Brochure "Laksefiskene og fiskeriet I vadehavsområdet"

Edited by Ribe Amt, Sønderjyllands Amt and Danmarks Fiskeriundersøgelser, December 1997

SUMMARY

From 1994 to 1997, the Danish Institute for Fisheries Research conducted an investigation of salmonoid stocks and fishing in the Wadden Sea area in collaboration with the Counties of Ribe and Southern Jutland. This was one of the most comprehensive studies of salmonoids ever carried out in Denmark. The reason for the research was the debate that arose in the early 1990s between net fishermen, anglers and authorities over the control of fishing and the exploitation of fish resources in the Wadden Sea area.

The investigation showed that 48,000 sea trout (Salmo trutta) smolts (migrating young fish) migrate annually from tributaries into the Wadden Sea. Of these, 40 % were produced naturally in watercourses, while the rest were the result of releases of fry and young fish. The migration figure of 48,000 should be seen in relation to the fact that a watercourse in good environmental condition can produce 7.5 smolts per 100 m2. This would correspond to 365,000 smolts for the tributaries of the Wadden Sea.

To compensate for the low number of smolts produced in the watercourses, 138,000 smolts were released into the rivermouths each year before the study. Fish from these rivermouth releases were, however, considerably under-represented both in catches and in the stock of spawners in the watercourses. This indicates that the smolts released in the river mouths had a very high mortality rate and/or exhibited a different behavior pattern to that of the smolts which grew up in the watercourses. The releases into the river mouths in the

Wadden Sea area did not create a subsequent increase in the spawning stock of sea trout. Stocking in the river mouths has increased in recent years to 300,000 fish annually, representing an annual expenditure of DKK 720,000.

There were large variations in the smolts production of the watercourses even when the differences in size of the various watercourses were taken into account. The majority of smolts produced came from the river Ribe Å, which accounted for more than 50% of the smolts in the Wadden Sea area. On the other hand, the outward migration of smolts was considerably smaller than expected in the rivers Kongeå, Brøns A, Brede Å and Vidå.

The outward migration of salmon (Salmo salar) smolts also varied between the different watercourses. Just a few years ago, salmon were extinct in these waters and stocks have only recently been reestablished through the release of hatchery stocks. Since 1995, when regular releases of 1-year old salmon were introduced, the total annual migration of salmon smolts from the watercourses has been estimated at 40,000. However, this figure may well be somewhat inaccurate.

A large number of sea trout smolts caught were the by-catch from fyke net fishing in the Wadden Sea. The annual catch was 15,000 smolts and sub-legal sized sea trout. It is estimated that 8,000 smolts died as a result of the fishing, as these fish are often re-released into small pools in partially dry tidal flats.

Approximately 200 net fishermen operate in the Wadden Sea. They caught 3,300 sea trout and 375 salmon above the minimum legal size. In comparison, 8,500 anglers caught 5,000 sea trout and 325 salmon above the minimum legal size in the watercourses. 3,400 houting (Coregonus oxyrhnchus) were caught in fyke nets in the Wadden Sea (of which approximately 800 were spawners). The houting is a protected species, but although the fish were released, it must be assumed that many died.

A total of 9,000 sea trout, 700 salmon and 8,700 houting returned to the watercourses as spawners. By far the majority of the sea trout entered the rivers Ribe Å and Brede Å (approximately 4,600 and 1,975 spawners, respectively) while the number entering the other watercourses was only between 175 and 650. The number of fish that entered these waters is so small that there is little or no basis for an increase of salmon and sea trout fishing here.

Test fishing with gill nets, (currently illegal in the inner Wadden Sea in order to protect the salmonoids), showed that when fishing with floating gill nets positioned far away from the shore and channels, numerous flounders were caught and only few salmon oids.

Any changes of the fishing regulations in the Wadden Sea should nevertheless also be seen in light of other interests in the area.

An important precondition for establishing healthy natural stocks of salmonoids is that the environmental condition of the watercourses be reestablished. The biggest obstacle to this is that the current physical environment is poor. This applies especially to the smaller watercourses. In many cases, the spawning areas of the fish have been destroyed as a result of previous watercourse regulations and many years of rough maintenance which has caused extensive sand movement. There is a lack of livestock fencing and the two meter limit for cultivation is being disregarded. Together, these two factors increase sand movement, which is detrimental for both eggs and fry.

In the near future, spawning areas for salmonoids should be reestablished by putting spawning gravel back in the watercourses where it has been removed. A targeted effort should be made to limit sand movement and protect the few remaining spawning areas. Likewise, the rearing conditions for young fish need to be improved through careful maintenance - especially in the smaller watercourses.

The larger watercourses which can support important salmonoid spawning and rearing areas are unproductive in several places. Extensive stretches of the rivers Varde Å, Sneum Å and Kongeå are affected by dams and water extraction by fish farms, obstructions of access to spawning areas and the pollution resulting from fish farming. The importance of the larger watercourses as production areas for sea trout and salmon is demonstrated by the fact that short stretches of the rivers Gels Å and Gram Å of the Ribe Å system account for up to 50% of the total smelts production of the watercourse. Ribe Å has, as mentioned earlier, by far the largest smolt production and sea trout population in the area.

Free passage is of vital importance for saving the houting stocks. Houting cannot use fish ladders and therefore do not have access to most of the spawning areas in the rivers Sneum Å, Kongeå and Ribe Å. As the releasing of houting stepped at the beginning of the 1990s, stocks will be endangered if the passage to the spawning areas is not improved. During the last 10 years the quality of the water has improved considerably. Today, there are only very few watercourses which are so polluted that they cannot support fish. The discharge of waste water from outlying houses and fish farms currently remains the most significant remaining source of pollution. Such discharge has impoverished the fauna in several smaller watercourses.

There are, consequently, a number of environmental problems in the watercourses, which the county and municipal authorities must solve before the watercourses can be expected to maintain natural fish populations of a satisfactory size. This can only happen by improving the environmental conditions of the watercourses whilst taking other related interests into consideration. Both the Danish Ministry of Food, Agriculture and Fisheries and the county and municipal authorities regard the stocking of hatchery fish as a temporary measure which can be discontinued once the watercourses are again able to maintain fish populations naturally.

Another important area for action is the by-catch of houting and sub-legal sea-size trout in trap and fyke nets in the Wadden Sea. This happens particularly during periods where catches of other valuable edible fish are small. Consequently, fishing should be planned in the future so as to avoid this undesirable by-catch.

The extent of angling in the watercourses in the winter period for immature sea trout should also be evaluated more closely. The amount of sub-legal sized fish caught by anglers is often five to ten times that of legal sized fish but the adverse effects of hooking and releasing is not known. The very limited success of the extensive smolt releases into the river mouths in the Wadden Sea area should lead to a closer evaluation of fish stocking activities in this area.

The way forward to larger stocks of salmonoids by:

• careful maintenance of watercourses;
• limiting sand movement in watercourses;
• establishing new spawning areas for salmonoids;
• improving conditions of passage for fish;
• reducing pollution from fish farms;
• reducing other pollution;
• limiting by-catches of houting and sub-legal size sea trout in trap and fyke nets in the Wadden Sea;
• closely evaluating the effect of anglers' catches of sub-legal sized sea trout (immature sea trout);
• evaluating the effect of river mouth releases of sea trout smolts and releases in general.

The brochure is available in Danish (Laksefiskene og fiskeriet I vadehavsområdet) and will be available in English (The Salmon Fishery in the Danish Wadden Sea Area) in July 1998 via:

Mads Ejby-Ernst
Ribe Amtskommune
Sorsigvej 35
DK - 6760 Ribe
Tel. +45 75 424200, Fax: +45 75 42 47 95

or:

Tom Knudsen
Sønderjyllands Amt,
Jomfrustien 2
DK - 6270 Tønder
e-mail: tom_knudsen@sja.dk