Coregonus sarnensis, Selz & Seehausen, 2023

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 sarnensis sp. nov.

Figs 8 , 14

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

Coregonus ‘Sarnerbalchli’: Steinmann 1950.

Coregonus ‘Sarnerfelchen’: Steinmann 1950.

Coregonus sp. ‘Sarnerfelchen’: Vonlanthen et al. 2012.

Coregonus zugensis : Vonlanthen and Périat 2018 (see also synonymy of C. muelleri and C. zugensis ).

Material examined.

Holotype. NMBE- 1078159, 230 mm SL, male; Switzerland: Lake Sarnen . Paratypes. All from Switzerland, Lake Sarnen: NMBE-1078143- NMBE-1078155, NMBE-1078157, NMBE-1078158, NMBE-1078160- NMBE-1078169, NMBE-1078171 - NMBE-1078173, NMBE-1078174, NMBE-1078175, N = 27, 188- 261.5 mm SL .

Diagnosis.

Coregonus sarnensis is a medium-sized whitefish (standard length at 3 years of age: range = 188-223, mean = 211) with weak pigmentation of the pectoral and pelvic fin and moderate pigmentation of the anal, caudal, adipose and dorsal fin and body; pale green to pale olive-brown colouration on the flanks above the lateral line; moderate number of pigmented small dots on the scales on the flanks; slender, elongated body; caudal peduncle mostly elongated (caudal peduncle depth: 7.1-8.6% SL, mean = 7.7; caudal peduncle length: 11.5-14.1% SL, mean = 12.6); tip of snout is fleshy, roundish, and often has an ~ 40-50° angle to the body axis anterior of the eye, such that the profile from the tip of the snout to the vertical projection where the anterior part of the eye crosses the dorsal profile is straight and afterwards slightly convex; large eye (eye diameter: 22.2-27.1% HL, mean = 23.9); many and long gill rakers (longest gill raker: 10.6-15.8% HL, mean = 13; total gill raker number: 33-40).

Description.

Shape: Body elongated and slender. Greatest body depth anterior of dorsal fin resulting in a slightly torpedo-like form. Ventral profile and dorsal profile similar and slightly arched. Dorsal and ventral profile from tip of snout to interorbital mostly straight and then slightly convex to dorsal and pelvic fin origin respectively. Head moderately long. Snout often has an ~ 40-50° angle to body axis anterior of eye, such that profile from tip of snout to vertical projection where anterior part of eye crosses dorsal profile is straight and afterwards slightly convex. Tip of snout if often roundish and seldomly fleshy resulting in a not strongly pronounced rostral plate. Mouth thick (i.e., width of upper and lower jaw), long and often terminal and only rarely slightly sub-terminal. Large eye with a variable eye-socket shape ranging from sickle cell-shaped to roundish. Pectoral fin moderately long and tapered. Anterior unbranched ray of erected dorsal fin ranges from almost vertically straight to an ~ 70-80° angle to body axis and only bent slightly posteriorly at end of ray. Caudal peduncle often narrow and elongated (seldomly stout) with caudal fin forked. Unbranched rays of anal fin straight. Anal fin longest anteriorly and progressively shortening posteriorly with outer margin of anal fin slightly concave. Meristics: Many and long gill rakers. Colour: Pigmentation of fins and body moderate in live specimens. Pectoral fin transparent and pelvic and anal fin mostly transparent. Pectoral fin is only pigmented at distal part of fin and anal and pelvic fin are moderately pigmented at median to distal parts of fin. Dorsal, caudal and adipose fin moderately pigmented. Silvery appearance along flanks. Dorsally above lateral line silvery appearance changes from a pale green colouration (e.g., to an olive-green colouration. Dorsal part of head and snout around nostrils moderately pigmented. Pre-operculum and operculum silvery with one black spot on lower margin of pre-operculum. Along flank and dorsum moderately pigmented small dots (aggregation of melanophores) on scales. Preserved specimens pale in colouration with similar pigmentation as described for live specimens. Silvery, translucent, not coloured or unpigmented parts of body become brown-yellowish, whereas pigmented parts are conserved and coloured parts (dorsally above lateral line) become brownish.

Differential diagnosis.

Coregonus sarnensis - Coregonus litoralis

Coregonus sarnensis can be differentiated from C. litoralis by having a shorter dorsal fin base (9.5-12.7% SL, mean = 11.5 vs. 11.9-15.1% SL, mean = 13.4), longer head (20.8-24% SL, mean = 22 vs. 19.2-20.9% SL, mean = 19.9), larger eye (eye diameter: 22.1-27.1% HL, mean = 23.9 vs. 18.2-21.4% HL, mean = 20.2; eye cavity: 26.3-31% HL, mean = 28.6 vs. 22.7-26% HL, mean = 24.6), a shallower head (62.7-74.3% HL, mean = 67.8 vs. 70.1-77.9% HL, mean = 73.8), less wide interorbital width (23.8-28.1% HL, mean = 26.2 vs. 26.3-29.8% HL, mean = 28.2), longer gill rakers (gill raker: 10.6-15.8% HL, mean = 13 vs. 9.2-13.1% HL, mean = 11) and more gill rakers (33-40, mode = 35, 36 vs. 24-32, mode = 26, 30) (Tables 2 , 7 , 13 ). Based on ratios C. sarnensis can be differentiated from C. litoralis by having a larger 'eye depth / head depth’ ratio (ED/HD: 0.33-0.39 vs. 0.25-0.30) (Table 10 )

Coregonus sarnensis - Coregonus intermundia

Coregonus sarnensis can be differentiated from C. intermundia by having a longer head (20.8-24% SL, mean = 22 vs. 19.1-21.5% SL, mean = 20.3) and a larger eye cavity (26.3-31% HL, mean = 28.6 vs. 23.8-27.9% HL, mean = 25.9) (Tables 3 , 7 ).

Coregonus sarnensis - Coregonus suspensus

Coregonus sarnensis can be differentiated from C. suspensus by having longer pectoral fins (pectoral fin 2: 16-21.3% SL, mean = 18 vs. 15.3-17.2% SL, mean = 16.4), a longer dorsal head length (14.1-17% SL, mean = 15.4 vs. 12.8-14.5% SL, mean = 13.8), longer head (20.8-24% SL, mean = 22 vs. 18.7-20.4% SL, mean = 19.6) and larger eyes (eye diameter: 22.1-27.1% HL, mean = 23.9 vs. 21.2-22.3% HL, mean = 21.8; eye cavity: 26.3-31% HL, mean = 28.6 vs. 25.1-26.4% HL, mean = 25.6) (Tables 4 , 7 ). Based on ratios C. sarnensis can be differentiated from C. suspensus by having a smaller 'predorsal length / eye depth’ ratio (PreD/ED: 7.42-10.21 vs. 10.73-11.40) (Table 10 ).

Coregonus sarnensis - Coregonus nobilis

Coregonus sarnensis can be differentiated from C. nobilis by having a longer erected and depressed anterior part of dorsal fin (erected: 16.7-19.5% SL, mean = 18.3 vs. 15.3-17.2% SL, mean = 16.3; depressed: 17.8-21.6% SL, mean = 19.8 vs. 16.7-18.8% SL, mean = 17.8), longer caudal fin (22.4-26.4% SL, mean = 24.2 vs. 20.1-23.8% SL, mean = 22.3), deeper caudal peduncle (7.1-8.6% SL, mean = 7.7 vs. 6.3-7.6% SL, mean = 6.8), longer dorsal head length (14.1-17% SL, mean = 15.4 vs. 12.8-14.9% SL, mean = 13.6), larger eye (eye diameter: 22.1-27.1% HL, mean = 23.9 vs. 20.2-23.1% HL, mean = 21.8; eye cavity: 26.3-31% HL, mean = 28.6 vs. 24.2-28% HL, mean = 26) and a shallower snout (6.2-9.2% HL, mean = 7.6 vs. 7.9-12.4% HL, mean = 10.5) (Tables 5 , 7 ). Based on ratios C. sarnensis can be differentiated from C. nobilis by having a smaller 'postdorsal length / eye cavity’ ratio (PostD/EC: 5.94-7.94 vs. 7.87-9.77) (Table 10 ).

Coregonus sarnensis - Coregonus muelleri

Coregonus sarnensis can be differentiated from C. muelleri by having a deeper caudal peduncle (7.1-8.6% SL, mean = 7.7 vs. 6.3-7.4% SL, mean = 6.9), being deeper bodied (22.4-27.8% SL, mean = 25.3 vs. 19.8-24.9% SL, mean = 21.9), having a wider eye socket (3.3-6.2% SL, mean = 4.3 vs. 1.9-4.6% SL, mean = 3) and wider head (43.7-53.3% SL, mean = 47.8 vs. 37.2-48.7% SL, mean = 43.8) (Tables 6 , 7 ).

Distribution and notes on biology.

Coregonus sarnensis occurs in Lake Sarnen. It has further been identified by genetic assignments to be present in Lake Alpnach (Suppl. material 1: figs S2, S3), which it most likely colonised naturally over the River Sarner Aa. It has also been shown to be present south of the alps in Lake Maggiore. The ‘Bondella’ (local name of the population) of Lake Maggiore derives from translocations and has been shown to group in a neighbour-joining tree with C. sarnensis from Lake Sarnen ( Hudson et al. 2011). Lake Sarnen was once part of Lake Lucerne (connected through Lake Alpnach respectively) and got disconnected by amassing of sediments from the rivers Grosse Schlieren, Kleine Schlieren, and Grosse Melchaa several thousand years ago ( Steinmann 1950; Pfiffner 2021). The occurrence of whitefish scales in sediment cores from Lake Sarnen that predate (scales found in the sediment layer of 1861-1857 (Suppl. material 1: fig. S1)) the earliest allochthonous whitefish introductions (1888) and independent genetic grouping of the Lake Sarnen population (AFLP data: Hudson et al. 2011; Microsattelite data: Suppl. material 1: figs S2, S3) from the lakes that seeded the allochthonous whitefish introductions (lakes Sempach, Zug, Lucerne) suggest that Lake Sarnen harbours an endemic whitefish species (this is discussed in more detail in the Suppl. material 1: paragraph 1). Information on the spawning season of C. sarnensis derive from two targeted spawning events by O.M. Selz and the fishery warden A. von Deschwanden in November of the year 2018 (pers. comm.). Thus, the spawning season of C. sarnensis is known only for November (although it may be stretching into December based on anecdotal information from recreational fishermen, which see large aggregations of putative whitefish in the deeper waters in December on their echosounders and in some cases they catch pike at these places with ripe whitefish in their stomachs in December) and it spawns at depth of 20 metres down to the lake bottom at 50 metres.

Etymology.

The specific name sarnensis refers to Sarnen, a village on the shores of the lake to which it gave its name. An adjective.

Common names.

Sarnerfelchen, Sarneralbeli.

Figures

Figure 8. Coregonus sarnensis, Lake Sarnen, Switzerland A holotype, NMBE- 1078159, 230 mm SL, male, freshly caught specimen B, C holotype, NMBE- 1078159, preserved specimen D paratype, NMBE- 1078146, Lake Lucerne, 223 mm SL, female. 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.