Coregonus muelleri, 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 muelleri sp. nov.

Figs 7 , 14

Coregonus ‘Albeli’: Steinmann 1950; Douglas et al. 1999; Douglas and Brunner 2002.

Coregonus exiguus albellus : Fatio 1890; Birrer and Schweizer 1935, 1936b.

Coregonus lavaretus nat. riusensis, oekot. nanus: Steinmann 1950 (see also synonymy of C. zugensis and C. sarnensis ).

Coregonus sp. ‘small’: Hudson et al. 2016.

Coregonus ‘Weissfelchen’: Steinmann 1950.

Coregonus ‘Weissfisch’: Douglas and Brunner 2002.

Coregonus zugensis : Kottelat 1997; Kottelat and Freyhof 2007; Wedekind et al. 2007a, b; Rudolfsen et al. 2008; Hudson et al. 2011, 2013; Ingram et al. 2012; Vonlanthen et al. 2012; Lundsgaard-Hansen et al. 2013; Roesch et al. 2013; Alexander et al. 2017a (see also synonymy of C. zugensis ).

Material examined.

Holotype. Contemporary specimen (year 2007): NMBE- 1078123, 180 mm SL, male; Switzerland: Lake Lucerne . Paratypes. All from Switzerland, Lake Lucerne: Contemporary specimens (year 2007): NMBE-1078106- NMBE-1078122, NMBE-1078124- NMBE-1078135, N = 29, 158-198 mm SL. Historical specimens (years 1892, 1940, 1947): NMBE-1076284, NMBE-1076289, NMBE-107628, NMBE-1076290 (Eawag-305-1, Eawag-305-2, Eawag-305-3, Eawag-305-4, Eawag-305-5), NMBE-1076291, N = 8, 158-193 mm .

Diagnosis.

Coregonus muelleri is a small whitefish species (standard length at 3 years of age: range = 160-232, mean = 194) with weak pigmentation of all fins and body; pale olive-brown colouration on the flanks above the lateral line; elongate slender body; large eye (eye diameter: 22.2-26% HL, mean = 24.1) with a subtle triangular eye socket; tip of snout pointy; many and long gill rakers (longest gill raker: 12.5-16.7% HL, mean = 14.5; total gill raker number: 33-43).

Description.

Shape: Body elongated and slender. Greatest body depth anterior of dorsal fin. 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 long. Snout long and tip of snout if often pointed and seldomly fleshy resulting in a not pronounced rostral plate. Mouth long and terminal. Large eye with a subtle sickle cell-shaped (seldom roundish) eye-socket in the historical specimens and a mostly roundish (seldom sickle cell-shaped) eye-socket in the contemporary specimens. The eye of the historical specimens is larger than those of the contemporary specimens. Pectoral fin moderately long and tapered. Anterior unbranched ray of the erected dorsal fin ranges from almost vertically straight to an ~ 70-80° angle to body axis and only bent slightly posteriorly at end of the ray. Caudal peduncle narrow and elongated with caudal fin forked and sometimes moderately to strongly asymmetrical with often ventral part being longer. Unbranched rays of anal fin straight and rarely bent posteriorly at end of ray. Anal fin longest anteriorly and progressively shortening posteriorly with outer margin of the anal fin slightly concave. Meristics: Many and long gill rakers. Colour: Pigmentation of fins and body weak in live specimens. Pectoral fin transparent and pelvic and anal fin mostly transparent. Pectoral fin very rarely pigmented at distal part of the fin and anal and pelvic fin rarely moderately pigmented at median to distal parts of fin. Dorsal, caudal and adipose fin moderately pigmented. Silvery appearance along flanks. Dorsally above the lateral line silvery appearance changes to a pale olive-brown. Dorsal part of head and snout around nostrils moderately pigmented. Pre-operculum and operculum silvery with one black spot on lower margin of the pre-operculum. Preserved specimens pale in colouration with similar pigmentation as described for live specimens. In contemporary 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. In historical specimens all body parts are brownish.

Differential diagnosis.

The differential diagnoses against the contemporary specimens of C. litoralis , C. intermundia , C. suspensus , C. nobilis and C. sarnensis and against the historical specimens of C. litoralis from Lake Lucerne and C. zugensis from Lake Zug are given under those species’ accounts.

Distribution and notes on biology.

Coregonus muelleri occurs in all basins of Lake Lucerne (Fig. 2 ) except for Lake Alpnach ( Steinmann 1950; J. Muggli, pers. comm.). Coregonus muelleri was (besides C. nobilis ) historically and is today the most abundant and commercially important whitefish species in Lake Lucerne ( Birrer and Schweizer 1935; Muggli 2015; Alexander et al. 2017a). Coregonus muelleri 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 1935). It is a small whitefish species with the size at 3 years of age of C. muelleri being considerably smaller than that of C. litoralis , C. intermundia and C. suspensus (Suppl. material 1: table S3). We cannot compare its size to C. nobilis since only older individuals of the latter species have been caught ( Hudson et al. 2016). It has a slow growth rate ( Birrer and Schweizer 1935; Steinmann 1950). Coregonus muelleri has a long spawning season with presumably two spawning peaks. The historical literature suggests that C. muelleri has a spawning peak in the early summer from July to August and a second peak in the late autumn to early winter from October to December at a spawning depth of between 60 to 200 m ( Fatio 1890; Surbeck 1913; Birrer und Schweizer 1935; Steinmann 1950; Muggli 2015). However, according to the fishery warden J. Muggli it is unclear if these summer-spawning C. muelleri were once present in Lake Lucerne, at least in the last few centuries such summer-spawning C. muelleri have not been caught. The population of whitefish that we have described as C. muelleri was originally grouped under the species name C. zugensis . However, independent multilocus microsatellite (Suppl. material 1: figs S2, S3) and large genomic AFLP ( Hudson et al. 2011) data sets have shown that the whitefish species from Lake Lucerne and the whitefish populations of Lake Zug, are two independent genetic groups suggesting that C. muelleri is an endemic species of Lake Lucerne and should not be grouped under the name C. zugensis . Furthermore, C. muelleri can be distinguished based on morphological characters and ratios from historical specimens of C. zugensis , as well as from the other two species of Lake Zug, C. obliterus and C. supersum (see details under those species’ account).

Etymology.

The species is named after the late Dr. Rudolf Müller, a fisheries biologist and former department head and research group leader at EAWAG, Center for Ecology, Evolution and Biogeochemistry (CEEB) in Kastanienbaum, Switzerland. He dedicated a large part of his career to understanding the ecology of whitefish in Swiss lakes, and confirmed the re-discovery of C. nobilis .

Common name.

Albeli.

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 7. Coregonus muelleri, Lake Lucerne, Switzerland A holotype, NMBE- 1078123, 180 mm SL, male, freshly caught specimen, (right side, reversed) B, C holotype, NMBE- 1078123, preserved specimen D non-type, Eawag- 59186, Lake Lucerne, 175 mm SL, male. 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.