Habitat characteristics of juvenile cowcod, <Emphasis Type=Italic>Sebastes levis</Emphasis> (Scorpaenidae), in Southern California

We characterized habitat requirements of juvenile cowcod, Sebastes levis, using information from surveys conducted aboard the manned research submersible Delta. We conducted 303 dive surveys on rocky banks and outcrops in water depths between 28 and 365 m in southern and central California, covering 483 km (963,940 m²) of seafloor. We counted 549,263 fishes from at least 134 species; 216 individuals were juvenile cowcod, S. levis, of 45 cm or less in total length (TL). Juvenile cowcod occupied depths between 52 and 330 m and demonstrated ontogenetic shifts in their habitat associations. Small fish (5–20 cm TL) lived primarily among cobbles or cobbles and small boulders. As fish grew, they moved into high-relief rock habitats, including boulder fields and rock ridges. Small cowcods were found with pygmy, Sebastes wilsoni, and swordspine, Sebastes ensifer, rockfishes. Larger juveniles often associated with juvenile bocaccio, Sebastes paucispinis, juvenile widow rockfish, Sebastes entomelas, and squarespot rockfish, Sebastes hopkinsi. Our study resulted in a characterization of seafloor habitats on a small spatial scale that is relevant to juvenile cowcod nursery areas, which is important when considering effective management strategies for this overfished species.     

Fish reproduction and the impact of acidification in the Kyrönjoki River estuary in the Baltic Sea

Synopsis Several freshwater species use the Kyrönjoki River estuary as a spawning and nursery area. The main reasons for this seem to be the morphology of the estuary, the abundance of shelter provided by aquatic macrophytes, high food production and favourable temperature conditions. Acidification of the estuary due to drainage from acidic soils has made part of the estuary unsuitable for fish reproduction. In addition, year to year fluctuations in the acidity of the estuarine water have affected the reproductive success of several species. The severity of the effects of the acidification at the population level is determined by the spatial and temporal distribution of the larvae and juveniles.     

The decline of the native fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced species,especially the Nile perch,Lates niloticus,and the Nile tilapia,Oreochromis niloticus

Synopsis There has been a decline, and in some cases an almost total disappearance, of many of the native fish species of lakes Victoria and Kyoga in East Africa since the development of the fisheries of these lakes was initiated at the beginning of this century. The Nile perch, Lates niloticus, a large, voracious predator which was introduced into these lakes about the middle of the century along with several tilapiine species, is thought to have caused the reduction in the stocks of several species. But overfishing and competition between different species also appear to have contributed to this decline. By the time the Nile perch had become well established, stocks of the native tilapiine species had already been reduced by overfishing. The Labeo victorianus fishery had also deteriorated following intensive gillnetting of gravid individuals on breeding migrations. L. niloticus is, however, capable of preying on the species which haven been overfished and could have prevented their stocks from recovering from overfishing. L. niloticus is also directly responsible for the decline in populations of haplochromine cichlids which were abundant in these lakes before the Nile perch became established. Even without predation by Nile perch, it has been shown that the haplochromine cichlids could not have withstood heavy commercial exploitation if a trawl fishery had been established throughout Lake Victoria. Their utilisation for human food has also posed some problems. The abundance of the native tilapiine species may also have been reduced through competition with introduced species which have similar ecological requirements. At present, the Nile perch and one of the introduced tilapiine species, Oreochromis niloticus, form the basis of the fisheries of lakes Victoria and Kyoga.Invited editorial     

Comparisons between the roles played by estuaries in the life cycles of fishes in temperate Western Australia and Southern Africa

Synopsis The rivers of south-western Australia and south-eastern Africa lie at similar latitudes, open into the Indian Ocean and frequently have estuaries that are periodically closed off from the sea by sand bars at their mouths. The present study has compared the species, genera and families represented in the fish assemblages of estuaries in south-western Australia and temperate southern Africa, i.e. below 31°S, and the way in which these estuaries are used by fish. The Clupeidae, Mugilidae, Atherinidae and Gobiidae were important families in both regions. However, the Terapontidae and Tetraodontidae, and the tropical families Apogonidae and Gerreidae, were represented by large numbers of individuals only in the estuaries of south-western Australia. Although 45 out of a total of 112 families and 32 of 233 genera occurred in both south-western Australia and temperate southern Africa, only 15 of the 326 species were found in both regions. The contributions made by the number of marine species which regularly enter estuaries in large numbers (marine estuarine-opportunists) to the total number of species recorded in the estuaries of south-western Australia and temperate southern Africa were similar (13.4 and 12.2% respectively) and the same was also true of species capable of completing their life cycles in estuaries (8.8 and 8.2%). The number of fresh water and diadromous species recorded in both regions was small. By contrast, the species of marine stragglers contributed approximately 70% to the total number of species in both regions. The adaptations of marine estuarine-opportunists and estuarine spawners to life in estuaries, and particularly to the effects of the closure of estuary mouths, is discussed. Although only one marine species was restricted to estuaries at any particular interval of its life cycle in south-western Australia, the juveniles of a number of marine species were confined to estuaries in temperate southern Africa. It is suggested that this difference can be attributed to the presence of a greater area and quality of alternative nursery habitats in the inshore marine environments in south-western Australia than in southern Africa.     

Assessing the importance of nursery areas of European hake (Merluccius merluccius) using a body condition index

In this study, we analysed the variability of reserve storage in juvenile European hake (Merluccius merluccius) off the western coasts of Italy (Central Mediterranean Sea). Reserve storage was measured by the hepatosomatic index (HSI), in relation to environmental and population covariates. HSI has been proved to be a consistent measure of energy storage in gadoids, thus reflecting quantity and quality of food availability for growth. Generalized Additive Models for Location, Scale and Shape (GAMLSS) were used to model the effect of depth, bottom temperature, bottom currents, fish density and fish body size on HSI of juvenile European hake. The results revealed that reserve storage in the liver appears to be maximized for juveniles living on the shelf break, between 120 and 170 m depth, with bottom temperature and current speed not exceeding 14 °C and 0.04 m s⁻¹ respectively. Furthermore, HSI significantly increased with fish density up to about 6000 individuals per km⁻² and decreased at higher densities indicating that reserve accumulation in the liver might be subject to density-dependent mechanisms (e.g. competition for food) as well. These findings suggest that the use of density as measure of nursery importance need to be further investigated. Finally, we found that HSI increased with fish size up to about 14 cm total length. Based on these results, HSI appears a reasonable index to indirectly measure the quality of habitats where juvenile European hake aggregate after their settlement on the bottom, and to potentially monitor habitat suitability as nursery across the spatial-temporal gradient.     

Fish communities in the African Great Lakes

Synopsis Ecological conditions in tropical lacustrine systems are considered by focusing on the evolution, maintenance, exploitation and vulnerability of fish communities in the African Great Lakes. The exceptionally high biodiversities in the littoral/sublittoral zones of the very ancient, deep, clear, permanently stratified rift lakes Tanganyika and Malawi, are contrasted with the simpler systems in their pelagic zones, also with biodiversity in the much younger, shallower Victoria, the world's largest tropical lake.Paper from the Canadian Society of Zoologists symposium Great Lakes of the World, organized by David L.G. Noakes     

Assessment of multiple paternity in single litters from three species of carcharhinid sharks in Hawaii

We tested for presence or absence of multiple paternity in single litters from each of three congeneric shark species in Hawaii: the sandbar shark, Carcharhinus plumbeus, bignose shark, Carcharhinus altimus, and Galapagos shark, Carcharhinus galapagensis. Based on eight polymorphic microsatellite loci, we excluded paternity by a single sire in sandbar and bignose sharks, but could not exclude a single sire for the litter from the Galapagos shark. This study doubles the number of shark species tested for multiple paternity, and is the first demonstration of multiple paternity in sandbar and bignose sharks.     

The Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) populations of Windermere,UK: population trends associated with eutrophication,climate change and increased abundance of roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>)

The north and south basins of Windermere in the English Lake District, UK, support autumn- and spring-spawning populations of Arctic charr, Salvelinus alpinus, which have been studied since the 1930s. Continuous investigations of the population dynamics of Arctic charr at this lake have involved gill netting since 1939, collection of fishery catch-per-unit-effort data since 1966, and hydroacoustic surveys since 1990. Analysis of these and associated long-term data on the abiotic environment and other components of the fish communities revealed recently contrasting fortunes of the Arctic charr populations of the north and south basins, the latter of which has been significantly impacted by eutrophication while both basins have shown elevated water temperatures and increasing roach, Rutilus rutilus, populations. Despite the introduction of phosphate stripping in 1992 and some subsequent initial improvement, the hypolimnion of the south basin still remains significantly eutrophicated and the fishery catch-per-unit-effort in this basin is now at record low levels. In addition, the spatial distribution of roach has expanded to form significant components of the fish communities of inshore and offshore surface habitats, where this cyprinid may compete with Arctic charr for zooplanktonic prey. It is concluded that the Arctic charr populations of Windermere, particularly those of the south basin, currently face a number of significant environmental pressures and continued management action is required to ensure their survival.     

The ecology of six Rhododendron species (Ericaceae) with contrasting local abundance and distribution patterns in Hong Kong,China

Six native Rhododendron species grow in thedegraded, fire-prone landscape of Hong Kong: R. simsii andR. farrerae are common and widespread, R.moulmainense is relatively restricted, and R.championiae, R. hongkongense, and R.simiarum are rare. For all species except the rare R.simiarum, there was direct or indirect evidence of regrowth afterfire, but only the two smallest and commonest species grow in sites which arefrequently burned. Both flowered within 18 months of a fire. Most populationsofall species, except R. simiarum, had a deficiency ofindividuals in the smaller basal circumference classes. Seedlings were foundonly in three out of four plots of R. simiarum, and one ofR. farrerae. A few seedlings of the other rare specieswereseen in open, litter-free microsites outside the study plots, but no seedlingsof the most common species, R. simsii, were seen anywhere.In logistic regression models, one or more measures of plant size weresignificant positive predictors of flowering at least once in the three yearstudy period for all species, while percentage cover by surrounding vegetationhad a significant negative impact on all except R. simsiiand R. farrerae, for which no populations arestrongly-shaded. Although the absence of current recruitment is not necessarilya cause for concern in long-lived species that can resprout after fire, werecommend that active vegetation management should be tried to enhance thesurvival and reproduction of R. moulmainense, R.championiae and R. hongkongense, and that newpopulations of these species and R. simiarum should becreated.     

Spawning habitat enhancement in the European bullhead (Cottus gobio), an endangered freshwater fish in degraded lowland rivers

Due to river regulation, the natural habitat of the European bullhead (Cottus gobio) has been degraded and often there is an apparent lack of suitable spawning substrates (hard objects like stones). Addition of artificial structures to degraded habitats may be a very promising tool for habitat enhancement. In this study, we evaluated the use of ceramic tiles as artificial spawning substrates in canalised and (remaining) meandering parts of anthropogenically perturbated lowland rivers in Flanders (northern part of Belgium). Furthermore, we examined whether water depth and velocity were important determinants for the choice of tiles in these different river trajectories. Tiles were successfully used by the bullhead as spawning substrates. In the meandering parts of the river, the number of egg deposits was significantly positively correlated with water depth, while in canalised river parts, water depth and velocity were of no importance for tile usage. In general, supplementation of rivers with artificial substrates like tiles may be a promising, inexpensive and easy-to-use enhancement technique for degraded bullhead spawning habitat.     

Characterization of genetic variance within and among five populations of Sperata seenghala (Skyes, 1839) revealed by random amplified polymorphic DNA markers

The genetic diversity among five populations (Bhadbada reservoir, Mohinisagar reservoir, Bansagar reservoir, Bargi reservoir and Gandhisagar reservoir) was revealed using random amplified polymorphic DNA markers. 10 random primers screened, 5 primers revealed various banding patterns and yielded 71 total loci as an average of which 39.60 (55.77%) were polymorphic between the population and 86.84% within the population of Sperata seenghala. Population wise the highest genetic polymorphism was obtained in Bhadbada reservoir as 67.61% whereas the lowest was in Gandhisagar reservoir as 49.30%. However, Analysis of Molecular Variance indicated low genetic diversity (H_pop = 0.0921 ± 0.1249; I = 0.1584 ± 0.1942) in Bansagar reservoir. Relative genetic differentiation (G_ST = 0.3993) and restricted gene flow (N_m = 0.7523) as an average indicated low gene diversity among the fish populations. The un-weighted pair group method with averages (UPGMA) dendrogram showed 05 major clusters, each cluster representing a population. Fish population of Mohinisagar reservoir showed high genetic distance (0.3981) with respective Bargi reservoir population and highest genetic identity (0.8846) reflected between Bansagar and Gandhisagar reservoir. Highest genetic distance between Mohinisagar and Bargi reservoir fish populations shows no significant correlation between genetic and geographical distance of the genotypes collected from different lentic and geographical isolated water bodies. This investigation indicated that lowest genetic diversity existed in different geographic populations of S. seenghala. All the five populations were found to be low in genetic variation, which is useful information for future conservation measures of S. seenghala confined in natural water bodies of Madhya Pradesh.     

Fisheries management in practice: review of 13 commercially important fish stocks

This paper comparatively reviews several commercially important fish stocks, their state and their management in various regions of the world including Japanese anchovy, Bay of Biscay anchovy, North Sea sandeel, North Sea herring, Icelandic cod, Barents Sea cod, South African cape hakes, sockeye salmon, chinook salmon, southern bluefin tuna, Pacific halibut, Greenland halibut and Patagonian toothfish. The reviewed fish stocks are systemized in three categories: (1) stock properties and status; (2) management structure and objectives; and (3) management advice. We gather evidence to outline qualities of management regimes that are recommended and highlight those that most often fail. Robust management, biological limits (reference points), implementation and consensus are critical points that separate successful and unsuccessful management regimes. We evaluate each fish stock’s management performance relative to its management objectives and current conservation issues. Furthermore, we point out the importance of stakeholder involvement in fisheries management as well as the problems that international fisheries commissions face through examples from the case studies. Management successes tended to be single-nation and single-stock fisheries with capacity control and clear stakeholder involvement. Fisheries with fleet overcapacity, unclear objectives and illegal activity characterized the case studies with management problems.     

Legacies of the past in the present-day forest biodiversity: a review of past land-use effects on forest plant species composition and diversity

Particularly in the temperate climate zone many forests have, at some moment in their history, been used as agriculture land. Forest cover is therefore often not as stable as it might look. How forest plant communities recovered after agriculture was abandoned allows us to explore some universal questions on how dispersal and environment limit plant species abundance and distribution. All studies looking at the effects of historical land use rely on adequate land use reconstruction. A variety of tools from maps, archival studies, and interviews to field evidence and soil analyses contribute to that. They allow us to distinguish ancient from recent forests and many studies found pronounced differences in forest plant species composition between them. A considerable percentage of our forest flora is associated with ancient forests. These ancient forest plant species (AFS) all have a low colonization capacity, suggesting that dispersal in space (distance related) and time (seed bank related) limit their distribution and abundance. However recent forests generally are suitable for the recruitment of AFS. There is clear evidence that dispersal limitation is more important than recruitment limitation in the distribution of AFS. Dispersal in time, through persistent seed banks, does not play a significant role. Ancient forests are not necessary more species-rich than recent forest, but if diversity is limited to typical forest plant species then ancient forests do have the highest number of plant species, making them highly important for nature conservation. The use of molecular markers, integrated approaches and modelling are all part of the way forward in this field of historical ecology.