Non-commercial Species Research Articles

Regeneration of timber trees in a logged tropical forest in North Bolivia

For sustainable forest management, it is important to know the response of timber species to the change in environment caused by logging. We performed a 2-year study on germination, survival and growth of four timber species, Cedrela odorata, Swietenia macrophylla, Hymenaea courbaril, and Cariniana micrantha, and one non-commercial species Tachigali vasquezii. We sowed seeds of these species in five microenvironments: log landing, gap-crown and gap-trunk, skidder trail and understory, in a tropical lowland moist rain forest in northern Bolivia. We related seed and seedling performance to light availability, soil compaction, and plant competition. Germination did not differ significantly between microenvironments but survival of germinated seeds for most species was significantly higher ( P < 0.05) in the log landing (46–100%) than in the understory (0–7%). After 2 years, the tallest plants were always found in the log landing (119–190 cm) and the smallest in the understory (12–26 cm) caused by a higher relative height growth rate (RHGR) in the log landing (0.003–0.004 cm cm −1 per day) compared to the understory (0.000–0.001 cm cm −1 per day). During the first year RHGR was positively related to canopy openness for all species and negatively to the number of overtopping competitors for three species. During the second year also water infiltration explained observed variation to RHGR. These results show that abandoned log landings and logging gaps are suitable environments for the regeneration of timber species studied. This finding suggests that the removal of competitors in log landings and logging gaps combined with leaving seed trees near these microenvironments or sowing seeds, will improve regeneration of timber species in tropical forests.

Community structure and diversity of demersal fish assemblages: the role of fishery

Seasonal experimental trawl surveys were carried out in the Northern Aegean and Thracian seas (NE Mediterranean, Greece), from summer 1990 to autumn 1993, during which a total of 172 fish species were caught. In these areas, fishing pressure is very high, since approximately 50% of the Greek otter trawl fleet operates there, producing more than 57% of the total demersal landings. Different statistics were used to assess spatial structure, seasonal changes and diversity of the demersal fish assemblages on the continental shelf and upper slope. The following measures were applied to the species abundance matrix: species diversity, species richness, evenness and dominance. The analysis of 501 bottom trawls revealed that, in general, species diversity, richness and evenness decreased with water depth, with the highest values at depths 200 m. The effect of depth on the diversity patterns observed was always significant, while seasonal trends were similar with those described for the overall diversity characteristics in each area. Classification and ordination methods showed the existence of 4 groups associated with the continental shelf and upper slope in each area. Classification of the top ranking species at each group and area revealed that commercially important species were dominant in the shallowest zone (<30 m), while non-commercial species predominated at depths below 200 m. At intermediate depths (30-200 m) almost 50% of the total catches were composed of non-commercially important fish species. However, since most species had a wide distribution range these differences were rather quantitative than qualitative. The results indicated that although spatial changes in abundance could be detected, temporal changes were not obvious. Environmental variability and overexploitation, as well as differences in species´ life-history strategies, have both influenced the structure of the demersal fish assemblages found along the depth gradient studied.

Which community indicators can measure the impact of fishing? A review and proposals

Population and community descriptors that might be used as indicators of the impact of fishing are reviewed. The criteria used for the evaluation of these indicators are meaning, expected effect of fishing, exclusiveness to fishing effects, and measurability. Population indicators such as total mortality rate, exploitation rate, or average length are the most operational indicators because their meaning is clear and the expected effect of fishing on them is well understood so that reference points can be set. On the other hand, indicators based on the composition of species assemblages such as diversity indices and ordination of species abundances are difficult to interpret, and the effect of fishing on them is not easily predicted. Robust indicators describing the community functions of interest (production and transfer of biomass to large fish), such as size spectra descriptors or the proportion of piscivorous fish in the community, are more promising but are not yet well developed. New candidate indicators are proposed: the change in fishing mortality required to reverse population growth rate, the proportion of noncommercial species in the community, and the average length and weight in the community.

Ichthyoplankton distribution off the Peninsula de Mejillones, Chile (23° S, 71° W), under variable hydrographic conditions during the austral summer and winter of the 1997 El Niño

This paper identifies the larval fish community distribution, emphasizing non-commercial species, in the coastal zone and the adjacent oceanic area off the Peninsula de Mejillones (23° S, 71° W) during the 1997 El Nino. We performed one survey in the austral summer (January) and one in the austral winter (July). In January, cold, upwelled water dominated the area off the Peninsula de Mejillones with a cold-water filament extending 60 nm offshore. In July, warm Subtropical Surface Waters affected the area. We identified a total of 56 taxa, which included taxa from different adult habitats (coastal, epipelagic, epi-mesopelagic and mesopelagic). The most abundant species were Engraulis ringens (18% and 21%), Bathylagus sp. (4% and 5%), Diogenichthys laternatus(12% and 39%), Lampanyctus parvicauda (9% and 2%), Triphoturus mexicanus (14% and 3%) and Vinciguerria spp. (21% and 23%), in January and July, respectively. A multidimensional scaling (MDS) ordination and similitude dendograms revealed changes in the larval fish community structure influenced by hydrographic conditions. The rank correlations between the assemblage similarity matrix and the physical variables matrix indicate the importance of the distance from shore and production processes (represented by chlorophyll-a) on the assemblage distributions. Off the Mejillones' coast, there is a complex spatial and temporal hydrographic system where ichthyoplankton of coastal and oceanic fish species coexist. Despite both short-term and longer-term disruptive oceanographic processes (e.g., mesoscale filaments, El Nino events), it seems that the numerically dominant species persist in the area due to their various behavioral strategies and physiological adaptations.

Performance of indicators derived from abundance estimates for detecting the impact of fishing on a fish community

Population and community indicators for the impact of fishing are often estimated using abundance estimates instead of raw sampling observations. Methods are presented for testing null hypotheses of nonsignificant impacts and, where possible, for calculating the statistical power. The indicators considered concern populations (intrinsic growth rate, total mortality, exploitation rate, and a new indicator, the change in fishing mortality required to reverse population growth) and communities (k- and partial-dominance curves, a biodiversity index, size spectrum, and proportions of various population groups). The performance of these indicators is compared for the Celtic Sea groundfish community based on achieved precision, statistical power, and availability and estimation method of reference points. Among population indicators, mean length of catch was most precisely estimated and the corresponding hypothesis tests had consistently large powers. Total mortality performed reasonably well. In contrast, both the intrinsic population growth rate and the exploitation rate gave unreliable results. All tested community indicators performed similarly well. Indicators for which the direction of change caused by fishing is predictable, such as the proportion of noncommercial species or piscivores in the community, are promising indicators at the community level.

Gill net and long-line catch comparisons in a hake fishery: the case of southern Portugal

SUMMARY: During 1998, a study of the European hake (Merluccius merluccius) static gear fishery was undertaken in southern Portugal. This study aimed to compare long-line and gill net catches within the same area in terms of catch composition, fishing yield, by-catch and discards, and specifically for hake, catch size frequency distribution and quality of the fished product. At least 35 species of fish and invertebrates were caught, with hake dominating the catches in terms of both weight and number. The by-catch represented 23% and 15% of the catch in weight for long-lines and gill nets respectively. No illegal sized hake (under 27 cm total length) were caught in either gear during the study period. Discards of non-commercial species were similar for both gears and considered to be negligible (<3% by weight). Hake discards were significantly different between gears (7% for long-lines and 42% for gill nets, by weight), due to fish deterioration related to soaking time. Higher daily yields were obtained for long-lines (258.37 kg / 9,000 hooks) compared with those for gill nets (127.12 kg / 10 km net). These findings will help to improve the management and conservation of this valuable hake fishery.

Structure and diversity of fish assemblages on rocky and soft bottom shores on the Swedish west coast

Density and biomass of fishes, from shallow rocky and soft bottom habitats on the Swedish west coast, showed large seasonal variation with low values in winter and spring and with peaks in June. Season was also the most important factor determining the fish assemblage structure. Within season, however, there was a clear separation in assemblage structure between rocky-and soft-bottom habitats. There were significantly higher total fish abundances and biomasses during night compared with day catches. On soft bottoms density and biomass of fishes decreased with increasing depth, but no such pattern was seen in rocky habitats indicating that the distribution of fishes was related to vegetation cover. Altogether, 53 fish species were recorded of which 30 were common to both habitats. Species richness was similar on rocky and soft bottoms. Of the 10 most abundant species found in rocky habitats four belonged to the Labridae and three to the Gadidae. The fish assemblage on soft bottoms were of a more mixed nature with representatives among the 10 dominants from six families (Clupeidae, Cottidae, Gadidae, Gobiidae, Labridae and Pleuronectidae). When ranking the 10 dominant fish species on rocky bottoms according to biomass c. 50% of the mass was Labridae, 19% Gadidae and 13% Cottidae. In soft bottom habitats, fish biomass was mainly distributed between six families. Pleuronectidae and Gadidae were dominant and each made up 25% of the biomass, whereas Labridae only contributed 4% of the fish mass. It is concluded that the fish assemblage in rocky habitats is dominated by permanent non-commercial species (63% of biomass), whereas soft bottoms mainly function as nurseries for juvenile fishes and as feeding grounds for seasonal migrants of commercial species (80% of biomass).

THE EFFECTS OF TIME, HABITAT, AND FISHERIES MANAGEMENT ON KENYAN CORAL-REEF-ASSOCIATED GASTROPODS

Populations of live snails were studied over a 13-yr period in 18 Kenyan reef locations. Sites were divided among three levels of management (old, new, and un- managed) and two types of habitat (reef lagoon and reef flat). Management prohibits the extraction of snails and predatory fishes, while both snails and their predatory fishes were removed in unmanaged sites. In reef lagoons I hypothesized that (1) fishing would result in increased total snail numbers in unmanaged reefs due to losses of their predators but no changes would occur in fully managed reefs, (2) the responses would be variable for commercial species depending on the balance between predatory fish effects and shell collecting; while on reef flats (3) commercial snails would be most abundant on managed reefs, and (4) there would be no population changes due to either high predation or stressful physical conditions. Most snail populations were stable with only 18% of the populations displaying statistically significant population fluctuations, and commercial species were more stable than noncommercial species. As predicted, reef lagoons had the greatest range of population densities with the fully managed lagoons having the lowest numbers. Numbers of noncommercial snails increased with time in all reef lagoons in support of the fishing effect, but against the stability prediction for managed reefs. Unmanaged reef lagoons did, however, have the largest recorded population increase. Protected reef flats did not have greater numbers of commercial snails compared to unmanaged reefs. They did, however, have a greater abundance of six commercial species while having the lowest noncommercial snail population numbers. Total reef flat snail abundance was stable except during the final sampling period in 1999 when the noncommercial snails increased in the new and unman- aged sites. This might be due to a chance or periodic oceanographic event, such as the 1997-1998 El Niiio, but could also suggest that predation on reef flats is more important than I hypothesized. The snail assemblage appears to be stable but some large-bodied species such as Cassis cornuta, Charonia tritonis, Lambis truncata, and Turbo marmoratus were found in insufficient numbers to evaluate their status.

Preliminary estimates of French deepwater fishery discards in the Northeast Atlantic Ocean

French deepwater fish exploitation (500 m) began off the West coast of the British Isles in 1973. It further developed in the 1980s, and intensified in the 1990s. In 1997, the French fleet comprised 49 boats, and since 1995 has landed yearly about 19,500 t of deepwater fish species, of which, the grenadier Coryphaenoides rupestris (Macrouridae) has been the most abundant. Discard data were sampled on-board by observers on French high sea trawlers from 1995 to 1997. Eight species were identified as totally landed, 43 non-commercial species as totally discarded and only one, the grenadier, as both landed and discarded. The mean discarding rate by haul was 48.5% in weight, whereas the mean grenadier discarding rate was 21.2%; these rates increased with depth. Discard species composition and discard quantities varied with depth, and depended on the specific composition of the fish communities, species abundance and their length–frequency distribution. The latter, established for grenadier and Alepocephalus bairdii (Alepocephalidae), assumes a bathymetric ontogenic migration. Annual discards of the fishery accounted for about 17,500 t in 1996 and 1997, but the results are quite uncertain.

Effects of Artisanal Fishing on Marine Communities in the Galápagos Islands

Abstract: The Galápagos Islands harbor some of the least impacted marine ecosystems in the tropics, but there are indications that local artisanal fishing is affecting exploited marine communities. To quantify these effects, I sampled communities of fishes and sea urchins at a number of heavily fished and lightly fished sites throughout the central islands of the archipelago. Sites were selected based on information collected as part of a local fisheries monitoring study and standardized across a number of abiotic factors. Abundance and biomass of the primary target species were significantly lower in the heavily fished sites than in the lightly fished sites. Community structure also differed between heavily and lightly fished sites. Cluster analyses of the full community of fishes and a subset of nontarget fishes revealed that sites within a treatment were more similar to one another than sites between treatments. Herbivorous fishes tended to be lower in abundance and sea urchins tended to be higher in abundance in heavily fished sites, but these differences were not significant. My results are encouraging in that the direct effects of artisanal fishing are limited to the primary target species, which probably results from a high specificity of fishing gear. The differences in community structure, however, suggest that artisanal fishing also has cascading effects on noncommercial species throughout the community. An improved understanding of important ecological interactions, increased ecological and fishery monitoring, and effective precautionary management are needed to ensure that human effects in these waters remain minimal.

Alimentation d'urgence de cerfs de Virginie lors d'hivers rigoureux: Rabattage de tiges non commerciales versus distribution de moulée

In northeastern regions of North America, deer sometimes face hard winters, which may kill more than 40 percent of the population. Management of their winter habitat is not enough to avoid extensive losses from starvation. Emergency feeding programs have therefore been developed to reduce population fluctuations, which make it difficult to manage the species. During the winters of 1996 and 1997, we simulated two emergency feeding programs for deer in two deer yards located in Bas Saint-Laurent, Quebec. One of the programs was linked to the cutting of stems of non-commercial species, and the other to the distribution of a specially adapted animal feed. In accordance to the regional intervention strategy, we supplied additional feed to satisfy about 50 percent of the deers' feed requirements. In this study, we have compared the costs of the two programs during four and eight week periods. In comparison to stem cuttings, feed distribution reduces by two to three times the expenses related to the program, while facilitating spatial distribution of the food. In conditions encountered in northeastern North America, feed distribution is definitely the most economically effective method of establishing an emergency feeding program for deer. Key words: costs, branch cutting, browsing, feed, emergency feeding, winter, deer yard, deer, Odocoileus virginianus

Can Timber Production Be Compatible with Conservation of Forest Biodiversity?–Two Case Studies of Plant Biodiversity in Managed Neotropical Forests

SUMMARY.A variety of practices can greatly diminish the impacts of forest management on biodiversity. A case study from a subtropical humid forest reserve in Misiones, Argentina is presented to illustrate a “uniform spacing” method of forest harvest. In this method, trees are selected for extraction or marked for retention according to their scarcity, their horizontal distribution, and their characteristics to serve as seed trees. Three years after harvesting, the forest cut by uniform spacing had the highest density of seedlings of total as well as commercial species, and it also exhibited high diversity of understory plants other than trees.A case study of a silvicultural experiment carried out by CATIE in Costa Rica is also presented, focusing on the effects of logging and post-harvest silvicultural treatments on forest species richness and composition during the first 6-7 yr following logging and 5 yr following the application of treatments. The forest studied was shown to exhibit marked compositional variation in relation to a topographical gradient after the implementation of the experiment; such □ or ecosystem diversity should be taken into account in all future evaluations of the effect of forest management on plant biodiversity. Post-harvest silvicultural treatments caused an immediate reduction in species-richness = 10 cm dbh in 1.0 ha due to the chance elimination of species represented by one or a small number of individuals in the plots, and may affect overall species composition in the medium term as they are directed to favoring commercial species by decreasing competition from non-commercial species. Species richness declined under both silvicultural treatments, however, no changes of species-richness or composition as a result of silvicultural treatment were evident in the forest understory (individuals 2.5-9.9 cm dbh). The only detectable changes in understory plant biodiversity were caused by the felling and extraction of timber, and these changes were restricted to the very localized areas disturbed by these management operations.The application of low-intensity logging methods with selection of remnant trees requires detailed pre- and post-harvest forest inventories and follow up of treatments to ensure successful regeneration and growth of desired species. The Costa Rican study shows that different forest management operations (logging and silviculture in this case) may have different effects on plant biodiversity; this perspective should be applied to future studies in order to better understand the balance between production and conservation in tropical forests. Long-term follow up is needed to assess the true effects of forest management on biodiversity, including natural regeneration as well as growth dynamics of trees, until a whole harvest cycle is completed.

Invasion of Non-Commercial Tree Species After Selection Logging in a Bolivian Tropical Forest

Single-tree selection logging will likely result in a 4.3% loss in the relative abundance and a 4.1% loss in basal area of trees of commercial species in one cutting cycle due to their removal by harvesting combined with their potential recolonization of only 31% of logging gaps in a Bolivian tropical dry forest. Densities of the most valuable species, Amburana cearensis and Cedrela fissilis, were particularly reduced by logging. To sustain the current harvesting rate, uses need to be developed for more non-commercial species and/or silvicul-tural treatments employed that increase regeneration of commercial species and remove non-commercial species using timber stand improvement techniques.

Improving height prediction of regrowth eucalypts by incorporating the of site trees in a modified Chapman-Richards equation

Summary Height and diameter equations were developed using the Chapman-Richards function for 30 species in the regrowth forests of southeast New South Wales. These species included all commercial species of eucalypts and non-commercial small tree species of acacia and allocasuarina in the region. To improve prediction accuracy, the mean height and mean diameter of 50 largest regrowth trees/ha were incorporated in a modified Chapman-Richards function: where H and D represent total tree height in m and diameter at breast height in cm, H50 and D50 are the mean height and mean diameter of 50 largest trees/ha in m and cm respectively, a, b, c and d are parameters. Detailed evaluation of prediction accuracy through resampling showed that the incorporation lead to unbiased and more precise prediction for tree height and stem volume of most species and for stand volume of the regrowth forests. The common practice of calibrating height prediction from species-specific individual tree height-diameter equations against measured stand height can underestimate total stand volume between 3%and 5%.

The Economic Impact of a Subsidy on Mexican Grains and Forestry: A CGE Analysis

Abstract This study first examines the economy-wide impacts of the "Pro-Campo" grains subsidy program. It then analyzes the effects of extending this program to forestry as a means of curbing further deforestation. To accomplish these objectives, we employ a computable general equilibrium (CGE) model of the Mexican economy. Our findings show that (1) the subsidies lead to a transfer of resources from the refining, natural gas, services, and financial services sectors into the various agricultural, manufacturing, and mining sectors; (2) All consumption sectors except the food and the alcohol and tobacco sectors decrease as a result of subsidies; (3) The lower income groups experience an increase in their income at the expense of the upper income groups when government revenue and expenditure are held constant. Such results suggest that extension of "Pro-Campo" benefits to the forestry sector should have the desired impact of keeping land and capital resources in forestry. Our results, however, only pertain to commercial species and do not include the off-side damages which may occur to useful noncommercial species. For. Sci. 44(4):578-586.

Leaf Gas Exchange and Growth Responses of Young, Container-grown Annona Trees to Flooding

Commercial Annona species such as sugar apple and atemoya, are sensitive to flooding. Annona glabra (pond apple) is a non-commercial species that grows well in flooded soils and may have potential as a flood-tolerant rootstock for commercial Annonas. The effects of flooding on net CO2 assimilation (A), stomatal conductance (gs), and vegetative growth of 2-year-old, container-grown Annona trees were studied under glasshouse conditions. Seedlings of A. glabra, A. muricata, and A. squamosa, and plants of `49-11' [a cross between atemoya (Annona. spp. hybrid cv. Gefner) × A. reticulata] grafted onto A. glabra or A. reticulata rootstock (`49-11'/A. glabra; `49-11'/A. reticulata) were exposed to 50 days of continuous flooding. Non-flooded (control) plants were irrigated daily. Flooded soil became anaerobic from day 3 of initiating the flooding treatment. Seedlings of A. glabra and A. muricata, and trees of `49-11'/A. glabra, produced more vegetative growth during flooding than A. squamosa and `49-11'/A. reticulata. Flooding decreased A and gs of A. squamosa and `49-11'/A. reticulata, and caused tree mortality (80%) of A. squamosa. Morphological adaptations of A. glabra (seedlings and rootstock) to flooding included adventitious root formation into flood water, development of hypertrophied (swollen) lenticels on trunk and adventitious roots, and development of trunk aerenchyma. All seedling trees of A. glabra and A. muricata, and all grafted trees of `49-11'/A. glabra survived 120 days of continuous flooding. A. glabra rootstock imparted flood tolerance to the `49-11' scion and may therefore impart flood tolerance to other Annona species. A. muricata seedlings may withstand extended periods of waterlogging under field conditions.

Mini-Symposium on Ecosystem Effects of Fishing, 1996 Introduction

For more than a century the main customers of advice from fisheries scientists have been the fishing industry and its managers. The focus to date has been on how to optimize the sustainable yield of the main target species in the short and long term. Rarely was advice sought regarding the wider consequences of fishing on other components of the marine ecosystem such as benthos, non-commercial species of fish, seabirds and marine mammals. Recently a new clientele has arisen which views fisheries as an anthropogenic perturbation of marine ecosystems, with important potential impacts on their overall structure and dynamics. Both old and new customers have begun to request advice on these potential impacts, particularly the negative ones. The papers in this section were first presented at a mini-symposium during the 1996 ICES Annual Science Conference in Reykjavik, Iceland. Together they provide an impression of the diversity of the topic. Fisheries affect marine ecosystems directly through mortality, the discarding of by-catch, and the physical disturbance of habitats. These direct effects can, in the long term, lead to changes in ecosystem structure and function, as well as to evolutionary changes in the genetic composition of the affected populations. The Mini-Symposium was convened in order to provide a forum for the exchange of ideas and insights on these issues. The eight papers included here do not provide a full coverage of how fishing affects marine ecosystems. At the Mini-Symposium it was therefore suggested that ICES should convene a more comprehensive symposium on this topic. This symposium is scheduled to take place in Montpellier, France, organized by ICES and SCOR, from 16 to 19 March 1999 and aims at providing a global synthesis of research on the impacts of fishing on marine ecosystems. In addition, the intention is to report on new methods for quantifying impacts at the ecosystem level, and to provide a forum for discussions of how objectives related to nature conservation can be integrated in future fisheries management. To understand and quantify how fisheries affect marine ecosystems in all ways is one of the great challenges for fisheries science at the turn of the century. We hope that the papers included in this volume will serve to attract wider attention to this important issue.

Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards

In the present study we compare the overall performance of the 14 mm (from knot-to-knot) diamond-shaped codend (14D), presently used in Hellenic waters, with those of 20 mm square-shaped (20S) and 20 mm diamond-shaped (20D) trawl codends. The experiments took place at 12 stations in the western Aegean Sea and were based on the covered codend method (cover codend: 10 mm from knot-to-knot, 10D). The results of applying multivariate techniques, to the different station/codend combinations suggest that they form groups which differ from each other in terms of species composition, species diversity, and catch numbers/weights per hour of fishing. In general, the 10D covers of 20D and 20S were separated from the 10D covers of 14D. The 20D and 20S codends were generally grouped together and separated from those of 14D and 10D. Finally, the 14D codend either form groups by themselves or group together with the 10D cover codends. In addition, the results indicated that the 20D and 20S codends, when compared with 14D, allow significantly more individuals and number of species to escape through the meshes and are characterised by considerably higher commerical/non-commercial ratios in terms of both weight and number. In absolute numbers and weights 14D caught a very large quantity of non-commercial species whereas the weight of the commercial species caught was among the lowest. The commercial/non-commercial ratios of 20D were higher than those of 20S and, in absolute numbers and weights, 20S caught relatively more non-commercial species than 20D. These facts clearly indicate that 14D is harmful in terms of species diversity for the Hellenic demersal stocks and hence its use should be prohibited.

Demersal Fish Assemblages in the Galician Continental Shelf and Upper Slope (NW Spain): Spatial Structure and Long-term Changes

The spatial structure and long-term changes of the demersal fish assemblage on the continental shelf (100–200m depth) and upper slope (200–500m) in Galicia (NW Spain) were analysed. Annual trawl research surveys were carried out (in autumn from 1980 to 1991 and in spring in 1986 and 1987) during which a total of 105 fish species were caught. The assemblage was dominated by a small number of species, the most prominent of which were the blue whitingMicromesistius poutassou(making up 57% of the total number of individuals caught and 67% of the biomass), hakeMerluccius merluccius, megrimLepidorhombus boscii, thickback soleMicrochirus variegatusand silver poutGadiculus argenteus(these species comprised a total of 91% of the specimens and 75% of the biomass). Average density and biomass were 3396 ind. and 91·0kg per 30min tow. An average of 16·8 species were caught per tow and mean diversity (index H′ of Shannon-Wiener) was 1·54. Density, biomass and species richness decreased significantly with depth, whereas the index H′ did not show a significant bathymetric change. However, all these parameters showed significant differences between geographical areas and, particularly, between years. Density and biomass increased in the southern area of the coast (between Miño and Estaca de Bares), while species richness and diversity were greater in the northern one (from Estaca to Ribadeo). The ordinations of the assemblage obtained through correspondence analysis were similar in autumn and spring. The variability in assemblage structure was determined mainly by temporal changes and, to a lesser extent, by depth and geographical location. Most of the species presented a wide distribution range within the study area, and faunal zonation with assemblages differentiated in the space were not detected. Important differences in assemblage structure were found between the period 1980–85 and 1988–91. In this sense, several non-commercial species (M. variegatus,Argentina sphyraena,Capros aper,Arnoglossus laterna) andL. bosciiandTrisopterus luscuspresented a positive temporal trend, whereas the monkfishesLophius piscatoriusandL. budegassadecreased significantly throughout the study period. Moreover, the density ofL. boscii,A. sphyraena,A. laternaandG. argenteushad a significant positive correlation with the upwelling index corresponding to the period immediately preceeding the cruise. The results are discussed in terms of the environmental factors that may determine the patterns observed, especially the great fishing effort that takes place in the area, as well as the inter-annual and spatial variability in upwelling processes.

The Effects of Fishing on Coral Reef Fish Abundance and Diversity

The effect of artisanal fishing on the abundance and diversity of coral reef fish assemblages was investigated in the Kisite Marine National Park and Mpunguti Marine National Reserve at Shimoni, Kenya. Fishing is prohibited within the Park whereas in the Reserve artisanal fishing using traditional methods is practised. Visual censuses of six representative reef fish families (Chaetodontidae, Lethrinidae, Lutjanidae and Serranidae in 1992 and 1994, and Labridae and Pomacentridae in 1994 only) were undertaken along 250×10 m band transects on two similar pairs of reefs subject to differing fishing pressure. The abundance of commercial species (Lethrinidae, Lutjanidae and Serranidae) was depressed in the Reserve. The unfished butterflyfishes (Chaetodontidae) and damselfishes (Pomacentridae) also showed a greater abundance in the Park than in the Reserve. However, neither species number nor Shannon diversity (H′) of any of these families was affected by fishing pressure. Possible reasons for these findings are discussed. The abundance of commercial species, though not of non-commercial unfished species, increased significantly in the Reserve between 1992 and 1994, suggesting that the unfished Park may be acting as a source of larvae or supply of emigrating adults for the depleted Reserve. The results are comparable with other recent studies describing the effects of fishing pressure and also with those studies detailing the effects of habitat refugia in coral reef areas.