Geigy Scientific Tables

While the impacts of high exploitation on fish populations and aquatic ecosystems are well-documented for commercial fishing, particularly in the marine environment, the potential biological impacts of angling received less attention. This paper discusses angling patterns within a framework of basic ecological and evolutionary literature and examines potential biological impacts of angling by focusing on study results associated with high exploitation rates and pronounced selective exploitation. The impacts range from impacts occurring directly on the exploited species (truncation of the natural age and size structure, depensatory mechanisms, loss of genetic variability, evolutionary changes), to those that occur on the aquatic ecosystem (changes in trophic cascades, trait-mediated effects). As a third category, impacts related to the angling activity per se are distinguished (habitat modifications, wildlife disturbance, nutrient inputs, loss of fishing gear). Although the main threats to fish often are l...

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Documented and Potential Biological Impacts of Recreational Fishing: Insights for Management and Conservation

In northern industrialized countries, the inland fisheries sector has long been dominated by recreational fisheries, which normally exploit fish for leisure or subsistence and provide many (poorly investigated) benefits to society. Various factors constrain the development and existence of inland fisheries, such as local user conflicts, low social priority and inadequate research and funding. In many cases, however, degradation of the environment and loss of aquatic habitat are the predominant concerns for the sustainability of inland fisheries. The need for concerted effort to prevent and reduce environmental degradation, as well as conservation of freshwater fish and fisheries as renewable common pool resources or entities in their own right is the greatest challenge facing sustainable development of inland waters. In inland fisheries management, the declining quality of the aquatic environment coupled with long-term inadequate and often inappropriate fisheries management has led to an emphasis on enhancement practices, such as stocking, to mitigate anthropogenic stress. However, this is not always the most appropriate management approach. Therefore, there is an urgent need to alter many traditional inland fisheries management practices and systems to focus on sustainable development.

This paper reviews the literature regarding the inputs needed for sustainability of inland fisheries in industrialized countries. To understand better the problems facing sustainable inland fisheries management, the inland fisheries environment, its benefits, negative impacts and constraints, as well as historical management, paradigms, trends and current practices are described. Major philosophical shifts, challenges and promising integrated management approaches are envisaged in a holistic framework. The following are considered key elements for sustainable development of inland fisheries: communication, information dissemination, education, institutional restructuring, marketing outreach, management plans, decision analysis, socioeconomic evaluation and research into the human dimension, in addition to traditional biological and ecological sciences. If these inputs are integrated with traditional fisheries management practices, the prospects for sustainability in the inland fisheries will be enhanced.

Reconciling traditional inland fisheries management and sustainability in industrialized countries, with emphasis on Europe

More than 50% of the world’s total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)‐(viii) listed above on total fishing mortality, and subsequent wide-scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch-and-escape or catch-and-discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of nontarget organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post-capture handling procedures that address the key causal factors listed above.

Estimating Collateral Mortality from Towed Fishing Gear

Thermal preference and performance provide the physiological frame within which fish species seek strategies to cope with the challenges raised by the low temperatures and low levels of oxygen and food that characterize winter. There are two common coping strategies: active utilization of winter conditions or simple toleration of winter conditions. The former is typical of winter specialist species with low preferred temperatures, and the latter is typical of species with higher preferred temperatures. Reproductive strategies are embodied in the phenology of spawning: the approach of winter conditions cues reproductive activity in many coldwater fish species, while the departure of winter conditions cues reproduction in many cool and warmwater fish species. This cuing system promotes temporal partitioning of the food resources available to young-of-year fish and thus supports high diversity in freshwater fish communities. If the zoogeographic distribution of a species covers a broad range of winter conditions, local populations may exhibit differences in their winter survival strategies that reflect adaptation to local conditions. Extreme winter specialists are found in shallow eutrophic lakes where long periods of ice cover cause winter oxygen levels to drop to levels that are lethal to many fish. The fish communities of these lakes are simple and composed of species that exhibit specialized adaptations for extended tolerance of very low temperatures and oxygen levels. Zoogeographic boundaries for some species may be positioned at points on the landscape where the severity of winter overwhelms the species’ repertoire of winter survival strategies. Freshwater fish communities are vulnerable to many of the shifts in environmental conditions expected with climate change. Temperate and northern communities are particularly vulnerable since the repertoires of physiological and behavioural strategies that characterize many of their members have been shaped by the adverse environmental conditions (e.g. cool short summers, long cold winters) that climate change is expected to mitigate. The responses of these strategies to the rapid relaxation of the adversities that shaped them will play a significant role in the overall responses of these fish populations and their communities to climate change.

The role of winter phenology in shaping the ecology of freshwater fish and their sensitivities to climate change

Stock assessment of pelagic three-spined stickleback (Gasterosteus aculeatus): A simultaneous up- and down-looking echo-sounding study

Side-aspect target strength of Atlantic salmon (Salmo salar), brown trout (Salmo trutta), whitefish (Coregonus lavaretus), and pike (Esox lucius)

SUMMARY 1. Acoustic scattering from fish and macroinvertebrates was studied in a boreal Finnish lake at three echosounder frequencies (38, 120 and 200 kHz). Split-beam transducers with partly overlapping 7� beams were employed. Acoustic, fish and invertebrate sampling were undertaken simultaneously. Vertical gradients of temperature and oxygen concentration were measured during the exercise. 2. At all frequencies, a narrow scattering layer coincided with the thermocline. At 38 kHz, fish were detected well with practically no reverberation from invertebrates while 200 kHz detected both fish and invertebrates. 3. Minor differences in the magnitude of acoustic scattering from fish were found between frequencies and between depth layers, but scattering at different frequencies was correlated at all depths. Acoustic scattering and fish density indices from trawl catches, consisting mostly of smelt (Osmerus eperlanus) (97%) and vendace (Coregonus albula )( 3%), were significantly correlated. 4. Acoustic scattering from invertebrates increased with sound frequency. Correlation analysis suggested that the invertebrate scattering was mostly induced by Chaoborus flavicans. A low frequency is recommended for estimating fish abundance without bias from reverberation induced by invertebrate scattering. Although fish and invertebrates can also be successfully discriminated at a single frequency by thresholding and cross filtering, the combination of a low and a high frequency is a more robust tool for effective fish-invertebrate discrimination.

Echo-sounding can discriminate between fish and macroinvertebrates in fresh water

All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining, trawling and hydroacoustics in two Finnish lakes in summer 2007 and 2008. Sampling methods were used ‘as such’, i.e. no special design was implemented for method comparison. In the shallow eutrophicated lake the species’ composition of gillnet sampling and seining were very different. The biomass-% of percids dropped from gillnet (61%) to seining (9%) and that of cyprinids grew from 39 to 90%, respectively. In the deep pelagic area of the oligotrophic lake, vendace and smelt predominated in trawl catches. The number of fish caught by gillnetting in that area was too small to make any conclusions about the species composition. In the eutrophicated lake, the combined length distribution for all fish species differed significantly between gillnetting and seining. In the oligotrophic lake, the gillnet catches were too small for any comparison of fish size. The difference in the length distribution of fish between trawl and echosounding was significant in most analysed depth layers. In upper depth layers acoustics sampled larger fish than trawling, and in deeper layers smaller fish. Using a combined acoustic-trawl method, the pelagic fish biomass was estimated to be approx. 17 kg ha−1 in the deep and oligotrophic lake. We conclude that in large and deep-water areas, the use of active gear is enough in fish sampling to evaluate the quality and status of fish stocks. Gillnetting together with seining is an appropriate method to work out the quality and status of fish stocks in shallow and littoral areas of large lakes. Variation in the catch selectivity of fish sampling gear requires a discrete ecological classification for each type of gear.

Juha Jurvelius

Papers

Stock assessment of pelagic three-spined stickleback (Gasterosteus aculeatus): A simultaneous up- and down-looking echo-sounding study

Side-aspect target strength of Atlantic salmon (Salmo salar), brown trout (Salmo trutta), whitefish (Coregonus lavaretus), and pike (Esox lucius)

Echo-sounding can discriminate between fish and macroinvertebrates in fresh water

Quality and status of fish stocks in lakes: gillnetting, seining, trawling and hydroacoustics as sampling methods

Spawning run of Atlantic Salmon ( Salmo salar ) in the River Tornionjoki monitored by horizontal split-beam echosounding