Management options for the unfavorable nutrient balance of recreational fishing in Lake Balaton (Hungary)

Figures & data

Figure 1. Lake Balaton (46°51′00″N 17°43′12″E) and its 5775 km² catchment area. The lake has several smaller and larger inflowing watercourses, whereas the only outflow is the Sió Canal located in the eastern basin. Anglers are fishing and using ground bait across the entire littoral zone.

Figure 2. Ground baiting intensity distribution of recreational (a) and multi-day tournament (b) anglers in Lake Balaton. IBCC: International Balaton Carp Cup in 2020; NBBH: International Balaton Boilie Fishing Competition in 2020.

Figure 3. Annual bait use and the relative importance of the main bait types (i.e., corn, other cereals + bread, ground cereal-based mixes, boilies and pellets) in recreational (a) and multi-day carp tournament (b) fishing in Lake Balaton.

Table 1. Compositions of different types of bait materials (ground cereal-based mixes, pellets, boilies, corn, bread) used commonly by anglers in Lake Balaton.

Sample type and No.	Dry matter content, %	Ash content, %	N % in dry matter	N % in the bait (in wet matter)	P % in dry matter	P % in the bait (in wet matter)	Molar N:P ratio	Available information
Ground cereal-based mix 1	93.0	11.3	1.5	1.4	0.3	0.3	11.8	Ingredients: corn, bread, sweet industry by-products, grains, flavorings
Ground cereal-based mix 2	95.2	9.8	1.8	1.7	0.8	0.7	5.2	Composition is not specified by manufacturer
Ground cereal-based mix 3	77.7	17.2	1.2	0.9	0.2	0.2	10.9	Ingredients: cereals, sweet industry by-products, flavorings
Ground cereal-based mix 4	92.5	1.1	1.8	1.6	0.5	0.5	7.2	Ingredients: cereals, bread crumb, oily seeds, flavorings
Ground cereal-based mix 5	92.3	0.9	1.6	1.5	0.3	0.3	10.7	Ingredients: cereals, bread, flavorings
Pellet 1	98.3	5.9	5.9	5.8	1.5	1.5	8.8	Small (1–2 mm) granulate. Ingredients: wheat, animal protein, fish oil, rapeseed, fish meal, calcium phosphate, sunflower seed. P content: 1–1.3%
Pellet 2	97.9	2.8	4.9	4.8	1.1	1.0	10.3	Large (15 mm) granulate. Ingredients: wheat, fish meal, soy bean, fish oil, palm oil, animal fat. P content: 1.1%
Pellet 3	96.1	1.2	1.4	1.3	0.3	0.3	11.5	Small (1–2 mm) granulate. Contains ingredients of plant and animal origin (not further specified)
Pellet 4	98.2	3.8	4.0	4.0	1.0	1.0	8.6	Small (1–2 mm) granulate. Contains ingredients of plant and animal origin (not further specified)
Pellet 5	96.6	2.9	3.5	3.4	0.9	0.9	8.9	Large (20 mm) granulate; Composition is not specified
Boilie 1	73.2	6.0	2.2	1.6	0.5	0.4	10.0	Ingredients: plant-based flour, seeds, eggs, flavorings, fish oil
Boilie 2	71.6	0.8	1.8	1.3	0.6	0.4	6.9	Ingredients: corn, wheat, soy bean, eggs, flavorings
Boilie 3	86.2	2.9	2.4	2.1	0.9	0.8	5.9	Contains ingredients of plant and animal origin (not further specified)
Boilie 4	74.8	7.1	2.4	1.8	0.6	0.5	8.2	Ingredients: plant-based flour, animal protein, eggs, sweet industry by-products, flavorings
Boilie 5	83.5	4.4	2.4	2.0	0.6	0.5	9.5	Contains ingredients of plant and animal origin (not further specified)
Corn	95.6	0.8	1.0	0.9	0.3	0.3	7.0	Dried corn grains
Bread	68.9	1.7	1.9	1.3	0.2	0.1	20.5	Coarse white bread

Figure 4. Annual nitrogen (a) and phosphorus (b) balance of angling-oriented fisheries management in Lake Balaton. The nutrient balance was calculated as: net nutrient load_N,P = – catch_N,P – carcass removal_N,P + stocking_N,P + recreational baiting_N,P + tournament baiting_N,P. Percentage values shown in brackets at each column represent the relative contribution of different fishing and fisheries management activities to the total annual “non-fishing” external nitrogen (a) and phosphorus (b) loads (data provided by the Central-Transdanubian Water Management Directorate of Hungary). “Catch” represents total amount of fish captured and not released back to the lake as documented in official fisheries diaries (both recreational and commercial). The dashed line at the zero level indicates the “neutral” nutrient balance of angling-oriented fisheries management, i.e., the hypothetical value where nutrient removal completely offsets nutrient loading.

Figure 5. Examples on the possible influences of an expansion of the “catch and release” (C&R) practice and use of bait materials with increasing nitrogen and phosphorus contents, as well as expectable effects of some feasible restrictions in bait use on the nitrogen (a) and phosphorus (b) balances of angling-oriented fisheries management in Lake Balaton.