Stock manipulation inland fisheries today (Cowx 1998a). There is little

17.4.1 Stock manipulation inland fisheries today (Cowx 1998a). There is little

evidence of successful enhancement of marine fish Management of the fish population size or com- stocks through stocking (Howell et al. 1999), and munity structure is based on a variety of stock thus it is a technique rarely considered for enhanc- manipulation techniques (Fig. 17.1).

ing recreational marine fisheries. Most countries

377 report stocking of freshwater fisheries as more of takeable-sized fish for easy capture in put-and-

Recreational Fishing

conventional approaches to management have take fisheries, or a large number of juveniles which failed to control fisheries exploitation or reduc- are intended to grow on to a large size and satisfy tion in stock biomass through environmental the demands of the angler. degradation. The importance of stocking to sup-

There are a variety of strategies used to ensure port recreational fisheries is demonstrated by the the success of a stocking exercise in inland waters huge stocking programmes that take place each (Cowx 1994a). Explanation of these strategies is year (see Table 17.4), and the economic value of the

beyond the scope of this chapter, but issues that activity was illustrated by Cowx and Godkin must be addressed are: sources of stocked fish; (2000), who estimated some US$90 million of fish species to be stocked; stocking density; age and were produced in aquaculture units in the Euro- size of fish to be stocked; choice of season for stock- pean Union countries in 1997. This represents an ing; acclimation of stocked fish; mechanism of estimated 7.6% of the value of inland fisheries stocking; potential interaction with wild fishes; and aquaculture production in these countries, transmission of parasites and disease; and genetic and does not account for the value-added revenue integrity of the wild stocks (see Cowx 1994a for generated by the fishing activity itself.

details).

Unfortunately, this strategy to enhance the fish stocks is often used to respond to anglers’ com-

plaints that the fishing is poor or just to increase Increasing species diversity the fish stocks in general. Stocking in natural One of the common complaints about recreational

waters should aim to improve recruitment, bias fisheries is poor diversity of species. To overcome fish assemblage structure to favoured species, or this problem there has been considerable move- maintain productive species that would not breed ment of fish from one water to another (trans- naturally in the system (Cowx 1994a). However, locations) or the introduction of exotic species all this should be carried out so that there is no throughout the world (Welcomme 1988, 1992, impact on the indigenous fish populations (see 1996; Cowx 1997, 1998a; also see Juanes et al., Section 17.5.2). In man-made water bodies stock- Chapter 12, Volume 1 and Section 17.5.2 for more ing is usually carried out to create fisheries discussion). The most commonly introduced or which satisfy the general demand of the public, for translocated species involve cyprinids, with 57 example to create specialist fisheries for trout, species put into European fresh waters, of which carp or large-mouthed bass. Irrespective of the type common carp is the most frequently involved; of water body, the technique involves the injection salmonids with rainbow trout, brook trout and

Table 17.4 Numbers of fish (millions) of different species stocked in fresh waters in North America and the European Union countries in 1998.

Sub-adults Total United States and Canada

67 188 276 241 Warm-water sport fishes

4 030 141 134 Cool-water sport fishes (Percidae and Esocidae)

169 1 269 404 European Community

Atlantic salmon

1 077 20 492 Salmonidae (all)

214 372 Non-salmonidae (coarse fishes)

Chapter 17

brown trout being the most common and, finally, largemouth bass (Micropterus salmoides). All these species groups are to enhance sport fishing. Although the movement of fish is highly regu- lated in most countries, indiscriminate actions are commonplace and lead to introduction of diseases, loss of genetic integrity and species extinctions in the worst possible case (Cowx 1997, 1998a; Cowx and Godkin 2000). Introductions have also arisen because of release or escape of fish used as live bait for predatory species such as pike (Welcomme 1988; Cowx and Godkin 2000). Such releases form more than 1% of cases.

Elimination of unwanted species

Elimination of unwanted species that either com- pete with, or prey upon, target species is another tool often used in recreational inland fisheries. Cropping can either target excessive numbers of fish of a species or species group to allow the re- mainder to grow to a larger size, or can target pre- dators, which are considered undesirable because they prey on the fish targeted by anglers. Cropping is a useful tool in fisheries that have a high stock density or biomass and the growth of the fish is poor. The culling of predators has been used with some success on fisheries where new species of predators have been introduced deliberately or accidentally and have caused the demise of the indigenous stocks. An example is the control of pike perch (Stizostedion lucioperca) in the Midlands of England (Smith et al. 1998). However, there is considerable debate over whether the method is inappropriate for controlling indigenous predator populations (see next section).

Predator control

Predator control is perhaps one of the most controversial methods of fishery management. It involves regulating the numbers of predators, usually fish or avian, to reduce predation pressure. The culling of piscivorous fish is a typical example of this approach, with many fisheries having a policy to kill major predators if they are caught.

This technique has rarely proved successful as it can create an imbalance in the fishery, which becomes dominated by large numbers of small, often planktivorous, fish (Templeton 1995; Pers- son, Chapter 15, Volume 1; Kaiser and Jennings, Chapter 16, this volume). The removal of the predators can also reduce predation pressure on the faster growing and prolific breeding species, which in many cases may not be the target of the anglers, and can ultimately be a nuisance. Furthermore, fish predators often control their own numbers through cannibalism, and the removal of larger individuals from a population can leave many smaller conspecifics which have a great impact in terms of reduction in prey density. In marine ecosystems, there is evidence of mixed effects of reductions in predatory fishes (Kaiser and Jennings, Chapter 16, this volume).

Of more concern at present is the control of fish- eating birds, particularly cormorants (Phalacroco- rax sp.) and herons (Ardea sp.). In recent years, their numbers have increased dramatically at a rate of around 16% p.a. to about 150 000 pairs be- tween 1978 and 1993 around inland waters in Europe and North America (Russell et al. 1996). They are perceived to cause considerable damage to fish stocks. Whilst there is no doubt they can cause damage to intensively stocked still-water fisheries, there is still debate over the damage to other natural freshwater fisheries (Feltham et al. 1999). For example, at least 57% of carp stocked into a still-water fishery near London were con- sumed over a period of 4 weeks (Feltham et al. 1999) and up to 75% of stocks can be removed from fish farms by cormorants (Russell et al. 1996). Consequently, there are calls for control of birds, especially cormorants, by fisheries managers and anglers, but this is hotly contested by conserva- tionists (Russell et al. 1996). Notwithstanding, control measures for cormorants, such as using scaring noise or visual methods or shooting small numbers of birds, have proved rather ineffective, and the creation of refuge habitats and stocking with larger fish at times when the birds are foraging off the coast are recommended to mini- mize the impact (McKay et al. 1999).

Recreational Fishing