Fabian Blanchard

A new multivariate mapping method for studying species assemblages and their habitats: Example using bottom trawl surveys in the Bay of Biscay (France)

Abstract This new numerical approach proposes a solution to a fundamental and difficult question in ecology, consisting of the correct geographical representation of multidimensional structures. Firstly, transformation was applied to the original matrix (n sites x q variables) in order to satisfy the condition of multinormality. Then, a hierarchical cluster analysis was used and each hierarchical level was studied and characterised by a certain probability level. For each cut off level an algorithm based on the computation of the Bayesian probabilities produced a smaller matrix (n sites x c groups). These conditional probabilities measure the chance that each site has in belonging to a predefined group of sites. Spatial distributions of these probability values for each group of sites were mapped using kriging interpolation. Finally, the maps were used to define homogenous zones on a single map by superimposing one map on the other. The maximal value of interpolated probability was used as criterion to assign each point of the map to the zones predefined by this classification. This method was applied to map demersal fish habitats by using a dataset from bottom trawl surveys in the Bay of Biscay (France) during October 1990. The boundaries between habitats wae identitied objectively. Then, the indicator species and species assemblages characterising the different habitats were identitied by using an indicator value index. This index integrates the speciticity and the fidelity quantities calculated for each species in each habitat. The obtained results showed that this method presented a robust tool to describe the habitat of exploited species. The obtained habitats were validated by their correspondence with depth strata, sediment type and also by the biological characteristics of the indicator species. The proposed method is useful in the study of temporal variations of habitats with regards to species assemblages and can also be generalised to other multivariate databases of different descriptors (physical, chemical, biological, etc.).

Relating Species and Community Dynamics in an Heavily Exploited Marine Fish Community

We examined the dynamics of fish species and how they relate to species assemblage coherence in the heavily exploited Georges Bank fish community. Coherence is defined as reduced temporal variability of total assemblage biomass. We assumed that a higher degree of compensation hence coherence occurs within competitively coupled species assemblages; therefore, fisheries may directly alter the dynamics of certain targeted species sizes but assemblage structure will be relatively more stable owing to compensatory interactions. Species-sizes were grouped, based on negative covariance coupling in biomass time series from survey data. Assemblages representing benthic feeders were clearly identified by this method; furthermore, the most heavily exploited species-sizes were decoupled from other species-sizes suggesting that fisheries have diminished their potential to compensate or to be compensated for by competitive interactions. Biomass of species-sizes within known trophic guilds strongly compensated other guild-member biomass fluctuations if the diet of guild members was more specialized. This is an indication that more competitive conditions (more specialization) foster greater compensatory responses between competitors biomass fluctuations.

A bio-economic model for the ecosystem-based management of the coastal fishery in French Guiana

This paper offers a theoretical and empirical modeling for ecosystem-based fishery management (EBFM). A multi-species and multi-fleets model integrating Lokta-Volterra trophic dynamics and profit functions is developed for the coastal fishery of French Guiana. This small-case fishery constitutes a challenging example with high fish biodiversity, several non selective fleets and a potentially increasing local food demand due to demographic pressure. The dynamic model is calibrated with thirteen species and four fleets using catch and effort data on a monthly basis from 2006 to 2009. Several contrasting fishing scenarios including status quo, total closure, economic and viable strategies are simulated and compared from both biodiversity preservation and socio-economic performance viewpoints. We show that fishing outputs including food supply and profitability of fleets can be sustained although a significant loss of biodiversity cannot be avoided.

Ecological-economic modelling for the sustainable management of biodiversity

Terrestrial and marine biodiversity provides the basis for both ecosystems functioning and numerous commodities or services that underpin human well-being. From several decades, alarming trends have been reported worldwide for both biodiversity and ecosystem services. Therefore the sustainable management of biodiversity requires a double viewpoint balancing ecological conservation with the welfare of human societies. Understanding the underlying trade-offs, synergies and interactions imposes the development of interdisciplinary researches and methods. In that respect, bio-economic or ecological economic modeling is likely to play a major role. The present paper intends to elicit the key features, strengths and challenges of bio-economic approaches especially in mathematical and computational terms. It first recall the main bio-economic methods, models and decisional instruments used in these types of analyses. Then the paper shows to what extent bio-economic sustainability lies between equilibrium, viability and optimality mathematical frameworks. It ends up by identifying new major challenges among which the operationalization of ecosystem based management, the precautionary principle and the implementation of governance are especially important.

Outbreaks of Disease Possibly Due to a Natural Avian Herpesvirus Infection in a Colony of Young Magnificent Frigatebirds (Fregata magnificens)in French Guiana

The Ile du Grand Connétable nature reserve is a rocky island off the Northern Atlantic coast of South America that hosts a unique population of Magnificent Frigatebirds (Fregata magnificens, Pelecaniformes). A high chick mortality, associated with nodular proliferative lesions, involving featherless areas, such as legs, neck, eyelids, and beak, was recorded during a consecutive 2 yr and affected almost half of the generation. Investigations were, therefore, conducted to determine the cause of these epidemics. Although histopathologic investigations suggested that malnutrition, because of fewer resources in the Frigates’ fishing area, could be the cause of the epidemic, a novel alphaherpesvirus, tentatively called Fregata magnificens herpesvirus, was detected in cutaneous crusts on the diseased birds. Although in this study, we do not prove the causal link of this new virus to the symptoms observed, it can nevertheless be suggested that in debilitated hosts, a productive herpesvirus infection might accelerate, and/or be accelerated by, population declines. These results emphasize the need to take into consideration the possible role of herpesviruses in weakened populations of wild birds in conservation management plans.

Temporal variability of total biomass in harvested communities of demersal fishes

The biomass variability of the demersal fish communities of the Bay of Biscay and the Gulf of Lions is analysed on a decadal scale using scientific surveys and fisheries data. The coefficient of variation of the total biomass is lower than the coefficient of variation of species biomass in both areas. Previous analyses from the Scotian Shelf have demonstrated that the total biomass of demersal fish is quite stable relative to individual species biomass. This result was interpreted as demonstrations of interactions between species due to energy limitation of systems. Moreover, the total biomass variability is lower in the Bay of Biscay than in the Gulf of Lions. As the distribution of the coefficients of variation of species in the Bay of Biscay does not differ from that in the Gulf of Lions, the difference of total biomass variability is not explained by the variability of species. Further, harvesting is investigated as a source of difference of total biomass variability between the Bay of Biscay, the Gulf of Lions and the Scotian Shelf. The mean of total biomass is the lowest in the area where the harvesting level is the highest (Gulf of Lions) and is the highest where harvesting is the lowest (Scotian Shelf), while the total biomass variability increases with the harvesting level. A hypothesis on fishing impact on the community dynamics is discussed and the total biomass variability is proposed to be a broad indicator of the fisheries impact on the demersal fish communities.

The Tragedy of Open Ecosystems

This paper investigates the role played by cooperation for the sustainable harvesting of an ecosystem. To achieve this, a bio-economic model based on a multi-species dynamics with interspecific relationships and multi-agent catches is considered. A comparison between the non-cooperative and cooperative optimal strategies is carried out. Revisiting the Tragedy of Open Access and over-exploitation issues, it is first proved analytically how harvesting pressure is larger in the non-cooperative case for every species. Then it is examined to what extent gains from cooperation can also be derived for the state of the ecosystem. It turns out that cooperation clearly promotes the conservation of every species when the number of agents is high. When the number of agents remains limited, results are more complicated, especially if a species-by-species viewpoint is adopted. However, we identify two metrics involving the state of every species and accounting for their ecological interactions which exhibit gains from cooperation at the ecosystem scale in the general case. Numerical examples illustrate the mathematical findings.

Primers for the amplification of the MHC IIβ chain exon 2 in the Atlantic goliath grouper ( Epinephelus itajara )

Abstract In the present study we designed a pair of primers to amplify the exon 2 of the MHC IIβ chain of the Atlantic goliath grouper, which is responsible for the recognition of pathogenic molecules and the regulation of the immune system. Future analyses of this region may provide an important database to understand the evolutionary processes affecting the populations of the goliath grouper, and to predict the conservation perspectives in the species.

The role of mangrove for the French Guiana shrimp fishery

ABSTRACT This paper investigates the role of mangrove as an habitat in the evolution of the French Guiana shrimp stock to explain the recent collapse of shrimp production. To achieve our aim, we use the open access fishery model developed by Barbier and Strand [1998. “Valuing Mangrove-Fishery Linkages-A Case Study of Campeche, Mexico.” Environmental and Resource Economics 12: 151–166] and integrate mangrove surface into the shrimp natural growth function. This enables to account directly for the effects of mangrove surface changes on the stock dynamics and thus production. Our results indicate that financial losses in the French Guiana shrimp fishery increase when mangrove surface decreases and are mitigated when mangrove surface increases. We show that changes in mangrove surface are not determinant in explaining the collapse of the shrimp stock but that mangrove should be preserved as it still mitigates the decline of the stock.