Fish Introductions in Africa and Some of Their implications

1991 ◽  
Vol 48 (S1) ◽  
pp. 8-12 ◽  
Author(s):  
Richard Ogutu-Ohwayo ◽  
R. E. Hecky
Keyword(s):  
Endemic Species ◽  
Algal Blooms ◽  
Fish Community ◽  
Trophic Ecology ◽  
Spatial Scales ◽  
Introgressive Hybridization ◽  
Small Fish ◽  
Fish Ponds ◽  
Food Web Structure ◽  
Fish Introductions

Fish introductions in Africa have been made at various spatial scales from small fish ponds to the largest lakes, primarily to sustain or increase production, though some were to develop sport fisheries and to control unwanted organisms. Some introductions have fulfilled their objective in the short term, but several "successful" introductions have created uncertainties about their long-term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into Lakes Victoria and Kyoga in 1950's and early 1960's; by the 1980's L. niloticus and O. niloticus dominated the fisheries, having virtually eliminated a number of endemic species. In Lake Victoria, the loss of genetic diversity has been accompanied by a loss of trophic diversity; the transformation of the fish community coincided with profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. By contrast, the introduction of a planktivore, Limnothrissa miodon into Lake Kivu and the Kariba reservoir has established highly successful fisheries with little effect on the pre-existing fish community or trophic ecology. The endemic species-rich African Great Lakes may be particularly sensitive to introductions. Species extinctions, introgressive hybridization and ecosystem alterations may occur following introductions.

Extending the forecast model: Predicting Western Lake Erie harmful algal blooms at multiple spatial scales

2019 ◽  
Vol 45 (3) ◽  
pp. 587-595 ◽  
Author(s):  
Nathan F. Manning ◽  
Yu-Chen Wang ◽  
Colleen M. Long ◽  
Isabella Bertani ◽  
Michael J. Sayers ◽  
...  
Keyword(s):  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Lake Erie ◽  
Spatial Scales ◽  
Forecast Model ◽  
Multiple Spatial Scales ◽  
Western Lake ◽  
Western Lake Erie

scholarly journals Ekologi Trofik Komunitas Ikan di Perairan Segara Menyan, Subang, Jawa Barat (Trophic Ecology of the Fish Community in Segara Menyan Coastal Lagoon, Subang, West Java)

2015 ◽  
Vol 20 (3) ◽  
pp. 170 ◽  
Author(s):  
Ahmad Zahid ◽  
M.F. Rahardjo ◽  
Lenny S Syafei ◽  
Rini Susilowati
Keyword(s):  
Temporal Variation ◽  
Fish Species ◽  
Trophic Level ◽  
Coastal Lagoon ◽  
Fish Community ◽  
Trophic Ecology ◽  
Diet Breadth ◽  
Gut Contents ◽  
Trophic Guild ◽  
Spatio Temporal

Pengetahuan mengenai ekologi trofik merupakan dasar dalam memahami ekosistem secara keseluruhan yang dapat dijelaskan melalui pola hubungan trofik interspesies ataupun interserikat. Penelitian bertujuan untuk menjelaskan ekologi trofik meliputi indeks trofik dan jenis makanan dominan, serikat dan tingkat trofik, dan variasi spasial dan temporal komunitas ikan di estuari Segara Menyan. Pengambilan ikan contoh dilakukan setiap bulan pada zona berbeda. Ikan contoh dipisahkan berdasarkan waktu dan lokasi pengamatan, dianalisis isi saluran pencernaannya. Analisa data meliputi indeks vakuitas, jumlah total organisme makanan, jenis makanan dominan, luas relung makanan, dan tingkat trofik.  Pada pengamatan 106 spesies ikan, sebanyak 1-380 saluran pencernaan ikan diamati. Sebanyak lima dari 106 spesies memiliki nilai indeks vakuitas “0” dan jumlah makanan yang dikonsumsi bervariasi mulai dari empat hingga 27 jenis makanan. Secara umum, luas relung ikan adalah rendah berkisar 0,20-0,78 dan kebanyakan berada pada kisaran 0,20-0,48. Zooplankton merupakan jenis makanan paling dominan dikonsumsi oleh ikan. Komunitas ikan dikelompokkan dalam tujuh serikat trofik, yaitu detritivora, fitoplanktivora, zooplanktivora, zoobentivora, moluskivora, krustasivora, dan pisivora. Tingkat trofik komunitas ikan berkisar 2,05-4,73. Faktor perubahan ontogenetik, persediaan makanan, karakteristik habitat, dan ruaya beberapa spesies ikan memengaruhi variasi spasio-temporal jejaring makanan di Segara Menyan. Kata kunci: interaksi trofik, laguna, ikan, variasi spasio-temporal, serikat trofik Knowledge of trophic ecology is one way to understanding the whole ecosystem which explained by trophic relationship pattern (interspecies or interguild). The objective research was described of the trophic ecology, i.e. trophic index and dominant prey, trophic guild and trophic level, and spatio-temporal variation of fish community in Segara Menyan coastal lagoon. Fish were collected monthly for one year at three zones. Fish samples were placed in separate labelled plastic bags according to the time scale and location sampling, then gut contents were analyzed. The data of vacuity index, number of prey, prey dominant, diet breadth, and trophic level were analyzed. For each of 106 fish species, between 1 and 380 stomachs, were examined. The vacuity index was also different among species. Five of 106 species had a vacuity index of “0” and total number of food items consumed varied between fish species, ranging from three items to 27 items. The overall diet breadth (Bi) was relatively low among species, ranging from 0.20 to 0.78, with most of them between 0.20 and 0.48. Calanoid copepods comprised the most common food item consumed by all the fishes examined. Fishes occurring can be broadly categorized into seven different trophic guilds. The trophic level of fish communities ranged from 2.05 to 4.73. Spatio-temporal variation of food web was influenced of ontogenetic shift, food availability, habitat characteristic, and migration of some species in Segara Menyan coastal lagoon. Keywords: trophic interaction, lagoon, fishes, spatio-temporal variation, trophic guild

scholarly journals Temperate fish community variation over seasons in relation to large-scale geographic seascape variables

2018 ◽  
Vol 75 (10) ◽  
pp. 1723-1732 ◽  
Author(s):  
Diana Perry ◽  
Thomas A.B. Staveley ◽  
Linus Hammar ◽  
Alyssa Meyers ◽  
Regina Lindborg ◽  
...  
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Seasonal Changes ◽  
Fish Community ◽  
Large Scale ◽  
Spatial Scales ◽  
Wave Exposure ◽  
Fish Assemblage Structure ◽  
Swedish West Coast ◽  
Latitudinal Position

In shallow-water marine environments, ecosystem functioning is a complex interworking of fine-scale characteristics and region-wide factors, and the importance of these variables can vary on multiple temporal and spatial scales. This underwater video study targeted seasonal changes in the fish community of seagrass habitats along the Swedish west coast and the influence of offshore seascape variables (latitudinal position, wave exposure, open ocean, and deep water). Results showed that fish assemblage structure exhibited seasonal changes between summer and autumn and strong spatiotemporal variations in the importance of offshore factors affecting shallow-water fish communities. In summer, abundance from the Gobiidae family responded to wave exposure, whereas the Gadidae family and juvenile migrant habitat preference guild responded to latitudinal position and proximity to deep water. In autumn, deep water was related to abundance of Gadidae and juvenile migrants, whereas latitudinal position influenced Gasterosteidae. These findings underscore the importance of understanding the influence of offshore factors on facets of coastal fish assemblages to address large-scale geographic connectivity along nearshore–offshore gradients.

scholarly journals Boreal river impoundments caused nearshore fish community assemblage shifts but little change in diversity: a multiscale analysis

2019 ◽  
Vol 76 (5) ◽  
pp. 740-752 ◽  
Author(s):  
Katrine Turgeon ◽  
Christian Turpin ◽  
Irene Gregory-Eaves
Keyword(s):  
Fish Community ◽  
River Flow ◽  
Spatial Scales ◽  
Temporal Trends ◽  
Ecosystem Functions ◽  
Anthropogenic Factors ◽  
Multiscale Approach ◽  
Sampling Station ◽  
Community Assemblage ◽  
Boreal River

River flow regulation, fragmentation, and changes in water quality caused by dams have varying effects on aquatic biodiversity and ecosystem functions, but are not clearly resolved in boreal ecosystems. We adopted a multiscale approach to quantify fish community trajectories over 20 years using a network of sites spread across four reservoirs in two hydroelectricity complexes in northern Quebec, where other anthropogenic factors have been negligible. Across three spatial scales, we found little evidence of directional temporal trends in diversity relative to reference sites. Using beta-diversity analyses, we also detected a high degree of stability in fish composition over time and space at the complex and reservoir scales. However, changes in species assemblage following impoundment were detected at the scale of the sampling station. At this scale, we found that some species consistently benefited (coregonids and pikes) from impoundment, whereas others were detrimentally affected (suckers and one salmonid). Overall, we conclude that examining different scales is key when trying to understand the impacts of humans on biodiversity and in formulating management recommendations.

Impacts of environmental change and direct and indirect harvesting effects on the dynamics of a marine fish community

2008 ◽  
Vol 65 (10) ◽  
pp. 2088-2104 ◽  
Author(s):  
Hugues P. Benoît ◽  
Douglas P. Swain
Keyword(s):  
Marine Fish ◽  
Fish Community ◽  
Prey Availability ◽  
A Priori ◽  
Small Fish ◽  
Trawl Survey ◽  
Ecological Traits ◽  
Ocean Climate ◽  
Selected Traits ◽  
Catch Rates

We describe dramatic shifts in the species composition of the marine fish community of the southern Gulf of St. Lawrence using a 35-year time series of catch rates in an annual bottom-trawl survey. We attempt to understand the causes of these changes using a traits-based approach that relates the similarity among species in their abundance trends to similarities in their ecological traits. We selected traits based on a priori beliefs of how each should reflect susceptibility to changes in a different external factor potentially affecting the community. We found evidence for an effect of ocean climate and top-down effects of fishing and seal predation, but not for bottom-up effects of prey availability on adult fishes. Mean body length in the community decreased dramatically in the 1990s. This reflected the removal of large-bodied fishes by fishing and sharp increases in the abundance of small fishes. The biomass of small fish was inversely correlated with an index of predation on those fish by larger fish, suggesting strong predator control of the abundance of small-bodied fishes. Our results suggest that changes in ocean climate combined with direct and indirect effects of harvesting can dramatically and rapidly alter the composition of marine fish communities.

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

2010 ◽  
Keyword(s):  
Endemic Species ◽  
Fish Assemblages ◽  
Spatial Scales ◽  
The United States ◽  
Common Species ◽  
Biotic Homogenization ◽  
Generalist Species ◽  
European Settlement ◽  
New Locations ◽  
Biotic Differentiation

<em>Abstract</em>.—Widespread introduction of common species coupled with extirpation of endemic species can cause fish assemblages to lose much of their regional uniqueness. This process of biotic homogenization contrasts with biotic differentiation, whereby initially similar fish faunas diverge due to introductions of different species. The relative importance of homogenization and differentiation in altering fish faunas has been examined across the world. Synthesis of these studies indicates that homogenization of fish faunas has been widespread and that introductions, especially of sport fishes, have played a bigger role in altering fish faunas than extirpations. In the United States, pairs of states now average 15.4 more species in common than before European settlement. Additionally, the 89 pairs of states that formerly had no fish species in common now share an average of 25.2 species. While homogenization is prevalent at large spatial scales, differentiation of fish faunas is evident at intermediate spatial scales such as among watersheds within an ecoregion. This differentiation is largely the result of the idiosyncratic nature of fish introductions among individual lakes and streams. In general, translocated species (i.e., species that are native somewhere in the region but that have been moved to new locations) cause homogenization, whereas exotic species (species not native to the region) cause differentiation. Habitat and flow homogenization are major drivers of biotic homogenization because altered habitats create conditions that favor a few generalist species at the expense of more-specialized endemic species.

Only a few key prey species fuel a temperate coastal fish food web

2020 ◽  
Vol 653 ◽  
pp. 153-166
Author(s):  
SSH Poiesz ◽  
JIJ Witte ◽  
HW van der Veer
Keyword(s):  
Food Web ◽  
Fish Species ◽  
Fish Community ◽  
Prey Species ◽  
Wadden Sea ◽  
Food Web Structure ◽  
Fish Food ◽  
Coastal Fish ◽  
Web Structure ◽  
Sea Fish

The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are present in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.

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