Comparison of seasonal activity of the lake minnow, Eupallasella percnurus (Pall.), and crucian carp, Carassius carassius (L.), in small water bodies in northern Poland
This paper presents preliminary results of a comparison of the seasonal activity of lake minnows, Eupallasella percnurus (Pall.), and crucian carp, Carassius carassius (L.), in a few small water bodies. Field studies were conducted based on catches made with baited traps in periods without ice cover from April to December 2006. E. percnurus became active earlier than did C. carassius and their period of intense activity was longer. The first E. percnurus appeared in the traps in early April when the ice was still melting, and these fish were caught at a temperature range of 3.5-29.2°C. C. carassius were caught most abundantly in the beginning of May at temperatures from 15°C; this species was usually noted in traps at a narrower, but higher, temperature range in comparison with the E. percnurus. Additionally, the activity of both these species was similar with regard to weather conditions; both species were less active on cloudy days and when atmospheric pressure was increasing.
A Simple Trap for the Capture New-Emergent Salmonid Fry in Streams
A simple trap was built for capturing salmonid fry emerging from natural spawning redds in streams. The trap is shaped like a cap with a vertical PVC tube. Since the trap is not attached permanently to the substrate, settled debris can be cleaned out regularly, and the trap can be deployed in streams with large amounts of drifting organic material. Its simple construction means that it is easy to use. Based on the comparison of the effectiveness of two types of traps on artificial redds, the catch efficiency of the newly constructed trap was determined to be 37%.
Some Characteristics of Lake Trout Salmo Trutta M. Lacustris L. Redds in the Upper WDA River System (North Poland)
Observations of lake trout, Salmo trutta m. lacustris L., spawning, including recording redd parameters, were conducted in the 2003-2004 to the 2007-2008 seasons at spawning grounds located in the upper Wda River system. Spawning was noted from mid October to early January at a temperature range of 1.1-10.8°C, but primarily within the 3.0-8.0°C range. Redds were measured following spawning in selected segments of the spawning grounds. The parameters measured were as follows: tailspill size, pot depth, water depth near the tailspill, water velocity above the tailspill. Substrate samples were taken from some of the redds in spring to determine particle size distribution. In total, 51 redds were measured, and substrate samples were collected from fifteen of them. The tailspill length ranged from 40-150 cm, and water depth was from 15 to 55 cm. The geometric mean diameter of the substrate (Dg) ranged from 3.0-17.4 mm, and the sand content (fraction < 1 mm) was from 3.0-36.5%. Water velocity above the redds ranged from 40 to 120 cm s-1, and this differed significantly statistically among the streams investigated; the lowest rates were noted in the upper reaches of the system (Pilica). Furthermore, in this part of the system the mean geometrical diameter of the substrate was twofold smaller and the share of sand twofold higher than in the lower part of the river system. The size of the tailspills was positively correlated with female size, pot depth, and water velocity. In practical terms, it can be generalized that female length corresponded to approximately 55% of the tailspill diameter.
Occurrence, threats and protection of the endangered lake minnow, Eupallasella percnurus (Pall.), in Pomorskie Voivodeship in Poland
This paper is a summary of the historic and current knowledge of the occurrence of lake minnow, Eupallasella percnurus (Pall.) in Pomorskie Voivodeship in Poland. It considers factors threatening the existence of this species, and determines possibilities for the conservation and protection of sites which it inhabits. Currently, E. percnurus is known to inhabit 102 sites in the voivodeship, which constitutes 59.3% of all known sites in Poland (172). The main threats to E. percnurus sites and/or populations in Pomorskie Voivodeship include the draining and drying up of water bodies and their transformation for recreational use. Currently, only 10 of the sites are classified as threatened to a low level, while 44 sites are endangered to a high level. Almost half of all the sites (45) are subject to protection within the framework of the European Ecological Natura 2000 Network, and these probably have the greatest chance of survival.
Lake minnow, Eupallasella percnurus (Pall.), in Kujawsko-Pomorskie Voivodeship in Poland - past and present occurrence and protection
Knowledge of the historical occurrence of the endangered cyprinid fish species, Eupallasella percnurus (Pall.), in today's Kujawsko-Pomorskie Voivodeship in Poland is sparse. However, a total of nine sites inhabited by this species had been identified by the end of the twentieth century, but only one of theses had survived into the early 2000s. The largest field inventory to date of this area was undertaken from 2005 to 2011 and nine new sites were recorded. Most of the newly discovered sites inhabited by E. percnurus are located in the Dobrzyńskie Lake District mesoregion, which is where this species has occurred in the past. Four of these sites have been designated as vulnerable and two as critically threatened. Immediate active protection measures are necessary to preserve E. percnurus at the two existing sites in the Special Protected Area PLH040013 "Cyprianka".
The age and growth of Vistula River migratory sea trout, Salmo trutta L., caught in commercial catches in the Vistula in 2017-2018 were analyzed. The mean length of the sea trout caught was 61.4 cm in 2017 and 62.8 cm in 2018. It was confirmed that the fish caught reached an average of 56.5 cm following the first year at sea, 69 cm after the second year, and 82 cm after the third. The dominant age class among the fish in the catches was a sea age 1+. No older age classes than 3+ were noted. The age at smoltification of the sea trout examined in most instances was 2+. The results obtained were compared and discussed in light of historical results. The condition coefficient calculated was lower than that of the 1960s.
Occurrence of juvenile salmon, Salmo salar L., from natural spawning in the Słupia River (northern Poland)
The native population of the salmon, Salmo salar L., in the Słupia River probably became extinct in the 1960s. The restoration of this species began in 1986, and is based on the population in the Daugava River. As indicated by historic data, salmon was decidedly less abundant than was sea trout, Salmo trutta L. This remains unchanged today. To date, it has been impossible to differentiate positively smolts of stocking origin from those of natural spawning. Since 2006, all salmon smolts released into the Słupia River have had their adipose fins clipped, which allows for easy identification. The aim of the current study was to present how many of the juvenile individuals caught in the Słupia River originate from natural spawning. During the 1999-2008 period, a total of 25 juveniles were caught that were classified as wild specimens. Although salmon spawning and redds were observed earlier, the catch of juvenile species is evidence of successful salmon spawning in the Słupia River.