Introducing Nature in Fisheries Research : the Use of Underwater

Aquatic Living Resources 16 (2003) 107–112 www.elsevier.com/locate/aquliv Foreword Introducing nature in fisheries research: the use of underwater acoustics for an ecosystem approach of fish population The changes in environmental conditions require an “eco- biomass, or more directly establishing total allocated catches system approach” be adopted when considering fish popula- (TACs) based on the stock biomass. However, in many cases tions. This new approach implies the design of new concepts the contribution of fisheries acoustics remained limited. and hypotheses including knowledge on ecology, behaviour Eventually we are entering a new era, which is based upon and fisheries. Being able to observe in real time and in three two observations. dimensions the living organisms and their environment be- • It is now recognised that fisheries activity in the world comes essential. These are precisely the capabilities of un- has reached and most probably exceeded its maximum derwater acoustics, which is going to play a major role in sustainable yield (Pauly et al., 2002; Myers and Worm, aquatic ecology research. 2003). • The failures of stock management in many cases have demonstrated that the study of a fish stock indepen- 1. Introduction dently from its biology and behaviour, and more generally from the ecosystem where this stock is living, usu- Based on pioneer works in the 1950s by Schaefer (1954), ally lead to erroneous conclusions on its status. Beverton and Holt (1957), Gulland (1969), Fox (1970), These two observations have oriented towards new among others, fisheries biology and its associated models of thoughts in fisheries biology, and to the conclusion that the the dynamics of populations represented a huge step forward understanding of stock dynamics would require an ecosys- in the analysis and monitoring of exploited fish populations. tem approach. These models helped to manage a number of important fisheries in the world, initially with great success. A major advantage was the ability to manage a stock on the basis of 2. Behavioural ecology in fisheries research limited data; mostly derived from the fishery itself. Implicit in these models was the concept of “stability” of the stock Such new approach implies new hypotheses, which and its insensitivity to any other parameter than the fishery. should explicitly include behavioural and other biological or Any change in the characteristics of the population was ecological parameters. Some of these hypotheses, in the expected to be due to changes in the pattern of the fishery. design of which teams of our institutes were involved, are The history of most studied fisheries has shown that these described below. assumptions are not completely valid. The adaptation of fish populations to changes in environmental conditions has the 2.1. The “meeting point” hypothesis potential to change the fundamental characteristics of the main parameters considered in conventional stock models. A Dagorn and Fréon (1999) have produced a simulation good, well-described example is the pattern of area occupa- showing that tuna fish will form a school from an originally tion by a stock with changes in abundance (Swain and Sin- dispersed population faster when the fish are attracted by a clair, 1994; Gauthiez, 1997; Fréon and Misund, 1998). floating object, than without one. This would be the basis of On the other hand, since its beginning in the 1970s, fish- the use of fish aggregating devices (FADs). Essentially, the eries acoustics has been developed in order to correct the object serves as a “meeting point” for the fish, in an ocean main biases present in indirect data such as fishing statistics. environment that otherwise lacks obvious spatial references. A well known bias is detailed by Fréon and Misund (1998) This hypothesis has an impact on the way we understand who show that, depending on the spatial strategy of a species, (and use) the aggregative behaviour of such large pelagic a decrease in the global biomass can result in a decrease or an fish. increase of the catch per unit of effort (cpue). Contrarily to fisheries data, acoustic methods provide direct abundance 2.2. The biological trap estimates (MacLennan and Simmonds, 1992). The echo- integration results were generally used for two purposes: The biological trap (Fréon and Dagorn, 2000) is basically tuning virtual population analysis (VPA) models using actual a development of the FAD argument, and is also derived from © 2003 Éditions scientifiques et médicales Elsevier SAS and Ifremer/IRD/Inra/Cemagref. All rights reserved. doi:10.1016/S0990-7440(03)00058-5 108 Foreword / Aquatic Living Resources 16 (2003) 107–112 observations on the aggregative behaviour of tuna. Fisher- 2.5. Other hypotheses men exploit the aggregation under FADs and introduce large numbers of rafts into the fishing area to concentrate the fish Other hypotheses along the same or similar lines, incorpo- for more efficient capture. One possible secondary effect of rating behaviour or other biological aspects, have also been this technique is that the fish may stay with the rafts as they postulated. These may also have important impacts on how drift. This drift may follow a different route from the normal we view and assess fish populations. Examples include con- migration pattern of the fish. In some situations and if the cepts such as meta-populations (McQuinn, 1997), and more effect is strong enough, the tuna may be “trapped” by the generally the evolutionary concepts synthesised by Cury FADs and end up in the “wrong” place, i.e. not where their (1994) and entitled “obstinate nature”. migration would have placed them. If this area is unfavour- Such new sets of hypotheses are likely to improve dra- able (poorer food resources, etc.) there would be a risk of matically the potential results of fisheries biology research. additional mortality or reduction in recruitment. In this con- These present a strong requirement: to be able to observe the text the large number of human introduced floating objects in nature and the fish living in their environment. the ocean would be of concern. This is the main reason of the parallel evolution of fisheries acoustics, described in details by Fernandes et al. (2002). 2.3. Fish learning and catchability This evolution can be seen simply through the changes in the titles of the ICES symposia related to underwater acoustics, It has been demonstrated that fishes are able to “learn” the from “Fisheries Acoustics” for the first ones (Bergen, 1973, effect of a fishing gear and increase their capability to avoid it 1982; Seattle, 1987) to “Fisheries and Plankton Acoustics” (e.g. Soria et al., 1993; Pyanov, 1993). In an evolutionary (Aberdeen, 1995), and finally “Symposium on Acoustics in perspective, the fish behaviour will adapt to high levels of Fisheries and Aquatic Ecosystems” (SAFAE) in Montpellier fishing activity through selection for those fish, which are (2002). better at avoiding, capture. This would result in a decrease in catchability, proportional to the fishing effort (Fréon and Misund, 1998). This response has been documented in some 3. Improving fisheries biology using acoustic data fisheries (e.g. Brehmer and Gerlotto, 2001). In order to adapt underwater acoustics to “fisheries ecol- 2.4. The “school trap” hypothesis (Bakun, 2001) ogy”, it is necessary to evaluate precisely the advantages that it can bring to ecological research, to gather the elements of Alternate dominance of one species has been observed in techniques and methods that are directly applicable to this many mixed pelagic fisheries. This has been well docu- discipline, and to define the points that need specific research mented, for instance, for Peruvian anchovy (Engraulis for an eventual adequacy of acoustics methods and tech- rigens) versus sardine (Sardinops sagax). A fast change in niques to ecology. dominance might be facilitated by the probability of indi- In this regard, three main objectives may be defined: viduals or groups of the declining species being included in a • Taking advantage of existing past research. To evaluate school of the dominant species. The fish may then be consid- the quantity and quality of information already present ered as “trapped” in this school with the possibility of them in acoustic surveys. Since the 1970s, many countries being in, for that species, sub-optimal biological conditions. have developed acoustic survey programs on the main Such behaviour would accelerate the declining of the domi- pelagic stocks in their respective EEZs (Fernandes et al., nated stock and be responsible for the fast changes in species 2002). At this time the ecological information (micron- dominance. ekton, bottom shape and type, school type and behav- Fig. 1. Some acoustic results on behavioural ecology of pelagic fish. (a) Peruvian landings of anchovy and sardine since 1983; (b) biomass of anchovy, sardine and horse mackerel in Peruvian waters estimated by acoustics since 1983. Foreword / Aquatic Living Resources 16 (2003) 107–112 109 iour, hydrological information, etc.) was considered as method has been designed and applied for decades by background noise and not exploited. Under a new per- Chile and Peru in the South-East Pacific Ocean (Gutier- spective, these data could be used to develop, define and rez et al., 2000). Although it will require some technical extract ecological indicators, allowing observation of improvement (principally the design of autonomous sci- decades of change in pelagic ecosystems. It is likely that entific echo sounders), it may already overcome a series some methods will be needed for transforming acoustic of drawbacks that appear in a single vessel survey; it data into ecological data. provides detailed information in the area of high produc- • Preparing the future. The set of new hypotheses will tion and abundance where fishing vessel are spending require new series of data to be collected, in a more most of their time; and it makes possible real time survey ecological and behavioural way.

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