Coregonus litoralis, 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 litoralis sp. nov.

Figs 3 , 14

Coregonus ‘Ballen’: Douglas and Brunner 2002; Douglas et al. 1999.

Coregonus ‘Balchen’: Steinmann 1950; Douglas and Brunner 2002.

Coregonus ‘Grossfelchen’: Svarvar and Müller 1982.

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

Coregonus schinzii supersum var. lucernensis : Fatio 1890; Birrer and Schweizer 1938 (see also synonymy of C. supersum ).

Coregonus sp. ‘Bodenbalchen’: 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.

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

Coregonus suidteri : Kottelat 1997; Kottelat and Freyhof 2007 (see also synonymy of C. supersum and C. suidteri ).

Material examined.

Holotype. Contemporary specimen (year: 2007): NMBE- 1078103, 326 mm SL, male; Switzerland: Lake Lucerne . Paratypes. All from Switzerland, Lake Lucerne: Contemporary samples (years: 2007, 2008): NMBE-1078064, NMBE-1078075, NMBE-1078079, NMBE-1078080, NMBE-1078083, NMBE-1078085, NMBE-1078091, NMBE-1078092, NMBE-1078098, NMBE-1078102-105, N = 12, 304-363 mm SL; Historical specimens (years: 1890, 1899, 1939): MHNG-717.046, NMBE-1076293-295 (Eawag-3081-1, Eawag-3081-2, Eawag-310-1, Eawag-310-2, Eawag-310-3, Eawag-309), N = 7, 222-392 mm SL .

Diagnosis.

Coregonus litoralis is a large whitefish (standard length at 3 years of age: range = 325-392 mm, mean = 353 mm) with strong pigmentation of all fins and body; greenish blue colour that sometimes has a pale mustard yellow undertone on the flanks above the lateral line; moderate to many pigmented small dots on the scales along the flank and the dorsum; deep bodied (23.4-30% SL, mean = 26.9); blunt snout; short head (19.2-20.9% SL, mean = 19.9); sub-terminal mouth; small eye (eye diameter: 18.2-21.4% HL, mean = 20.2) with a thick and triangular-shaped eye socket; short and stout caudal peduncle (caudal peduncle depth: 7.5-8.4% SL, mean = 8.1; caudal peduncle length: 11.5-14.3% SL, mean = 12.6); few and short gill rakers (longest gill raker: 9.2-13.1% HL, mean = 11; total gill raker number: 24-32).

Description.

Shape: Generally deep bodied with greatest body depth anterior of the dorsal fin. Dorsal profile from tip of snout to anterior origin of dorsal fin is strongly convex and ventral profile moderately convex from interorbital area to pelvic fin origin. Head short. Mouth short and sub-terminal. Rostral plate pronounced and a bit wider than deep resulting in a slightly rectangular shape. Tip of snout often blunt. Small eye with a thick and sickle cell-shaped eye-socket. Pectoral fin moderately tapered and moderately short. Dorsal fin long with anterior unbranched ray of the erected dorsal fin mostly 60-70 ° angle to body axis and slightly bent posteriorly at the end of the ray. Dorsal fin longest anteriorly and progressively shortening posteriorly with the outer margin of dorsal fin straight. Caudal peduncle stout and short with caudal fin moderately forked. Unbranched rays of anal fin slightly bent posteriorly. Anal fin longest anteriorly and progressively shortening posteriorly with the outer margin of anal fin mostly straight and only rarely slightly concave. Meristics: Few and short gill rakers. Colour: Pigmentation of fins and body overall strong in live specimens. Pectoral fin moderately pigmented at median to distal parts of the fin. All other fins are strongly pigmented. Silvery appearance along flanks with moderate to many pigmented small dots (aggregation of melanophores) on the scales along flank and dorsum. Distribution of dots bound to scale patterning such that dots are found at edge of the scales or at boundary point of two scales. Dorsally above lateral line the silvery appearance changes to a pale greenish or dark greenish blue colour. Seldomly, especially in older specimens, general greenish blue colour can have a pale mustard yellow ground colour (see also colour description in Fatio (1890) and Birrer and Schweizer (1938)). Dorsal part of head and snout around nostrils is strongly pigmented. Pre-operculum and operculum are silvery with one black spot on lower margin of the pre-operculum. Preserved specimens are pale in colouration with similar pigmentation as described for live specimens. Silvery, translucent, not coloured or unpigmented parts of body brown-yellowish, whereas pigmented parts conserved and coloured parts (dorsally above the lateral line) brownish.

Differential diagnosis.

Based on contemporary specimens the total number of gill rakers of 24-32 (modes = 26 and 30) distinguishes C. litoralis from three of five of the other whitefish species of Lake Lucerne by having fewer gill rakers than the other species (34-40, mode = 38 in C. nobilis , 33-37, mode = 35 in C. suspensus , 33-43, mode = 36 in C. muelleri ) (Table 13 ). Furthermore, the average standard length of three old contemporary specimens distinguishes C. litoralis from all other whitefish species of Lake Lucerne except for C. nobilis , where only specimens of 5 years of age or older were caught. The average standard length at 3 years of age of C. litoralis (range = 325-392 mm, mean = 353 mm) is larger than that of C. muelleri (160-232 mm, 194 mm), C. suspensus (266-315 mm, 289 mm) and C. intermundia (243-300 mm, 273 mm) (Suppl. material 1: table S3). The differential diagnoses against contemporary specimens of C. sarnensis from Lake Sarnen and against historical specimens of the three whitefish species from Lake Zug and C. suidteri from Lake Sempach are given under those species’ account.

Coregonus litoralis - Coregonus intermundia

The specimens of C. litoralis differ from those of C. intermundia in being deeper bodied (23.4-30% SL, mean = 26.9 vs. 21.6-27.1% SL, mean = 23.9) and having a smaller eye (eye diameter: 18.2-21.4% HL, mean = 20.2 vs. 20.4-23.3% HL, mean = 22.1) (Tables 2 , 3 ). Based on ratios C. litoralis can be distinguished from C. intermundia by a larger 'predorsal length / eye diameter’ ratio (PreD/ED: 10.89-12.75 vs. 9.92-10.59) and a larger 'snout length / maxilla length’ ratio (SN/M: 1.17-1.39 vs. 1.02-1.17) (Table 10 ).

Coregonus litoralis - Coregonus suspensus

Coregonus litoralis differs from C. suspensus by being deeper bodied (23.4-30% SL, mean = 26.9 vs. 21.5-25.1% SL, mean = 23.6), having a longer dorsal fin base (11.9-15.1% SL, mean = 13.4 vs. 10.5-12.1% SL, mean = 11.3), a deeper caudal peduncle (7.5-8.4% SL, mean = 8.1 vs. 7.1-7.5% SL, mean = 7.3), a smaller eye (eye diameter: 18.2-21.4% HL, mean = 20.2 vs. 21.1-22.3% HL, mean = 21.8), a deeper head (70.1-77.9% HL, mean = 73.8 vs. 63.6-70.8% HL, mean = 67.5) and shorter gill rakers (middle gill raker: 7.8-11.8% HL, mean = 10 vs. 11.5-14.3% HL, mean= 13.1; longest gill raker: 9.2-13.1% HL, mean = 11 vs. 13.2-16.4% HL, mean = 14.7) (Tables 2 , 4 ). Coregonus litoralis can be distinguished from C. suspensus based on a larger 'caudal peduncle depth / upper jaw width’ ratio (CD/UJW: 1.74-1.97 vs. 1.5-1.68) and a larger 'caudal peduncle depth / predorsal length’ ratio (CD/PreD: 0.16-0.18 vs. 0.15-0.16) (Table 10 ).

Coregonus litoralis - Coregonus nobilis

Coregonus litoralis can be differentiated from C. nobilis by being deeper bodied (23.4-30% SL, mean = 26.9 vs. 20.7-25.5% SL, mean = 23.8), having a longer dorsal fin base (11.9-15.1% SL, mean = 13.4 vs. 10.3-12.6% SL, mean = 11.2), a anteriorly longer erected and depressed dorsal fin (erected dorsal fin: 16.9-20.9% SL, mean = 18.9 vs. 15.3-17.2% SL, mean = 16.3; depressed dorsal fin: 17.6-22.6% SL, mean = 20.4 vs. 16.7-18.8% SL, mean = 17.8), a deeper caudal peduncle (7.5-8.4% SL, mean = 8.1 vs. 6.3-7.6% SL, mean = 6.8) and shorter gill rakers (middle gill raker: 7.8-11.8% HL, mean = 10 vs. 10.2-16.6% HL, mean= 13.4; longest gill raker: 9.2-13.1% HL, mean = 11 vs. 10.6-17% HL, mean = 14.2) (Tables 2 , 5 ). Based on ratios C. litoralis differs from C. nobilis by having a larger 'caudal peduncle depth / postdorsal length’ ratio (CD/PostD: 0.17-0.21 vs. 0.14-0.16) and a smaller 'pectoral fin length / length of erected anterior part of dorsal-fin’ ratio (PecF2/DFAe: 0.84-0.92 vs. 0.94-1.1) (Table 10 ).

Coregonus litoralis - Coregonus muelleri

Contemporary specimens: Coregonus litoralis differs from C. muelleri by having strong pigmentation of all fins vs. none or very little pigmentation of the pectoral, anal, caudal and dorsal fin in C. muelleri , by being deeper bodied (23.4-30% SL, mean = 26.9 vs. 19.8-24.9% SL, mean = 21.9), having a longer dorsal fin base (11.9-15.1% SL, mean = 13.4 vs. 9.2-12.7% SL, mean = 11), a shorter adipose fin base (3.8-5.8% SL, mean = 5 vs. 4.6-8.5% SL, mean = 6), a shorter head (19.2-20.9% SL, mean = 19.9 vs. 20.3-23.5% SL, mean = 22), a smaller eye (eye diameter: 18.2-21.4% HL, mean = 20.2 vs. 22.2-26% HL, mean = 24.1; eye cavity: 22.7-26% HL, mean = 24.6 vs. 26.4-31.1% HL, mean = 27.7), eye socket shape (sickle cell-shaped vs. roundish), deeper head (70.1-77.9% HL, mean = 73.8 vs. 59.6-70.8% HL, mean = 63.7), a shorter lower jaw (36.8-42.5% HL, mean = 39.6 vs. 40.3-45.8% HL, mean = 42.7), a shorter maxilla (17.4-20.5% HL, mean = 19.1 vs. 19.4-24% HL, mean = 21.4), a deeper snout (6.9-10.5% HL, mean = 8.6 vs. 4.9-8.7% HL, mean = 7), a wider head (46.4-51.2% HL, mean = 49.1 vs. 37.2-48.7% HL, mean = 43.8) and shorter gill rakers (middle gill raker: 7.8-11.8% HL, mean = 10 vs. 9.6-15.9% HL, mean = 13.5; longest gill raker: 9.2-13.1% HL, mean = 11 vs. 12.5-16.7% HL, mean = 14.5) (Tables 2 , 6 ). Based on ratios C. litoralis can be distinguished from C. muelleri by having a larger 'caudal peduncle depth / eye diameter’ ratio (CD/ED: 1.87-2.25 vs. 1.12-1.43) and a larger 'head depth / snout width’ ratio (HD/SW: 4.45-5.55 vs. 3.45-4.45) (Table 10 ).

Historical specimens: Coregonus litoralis differs from C. muelleri by being deeper bodied (21.8-29.9% SL, mean = 26.2 vs. 20-24.7% SL, mean = 22.5), having a deeper caudal peduncle (6.9-8.5% SL, mean = 7.7 vs. 6.1-6.8% SL, mean = 6.5), smaller eye (eye diameter: 17.9-22.7% HL, mean = 20.4 vs. 23.2-26.6% HL, mean = 24.3; eye cavity: 24.1-27.7% HL, mean = 26 vs. 27-31.9% HL, mean = 29.2; eye height: 20.3-24.8% HL, mean = 22.2 vs. 23.5-28.3% HL, mean = 25.3), longer postorbital length (51.6-56.2% HL, mean = 53.5 vs. 47.4-51.9% HL, mean = 49.9), a deeper head (68.1-77.1% HL, mean = 72.5 vs. 61.8-69.7% HL, mean = 65.2), more transverse dorsal scales (10-11, mode = 10 vs. 8-9, mode = 9) and less gill rakers (upper arch gill raker number: 7-11 vs. 13-16; lower arch gill raker number: 12-22 vs. 22-25; total gill raker number: 19-33 vs. 36-39) (Tables 2 , 6 , 12 , 13 ). The contemporary gill raker range of C. litoralis (24 to 32, modes = 26 and 30) overlaps mostly with the historical gill raker ranges given in Fatio (1890: 23-28), Birrer and Schweizer (1938: 23-30, mode = 26) and Steinmann (1950: 20-31) and counted on historical specimens (this study: 19-33). Based on ratios C. litoralis can be distinguished from C. muelleri by having a larger 'caudal peduncle depth / dorsal head length’ ratio (CD/DHL: 0.46-0.58 vs. 0.37-0.44) (Table 11 ).

Distribution and notes on biology.

Coregonus litoralis occurs in all basins of Lake Lucerne (Fig. 2 ). Based on genetic assignments it has been identified to be present in Lake Sarnen (Suppl. material 1: figs S2, S3). It is unclear if C. litoralis occurs naturally in Lake Sarnen or has been introduced (this is discussed in more detail in the Suppl. material 1: paragraph 1). Coregonus litoralis feeds predominantly on benthic prey (e.g., chironimid, pisidium) and parts of the year on zooplankton (e.g., bythotrephes, daphnia) (stomach content: Cysat 1661; Birrer and Schweizer 1938; isotopic signature: Selz 2008; Hudson 2011; Ingram et al. 2012). Feeding experiments with individuals of this species and other whitefish species from lakes Thun and Lucerne ( Lundsgaard-Hansen et al. 2013; Roesch et al. 2013) suggest - based on the functional properties of the number of gill rakers - that the low-rakered C. litoralis feeds predominantly on benthic prey. Coregonus litoralis has a fast growth rate ( Svarvar and Müller 1982; Müller et al. 2007) and is a large whitefish species. The size (i.e., standard length) at 3 years of age of C. litoralis is larger than that of C. suspensus and C. intermundia and considerably larger than that of C. muelleri (Suppl. material 1: table S3). We cannot compare its size to C. nobilis since only older individuals of C. nobilis have been caught ( Hudson et al. 2016). Coregonus litoralis has a short spawning season in winter. The peak spawning period varies over the years from mid-November to late December, which has been attributed to a decrease in lake water temperature below 7-8 °C (per. comm. from fisheries authorities of Lake Lucerne; Birrer and Schweizer 1938). The spawning season lasts for approximately two weeks and the spawning depth is mostly in very shallow waters (1-5 m) but can reach down to 30 m and rarely to 40 m in the main basins of Lake Lucerne excluding Lake Alpnach ( Birrer and Schweizer 1938; Steinmann 1950; Hudson et al. 2016). In all the basins of Lake Lucerne except Lake Alpnach the spawning depth of C. litoralis overlaps with that of C. intermundia ( Hudson et al. 2016). Populations of C. litoralis in Lake Alpnach usually spawn earlier in the year than in the rest of Lake Lucerne, which has been suggested to be due to a more rapid cooling of the lake water in Lake Alpnach than in the rest of the basins of Lake Lucerne ( Svarvar and Müller 1982; A. von Deschwanden and A. Blättler, pers. comm.). Coregonus litoralis mostly spawns though next to the entrance of Lake Alpnach in the adjacent basin ‘Kreuztrichter’ and less so directly in Lake Alpnach (this is discussed in more detail in the Suppl. material 1: paragraph 2). The spawning behaviour of C. litoralis has been recorded by Selz and Hofmann (2018). The video by Selz and Hofmann (2018) shows communal pair-spawning behaviour whereby a female is often accompanied by up to three males. Towards the end of the video a pair spawning event can be observed in which the female and male align side by side and synchronically dart from near the bottom up towards the surface. This is the first observation of this behaviour in pre-alpine whitefish species; it had previously only been observed in the vendace ( Coregonus albula ) in an experimental setting ( Karjalainen and Marjomäki 2017).

Etymology.

The specific name in Latin means 'coming from the shore’. The name refers to the specific spawning habitat of this species, spawning in very shallow water of a few metres close to or directly at the lake shore. An adjective.

Common names.

Balchen, Bodenbalchen.

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 3. Coregonus litoralis, Lake Lucerne, Switzerland. Contemporary (A-C) and historical (D, E) specimens A holotype, NMBE- 1078103, 326 mm SL, male, freshly caught specimen (right side, reversed) B, C holotype, NMBE- 1078103, preserved specimen D, E paratype, MHNG- 717.046, 361.5 mm SL. 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.