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<strong><strong>Fish</strong>eries</strong> <strong>Research</strong> 123–124 (2012) 1–3<br />

Contents lists available at SciVerse ScienceDirect<br />

<strong><strong>Fish</strong>eries</strong> <strong>Research</strong><br />

jou rn al hom epage: www.elsevier.com/locate/fishres<br />

Editorial<br />

<strong>Fish</strong> <strong>sampling</strong> <strong>with</strong> <strong>active</strong> <strong>methods</strong><br />

a r t i c l e i n f o<br />

Keywords:<br />

<strong>Fish</strong> stock assessment<br />

Active and passive gear<br />

Intercalibration<br />

Standardization<br />

Accuracy<br />

Ground truthing<br />

Interpretation<br />

Selectivity<br />

Avoidance<br />

a b s t r a c t<br />

The conference ‘<strong>Fish</strong> Sampling <strong>with</strong> Active Methods’ (FSAM) was held in September 2010 in Ceske Budejovice,<br />

Czech Republic. A total of 108 participants from 29 countries attended the meeting and 100 lectures<br />

and posters were presented. The meeting brought together scientist working <strong>with</strong> an interesting combination<br />

of techniques for investigation of fish populations in seas, lakes, reservoirs and rivers (mostly<br />

hydroacoustics, trawling, electric fishing, comparison of <strong>active</strong> <strong>methods</strong> <strong>with</strong> the use of gillnets and use<br />

of visual approaches). In contrast to passive <strong>methods</strong>, <strong>active</strong> <strong>methods</strong> can be used to measure absolute<br />

fish abundance because the <strong>sampling</strong> volume can be defined and estimated. If fish welfare precautions<br />

are applied, <strong>active</strong> <strong>methods</strong> can be less destructive than passive. But there is still a need for using combinations<br />

of multiple <strong>sampling</strong> <strong>methods</strong> and for improved understanding of gear efficiency, scrutinizing<br />

the efficiency through independent <strong>methods</strong> or by studying of variation in <strong>sampling</strong> efficiency due to the<br />

robustness of the <strong>sampling</strong> strategy (comparing the nets of different dimensions, mesh sizes, speed etc.).<br />

© 2011 Published by Elsevier B.V.<br />

The international conference <strong>Fish</strong> Sampling <strong>with</strong> Active Methods<br />

was held September 8–11, 2010 in the Biology Centre, Academy<br />

of Sciences of the Czech Republic, České Budějovice. Over one hundred<br />

participants from 29 countries presented 63 oral and 37 poster<br />

communications. This conference was a follow­up of an earlier<br />

meeting (<strong>Fish</strong> Stock Assessment Methods for Lakes and Reservoirs:<br />

Towards the True Picture of <strong>Fish</strong> Stock) held at the same location<br />

September 11–15, 2007 (published as a special issue of <strong><strong>Fish</strong>eries</strong><br />

<strong>Research</strong>, Kubečka et al., 2009). A true picture of the fish present<br />

in the sea, lake or river can only be obtained if we understand the<br />

efficiency of our various <strong>methods</strong> for <strong>sampling</strong> different fish species<br />

and size groups. Although <strong>active</strong> gear may be more difficult to operate<br />

than passive gear, these <strong>methods</strong> often provide a “truer” picture<br />

of species composition and size structure, and have the potential<br />

to provide absolute abundance. Continued development of <strong>active</strong><br />

<strong>sampling</strong> gear is important for improving our ability to provide a<br />

realistic picture of fish stocks. The papers in this special issue on<br />

fish <strong>sampling</strong> <strong>with</strong> <strong>active</strong> <strong>methods</strong> are a contributing to this goal.<br />

1. Structure of the meeting<br />

Active <strong>sampling</strong> is used in both marine and freshwater fisheries<br />

research and the problems associated <strong>with</strong> <strong>active</strong> <strong>sampling</strong><br />

are similar across systems. This meeting provided a forum for<br />

marine and freshwater scientists to meet and discuss these common<br />

problems, including topics such as gear avoidance, <strong>sampling</strong><br />

efficiency, replicability, standardization, and gear comparisons. The<br />

meeting was divided into sessions covering <strong>sampling</strong> <strong>with</strong> electrofishing<br />

gear, trawls, seines, larval fish nets, visual <strong>methods</strong> and<br />

acoustics (Table 1). Many presentations compared different <strong>sampling</strong><br />

<strong>methods</strong>, including comparisons between <strong>active</strong> and passive<br />

gears. In marine environments, the three main approaches investigated<br />

were trawling, acoustics and visual <strong>methods</strong>. These <strong>methods</strong><br />

were also discussed in the freshwater presentations, but freshwater<br />

<strong>methods</strong> also included electrofishing, which is much less applicable<br />

in salt water. Acoustic applications were used in larger waters,<br />

typically seas, lakes and reservoirs, while electrofishing most often<br />

applied to small wadeable streams. We also noted an increased<br />

attention to trawling in freshwater surveys. Other <strong>active</strong> <strong>methods</strong><br />

discussed in both marine and freshwater studies included hand and<br />

cast nets, use of commercial fishers, explosives, and toxicants. In<br />

addition comparisons were made <strong>with</strong> passive gear such as longlines,<br />

gillnets and traps (Table 2).<br />

2. Active and passive <strong>sampling</strong> gear<br />

The distinction between <strong>active</strong> and passive fishing gear is important.<br />

Efficiency of <strong>sampling</strong> <strong>with</strong> passive gear depends on the<br />

activity of the fish to encounter the gear and the retention probability<br />

once a gear has been encountered (Hamley, 1975; Rudstam<br />

et al., 1984; He and Pol, 2010) – <strong>Fish</strong> activity most certainly varies<br />

Table 1<br />

The numbers of oral and poster lectures in individual sections of the conference.<br />

Section Oral lectures Posters Total<br />

Large rivers, estuaries 6 1 7<br />

Streams and electrofishing 8 5 13<br />

Trawling 14 6 20<br />

Seining 5 4 9<br />

Small fish <strong>sampling</strong> 7 2 9<br />

Commercial fishing issues 2 2 4<br />

Visual <strong>methods</strong> 5 4 9<br />

Acoustics 12 7 19<br />

Standardization 4 3 7<br />

Combination of <strong>methods</strong> 3 3<br />

Total 63 37 100<br />

0165­7836/$ – see front matter © 2011 Published by Elsevier B.V.<br />

doi:10.1016/j.fishres.2011.11.013


2 Editorial / <strong><strong>Fish</strong>eries</strong> <strong>Research</strong> 123–124 (2012) 1–3<br />

Table 2<br />

Absolute and relative frequencies of different gear scrutinized in conference<br />

contributions.<br />

Gear<br />

Marine<br />

systems<br />

Freshwater<br />

systems<br />

% of total<br />

Acoustic surveys 23.6 22.2 22.8<br />

Trawling 27.3 16.7 20.7<br />

Electrofishing 0.0 21.1 13.1<br />

Gillnets 10.9 14.4 13.1<br />

Seining 7.3 11.1 9.7<br />

Visual surveys 18.2 3.3 9.0<br />

Traps 1.8 6.7 4.8<br />

Hand and cast nets 3.6 3.3 3.4<br />

Explosives/toxicants 1.8 1.1 1.4<br />

Longlines 3.6 0.0 1.4<br />

Industry information 1.8 0.0 0.7<br />

Total number of comparisons 55 90 147<br />

<strong>with</strong> season, time of day, species, size, sex and even the physiological<br />

state of an individual fish. Active gear on the other hand relies on<br />

the movement of the gear rather than the fish, although fish behavior<br />

is still important as fish may avoid the gear or the boat, and<br />

may escape the gear after encounter (as discussed in Winger et al.,<br />

2010; Rakowitz et al., in this issue). Active <strong>methods</strong> are likely more<br />

efficient when fish are in<strong>active</strong> (often at night) whereas passive<br />

<strong>methods</strong> are more efficient when the fish are <strong>active</strong> (often during<br />

dusk and dawn or the spawning period). Complexity is added<br />

to this picture by the modifying effects of diel patterns in habitat<br />

choice by different fish species. This also determines when they are<br />

vulnerable to a particular gear.<br />

Another advantage of <strong>active</strong> <strong>sampling</strong> <strong>methods</strong> is that the <strong>sampling</strong><br />

volume can often be defined (area or volume swept by a trawl,<br />

area covered by electrofishing, volume insonified by acoustics). For<br />

passive gear, we are usually limited to correlations of catch per<br />

unit effort (CPUE) <strong>with</strong> some measure of population size and such<br />

correlations are often lake specific (e.g. Irwin et al., 2008). More<br />

comparisons of CPUE of passive gears <strong>with</strong> absolute density or<br />

biomass estimated using <strong>active</strong> <strong>methods</strong> would be valuable given<br />

the increased use of standardized gill nets for fish community surveys<br />

in both North America and Europe. When properly operated,<br />

<strong>active</strong> and passive <strong>sampling</strong> <strong>methods</strong> represent two “true” but different<br />

pictures of the target stock or ecosystem, like pictures of<br />

an object from different angles. The move towards <strong>methods</strong> giving<br />

absolute estimates depends both on appropriate spatio­temporal<br />

coverage as well as reliable ways of combining information from<br />

various gears. Several meeting presentations demonstrated that<br />

a steadily improving technology prepares the ground for future<br />

developments in this direction.<br />

The destructiveness of the <strong>sampling</strong> gear to fish and habitat is<br />

another cause for concern. This is gear­specific and not related to<br />

whether the gear is passive or <strong>active</strong>. Passive traps can be very fishfriendly<br />

while fish caught by gillnets and longlines seldom survive.<br />

When fish welfare is receiving appropriate care, the survival from<br />

the catch of <strong>active</strong> gear (trawls and electrofishing) can be good<br />

(Jurvelius et al., 2000; Broadhurst et al., 2006; Gatz and Linder,<br />

2008), although trawl catches are often lethal and bottom trawls<br />

can damage the sampled habitat (Watling and Norse, 1998). The<br />

conference audience clearly indicated a move from highly destructive<br />

<strong>active</strong> approaches like the use of toxicants and explosives<br />

towards non­intrusive <strong>methods</strong> like acoustic, visual and photographic<br />

techniques (Table 2).<br />

3. Perspectives<br />

Many of the contributions confirmed that obtaining “the true<br />

picture of the fish stock” (a notion introduced in the preceding conference<br />

FSAMLR; Kubečka et al., 2009) is the goal of fish <strong>sampling</strong>,<br />

although an elusive one. With the need to develop an ecosystem<br />

approach to the fisheries management (FAO, 2003) comes a need<br />

to obtain absolute information on fish quantity, species and age<br />

distribution. In many cases we are not yet satisfied <strong>with</strong> the representativeness<br />

of the information collected. Comparing several<br />

different <strong>sampling</strong> <strong>methods</strong> is important but suffers from a lack<br />

of ground truth information (Axenrot et al., 2010; Emmrich et al.,<br />

2010; Draštík et al., 2010). Rarely is the true status of the fish stock<br />

known during <strong>sampling</strong>, but see Godlewska et al. (in this issue)<br />

for a comparison of <strong>active</strong> <strong>sampling</strong> <strong>with</strong> a complete enumeration<br />

of fish after draining the waterbody. Another very promising<br />

approach is to scrutinize the efficiency of <strong>sampling</strong> using independent<br />

remote <strong>methods</strong> like optical or acoustical cameras (Winger<br />

et al., 2010; Handegaard, 2010; Rakowitz et al., in this issue). Such<br />

approaches can lead to an understanding of the species and size<br />

specific catchabilities of the gear in question. Increasing efficiency<br />

of a single <strong>sampling</strong> method and comparing the estimates obtained<br />

<strong>with</strong> the improved and earlier <strong>methods</strong> are also valuable (Jůza et al.,<br />

in this issue; Baldwin and Aprahamian, in this issue). When further<br />

increase in net dimensions, towing speed, and/or change of mesh<br />

sizes fail to increase catches, it may be assumed that the asymptotic<br />

catch rates are obtained <strong>with</strong> 100% efficiency.<br />

This meeting invited contribution from both marine and fresh<br />

water ecosystems. Differences in approaches and <strong>methods</strong> were<br />

well demonstrated, and the obvious mutual benefit from comparison<br />

and interaction between them was enlightened. The smaller<br />

water bodies in fresh water system permit controlled ecological<br />

experimentation that is unrealistic in the ocean. The extensive<br />

research in fishing and acoustic gear technologies taking in place in<br />

the marine environment can easily be made available for freshwater<br />

research. Both issues would benefit from extended interaction<br />

between the two scientific communities.<br />

Obtaining reliable data on fish stocks remains an extremely difficult<br />

task especially in larger waters (seas, large rivers, lakes and<br />

reservoirs). However, fisheries scientists are making progress in<br />

this direction thanks to new developments in <strong>sampling</strong> and validation<br />

technology. There is no method that suites all fish species<br />

and sizes but improved understanding of the efficiency of various<br />

<strong>methods</strong> will lead to better choices of the complement of <strong>methods</strong><br />

required to get a true picture of the fish stock. This meeting<br />

represents a step forward towards this goal.<br />

References<br />

Axenrot, T., Sandström, A., Asp, A., Setzer, M., 2010. Can gill­netting data improve<br />

accuracy and precision in hydroacoustic estimates of fish abundance? In:<br />

Kubečka, J., Hohausová, E., Soukalová, K. (Eds.), <strong>Fish</strong> Sampling <strong>with</strong> Active Methods,<br />

Book of abstracts. Biology Centre AS CR, 3.<br />

Baldwin, L., Aprahamian, M. An evaluation of electric fishing for stock assessment<br />

of resident eel in rivers. <strong><strong>Fish</strong>eries</strong> <strong>Research</strong>, in this issue.<br />

Broadhurst, M.K., Suuronen, P., Hulme, A., 2006. Estimating collateral mortality<br />

from towed fishing gear. <strong>Fish</strong> and <strong><strong>Fish</strong>eries</strong> 7, 180–218, doi:10.1111/j.1467­<br />

2979.2006.00213.x.<br />

Draštík, V., Kubečka, J., Čech, M., Frouzová, J., Říha, M., Jůza, T., Tušer, M., Muška,<br />

M., Prchalová, M., Peterka, J., Vašek, M., Kratochvíl, M., 2010. Intercalibration<br />

between hydroacoustics and gillnet <strong>sampling</strong> in temperate reservoirs. In:<br />

Kubečka, J., Hohausová, E., Soukalová, K. (Eds.), <strong>Fish</strong> Sampling <strong>with</strong> Active Methods,<br />

Book of abstracts. Biology Centre AS CR, 21.<br />

Emmrich, M., Helland, I.P., Busch, S., Schiller, S., Mehner, T., 2010. Hydroacoustic<br />

estimates of fish densities in comparison <strong>with</strong> stratified pelagic trawl <strong>sampling</strong><br />

in two deep, coregonid­dominated lakes. <strong><strong>Fish</strong>eries</strong> <strong>Research</strong> 105, 178–186,<br />

doi:10.1016/j.fishres.2010.05.001.<br />

FAO, 2003. The ecosystem approach to fisheries. FAO Technical Guidelines for<br />

Responsible <strong><strong>Fish</strong>eries</strong>. No. 4, Suppl. 2. Rome: FAO. 2003. 112 pp.<br />

Gatz, A.J., Linder, R.S., 2008. Effects of repeated electroshocking on condition, growth,<br />

and movement of selected warmwater stream fishes. North American Journal<br />

of <strong><strong>Fish</strong>eries</strong> Management 28, 792–798, doi:10.1577/M07­031.1.<br />

Godlewska, M., Frouzova, J., Kubecka, J., Wiśniewolski, W., Szlakowski, J. Comparison<br />

of hydroacoustic estimates <strong>with</strong> fish census in shallow Malta reservoir – which<br />

TS/L regression to use in horizontal beam applications? <strong><strong>Fish</strong>eries</strong> <strong>Research</strong>, in<br />

this issue.


Editorial / <strong><strong>Fish</strong>eries</strong> <strong>Research</strong> 123–124 (2012) 1–3 3<br />

Hamley, J.M., 1975. Review of gillnet selectivity. Journal of the <strong><strong>Fish</strong>eries</strong> <strong>Research</strong><br />

Board of Canada 32, 1943–1969.<br />

Handegaard, N.O., 2010. Fitting observed fish trajectories to catchability models.<br />

In: Kubečka, J., Hohausová, E., Soukalová, K. (Eds.), <strong>Fish</strong> Sampling <strong>with</strong> Active<br />

Methods, Book of abstracts. Biology Centre AS CR, 28.<br />

He, P., Pol, M., 2010. <strong>Fish</strong> behaviour near gillnets: capture processes and influencing<br />

factors. In: He, P. (Ed.), Behaviour of Marine <strong>Fish</strong>es. Wiley­Blackwell, Ames, Iowa,<br />

USA, pp. 205–236.<br />

Irwin, B.J., Treska, T.J., Rudstam, L.G., Sullivan, P.J., Jackson, J.R., VanDeValk, A.J.,<br />

Forney, J.L., 2008. Estimating walleye (Sander vitreus) density, gear catchability,<br />

and mortality using three fishery­independent data sets for Oneida Lake,<br />

New York. Canadian Journal of <strong><strong>Fish</strong>eries</strong> and Aquatic Sciences 65, 1366–1378,<br />

doi:10.1139/F08­062.<br />

Jurvelius, J., Riikonen, R., Marjomaki, T.J., Lilja, J., 2000. Mortality of pike­perch (Stizostedion<br />

lucioperca), brown trout (Salmo trutta) and landlocked salmon (Salmo<br />

salar m. sebago) caught as by­catch in pelagic trawling in a Finnish lake. <strong><strong>Fish</strong>eries</strong><br />

<strong>Research</strong> 45, 291–296, doi:10.1016/S0165­7836(99)00116­2.<br />

Jůza,T. Čech, M., Kubečka, J., Vašek, M., Peterka, J., Kratochvíl, M., Frouzová, J., Matěna,<br />

J. The influence of the trawl mouth opening size and net colour on catch efficiency<br />

during <strong>sampling</strong> of early stages of perch (Perca fluviatilis) and pikeperch<br />

(Sander lucioperca) in the bathypelagic layer of a canyon­shaped reservoir. <strong><strong>Fish</strong>eries</strong><br />

<strong>Research</strong>, in this issue.<br />

Kubečka, J., Amarasinghe, U.S., Bonar, S.A., Hateley, J.A., Hickley, P., Hohausová, E.,<br />

Matěna, J., Peterka, J., Suuronen, P., Tereschenko, V., Welcomme, R., Winfield, I.J.,<br />

2009. The true picture of a lake or reservoir fish stock: a review of needs and<br />

progress. <strong><strong>Fish</strong>eries</strong> <strong>Research</strong> 96, 1–5, doi:10.1016/j.fishres.2008.09.021.<br />

Rakowitz G., Tušer M, Řiha M., Jůza T., Balk H., Kubečka J. Use of high­frequency<br />

imaging sonar to observe fish behaviour <strong>with</strong> respect to an <strong>active</strong> surface trawl.<br />

<strong><strong>Fish</strong>eries</strong> <strong>Research</strong>, in this issue.<br />

Rudstam, L.G., Magnuson, J.J., Tonn, W.T., 1984. Size selectivity of passive fishing<br />

gear: a correction for encounter probability applied to gill nets. Canadian Journal<br />

of <strong><strong>Fish</strong>eries</strong> and Aquatic Sciences 41, 1252–1255.<br />

Watling, L., Norse, E.A., 1998. Disturbance of the seabed by mobile fishing gear:<br />

a comparison to forest clearcutting. Conservation Biology 12, 1180–1197,<br />

doi:10.1046/j.1523­1739.1998.0120061180.x.<br />

Winger, P.D., Eayrs, S., Glass, C.W., 2010. <strong>Fish</strong> behaviour near bottom trawls. In:<br />

He, P. (Ed.), Behaviour of Marine <strong>Fish</strong>es. Wiley­Blackwell, Ames, Iowa, USA, pp.<br />

205–236.<br />

Jan Kubečka ∗<br />

Biology Centre of the Academy of Sciences of the<br />

Czech Republic, v.v.i., Institute of Hydrobiology, Na<br />

Sádkách 7, 370 05 České Budějovice, Czech Republic<br />

Olav Rune Godø<br />

Institute of Marine <strong>Research</strong>, P. O. Box 1870 Nordnes,<br />

5817 Bergen, Norway<br />

Phil Hickley<br />

Environment Agency, Hoo Farm Industrial Estate,<br />

DY11 7RA, Kidderminster, UK<br />

Marie Prchalová<br />

Milan Říha<br />

Biology Centre of the Academy of Sciences of the<br />

Czech Republic, v.v.i., Institute of Hydrobiology, Na<br />

Sádkách 7, 370 05 České Budějovice, Czech Republic<br />

Lars Rudstam<br />

Cornell University, Dept Nat Resources, 900<br />

Shackelton Point Rd, Bridgeport, NY 13030, USA<br />

Robin Welcomme<br />

Department of Life Sciences, Imperial College London,<br />

Ascot, SL5 7PY, UK<br />

∗ Corresponding author. Tel.: +420 604344267.<br />

E­mail address: kubecka@hbu.cas.cz (J. Kubečka)

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