Coregonus suidteri Fatio, 1885

Selz, Oliver M. & Seehausen, Ole, 2023, A taxonomic revision of ten whitefish species from the lakes Lucerne, Sarnen, Sempach and Zug, Switzerland, with descriptions of seven new species (Teleostei, Coregonidae), ZooKeys 1144, pp. 95-169 : 95

Coregonus suidteri Fatio, 1885

Figs 12 , 14

Coregonus annectus : Fatio 1885.

Coregonus annectus balleoides : Fatio 1885.

Coregonus lavaretus nat. riusensis, oekot. Primigenius : Steinmann 1950 (see also synonymy of C. sarnensis , C. supersum , and C. litoralis ).

Coregonus Schinzii helveticus var. zugensis : Fatio 1890.

Coregonus Schinzii helveticus var. lucernensis : Fatio 1890.

Coregonus ‘Sempacherballen’: Douglas and Brunner 2002.

Coregonus suidteri : Kottelat 1997; Kottelat and Freyhof 2007; Vonlanthen et al. 2011, 2015 (see also synonymy of C. litoralis and C. supersum ).

Coregonus lavaretus fera natio vogti: Berg 1932.

Coregonus lavaretus natio riusensis: Steinmann 1950.

Material examined.

Syntypes. All from Switzerland, Lake Sempach : Historical specimens (years 1885, 1899): MHNG-715.089, MHNG-816.026, N = 2, 311 mm and 312 mm SL, sex unknown; MHNG-676.007, branchial arch, which probably belongs to one of the syntypes (used for gill raker measurements) .

Diagnosis.

Coregonus suidteri is a large whitefish species with strong pigmentation of all fins and the body; greenish blue colour on the flanks above the lateral line; deep bodied (body depth: 25.4 and 29% SL); blunt snout; short head (20 and 22% SL); sub-terminal mouth; moderately large eye (eye diameter: 21.9 and 23.9% HL) with a thick (4.5 and 6.5% HL) and triangular-shaped eye socket; short and stout caudal peduncle (caudal peduncle depth: 7.8 and 8.7% SL; caudal peduncle length: 13.3 and 13.5% SL); many but rather short gill rakers (longest gill raker: 9.1% HL; total gill raker number: 35).

Description.

Shape: Generally, deep bodied with greatest body depth anterior of dorsal fin. Dorsal profile from tip of snout to anterior origin of dorsal fin strongly convex and ventral profile moderately convex or almost straight from interorbital area to pelvic fin origin. Head short. Mouth short, wide and sub-terminal. Rostral plate pronounced. Tip of snout blunt. Large eye with a thick and sickle cell-shaped eye-socket. Pectoral fin moderately tapered and short. Dorsal fin long. Caudal peduncle stout and short. Meristics: Many but rather short gill rakers. Colour: Pigmentation of fins and body overall strong with a silvery appearance along the flanks and dorsally above the lateral line the silvery appearance changes to a greenish blue colour (based on preserved specimens and by the description by Fatio (1890)). The dorsal part of the head and the snout around the nostrils is strongly pigmented. Preserved fish are brownish in colouration.

Differential diagnosis.

The differential diagnoses against the historical specimens of C. supersum from Lake Zug are given under that species account.

Coregonus suidteri - Coregonus litoralis

Coregonus suidteri can be differentiated from C. litoralis by having a shorter length from the posterior part of the adipose fin to the caudal fin base (13.7-15.6% SL, mean = 14.6 vs. 15.8-22.9% SL, mean = 19.3), shorter snout (20.8-21.5% HL, mean = 21.1 vs. 19-29% HL, mean = 23.4), a larger eye cavity (29.6-30% HL, mean = 29.8 vs. 24.1-27.7% HL, mean = 26), a shorter postorbital length (50.9-51.7% HL, mean = 51.3 vs. 51.6-56.2% HL, mean 53.5), a deeper head (74-78.7% HL, mean = 76.4 vs. 68.1-77.1% HL, mean = 72.5), a less wide interorbital width (19.7-25.4% HL, mean = 22.6 vs. 23.5-31.3% HL, mean = 28.1), a wider internarial width (13.8-15.4% HL, mean = 14.6 vs. 10.7-14.5% HL, mean = 12.9) and a wider lower jaw (11.7-12.3% HL, mean = 12 vs. 6.9-9.2% HL, mean = 8.1) (Tables 2 , 8 ).

Distribution and notes on biology.

Coregonus suidteri is found in Lake Sempach. Coregonus suidteri was previously thought to naturally occur in several lakes in Switzerland, namely lakes Lucerne, Zug, Sempach, Hallwil and Baldegg. Independent multilocus microsatellite (Suppl. material 1: figs S2, S3) and large genomic AFLP ( Hudson et al. 2011) data sets have shown that C. suidteri is composed of multiple species endemic to different lakes in Switzerland. Both population-based neighbour-joining tree’s and individual-based population structure analysis suggest that contemporary samples of whitefish from Lake Zug, Sempach and Lucerne group into independent genetic clusters (Suppl. material 1: figs S2, S3; Hudson et al. 2011). The status of the extinct species C. cf. suidteri from lakes Hallwil and Baldegg is unresolved since no genetic material is present to date. The extant population of Lake Sempach whitefish on which these independent multilocus microsatellite and large genomic AFLP analyses are based on, show strong signals of genetic association with whitefish from Lake Zug and Lake Lucerne. As has been noted before for the other lakes in this study (and many more lakes in Switzerland) historical records report several incidences of introductions of whitefish from other Swiss, German and even North American lakes into Lake Sempach ( Surbeck 1920; Steinmann 1950). Surbeck (1920) and Steinmann (1950) note that in the years from 1895-1902 there were several introductions of ‘Balchen’ (most likely C. litoralis and/or C. intermundia ) from Lake Lucerne into Lake Sempach. Steinmann (1950) further notes that other species of whitefish from many lakes were also introduced, but then only specifically mentions C. maraena and whitefish individuals from North America. Most likely many different whitefish species from Swiss lakes and beyond were introduced. This is not unique to Lake Sempach and was unfortunately common practice at that time. These deliberate introductions from other lakes took place after the population decline of whitefish in Lake Sempach, which were attributed to the lowering of the lake level in the 19th century ( Steinmann 1950). Prior to this population decline in 19th century Lake Sempach seemed to harbour a large and productive whitefish fishery according to fisheries catch accountings ( Steinmann 1950). Interestingly though, the catches of whitefish of the years 1418-1795 reported that the whitefish species in those times were rather small individuals (125 grams) compared to the larger individuals of the late 19th century (375-750 grams) which led Steinmann (1950) to suggest that Lake Sempach may have harboured more than one species of whitefish. Fatio (1890) also notes that the size of the whitefish species in Lake Sempach were smaller and increased with the population decline towards the end of the 19th century. Steinmann (1950) named the small type whitefish of Lake Sempach 'Kleiner Balchen des Sempachersees’ and the large-type whitefish species ‘Sempacherbalchen’. It is the latter species that is most likely represented by the type specimens of C. suidteri that were given to Victor Fatio in the 1880s by Otto Suidter ( Steinmann 1950). Furthermore Steinmann (1950) suggests that the ‘Sempacherbalchen’ (i.e., C. suidteri ), which he could examine in the last half of the 20th century, should be regarded as a 'mixtum compositum’, i.e., a mixed population composed of different whitefish species including the original large-type whitefish species of Lake Sempach. Indeed, Fatio (1890) already questioned if the small whitefish individuals from Lake Sempach would have had to be described as an independent species, which was displaced by larger individuals of a less common second whitefish species after the decline of the former. Given these uncertainties expressed both by Fatio (1890) and Steinmann (1950) regarding the number of species that were initially present in Lake Sempach, coupled with 1) a population decline in the 19th century of smaller individuals of a putative small-type species resulting in fewer but larger individuals of a second large-type species, 2) deliberate introductions in the late 19th and early 20th century, and 3) a strong anthropogenic-induced eutrophication during the last half of the 20th century in Lake Sempach, which may have been accompanied (as has been shown for other lakes) by population collapse, speciation reversal, and extinction ( Vonlanthen et al. 2012; Frei et al. 2022a, b), it has to be considered that the extant population of C. suidteri does not represent the original population of this species in Lake Sempach and thus should be considered extinct. Future work comparing individuals of the extant population of Lake Sempach with ancient DNA samples from sediment cores or museums samples may help to resolve if the extant population still carries a genetic legacy from the original species. We suggest that the extant population of whitefish in Lake Sempach are most likely a hybrid population with a possible genetic legacy of the original population of C. suidteri from Lake Sempach. According to Fatio (1885, 1890) C. suidteri spawned rather shallow in the month of November.

Common names.

Sempacherfelchen, Sempacherbalchen.

Comparative material.

All the fish detailed below were collected from Switzerland, Lake Constance. They are illustrated in Fig. 13 and listed in Tables 9 , 12 - 14 .

Figures

Figure 12. Coregonus suidteri, Lake Sempach, Switzerland A, B syntype, MHNG- 715.089, 311 mm SL, sex unknown, preserved specimen C syntype, MHNG- 816.026, 312 mm SL, sex unknown, preserved specimen. Scale bars: 1 cm.

Figure 13. Coregonus species of Lake Constance, Switzerland A Coregonus gutturosus, non-type, NMBE- 1076232 (Eawag- 248 - 1), 250 mm, sex unknown, preserved specimen B Coregonus arenicolus, holotype, 296 mm, NMBE- 1076223 (Eawag- 239 - 1), sex unknown preserved specimen C Coregonus macrophthalmus, syntype, MHNG- 716.052, 215 mm, sex unknown, preserved specimen D Coregonus wartmanni, non-type, NMBE- 1076206, 301 mm, female, preserved specimen. Scale bars: 1 cm.

Figure 14. Illustrations of specimens of each species of Coregonus from Lake Lucerne and Sarnen. Illustrations of Lake Lucerne species are based on several individuals. Illustration of C. sarnensis is based on NMBE- 1078159, 230 mm, male. Scale bar for C. sarnensis: 1 cm.