Coregonus nobilis Haack, 1882

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 nobilis Haack, 1882

Figs 6 , 14

Coregonus crassirostris : Fatio 1885.

Coregonus ‘Edelfisch’: Steinmann 1950.

Coregonus lavaretus nat. riusensis, oekot. pelagicus: Steinmann 1950.

Coregonus nobilis : Kottelat 1997; Kottelat and Freyhof 2007; Müller 2007; Hudson et al. 2011, 2013, 2016; Ingram et al. 2012; Vonlanthen et al. 2012; Alexander et al. 2017a.

Coregonus wartmanni nobilis : Fatio 1890; Birrer and Schweizer 1936a.

Material examined.

Neotype. Historical specimen (year 1885): MHNG- 656.056, 207 mm SL, sex unknown; Switzerland: Lake Lucerne. Non-types. All from Switzerland, Lake Lucerne: Contemporary specimens (year 2005): NMBE-1078053-1078063, NMBE-1078065-1078074, N = 21, 253-315 mm SL. Historical specimens (years 1882, 1885): MHNG-807.26, N = 2, 247 and 254 mm SL.

Diagnosis.

Coregonus nobilis is a medium-sized whitefish with weak pigmentation of the pectoral and pelvic fin and moderate pigmentation of the anal, caudal, adipose and dorsal fin and body; pectoral and pelvic fin with yellowish undertone; pale olive-brown colouration on the flanks above the lateral line with pale greenish undertone that is most pronounced on dorsal part of the head; moderate number of pigmented small dots on the scales on the flanks; slender, elongated, and slightly torpedo-like body; caudal peduncle elongated (12.4-15.3% SL, mean = 13.9); tip of snout is fleshy and ranges from being square-like to roundish; large eye (eye diameter: 23.5-25.6% HL, mean = 25.6) with a thick (4.6-5% HL, mean = 4.7) and triangular eye socket; many and long gill rakers (longest gill raker: 15% HL; total gill raker number = 41).

Description.

Shape: Slender body. Slender bodied with greatest body depth anterior of dorsal fin resulting in a slightly torpedo-like form. Dorsal and ventral profile similar and slightly arched. Dorsal and ventral profile from tip of snout to interorbital area mostly straight and then slightly convex to dorsal and pelvic fin origin respectively. Head moderately short. Mouth long and terminal or subtly sub-terminal. Lower jaw wide. Rostral plate equally wide as deep, quite pronounced with tip of snout fleshy and either roundish or blunt (square-like form). The eye is moderately large and that of historical specimens is larger than of contemporary specimens. Eye-socket thick and sickle cell-shaped. Pectoral fin moderately tapered and moderately long. Dorsal fin moderately long. Caudal peduncle narrow and elongated with caudal fin moderately forked and sometimes moderately to strongly asymmetrical. Meristics: Many and long gill rakers. Colour: Pigmentation of fins and body overall weak in live specimens. Pectoral and pelvic fin mostly transparent with yellowish ground colour, which is more pronounced in pectoral fin than pelvic fin. Pectoral fin rarely pigmented at distal part of fin and pelvic fin rarely moderately pigmented at median to distal parts of fin. Dorsal, anal, caudal and adipose fin moderately pigmented. Body weakly pigmented. Silvery appearance along flanks with moderate amount of pigmented small dots (aggregation of melanophores) on scales along flank and dorsum. Dorsally above the lateral line silvery appearance changes to a pale olive-brown and with a pale greenish ground colour that is most pronounced on dorsal part of head. 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. 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 the lateral line) become brownish.

Differential diagnosis.

We compare the contemporary specimens of C. nobilis to the contemporary specimens of the other species from Lake Lucerne. The differential diagnoses between C. litoralis , C. intermundia and C. suspensus , and C. sarnensis are given under those species’ accounts.

Coregonus nobilis - Coregonus muelleri

Coregonus nobilis differs from C. muelleri by having an anteriorly shorter erected and depressed dorsal fin (erected dorsal fin: 15.3-17.2% SL, mean = 16.3 vs. 16.4-20.3% SL, mean = 18.1; depressed dorsal fin: 16.7-18.8% SL, mean = 17.8 vs. 17.3-21.1% SL, mean = 19.2), a shorter caudal fin (20.1-23.8% SL, mean = 22.3 vs. 22-26.4% SL, mean = 23.9), a shorter dorsal head length (12.8-14.9% SL, mean = 13.6 vs. 14.4-17% SL, mean = 15.7), smaller eye (eye diameter: 20.2-23.1% HL, mean = 21.8 vs. 22.2-26% HL, mean = 24.1; eye cavity: 24.2-28% HL, mean = 26 vs. 26.4-31.1% HL, mean = 27.7; eye height (20.7-24% HL, mean = 22.3 vs. 22.3-26.2% HL, mean = 24.3), differently shaped eye socket (sickle cell-shaped vs. roundish), a deeper head and snout (head depth: 65.9-77.8% HL, mean = 71.2 vs. 59.6-70.8% HL, mean = 63.7; snout depth: 7.9-12.4% HL, mean = 10.5 vs. 4.9-8.7% HL, mean = 7) and a wider head and lower jaw (head width: 46.2-55% HL, mean = 50.6 vs. 37.2-48.7% HL, mean = 43.8; lower jaw width: 7.8-10.2% HL, mean = 9 vs. 5.9-8.7, mean = 7.3) (Tables 5 , 6 ). Based on ratios C. nobilis can be differentiated from C. muelleri by having a smaller 'eye diameter / head depth’ ratio (ED/HD: 0.27-0.33 vs. 0.35-0.42) (Table 10 ).

Distribution and notes on biology.

Coregonus nobilis occurs in all basins of Lake Lucerne (Fig. 2 ) except for Lake Alpnach ( Nufer 1905). Since the species is endangered no commercial and recreational fisheries are permitted all year round (details on the decline of the population of C. nobilis and its putative extinction and its rediscovery is discussed in the Suppl. material 1: Paragraph 3). Hence, to understand the distribution of C. nobilis outside of the spawning season we can only consult historical catch records. These suggest that it was caught in large quantities and migrated heavily throughout the year within the basins of Lake Lucerne except for Lake Alpnach ( Birrer and Schweizer 1936a; Steinmann 1950). Specifically, it was caught in water depths of 5-25 m in the pelagic habitats in the basins ‘Kreuztrichter’, ‘Gersauerbecken’, ‘Urnerbecken’, ‘Vitznauerbecken’ and ‘Küssnachtersee’ ( Birrer and Schweizer 1936a; Fig. 2 ). Coregonus nobilis feeds - depending on the time of the year - on different pelagic prey (i.e., variety of zooplankton such as Bythotrephes , Daphnia , Bosmina , Copepoda, Leptodora, and rarely Chironomidae ) ( Birrer and Schweizer 1936a). It is a medium-sized whitefish species and has a moderate growth rate ( Müller et al. 2007). It is the only whitefish species in Lake Lucerne that spawns in late summer in great water depths. The spawning season of C. nobilis stretches from late July to mid-September in water depths of 80 to 214 m ( Birrer and Schweizer 1936a; Müller 2007; Vonlanthen et al. 2012; Hudson et al. 2016; Alexander et al. 2017a). During the spawning season it has been caught both historically and more recently in the inner basins of Lake Lucerne; ‘Gersauerbecken’ ( Birrer and Schweizer 1936a; Hudson et al. 2016) and ‘Vitznauerbecken’ ( Alexander et al. 2017a). Birrer and Schweizer (1936a) note that the spawning grounds can also be found in the deeper waters at gravel beds that are fed by nearby stream mouths.

Common name.

Edelfisch.

Figures

Figure 2. Map of Switzerland with the lakes studied; 1. Lake Constance, 2. Lake Sempach, 3. Lake Zug, 4. Lake Lucerne, 5. Lake Sarnen. On the right is a bathymetric map of Lake Lucerne with the German names of each basin (modified from Alexander et al. 2017 a).

Figure 6. Coregonus nobilis, Lake Lucerne, Switzerland A neotype, MHNG- 656.056, 207 mm SL, sex unknown, preserved specimen, (right side, reversed) B non-type, NMBE- 1078071, freshly caught specimen, 287 mm SL, male C non-type, freshly caught specimen, not preserved, Lake Lucerne, 280 mm SL, sex unknown. 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.