Coregonus steinmanni Selz, Doenz , Vonlanthen & Seehausen, 2020

Selz, Oliver M., Doenz, Carmela J., Vonlanthen, Pascal & Seehausen, Ole, 2020, A taxonomic revision of the whitefish of lakes Brienz and Thun, Switzerland, with descriptions of four new species (Teleostei, Coregonidae), ZooKeys 989, pp. 79-162 : 107-113

Coregonus steinmanni Selz, Doenz, Vonlanthen & Seehausen sp. nov.

Coregonus "Albock": Rufli 1978, 1979; Kirchhofer and Tschumi 1986; Kirchhofer 1995 (see also synonymy of C. alpinus and C. acrinasus )

Coregonus "Balchen": Heuscher 1901; Surbeck 1917 (see also synonymy of C. alpinus )

Coregonus "Balchen", "THU2": Douglas et al. 1999, 2003; Douglas and Brunner 2002 (see also synonymy of C. alpinus )

Coregonus lavaretus natio arurensis, oekot. primigenius: Steinmann 1950 (see also synonymy of C. fatio and C. alpinus )

Coregonus sp. "Balchen": Hudson et al. 2011, 2013, 2016; Ingram et al. 2012; Vonlanthen et al. 2012, 2015; Vonlanthen and Périat 2013 (see also synonymy of C. alpinus and C. brienzii )

Coregonus sp. "Balchen 2": Dönz et al. 2018 (see also synonymy of C. brienzii )

Coregonus "Wanderalbock", "Bodenalbock", "Albock": Steinmann 1950 (see also synonymy of C. alpinus , C. fatioi , C. steinmanni and C. brienzii )

Material examined.

Holotype. NMBE-1077219 , Switzerland, Lake Thun (46°40'N, 7°46'E), 301 mm SL, female.

Paratypes. NMBE-1077132 , NMBE-1077212-1077218 , NMBE-1077220 , NMBE-1077262-1077265 , Switzerland, Lake Thun (46°40'N, 7°46'E), N = 13, 211-323 mm SL.

Diagnosis.

Coregonus steinmanni is a large whitefish with moderate pigmentation of all fins and body; light to dark greenish blue colour on the flanks above the lateral line; moderate to many pigmented small dots on the scales along the flank and the dorsum; deep bodied; stout caudal peduncle; short head; sub-terminal mouth; small eye with a thick and triangular shaped eye socket.

Differential diagnosis.

Coregonus steinmanni occurs only in Lake Thun and we therefore compare the characters of this species specifically with the species of Lake Thun. Differential diagnoses against C. albellus , C. alpinus , and C. fatioi are given under those species’ accounts.

Coregonus steinmanni - Coregonus profundus

Coregonus steinmanni can be distinguished from C. profundus by having more and longer gill rakers (upper arch gill raker number: 10-12, mode = 11 vs. 5-10, mode = 9; lower arch gill raker number: 19-23, mode = 20 vs. 10-18, mode = 14; total gill raker number: 30-35, mode = 31 vs. 15-27, mode = 21; middle gill raker length: 9.1-14.3% HL, mean = 11.5 vs. 7.6-11.7% HL, mean = 9.2; longest gill raker length: 10-14.4% HL, mean = 12.1 vs. 7.8-12.4% HL, mean = 10.1), shorter pectoral fin (pectoral fin 1 length: 13.9-18.2% SL, mean = 16.2 vs. 16.6-21% SL, mean = 18.4; pectoral fin 2 length: 15.2-19.1% SL, mean = 17 vs. 17.7-23.2% SL, mean = 20.2), a shorter head (13.2-15.1% SL, mean = 14 vs. 15.5- 18.4% SL, mean = 16.4), a smaller eye cavity (24.2-27.8% HL, mean = 26.2 vs. 26.2-32.1% HL, mean = 29.2), a narrower underjaw (19.3- 25, mean = 23% HL vs. 22.7-29.2% HL, mean = 26), and a shorter prepelvic distance (48.6-54.3% SL, mean = 51.7 vs. 51.2-58.1% SL, mean = 54.2). Based on ratios C. steinmanni can be differentiated from C. profundus by having a larger "caudal fin depth / dorsal head length" ratio (0.53-0.63 vs. 0.4-0.49) (Tables 6 , 8 , 10 , Suppl. material 1: Table S6).

Coregonus steinmanni - Coregonus acrinasus

Coregonus steinmanni differs from C. acrinasus by having a shorter maxilla (18.1-21.8% HL, mean = 19.7 vs. 19.4-23.8% HL, mean = 21.8) (Tables 6 , 8 ) and can be differentiated based on ratios from C. acrinasus by having a larger "caudal peduncle depth / maxilla length" ratio (1.86-2.24 vs. 1.4-1.9) (Tables 6 , 9 , 10 ).

Description.

General appearance is shown in Figure 7. Morphological and meristic characters of both sexes can be found in Table 6 and Suppl. material 1: Table S6 and first- and second-best ratios for both sexes combined can be found in Table 10 . The description is valid for both sexes.

Shape: Generally deep bodied with greatest body depth anterior of the dorsal fin. Dorsal profile strongly arched compared to ventral profile. Dorsal profile from the tip of snout to the anterior origin of dorsal fin moderate to strongly convex, whereas the ventral profile is slightly arched such that it is almost straight or slightly convex from the interorbital area to the pelvic fin origin. Mouth is rather thin (i.e., width of upper and lower jaw), short and sub-terminal. Snout is pronounced and almost equally wide as deep resulting in an almost square shape. Small eye. Eye-socket is thick and triangular (i.e., sickle-shaped). Pectoral fin moderately tapered. The anterior unbranched ray of the erected dorsal fin has an approx. 60° angle to body axis and at the end of the ray it is bent posteriorly. Caudal peduncle is stout and short. Caudal fin forked and sometimes slightly asymmetrical with the dorsal part being longer. Un-branched ray of anal fin mostly straight and only sometimes slightly bent posteriorly. Anal fin longest anteriorly and progressively shortening posteriorly with the outermargin of the anal fin mostly slightly concave and only rarely straight.

Meristics: Few and short gill rakers.

Colour: Pigmentation of fins and body overall moderately strong in live specimens. Pectoral fin is moderately to strongly pigmented. Dorsal, adipose, pelvic, anal, and caudal fins are moderately to strongly pigmented. Silvery appearance along the flanks with moderate to many pigmented small dots on the scales. The dots are found along the flank and the dorsum. Distribution of the dots is bound to the scale patterning such that the dots are found at the edge of the scales or at the boundary point of two scales (as can be found for the species of C. fatioi , C. alpinus and C. brienzii ). Dorsally above the lateral line the silvery appearance changes to a light (e.g., RGB (135, 236, 179)) or darker greenish blue colour (e.g., RGB (7,168,125)). Dorsal part of the head strongly pigmented. Snout around the nostrils strongly pigmented with a gap of moderate pigmentation posteriorly of the nostrils up to the height of the middle of the eyes. Pre-operculum and operculum are silvery with one black dot on the lower margin of the pre-operculum. For a comparison to the main colouration found in the other species see Suppl. material 1: Figure S8. Preserved specimens are pale in colouration with similar pigmentation as described for live specimens. Silvery, translucent, not coloured or unpigmented parts of the body become brown-yellowish (e.g., RGB (239, 210, 40)), whereas the pigmented parts are conserved and the coloured parts (dorsally above the lateral line) become brownish (e.g., RGB (186, 140, 100)).

Distribution and notes on biology.

Coregonus steinmanni is found in Lake Thun (46°40'N, 7°46'E), which is connected to Lake Brienz through the river Aare at Interlaken. Based on isotopic signatures C. steinmanni feeds on a mix of benthic prey and zooplankton ( Selz 2008; Hudson 2011; Ingram et al. 2012) and has a fast growth rate ( Bittner 2009). It has to be noted that the work by Selz (2008), Hudson (2011) and Ingram et al. (2012) did not yet separate C. alpinus from C. steinmanni , which are phenotypically difficult to distinguish. Only recently has genetic work by Dönz and colleagues (2018) clearly resolved that these are two distinct species. Thus, the isotopic work by Selz (2008), Hudson (2011) and Ingram et al. (2012) most likely comprises of specimens of both species. The gill raker number of C. steinmanni (more gill rakers) and C. alpinus (fewer gill rakers) suggests - based on the functional properties of the number of gill rakers on feeding on different prey items ( Lundsgaard-Hansen et al. 2013; Roesch et al. 2013) - that C. steinmanni feeds more on zooplankton and less on benthic prey than C. alpinus , but this assumption needs to be verified in the future with stomach content analyses. Interestingly, the relative species abundances in the pelagic and benthic habitat from a habitat stratified random sampling in Lake Thun (mid-October 2013: Vonlanthen et al. 2015) shows, that C. steinmanni is occupying the moderately deep waters of the benthic habitat (76 m; N = 1) and the shallow waters of the pelagic habitat (8 m; N = 1) ( Dönz et al. 2018). Coregonus alpinus on the other hand can exclusively be found in shallow water in the benthic habitat (first 13 m; N = 1) and is completely absent from the pelagic habitat in Lake Thun ( Dönz et al. 2018). It is to note that the habitat-stratified random sampling data only covers a short period of time (one month in late summer) and it is thus not clear how the species are distributed spatially through the rest of the year.

Coregonus steinmanni resembles phenotypically C. alpinus and to some extent C. acrinasus . The average size (total length) at 3 years of age for specimens in this study is 328 ± 23 mm (mean and standard deviation, N = 11) (Suppl. material 1: Figures S4-S6). The average size at 3 years of age for the specimens of C. steinmanni from this study is similar to that for the years 2004-2005 (338.5 ± 19 mm, N = 8) (Bittner et al. unpublished; Vonlanthen et al. unpublished). The size of 3-year-old specimens of C. steinmanni is similar to that of C. alpinus , larger than that of C. acrinasus and considerably larger than that of C. albellus , C. fatioi and C. profundus (Suppl. material 1: Figure S6). Coregonus steinmanni has a short spawning season in late December and only rarely can be found spawning in late autumn (Suppl. material 1: Figure S3; Dönz et al. 2018). Coregonus steinmanni spawns mostly in moderately shallow waters of 10 m down to approx. 120 m (Suppl. material 1: Figure S3; Bittner 2009; Dönz et al. 2018). The spawning season and depth of C. steinmanni overlaps largely with that of C. acrinasus and C. alpinus and partially with that of C. fatioi . To a much lesser extent the spawning depth and time of C. steinmanni also overlaps with that of C. albellus and C. profundus .

Etymology.

The specific epithet steinmanni is the genitive of Steinmann. We name this species after the high school teacher and researcher Paul Steinmann, a zoologist from Switzerland who wrote the most comprehensive compendium on Swiss whitefish to date and compiled throughout his lifetime a large collection of preserved specimens of Swiss, but also European, fishes ( Steinmann 1950). This collection and his work on the revision of Swiss whitefish together with work by Fatio (1890) has been essential to describe the whitefish diversity that was present in Switzerland just before or at the beginning of the strong anthropogenic-induced eutrophication of many Swiss lakes which was accompanied by population collapse, speciation reversals, and extinction of Swiss whitefish ( Vonlanthen et al. 2012). For example, the only existing specimens of a now-extinct whitefish species, C. gutturosus Gmelin 1818, can only be found in the collection of Paul Steinmann.

Common name.

None; this species was not recognized by local fishermen or fisherwomen as distinct from C. alpinus and was thus also called "Balchen". We suggest the German name " Steinmann’s Balchen".