Marine ecosystem management: Fish abundance and size under exploitation

This study is targeted on policy makers and environmental scientists to illustrate the typical historical scale of depletion of our fish stocks, and what current and emerging legislation might mean for fisheries management and the metrics of fish stocks. The population demography of the Bristol Channel sole is described since 1820. Their decline in abundance, and change in length compositions, are modelled. By 2000, the mature stock had been depleted to less than 5% of its original size, and larger sole were rarely caught. The implications of maximum sustainable yield targets, and of good environmental status, are examined.     

Institutional change,fishing rights and governance mechanisms: The dynamics of the Spanish 300 fleet on the Grand Sole fishing grounds

The “Spanish 300 Fleet” on the Grand Sole fishing grounds has been one of the most important fleets in Europe for decades. This paper analyses the process of institutional change that has determined the governance mechanisms and the property-rights system in the case of the Spanish 300 fleet. It studies the centralized top-to-bottom process of institutional change that has included some relevant legal norms such as the approval of the compatibility of the vessel scrapping grants while retaining ownership of the fishing rights, the transferability of rights and lastly the implementation of ITQs in 2007, among other changes. This evolution of the governance mechanisms has facilitated the modernization and size adjustment of this fleet, which has been oversized for the fishing opportunities provided by the TACs. The paper explains how this process of institutional change has implied a reduction of the “300 fleet” to a 100 fleet while shedding light on the relationships between institutional change, governance mechanisms and the property-rights system in this case of fisheries management.     

Sole Marks at the base of the late Pleistocene Abrigo Ignimbrite,Tenerife: implications for transport and depositional processes at the base of pyroclastic flows

Sole marks, which are common in turbidites, have been observed as casts at the base of the Abrigo Ignimbrite on Tenerife, Canary Islands. They have been engraved by pebble to cobble-sized lithic tools in a soft, cohesive fine-grained substrate. The casts range from long, parallel groove marks, often with the tool embedded at their termination, to short, elongate impact marks and are useful as a flow-direction marker. They were formed from a highly energetic pyroclastic flow pulse and were almost immediately infilled with ash after rapid waning of flow. Large lithic tools, which formed groove marks, were held in place under high gas and grain dynamic pressures and moved forward by their own momentum and the drag force exerted by a highly concentrated granular flow. Impact marks were formed by smaller lithic tools, which had more freedom of movement within the agitated, chaotic flow. Scour structures on the lee side of stationary lithic tools may have formed by local turbulence in their wake.Editorial responsibility: T. Druitt     

Age compositions of flatfish stocks as determined by a new otolithometric method, its application in the estimation of growth, spawning potential and fisheries management

We developed an ageing methodology and examined age composition of three flatfish stocks inhabiting the Seto Inland Sea, Japan. Ages were difficult to determine for three-lined tongue sole (Cynoglossus abbreviates) and ridged-eye flounder (Pleuronichthys cornutus) because the first year annulus ring was often indistinct; therefore, we used directional change in otolith growth to distinguish it. Sectioning and etching methods were powerful tools for identifying annual checks for red tongue sole (Cynoglossus joyneri). Using these ageing methods, we determined age–length relationships and growth curves. The age composition of the populations studied and of the landings showed that a large proportion of the latter consisted of individuals under the mean age of sexual maturity, thereby reducing the percent spawning potential ratio (%SPR) to ≈ 20% for all species. These findings suggest that fishing pressure on immature fish is leading to overfishing of these flatfish stocks.     

A description of chloride cell and kidney tubule alterations in the flatfish Solea senegalensis exposed to moderately contaminated sediments from the Sado estuary (Portugal)

The effects of sediment-bound contaminants on kidney and gill chloride cells were surveyed in juvenile Solea senegalensis exposed to fresh sediments collected from three distinct sites of the Sado Estuary (Portugal) in a 28-day laboratorial assay. Sediments were analyzed for metallic contaminants, polycyclic aromatic hydrocarbons and organochlorines as well as for total organic matter, redox potential and fine fraction. The potential for causing adverse biological effects of each surveyed sediment was assessed by comparison of contaminant levels to available guidelines for coastal sediments, namely the Threshold Effects Level (TEL) and the Probable Effects Level (PEL). The Sediment Quality Guideline Quotient indices (SQGQ) were calculated to compare the overall contamination levels of the three stations. A qualitative approach was employed to analyze the histo/cytopathological traits in gill chloride cells and body kidney of fish exposed to each tested sediment for 0, 14 and 28 days. The results showed that sediment contamination can be considered low to moderate and that the least contaminated sediment (from a reference site, with the lowest SQGQ) caused lesser changes in the surveyed organs. However, the most contaminated sediment (by both metallic and organic xenobiotics, with highest SQGQ) was neither responsible for the highest mortality nor for the most pronounced lesions. Exposure to the sediment presenting an intermediate SQGQ, essentially contaminated by organic compounds, caused the highest mortality (48%) and the most severe damage to kidneys, up to full renal necrosis. Chloride cell alterations were similar in fish exposed to the two most contaminated sediments and consisted of a pronounced cellular hypertrophy, likely involving fluid retention and loss of mitochondria. It can be concluded that sediment contamination considered to be low or moderate may be responsible for severe injury to cells and parenchyma involved in the maintenance of osmotic balance, contributing for the high mortality levels observed. The results suggest that sediment-bound organic contaminants such as PAHs (polycyclic aromatic hydrocarbons) and PCBs (polychlorinated biphenyls) may be very toxic to the analyzed organs, especially the kidney, even when present in low-risk concentrations.     

Intra- and interspecies comparison of energy flow in North Atlantic flatfish species by means of dynamic energy budgets

The quantitative aspects of growth and reproduction in four flatfish species (plaice, flounder, dab, sole) in terms of energy flow are described on the basis of a dynamic energy budget (DEB theory). This theory consists of general assumptions about energy uptake, storage and utilisation and describes an individual by two state variables: structure and reserve, whereby body size exerts its influence through the ratio between surface area and volume. Comparison between model estimates and field data shows that the DEB model successfully describes the energetics of growth and reproduction in a number of flatfish species. Differences between species could be captured in the same model using different parameter values. Intraspecific differences in growth between males and females are mainly caused by differences in maximum surface area-specific ingestion rates. Differences between species are reflected in the surface area-specific maximum ingestion rate, the energy partitioning over growth and reproduction, and in egg volume. According to these parameters at 283 K (10°C), the species could be ranked as follows: surface area-specific maximum ingestion rate (W m⁻²) plaice: 56.6; flounder: 54.5; sole: 45.1 and dab: 36.1 W m⁻². Fraction of energy allocated to reproduction (–): flounder: 0.35; plaice: 0.15; dab: 0.15 and sole 0.10. As a consequence of these differences in surface area-specific maximum ingestion rate and in the fraction of utilised energy allocated to reproduction, the gonad masses (g) of females of 0.5 kg wet mass differ considerably: flounder: 149 g; plaice: 86 g; sole: 70 g; and dab: 69 g. However, due to differences in egg size between species, the potential annual egg production shows a completely different pattern: dab: 2200 10³; flounder: 1560 10³; sole: 343 10³ and plaice: 130 10³ eggs.