning of the foraging strategy and life cycle of the species. It is speculated that, as an active predator of a sparse food resource, orange roughy has developed adaptations to exploit areas with specific hydrological conditions which offer high prey encounter rates and shelter during metabolic relaxation phases between foraging trips.

Strengths and Weaknesses of the Management and Monitoring of Deep-Water Stocks, Fisheries, and Ecosystems in Various Areas of the World—A Roadmap Toward Sustainable Deep-Water Fisheries in the Northeast Atlantic?

Scientific interest in deep-water marine resources has increased dramatically over the last 10–20 years as management bodies have sought advice on how to manage deep-water fisheries and protect deep-water ecosystems. The strengths and weaknesses of the management and monitoring of deep-water stocks, fisheries, and ecosystems in various areas of the world are described, with the objective of informing the EU FP7 DEEPFISHMAN project so that it can fulfill its primary aim, which is to develop strategic options for a short- and long-term management and monitoring ecosystem-based framework for the northeast Atlantic. To provide a baseline, the current monitoring and management regime in the northeast Atlantic is reviewed, followed by a brief description of the regimes applying to deep-water fisheries in the northwest Atlantic, the southeast Atlantic, off Brazil, in the Antarctic, off Australia and New Zealand, and in the Mediterranean. The strengths and weaknesses of these are discussed, taking into account additional information available from DEEPFISHMAN case study stocks, outcomes from consultations with stakeholders in the deep-water fishing industry in the northeast Atlantic, and the requirements of EU regulations and developing policy that will likely impact deep-water fisheries in the northeast Atlantic.

Assessment of the roundnose grenadier (Coryphaenoides rupestris) stock in the Rockall Trough and neighbouring areas (ICES Sub-areas V-VII)

The catch (landings and discards) at age of roundnose grenadier (Coryphaenoides rupestris) were used to assess the stock in the areas exploited by French trawlers. A pseudo-cohort analysis, corrected for changes in fishing effort in the period before the year which catch at age are analysed, was carried out for the years 1996 and 1997. Age distributions were derived from length measurements and an age length key (ALK) estimated from 1529 otoliths. Although, unvalidated in the size range of adult fish, this ALK looked consistent with validated length at age of juveniles and former age estimates of adult fish. It was also combined with length distributions data from surveys prior to exploitation and from landings in 1990 (early in the history of the fishery) to estimate the total mortality then equivalent to the natural mortality. This poorly converged pseudo-cohort suggested a low annual fishing mortality. However, the behaviour of the stock was further investigated from yield per recruit (Y/R) analysis. Because of a series of gaps in the knowledge of this species (stock(s) distribution, unvalidated ages, …), the estimates of fishing mortality must be considered with caution. The main interest of the analysis is probably to stress the impact of the discards on the potential yield of roundnose grenadier.

Point, alpha and beta diversity of carnivorous fish along a depth gradient

The catch from bottom longline stations sampled from a series of research cruises around Lanzarote and Fuerteventura (Canary Islands, NE Atlantic) was analysed in terms of fish distribution, density and diversity. The distribution of the number of species and individuals caught per station appeared to fit well the Poisson and Exponential distribution function, respectively. In particular, the parameter of the Poisson’s distribution appeared to provide an index of the point (at station scale) diversity, and its confidence interval, allowing for statistical comparisons. The relationships between point diversity, the alpha diversity (in the depth strata) and the beta diversity (along the depth gradient) were investigated. Around the islands, the density and the point diversity of the predator fish declined with depth down to about 800 m and then increased in the deeper stratum. The alpha diversity was the lowest in the deeper stratum but the taxonomic distinctness was similar to that of shallower strata. The beta diversity showed some faunal breaks along the depth gradient. The carnivorous fish fauna can be understood as comprised of three major assemblages: shelf, upper slope and mid-slope that are different both in terms of species composition and point, alpha and beta diversities. The relevance of this simple method for ecological studies of fish assemblage in the context of non-trawlable grounds is discussed, in particular for the slope and other areas of established or developing deep-water fisheries.

Effects of density dependence, zooplankton and temperature on blue whiting Micromesistius poutassou growth

Blue whiting Micromesistius poutassou mean total length at age in the north-east Atlantic Ocean was found to vary by around ±6% during the period 2004-2011 and mean mass at age by ±22% during the years 1981-2013. Linear modelling provided strong evidence that these phenotypic growth variations can be explained by trophic conditions, mainly negative density dependence and also food availability, and a negative long-term temperature effect on asymptotic size.

Interannual Variability of Fisheries Economic Returns and Energy Ratios Is Mostly Explained by Gear Type

According to portfolio theory applied to fisheries management, economic returns are stabilised by harvesting in a portfolio stocks of species whose returns are negatively correlated and for which the portfolio economic return variance is smaller than the sum of stock specific return variances. Also, variability is expected to decrease with portfolio width. Using a range of indicators, these predictions were tested for the French fishing fleets in the Bay of Biscay (Northeast Atlantic) during the period 2001–2009. For this, vessels were grouped into eight fishing fleets based on the gears used and exploited species were grouped into five functional groups. The portfolio width of fleets ranged from 1–3 functional groups, or 4–19 species. Economic fleet returns (sale revenues minus fishing costs) varied strongly between years; the interannual variability was independent of portfolio width (species or functional groups). Energy ratio expressed by the ratio between fuel energy used for fishing and energy contained in landings varied from 0.3 for purse seines to 9.7 for trawlers using bottom trawls alone or in combination with pelagic trawls independent of portfolio width. Interannual variability in total sale revenues was larger than the sum of species specific sales revenue variability, except for fleets using hooks and pelagic trawlers; it increased with the number of species exploited. In conclusion, the interannual variability of economic returns or energy ratios of French fisheries in the Bay of Biscay did not decrease with the number of species or functional groups exploited, though it varied between fleets.

Indicators for Ecosystem-Based Management: Methods and Applications

Indicators are essential tools for policy making, public communication and the provision of scientific advice. In fisheries science, indicators have been increasingly used to advising on fish and shellfish stock management, especially since the precautionary approach to fisheries management was developed. They are now becoming a cornerstone of the wider ecosystem approach to the management of all human activities. In this section, we provide some recent examples of methods we developed for creating and selecting pressure indicators and ecological indicators derived from different types of information (scientific survey data, commercial fisheries data) for a range of ecosystems, covering pelagic, demersal and deep-water systems.